▁of ▁the ▁tunnel ▁south ▁of ▁the ▁river ▁at ▁Mah on . ▁Each ▁segment ▁we ighed ▁appro x ▁ 2 7 , 0 0 0 ▁t onnes . ▁Cont ract ors ▁T arm ac ▁W alls ▁J V ▁engaged ▁R MD ▁K wik form , ▁a ▁global ▁construction ▁form work ▁and ▁sh oring ▁solutions ▁company , ▁for ▁the ▁form work ▁on ▁the ▁tunnel ▁and ▁open ▁section ▁elements ▁of ▁the ▁river ▁crossing . ▁ ▁Each ▁box ▁section ▁compr ised ▁two ▁ 9 . 8 - met re - wide ▁dual ▁l ane ▁traffic ▁tub es ▁and ▁a ▁ 1 . 3 5 - met re - wide ▁tw in ▁w alled ▁central ▁t ube ▁for ▁services ▁and ▁emer gency ▁access . ▁The ▁ 1 . 2 - met re - thick ▁base ▁sl ab ▁was ▁cast ▁first , ▁followed ▁by ▁the ▁ 5 0 - cent imet re - thick ▁central ▁walls . ▁ ▁The ▁outer ▁walls ▁and ▁roof ▁were ▁cast ▁together ▁in ▁a ▁single ▁operation , ▁in ▁six ▁nom inal ▁ 2 0 - met re ▁lengths , ▁using ▁special ▁trav elling ▁form work . ▁ ▁This ▁was ▁struck ▁inside ▁the ▁formed ▁section , ▁moved ▁along ▁to ▁the ▁next ▁length ▁and ▁then ▁jack ed ▁up ▁into ▁position , ▁each ▁within ▁a ▁ 7 2 - hour ▁cycle . ▁ ▁Each ▁ 1 0 0 0 - c ub ic - met re ▁pour ▁required ▁approximately ▁ 1 5 0 0 ▁square ▁metres ▁of ▁form work . ▁The ▁inside ▁shut ters ▁for ▁the ▁outer ▁walls