SITE MONITORING ANALYSIS ON CONSTRUCTION DEFORMATION OF LONG LARGE DEEP FOUNDATION PIT IN COASTAL COMPLEX STRATUM

Amoy is a city with complex ground-environment. With the development of science and technology, urban rail transit project gradually becomes a sign of the level of development. In recent years, the construction of urban rail transport projects in the country has emerged in large and medium cities. Metro Line 2 in Amoy was built on January 31^st, 2016. As we all know, excavation not only influences the foundation pit itself, but also is related to the surrounding buildings and structures, as well as the safety of various municipal facilities. The purpose of this paper is to study the stability of long and deep foundation pits in operation and the rule when soil is destabilized by excavating foundation pits. Especially this engineering project is in the complex ground-environment of Amoy coast. By measuring the monitoring data of the foundation pit in Haicang road station of Amoy Metro Line 2,this article conducts the research from three aspects: horizontal displacement of the underground continuous wall, surface subsidence and groundwater level changes. The article concludes that:(1) The maximum horizontal displacement of the underground continuous wall is 24.5mm, about 0.35% of the depth of foundation pit(H),slightly lesser than the other soft soil area. (2) Surface subsidence trough shows "√" shape distribution. The maximum appears at a distances of 0.5 times of the foundation pit depth(H) from the pit side, the range of influence is about 1.76 times of the depth of foundation pit. The maximum surface subsidence of monitoring sections is 22.4mm. (3) During the construction of excavation, the groundwater level of coastal areas shows fluctuations as a change in performance, showing a rising trend in whole. The maximum cumulative variation is about 0.72cm. (4) Change of seawall horizontal displacement and sedimentation change is unstable, but always small. For the long and deep foundation pit under the environment of coastal complex formation, the research results have reference value and guiding significance.