Experimental Study On Earth Pressure Of Gravity Retaining Wall Under Geogrid Composite Soil

The gravity reinforced earth retaining wall embeds geosynthetics such as geogrids with high tensile strength in the backfill behind the wall,and uses the complex interaction between reinforcement and soil to laterally restrain the backfill behind the wall,reducing the earth pressure on the wall surface and improving the stability and economy of the structure.However,there is a lack of systematic research on the working properties and design principles of gravity reinforced soil retaining walls,and there are engineering application problems that rely on experience rather than scientific basis in design.In order to explain the mechanism of reinforced soil in gravity reinforced earth retaining wall,reveal the evolution law of structural behavior of gravity reinforced earth retaining wall under various wall displacement failure modes,explore the reasonable reinforcement layout of retaining wall,and carry out the experimental study on earth pressure of gravity reinforced earth retaining wall under the action of geogrid-coarse gravel soil composite soil.The main research work and achievements are summarized as follows :1.Based on the special visual pull-out system and digital photographic measurement technology,the geogrid pull-out test is carried out with top load,geogrid type,coarse grain content and particle shape as variables.The evolution,distribution and soil particle displacement of geogrid-coarse grained soil reinforced influence zone are analyzed.The influence of various factors on the forming speed of reinforced influence zone,the thick Ness of each gradient layer and the microscopic characteristics of particle displacement are discussed.2.The model box which can realize the top loading and wall displacement is used to carry out the model test of the retaining wall under six working conditions by changing the number of reinforcement layers,the strength of the reinforcement,the connection mode of the reinforcement and the retaining wall,the length of the reinforcement and the displacement mode of the retaining wall.The distribution and evolution of the structural performance of the retaining wall,such as the maximum displacement required to reach the limit active state,the vertical earth pressure in the wall,the horizontal earth pressure on the back of the wall,the vertical displacement of the wall top and the tensile strain of the grid,are studied under the three basic active displacement modes of RB mode,T mode and RT mode.According to the test results and analysis,on the basis of reducing the displacement of the wall,improving the stability and reducing the cost,the reinforcement form of gravity reinforced earth retaining wall against the influence of wall displacement is put forward.3.Based on the quasi-cohesion theory and working stress principle of reinforced soil,it is assumed that the tensile strength of the reinforcement and the cohesion of the reinforced soil composite have the same relationship with the displacement.According to the geometric relationship of the Mohr circle of the reinforced soil stress,considering the strength reduction of the reinforcement in the reinforced soil composite,the calculation method of the cohesion of the reinforced soil composite and the tensile force of the reinforcement with different buried depths changing with the wall displacement is derived.According to the applicable conditions of Rankine and Coulomb earth pressure theory,two kinds of earth pressure calculation methods,quasi-cohesive force method and working stress principle method,which are suitable for three kinds of foundation displacement modes of retaining wall,are derived.The calculation model is designed for comparative analysis of the results,which shows that the difference between the results of the two calculation methods is the difference in the tension zone caused by the cohesive force and the tensile strength of the reinforcement.The two calculation methods proposed in this thesis have certain theoretical significance for the calculation of earth pressure of gravity reinforced earth retaining wall under different reinforcement strength and pressure state,and also have corresponding guiding value for the practical application of the structure.