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J. T. Shahu
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Civil Engineering, Building, Construction & Architecture Engineering Transportation

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CUMULATIVE PLASTIC STRAIN AND THRESHOLD STRESS OF A QUASISATURATED COMPACTED SILTY CLAY J. T. Shahu; Yudhbir .; S. Hayashi
Lowland Technology International Vol 10 No 2, Dec (2008)
Publisher : International Association of Lowland Technology

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Abstract

The knowledge of cumulative plastic strain and stability threshold of subgrade soil under cyclic loading is of prime importance in a proper design and maintenance planning of highway pavement structures and railway tracks. The soil beneath a pavement or a track usually exists under quasi-saturated conditions wherein the water voids in the soil remain continuous. Quasi-saturated specimens are essentially partially saturated at low confining pressures. However, with the increase in confining stresses, the air voids in the quasi-saturated specimens are dissolved into solution and the soil behaves like saturated material. Both monotonic and cyclic undrained triaxial tests have been carried out on quasi-saturated compacted specimens of a silty clay. The monotonic tests have been used to develop critical state soil mechanics framework for quasi-saturated behavior. The cyclic undrained behavior of quasi-saturated specimens has been then interpreted using this critical state framework. A generalized bilinear log-log model is proposed for the prediction of cumulative plastic strain with number of load cycles for fine-grained soils. Threshold stress is evaluated using both plastic strain development and pore pressure generation criteria. A generalized relationship between threshold stress ratio and plasticity index is proposed for a variety of soils at low and relatively high confining stresses.
Performance of geosynthetic reinforcement on the ballasted railway track L. S. Sowmiya; J. T. Shahu; K. K. Gupta
Lowland Technology International Vol 17 No 2, Sep (2015)
Publisher : International Association of Lowland Technology

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Geosynthetics provide an important option to improve track support stabilization and thereby reduce the track maintenance costs and operation costs due to train delays. In railroad construction, geosynthetics may be installed within or beneath the ballast or subballast layers. In this present study, model tests were performed on model tracks laid at 1:3 scale to the prototype with adequate thickness of subballast layer and placed on soft subgrade soils. Model tracks were adequately instrumented to record induced stresses and displacements in the track. Model tracks were reinforced with geogrid or geotextile or both at suitable interfaces. Track condition after a heavy rainfall was simulated. In this present study, three dimensional finite element analyses of geosynthetic reinforced railway track sections have been carried out using MIDAS/GTS 2013 and compared with unreinforced sections. The result shows that the reinforcement can be used to improve the performance of railway tracks on clayey subgrade.
A nonlinear analysis for GRS walls conceiving kinematics of failure against pullout S. Patra; J. T. Shahu
Lowland Technology International Vol 20 No 3, Dec (2018)
Publisher : International Association of Lowland Technology

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A modified nonlinear analysis is presented to investigate the pullout response of geosynthetic reinforced soil (GRS) walls. The analysis conceives a hyperbolic stress-strain relationship for the backfill, the kinematics of the failure and the deformation compatibility between the soil and the reinforcement. The deformation compatibility is incorporated by introducing an updated discretization technique, and the true projected length of the reinforcement after deformation is evaluated by a simple computational scheme. A case study is presented for an instrumented full-scale reinforced soil wall to validate the present analysis. The maximum tension in the reinforcement at each level is computed considering the effect of compaction, and the results are compared with the measured values and those predicted by AASHTO simplified method. The comparison shows that the present analysis gives a better estimation of the reinforcement tension thus can be easily integrated with the existing method. A parametric study is also conducted mainly to determine the effect of stiffness and strength parameters of the subgrade which have a significant influence on the design of GRS walls against pullout failure for all practical applications.
Co-Authors K. K. Gupta L. S. Sowmiya S. Hayashi S. Patra Yudhbir .