Advanced Tangent Modulus Method And Its Application To The Foundation Settlement Calculation

With the rapid development of modern society,the construction of various infrastructure has higher requirements for the bearing capacity and deformation control of soil.In soil mechanics,how to calculate the foundation settlement scientifically and accurately has always been a difficult problem to be solved.At present,the most commonly used settlement calculation method in China is the layered summation method recommended by the national code.Because the empirical coefficient of the standard method is 0.2-1.4 and the error is large,it is a semi-theoretical and semi-empirical settlement calculation method.And the calculation is based on the compression modulus obtained through laboratory tests,which can not reflect the original state of the soil.The tangent modulus method established based on the field in-situ test can overcome the shortcomings of the laboratory test,the method is simple and has few parameters.The study shows that this method has high accuracy in calculating the foundation of conventional size,but for the large size foundation such as raft foundation,due to the deep influence of stress,the tangent modulus of soil will increase rapidly under deep high confining pressure.However,the initial tangent modulus in the current tangent modulus method does not take into account the effect of depth,or there is a possibility that the calculation result is too large.Although the finite element method of small strain hardened soil model can better reflect the deformation of deep soil,the selection of model parameters is relatively complex and there are some limitations in application.In this paper,aiming at an ideal model,the finite element method of small strain hardened soil model is used to calculate the load-settlement curve of the soil at the center point of the bottom of the compression plate at different depths.Under this condition,the law of the variation of the initial tangent modulus with depth in the tangent modulus method is analyzed,and an advanced tangent modulus method considering the increase of the initial tangent modulus with depth is proposed.The calculation results of the same example are compared with those of other methods,the results show that this method not only retains the advantage of less calculation parameters of the original tangent modulus method,but also better reflects the deformation law of soil under large size foundation,compared with the finite element method of small strain hardened soil model with similar effect.the parameters of this method are easier to obtain and can be better applied to practical engineering.Furthermore,the adaptability of the advanced tangent modulus method and the original tangent modulus method to different foundation sizes is studied,and it is found that the original tangent modulus method is safe and available when the influence depth of conventional foundation size or stress is not too deep,but for large size raft foundation,when the stress influence depth is deep,the settlement value calculated by the original tangent modulus method will be larger,so the advanced tangent modulus method should be used in calculation.Finally,the advanced tangent modulus method proposed in this paper is used to calculate the foundation settlement of three engineering examples with large size foundation design,and the results are compared with the measured data,the tangent modulus method and the finite element method of small strain hardened soil model.the calculation results are good,and the accuracy and rationality of the method are further verified.in addition,combined with the above engineering cases,the values of reference stress p0 and coefficient m are studied.