Suction stress is one of the most significant factors affecting the serviceability and stability of soil structures. This study presents a framework for analyzing the stability of geosynthetic reinforced soil (GRS) walls and slopes under unsaturated conditions. An analytical formulation of suction stress-based effective stress was implemented into a limit equilibrium solution, namely, the top-down procedure. The developed framework enables the prediction of the tensile load distribution and connection load between the reinforcement and wall face considering the pullout resistance of reinforcements in GRS walls backfilled with granular and marginal soils under unsaturated conditions. The applicability of the framework was demonstrated by providing an illustrative example followed by three series of parametric studies to understand the effects of pore size distribution, air entry pressure, and infiltration rate on the performance of an unsaturated GRS wall. The results quantify the impact of suction, showing that as it increases, the maximum tensile loads and connection loads decrease while pullout resistance increases. Mostly affected by the suction effect are upper reinforcement layers, where combined effects of reduced tensile load and increased pullout resistance decrease connection load and reinforcement length requirements. The current study strongly discourages counting on the contribution of suction for the design of new GRS walls. The suction value cannot be accurately and reliably determined for the entire lifespan of the GRS wall, and it may decrease or diminish in an uncontrolled and random manner under infiltration. However, by quantifying the effect of suction, the proposed framework in this study provides a valuable tool for analysis purposes, enabling a rigorous interpretation of field-measured reinforcement loads during wall service as well as evaluation of the forensics of failed GRS walls.
ABSTRACT: This paper presents the results of centrifuge model testing on slopes reinforced by anchored geosynthetics and subjected to seepage conditions. The tests were conducted on 2V:1H slope models under steady seepage condition at 50g. Surface settlements and pore water pressures at different locations were recorded during the test. The influence of anchor stiffness, anchor length, and anchor pretensioning were examined. With an increase in anchor strength or stiffness, a considerable decrease in crest settlements and face movements was observed. Further, pretensioning of strands was found to be effective in enhancing the efficiency of anchored geosynthetic systems. Limit equilibrium stability analyses were in good agreement with the experimental results of slope models at failure.
The anchored geosynthetic system (AGS) is a technique to improve the stability of unstable or quasi-stable slopes. In this study, the behaviour of geosynthetic in slopes reinforced with AGS subjected to seepage is investigated. Centrifuge model tests were carried out at 50g centrifuge acceleration on silty sand slopes with an inclination of 63·4° (2V:1H) and reinforced with AGS. Seepage was generated by gradually raising the water table within the reinforced slope models. By means of a digital image analysis technique, the behaviour of the surface geosynthetic during the seepage was studied and the compressive stresses produced beneath the geosynthetic were determined. Limit equilibrium stability analyses were conducted with the application of AGS loads measured by digital image analyses. The results indicate that the maximum tension mobilised in the geosynthetic during seepage depends on the tension induced in the geosynthetic due to the anchorage prior to introducing seepage. Furthermore, including the compressive stresses produced by the tensioned geosynthetic in the analyses gives a more realistic value for the safety factors.
An anchored geosynthetic system (AGS) is an in situ reinforcing system that can be utilised to improve the stability of earth slopes. In this study, performance of AGS slopes under seepage conditions was investigated through a series of centrifuge model tests. These tests were conducted at an acceleration of 50g on silty sand slopes having 2V:1H and 1V:1H inclinations and reinforced with AGS in a large beam centrifuge located at the Indian Institute of Technology Bombay, India. Seepage was induced through a seepage simulator system to raise the water table within the reinforced slopes. The stability and seepage analysis was carried out for AGS slope models and the results were compared with those obtained from the centrifuge model tests. The results indicated that the location of the predicted failure surface in AGS slopes depended on the type of AGS load used for the analysis. The results of seepage analyses indicate that when the phreatic line was close to the physically observed phreatic line it nevertheless exits the face at higher elevation than physically observed in the centrifuge.
