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This video from the World Science Festival in 2009 spread like wildfire online. Join along as McFerrin leads the audience in singing the pentatonic scale.
He is a genius of improvisation; a genre-bending vocal magician and conductor. And he sings the territory between music, mystery, and spirit. Who better to contemplate the human voice — its delights, its revelations, and its mystery — than Bobby McFerrin?
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is a ten-time Grammy Award winner. He is one of the world's best-known vocal innovators and improvisers, a world-renowned classical conductor, and a passionate spokesman for music education.
Pertinent Posts
Video Interviews with Krista Tippett
Watch our unedited, behind-the-scenes video of Krista interviewing Bobby McFerrin on Good Friday at Orchestra Hall in downtown Minneapolis. A marvelous experience not to be missed!
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Bobby McFerrin stretches and focuses before his interview with Krista Tippett at Orchestra Hall in Minneapolis, Minnesota.
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Normally, I do not post comments, but I really felt the urge to share with you! I was blown away by this interview-I could feel his spirit come right thru my screen and stir me! Thank you for such an insightful and inspiring interview- my day has started better because of it! Babs Richardson
Catching song, a gatherer, a sweeper, a weaver , shaman, Christian, mix, stew yourself in song, spirit, reverence for story, family, relationship, love… prayer… singing prayers in the morning…intense beauty-love fire.
I feel perhaps a bit like the woman a the question and answer period that he describes…Just Good all over. I am grateful he is doing his work and bringing his gift to the world. It inspires me to go out and shine myself… he is shambhala singing warrior. Spreading the love light.. Lighting the love fire...
For me I would like to hear more about his relationship and the lessons that he learned from his FATHER.. I was struck first when he described his dad singing up the "dirt and the bones" of the Negro spiritual… I'd like to delve into that a little more… the dirt and the bones and the soul.. I see it as being quite connected to the stories that he told of his father encouraging students to be THEMSELVES. About being truthful. Having integrity.. being that unique person that each of us is.
Oh, and…
The words leading to laughter at 48:30 - magic.
Yesterday, I was privileged to be one of two lectors at my friend Helen's Funeral Mass. Her family decided on the first reading from the Book of Ecclesiastes 3:1-8,11. It was the first time I proclaimed this passage although it is familiar to most of us over 60 years. Line 11 was new to me. I read it again and again, trying to grasp its meaning, to better convey it to this group of grieving family and friends.
Then this morning, toward the end of the interview was the part about the woman who had studied at Berkely coming backstage in Paris (if I remember) to ask how Mr. McFerrin could be singing from in a lost African language. Immediately I went back to what I had been pondering since last Monday. Thank you for this opportunity to share a tiny bit of insight I achieved because of this wonderful interview with a kind, patient and gentle man.
thx for bobbie mcFarrin , he was a total cool guy & musician. i loved the part about genetic/ancestral memory of languagr, when my daughter was about 5 we played making up a language & mine came out very like Polish/Russian, which I do not speak but my grandparents did!
Q: What would you like to tell us?
A: Inspired by your interview with Bobby McFerrin. My recently deceased mother had this quote on her bedroom wall, I'm sorry I don't have it available to send you word for word. Katzanzakis in 'Zorba the Greek', goes something like: "Every day, in every moment, we are all involved in the same terrible struggle. What's that boss? Turning matter into spirit." And then Zorba says something about that being too complicated, but asks him "to dance it, or tell it in a story." ******************** Thank you for a GREAT show. Brought me to tears. Paul
As I watched the video transcript, and heard Bobby McFerrin describe the sing-for-10-minutes improv assignment, I was immediately reminded of Natalie Goldberg's similar assignment for writing practice. In her book Writing Down the Bones, informed by Buddhist practice, Goldberg gives some guidelines for what she calls the timed exercise. Pick a session length, long or short, but commit to it: write for the full period, whether it's three minutes or an hour. "Keep your hand moving ... Don't cross out ... Don't worry about spelling, punctuation, grammar ... Lose control ... Don't think. Don't get logical ... Go for the jugular."
The discipline of freedom. Most of us almost have to be commanded to go there, to play and be loose once more. What a gift to hear the call in another voice, to another road.
Tammerie Day
Tammerie Day
I loved your photgraph and comments. If you liked Natalie Goldberg's writing practice advice you may enjoy Thinking Anew: Harnessing the Power of Belief, a book within a composition book that uses the power of writing to help people in crisis find the passion to make change stick. I wish I knew Natalie Goldberg and Bobby McFerrin before I co-authored the book as it would have made writing it so much easier.
I'm not an early morning riser, but happened to catch most of this episode while up at 7:00 on Father's Day morning. I was fetching a gift I had stowed at the office (so my husband wouldn't find it).
How could I have possibly missed Bobby McFerrin in concert when he was here in Lincoln a couple of years ago? How could I not know what an incredibly amazing experience it would have been? Listening to your program, I now know.
While not a spiritual person, I can entirely understand why Mr. McFerrin is. Music can do that to a person. I grew up in a very musical family. My parents, grandparents and almost all my aunts and uncles sang. My cousins sing. Nearly everyone in the family sings. My sister has a musical performance degree, she's currently a soprano with the Kennedy Center choir.
Our mother sang Ave Maria for nearly every wedding in her large Catholic family, and it often brought tears to my eyes. But listening to McFerrin perform it, I nearly broke down in sobs. What a stunningly beautiful rendition.
Thank you for making my morning.
Heck, thank you for making my week.
I am a church organist. When I was listening to Bobby talk about what he wants to happen at a "performance" it suddenly struck me that, as an organist, this is what I hope for when I play for worship. That people will want to sing, that they'll feel the grace and love of God deep within them through the music and that they'll leave worship with a feeling of joy. That through the singing with others of faith around them, they will express themselves. I have never thought of myself as a performer, but I guess the best word is facilitator. Every piece of music I prepare for before, during and after the service, the way I play the liturgy and hymns, all of it is meant to facilitate worship within each individual person.
I am also a Preschool teacher. When he talked about singing when you're tempted, it reminded me of how, many times when things are chaotic in the classroom or behavior is not as I expect, I will just start to sing - not a song, but just words, names, etc and it has this calming effect on the children. Part of it is just probably that they're so shocked it gets their attention and diverts them from what they were doing. But it is almost magic that when I sing, they listen and respond so much more quickly than if I am talking.
All the World Is Sad and Lonely
Lyrics catch in the current of thought and a melody eddies in snagged memory. My flow is disrupted; my concentration miscarried. More notes and words burble to the surface and sink in the cool clarity of not now. My mother sings the prayer from Hansel and Gretel. Julie Andrews brings the hills alive. Gerry Rafferty winds me through Baker Street. A song is hooked and lured from my throat
It's summertime but who sings to me? Is it George Benson or Cleo Laine? Am I sad or mellow? Do I just need to hear a little beauty or find a private place within to weep for no reason other than give myself permission? I know no tear before song.
I sang at the office. Something about the end of work demanded acknowledgment, celebration. I did not choose to sing or the song that came forth. Which Grace exceeds song in the heart of man?
Road trips are made for song, childhood songs. On Top of Old Smokey. Erie Canal. Clementine. Or even something more contemporary. Maybe Windmills of Your Mind. Unchained Melody. Yesterday. Songs I am not too old to forget.
My grandchildren know no musical heritage before MP3s. My LPs are curiosities. They do not hear what has not been electronically remastered. They have never sung in class. They do not ask Who Will Buy This Wonderful Morning. They do not know the way to San José. They do not Dream the Impossible Dream. But they can rap. Would that my tongue and lips be so limber.
When my dog was sick I sang to him as I staunched the blood pouring from his nose. When the nosebleed abated I was rewarded by a large hug but only if I had remembered all the lyrics to a song. Otherwise my humming was acknowledged by a disdainful parting look over his shoulder as if he escaped not from perdition of pain but the embarrassment of my failure. Now well but old he joins me in the living room when the stereo plays. We lie on our backs soothed by the crack and pop of whatever hooks me. He knows those other voices don't forget the words; there will be no build-up to disappointment.
A friend dies. Will the chariot swing low if we do not celebrate its arrival?
Absent song, all the world is sad and lonely.
The moment I heard Bobby speaking about improv in music, how it moves the soul in a unique way, I became very aware of my practice of improv in dance. Music and dance, truly are one in the same, can hardly be separated. Indeed Bobby kept referring to music as movement.
I attend a dance group in Seattle, that meets once a week to dance, purely dance, with no other agenda. These groups are all over the country. I've danced in them in Texas, Hawaii, California, and here in Washington. Some go by the name Ecstatic Dance, some go by a variety of other titles. Usually the rules are: no talking, no shoes, and respect boundaries. From there one is free to do whatever arises. If you have the instinct to crawl across the floor like a cat, do it!
