Study On Vertical Bearing Capacity Of Inner Steel Plate With High-strength Reinforced Concrete Composite Shaft Wall

At present,with the rapid development of the economy of China,the demand for underground energy is expanding.It is necessary to build a large number of underground space structure to meet the mining needs.Because shallow energy resources are increasingly depleted,new mines often have the characteristics of crossing deep unstable strata and fractured water-bearing rock formations,withstand huge pressure,complex surrounding geological conditions and so on.The freezing method has the advantages of large drilling depth,adaptability ability,can be used in unstable aquifer,and can be used in bedrock aquifer,which has little environmental impact,so it is widely used in mine production which needs to cross the deep topsoil.With the increase of freezing depth,the well wall is prone to cracks and even structural breakage brought about by cracking water inrush sand and other engineering problems.Nowadays scholars generally believe that the aquifer water level decline,soil consolidation compression,so that the wellbore by a considerable vertical downward friction,which is the key factor neglected in the design of the wall in the past.The wellbore produces stress greater than the strength of the well wall under the combined action of vertical additional force and horizontal ground pressure,the well wall damage.Based on Banji coal mine as the engineering background,this paper adopts the high strength concrete composite well wall of the inner sleeve steel plate of the broken part.Studying whether the composite well wall meets the engineering strength requirements by means of analytical calculation analysis and finite element software ANSYS.The change of stress and strain caused by the increase of inner plate and concrete with vertical load is obtained.After the completion of wellbore repair,the fuzzy mathematics theory is adopted to judge the effect of wellbore repair,which provides reference for the rest of the actual problems of well wall breakage engineering.The specific research contents can generalize the following aspects:Firstly,the calculation model of high strength reinforced concrete composite well wall analysis method of inner plate is established,and according to the principle of stress superposition.It is analyzed that well wall breakage is mainly caused by vertical additional force and horizontal ground pressure,among which vertical additional force is the main factor leading to the damage of well wall during coal mining.By resisting or dispersing vertical loads,the probability of wellbore damage caused by the settlement of overlying soil layer can be greatly reduced.Secondly,The finite element simulation model of high strength reinforced concrete composite well wall of inner steel plate is established,and the stress and strain changes of inner plate and concrete with the increase of external load are analyzed,and the results obtained by analytic method are in good agreement with the numerical simulation results,which shows that it is feasible to study composite well wall by numerical simulation analysis.The relationship between vertical ultimate bearing capacity of composite well wall,concrete strength,thickness ratio,steel plate thickness and yield strength of steel plate is obtained by regression analysis with numerical simulation results.Thirdly,based on fuzzy mathematics theory and analytic hierarchy process,a comprehensive evaluation model of wellbore repair effect is established,and different membership functions are adopted for quantitative and qualitative indexes respectively,and the damage part of main well of plate set coal mine is judged by the repair scheme of high strength reinforced concrete composite wall of inner steel plate,which has some problems in the restoration scheme.However,there is no need for large rectification,subsequent production safety work can continue to implement.