Finite Difference Numerical Analysis Of Earth Berm Effect In Pile-anchor Pit

In order to the sustainable development of cities,cities are gradually developing to the higher altitude and deeper undergroud,a lot of tall buildings and large-scale undergroud municipal constructions have been turnning up in central aeras of cities,so the development characteristics of deep foundation pit engineering are deep,large and close,and this also promote some new processes of deep foundation pit supporting. Pile-anchor support technology was created in1958,and in the1980s,it began to be applied to the deep foundation excavation of high-rise buildings in our country Because of its great applicability,huge technical advantage and enormous economic benefits,pile-anchor structure is widely used in the deep foundation pit construction in our county.Earth berm,a new pit constructing means,is also called as mound.when larger foundation pit is designed to use center island method to excave the pit,there will be earth berm in the pit.Among current foundation pit with earth berm as temporary supporting,earh berm is not a design factor considered during the pit design,but an meaning to control the derformation of supporting structure and the influence to surrounding environment.But earth berm can reduce the deformation and force of supporting structure,sometimes it even can replace the horizontal support in the pit,so that earth berm cut the project cost and shorter the construction period,which has great economic benefits,social efficiency and environmental efficiency.In order to study the effect of earth berm to pile-anchor structure,establish a3-dimention numerical model of pile-anchor supporting pit by finite difference analysis sofeware——LAC3D.In the thesis,effect of earth berm,influence change the width and height of earth berm lead to are analysed by quantification.According to caculation results of different working conditions,get the following conclusion:earth berm can greatly increase the foundation soil vertical stress within the scope of earth berm,especially near the pit walls;earth berm can reduce the pile’s displacement in the range from the height of earth berm to the bottom of pile;earth berm can effectively cut down supporting pile’s moment,especially in the height of earth berm decrease amplitude is the largest,and it also can reduce cable axial force,the largest decrease amplitude can reach to20%;as the increase of earth berm’s width or height,the horizontal displacement and moment of supporting pile,the cable axial force will gradually decrease,but when the width or height increase to a critical value,the decrease amplitude will be very small;compared with the increase of earth berm’width,the pile’s horizontal displacement will be obviously reduced by increasing earth berm’s height,and with the increase of the height,pile’s moment,cable axial force will descend.