When I'm dancing, I am often surprised by a movement that comes over me, as if it came through me, not from me. Just my shaking my head a certain way, or tilting my hips, and suddenly a new movement can come out. I feel a sense of power, of connection. As as if the movement unlocks something in my body, and something mysterious comes out.
What is even more powerful is the experience of dancing with others. Sometimes at these dances, one might feel drawn to dance with another. You learn to ask with your eyes and with your body to see if they will join you. Recently I danced with a man I had never met before. We had a beautiful dance, with our eyes closed, sensing each other, supporting each other in whatever movement we made. It was profoundly intimate, though not at all sexual, and I felt that in our dance, that we were there to love each other, the way God loves us. I felt that my body was a conduit to show universal love.
I haven enjoyed Bobby McFerrin for many years and since my children were little I've played his music in our house and danced and sang along. My children laugh and tell me I'm silly. I listened to the unedited interview Ms Tippet did with Mr McFerrin and was so moved by the many beautiful layers of the conversation that I then listened to the edited version as well - (also wanting to hear the music!)
It was such an amazing experience that I offered my 8yr old son a listen to the edited version. He sat rapt listening to the ENTIRE hour. We discussed various aspects of the interview and what was discussed. He really enjoyed the whole interview, "especially the music" he said with glowing eyes.
Thank you Ms Tippet for your amazing and wonderful show but mostly for your unequaled ability to humanize and to touch the soul.
Blessing - Melissa Mead
I'm taking his challenge to sing for 10 minutes - and it is VERY hard. But I'm also considering how I could model his ability to work with the audience. I'm the pastor of a church and more and more we're finding that the congregation is the primary "choir" for the day. We've used all kinds of interesting congregational songs to get us working together but I was challenged to go further. Wonderful podcast!
Mr McFerrin relates how
Mr McFerrin relates how singing can make him feel better physically and emotionally. I agree totally.
In my 20s and 30s I had migraines as a regular thing, and I learned that very often singing for an hour or so would make the migraine go away. I would sing what I was familiar with -- songs by Carole King or Claudia Schmidt -- anything like that.
What a gift song can be!
Bobby McFerrin summed up
Bobby McFerrin summed up perfectly the reasons why playing music is still part of my life and possibly the lives of the several hundred other musicians who gathered for a festival of community bands in NH yesterday (10/13/12). The joy one gets from sharing one's self this way cannot be put into mere words, but Mr. McFerrin almost did.
When I heard him talk about
When I heard him talk about the language of ancestors it reminded me of the native American chants you hear at drum circles. Before there was language there was song for communication and prayer.
Sister Wendy Becket
Sister Wendy Becket effectively used art to explain the Divine in her famous interview with Bill Moyers. Bobby McFerrin just as effectively uses music to get you to experience the Divine in his interview wih Krista Tippett.
Richard Quis, co-author, Thinking Anew: Harnessing the Power of Belief
I am almost 65 and took our
I am almost 65 and took our son, a married man, on a "date" first for sushi and then to see Bobby McFerrin in Cedar Fals, Iowa. Luke had purchased the CD with he and Yoyo Ma and one of the songs on the CD was Ave Maria, along with many wonderful, spine tingling, arrangements. So, my 30 something son and I go and when it is time for the program, out walks ONE person and sits on ONE chair withe ONE bottle of water and the awesome experience begins. But the truly wonderful time was when he stareted with the intro to Ave Maria and we, except for Luke, started doing our "thing" with master leading us.
Krista, it was a joy to listen to you interview him, then to watch the interview. Your programs have been inspirational to me, and like another person said, I do not "put myself" out there, but I am doing it as I was truly touched. Thank you, and if there are any typos, sorry!
Truly one of your best shows.
Truly one of your best shows. You hit so many high notes: a wonderful human connection, a great story, fine research, and genuine moments of unvarnished truth. As a musician and human, I thank you. Listened to it twice!
Yours is one of my favorite
Yours is one of my favorite shows. Thanks you for what you do.
I would love to hear from a Hindu one of these days. Perhaps you have already done this and I simply missed.
Thank you agin.
Bobby Mac Ferrin is a genius
Bobby Mac Ferrin is a genius at his music.He truly understand the power of the mind and how powerful and creative we can be as individuals as we work on our life passions in life.H is music and creativity is awesome.This is a very powerful Interview.Thank you for what you do and the quality interviews you present to the world.
Unbelievable photo. Captures
Unbelievable photo. Captures the music in his soul.
Bobby Mc Ferrin. Oct 18. In
Bobby Mc Ferrin. Oct 18. In response of his interview!
As I was creating my Playlist of Music for my Virtual Class today, I stumbled across....Don t Worry Be Happy and as Memories thru Music JUST IS, I decided to use it !
I watched the Interview and could almost pre think what He would say about How important Improv and Music are to the Human Condition and for the Ultimate goal of Uniting your audience in A Circle of Music.
My Dad was a Musician too, so of course I was raised in the Memories of not only his Music era but his parents Music as well. So my repertoire has full range of the 20 s to current Music.
The spiritual and gift of Music comes thru to others ONLY if they can feel YOU coming thru First... I was very up lifted by catching this interview as well as a confirmation of my own learnings,, experiences, craftsmanship of the art of Improvisation which my Dad would also call "The Ability FOR Quick Recovery" when a Note goes up instead of down.
Thank You God for leading me to this Interview which will now enhance my class this week not only with Bobby Mc Ferrin s music but with his Generosity of Spirit, Knowledge, Wisdom and Musicality.
As a musician and Grandma in Queens, NY I have been blessed with providing Music, Dance and Exercise programs within our Senior Communities during the day. Both my Grans are Musicians, one classical pianist and one Rock n Roll drummer.
If, Mr. Mc Ferrin is ever in Queens, NY and would like to do a Mitvah he is INVITED to attend my Virtual music class and speak with my seniors in person or Virtually and to see how Music has rolled back time in their Hearts, Soul, Body, and Health.
Queens, NY


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Topic: Credit card processing in the UK
I'm looking to develop an online store built in Rails and based in the UK.
Can anyone recommend somewhere that processes online transactions or any tutorials on the subject?
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A forum for Ruby on Rails users
Rails Forum - Ruby on Rails Help and Discussion Forum » Other Rails Programming » Credit card processing in the UK
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I'm looking to develop an online store built in Rails and based in the UK.
Can anyone recommend somewhere that processes online transactions or any tutorials on the subject?
Worldpay is quite good, but with relatively high setup/subscription costs (at least compared to the 'free' of less customisable solutions like PayPal).
Can't think of any other UK-specific ones off the top of my head.
Protx (www.protx.com) are very good, with a simple system and great rates - I use them with clients presently and things are good.
Ah yes, forgot them. They do require you to have your own Internet Merchant Account though, while Worldpay will sort it for you.
Hi Baltar,
Did you find it easy to integrate the protx gateway into a rails app?
And did you use the form or server product.
I am about to do the same and would be grateful for any advice on any potential gotcha's
Hi Baltar,
Did you find it easy to integrate the protx gateway into a rails app?
And did you use the form or server product.
I am about to do the same and would be grateful for any advice on any potential gotcha's
Hiya, sorry missed your post, didn't subscribe to the thread... I haven't actually needed a payment processor for any of my rails apps as of yet but it certainly shouldn't be too hard to get it to work, (I'm talking of the form product - that's the only one clients have needed) - at the end of the day it just outputs html form tags and receives a confirmation back from Protx so if I could implement it in php I don't see it being a problem in our beloved ruby that having been said, if I do get called upon to use payments in a rails app I would probably just release the code out under MIT license, libraries for stuff like payment processing are the ideal open source code since money is involved and you want as many eyes on the code as possible looking for errors - someone might have already written one for all I know, haven't searched to be honest!
I think it's better to choose a payment gateway based upon client (or you own) needs and the services they offer rather than a particular ease of implementation (not suggesting that protx is hard to implement but you get my drift)
I'll shut up now because I'm starting to ramble....
Does anyone have the simpleXOR function converted for use in ruby?
I am currently implementing the ProtX Form VSP on an e-commerce site and having trouble getting the XOR to work correctly
I have the output of the PHP function and my ruby function and they differ slightly
function simpleXor($InString, $Key) {
// Initialise key array
$KeyList = array();
// Initialise out variable
$output = "";
// Convert $Key into array of ASCII values
for($i = 0; $i < strlen($Key); $i++){
$KeyList[$i] = ord(substr($Key, $i, 1));
// Step through string a character at a time
for($i = 0; $i < strlen($InString); $i++) {
// Get ASCII code from string, get ASCII code from key (loop through with MOD), XOR the two, get the character from the result
// % is MOD (modulus), ^ is XOR
$output.= chr(ord(substr($InString, $i, 1)) ^ ($KeyList[$i % strlen($Key)]));
// Return the result
return $output;
def simple_xor(to_encode, password)
keylist = Array.new
output = ""
#convert password into arrray of ascii values
password.each_byte {|b| keylist << b}
len = to_encode.length - 1
(0..len).each do |i|
temp = to_encode[i] ^ keylist[i.modulo(password.length)]
output = output + temp.chr
thanks in advance for any help
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Moderator: Mike
james1985 wrote:I'll be trying in two hours time...expecting to be disappointed!
