| In 2009,the auxiliary shaft of a mine was subjected to stress and secondary damage due to water burst and sand burst.According to the characteristics of the damage,experts proposed that the original shaft wall should be repaired and strengthened by the form of inner casing steel plate concrete shaft wall.The original shaft wall and inner casing shaft wall should be combined into a whole to jointly resist the external action.After the repaired wellbore is put into use,it still faces the influence of complex geological conditions,coal mining and other factors,so it is very necessary to judge the running state of wellbore.The state of the auxiliary shaft is analyzed by means of theoretical analysis,numerical simulation and field monitoring.According to uniform load and non-uniform load,the stress of composite shaft wall is calculated and analyzed.Under uniform load,the formula of compound wellbore stress is obtained by using the principle of combined cylinder method.Under the non-uniform load,the wellbore is first simplified into the form of plane curved rod,and the non-uniform load is applied in the form of function P_b=P_a[1-?/2(cos2?-1)].After the internal force of the wellbore section is calculated,the formula for calculating the composite section stress of the wellbore is obtained according to the principle of solving the section stress of curved rod with,large curvature.The expression of borehole stress under non-uniform load shows that,in the range of 0°?90°,the circumferential stress on the inner edge of borehole decreases with the increase of Angle.The greater the degree of non-uniform load is,the greater the circumferential stress is,and the relationship between them is linear.Through the analysis of calculation examples,it can be seen that under the non-uniform load,the theoretical calculation result when,?=0 is about 12%higher than the calculated value under the uniform load.Therefore,when the sidewall section is converted into the same material,it is assumed that the influence of the intermediate steel plate layer will lead to the overestimation of sidewall stress.When ?=0,the numerical calculation results are close to those obtained by using the combined cylinder method,and the results obtained by using the numerical calculation are more accurate.Through numerical simulation of borehole walls at different depths,it is known that when the non-uniform lateral pressure coefficient increases to a certain value,0°of the inner edge of borehole wall at 473m depth is generally destroyed under pressure,while 900 is generally destroyed under tension.Generally,the non-uniform lateral pressure coefficient will not exceed 0.5.According to the numerical simulation results,when the non-uniform lateral pressure coefficient exceeds 0.88,the borehole wall with a depth of 473m will be damaged by pulling.When the non-uniform lateral pressure coefficient is 0.8,the wall with a depth of 540m has not been damaged.The above results verify that the shaft repaired by inner casing steel plate concrete shaft wall can resist uneven horizontal load well.The change of wellbore stress state causes the change of strain,so the stress change value can be obtained according to the monitoring data.The maximum stress change value of each level is superimposed with the stress value of inner edge of shaft lining at that time,and the stress value after superposition is compared with the yield stress of material,so as to determine the state of shaft lining.Figure[51]table[8]reference[55]... |
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