Elastoplastic Analysis And Engineering Application Of Ellipsoidal Hole Expand In Unsaturated Loess

Cavity expansion theory has been widely used in many geotechnical engineering problems,such as in-situ soil test,calculation of pile bearing capacity and analysis of pile compaction effect,but most of them are transformed into traditional cylindrical or spherical expanding problems for analysis.However,there are few studies on ellipsoidal hole expansion between cylindrical and spherical holes.At present,this kind of problem is mainly based on complex function theory,and the elastic-plastic analysis is complex.At the same time,the exact solution can not be obtained when the soil conditions are complex,It also needs numerical simulation to solve,which is not easy to be applied to practical engineering.In this paper,the elastic-plastic analysis and engineering application of ellipsoidal hole expansion in unsaturated loess are studied.The ellipsoidal hole expansion problem with different ratio of long axis to short axis is changed into the problem of circular hole expansion with diff erent radius in plane.Based on the unified strength criterionthe and the modified Cam-clay model of structured loess considering anisotropic character,the ellipsoidal pore expansion of saturated and unsaturated loess is theoretically analyzed by using t he method of equilibrium coefficient k.Finally,the ultimate pore expansion pressure derived is applied to the prediction of the opening pressure of splitting grouting,and verified by field grouting test.After the problem of ellipsoidal hole expansion is transformed into the problem of circular hole expansion on the?plane by mapping function,the radial and circumferential stresses(?_r,?_?)around the hole on the?plane correspond to the curves stresses(?=const,?=const)on the original physical plane ellipsoid,respectively.According to the relationship between the ratio of the long axis to the short axis of the ellipsoidal hole and the equilibrium coefficient k,the equilibrium coefficient k is defined as the expanding shape coefficient,solving a series of elastic-plastic solutions in?plane for ellipsoidal hole enlargement with different long and short axes.The main work and achievements of this paper are as follows:(1)The problem of ellipsoidal hole expantion is transformed into the problem of circular hole expansion in?plane by mapping function.The soil around the hole in?plane is divided into elastic and plastic regions.The stress-strain field distribution solution,radius of plastic zone and limit hole enlargement of saturated and unsaturated loess ellipsoidal hole enlargement under drainage and undr ained conditions are derived respectively by using unified strength criterion and unified strength criterion of unsaturated soil.The relationship between cohesion of unsaturated undisturbed loess and matrix suction is introduced into the study of ellipsoidal hole enlargement of unsaturated loess,and the effects of soil shear dilation,matrix suction and different yield criteria on stress-strain field,radius of plastic zone and ultimate hole expantion pressure are analyzed.(2)Considering the volume deformation,the Loess around the circular hole in the plane is divided into elastic zone,plastic zone and failure zone.The elastic zone obeys the theory of small deformation,the plastic zone and failure zone obey the theory of large deformation and adopt the rule of non-correlated flow.Based on the modified Cambridge model of structural loess,by introducing the rotation angle of yield surface(?)to represent anisotropy,the formulas for calculating the stress distribution,the ultimate expansion pressure and the radius of failure zone of unsaturated loess under drainage conditions are deduced,considering anisotropy and structure.Finally,the parameters of the theoretical analysis are analyzed and discussed in combination with the software MATLAB.When the ultimate reaming pressure is reduced to cylindrical and spherical holes,it is compared with the reaming pressure of loess considering only structural properties.(3)Based on the mechanics mechanism of splitting grouting and the unified strength criterion of unsaturated soil and the modified Cambridge model of structural loess considering anisotropy,a formula for predicting the splitting grouting pressure in unsaturated loess area is derived.The formula is verified by the measured grouting pressure in field grouting test,and the structural loess considering anisotropy is pointed out.The splitting grouting pressure formula of modified Cambridge model is more in line with the actual situation and has certain theoretical value in engineering application.