Mike wrote:Our friend and huge fan, Bob Gannon managed to get tickets for all three shows. He will be reporting to us. I will be away on a hockey tournament but I expect to have internet access and plan to post his reports. At the very least I'll get it up when I get back Sunday.
eggman1979 wrote: What does it mean "most intimate? Is it going to be intimate just because it will be in a small place but playing the same songs as usual or can we expect surprises like Little lamb dragonfly, Rocky Raccoon or Back seat of my car?
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A new study reveals how the amygdala is involved in controlling predatory behavior in mice.
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Antibiotic cycling makes a comeback in the lab; how life scientists can learn from astronauts; napping to conquer fears; deconstructing the cancer R&D crisis
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Scientists document common genetic alterations in cancers of different origins.
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|Best hindi shayari to welcome guests
Best hindi shayari to welcome guests
Category: Hindi Shayari
Urdu Poetry SMS Shayari Romantic Poetry, Hindi Shayari, Ghazals, Love Shayari, Funny Shayari, Romantic Shayari, Urdu Sad Poetry, Friendship Shayari hindi. shayari on love. love poetry, funny poetry, urdu love poetry about life, allama iqbal poetry sms, wasi shah poetry about love, sms poetry, iqbal poetry in urdu, sad urdu poetry.
|Best hindi shayari to welcome guests


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Too Much Spending, Giving Force Osborne Family To Auction Assets
by George Waldon on Monday, May. 14, 2012 12:00 am
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Brantley, who resides in Oak Ridge, Tennessee, said his father was in the United States Air Force and from a young age, he wanted to be a pilot
"My plan all along was to go to WestPoint," said Brantley.
When he was a kid, however, Brantley had a fishing accident that caused him to lose an eye and he soon found out that flying for the army was no longer a possibility. That didn't deter him from fulfilling his dream, though.
"In high school, I saw an advertisement for flight training. I saved my money from delivering papers in order to take the flight test, but I didn't qualify due to only having one eye," Brantley said.
Nevertheless, Brantley wasn't going to give up. He read and studied Wiley Post, the one-eyed, famed pilot who was the first to fly around the world alone in 1931, and decided to continue with his plan to fly.
"I wrote to the Federal boys and told them I wanted to fly. A few weeks later an examiner from Chicago came down to administer the test and I passed," said Brantley.
When it came time to attend college, Brantley briefly put his passion on hold, and received his undergraduate and medical degrees from the University of Alabama. He then entered the U.S. Army as part of the Vietnam draft and was assigned to Alaska as a surgeon, spending three years there. While in Alaska, Brantley began flying again, became President of the Fort Wainwright Army Flying Club, and the bug never left. He encouraged his wife and sons to successfully get their pilots' licenses as well.
After Brantley's retirement, an engineer friend, Calvin Hopper, talked to him about the two of them building a plane. The pair set off on building their dream plane, appropriately named "241 Zulu." This two-day a week labor of love took eight years, more time than they both anticipated, and culminated in the Zenith 701 STOL (short take-off and landing) light sport aircraft. They got it certified by the Federal Aviation Administration (FAA) as airworthy last year.
Subsequently, Brantley, now age 75, had a car wreck caused by an unexplained medical condition and decided to give up the notion of ever safely flying the plane. His friend Calvin had also aged eight years in the process and both of them thought it best to call it quits. Suddenly, they were left with an airplane they were both fearful of flying.
Instead of selling the aircraft they built, Brantley and Hopper decided to donate it to an aviation program. Luckily for SCC, Bert Loupe, the airport manager in Campbell County, Tennessee, knew of the SCC Aviation Maintenance Technology program and its outstanding reputation. He recommended gifting the airplane to the college, and after contacting the program director, the donation was arranged.
"In general, I feel like aviation has slipped," said Brantley. "Now that the economy is coming back, I think aviation as a profession and a hobby will also return. Current aviation mechanics, as well as pilots, are aging and nearing retirement. We need young blood, passionate about careers in aviation, and we hope that 241 Zulu will assist in their education."
David Phelps, SCC Aviation Maintenance Technology Associate Professor, said he was grateful for the donation, which has a fair market value of nearly $40,000. Once the plane arrived at SCC, students assembled it, worked on wiring and got the plane ready to run. Next semester, it will get a new paint job during the college's finishing class. It will also be used in engine class and for taxiing and ground handling.
"This plane has every log book and was ready to go when we got it," said Phelps. "It is 100 percent functional and is one of the nicest donations ever to come to our program."
In addition to being an associate professor, Phelps also holds certification as an airframe power plant mechanic, FAA inspection authorization and is a designated FAA mechanic examiner.
"We are very grateful to Mr. Brantley and Mr. Hopper for their donation," said Phelps. "It will certainly make a difference for our students for many years to come."
To find out more about the Aviation Maintenance Technology program at SCC, contact David Deaton, Program Coordinator, at (606) 451-6772 or firstname.lastname@example.com.


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"The Jewish Kitchen: Recipes and Stories from Around the World" by Clarissa Hyman (Interlink Books, $29.95).
Clarissa Hyman's new cookbook, "The Jewish Kitchen," is alive with miracles -- stories of Jewish life and war-torn Jewish communities, bringing with them their glorious history, rich culture and a cuisine passed through the generations, itself a story of miraculous survival.
This award-winning author crisscrossed the globe, visiting eight families in nine months, recording their stories and recipes.
"The stories were as important to me as the recipes, because I believe in context and background, and I wanted to give snapshots of the Jewish world today to show that there are so many different aspects to the Jewish experience," Hyman said.
From the Israeli food and wine writer Daniel Rogov come pineapple fritters, a classic for Chanukah in Lyon, France, where owner Celestine Benditte-Strauss served them at her renowned Restaurant Cercle.
And rugelach for Chanukah? Hyman describes the lesser-known Chanukah tradition of eating cheese and dairy products in memory of Judith, a brave Jewish widow who beheaded the enemy general Holofernes after feeding him -- what? Hyman said "fatal small cakes."
Some say perhaps she got him thirsty on cheese so that he would drink wine and fall asleep. Others insist it was rich, creamy food for the same reason. While stories differ, the message is clear.
"One Jewish dish, 20 different versions. One Jewish story, 20 different tales," Hyman said. "It's one of the wonderful things about Jewish food: We are as lavish with our symbolism and myths as we are with the sour cream. Any excuse for something delicious to eat."
PineappleIe Fritters a La Celeseine
2 large pineapples peeled, cored and
thickly sliced
Superfine granulated sugar for dredging
1/4 cup Kirsch (cherry brandy)
3 cups all-purpose flour
1 cup warm water
7/8 cup beer
1 tablespoon vegetable oil
1 tablespoon brandy
Pinch of salt
2 egg whites whisked
Apricot jam for spreading
Vegetable oil for deep frying
Superfine granulated sugar for sprinkling
Dredge the pineapple with sugar, then sprinkle generously with the Kirsch. Let steep 30-40 minutes.
Sift the flour and mix with the water, beer, oil, brandy and salt to make a batter. Dry the pineapple slices on a paper towel, then coat them with a thin layer of apricot jam.
While the oil is heating, fold the whisked egg whites into the batter. Take the fruit and batter to the stove. When the oil is hot (350 F), dip the pineapple slices into the batter, then fry until golden brown on both sides. Serve hot, sprinkled with sugar if desired.
Serves 6-8.
Hazelnut Rugelach
13 tablespoons butter, softened
7 ounces cream cheese
2 teaspoons superfine granulated sugar
2 cups all-purpose flour sifted with a pinch of salt
1/4 cup brown sugar
4 tablespoons cocoa powder
2 teaspoons cinnamon
7/8 cup finely chopped hazelnuts (or walnuts)
2 tablespoons butter melted
1 egg white beaten with a little water
Granulated sugar (optional)
Cream the butter and cheese until well blended. Stir in the superfine sugar, then the flour and mix until the dough begins to hold together. Gather into a ball, wrap in plastic wrap and chill overnight.
Preheat the oven to 350 F. Combine the brown sugar, cocoa, cinnamon and nuts and set aside. Cut the dough ball in half and return one half to the fridge while you work with the other.
On a lightly floured surface, roll out the pastry into a thin circle about 10 inches in diameter. The pastry may feel hard at first but it quickly softens. Use a cake pan or plate to help cut out a neat circle. Cut the dough circle into 16 or 8 equal pie-shaped wedges.
