Journal of Engineering Geology

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In this study using finite element procedure was used to simulate the dynamic behavior of reinforced soil walls, to evaluate their dynamic response on all types of deformation modes, different mechanisms of failure detection and identification of parameters in each of the modes and the mechanisms. Detailed numerical modeling, behavioral models and materials were described and Dynamic response of the physical model has been validated experimentally. Parametric study has been of the wall height of 5 meters by the effective parameters such as hardness, length to height ratio, the vertical reinforcement, wall height, and acceleration inputs. Three modes of deformation were observed. The study showed that occur bulging deformation mode while the use of flexible reinforcement and occur overturning deformation mode while the use of stiffness reinforcement. Stiffness reinforcements have the most effective in changing the type of deformation. Length to height ratio of reinforcements has the minimum effective in changing the type of deformation.

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The choice of a suitable bearing capacity of soil becomes the most important issue to be considered in any project. This paper describes analytical investigation conducted to evaluate the ultimate bearing capacity of adjacent footings in various spacings of footings. Bearing capacity of adjacent footings is determined based on virtual retaining wall method by applying equilibrium between active and passive forces. Results indicate the ultimate bearing capacity of each foundation changes due to the interference effect of the failure surface in the soil and it depends on footings spacing. In the present study, effect of soil type, depth of adjacent footings and reinforced soil is investigated on bearing capacity of adjacent footings. Results indicate closely spaced footings, can decrease or increase bearing capacity of adjacent footings with respect to single footings. Also, reinforced soil increases bearing capacity of closely spaced footings with respect to single footings on unreinforced soil, it depends on footings spacing. Finally, the predicted results are compared with those reported from experiments, analytical and numerical results performed by others, indicating an acceptable agreement.
 

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This paper describes triaxial compression tests conducted to determine the effect of fiber inclusion on stiffness and deformation characteristics of sand-gravel mixtures. Tested soil was a mixture of Babolsar sand from the shores of the Caspian Sea and Karaj River gravel. Portland cement was used as the cementing agent and fibers 12mm in length and 0.023mm in diameter at 0%, 0.5% and 1.0% were added to the mixtures. Triaxial tests were performed on saturated samples in consolidated drained and undrained conditions at confining pressures of 100, 200 and 300 kPa. Deviatoric stress-axial strain, volumetric strain-axial strain, pore pressure-axial strain curves with deformation and stiffness characteristics were investigated. Tests results show that fiber addition increased peak and residual shear strength of the soil. Fiber addition resulted in an increase of the maximum positive and negative volumetric strains. In undrained condition, fiber inclusion caused increase in initial positive pore pressure and final suction. It has also been observed that fibers decreased initial tangent stiffness of the cemented sand-gravel mixture.

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As usage of reinforced soil structures is highly increased in seismic active zones, the analysis of dynamic behavior of these structures begins to be of great significance.  The present paper is an attempt to study the seismic behavior of reinforced soil retaining walls with polymeric strips. The consequences of the most principal parameters counting the length of reinforcement, reinforcement arrangements (zigzag vs. parallel), maximum base input acceleration and wave frequency on the wall displacement have been investigated for sensitivity analyses. The main drawback of numerical methods in dynamic analysis is being very time consuming. Therefore, determination of equivalent coefficients is a suitable, easy and beneficent approach to converge   results of   pseudo-static and dynamic methods. In this case, a relatively accurate design is achieved by using pseudo-static method that takes less time. To this end, an earthquake equivalent horizontal acceleration coefficient is proposed by considering horizontal displacement of the wall as the basis for comparison

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In this paper, the bearing capacity of strip footings on fiber reinforced granular soil has been studied. The stress characteristics or slip line method has been used for the analysis. In the selected failure criterion, the orientation of the fibers are isotropic and fibers are not ruptured. Seismic effects have been considered in the equilibrium equations as the horizontal and vertical pseudo-static coefficients. The equilibrium equations have been solved using the finite difference method. The provided computer code can solve the stress characteristics network and calculate the bearing capacity. The bearing capacity has been presented as the bearing capacity factors due to the unit weight of the soil and surcharge. Several graphs have been prepared for the practical purposes. Also, a closed form solution has been presented for the bearing capacity factor due to the surcharge. By the parametric studies, the effects of the geometry and soil properties have been investigated. Results show that the bearing capacity increases with an increase on the average concentration and aspect ratio of the fibers, the fiber/matrix friction angle and the soil friction angle. Furthermore, the extent of the failure zone is increased with increasing the pseudo-static coefficients and decreasing the surcharge.

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In the narrow geosynthetic-reinforced retaining walls a stable rear wall exists in a short distance and so there is no enough space to extend appropriate length of reinforcements. In this case, the probability of overturning of retaining wall increases especially when subjected to earthquake loading. To increase the stability of the wall, reinforcements may be connected to the stable rear surface. Alternative solution is the utilization of full-height cast in-place concrete facing in order to resist the earth pressure by combined actions of reinforcements pullout capacity and facing flexural rigidity. One of the main questions about this type of walls is the portion of earth pressure resisted by the facing. In this study, the seismic earth pressure of narrow geosynthetic-reinforced backfill on rigid facing was evaluated using limit equilibrium approach and horizontal slices method. The critical failure surface was assumed to extend linearly from the wall toe to the rear surface and then moves along the interface of the backfill and rear surface up to the backfill surface. The effects of various parameters such as wall aspect ratio have been investigated. The obtained results show that the applied soil pressure on wall facing will be increased with depth in the upper part of the wall according to the Mononobe-Okabe equation, but its pattern is inversed in the lower part of the wall and it decreases until it reaches to zero at the wall toe. The results of analyses indicate that the attracted soil thrust by the facing increases with lessening of backfill width.