Study On Calculation Method Of Loess Foundation Collapse Settlement Due To Loading-wetting

Guanzhong area of Shaanxi Province is located in the loess area.Loess has engineering characteristics of collapsibility,easy dissolution and anisotropy,which leads to many engineering problems in the foundation of Guanzhong area.One of the most common and harmful problems is that the collapse settlement occurs after the site is wetted,and the normal operation of the structure has certain requirements for the foundation settlement,so the accurate calculation of the collapse settlement of the loess foundation can provide the basis for the foundation treatment method.In this paper,based on the existing basic theory of loess collapse settlement,combined with the existing test examples,the standard method,one-dimensional collapsibility coefficient method,chord modulus method and tangent modulus method are used to calculate collapse settlement of original loess foundation and compacted loess foundation respectively,analyze the rationality of calculation by various methods.Studying the stress adjustment process and the development law of collapse settlement during loading-wetting of compacted loess foundation,further revealing the mechanism of loess collapse settlement,and providing reference for the calculation of loess foundation collapse settlement.The main conclusions are as follows:For original loess foundation and compacted loess foundation,the collapse settlement caused by load wetting is mainly concentrated in the upper part of soil layer.When original loess foundation is wetted and the pressure is large,its layered collapse settlement is gradually increased first along the foundation centerline,then decreased,and the corresponding modulus is decreased first,then increased.The maximum collapse settlement of the soil layer corresponds to the depth (?).At this time,the foundation is close to failure.When the size of the foundation is small,the actual collapse settlement mainly concentrates in the shallow depth.If using the standard method to calculate collapse settlement,it will lead to a higher demand for treatment in deep depth,which will cause a certain waste to the project.The actual engineering foundation,especially the raft foundation,is always larger in size,and influence range is deeper.For this case,the collapse settlement calculated by the standard method may be reasonable.One-dimensional collapsibility coefficient method is used to calculate the collapse settlement according to the collapsibility coefficient corresponding to the real pressure under the load plate.Based on the loading-wetting test of original loess foundation and compacted loess foundation,When the pressure is large,the calculated collapse settlement by this method with the correction coefficient taken as 1.5 considering lateral extrusion is far less than the measured settlement because the lateral extrusion is very large and this method cannot consider the lateral extrusion well.;based on loading-wetting test of compacted loess foundation,the laws of the development of the collapse settlement obtained by one-dimensional collapsibility coefficient method and the tangent modulus method show that the first rapid growth,and then tend to be stable,which is consistent with the actual development law.The tangent modulus method can simulate the non-linear law of collapse settlement with the increase of load,but because the elastic settlement in the initial yield surface is not considered well,the calculated load settlement curve appears the reverse bending point earlier.The chord modulus method is suitable for calculating collapse settlement of original loess foundation caused by loading-wetting.The method is based on the additional stress,and the change law of the chord modulus under the foundation center line is inconsistent with the change law of the real modulus,that is,the collapse settlement of the layers along the foundation center line is inconsistent with the measured collapse settlement;the chord modulus method is not suitable for calculating collapse settlemen of compacted loess foundation.The tangent modulus method is suitable for calculating collapse settlemen caused by loading-wetting of original loess foundation.And the method is based on the soil stress level,not only the additional stress,which is close to the real stress state of the foundation,so the law of calculating the collapse settlemen of each layer by tangent modulus method is consistent with that of the measured collapse settlemen of each layer.For load wetting model test of original loess foundation with large settlemen,the range of stress effect is expanded,and the soil layer with the largest collapse settlemen moves downward;for the compacted loess foundation,the tangent modulus method cannot consider the elastic deformation inside the initial yield surface of soil very well,so that the calculated collapse settlement is greater than the measured collapse settlement.