TBM/MTBM/HDD Rescues Using Ground Freezing

摘要

This paper presents case histories of five below-ground rescues of tunnel boring machinesrn(TBM), microtunnel boring machines (MTBM) and horizontal directional drilling (HDD) using groundrnfreezing as the primary technology. In all five cases, the tunnel machines/casing became stuck and the tunnelingrncontractors had been unable to fix or retrieve the machines/casing. The case histories include:rn• A 5' diameter MTBM stuck 10 feet from the receiving shaft in Los Angeles, CArn• A 3' diameter MTBM stuck 30 feet deep between a river and an airport runway in Renton, WArn• A 17' diameter TBM stuck 300 feet below a residential area in Lake Forest Park, WArn• A 3' diameter HDD pull-head stuck 65 feet beneath an interstate off-ramp in Marysville, WArn• An 18' diameter TBM stuck inside a broken, leaking portal 90 feet deep in Newark, CArnGround freezing was used on all five projects to create a stable access to either repair or replace the tunnelingrnequipment. Most of the freezing was accomplished with small, cost-effective freeze equipment usingrnchilled calcium chloride brine pumped through either vertical, horizontal or angled steel freeze pipes. Two ofrnthe projects also involved the use of liquid nitrogen in addition to calcium chloride brine. Freeze pipes wererninstalled from ground surface, from inside the access shaft, and from inside the tunnel. In all cases, a solid massrnof frozen soil was created around, above and below the TBM/MTBM/HDD in sandy and silty, unstable soilsrnwith high groundwater conditions. In one case, the pressure on the frozen soil shoring was well over 5 barsrn(70 psi). The five rescue projects were all successful—the contractors were able to complete the tunnels andrnthe project. An overview regarding the basic engineering design, construction difficulties and the final groundrnfreezing solution is presented for each case history.