Brush the surface of the wedges with melted butter, then sprinkle evenly with half the nut mixture. Cover with a piece of plastic wrap and use a rolling pin to press the filing lightly down into the dough.
Remove the plastic wrap and roll up each wedge from the outside, wide end toward the point, so you end up with minicroissants. Place on a lightly greased baking sheet and brush with the beaten egg white. Sprinkle with a little sugar if desired.
Repeat with the remaining dough and bake for 20-30 minutes until golden brown. Let cool slightly before transferring to a wire cooling rack.
Makes 32 small or 16 large rugelach. Â
Judy Bart Kancigor is the author of "Melting Pot Memories" and can be found on the Web at www.cookingjewish.com.
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Day Two with Bella Blvd–Tips and Tuts
June 19, 2012 by Ellen
Filed under Core Blog, Provocraft, Sizzix
We are here ALL WEEK LONG with Bella Blvd and couldn't be more excited. Our team has create some really gorgeous projects showing off just how great Core'dinations Cardstock goes with the beautiful Bella products. From fabulous patterned papers …to alpha letters …to super fun decorative tape…Bella Blvd. has products for every paper crafter.
So sit back, relax, and get ready to be inspired. Our Design Teams have worked hard for you! If you were here yesterday than you saw some gorgeous layouts from Design Team Member Shaunte Wadley.
We would LOVE it {and I know they would, too} if you could head over to their Facebook page and give them a great big "HI!" from us and the Bella Blvd blog is looking mighty fine, too! Head over there and check out all the gorgeous projects their team has been cooking up this week. You won't be disappointed.
And are you ready for our FIRST giveaway? Get commenting on THIS post to win a Core Prize pack including some of this silky smooth cuts like butter Glitter Silk cardstock….
Tuesday's Tip comes from Design Team Member Lydia Jackson. Lydia pretty much created an entire baby album with Bella and Core. What is so great about this is that it EASY! You have all of your coordinating Bella Blvd embellishments, papers, and alphas AND now you know that our Core Cardstock matches PERFECTLY! I don't know about you, but having all of that at my fingertips makes creating a unified (and super cute) baby album EASY! Not to mention I have always LOVED Bella Blvd chipboard shapes and pieces.
Let's check out what Lydia did…she created her own patchwork background with different pieces of Core Essentials and different embossed patterns. Don't forget to print right on that Core! Gosh this baby boy line is SO CUTE.
And another layout for this super cute baby boy album…Lydia used some Fancy Pants Core Impressions along with some Core Essentials and Core Tags. LOVE that piece of tape right over the photo.
And next up we have a Tuesday Tutorial for you from Design Team Member Andrea Amu using the very cool Designer Tape from Bella Blvd that we have all fallen deeply and passionately in love with here at Core. She cut it on her Cricut…SO COOL! Here is a little bit about this project in her own words, "I added a strip of the yellow chevron designer tape from Bella Blvd to a scrap of yellow Brights Core Essentials and I used my Cricut to diecut 1/2″ alphas (Lyrical Letters Cricut cart – Jack Sprat font). I also folded some of the paper tape into tabs and used them on the neck of the giraffe diecut which was cut from some yellow WhiteWash Core. I embossed the giraffe (Cricut New Arrival cart – cut at 6″) with a Sizzix animal print folder, sanded the spots and went in and added some extra brown tones with a Ranger ink pad and the Ranger blending tool."
LOVE it! What do you think?
The blending looks so great on the giraffe. By embossing, then sanding and then adding the ink really makes it look realistic and adds another layer of depth. But remember…emboss, sand and THEN ink.


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Journal of the Southern African Institute of Mining and Metallurgy
On-line version ISSN 2411-9717
Print version ISSN 0038-223X
J. S. Afr. Inst. Min. Metall. vol.111 n.12 Johannesburg Dec. 2011
The design of stable pillars in the Bushveld Complex mines: a problem solved?
D.F. MalanI; J.A.L. NapierII, I
IDepartment of Mining Engineering, University of Pretoria, Pretoria, South Africa
IICSIR, Pretoria and Department of Mining Engineering, University of Pretoria, South Africa
This paper gives an overview of the difficulties associated with determining the strength of hard-rock pillars. Although a number of pillar design tools are available, pillar collapses still occur. Recent examples of large-scale pillar collapses in South Africa suggest that these were caused by weak partings that traversed the pillars. Currently two different methods are used to determine the strength of pillars, namely, empirical equations derived from back analyses of failed and stable cases, and numerical modelling tools using appropriate failure criteria. The paper illustrates that both techniques have their limitations and additional work is required to obtain a better understanding of pillar strength.
Empirical methods based on observations of pillar behaviour in a given geotechnical setting are popular and easy to use, but care should be exercised that the results are not inappropriately extrapolated beyond the environment in which they are established. An example is the Hedley and Grant formula (derived for the Canadian uranium mines), which has been used for many years in the South African platinum and chrome mines (albeit with some adaptation of the K-value). Very few collapses have been reported in South Africa for layouts designed using this formula, suggesting that in some cases it might yield estimates of pillar strength that are too conservative.
As an alternative, some engineers strongly advocate the use of numerical techniques to determine pillar strength. A close examination unfortunately reveals that these techniques also rely on many assumptions. An area where numerical modelling is invaluable, however, is in determining pillar stresses accurately and for studying specific pillar failure mechanisms, such as the influence of weak partings on pillar strength.
In conclusion, it appears that neither empirical techniques nor numerical modelling can be used solely to provide a solid basis for conducting pillar design. It is therefore recommended that both these techniques should be utilized to obtain the best possible insight into a given design problem. Owing to the uncertainties regarding pillar strength and loading stiffness, monitoring in trial mining sections and in established mining areas is also an essential tool to test the stability of pillar layouts in particular geotechnical areas.
Keywords: pillar design, bord and pillar mining, stable pillars.
Appropriate pillar design is a fundamental building block of mine design to ensure the safe and economic extraction of valuable national resources. It is therefore worthwhile to take a critical look at the tools currently available to rock engineers to conduct these designs. This paper focuses only on stable pillars and does not address the issues associated with crush/yield pillars. The design of stable pillars is currently very topical in the shallow hard-rock mining sector in South Africa, and this paper will highlight a number of examples from this country. Hard-rock pillar design nevertheless appears to be of universal interest, as shown by the examples described below.
Zipf1 describes collapses of room and pillar mines in the USA. The term catastrophic pillar failure or CPF is used to describe the mechanism whereby a few pillars fail initially; their load is then transferred to adjacent pillars, which also fail. This may result in a 'pillar run' and hundreds of pillars may fail in the process. A number of examples of CPF collapses in 'metal' mines are given in Zipf's paper, and apparently at least four such examples have occurred in the USA since 1972. One of the more recent examples is a large pillar collapse in a room and pillar base metal mine2. Figure 1 illustrates the area of the collapse. The failure began in four centrally located pillars and spread rapidly to include almost 100 pillars. The pillar width was 8.5 m and the room width was 9.7 m. The pillar height was about 12 m, resulting in a widthheight ratio of 0.70. The extraction ratio was approximately 78%. Based on the examples available to him, Zipf1 made the comment that mines experiencing CPF generally exhibit the following characteristics (quoted directly from his paper):
'(1) Extraction ratios are usually more than 60%. A high extraction ratio will put pillar stress close to peak strength and provide ample expansion room for the failed pillar material.
(2) Width-height ratios of pillars are always less than 3 for coal mine failures, usually much less than 1 in metal mine failures, and less than about 2 for nonmetal mine failures. A low width-height ratio ensures that the failed pillar material can easily expand into the surrounding openings and that the failed pillar will have little residual load-bearing capacity.
(3) The number of pillars across the panel width is always at least five and usually more than 10, which typically ensures that pillars have reached their full tributary area load. Minimum panel widths for CPF are at least 80 m.
(4) Substantial barrier pillars with width-height ratios more than 10 are absent from the mine layout.
(5) Although CPF seems more prevalent in shallow mines less than 100 m deep, this may be only a reflection of the prevalence of shallow room-and-pillar coal mines.'
An extensive database of hard rock pillar failures was compiled by Lunder and Pakalnis3, who analysed 178 case histories from hard-rock mines of which 98 were located in the Canadian Shield. Of the pillars investigated, 76 were classed as stable; 62 were classed as failed; and 40 were classed as unstable. Many of these pillars were rib or sill pillars from steeply dipping ore bodies. Lunder and Pakalnis proposed that the pillar strength can be adequately expressed by two factor-of-safety (FOS) lines. Pillars with a FOS < 1 fail, while those with a FOS > 1.4 are stable. The region 1 < FOS < 1.4 is referred to as unstable and pillars in this region are prone to spalling and slabbing, but have not completely failed. The data collected by these authors is given later in this paper.
