Interaction Mechanism And Stability Analysis Method Of Unsaturated Slope And Retaining Structure

As a very common retaining structure of the slope,the design and calculation of retaining wall and anti-slide pile have obtained a lot of research achievements.However,the current design method of retaining structure mainly includes the calculation of lateral earth pressure of retaining structure and the stability analysis of the reinforced slope.It only focuses on the saturated or dry state of the slope and ignores the gradual process from unsaturated to partial saturated or saturated to unsaturated.In fact,due to the presence of matric suction in the unsaturated zone of the slope,on the one hand,the tangential contact characteristics between the soil and the retaining structure and the distribution of normal earth pressure become more complicated.On the other hand,the hydraulic characteristics of the unsaturated slope are different from those of the fully saturated or dry slope.Because the dry-wet cycle will change the size of unsaturated area,it will also affect the stability and prevention effect of the slope and the retaining structure system.In practical engineering,the failure of retaining structure and slope instability often occur due to the decrease of matric suction.These experiences and lessons indicate that it is very important to adopt the concept and method of unsaturated soil mechanics and explicitly consider the matric suction effect above the groundwater level in the different stages of the design,construction and post-construction monitoring of retaining structures.Consequently,on the basis of previous studies,this paper,by means of laboratory test,theoretical calculation and numerical simulation,conducts an in-depth discussion on the interaction mechanism and stability analysis method between unsaturated slope and retaining structure respectively.The main research work is as follows:1.The interaction mechanism between unsaturated soil slope and retaining structure(1)Experimental and theoretical study on shear strength of interface between unsaturated soil and structure.The large-scale shear test of the interface between unsaturated soil and structure is carried out,the effects of matric suction and interface roughness on the interface shear behavior are studied,and the shear strength method of unsaturated soil-structure interface based on generalized effective stress is put forward.The rationality of this method was verified by comparing the existing literature data.Based on the results of conventional saturated interface direct shear test and soil-water characteristic curve test,a simplified method for estimating the shear strength envelope of unsaturated soil interface is proposed;(2)Experimental study on interaction between unsaturated soil and rigid retaining wall.Under translational mode,a series of the laboratory model tests of active earth pressure against rigid retaining wall with different wall roughness and backfill water are carried out,in which matric suction and earth pressure are measured by embedding osmometer and soil pressure cell respectively,and the position of the failure surface is obtained by using the DIC technique,and the effects of matric suction and interface roughness on the earth pressure and the shape of the failure surface are discussed;(3)Theoretical calculation of the earth pressure for unsaturated rigid retaining wall.Based on the improved Coulomb soil wedge calculation model and introducing the generalized effective stress principle,the limit equilibrium method is used to solve the active/passive earth pressure of unsaturated soil considering the effect of interfacial shear strength.By comparing the experimental results and theoretical calculation results,the reliability of these methods is verified,and the parameters are discussed in detail;(4)Theoretical calculation of effective earth pressure of unsaturated soil on antislide piles.Based on the theory of plastic deformation,the expression of the distribution of the external force of the anti-slide pile body along the pile length considering the influence of suction stress is derived.The results are obtained by comparing the Optum G2 numerical software to verify the rationality of the equation,and the effective soil pressure distribution along the pile length of the anti-slide pile is discussed in detail when the anti-slide pile was placed in four hypothetical soils.2.The stability analysis method of unsaturated slope and retaining structure(1)Upper bound theorem of unsaturated soils.Based on the principle of generalized effective stress,regarding the suction stress as an external stress variable,the workenergy balance equation is given again.(2)Upper bound solution of stability coefficient of rigid retaining wall-unsaturated slope.Considering the effect of interfacial shear strength,the unsaturated backfill and retaining wall are regarded as a whole system,the external power and internal energy dissipation rate of the system are calculated,and the method for calculating the stability coefficient of the wall-soil system is proposed by the energy method.The reliability of the method is verified by comparing with the Optum G2 numerical software and theoretical calculation results,and the parameters are discussed in detail.(3)Upper limit solution of ultimate lateral resistance of anti-slide pile-unsaturated slope.Regarding the lateral resistance provided by the anti-slide pile as an unknown external force,the ultimate lateral resistance on stabilizing pile which satisfies a given stability coefficient of the unsaturated slope under steady seepage condition is solved by using the strength reduction method and the upper theorem of unsaturated soil.The reliability of this method is verified by an example,and the parameters are discussed in detail.(4)Upper limit solution of ultimate bearing capacity of anti-slide pile-unsaturated slope.The ultimate lateral resistance provided by the anti-slide pile is calculated by using the expression of the effective earth pressure of the unsaturated soil on the stabilizing pile,and the ultimate bearing capacity of the unsaturated slope strengthened by the anti-slide pile under steady seepage condition is solved by combining the strength reduction method and the upper limit analysis method,the reliability of the method is verified by an example,and the parameters are discussed in detail.