Sarvesh Chandra

A generalized mechanical model for geosynthetic-reinforced foundation soil

Abstract The present paper describes a mechanical model for idealizing the settlement response of a geosynthetic-reinforced compressible granular fill-soft soil system, by representing each sub-system by commonly used mechanical elements such as stretched, rough, elastic membrane, Pasternak shear layer, Winkler springs and dashpot. The model considers, simultaneously, several factors governing its behaviour, such as the compressibility of the granular fill, the compaction of granular fill, the time-dependent behaviour of soft soil and pre-stress in the geosynthetic reinforcement, besides the material and soil-geosynthetic interface characteristics. The response function of the model has been derived for strip loading in plane strain conditions. The resulting equations, in nondimensional form, are solved using an iterative finite difference method. The parametric studies carried out show the effects of various parameters on the settlement response.

THE EFFECT OF PRESTRESSING ON THE SETTLEMENT CHARACTERISTICS OF GEOSYNTHETIC-REINFORCED SOIL

Abstract In this paper, the effect of prestressing the geosynthetic reinforcement on the settlement behaviour of geosynthetic-reinforced granular fill-soft soil system is studied. The foundation model element proposed by Madhav and Poorooshasb (Computers & Geotechnic, 6, 277–290, 1988), which has a rough membrane embedded in a granular layer, has been modified to include the prestressing effect in the geosynthetic reinforcement. Parametric studies reveal that the settlement reductions within the loaded region are observed even for low prestress in the reinforcement. It is concluded that prestressing the geosynthetic reinforcement is a significant ground improvement technique to enhance the settlement characteristics of the soft soils where the membrane effect of reinforcement is felt.

A study of settlement response of a geosynthetic-reinforced compressible granular fill-soft soil system

Abstract The compressibility of granular fill in a geosynthetic-reinforced granular fill - soft soil system has been disregarded in most of the studies carried out so far. It is appropriate to consider this aspect in situations where the system is used as a foundation for structures which need accurate settlement predictions. In this paper, a foundation model is proposed to incorporate the compressibility of the granular fill by attaching a layer of Winkler springs to the Pasternak shear layer. The parametric studies carried out reveal that the consideration of the compressibility of the granular fill results in a significant increase in the settlement of the reinforced foundation soil.

A STUDY ON A NEW MECHANICAL MODEL FOR FOUNDATIONS AND ITS ELASTIC SETTLEMENT RESPONSE

In the present paper, a new foundation model has been proposed by introducing a stretched rough elastic membrane in the Pasternak shear layer sandwiched between two spring layers which is an extension of Kerr model. Considering the equilibrium of different elements, the equations governing the elastic settlement response of the model are derived. Finite difference scheme has been employed to solve the governing equations. The parametric studies carried out show the effect of several parameters on the elastic settlement response of the model. The proposed model is well suited for idealizing the behavior of geosynthetic-reinforced granular fill-soft soil system besides other applications.

The permeability of hydraulic fills under surcharge

Abstract Hydraulic fill is the most common type of backfill used in the underground mines in Australia and world-wide. These fills are granular in nature and are expected to have adequate drainage characteristics when placed underground in the form of slurry, enabling quick discharge of all excess water through the horizontal drives placed at various levels. Problem with drainage is often attributed as the main cause of failures of several barricades that are used to cover the drives and retain the hydraulic fill while the stope is being filled. Barricade failures can be catastrophic, claiming lives and causing significant economic losses. Permeability of the hydraulic fill plays a key role in the selection of the hydraulic fill for the underground mines. Most permeability measurements reported in the literature are from undisturbed or reconstituted samples in the laboratory under no surcharge. However, in the mine stopes the hydraulic fill is subjected to significant surcharge due to the overburden. The objective of this paper is to report some laboratory measurements of permeability of hydraulic fill samples subjected to surcharge pressures, and attempt to relate the permeability to effective vertical stress, void ratio and relative density.

