Before the Colorado Department of Transportation can begin an ambitious project at the Twin Tunnels next year, it will be taking steps to prevent a potential cave-in.Jim Bemelen, CDOT I-70 Mountain Corridor Program Manager, said there is no immediate danger of the tunnel to collapse. But before work crews can begin blasting to widen the eastbound lanes of Interstate 70 in the south tunnel, they need to shore up its twin to the north."Our bridge inspectors discovered the eastbound tunnel had voids behind the lining," he said. "The concrete lining that you see when you drive through the tunnel was up flush against the rock. Over the last 40, 50 years either there has been erosion behind there, or possibly during construction... they might have had just filler material such as hay, wood to fill the void."CDOT engineers have discovered while they were surveying the south tunnel, the voids were sometimes more than three feet from the rockbed. That could be enough space for a boulder to detach from the hillside and pick up enough inertia and cause damage to the tunnel liner.Work crews will be using a special grout to fill the voids in the north tunnel. The process will take six weeks and Bemelen said there will be lane closures while CDOT crews work in the tunnel.Next March, CDOT will begin a project that will bore into the outcrop of rock and widen the eastbound lanes to three lanes with full-sized shoulders on each side. Currently the tunnel only accommodates two lanes."We're doing a little bit of over-widening if you will in the eastbound direction, so when we come back to widen the westbound (lanes), we can actually have eastbound and westbound, in a tight detour in the eastbound tunnel," Bemelen said. "But at least we will have two lanes flowing in each direction."The project will add several miles of a new third lane from Idaho Springs to where I-70 turns into three lanes at the bottom of Floyd Hill.While crews are working on the eastbound lanes, they will be detoured onto Clear Creek County Road 314, which is being reconstructed currently to widen it, add a separate bike and pedestrian path, and build retaining walls. The frontage road lies on the old US Highway 40 roadbed and traffic will be slowed significantly, Bemelen said.Work crews have an ambitious deadline of Nov. 1 to be finished with the widening project. To accomplish it, crews will work 6 days a week, 24 hours a day."On Sunday, they'll fix all the tools that they broke that week," Bemelen said.The project is estimated to cost between $40 and 50 million.