Theoretical Analysis Of The Problem Of Loess Cavity Expansion And Its Application In Splitting Grouting

cavity expansion theory has a wide range of applications in geotechnical engineering,such as analysis of pile foundations and bearing capacit y of ground anchors,geophones,tunneling and underground excavation.The early cavity expansion theory considered that the soil surrounding the circular hole is incompressible plastic solid,and does not involve the effects of bulk deformation and large deformation.Especially,the structural factors of loess are rarely involved.It belongs to the elasto-plastic problem based on pure shear theory..In this paper,Based on the theory of compressor and large deformation,in view of the limitations of the traditional M-C criterion and cavity expansion theory,the principle of large deformation is first used to analyze the problem of cavity expansion loess in unsaturated loess that obeys the general strength criterion.Then,considering the structural properties of loess,the problem of cavity expansion in unsaturated loess under drainage and undrained conditions was studied.Finally,the research results are applied to analyze the mechanical mechanism of cracking and grouting in loess area and estimate the fracturing grouting pressure.This paper analyzes the theoretical analysis and field test,and mainly achieves the following main results:(1)The loess surrounding the cavity is divided into elastic zone and plastic zone.In the elastic zone,the assumption of small deformation theory is adopted.In the plastic zone,the assumption of large deformation theory is used to combine the practical shear strength theory of unsaturated undisturbed loess in eastern Gansu..The theoretical analysis of the pore water pressure under the plastic zone radius,the limiting reaming pressure and the undrained condition are deduced,and the distribution laws of the stress field and displacement field in the elasto-plastic zone are deduced.Finally,the parameters of the obta ined theory are analyzed.The above theory considers the properties of loess soil,dilatancy,drainage and undrained conditions,large deformation and different yield criteria(MC,Land-Duncan,SMP)and other factors.Finally,it compares classical theory and engineering examples to verify the The reliability of the results.(2)On the premise of considering volumetric deformation,based on the expansion theory of the structural loess Cambridge model,It is assumed that the elastic zone obeys the small de formation theory,and that the large deformation theory and the non-associative flow rule obey the plastic zone and the failure zone.The stress-strain distribution solution of the unexpanded loess under the drainage condition considering the structural f actors and the calculation formula of the final reaming radius,the radius of the failure zone and the limiting reaming pressure are deduced.The parameters of the calculation formula were analyzed and discussed in conjunction with MATLAB,and compared wit h Vesic AS theoretical solutions under drainage conditions.(3)Suppose that the small deformation theory obeys the elastic region,and the large deformation theory and the non-associative flow rule obey the softening regio n and the plastic flow region.Considering the effects of dilatancy,softening and structure,the strain softening drop model and the general strength criterion were used to derive the stress-strain distribution solution of the soil around the strain softening loess in undrained conditio ns,and the final reaming radius and flow area radius.,Limit reaming pressure and excess pore water pressure calculation formula.The parameters of the formula are analyzed and discussed with MATLAB.Finally,the CAO Lai-Fa theoretical calculations under undrained conditions are compared and verified.(4)In order to better understand the design and calculation of mechanical mechanism and grouting pressure of collapsible loess,a field grouting test was conducted to obtain the time history curves of grou ting pressure P and grouting Q.The mechanical mechanism of loess fracturing grouting was systematically analyzed.The P-Q-t three-dimensional scatter plot analysis shows that the calculation results of the hole expansion theory based on the structural lo ess Cambridge model are more suitable for the estimation of loess fracturing grouting pressure,and have better reliability.