Nonlinear Settlement Analysis And Engineering Application Of Multilayer Soil Composite Foundation Based On Tangent Modulus

Based on the plate test of undisturbed soil,the tangent modulus method can obtain the tangent modulus under different stress levels and different depths of soil layers,and the nonlinear characteristics of foundation settlement can be reflected.This method adopts hyperbolic fitting method for typical in-situ plate load test curve,when the load settlement curve of undisturbed soil plate test in engineering practice is close to a straight line at the initial loading stage,The P-S curve fitting algorithm of straight line segment needs further research.Based on the tangent modulus,this paper analyzes the settlement of multi-layer soil composite foundation and multi-layer soil rigid pile composite foundation(1)The tangent modulus method uses hyperbola to fit the P-S curve,but the load settlement curve of undisturbed soil plate test in engineering practice is close to a straight line at the initial loading stage.When the test load is less than the proportional limit load,the tangent modulus is calculated according to the linear elastic method;when the test load is greater than the proportional limit load,the tangent modulus is calculated by the tangent modulus formula.This paper compares and analyzes the two methods of full curve fitting and piecewise fitting,and the results show that although the piecewise fitting is in theory It is more reasonable,but from the calculation results of the example,the calculation accuracy is equivalent.(2)For the settlement calculation of multi-layer soil composite foundation,it is difficult to carry out the plate test of deep soil.In this paper,the deformation modulus of the completely weathered rock in the lower layer is determined according to the standard penetration blow number,and then the initial tangent modulus is used as the initial tangent modulus of the lower layer after appropriate correction.Then the ultimate bearing capacity of the lower layer is calculated according to the cohesion and friction angle of the lower layer The tangent modulus of the lower soil is calculated.Combined with two engineering examples,this paper calculates and analyzes the theoretical settlement of multi-layer soil composite foundation and multi-layer soil rigid pile composite foundation.The results show that for multi-layer soil composite foundation,the theoretical settlement calculation results of this method are basically consistent with the actual monitoring results.(3)The loads are classified by self-made EXCEL program,and the tangent modulus of soil under different load levels and soil depths is calculated.Instead of the compression modulus in the specification,the average settlement of composite foundation soil is calculated by the layered summation method.The subgrade coefficient of composite foundation soil is obtained by dividing the average additional stress of the base by the average settlement of the raft,and the calculated subgrade coefficient is substituted into the common value According to the P-S curve of static load test of pile foundation,the foundation settlement contour map of multi-layer soil composite foundation and multi-layer soil rigid pile composite foundation under superstructure load is obtained.The results show that the settlement contour map calculated by tangent modulus method is the same as that calculated by subgrade coefficient The monitoring data of building settlement is close,and the accuracy is obviously higher than the calculation result of subgrade coefficient based on compression modulus.