Esterhuizen4 conducted an evaluation of the strength of slender pillars. Figure 2 illustrates published case histories of failed pillars from hard-rock metal mines. This figure illustrates that the pillar strength becomes highly variable as the width to height ratio decreases. For a ratio of 1, the pillar strength is not expected to exceed 65% of the laboratory strength (but it can also be significantly lower than this value). Esterhuizen4 suggests that a larger factor of safety is required for these pillars to account for the increased variability in strength. Numerical modelling indicated that for slender pillars, the difference between the pillar load at the onset of spalling and the ultimate pillar strength can be small. This implies that slender pillars are at or near the point of failure at the onset of brittle spalling.
Although a large number of additional papers on pillar design can be found in the literature, the objective of this paper is not to give an overview of all of these, but rather to highlight the difficulties associated with pillar design in South Africa and to emphasize the need for additional research. Some examples of pillar failures in South Africa are therefore described below, and the commonly used pillar design methodologies are critically examined.
The Coalbrook disaster and the evolution of pillar design in South Africa
Although this paper focuses on pillar design in hard rock mines, it is worthwhile to investigate the evolution of pillar design in South Africa in general. This will shed some light on the apparent lack of appropriate pillar design tools for shallow hard rock mines.
Initially, pillar dimensions and mining spans in South African coal mines were based on experience obtained through trial and error. This resulted in a number of collapses. The first report of a coal pillar collapse in South Africa was in 1904 at the Witbank colliery5. Since that date, 81 pillar collapses have been recorded in 31 collieries in the former Transvaal and the Free State. Between 1904 and 1965, there were 50 pillar collapses6. The research into coal pillar strength in South Africa gained momentum after the Coalbrook disaster. As described by Van der Merwe7, the major need for coal mine research in South Africa was identified when the Coalbrook disaster occurred on 21 January 1960. In total, 437 workers lost their lives when pillars over an area of 324 hectares collapsed (Figure 3). Following the disaster, the South African government sponsored research into coal mine safety by forming the Coal Mines Research Controlling Council (CMRCC). Research into coal pillar strength received top priority from the Council for Scientific and Industrial Research (CSIR) and the Chamber of Mines Research Organization (COMRO). A large in situ testing programme to determine pillar strength was conducted by the CSIR8 and tests were also conducted by the Chamber of Mines9.
A key study on coal pillar strength was conducted by Salamon and Munro10 and the findings as described in their paper are still being used today. It was postulated that the strength of the pillars can be expressed, in the given range of dimensions, as a power function of the height and width. Of interest is that this 'power law' was originally proposed by Greenwald, Howard, and Hartmann11. Salamon and Munro10 derived their equation by estimating the value of the constant K and the powers of width and height by the method of maximum likelihood. The derivation was empirical and was based on data from stable and collapsed cases. The analysed data included 125 cases of which 27 were collapsed pillars. It is noteworthy that they warned in the paper against the following mistake commonly made in rock engineering:
'The work described in this paper is essentially empirical, and the results, therefore, should not be extrapolated beyond the range of the data which were used to derive them.'
Although the formula is well known, it is repeated below for completeness:
where K reflects the fitted 'strength' of a metre cube of coal (7.2 MPa), w is the width of the (square) pillar, and h is the height in metres. The parameters a and b are equal to 0.46 and 0.66 respectively. The pillar volume is given by V=w2h. Defining the width:height ratio, R = w/h, Equation [1] can be expressed in the alternative form12:
It can be seen from Equation [2] that if a = b, the pillar strength is independent of the pillar volume whereas if b > a, as in Equation [1], the pillar strength is predicted to decrease as the pillar size is increased even if the pillar shape is unchanged.
Did the use of Equation [1] improve pillar designs? Wagner and Madden13 reported that since 1967, approximately 1100 million tons of coal had been mined in South Africa and they estimated that 1.2 million pillars were left underground during that time. During the same period, 13 cases of pillar collapse were reported, involving a total of about 4000 pillars. This corresponded to a probability of failure of only 0.003. In spite of the satisfactory performance of the pillar design procedure, three areas requiring further research were identified. These were:
Regional differences in coal seam strength
Effect of mining method on pillar strength
Strength of squat coal pillars.
Regarding the strength of the squat pillars, the original database used by Salamon contained no pillar with a width to height ratio greater than 3.8. Evidence collected in the field suggested that beyond a critical width to height ratio, the pillar strength exceeds that suggested by Equation [1]. Salamon14 proposed therefore that when the width to height ratio exceeds a critical ratio, the pillar strength formula should be replaced by the following:
K = the strength of a unit cube of coal
V = the pillar volume (m3)
R = the pillar width to height ratio
Ro = the critical width to height ratio
ε = rate of pillar strength increase.
From field data, no evidence was available of a collapse of a pillar with a width to height ratio greater than 4. Therefore the critical width to height ratio was selected as 5. A value of 2.5 was chosen for ε as it was considerably lower than that obtained from laboratory tests on sandstone.
Regardless of the apparent success of the coal pillar power strength formula, some criticism can be raised regarding its applicability. Virtually all laboratory and field evidence indicates that the width-height strengthening curve has a zero or positively upwards curvature15. The power formula forces downward curvature and this leads to the inelegant form of the squat pillar formula. An objection raised by Bieniawski16 is that according to the power law formulation, the cube strength (w =h) would continue to decrease indefinitely with side length. This is considered unreasonable17.
Based on these criticisms, an alternative 'linear' equation, with no volumetric size effect, was proposed which directly expresses the strengthening effect of the width-height (w/h) ratio16.
As noted above, Equation [1] implies that pillars with self-similar dimensions (the same ratio of w to h) will have different strengths and that the predicted strength decreases as the pillar volume is increased. By contrast, Equation [4] has no size effect in that the strength depends only on the ratio of w to h. York and Canbulat18 compared the relative goodness-of-fit power formula versus linear forms for both coal and hard-rock materials, and concluded that the latter behaved at least as well.
Further work regarding coal pillar design was conducted by other workers (e.g. Van der Merwe7), but it is beyond the scope of this paper and the reader is referred to this reference for additional information. In conclusion, Ryder and Jager15 state:
'The power law and its derivatives are perhaps too entrenched in coal engineering to warrant withdrawing from them at this time, but in hard rock engineering, the simpler and probably more realistic linear forms are advocated for general use.'
Regarding the gold mining industry in South Africa, the pillar problem was a completely different issue owing to the great depth of these mines and the associated seismicity. Leaving small pillars or remnants in stopes is in fact detrimental to stability as these may become a source of seismicity. This was a key motivation for the early adoption of the longwall mining method as it minimized the formation of remnants19. These longwalls remained vulnerable to seismicity and one method to reduce this risk was to leave strips of ground behind as strike stabilizing pillars. A key function of these pillars is to reduce the levels of energy release rate15. Owing to the size of the gold mining industry and the role it played in the South African economy, significant research into the behaviour of these pillars was conducted over the years. Their widths typically vary from 30 m to 40 m and at a typical stoping width of 1.5 m, this gives a width to height ratio of at least 20. These pillars are therefore considered 'indestructible'. Seismic problems are nevertheless experienced when these pillars 'punch' into the footwall, and a simple empirical formula is used during design to ensure that that the average stress on these pillars does not exceed a specified multiple of the strength of the rock in the footwall or hangingwall. So-called bracket pillars are also used to clamp seismically active geological structures in the gold mines. As the nature and function of the bracket and stabilizing pillars are different to those found in shallow hard-rock mines, these topics are not discussed in this paper and the reader is referred to Ryder and Jager15 for additional information.
In comparison to the gold and coal mining industries in South Africa, the platinum and chrome mines were the proverbial 'stepchildren' and have never received the same attention in terms of research efforts and funding. Fortunately, the mines in the Bushveld Complex have never had catastrophic pillar failures analogous to the Coalbrook disaster or rockbursts to kick-start research, and it was only with the rapidly increasing price of platinum from 1999 onwards that research activity started to receive more attention. In terms of rock engineering knowledge, much was therefore 'borrowed' from the other mining sectors and overseas research findings. A contributing factor may also have been that pillar cutting in the hard-rock industry is not as precisely controlled as in the coal industry, and it is therefore rather difficult to repeat the statistical approach followed by Salamon and Munro10. An example is shown in Figure 4, which illustrates a mapped survey of typical pillar cutting in one of the Bushveld mines, where the pillars can be seen to have a wide variety of shapes. Gay et al.20 stated that at that time:
'The design of pillar layouts in shallow to medium depth chromium and platinum mines has not reached the same advanced stage as has the design of pillars in coal mines.'
Three reasons for this were given in the paper namely:
Very little is known about the strength of small pillars composed of chromitite or pyroxenitic platinum ore
Because of the very competent and stiff strata in the hangingwall, it is difficult to determine the pillar loads accurately
The presence of and shear along near vertical faults can change the loading condition from a stiff displacement controlled system to a soft load controlled system.
