Deformation Law And Design Method Of Deep Frozen Soil Wall Considering The Support Of Shaft Lining And Frozen Soil In Shaft

Although China has basically mastered the key technology of freezing shaft sinking in 800m-deep soil layer,the theory of frozen soil wall design seriously lags behind the engineering practice.Developing more practical theory of frozen soil wall design accords with the national demand to promote the shaft sinking capacity in deep soil layer(DSL).In this study,through comprehensive consideration of the working conditions(i.e.,“radial partial unloading”,“interaction with surrounding soil”and“support from shaft wall and frozen soil in shaft”)of frozen soil wall,the deformation law of frozen soil wall in DSL was investigated systematically in depth by means of analytical analysis,numerical calculation and simulation test.Besides,the new method for designing the thickness of frozen soil wall in DSL was discussed thoroughly from two aspects,namely the safety and economic rationality of frozen soil wall displacement control.(1)In view of the characteristics of frozen soil wall in DSL,an elastic-plastic plane strain model of interaction between frozen soil wall and surrounding soil was established under comprehensive consideration of multiple factors,including the initial in-situ stress field,the radial unloading effect of inner edge,the interaction with surrounding soil,and the support from outer wall and frozen soil in the shaft core below the working face.Next,the analytical solutions of stress and displacement were derived and verified by finite element calculation.Furthermore,the influences of various factors on plastic zone radius,inner edge displacement and outer wall supporting force were explored.(2)A numerical calculation model of spatial axisymmetric frozen soil wall was established to simulate short-section excavation and masonry construction.Then,the distribution and evolution characteristics of stress and deformation of frozen soil wall during construction were grasped.Moreover,the influences of construction process parameters and frozen soil wall parameters on side displacement,plastic zone radius and outer wall supporting force were concluded.(3)A large-area,high-pressure steel hydraulic capsule was designed and successfully manufactured,and a method for simulating the radial partial unloading of frozen soil wall was innovated.In addition,the similar materials of frozen soil wall that could meet the test requirements for initial setting time,elastic modulus,strength and flow state were developed.Besides,a large-scale physical simulation test was successfully conducted on frozen soil wall and shaft wall deformation in DSL.On the basis of the test results,the force and deformation laws of frozen soil wall and shaft wall were obtained.(4)This study established the model for analyzing the output-input ratio of frozen soil wall,acquired the output-input ratio criterion for judging the inner edge displacement of frozen soil wall,and proposed a new concept of designing the thickness of frozen soil wall based on a reasonable output-input ratio.Considering the support from outer wall and frozen soil below the working face,radial unloading conditions and interaction between frozen soil wall and soil layer,the formula for calculating the thickness of frozen soil wall based on the output-input ratio was derived,and a new method for designing the thickness of frozen soil wall in DSL,which balanced the requirements for safety and economic rationality,was successfully constructed.The following results were drawn:(1)The supporting force of outer wall pc,the cohesion of frozen soil cf and the internal friction angle of frozen soil φ are all important factors.The inner edge of frozen soil wall u0,the outer radius of plastic zone rp and the designed outer radius of frozen soil wall r1 all decrease linearly or strongly nonlinearly with the increases in pc,cf andφ.(2)The ratio of the shear modulus ratio of frozen soil wall to that of surrounding soil has a significant influence on the radial external load on the frozen soil wall when Gf/Gu=1～3.The influence weakens when Gf/Gu>5,and it becomes negligible when Gf/Gu>10.The increases in Gf and Gu are both conducive to reducing the displacement of frozen soil wall.(3)The influences of Poisson’s ratios of soil and frozen soil can be ignored.(4)The outer wall can be approximately regarded as a rigid body whose supporting force pc is mainly affected by the thickness of foam board behind it.(5)After the value of dimensionless frozen soil wall thickness input Δδ/δ exceeds 0.5,the dimensionless output-input ratio becomes smaller than 0.5 on the whole and rapidly approaches 0.Hence,the thickness of frozen soil wall should be designed based on a reasonable output-input ratio on the premise of ensuring safety.(6)The design method newly constructed following the above novel concept in Conclusion 5,which balances the requirements for safety and economic rationality,is pretty applicable to the design of frozen soil wall in DSL.(7)In engineering design,the support from outer wall and frozen soil in shaft should be taken into account to make cf/ph>0.5,so as to effectively reduce the thick ness of frozen soil wall.This study reveals the deformation law of frozen soil wall in DSL and constructs a pretty practical new method for designing the thickness of frozen soil wall.The research results boast crucial theoretical significance and practical value for promoting the freezing shaft sinking technology in China.The thesis has 157 figures,23 tables,and 143 references.