A. Hegde

Experimental and numerical studies on footings supported on geocell reinforced sand and clay beds

Abstract This paper presents the results of laboratory model tests and numerical studies conducted on a square footing resting on geocell reinforced sand and clay beds. Using suitable scaling considerations, a model footing size was arrived from the prototype raft foundation. Commercially available geocells made up of polyethylene having an equivalent pocket diameter of 0⋅25 m and aspect ratio of 0⋅6 were used in the experimental investigation. Clean sand was used to fill the geocell pockets in both sand and clay bed tests. Test results of unreinforced, geocell reinforced, and geocell reinforced with additional planar geogrid at the base of the geocell cases are compared separately for sand and clay beds. Results reveal that the use of geocell increases the ultimate bearing capacity of the sand bed by 2⋅4 times and clay bed by 3⋅2 times. Provision of the planar geogrid at the base of the cellular mattress arrests the surface heaving and prevents the rotational failure of the footing. Moduli of subgrade reaction values indicate that the contribution of the geocell reinforcement exists even at very low settlements. Using the concept of equivalent composite model, the three-dimensional nature of the geocell is numerically simulated in the fast Lagrangian analysis of continua in 2D (FLAC2D). Experimental and numerical results are in good agreement with each other.

Effect of infill materials on the performance of geocell reinforced soft clay beds

The present study deals with model plate load tests conducted on geocell reinforced soft clay beds to evaluate the effect of infill materials on the performance of the geocell. Commercially available Neoweb geocells are used in the study. Three different infill materials namely aggregate, sand and local red soil were used in the study. The load carrying capacity of the geocell reinforced bed (as compared to an unreinforced bed) was found to be increased by 13 times for the aggregate infill, 11 times for the sand infill and 10 times for the red soil infill. Similarly the reduction in the settlement was in the order of 78%, 73% and 70% aggregate, sand and the red soil infill materials respectively. Results suggest that the performance of the geocell was not heavily influenced by the infill materials. Further, numerical simulations were carried out using FLAC2D to validate the experimental findings. The results from numerical studies are in reasonably good agreement with the experimental findings. The outcome of this work is successfully implemented in the construction of the geocell foundation to support a 3 m high embankment in the settled red mud in Lanjighar (Orissa) in India.

Joint Strength and Wall Deformation Characteristics of a Single-Cell Geocell Subjected to Uniaxial Compression

Geocells are three-dimensional expandable panels with a wide range of applications in geotechnical engineering. A geocell is made up of many internally connected single cells. The current study discusses the joint strength and the wall deformation characteristics of a single cell when it is subjected to uniaxial compression. The study helps to understand the causes for the failure of the single cell in a cellular confinement system. Experimental studies were conducted on single cells with cell pockets filled up with three different infill materials, namely silty clay, sand, and the aggregates. The results of the experimental study revealed that the deformation of the geocell wall decreases with the increase in the friction angle of the infill material. Experimental results were also validated using numerical simulations carried out using Lagrangian analysis software. The experiment and the numerical results were found to be in good agreement with each other. A simple analytical model based on the theory of thin cylinders is also proposed to calculate the accumulated strain of the geocell wall. This model operates under a simple elastic solution framework. The proposed model slightly overestimates the strains as compared with experimental and numerical values

Use of Bamboo in Soft-Ground Engineering and Its Performance Comparison with Geosynthetics: Experimental Studies

The results of the laboratory investigation performed on clay beds reinforced with natural (bamboo) and commercial (geosynthetics) reinforcement materials are reported in this paper. To use bamboo effectively, three-dimensional cells (similar to geocells) and two-dimensional grids (similar to geogrids) are formed using bamboo (termed bamboo cells and bamboo grids, respectively). The performance of clay beds reinforced with bamboo cells and bamboo grids is compared with that of clay beds reinforced with geocells and geogrids. The bearing capacity of the clay bed increased by six times when a combination of geocell and geogrid was used. The ultimate bearing capacity of the clay bed reinforced with bamboo cell and bamboo grid was found to be 1.3 times more than that of clay bed reinforced with geocell and geogrid. In addition, substantial reduction in the footing settlement and the surface deformation was observed. The tensile strength and surface roughness of bamboo were found to be nine times and three times, respectively, higher than geocell materials. The bamboo was treated chemically to increase its durability. Although the performance of bamboo was reduced by 15-20% after the chemical treatment, its performance was better than its commercial counterparts

