The Study On The Soil Parameters For Foundation Excavation Design Of The Expansive Soil In Chengdu Area

As an unsaturated cohesive soil,expansive soil has the engineering characteristics of water swelling,shrinkage of water loss,high plasticity and over-consolidation.It is easy to cause slope failure,foundation pit collapse,embankment settlement and other engineering accidents.In Chengdu,the main cause of engineering accidents in expansive soil foundation pit is water and fissure.Considering the effect of swelling and shrinkage of expansive soil,only the shear strength parameters of expansive soil are greatly reduced in the design of expansive soil foundation pit,and the effect of swelling force is not taken into account.Based on the analysis of the structural system,a new calculation method is proposed.The expansion force is regarded as a horizontal concentrated force acting on the support structure.Taking a typical expansive soil foundation pit in Chengdu as an example,the expansion force is applied to the supporting structure.By this way,the results of the design are in good agreement with the monitoring results,which indicates that the method is feasible.At the same time,the expansion force,cohesion and inner friction angle are reduced by different degrees,and the results of design and calculation are compared with those of conventional direct reduction shear parameters.The range of coefficient is proposed such as the expansion coefficient,the cohesive force reduction coefficient and the inner friction angle reduction coefficient.In the design and construction of the expansive soil foundation pit,it is suggested to consider the effect of the expansion force.Meanwhile,the points should be noticed during the construction of expansive soil foundation pit,such as the investigation,the monitor,standardization construction and the control of water.