Analysis And Research On Penetration Resistance Of Cone Penetration Test In Sand Based On Reaming Theory

Static cone penetration technology has been widely used in engineering.According to the measured data,various parameters of soil can be estimated to judge the type of soil,physical parameters of soil,divide natural soil layer,estimate the bearing capacity of foundation and single pile,and so on.With the Development of Modern Civil Engineering,the parameters of foundation soil are required to be more precise.The traditional empirical or semi-empirical semi-analytical formulas can not meet the requirements.Therefore,on the basis of collecting the previous research results,the main research contents and achievements are as follows:Considering the obvious strain softening and dilatancy phenomena of sand,and neglecting the defect of intermediate principal stress in the traditional Mohr-Coulomb yield criterion,the stress-strain drop model is adopted to reflect the softening degree of soil,and the relationship between three-dimensional principal strain and volume strain is established by introducing the dilatancy coefficient.Based on these,the cylindrical hole expansion in cone penetration process is analyzed by SMP criterion and hole enlargement theory.The analytical solutions of stress field,displacement field,radius of plastic zone and ultimate hole enlargement pressure in elastic and plastic zone are derived based on the theory of small deformation,and reasonable parameters are set for trial calculation and analysis.The results show that:(1)The more obvious the dilatancy of soil is,the larger the corresponding expansion pressure,radius of plastic zone and displacement are.The larger the degree of softening,the faster the hole expansion pressure decreases.When the hole expansion pressure is constant,the more obvious the softening is,the larger the hole expansion displacement is.(2)The difference between the two theories is more than 10%,which reflects the importance of medium principal stress in geotechnical engineering hole enlargement and needs to be considered in practical engineering.The radius of plastic zone is calculated by introducing the principal stress difference,and the analytical solution of cone head resistance is further deduced by combining the geometric size of probe and the actual demand parameters.The conclusion shows that:(1)the cone head resistance is related to the properties of soil(initial internal friction angle,softening characteristics,bulk density)and penetration depth,and the formula is obtained when a certain depth(critical depth)is reached.The depth value and softening coefficient will offset each other,and the pressure value will not increase,that is,the critical depth phenomenon;(2)In the process of the probe crossing the soil layer,the difference between the properties of the upper and lower soil layers will lead to the change of the parameters brought in by the calculation formula,and then the cone resistance will also change,the size of deformation zone determines the range of curve fluctuation.The range of curve fluctuation and the difference of soil properties determine the intensity of curve fluctuation,that is,the phenomenon of"ahead" and "lag" in layered soils.According to the measured curve,the specific location of soil boundary can be deduced.Considering the characteristics of soil dilatancy and large strain,ABAQUS software is used to simulate the penetration of the probe,and the influence of the main soil parameters on the stress and displacement is analyzed.Based on the results of numerical simulation,the theoretical deduction is verified.The simulation results show that:(1)the soil around the side wall is mainly transverse stress,while the bottom of the cone tip is mainly radial stress.Vertical stress is the dominant factor in the part of soil,and both of them decrease with the distance from the cone.Vertical stress decreases faster and the range of influence is smaller.(2)The simulation results verify the rationality of the deduction theory to explain the phenomenon of "critical depth".With the increase of depth,both transverse and vertical stresses have limit values.(3)The results also prove that the theory of large strain is consistent in rock mass.The rationality of the problem is smaller than that of the simulation results based on the small strain theory.(4)Through comparative analysis,the elastic modulus,dilatancy angle and internal friction angle all have influence on the stress value,but beyond the deformation zone,the influence will be weaker and weaker,and the larger the dilatancy angle and internal friction angle,the smaller the influence will be.