Analysis Of Mechanical Effects And Optimal Design Of Underground Continuous Wall Of Deep Silty Clay Foundation Pit

Based on the foundation pit engineering of Taiyuan, together with the analysis of topography, lithology, climate condition of Taiyuan, it makes appropriate supporting scheme for the underground continuous wall and makes research on the deformation characteristics of the underground continuous wall which supports the deep foundation pit and the deformation characteristics of foundation pit. According to the needs of practical engineering, the thesis uses FLAC3 D to make a detailed analysis about fractional excavating construction and supporting process and establish three dimensional numerical model of foundation pit excavation under the foundation pit’s supporting form of underground continuous wall and also, it discusses the changes of soil stress of foundation pit, lateral deformation of underground continuous wall, soil settlement around foundation pit and the deformation characteristics of the bottom of the deep foundation pit. Finally the thesis aims to make a optimal design about the supporting structure of underground continuous wall of the foundation pit, it discusses the influence of the variations ofthe inserted depth of the underground continuous wall, the strength of concrete of the wall, and the thickness of the wall on the deformation effect of the deep foundation pit under the supporting form of the underground continuous wall and then optimizes each influencing factor and gives a reasonable range to each factor. The increasing difficulty of design of the deep foundation pit leads to the significant increase of the construction costs. In order to ensure the feasibility and science of the design scheme of deep foundation pit, it is necessary to optimize the design scheme of deep foundation pit which is of great value to the optimization and improvement of future design scheme of deep foundation pit in Taiyuan.(1)In the dominated silty clay strata of Taiyuan, the depth-15 m foundation pit engineering, with supporting form of underground continuous wall, has a connected relations with horizontal displacement of the underground continuous wall, soil settlement around foundation pit and the deformation characteristics of the bottom of the deep foundation pit, which gradually increase with the increasing depth of the deep foundation pit excavation.(2)In the process of deep foundation pit excavation, the maximum horizontal displacement of the underground continuous wall is closely related to the excavation depth and time. The horizontal displacement of the underground continuous wall gradually increases with the excavation of the foundation pit,and the characteristic of final deformation is the "bulge" in the pit ", which isconsistent with the majority of deep foundation pit excavation. For each layer of foundation pit excavation, the horizontal displacement curve of the underground continuous wall is almost the same.(3)With the excavation of foundation pit excavation, the value of surface subsidence around the foundation pit gradually increases, and the settlement range also gradually increases with the increase of excavation step by step. After the excavation, the form of surface subsidence around foundation pit shows that the value is relatively small near the foundation pit and reaches the maximum at a certain range of foundation pit. The form of surface subsidence around foundation pit is a non-symmetrical groove type. The settlement curve of the surrounding ground surface is almost the same in each layer of foundation pit excavation.(4)By calculating it comes to a conclusion that when the excavation of underground continuous wall of deep foundation pit in the areas of Taiyuan ends,the maximum horizontal displacement of the underground continuous wall is30.277 mm, i.e. 2.3 ‰ depth of excavation. The maximum settlement of foundation pit is 11.645 mm, equal to the 0.89 ‰ depth of excavation. The maximum settlement value is about 12 m from the edge of the foundation pit,and the maximum settlement point is 0.9 times of the depth of excavation from the edge of the foundation pit. The ratio of the maximum lateral displacement of the diaphragm wall and the maximum vertical displacement of the foundation pit around it is 2.6.When the excavation of foundation pit completes, themaximum upheaval of foundation pit bottom in excavation is 11.296 cm and the upheaval increases as the depth of excavation increases.(5)After the optimization of the parameters of underground continuous wall,the strength of concrete of the underground continuous wall is C30, the thickness of the underground continuous wall best takes 600 mm and the buried depth of the underground continuous wall is 0.39 h, h for foundation pit depth.in the depth-15 m foundation pit engineering adopting the supporting form of the underground continuous wall in the silty clay layer of the areas of Taiyuan.