Study On Post-construction Settlement Of New-built Sea Embankment After Tunnelling

Deformation behavior of soft estuarine deposit under large area uniform surcharge is essential to embankment construction and land reclamation in coastal areas. Based on the laboratory tests, a soft soil model was proposed, which is derived from modified cam-clay model, taking into account the inherent structure characteristics of soft estuarine deposit. A finite element numerical model was established to analyze ground deformation and pore-water pressure dissipation procedure of the soft estuarine deposit under large area uniform surcharge loads and newly-built sea embankment. The analyses incorporated prefabricated vertical drains installed in the foundation soils and stage construction of the embankment. Compared with the in-situ monitoring data, the simulations were found closely matched the measured deformations of soil ground beneath the embankment and in backfill areas, both for vertical settlement and horizontal deformation. At the same time, the accumulation and dissipation of excess pore-water pressure at different depth beneath embankment and backfill can be accurately described by this improved model. Soil structure characteristic is an intrinsic feature of soft estuarine deposit. Regardless of structure characteristics will lead to underestimating the amount of ground deformation, the time deformation last, as well as excess pore water pressure and so on. The soft estuarine deposit involved in the project is high compressed; newly-built sea embankment and large-scale area loading will lead to huge settlement, which reaches 7.58m after full consolidation. The effect of PVDs is obvious, a settlement of 7.11m achieved one year later after construction.Settlement will last a long time beneath newly-built seaembankment. Differential post-constuction settlement will cause rather large longitudinal deformation when followed tunneling, which seriously endangering the safe operation of tunel. How to envaluate the safety of soft soil tunnel has become a key engineering problem. In this paper, a detailed analysis was conducted on the experimental data and an in-situ monitoring was made at the key tunnel cross-section. According to the distribution of the settlement at the tunnel centerline, a curve fitting was carried out and the curvature of tunnel was derived. Equivalent continuum model was employed to calculate the longitudinal stiffness of shield segment, through the mechanical analysis to identify the relationship among the tunnel curvature, deformation and cracks and carried out stress state analysis of the tunnel to provide advices for foundation treatment, and solve the key engineering problems.