Analysis On Characterics Of Geogrid Reinforced Sand And Bearing Capacity Of Geosynthetics Reinforced Cushion

The new triangular geogrid products with a triangular aperture shape recently introduced into the market are expected to have a more stable grid structure, which can provide more uniform resistance in all directions. However, limited test data related to triangular geogrid-reinforced bases has been published so far. Therefore, tests are needed to evaluate their behavior and mechanisms when used in the reinforced bases. Laboratory direct shear and plate load tests were conducted in the apparatus designed and fabricated at Department of Civil, Environmental, and Architectural Engineering at the University of Kansas to investigate the behavior and mechanisms of triangular geogrid reinforced sand bases. The tensile behavior of the geogrids with triangular and rectangular apertures under different uniaxial tensions was modeled using the numerical software-FLAC2D. The effects of installation damage on the geogrid under uniaxial tensions were also investigated. A simplified method for calculating the bearing capacity of geosynthetic reinforced bases was proposed, which can provide the reference data for the revision of the Technical Code for Ground Treatment of Buildings. The main conclusions can be drawn out from this study as follows:(1) It was the first time using the direct shear test method to study the interface strengthbetween the new triangular geogrid and Kansas River sand. The ratio of frictional coefficients was introduced to evaluate the interface properties. As obtained from the test data, the relationships between shear stress versus shear displacement are nearly the same and the shear strength increased linearly with the increase of vertical stress. The friction angles between biaxial geogrid and the sand are nearly equal to the internal friction angle of the sand. The increment of interface shear strength between biaxial geogrid and sand was mainly due to interlocking between geogrid and sand. Indition to the interlocking between geogrid and sand, the contribution of aperture shape on the increase of the friction angle was considered for the triangular geogrid. The shape parameters of geogrid were introduced to analyze the effect of the aperture shape on the interface action between geogrid and sand. The interface failure mechanisms between geogrid and sand were investigated from four stages.(2) It is the first time using the numerical software-FLAC2D to model the tensile behavior of the geogrid with triangular and rectangular apertures under different uniaxial tensions. In addition to the loading direction, this study studied the influence of the following factors on the tensile stiffness of the geogrids:aperture shape, elastic modulus, and cross-section area of geogrid ribs. The tensile strength and stiffness of the geogrid with rectangular apertures were highly dependent on the direction of the uniaxial tension relative to the orientation of ribs. The tensile strength and stiffness of the geogrid with triangular apertures were relatively uniform at all the loading directions relative to the orientation of ribs even though those at the 45°loading were slightly lower. An increase of the elastic modulus and/or cross-sectional area of ribs increased the tensile stiffness of the geogrid with triangular apertures.(3) As discovered from the numerical results, it was found that the tensile strength decreased linerly with the increase of the extent of damage. The extent of damage was referred to the tensile strength loss in the middle ribs at 0°direction. The reduction of the tensile strengths under 30°tension was significant than other directions. The ultimate tensile strengths of the biaxial geogrid are more sensitive to the installation damage than the triangular geogrid. An installation damage reduction factor of the triangular geogrid based on the tensile strength reduction under 30°tensions was given for reference.(4) The plate load tests were performed to study the behaviors of triangular geogrid reinforced sand. An unreinforced base and biaxial geogrid reinforced sand base were also tested for the comparasion purpose. The reinforced sections were found to perform better than the unreinforced sections when the geogrid was placed at 5 or 10cm. The triangular geogrid at the depth of 1/3 to the width of base performed the best. At the range of effective displacement of base, single layer reinforcement, with a similar tensile strength, the triaxial geogrids had a higher interface shear resistance than biaxial geogrids. The bearing capacity to weight ratio was introduced to investigate the advantages of triangular geogrid. According to the actual site conditions, the types, aperture shape, reinforcement parameters should be considered when geogrid is chosen for reinforcement. The bearing capacity rario was suggested for reference.(5) The modified Terzaghi method and Binquet method were compared first. Based on the site conditions of the reinforced projects, a coefficient of tensile strength of geosynthetic was introduced for calculation. A simplified method to calculate the bearing capacity of geosynthetics-reinforced base by forms of characteristics value method and modified Terzaghi method was given in this paper. The formulations were found to match the test data reseasonably well.