A new model for nonlinear subgrades

Abstract The earliest mathematical idealisation of foundation medium is due to Winkler, who assumed a linear load versus settlement relation. Extending this for soils, Terzaghi introduced the concept of modulus of subgrade reaction. As observed from the plate load test results, the load versus settlement relationship of the soil is nonlinear and hence cannot be idealised truly, by the Winkler model. For soft soils, the settlements are large even at working loads and the nonlinearity in the soil response has to be considered to correspond to a more realistic behaviour of the foundations resting on such soils. The present study is mainly concentrated on cubic type of nonlinear response which incorporates the third order term in addition to the linear term. A procedure for finding out the nonlinear soil moduli from the plate load test data is suggested and the effect of size of plate and soil parameters on these, is studied.

Sustainability of Railway Tracks

The infrastructural growth of the railways has brought the railway track sustainability into a fresh perspective. Safe, stable, durable, and sustainable tracks are of paramount importance for the efficient function of the railways. In this paper, the development of the railway track from its inception to the present-day scenario has been presented. Numerous studies, conducted by researchers all over the world, that are aimed at studying the track response and improving its performance have been discussed. The analytical and numerical models developed to study the stresses and deformations in the track structure have been examined. It has been established that reinforcement of the track structure with geosynthetics reduces its settlement, increases the bearing capacity, and improves the drainage performance.

Evaluation of residual strength and liquefaction potential of pond ash

AbstractLiquefaction potential of pond ash obtained from the ash pond located at Panki Thermal Power Station, Kanpur, India is evaluated by laboratory static triaxial tests and standard penetration tests (SPT) up to a depth of 20 m. Residual strength approach by Norris et al. (1997) has been used to study the residual state characteristics of remolded ash samples. Consolidated rebounded drained triaxial tests with volume change measurements are performed on the remolded ash samples with three relative densities of 30%, 50% and 75%. The results obtained are compared with the stress-controlled consolidated undrained triaxial test, the method reported by Poulos et al. (1985). It is observed that the liquefaction behaviour can be predicted for 30% relative density within the strain levels. The steady state line obtained from laboratory experiments is compared with the model reported by Cubrinovski and Ishihara (2000). The liquefaction potential based on penetration data is evaluated by the model proposed by S...

Slippage effect on the settlement response of a granular soft soil system

In this paper a numerical study using the finite element method is undertaken to predict the settlement response of a footing, considering plane strain conditions, resting on a reinforced granular bed on soft soil. The granular fill, soft soil and geosynthetic reinforcement are considered as non linear materials. The geosynthetic reinforcement is modelled with interface elements for allowing slip between the soil and reinforcement. The results obtained from the present investigation showed close agreement when compared with the results of finite element analysis and lumped parameter modelling carried out by previous researchers, assuming no slip conditions. The number of reinforcement layers was taken as one or three (multilayer). A parametric study has been carried out to illustrate the effect of slippage of the reinforcement layer on the settlement response. The increase in the settlement is not significant when the slippage of the reinforcement is considered.

Effect of rheological behavior of geosynthetics on settlement response

Abstract In this paper the effect of rheological or long-term behavior of geosynthetic layer on the settlement response of reinforced granular fill-soft soil system has been studied. The system is modeled by mechanical elements such as the standard linear solid (SLS) model to predict the rheological behavior of the geosynthetic reinforcement at low stress level over a limited time period, spring-dashpot elements for the soft foundation soil and shear layer for granular fill. The consolidation effect of the soft soil has also been incorporated in the model. The resulting governing differential equations are solved using finite difference method in an iterative manner and the obtained results are presented in a nondimensional form. Parametric studies carried out for a uniformly loaded strip footing resting on the reinforced bed show that apart from loading intensity and soil properties, the nondimensional model parameters reflecting the rheological behavior affect significantly the settlement response of the reinforced foundation.