A large collapse involving pillars at the No 6 Shaft, Bafokeng North mine is described by Kotze21. The collapse occurred in February 1975. Luckily, nobody was injured during this collapse as it occurred overnight. This collapse is referred to as the 'Hospital collapse' by mine personnel as the mine's hospital was located on surface above the collapsed area and some damage was sustained by the hospital building owing to the resulting subsidence. The building was repaired and it is still being used today. Extraction of the reef in this area was by room and pillar methods, with rooms approximately 25 m wide and pillars nominally 5 m square, providing an extraction of 96%. It appears as if the pillars were cut smaller than this, as Kotze21 estimated from the mine plans that the equivalent 'average' pillar width in this area was 3.6 m with an associated extraction of about 98%. Unfortunately no mention is made in the paper of the pillar height. Local hangingwall support was provided by timber sticks and mat packs. The strike span of the stope at the time of the collapse was approximately 400 m, and the average depth of the overburden was 58 m. The extent of the collapse was of the order of 350 m on strike and 350 m on dip, and the outline of the collapsed region is shown in Figure 5. The upper and lower limits of the fall were bounded by two faults. Up to the time of the collapse there were no signs of pillar scaling and no timber poles were broken, suggesting that conditions were indeed stable. This condition, however, changed overnight with the entire rock mass to surface moving down between the two faults shown in Figure 5. No doubt this observation resulted in the hypothesis given by Gay et al.20 that the presence of and shear along near vertical faults can change the loading condition from a stiff displacement controlled system to a soft load controlled system. Kotze21 used numerical modelling and stress measurements conducted by the CSIR in 1975 in pillars adjacent to the collapse area to estimate a Merensky pillar strength of 75 MPa (for a pillar with an effective width of 4.3 m). This value is of course applicable only to the particular width to height ratio of the pillars (the pillar height was given by Kotze21 as 1 m).
Empirical methods to estimate hard rock pillar strength
Martin and Maybee22 give a very good overview of the different empirical strength formulae that were developed to predict pillar strength. A comparison of these formulae is given in Figure 6. These curves were calculated for a pillar height of 5 m.
In South Africa, based on the success of the Salamon and Munro strength formula in the coal mines, it was natural for the shallow hard-rock mines to adopt a similar power-law strength formula. The necessary research to develop and calibrate a formula for local conditions was, unfortunately, never conducted. Instead, the Hedley and Grant formula23 developed for the Canadian uranium mines was adopted. Only the K-value was modified to reflect local rock strengths. This approach seemed to work well and over the years it has become firmly entrenched. It would not be incorrect to state that it is currently the 'industry accepted' method for designing pillars in shallow hard-rock mines in South Africa. Ryder and Jager15 comment that this original formulation: 'for want of local data, have subsequently been applied in South African hard-rock mines'. This is a good example of what frequently happens in rock engineering. Over time, initial assumptions and interim solutions become entrenched as common practice and the original assumptions are rarely revisited or questioned. Based on this wide acceptance of the Hedley and Grant formulation and lack of local research into more appropriate formulations, it will be worthwhile to examine the assumptions made in the original paper.
The uranium mines in the Elliot Lake area used a stope and pillar layout to mine the orebody. Narrow pillars about 250 ft (76 m) long were left along dip (see Figure 7). The pillars which were chosen for analysis were typically conducted 10-20 ft wide (3-6 m) and 8-20 ft high (2.5- 6 m). The width to height ratio of most of the pillars was close to 1 and only a very few (3 in the database) had a width to height ratio of 2.5. It is clear that this original formulation was derived for slender rib pillars and it can be questioned whether it is applicable to square pillars with a width to height ratio greater than 2.5. The original data used by Hedley and Grant is reproduced in Table I. It is immediately obvious that the dataset used was very small (28 pillars). This should be compared to the coal database of Salamon and Munro10, which included 125 pillars of which 27 were collapsed. The width to height ratio of the failed pillars varied from 1.1 to 1.5. Only 3 of these pillars were 'crushed' and 2 were 'partially crushed'. Of further concern is that it is stated in the paper that: 'The information on complete pillar crushing was obtained second-hand because it happened in mines which are closed.' This work was conducted in the days before computer-based numerical modelling could be used to determine pillar stress. The approach followed was therefore to use tributary area theory, which relates the pillar stress to the pre-mining stress and the extraction ratio by:
σP = pillar stress
So = pre-mining stress normal to the orebody
e= extraction ratio.
For workings inclined at an angle α to the horizontal, the normal stress So is a combination of the vertical stress component Sv and the horizontal stress component Sh:
The vertical stress was assumed to be simply a function of the weight of the overlying strata and the horizontal stress perpendicular to strike was assumed to be 3000 pound per square inch based on measurements in two mines. The stress given in the Table I for each pillar is therefore only a rough estimate. The methodology followed in the paper to derive the pillar strength formula can be summarized as follows:
The first step was to adopt the power law strength formulation used by Salamon and Munro10. In the notation of Hedley and Grant23 it is given as:
Qu = pillar strength (psi)
w = pillar width (ft)
h = pillar height (ft)
K = strength of 1 ft cube (psi)
a and b are constants
Hedley and Grant23 acknowledge that this equation refers to square pillars, whereas those in the uranium mines are long and narrow. Their assumption was therefore that the strength of the slender pillars will not be much greater than a square pillar of width equalling the minimum width of the long pillar.
Secondly, from extrapolation of laboratory tests, it was estimated that the value of K is 26 000 psi for a 1-ft cube.
Thirdly, appropriate values for parameters a and b had to be derived. Three different sets of values were available to them at that stage in the literature. The value for a was relatively constant at 0.5 and Hedley and Grant23 therefore decided to also adopt this value. As b varied more, a new value was computed and their approach was to focus on the three failed pillars in the database. For each of these pillars, the tributary area stress in the table was assumed to be the pillar strength. This value, as well as the K-value and a = 0.5, were substituted into Equation [7] and the value of b was solved for each pillar. The calculated values of b ranged from 0.736 to 0.768 with a mean of 0.75. This value was adopted and it resulted in the now familiar Hedley and Grant formulation.
Clearly the formulation above is based on a large number of assumptions, and the applicability of this formulation to the design of hard-rock pillars in the Bushveld Complex in South Africa becomes highly questionable. The first use of this formula in a South African mine is not clear, but Ozbay et al.25 stated that it was 'popularized by Wagner and Salamon26 as quoted by Kersten27'. Kersten27 used it to design pillars for Agnes Gold Mine. Subsequently, it has been used to design a large number of bord and pillar layouts in the country with an appropriate modification of the value of K. The rule frequently used in South Africa is to estimate K at between one-third and two-thirds of the Uniaxial Compressive Strength (UCS) of the pillar material (e.g. see Ozbay et al.25). Almost no collapses in the Bushveld Complex have been reported to date using this formulation (except where weak clay layers are present in the pillar, see sections below), so the uncomfortable question therefore remains: Why does it work and are the current designs perhaps too conservative? One hypothesis is that the 'squat' behaviour of hard-rock pillars may occur significantly earlier than the w:h ratio of 5 assumed for coal pillars15.
As an alternative to the estimate of K being one-third of the UCS of the pillar material, Stacey and Page28 and Stacey and Swart29 suggested that the value of K be chosen as the design rock mass strength (DRMS). The DRMS takes into account the rock quality, unfavourable joint orientations, and the excavation method30. Wesseloo and Swart31 conducted a study on LG6 Chromitite pillars to determine the constants K, a and b (see Equation [7]) more accurately for these pillar types. The study showed that the value of the exponents a and b suggested by Hedley and Grant23 do not apply to these chromitite pillars. They indicated in the study that values of a = 1 and b =1 may be more applicable to these pillars.
As a further attempt to develop a new formula for the South African mines, Watson et al.32 derived new values for the power law formulation given in Equation [7]. They used a maximum likelihood evaluation similar to that used by Salamon and Munro23. Their database consisted of 179 Merensky Reef pillars of which 109 were stable. The width to height ratio of the pillars in the database ranged from 1 to 8, with the majority between 3 and 6. Only one pillar had a width to height ratio of less than 1. The values derived are K = 86 MPa, a = 0.76, and b = 0.36. It is interesting to note that the b parameter is much lower than for the Hedley and Grant formula. The formula predicts pillar strengths that are much greater than the traditional Hedley and Grant formulation, with K values assumed to be a third of the UCS (see Figure 8). Unfortunately, it is not known if this formula has been tested in any trial mining sections.
