Analysis For Deformation And Shear Zones Of Reinforced Embankment

On the base of numerous references and the subject " The application and mechanism of the reinforced soil with geosynthetics" from the Science Committee of Hunan Province, the laboratory model tests, the observations of settlements in the practical embankment reinforced with geosynthetics and finite element analysis were carried out in this paper to investigate the behaviors of strength and deformation of soil reinforced with geosynthetics, and to analyze the settlements of reinforced embankment, as well as the performances of shear zones and failure modes. Meanwhile a theoretical formula to calculate the vertical displacement of reinforced foundation and some design charts were also proposed. The main works in the paper included as followed:(1) The consolidated-drained and unconsolidated-undrained triaxial tests were run on red sandy silt clay reinforced with two various types of geosynthetics to investigate their strength and deformation performances. The influence parameters included reinforcement layers and modulus, the soil compactness, saturation degree, as well as the surrounding pressures and drainage conditions of test. The results showed that geosynthetics reinforcements enhanced the strength and ductility of red sandy silt clay, and the stress-strain behaviors were improved greatly. Reinforcements decreased remarkablely the dilation of soil, but appeared little influence on the volume shrinkage, as a result, to the soil with various compactness the role and function of reinforcement differed greatly during shear. Under undrainage conditions, the excess pore-water pressures almost counteracted the effects of reinforcement on initial compression stages, reinforcement even appeared negative impact on the strength of red sandy silt clay, even the increasing reinforcement modulus and layers could not enhance their strengths significantly. Consequently, the drainage conditions became the decisive factors to ensure the effects of reinforcement as compared with reinforcement modulus and layers.(2) A finite element model was presented and a calculation program was developed to investigate the deformation performances of reinforced embankment and the mechanism of its reducing settlements, the effects of reinforcement density, length and types were all considered in the paper.Results showed that the soil stresses exhibited redistribution due to reinforcement that the vertical and horizontal stresses decreased, while the shearstress and the ratio of the mobilized friction increased, thus the mechanical performances of the reinforced earth were improved greatly. As a result of reinforcement, the vertical settlement and lateral displacement reductions were noted, and the global stability, the bearing capacity and resistance to deformation of the reinforced embankment were strengthened.Reinforcement reduced greatly the differential settlement in bridge approach embankments, and turn the jump settlement at joint of the backfill and abutment into a transitional zone, and this proposed an effective way against differential settlement in highway engineering.The finite element program of reinforced embankment were developed in the paper, its calculations had good agreement with the laboratory model tests and the measured data of 12 bridge approach embankments in Highway 107 and Ningheng Highway, the program can be applied to analyze for settlement and stress of reinforced embankment; An optimal design on length and space of reinforcement in a reinforced embankment were also proposed in the paper. Some conclusions had been adopted by ((Technical Specifications for Application of Geosynthetics in Highway)) .(3) Based on Mindlin's problem, a theoretical formula to calculate the vertical displacement of reinforced foundation were suggested in the paper, and some design charts were also put forward.Analyses showed that settlement reductions were noted to be largest only when the reinforcement had a length 1.0 to 2.0 times the width of foundation, and the first layer were located at a depth less than 0.25 times the width of foundation and the rest at a depth less than 1.0 times the width of the same. However, the settlement reductions of foundation edge were always distinguished to that of central point.(4) Finite element analyses were employed to simulate the interaction between soil and reinforcement, and to investigate the shear zones and failure modes of slope reinforced with geosynthetics, and the influences on them of reinforcement modulus, density and soil modulus. Based on the comparisons of these calculations with the results of direct shear tests and the observed in the centrifuge tests, a further explain to the mechanics of reinforced slope stability were suggested.The performances of the shear zones of reinforced slope were correlated directly with the stabilizing effect of reinforcement, they explained possibly the mechanics of the reinforced slope stability. The finite element analysis showed that the shear zones and modes of shear failure in reinforced soil slopes varied with different density and stiffness of reinforcements. With the increasing density and modulus, the shear zonesin reinforced slopes became wider, and tended to move into the slopes, and to some extent the relative strength and stiffness of slope and subgrade changed, and the shear zones would go through the foundations of slopes, as a result, it is more reasonable to limit the modulus and density in some range in reinforced slopes. The results also indicated that reinforced slopes appeared three various failure modes with the increasing density and modulus of reinforcement;As compared with that in earth slopes, the influences of the soil modulus Es on the reinforced slope stability appeared significant, the results showed that only when reinforcement modulus Er and soil modulus Es in some range, a better reinforcement effect could be gained, the compatibility of Es and Er would contribute to the reinforcement effects and the slope stability.