Abstract
Ground settlement and relevant prediction methods related to underground tunneling have been investigated extensively in previous studies. However, the effects of the existence of service pipelines on the ground movement induced by tunneling have not been well addressed. This study involved a series of physical modeling tests on ground responses to tunneling in sand considering the existence of high-density polyethylene (HDPE) pipes using a custom-made physical modeling system. The system included a model box, a pipe fixing frame, and a number of settlement plates. The developed model box had dimensions of 2.0 m by 2.0 m by 1.5 m, and the bottom of the box consisted of eight movable plates with dimensions of 0.25 m by 2 m by 0.1 m. The plates were lowered down at four levels of maximum vertical distance (10, 20, 30, and 40 mm) to form normal distribution curves, simulating tunneling effects in the sand stratum. Four normal distribution curves were created with maximum lowering distances of the movable plates of 10, 20, 30, and 40 mm to simulate different volumes of ground loss in the tunnel. We performed the four tests one after another by successively lowering down the movable bottom plates. Prior to filling, the required density of backfilled sand was determined using a self-designed instrument. The HDPE pipes, with two diameters (i.e., 300 and 200 mm), were installed in the model box at two different buried depths (i.e., 1.05 and 0.75 m from the spring line of the pipes to the fill surface) using a custom-made fixing frame. The test results demonstrate that the existence of the HDPE pipes resulted in a wider but shallower settlement trough than in the greenfield (without pipe) case. The width of the settlement trough at a given depth decreased with decreasing buried depth of the pipe, whereas it increased with decreasing pipe diameter. The volume of the settlement trough at a given depth was approximately constant, regardless of the existence of pipes, and the vertical displacement of the pipes increased with decreasing diameter and buried depth of the pipe.