The stability of earth slopes can be enhanced by introducing an anchoring system. The factor of safety of an anchor-reinforced slope is one of the essential items required to evaluate stability. This parameter can be predicted using limit equilibrium and numerical approaches by relevant software. Taylor's stability chart has been frequently used to estimate the factor of safety of an unreinforced homogeneous cohesive-frictional soil slope. An analytical expression was developed in this study based on the friction circle method by which the factor of safety of anchor-reinforced slopes can be predicted using Taylor's chart. The anchor-reinforced slope considered in the analysis consisted of homogeneous cohesive-frictional soil. The analyses were carried out considering different slope inclinations, anchor loads, anchor orientations, and slip circles. An illustrative example explained the procedure for finding the factor of safety and showed how the developed method could be used by practicing engineers. A comparison between the factor of safety estimated by Taylor's chart and the limit equilibrium method using SLIDE indicates a good agreement.
Abstract Natural and man-made slopes can undergo a retrogressive landslide when subjected to seepage. Studying the mechanism of retrogressive landslides contributes greatly to the employment of effective mitigation approaches. A multi-stage limit equilibrium-based study was performed to explore how the geometry of initial failure affects the progress of a retrogressive, multiple-rotational landslide caused by seepage flow. Seepage-stability analyses were carried out on two silty sand slopes which were previously found to experience successive rotational failures upon raising the water table in centrifuge tests. Analyzed in prototype dimensions were the slope models with the height of 24 cm and inclinations of 45° (1V:1H) and 63.4° (2V:1H) tested at different centrifugal accelerations. According to the tests, the initial shallow failures were assumed to be circular initiating from the face and emerging from the toe of the slopes in the stability analyses. The impact of curvature and length of the initial failure surface (referred to as IFS) as well as the height of the scarp shaped at each failure episode were investigated. The results show that the landslide continues until the slope profile finds a stable curvature. For the landslides that occur in the 45° inclined slope, when the initial failure initiates at a higher elevation on the slope face, the landslide retrogresses further. In addition, with an increase in the length or curvature of IFS, the final retrogression distance decreases. Further, it was observed that the progress of landslides depends on the height of the scarp exposed at each failure episode.
'%3e%3ccircle r='20' fill='%23008'/%3e%3ccircle r='17.5' fill='%23fff'/%3e%3ccircle r='3.5' fill='%23008'/%3e%3cg id='d'%3e%3cg id='c'%3e%3cg id='b'%3e%3cg id='a' fill='%23008'%3e%3ccircle r='.875' transform='rotate(7.5 -8.75 133.5)'/%3e%3cpath d='M0 17.5.6 7 0 2l-.6 5L0 17.5z'/%3e%3c/g%3e%3cuse xlink:href='%23a' transform='rotate(15)'/%3e%3c/g%3e%3cuse xlink:href='%23b' transform='rotate(30)'/%3e%3c/g%3e%3cuse xlink:href='%23c' transform='rotate(60)'/%3e%3c/g%3e%3cuse xlink:href='%23d' transform='rotate(120)'/%3e%3cuse xlink:href='%23d' transform='rotate(-120)'/%3e%3c/g%3e%3c/svg%3e)
'/%3e%3c/defs%3e%3cpath fill='%23012169' d='M0 0h10080v5040H0z'/%3e%3cpath stroke='%23fff' stroke-width='.6' d='m0 0 6 3m0-3L0 3' clip-path='url(%23b)' transform='scale(840)'/%3e%3cpath stroke='%23e4002b' stroke-width='.4' d='m0 0 6 3m0-3L0 3' clip-path='url(%23c)' transform='scale(840)'/%3e%3cpath stroke='%23fff' stroke-width='840' d='M2520 0v2520M0 1260h5040'/%3e%3cpath stroke='%23e4002b' stroke-width='504' d='M2520 0v2520M0 1260h5040'/%3e%3cg fill='%23fff'%3e%3cuse xlink:href='%23d' x='2520' y='3780'/%3e%3cuse xlink:href='%23a' x='7560' y='4200'/%3e%3cuse xlink:href='%23a' x='6300' y='2205'/%3e%3cuse xlink:href='%23a' x='7560' y='840'/%3e%3cuse xlink:href='%23a' x='8680' y='1869'/%3e%3cuse xlink:href='%23e' x='8064' y='2730'/%3e%3c/g%3e%3c/svg%3e)
