Distribution law of principal stress difference for backfilling boreholes in unequal stress field
To explore the distribution law of principal stress difference(PSD)and evaluate its stability for backfilling boreholes in unequal stress field,the distribution laws of principal stress difference and plastic zone for borehole at various diameters,vertical principal stress σV,maximum horizontal principal stress σH,and horizontal principal stress ratio λ′ were analyzed through theoretical analysis,numerical simulation and engineering case methods.The results show that the area of maximum PSD lies in the inwall of the borehole parallel to the direction of minimum horizontal principal stress σh.A calculation model was established for the position of maximum PSD,which can provide theoretical guidance for predicting the development direction of borehole fracture at different depths of surrounding rock.The numerical simulation results of the distribution of PSD in the borehole are consistent with the theoretical calculation results,verifying the correctness of the theoretical analysis.When the rock parameters are constant,the distribution of PSD is like an"8"shape at various borehole diameters,σH and σV,while the transition of the PSD shape at various λ′ is from round→ellipse→similar"8"shape.The plastic deformation zone in the surrounding rock initially emerges in the direction with the largest PSD,that is,the direction of σh,and subsequently progresses in the direction of σH.The presence of the plastic zone may lead to instability in the surrounding rock and result in the transition of the borehole cross-section from round to ellipse.Taking the backfilling boreholes from a foreign copper mine as an example,the distribution law of PSD plastic zone in the surrounding rock was analyzed.Additionally,the minimum mud pressure for boreholes was calculated.This analysis can provide engineering guidance for improving borehole stability.
万方数据
维普
