The hole, which opened up in Grays, Essex, on Wednesday afternoon, also caused a gas leak.
Thurrock Council said experts believe a tunnel below the road - Hogg Lane - that links two quarries collapsed.
Further work will be done to establish if the collapse was "triggered by the road issue or vice versa," he added.
A National Grid spokesman said engineers were working to decommission a section of gas main where the sinkhole had caused a leak.
Meanwhile, the owner of the stranded lorry said he could lose up to Â£20,000 if the vehicle cannot be moved easily.
A hazard zone is still in place and the vehicle cannot be moved until surveyors have finished checking the road.
"I'm sick as a parrot. Every moment my truck's sat there, it's costing me money," said owner Steve Robinson.
His company, Robinsons LGV training based in Purfleet, has several pupils booked in for training and tests using the vehicle.
"It's got huge implications for me. As a rough estimate, if I don't get it back by Saturday, I'll have lost about Â£4,000, which is a lot of money for a small business.
He said he was concerned that if the lorry were to be damaged while being removed by tow truck or crane, he might have to pay out "anything up to Â£20,000".
David Bull, director of planning and transportation at Thurrock Council, said structural engineers were on site giving advice.
"We don't want to put someone in the lorry and cause vibration and then find the lorry falls further in through the hole," he told BBC Essex.
A 10ft (3m) wide sinkhole that left a lorry stranded was caused by the collapse of a 100-year-old tunnel, experts have discovered.