Research On The Borehole Wall In-situ Stress Distribution And Stability Based On Damage Mechanics

In previous research of the rock mass near borehole wall under non-uniform in-situ stress,most of scholars in order to simplify the model concluded the stress distribution equation.Thus ignore the non-uniform in-situ stress of rock infinitesimal shear stress. But the size anddirection of the shear stress and the impact on the calculation of other stress near the wall dueto ignoring it is not clear. This paper, on the basis of damage mechanics, doesn’t ignore theshear stress and gets the solving the stress calculation method and calculation results.This paper studied the stress veer of infinitesimal body stress under the influence ofshear stress and its impact on the determine of the damaging and failure area. Using stressequilibrium equations of the cylindrical coordinates, Mohr-Coulomb failure criterion andcombining damage theory, it deduced infinitesimal body stress equation of the damaging andfailure area. The stress equilibrium equation of the damaging and failure area is obtainedbased on damage theory under non-uniform in-situ stress damage. In the case of spacediscrete borehole surrounding rock mass, the calculation model is established. Use theforward and backward difference method to solve the approximate iterative initial value. Usethe central difference method to get the iterative formula of the damaging and failure areanode. Finally get the damaging and failure area distribution near borehole wall, and solve thethe radial stress, circumferential stress and shear stress of each point near borehole wall. Thesize and shape of the damaging and failure area are related to the maximum, minimumprincipal stress and the bottom hole pressure. Analysis of the influence of the in-situ stressand bottom hole pressure on the most destructive area radius of the damaging and failure areanear borehole wall is done. Thus get the rule of the influence of in-situ stress on borehole wallstability and provide theoretical guidance for bottom hole pressure adjustment to avoid thesidewall instability.