Study On Mechanical Properties And Reinforcing Mechanism Of Geogrid Reinforced Gravelly Soil

The particle size,particle shape and mechanical properties of gravelly soil are significantly different from those of sandy soil and clay.Compared with clay,gravelly soil has relatively higher compressive strength and shearing strength but lower tensile strength.Mechanical Properties and Reinforcing Mechanism of Geogrid Reinforced Gravelly Soil,which is one of the effective ways to improve the properties of gravelly soil.Currently,there is a lot of interest on conducting research studies on the mechanical properties of the contact interface between gravelly soil and geotechnical reinforcement materials.However,despite of the interest,there is still a shortage of studies on the intensity parameters and factors that influence the interface of the gravelly soil and reinforcement soil in Xinjiang area in China.Further,there salsa shortage of studies on the strength characteristics of the reinforcement complex,failure modes,reinforcement effect,etc.,which is preventing further popularization on the use of geogrid reinforced gravelly soil in engineering projects.By understanding the reinforcing mechanism and operating characteristics of gravelly soil,the strength,deformation and failure characteristics of gravelly soil-geogrid reinforcement complex can be revealed.Further,the continuous progressive development of soil reinforcing technology can bepromoted according to the requirements of research and major practical engineering projects.In this study,an investigation on the mechanical properties and reinforcing mechanism of geogrid reinforced gravelly soil has been carried out.The main research work and the results are summarized as follows:1)Use of large-scale triaxial test to investigate gravelly soil and geogrid reinforced gravelly soil.Typical gravelly soil from Xinjiang area has been used as the specimen for conducting large-scale triaxial tests on the unreinforced gravelly soil and the gravelly soil reinforced with geogrids at different spacings.The shearing strength,deformation characteristics,internal friction angle,etc.of the gravelly soil with different particle shapes have been compared.The stress-strain relationship,strength characteristics,failure modes,and reinforcement effect of the gravelly soil before and after reinforcement have been investigated.The results are of practical value in reinforcing gravelly soil and in selecting design parameters for major engineering projects.2)Use of pull-out test to investigate geogrid-gravelly soil interface characteristics.Based on the results of the pull-out test,the gravelly soil-geogrid interface characteristics,and the factors that influence the interface characteristics,reinforcement soil interface interaction mechanism,friction coefficient,interface shear stress and the relative displacement relationship between the reinforcement and the soil have been investigated.Using the strain hardening pullout curve and the determination methods of the ultimate pullout force,this study has also developed failure criterion for the pullout specimen.By considering the influence of grid elongation on the grid-soil contact area in real-time,a formula which can determine the length of reinforcement-soil interface in the pullout process in real-time has been developed.The concept of the interface comprehensive friction angle?^*_s has been introduced.The two-parametric function?^*_sg?K,??is also provided involving the compactness K,normal pressure?,and reinforcement gravelly soil interface comprehensive friction angle?^*_sg.Using experiments,the influence of the compactness and moisture content on the interface strength parameters has been investigated.The results can be used as a theoretical basis for improving theories of reinforced soil calculation.3)Analysis of the influence zone of geogrid-gravelly soil contact interface and stability of reinforced steep slopes.By transforming traditional geosynthetics pull out apparatus,a device that can be used to observe the displacement of soil particles near geosynthetics-gravelly soil interface has been developed.Further,the influence zone of the interface between the reinforcement and soil has been measured and observed directly.The discrete element method has been used to show the microscopic change of the reinforcement-soil interface region during the gravelly soil-geogrid pullout test in microscopic scales.By fully considering the indirect reinforcement effect of geogrid on soil body,a simplified method?i.e.influence zone method?which can analyze the stability of geogrid reinforced soil slope with reinforcement influence zone has been developed.In this method,by simplifying complex reinforced soil slopes into stratified soil slopes,the calculations are considerably simplified.4)Use of centrifugal model test to investigate geogrid gravelly-soil reinforced steep slope embankment.Using the centrifugal model tests,the geogrid reinforced steep slope embankment without reinforcement and with different spacing's of reinforcement layers have been conducted to investigate the strain laws,side slope deformation laws,and failure modes of geogrid reinforced gravelly-soil slopes.Further,the rationality and structural safety of the design scheme for reinforced steep slope embankment that is sometimes applied to engineering projects have been verified.The results of the test show that the geogrid reinforcement affect the failure mode of side slopes and that reinforced side slopes generally fail to form continuous sliding surfaces due to the separation of the geogrids.The failure modes mainly include local deformation of slopes and continuous progressive deformation of the soil between the geogrids.Combined with the theory of influence zone,it provides a theoretical basis for the determining the reinforcement layer spacings in the design.5)Use of field test to investigate geogrid gravelly soil reinforced steep slope embankment.The prototype field tests of geogrid reinforced steep slope embankments with two different gradients of sub grade side slopes have been carried out in order to observe the soil pressure,grid strain and deformation of the embankment slopes during and after the filling process.Further,the vertical and horizontal soil pressures of the reinforced gravelly-soil steep slope sub grade,the strain of geogrid reinforcement,and the distribution and change laws of the lateral displacement of reinforced soil slope have been analyzed.Then,the mechanism of action,operating characteristic and construction technology of reinforced gravelly soil steep slope sub grade that are sometimes applied to engineering projects have been investigated.