Conference Paper

Deformation behaviour of reinforced soil slopes subjected to rainfall induced subsidence

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Major part of Kerala is covered with lateritic soil. Lateritic soils, in general, can withstand high stress under unsaturated conditions. However, during rainfall infiltration, there is a tendency that the lateritic soil may undergo large and sudden deformation. In the recent past, Kerala experienced heavy rainfall induced distress. Associated with the rainfall event, a series of landslides and formation of cavities and subsidence of ground were observed in many parts of Kerala. Mechanically stabilised earth (MSE) structures such as reinforced soil walls and slopes can be used in landslide mitigation; especially in slide repair using the slide mass as the backfill. In the present study, soil was collected from a nearby site where landslide has occurred due to heavy rainfall. Experimental studies were conducted to study the collapse potential of the soil. An attempt was also made herein to investigate the deformation behaviour of geosynthetic reinforced soil slope resting on foundation soil subjected to rainfall induced subsidence.

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... Adaptation of geotechnical infrastructure to a changing climate like extreme precipitation events is required in the design of future MSE walls [28]. Recently, several rainfallinduced failures in lateritic soils were observed in Kerala during the rainy seasons in the years 2018 and 2019 [29]. Performance assessment of MSE structures during rainwater infiltration is complex which includes studies on seepage, Fig. 1 View of MSE wall with locally available lateritic backfills shear strength and associated volume change in the soil [19]. ...
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In the present study, performance of geosynthetic reinforced MSE walls backfilled with locally available marginal lateritic soil at the onset of rainfall infiltration was investigated. Two different types of geosynthetics reinforcements were used. One was a conventional type of geogrids usually used in MSE walls, and the other was composite geogrids. Seepage analysis, stability analysis and strength and deformation analysis were carried out on MSE walls with rainfall simulated for a duration of 3 days. In case of geogrid reinforced soil wall (GR-W), the suction within the backfill was lost completely at the end of 2.176 days of rainfall, whereas suction was maintained even at the end of 3 days of rainfall in walls reinforced with composite geogrids (CGR-W). From the stability analysis, it was observed that the factor of safety of GR-W decreased at the onset of rainfall infiltration with time and reached less than the desirable value of less than 1.5 in 2.125 days of rainfall. The factor of safety of CGR-W was maintained at 1.88 throughout the period of rainfall. The facing deformation in GR-W was found to increase, with a maximum of 3.2 times increase at the end of three days of rainfall. Similarly, there was an increase in maximum tensile load mobilized in the reinforcements in GR-W, whereas in the case of CGR-W, the influence of rainfall was negligible. From the present study, it can be concluded that the presence of composite geogrids improves the overall performance of MSE walls backfilled with marginal lateritic backfills.
The scarcity and fast depletion of granular materials necessitated to find alternative backfill materials in MSE walls. In the present study, application of construction and demolition waste (CDW) as a backfill for MSE walls was investigated. The physical, chemical, hydraulic and mechanical properties of CDW were found to meet the requirements of ideal backfills mandated by various design standards of MSE walls. At the end of construction, maximum facing deformation was at lower one-third height of the wall for MSE wall resting on a firm foundation. Influence of yielding foundation on the performance of MSE wall was also studied by varying the distortion levels to 0.2, 0.4 and 0.6. At the onset of differential settlements, the location of maximum facing deformation changed to the bottom of the wall. The maximum facing deformation and axial strain increased by 15 times and 2.5% respectively, when the wall underwent a distortion of 0.6.
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Loess soil deposits are widely distributed in arid and semi-arid regions and constitute about 10% of land area of the world. These soils typically have a loose honeycomb-type meta-stable structure that is susceptible to a large reduction in total volume or collapse upon wetting. Collapse characteristics contribute to various problems to infrastructures that are constructed on loess soils. For this reason, collapse triggering mechanism for loess soils has been of significant interest for researchers and practitioners all over the world. This paper aims at providing a state-of-the-art review on collapse mechanism with special reference to loess soil deposits. The collapse mechanism studies are summarized under three different categories, i.e. traditional approaches, microstructure approach, and soil mechanics-based approaches. The traditional and microstructure approaches for interpreting the collapse behavior are comprehensively summarized and critically reviewed based on the experimental results from the literature. The soil mechanics-based approaches proposed based on the experimental results of both compacted soils and natural loess soils are reviewed highlighting their strengths and limitations for estimating the collapse behavior. Simpler soil mechanics-based approaches with less parameters or parameters that are easy-to-determine from conventional tests are suggested for future research to better understand the collapse behavior of natural loess soils. Such studies would be more valuable for use in conventional geotechnical engineering practice applications.
Marginal fill materials that do not follow the guidelines are used in constructional activities due to ease in its availability and economic benefits. But several cases of geogrid reinforced soil wall failures indicate the loss of interfacial shear resistance due to wetting of backfill as a possible reason. In the present study, centrifuge tests were performed on geogrid reinforced soil wall models with wrap-around facing using a 4.5 m radius large beam centrifuge facility available at IIT Bombay at 40 gravities. A marginal soil with 21% fines was chosen as backfill in the study. Two geogrid types of different stiffnesses were modelled based on scaling considerations and used in the study. The models were prepared at wet of optimum to simulate wet backfill conditions. The surface settlements of the models during centrifuge tests were monitored with the help of Linear Variable Differential Transformers (LVDTs). Digital Image Analysis (DIA) was performed on photographs of the front elevation of the model captured during flight, to obtain face movements and reinforcement strain distribution along geogrid layers during centrifuge tests. Interpretations of centrifuge model test results reveal that the soil wall reinforced with low stiffness geogrid layers was observed to deform excessively and undergo pullout failure along soil–geogrid interface. However, the provision of geogrid layers with higher stiffness limited the excessive outward deformations of geogrid reinforced soil walls with marginal backfills. Further, the effect of moulding water content and stiffness of the geogrid on the mobilization of pullout resistance was evaluated through pullout tests in the laboratory. Based on the observations made from pullout tests and centrifuge tests, provision of stiffer geogrids in geogrid reinforced soil walls was found to be one of the viable options to mitigate the problems posed by marginal backfills.
Following the introduction of mechanically stabilized earth walls with metallic reinforcement in 1966, polymeric reinforced structures (both geotextile and geogrid) followed shortly thereafter. A major item that accompanied this change in reinforcement type was the nature of the backfill soil. Corrosion of metallic reinforcement was no longer an issue with polymer-related geosynthetics and thus locally available fine-grained soils were generally used in place of quarried coarse-grained gravel soil. The cost savings are obvious as are the implications for concerns over inadequate performance. While failures have occurred in both types of reinforced walls, this paper focuses only on geosynthetic reinforced walls.
Mechanically stabilised earth walls and reinforced soil slopes, design and construction guidelines
  • Elias
  • B R Christopher
  • D C Fhwa
Elias, V and Christopher, B.R. (1997) "Mechanically stabilised earth walls and reinforced soil slopes, design and construction guidelines", FHWA,DC, USA.