Corrections for rectangular pillars
Equation [7] is applicable to square pillars. Another awkward assumption commonly made when designing pillars is to calculate the 'effective width' for rectangular shaped pillars. Holland and Gaddy33 state that only the minimum lateral dimension, w, affects the strength of a pillar, while the other dimension, L, has no effect. Wagner9 suggested that the effective width of a pillar should take the form:
where A is the cross-sectional area of the pillar and C is the perimeter. This formula is based on observations made by Wagner during large scale underground tests, namely that: 'the strength of the circumferential portions of a pillar is virtually independent of the width-to-height ratio, whereas the strength of the centre increases with increasing ratio.' The effective width as defined by Equation [8] approaches a finite value of twice the minimum pillar width for very long and narrow pillars. It is not clear if this assumption is correct and Ryder and Ozbay34 suggested an alternative shape strengthening factor of the form f= 1.0/1.1/1.2/1.3 for pillars having w 1/ w 2 ratios of 1/2/4/∞. This implies that Wagner's perimeter rule may be overestimating the strengthening effect of very long pillars.
Unfortunately no good experimental evidence is available regarding the effect of pillar shape on strength for hard-rock pillars in South Africa and this area requires further research. Somewhat concerning is that the whole empirical design philosophy rests on a huge number of unproven assumptions, and pillar strength is clearly an area that requires systematic research in future.
Recent examples of pillar failures
To illustrate the inherent dangers of using empirical design formulae for rock masses in environments for which they were not originally designed, consider three case studies of recent mine collapses in the South African Bushveld Complex.
Spencer35 reported on the failure of the pillar system and the subsequent closure of the Wonderkop Chrome Mine in May 1998 (stoping commenced only in September 1996). The mine is located close to Rustenburg and exploited the Lower Group chromitite seams, namely the LG6 and LG6A. An internal pyroxenite waste band is found between these two reefs and this results in the pillars having a multi-layered appearance (Figure 9) wherever these two reefs are mined. The Wonderkop Mine was the most easterly situated LG6 mining operation in the Rustenburg area and was situated adjacent to the Spruitfontein dome (an upfold structure which separates the Rustenburg section from the Marikana section). Its close proximity to the Spruitfontein dome has influenced the structure of the LG6 and LG6A seams and this has resulted in thick clay layers (up to 300 mm in some places) traversing the pillars in some areas (Figure 10). The position and thickness of this weak layer is highly variable (e.g. see Figure 11).
The original pillar design at the mine was conducted using the Hedley and Grant pillar strength formula. The pillar sizes were 12 m x 6 m giving an 'effective width' of 8 m according to Wagner's perimeter rule. K was assumed to be 27.3 MPa, which was a third of the laboratory strength of the rock (using samples obtained from another mining section). Owing to the complex multilayer structure of the pillars, it is not clear which of these layers were tested. The stoping width was 2 m, so the width to height ratio was at least 3 if the smallest dimension of the pillars is considered. When using the 'effective width' of the pillars as 8 m, the strength of the pillars was estimated to be 45.9 MPa.
The first underground inspection of the pillars by the consulting rock engineer was conducted in July 1997. During this visit it was noted that some joints were beginning to open at the corners of some pillars. Some joints were also opening up at the sides of the pillars and in a few cases sliding along the clay layer was noted. Figure 12 illustrates the layout and the positions where pillar failure was observed. Following these observations, steps were taken to introduce a system of barrier pillars (Figure 13) with a width to height ratio of at least 10 (it is generally believed that at this ratio the pillar becomes indestructible). During the following nine months, the condition of the pillars continued to deteriorate. To strengthen the pillars along the main dip belt and road declines, two strategies were adopted; namely waste stowing between the pillars and mesh and lacing of the pillars. The success of the mesh and lacing of the pillars appeared to be doubtful, as the drilling process introduced additional water into the clay which probably weakened the pillars further. During April 1998, the failure process accelerated and the rate of closure in some areas increased to 1.8 mm/day. Numerous falls of ground occurred and management decided to cease operations at this stage. Recently, a back analysis of this pillar failure was conducted by the authors using the TEXAN boundary element program36, which can explicitly simulate the individual pillars and calculate the stresses on these pillars relatively accurately. The results are shown in Figure 14. Two face positions were simulated; namely July 1997 (Figure 12) and July 1998 (Figure 13). From this study, the Hedley and Grant formulation was used to back-calculate the K-value for the pillars. A value as low as 6 MPa was obtained, which is in agreement with earlier back analysis studies by Spencer35, who estimated a value as low as 4.6 MPa. It should nevertheless be noted that a power law strength formula might not be applicable to these pillars owing to the presence of the clay layer. Although the mechanism of pillar failure needs further investigation, the low strength of the pillars can probably be attributed to the low friction angle of the clay layer, which allowed lateral deformation of the pillar and a reduction of confinement.
Two other large scale pillar collapses recently occurred in the Bushveld Complex. Detailed information regarding these collapses is not available in the public domain, and therefore these mines will only be referred to as Mine A and Mine B.
Mine A is a platinum mine located in the eastern portion of the Bushveld Complex. At this mine, a clay layer is also present at the hangingwall/pillar contact (Figure 15). The reef exploited in this area is the UG2. The original mine design was conducted using the Hedley and Grant pillar strength formulation with a K value of 35 MPa. The mining height was 2 m. In mid 2008, some concern was expressed regarding the stability of the pillars and a minor collapse occurred during this time. In an attempt to reinforce some of the pillars, many were supported using fibre-reinforced shotcrete. This did not stop the deterioration, however, as shown in Figure 16 with the cracked shotcrete clearly visible. During December 2008, operations were temporarily suspended at the mine when the decline was affected by the instability.
Similar to Wonderkop Mine, Mine B also exploits the LG6/LG6A chromitite reefs. The problem is essentially similar to that experienced at Wonderkop Mine with the presence of a clay layer in some of the pillars. This resulted in collapses in parts of the mine. Typical pillar failure at the mine is shown in Figure 17. Experience has indicated that increasing the pillar sizes does not necessarily work in these cases.
From these studies, the drawbacks of using empirical pillar strength formulae are obvious. The failure in all three cases is caused by the presence of clay layers which substantially weaken the pillars. The original empirical formulae were developed for different rock types and the application of these formulae outside the limits for which they were developed resulted in the large mine collapses described here.
Numerical modelling to estimate pillar strength
From the sections above, it is clear that the applicability of the current empirical formulas in hard-rock mines is highly uncertain and additional verification and calibration work is required. The orebodies in the Bushveld Complex are very different to that for which the Hedley and Grant formulation23 was derived. Furthermore, the restricted range of slender width to height ratios used when deriving the equation is unfortunate and the choice of the appropriate K value is undefined and highly uncertain.
The alternative to the empirical approach is to use numerical modelling with appropriate failure criteria to determine pillar strength. A vast amount of literature is available on attempts to simulate pillar failure, and it is not the objective of this paper to summarize all these findings. Focus will rather be placed on recent work that is applicable to the pillars in the Bushveld Complex.
Joughin et.al38 presented a risk based approach to the design of chromitite pillars. Numerical modelling was conducted using the finite element program PHASE2 and a Hoek and Brown failure criterion. The variability of the strength properties, pillar dimensions, and spans were taken into account by applying the Point Estimate Method. Many numerical analyses were conducted with varying input parameters to obtain statistical distributions of pillar safety factors. Probabilities of failure were then determined from the distributions. Back analysis of an area with a large collapse and another in which only a few pillars had failed indicated good agreement with the actual number of pillar failures.
Day and Godden39 presented a paper describing the design of panel pillars on Lonmin's platinum mines. They state that the validity of their approach is supported by extensive underground surveys and by computer backanalysis studies. According to the authors, over 300 pillars per month were cut at Lonmin at that stage and these pillars behaved as expected. The method apparently works well up to width to height ratios of 5.5, but not at greater values owing to the onset of squat pillar effects. This seems rather disappointing as the expectation is that a numerical method with an appropriate constitutive model will 'automatically' take care of the onset of squat pillar behaviour. Pillar strength was estimated by two-dimensional FLAC modelling using the original Hoek and Brown40 failure criterion:
where σc = uniaxial compressive strength (MPa) and m and s are constants that depend on the properties of the rock. The constant m was determined from laboratory testing, and s equals to 1 for intact specimens. In situ values for the constants m and s were derived by application of rock mass quality ratings using the equations of Priest and Brown41 for undisturbed rock masses:
The authors39 derived in situ values for m and s for the UG2 and Merensky reefs at Lonmin's Mines. Typical values used in the modelling are as follows: UG2; m = 25.83, s = 0.51 for a RMR of 94, Merensky (Type B); m = 8.7, s = 0.57. The resulting simulated pillar strengths seem plausible when the pillar width to height ratio is low. The authors nevertheless acknowledge that squat pillar behaviour is not correctly simulated by this approach and that this will probably result in pillars being over-designed at depths exceeding 700 m.
A further concern regarding this approach is that the failure criterion is still empirical and the unmodified Equations [10] and [11] may not be appropriate for the pillar material in the Bushveld Complex. Pells42 also expressed some concern about the Hoek and Brown failure criteria and quoted Mostyn and Douglas43 which provided a detailed critique of this failure criterion for intact rock.
