Effects Of Deep Excavation On The Bearing Capacity Of Engineering Piles

With the rapid development of national economy and the acceleration ofurbanization process, a large number of high-rise buildings and undergroundengineering are constantly emerging, and meet deep foundation pit excavationproblems inevitably. Large scale deep excavation is normally followed by theconstruction of compact engineering piles inside the excavation zone, and soilunloading and rebound induced by deep excavation have a great influence on theseengineering piles. At present, the research of engineering piles in the bottom ofexcavation is not comprehensive at home and abroad, and it often causesconstruction accidents because of unreasonable excavation or wasting resourcesdue to blind piling with little understanding of this in actual engineering. Based onstudies on effects of deep excavation on the bearing capacity of engineering piles asthe core, has studied foundation pit deformation behavior and retaining structurestress characteristics under deep excavation unloading conditions, mechanicalcharacteristics of single pile and group piles, and the main effect factors includingthe effect laws of bearing capacity of engineering piles through the finite analysis.At first, this paper systematically summarizes the domestic and foreignresearch status about the deformation due to foundation pit excavation and theinfluence of foundation pit excavation on the pile foundation. And summarizes theresearch priorities and shortage of the retaining structure deformation, the soiluplift on the bottom of foundation pit, the ground surface displacement, theinfluence of foundation pit excavation on adjacent piles and the influence offoundation pit excavation on piles under the bottom of foundation pit.Second, the theory of finite element analysis of foundation pit excavation issummarized. The basic principle, main characteristics, solving method and theanalysis process of finite element method are briefly introduced, and the basicfunctions, the key problems of modeling and the specific process of modeling ofABAQUS software are illustrated.Then, the mechanism of pile-soil interaction under deep excavation unloadingconditions is studied in detail through the establishment of plane finite elementanalysis model. The deformation behavior of foundation pit and stress characteristics of retaining structure is analyzed, and no pile and group piles in thebottom of excavation conditions are compared. The ground surface displacement,the soil uplift on the bottom of foundation pit, and the retaining structuredeformation can be effectively reduced by add pile at the bottom of foundation pit.But the maximum bending moment of retaining structure under the surface offoundation pit excavation and the earth pressure in front of or behind the wall willbe increased. The mechanical characteristics of single pile and group piles arerespectively studied. The results show that pile-soil relative displacement at the toplocation of pile is the largest, and pile shaft force first increases then decreasesalong the pile from top to bottom. The top part of pile is bearing positive sidefriction, on the contrary, the lower part is bearing negative side friction, and both ofthem are first increases then decreases along the pile. With the increase ofexcavation depth, pile-soil relative displacement at the top part of pile is increasinggradually, pile shaft force has some increase and the position of maximum movesdown step by step, and neutral point of side friction moves down step by step. Forgroup piles, engineering piles near the center of foundation pit have bigger pile-soilrelative displacement at the top location of pile and pile shaft force along the pile.And the neutral point of side friction is lower, positive side friction at the top partof pile is bigger, but negative side friction at the lower part of pile is smaller.In the end, the main effect factors including the effect laws of bearing capacityof engineering piles under deep excavation unloading conditions is studied in detailby the establishment of plane finite element analysis model. Pile properties,excavation conditions and soil parameters obviously affect compressive bearingcapacity and uplift bearing capacity of engineering piles. Compressive bearingcapacity of engineering piles increases with the pile length, pile diameter,excavation depth and effective unit weight of soil. But decreases with the pilenumber, pile unit weight, Poisson’s ratio and effective angle of internal friction ofsoil. Uplift bearing capacity of engineering piles increases with the pile length, pilediameter, pile unit weight, excavation depth, Poisson’s ratio, effective unit weightand effective angle of internal friction of soil. But decreases with the pile number.Other factors have lesser effects on the bearing capacity of engineering piles, weshould focus on considering the main effect factors when designing or constructingengineering piles in the practical engineering.