Abstract: A finite effective range of soil cover thickness exists for underwater pipe-jacking, within which construction issues such as uplift or lateral deviation—detrimental to pipe stability—can be effectively avoided. Establishing an appropriate cover thickness is therefore fundamental to ensuring construction safety. Using the Tangxun Lake underwater pipe-jacking project in Wuhan as a case study, numerical analyses were performed to evaluate the effective cover thickness for pipe-jacking through lacustrine deposits. The analyses identified both the applicable range and the threshold value of effective soil cover. The results show that when the soil cover above the pipe is insufficient, pronounced uplift occurs in both the pipe and the overlying soil mass. With increasing burial depth, the deformation of the upper soil transitions from uplift to settlement. At greater depths, both the settlement of the upper soil and the uplift of the lower soil gradually diminish. For the Tangxun Lake project, a cover thickness of 8~15 m constitutes an effective range for underwater pipe-jacking. When the pipe depth reaches 15 m, further increases in cover thickness produce only marginal reductions in crown and invert displacements. However, additional cover substantially increases construction difficulty, cost, and duration. Accordingly, 15 m can be regarded as the threshold cover thickness.

Key words: Pipe Jacking, Effective Cover Layer Thickness, Uplift, Lacustrine Strata, Threshold Value