Research And Design Theory On Deformation Control Of Variation Rigidity Composite Foundation

Composite foundation, which force mechanism is complex, has many influence factors for its deformation, such as the physical characteristics of natural foundation, pile strength, pile spacing, pile’s length, pile’s geometry dimension, the upper structure rigidity and so on. In view of these problems, theory analysis and numerical simulation methods were used to system research the foundation deformation under the condition of piles’different arrangements, and qualitative analysis was made to analysis the various Influence factors. Based on this, optimum design method was proposed to control the deformation of composite foundation. Engineering practice proves that the method is applicable and economic, which can satisfy the request of engineering.In light of pile foundation of 3D layered foundation with single stressed region, generalized Kelvin basic solution’s BEM about layered properties media was used to made theory analysis on the cooperation work between single pile displacement and pile groups, and boundary integral equation was established about pile foundation’s boundary value problem in layered foundation, in which the integrate on layered properties’interface was not included. The foundation adjacent stressed region was analysized according to rigid foundation, assuming basement and foundation soil of rigid foundation were close contact, under the influence of upper loads and adjacent foundation load, the surface contact was divided into n rectangular grids. Considering embedded depth of foundation and building height impact on inclination, subgrade reaction and overall inclination of rigid foundation basic equation is presented, and iterative method is obtained by the analysis above.Three-dimensional finite-difference software FLAC3D, considering pile’s length L, pile spacing S, Poisson ratio of natural foundation soil and displacement ratio of composite foundation, was adopted for the simulation of deformation characteristic of ground soil, in this paper. Depending on different arrangements of piles,39 numerical models (8 groups) were set. A series of numerical simulations on loading mode of nonuniform load and uniform load were respectively carried out, and qualitative analysis of various influence factors was conducted.The numerical simulation showed that the horizontal deformation of the location of composite foundation pile head, variable stiffness in all modes of vertical deformation of the key features are in line with exponential decay, the maximum deformation in the load centroid, the minimum is located in the base-side corner, followed by is the edge. Horizontal contour deformation showed a concentric shape, and it is not close to the foundation shape and the loading area shape; the vertical deformation of the continuity of the shear displacement showed better adaptive ability in the pile location, and all variable stiffness does not appear in the deformation mode of mutation, the pile length have the greatest impact on the pile bottom deformation. Pile spacing and pile diameter has no effect on the deformation, and the gradual deformation of a smooth transition is going to be the bowl shape with the increase of soil depth.Vertical deformation of pile top position is characterized as "concentric cylindrical", and this situation will continue until about half the pile length; and the bottom of the pile is in relation to the flat pile in the form the form of vertical pile because there is no upper bound stiffness.Through numerical simulations show that stress distribution on pile top position:the basic four horns including principal stress and the vertical force appears highly stress concentration, makes the scope of composite foundation bearing capacity limit state into, but the deformation of neighborhood influence will continue to develop, the scope of variable stiffness mode adjust ability is limited, Sub-tissue stress concentration phenomenon appear in central plate edge, forming a foundation with the stress around, Internal stress level ground by vertical stiffness foundation changes for greater influence over stiffness and strengthening, varied length of piles to adjust the stress distribution pattern is the most effective and varied diameter of piles, varied distance of piles has little effect. The pile bottom position stress characteristics show that pile body make the vertical load transfer to the deep layer, the vertical stress level in the pile tip is somewhat increased.Variable pile height has strong adjusted ability on foundation deformation. With the load area length of pile centroid increases, the edge area and corner area will significantly reduce the amount of ground deformation; the increase of the pile length of the edge area and comer area will reduce the ground deformation of the central area, and the key points of each total deformation and the overall composite foundation pile volume replacement ratio have linear inverse relationship.Optimal control by numerical simulation of the pile foundation deformation mode:in the uniform load calculation mode, the central, border, corner area of the pile length (consistent with other design parameters) is to satisfy the law 5:4:3; in non-uniform loads under the area, border, corner area the ideal length of pile is to satisfy the law 5:4:3 multiplied by the size of their respective regional load scale factor.Stress level of composite foundation varies complicatedly on the grounds that pile diameter and pile spacing are adjusted. While often adjustment of pile diameter and pile spacing have no effect on local foundation inclination, model of pile with varying diameter improves local foundation stiffness,and regions of larger stiffness gather to accumulate vertical force gradually, and pile-soil interaction weakens gradually and deformation quantity of local ground foundation shows an increasing tendency.Based on the principle of valuation after resistance, this paper presents some effective solutions to designs of varying stiffness composite foundation.Specifically,it can be classified into seven essential points:medium-edge-angle, five to four to three, strongly inner weakly outer,interaction,considered as a whole,consideration of adjacent elements and repeated iteration.In this paper, some regularity conclusions and design concept are obtained. On the premise of general bearing capacity satisfied, conducting a study is of important directive significance in deformation control of composite foundation, minimization of deformation difference, reduction of secondary stress for foundation and superstructure, improvement of durability and service life for building and development plans of main design ideas for geotechnical engineering.