Experimental Study On Constitutive Model Parameters Of Hardened Soil In Typical Sand And Gravel Stratum In Beijing Area

In recent years,numerical simulation methods have been widely used to analyze a variety of practical engineering problems,but the accuracy of numerical analysis results largely depends on the degree of matching between the constitutive model of soil and the actual mechanical behavior,as well as the degree of difference between the model parameters and the real parameters of the actual state of soil.Due to the large particle size and high strength of undisturbed sandy pebble formation,it is difficult to measure its soil parameters through conventional laboratory tests,which increases the difficulty of engineering numerical analysis in sandy pebble formation to a certain extent.In order to obtain the constitutive parameters of undisturbed sandy pebble soil reasonably,efficiently and accurately,this paper takes the typical sandy pebble stratum in Beijing area as the research object,and based on the framework of hardened soil（HS）model,conducts laboratory large-scale triaxial test,finite element model verification,and discrete element scaling model triaxial simulation test respectively.The key parameters of HS model of typical sand-pebble formation in Beijing area are studied.The main conclusions are as follows:（1）Three stiffness parameters based on the constitutive model of hardened soil are obtained from the laboratory consolidation drainage shear experiment,loading-unloading-reloading experiment and standard consolidation experiment,the reference secant modulus of the triaxial compression test E₅₀^ref,the reference tangent modulus E_ur^ref of the unloading and reloading experiment and the reference tangent modulus E_oed^ref of the consolidation experiment.The proportional relationship of three key stiffness parameters of HS model of typical sand and pebble stratum in Beijing area is established,which provides some experience reference for engineering numerical simulation of sand and pebble stratum in Beijing area.（2）The finite element software MIDAS was used to establish a numerical model of a foundation pit in Wangfujing,Beijing.The proportional relationship obtained from laboratory tests was used to assign values to the soil in the sandy pebble stratum.The numerical results were compared with the actual monitoring data using the surface settlement and the horizontal deformation of retaining piles as indexes.The results show that the key stiffness ratio relation obtained from the laboratory test has certain applicability to the numerical simulation of sand and pebble formation engineering in Beijing area.（3）In order to explore the simplified way of indoor sand and pebble soil test,the gradation scale method was adopted and the numerical stress-strain curves of triaxial test for each grade of substitute materials were obtained by using particle flow software PFC.By fitting,it is found that there is an exponential correlation between the ratio of stiffness modulus of reference secant E₅₀^ref before and after scaling and the ratio of maximum particle size D of the sample.