Study On Reduction Law Of External Water Pressure Of Rich Water Depth Shaft Lining And Engineering Influence

With the development of society,the larger the underground engineering area and buried depth,the shaft construction will develop towards the deep and general direction.The geological conditions of the shaft are more complex and restricted by environmental factors.It is prone to well flooding accidents during construction in the water rich area with broken rocks and developed fissures.The occurrence of well flooding accidents is mostly caused by the breakage of grouting ring and lining under high water pressure.Therefore,appropriate means should be adopted to reduce the water pressure.However,the existing research and specifications on the reduction of external water pressure of lining are focused on the tunnel,and there is little research on the shaft.In addition,due to the spatial random distribution of cracks,the external water pressure of the lining in the fractured rock shaft leads to a certain non-uniformity of the water pressure around the shaft.The degree of non-uniformity is related to the degree of crack development,which is obviously different from the shaft in layered soil.The uneven external water pressure of lining will have a great impact on the engineering design.Therefore,in order to ensure the engineering safety and provide design reference for subsequent projects,it is of great significance to carry out the research on the reduction law and engineering impact under the uneven external water pressure of lining.Gaoligongshan No.1 shaft has the characteristics of high fracture water pressure and steep dip and large fracture.Based on the Gaoligongshan No.1 shaft,taking the design demand problem research result feedback as the research direction,taking the general law as the research basis,taking theoretical derivation,field measurement and numerical simulation as the research means,this paper makes a detailed analysis on the reduction law of external water pressure of lining of rich water depth shaft and the engineering impact caused by uneven water pressure,At the same time,the correlation ranking of different factors on the effect of water pressure reduction is given.The main research results are as follows.1)The simulation results of equivalent continuous medium are roughly the same as the theoretical calculation results.Except for the initial head height,lining thickness and excavation diameter,other factors exist in the water pressure reduction sensitive area.Changing the corresponding factors in this area can effectively reduce the water pressure.(1)Lining parameters: the smaller the lining thickness,the better the water pressure reduction effect.The ratio of lining permeability coefficient / surrounding rock permeability coefficient is between 1.67e-02 and 1.67e-05,and the lining permeability coefficient is between 1.44e-9 m/s and 1.44e-13 m/s.reasonable control of lining permeability coefficient can effectively reduce water pressure.(2)Grouting parameters: the ratio of grouting permeability coefficient / surrounding rock permeability coefficient is between 4.19e-01 and 4.19e-05,the range of grouting permeability coefficient is between 3.60e-9 m/s and 3.60e-13 m/s,and the grouting thickness is between 0 and 6m.Reasonable grouting thickness and grouting materials can effectively reduce the water pressure,and the reduction effect outside this area is poor.(3)Initial geological conditions: the larger the opening diameter is,the better the water pressure reduction effect is.The permeability coefficient of surrounding rock is between 8.6e-9 m/s and 8.6e-13 m/s.The water pressure reduction effect is good.The reduction effect outside this area is poor.The change of initial head height basically has no effect on the reduction coefficient of external water pressure of lining.2)In addition to the excavation diameter and lining thickness,the general laws reflected by the calculation results of dual medium and equivalent continuous medium and theoretical formula are the same,but the values are different,but not large.The closer the crack is to the lining,the greater the impact on the reduction effect of external water pressure of the lining.There is a certain deviation in the water pressure reduction values at different measuring points,but the size law is consistent with the measured results.(1)Lining parameters: under different lining permeability coefficients,the influence of cracks on the external water pressure of lining changes little,and the calculation result of maximum water pressure of dual medium is close to that of equivalent continuous medium;The calculation results of dual media under different lining thickness and different excavated tunnel diameter are closely related to the spatial distribution of cracks.The water pressure near the cracks is the largest,that is,the difference of excavated tunnel diameter and lining thickness will change the position of the maximum external water pressure of the lining.(2)Grouting parameters: under different grouting permeability coefficients,there are certain differences in the calculation results of the maximum water pressure between dual medium and equivalent continuous medium,and the difference range is determined by the proportion of cracks within the grouting range;With the increase of grouting thickness,the influence of cracks on the reduction effect of water pressure after grouting decreases gradually.The order of water pressure at different measuring points is not affected by the grouting range,but the dispersion decreases gradually.(3)Initial geological conditions: the higher the initial head,the greater the dispersion of water pressure at different measuring points,and the reduction coefficient remains almost unchanged;The smaller the permeability coefficient of surrounding rock,the smaller the difference of water pressure at different measuring points.3)The correlation degree calculation results of equivalent continuous medium and dual medium reflect the same law,and the influence degree of different factors on the reduction of external water pressure of lining is different.Calculation results of equivalent continuum correlation degree: grouting permeability coefficient > lining permeability coefficient > surrounding rock permeability coefficient > excavation diameter > grouting thickness > lining thickness;Double medium calculation results: lining permeability coefficient > surrounding rock permeability coefficient > grouting thickness.4)On the basis of considering the elastic brittle damage characteristics of rock mass,the medium coupling method is used to simulate the excavation process of the original scheme of shaft.The error between the hydraulic simulation results and the measured results is no more than 6%.The proposed scheme based on the two-dimensional section reduction law has better water pressure reduction effect and smaller lining displacement.The uneven phenomenon of external water pressure of lining in the original scheme and optimization scheme is obviously different from the simulation results under the idea of horizontal isotropy.After the division of different regions,the external water pressure of lining,lining deformation and surrounding rock deformation are uneven.The deformation of shaft lining is mainly affected by the external water pressure of lining,which should be paid attention to in similar projects.