Cavity Expansion Based On The Linear And Nonlinear Failure Criteria And It's Engineering Applications

The cavity expansion theory has been widely used in the analysis of geo-technical problem such as the bearing capacity of deep foundation, interpretation of pressure-meter test and cone penetration tests. In order to study the cavity expansion, the factors of dilation, large strain, intermediate principal stress, radius of cavity, limited cavity expansion pressure, high stress state, non-associated flow rules, undrained, excess pore water pressure, hardening and softening of strain, hydro-fracture and nonlinear failure criterion are considered. The main results are obtained from test validating, theory and calculation of analysis, and application of engineering example. The conclusions are as follows:(1) Based on the theory of compression mechanism to analyze the cavity expansion, some equations are derived according to the linear Mohr-Coulomb failure criterion, the stress-strain-volume change relationships, volume balance and energy conservation equations, the large strain theory and non-associated flow rule under high stresses. The volume change of cavity expansion is balanced with the compression of soil, and the energy given out from cavity expansion is absorbed by the volume change and shear strain caused in soil. The limit pressure of cavity expansion is presented considering the large strain and change of volume. The proposed theory considering the large strain agrees with the results of locale test more than the theory considering the volume change by comparing and analyzing. Forthmore, the compaction grouting pressure is successfully estimated by using the theory considering the large strain.(2) The stress distribution due to the cavity expansion is considered as the plastic zone and elastic zone. On the assumption that the deformation abided by small deformation in the elastic zone and large deformation in the plastic zone, the stress distribution in two zones, the plastic radius, the excess pore pressure and pressure of terminal cavity expansion are obtained during the cavity expansion and on the bases of the stress equilibrium equation and continuance of stress and deformation. Via calculation, the outcome of above theory is very near to the test.(3) The soils around the cavity expansion are divided into three zones. The first zone is failure zone, the second is plastic zone and the third is elastic zone. On the assumption that the deformation abided by small deformation in the elastic zone and large deformation in the softening and flowing zone, the stress distribution in three zones, the radius and pressure of terminal cavity expansion are obtained on the bases of the stress equilibrium equation and continuance of stress and deformation. At the same time, a closed-form formula of excess pore water pressure of the soil in the three zones during the cavity expansion is derived. Via calculation, the outcome of above theory is very near to the previous results.(4) On the bases of the plastic mechanics, hydro-fracture, pore water pressure theory, intermediate principal stress and the large strain, the calculation formulation of fracture grouting pressure gained considering the hydro-fracture and principal stress. According to the compassion, the results of the present theory considering the middle main stress are very near to that of the engineering practice.(5) The local grouting test is put in practice and the curve between grouting of pressure and speed and the time is obtained. The present calculations of grouting pressures agree with the local test results. The compare results show that the present theory for calculation has an engineering application value.(6) Based on the Hoek-Brown failure criterion as the initial yield function and considering the shear dilatation characteristic, the crashed rock around the cavity is divided into elastic and plastic zones. The Hoek's theory in the elastic zone and the equilibrium principle in the plastic zone are adopted. The analytical solutions to the stress, strain, and displacement fields for the cavity expansion are presented with the non-associated flow rules for the shear dilatation characteristic. According to the compassion of plastic radius, the result of the present theory is very near to the outcome of the engineering practice.