'...there are inadequacies in the Hoek-Brown empirical failure criterion as currently proposed for intact rock and, by inference, as extended to rock mass strength. The parameter mi can be misleading, as mi does not appear to be related to rock type. The Hoek-Brown criterion can be generalized by allowing the exponent to vary. This change results in a better model of the experimental data.'
Martin and Maybee22 investigated the strength of hard rock pillars by using both empirical pillar strength formulae and numerical modelling using a Hoek-Brown failure envelope. Figure 18 illustrates a comparison between the pillar stability graph developed by Lunder and Pakalnis3, the Hedley and Grant equation and Phase 2 - Hoek and Brown modelling using different values of GSI. Figure 19 illustrates the same data using the Hoek and Brown brittle parameters. The conclusion reached by Martin and Maybee22 is that twodimensional finite element analyses using conventional Hoek and Brown parameters for typical hard-rock pillars predicted rib pillar failure envelopes that did not agree with empirical pillar failure envelopes. It appears that the conventional Hoek-Brown failure envelopes over-predict the strength of hard rock pillars. This occurs because the failure process is fundamentally controlled by a cohesion loss process in which the frictional strength component is not mobilized. Their recommendation is that Hoek-Brown brittle parameters (mb = 0 and s = 0.11) be used to simulate pillar strength.
Hoek, Kaiser, and Bawden44 summarized the rock mass conditions for which the Hoek-Brown failure criterion can be applied. The criterion is strictly applicable only to intact rock or heavily jointed rock masses that can be considered to be homogenous and isotropic. For cases in which rock mass behaviour is controlled by a single discontinuity or joint set, a criterion that describes the shear strength of joints should rather be used (e.g. see the pillar shown in Figure 20). The implication of this is that for the three case studies of pillar failure in the Bushveld Complex discussed above, explicit simulation of the clay layer will be required. An example was conducted for the authors by Dr John Ryder using the FLAC code, and this is presented below to illustrate the value of modelling.
The pillar composition simulated was the LG6/LG6A 'sandwich' shown in Figure 10. The qualitative effect of a strong pyroxenite layer within a chromitite pillar (with weak contacts, including weak hangingwall and footwall contacts) was therefore modelled in plane strain. A generic model was built to investigate the effect of an inhomogeneous pillar with weak interfaces. Estimated in situ strain-softening parameters were drawn directly from studies carried out in the Bushveld Complex. The hangingwall and footwall were assigned the same properties as the pyroxenite layer, and symmetry was assumed for both the vertical and horizontal centrelines in the following layout in the FLAC finite difference code (Figure 21). The grid size was 0.1 m × 0.1 m. By applying slow displacement loading (velocity 5 × 10-4 mm/step), complete stress-strain and lateral deformation curves could be modelled (Figure 22). Lateral deformations showed no dramatic effects owing to the presence of the 'strong' layer of pyroxenite in the pillar, possibly because the modelled contrasts in strength, Poisson's ratio and dilatancy were not particularly marked. (Note that the horizontal scale in Figure 22b is in millimeters whereas the vertical scale is in metres). Likewise, the presence of a weak interface between the layer and the body of the pillar had virtually no effect, even if the friction angle of interface 1 was set as low as 6º. In contrast, low friction angles on the hangingwall contact (interface 2) had a powerful effect, reducing the peak strength p of the pillar by allowing lateral deformation and reduction of confinement, and reducing also the residual strength (Figure 23).
A further illustration of the value of numerical modelling to investigate pillar strength is given by Esterhuizen45. The UDEC code was used to simulate pillars of different width to height ratios and the effect of jointing on these pillars. The most significant result obtained was that the effect of jointing on pillar strength decreases as the width to height ratio of the pillar increases. This indicated that when designing pillars, it would not be correct to simply determine the rock mass strength and use it in the pillar formulae regardless of the width to height ratio of these pillars. Further work was conducted by Esterhuizen et al.46 to investigate on the effect of large discontinuities on pillar strength. UDEC simulations were used to investigate the effect of these large discontinuities on pillars with width to height ratios of 0.5 to 1.5. A revised empirical pillar strength formula was developed for the slender pillars in the stone mines in the USA. The form of the equation is:
where UCS is the uniaxial compressive strength of the intact rock and LDF is a large discontinuity factor. The authors recommended that a factor of safety of at least 1.8 be used for designs where the pillar strength is assumed to be given by Equation [12]. This will ensure that the pillars remain within the limits of previously successful stone pillar layouts.
The need for monitoring in pillar mining sections
The report of the Government Mining Engineer47, published five years after the Coalbrook disaster, made the following statements regarding instrumentation in the experimental section at the mine:
'There is no evidence that during these operations any systematic inspections were made of the northern portions of No. 10 Section or that any measuring apparatus was installed to ascertain if stability was being affected by the reduction of the abutment support.'
'It appears that no scientific controls were applied to the experiment nor was an attempt made to ascertain what reduction in their support strength was caused by cutting the pillars and increasing their height. The effects of the experiment on the roof and pillars were judged by eye and ear and the results were gauged by the tally board.'
Although monitoring is currently being conducted in some of the Bushveld Complex mines on a limited scale, routine monitoring is probably required in the many bord and pillar sections owing to the uncertainties associated with pillar strength and loads. One example of the type of monitoring that may be valuable is closure monitoring using sensitive instruments. It has been shown that in shallow mining areas, the rate of closure is essentially zero (less than the sensitivity of the instruments) in the stable back areas. Once an area becomes unstable, the rate increases from zero to a very small rate, e.g. 0.3 mm/day. This rate may persist for many days or even weeks48. As this rate is so small, sensitive instruments are required to give early warning of impending instability. In pillar areas, compiling a photographic record of selected pillars over time will also be extremely useful to provide an unbiased opinion whether the pillars are scaling or not (care should be taken that the pillars are appropriately marked and that the successive photographs are taken from the same positions).
As a final comment, in contrast to rock engineering, routine monitoring is commonly used in many of the other engineering disciplines. Civil engineers work with materials that are better characterized and better understood than rock masses, but still conduct routine monitoring of their structures. Structural health monitoring of civil infrastructure systems is a very active field and readers will be able to find a large number of references by searching for this topic on the internet. Many other examples can be quoted from other engineering disciplines, but in general the rule applies that if uncertainty is associated with an engineering design, monitoring should be used to reduce the risk associated with failure of the design.
This paper gives an overview of the difficulties associated with determining the strength of hard-rock pillars. Although a number of pillar design tools are available, pillar collapses still occur. Recent examples of large scale pillar collapses in South Africa were caused by weak partings that traversed the pillars. Currently, two different methods to determine the strength of pillars are used; namely, empirical equations derived from the back analysis of failed and stable cases and numerical modelling using appropriate failure criteria. Both techniques have their limitations and additional work is required to obtain a better understanding of pillar strength.
Empirical methods are popular and easy to use, but care should be exercised that the results are not extrapolated beyond the range of the data which were used to derive them. An example is the Hedley and Grant formula (derived for the Canadian uranium mines) that has been used for many years in the South African platinum and chrome mines (albeit with some adaptation of the K-value) to design pillar layouts in these mines. A careful study of the original publication by Hedley and Grant indicates that this formula was derived for conditions and rock types that are very different to those found in the South African mines. Nevertheless, very few collapses have been reported and in some cases it appears that the Hedley and Grant formula might underestimate pillar strength significantly.
As an alternative, some engineers strongly advocate the use of numerical techniques to determine pillar strength. A close examination unfortunately reveals that these techniques also rely on many assumptions, and extreme care needs to be exercised when using this approach. Pillar load is another unknown not discussed in this paper and care should also be exercised when this is estimated using numerical procedures (some difficulties are outlined in a companion paper in this issue). An area where numerical modelling is invaluable, however, is to study specific pillar failure mechanisms, such as the influence of weak partings on pillar strength. The modelling indicated that a likely failure mechanism in the case studies was that the presence of a parting with a low friction angle that allowed lateral deformation and a reduction of confinement in the pillars. This reduced the peak strength of the pillars considerably.
In conclusion, it appears that neither empirical techniques nor numerical modelling can be used solely to provide a solid basis to predict pillar strength. It is therefore recommended that both these techniques be utilized when addressing pillar design problems in order to obtain the best possible insights. Owing to the uncertainties regarding pillar strength, pillar stress, and loading stiffness, monitoring in trial mining sections (and even in established mining areas) is considered to be an essential tool to assess the stability of pillar layouts in particular geotechnical areas. The need for additional research into pillar strength should also be emphasized strongly as this problem has clearly not yet been solved!
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Paper received Jun. 2010; revised paper received Jul. 2011.
© The Southern African Institute of Mining and Metallurgy, 2011. SA ISSN 0038-223X/3.00 + 0.00.