Analysis Of The Mechanical Characteristics Of The Existing And Newly Built Shaft Wall During The Freezing Repair Of The Damaged Shaft

With the continuous development of mine construction in China,some engineering problems,such as shaft wall damage and water inrush,have occurred successively during the service period in deep alluvium.Shaft repair has become an important part of mine construction.Aiming at the complex engineering problems of the auxiliary shaft repair in Banji Coal Mine,this thesis used numerical simulation,actual measurement analysis,and based on the thermal-mechanical coupling methods,to separately the frost heave force and the inter-wall pressure in the freezing repair process of the damaged shaft in deep alluvium.(1)This thesis systematically studies the application of local differential freezing technology in the freezing repair process of auxiliary shaft,and the results show that,at the time of 172 days,the shaft wall temperature of the differential freezing layer is-2.74?,which is 15.44%of that in full-depth freezing layer,the average temperature of the freezing wall is-16.33?,which is 75.85%of that in full-depth freezing layer,and the average thickness of the freezing wall is 84.22%of that in full-depth frozen layer.The temperature drop rate of the average temperature of the frozen wall in the differential freezing layer is 0.258?/d,which is 86.29%of the full-depth freezing layer.The differential freezing technology effectively limited the inward expansion speed of the frozen wall.(2)The analysis results of the frost heave force at the position of the existing shaft wall in the freezing repair engineering shows that the growth rate of the frost heave force,the maximum frost heave force,and the average frost heave force of the different frozen layers are less than those in full-depth frozen layer.The differential freezing control effect is significant,and the local differential freezing technique can effectively reduce the influence of soil frost heave on the existing shaft wall,and avoid the secondary damage of the shaft wall due to frost heave.The safety of the existing shaft lining was evaluated,and the result shows that the maximum freezing pressure of the differential freezing layer was 4.59 MPa at the time of 172 days,which was 55.56%of the full-depth frozen layer in the same period;the maximum equivalent stress of the existing shaft lining concrete is 49.97%of the fully-frozen layer,and the maximum hoop strain is 35.28%of the fully-frozen horizon.(3)Through field measurement and analysis,the force and deformation law of the auxiliary shaft wall is obtained.In the initial stage of the new shaft wall pouring,the freezing pressure is mainly borne by the existing shaft wall.The force on the new shaft wall is small,and the hoop concrete strain shows a slow increase trend.The three monitoring levels of the new shaft wall ring steel are stressed in the early stage of the casing wall.Tensile stress is generated due to the temperature effect,but the value is small;in the middle of the casing wall,the force of the newly-built shaft wall varies with seasonal temperature to a certain degree;after 300 day s,the circumferential strain of the concrete and the stress of the circumferential steel bar change law.The force is basically the same as that of the newly-built shaft wall,and gradually increases with the thawing of the frozen wall,and there is a trend of co-acting with the newly-built shaft wall.(4)The thermal-mechanical coupling analysis of the third monitoring level(depth 580m)of the auxiliary well is carried out using numerical calculation methods.The calculation results show that the newly-built shaft wall has a weakly uneven development pattern of concentric circles,and the pressure in the southwest direction is relatively small,while the pressure in the northeast direction is larger.At the same time,the load distribution of the existing and newly built shaft walls is extremely uneven.When the frozen wall is not thawed,94.24%of the freezing pressure is borne by the existing shaft wall.Compared with the development mode of the frost heave force acting on the existing shaft wall,the force on the new shaft wall is weakly uneven.(5)The circumferential strain change law of the newly-built shaft lining concrete is basically consistent with the force characteristics of the shaft lining structure.213 days after the completion of the casing wall,the hoop strain of the newly-built shaft lining concrete is dominated by compressive strain,showing weak inhomogeneity.The maximum hoop strain of the concrete inside the shaft lining structure is-116.57??,and the minimum hoop strain is-67.79??;The maximum hoop strain of the concrete outside the shaft lining structure is-97.73?? the minimum hoop strain is-55.44??,and the range of the hoop strain of the concrete inside and outside the shaft wall is between 25?50??.It is far less than the ultimate compressive strain of C90 concrete and is in the state of elastic stress.Figure[27]Table[14]Reference[66]...