Protection of Buried Pipelines Using a Combination of Geocell and Geogrid Reinforcement: Experimental Studies

This paper describes the laboratory tests on small diameter polyvinyl chloride (PVC) pipes buried in unreinforced and geosynthetic reinforced sand subjected to static loading. The aim of the study was to evaluate the appropriateness of the combination of geocell and geogrid reinforcement system in protecting the underground utilities and buried pipelines. A pipe with external diameter of 75 mm and thickness of 1.4 mm was placed below the footing at different depths ranging from 1B to 2B (where B is the width of the footing). Commercially available Neoweb geocells and biaxial geogrids (SS-20) were used as the reinforcements. Results indicate that the use of the combination of geocell and the geogrid reinforcement system considerably reduces the deformation of the pipe as compared to an unreinforced bed. Above 50% reduction in the pressure and more than 40% reduction in the strain values were observed in the reinforced bed as compared to the unreinforced bed at different depths. Conversely, the performance of the foundation bed was also found to be marginally influenced by the position of the pipe, even in the presence of the relatively stiff reinforcement system.

Stability analysis of rock-fill tailing dam: an Indian case study

This paper presents the comprehensive stability analysis of the rock-fill tailing dam constructed at Rampura Agucha zinc mine in Rajasthan, India. The results of the feasibility study carried out prior to the expansion of the dam height from existing 27 to 51 m have been presented. The final cross-section of the tailing dam was arrived based on the extensive stability analysis considering both the upstream and downstream methods of embankment rising. The factor of safety values was calculated from Bishop’s simplified method, Janbu’s method and Spencer’s method by considering the circular failure surfaces. Further, the dynamic stability analyses were also carried out using the pseudostatic approach. The results from the limit equilibrium approaches were validated with the shear strength reduction technique using finite difference-based Fast Lagrangian Analysis of Continua in 2D analysis. The factor of safety values calculated from the different approaches was found to be in good agreement with each other. In addition, the safety and stability of the tailing dam was found unaffected by the ongoing mining activities as the observed peak particle velocity at the site was less than 15 mm/s. Analysis of the last 25 year’s rainfall data suggested that the designed freeboard of 2 m above settled tailings can accommodate a single rainfall spell of approximately 2000 mm without endangering its structural stability.

Use of Geocells to Protect Buried Pipelines and Underground Utilities in Soft Clayey Soils

This paper describes the results of laboratory static plate load tests conducted on small diameter PVC (polyvinyl chloride) pipes buried in geocell and geogrid reinforced soft clay bed. The aim of the study was to evaluate the suitability of the combination of geocell and geogrid reinforcement system in protecting the underground utilities and buried pipelines. Commercially available neoweb geocells and biaxial geogrids were used as the reinforcements. A pipe with external diameter 75 mm and thickness 1.4 mm was used in the experiments. Results suggest that the use of the combination of geocell and the geogrid reinforcement system considerably reduces the deformation of the pipe as compared to unreinforced bed. More than 40% reduction in the pressure and more than 60% reduction in the strain in the pipe were observed in the presence of reinforcements as compared to the unreinforced bed. Conversely, the performance of the foundation bed was also found to be marginally influenced by the position of the pipe, even in the presence of the relatively stiff reinforcement system. The study revealed that the depth of placement of pipe can be significantly reduced in the presence of the geocell and geogrid. The outcome of the study has the huge financial implications in the large projects, where the pipelines are laid for several hundred kilometers.