Bearing Capacity and Settlement Response of Ordinary and Geosynthetic Encased Granular Columns in Soft Clay Soils: Analy
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ORIGINAL PAPER
Bearing Capacity and Settlement Response of Ordinary and Geosynthetic Encased Granular Columns in Soft Clay Soils: Analysis and Design Charts Jayapal Jayarajan1 • Rajagopal Karpurapu1
Received: 15 May 2020 / Accepted: 23 September 2020 Ó Indian Geotechnical Society 2020
Abstract This paper discusses the bearing capacity and settlement response of granular columns with and without geosynthetic encasement using the currently available design procedure. The design procedure is modified to include the influence of the geosynthetic encasement. The key parameters influencing the load bearing capacity and settlement are studied through comprehensive parametric analyses. The results portray the advantage of geosynthetic encased granular columns in enhancing the bearing capacity and reducing the settlements compared to granular columns without encasement. Different installation patterns of granular columns were considered in this investigation. The maximum bearing capacity improvement and settlement reduction are observed with granular columns installed in triangular plan arrangement. The hexagonal pattern results in the lowest area replacement ratio and also the lowest improvement factors. It is shown that with geosynthetic encasement, the performance with hexagonal pattern could be improved to match with other more efficient patterns like square and triangular. Some selected results are validated through detailed finite element results. A quick assessment of the settlement improvement with geosynthetic encapsulated granular columns is possible with the design charts presented. Keywords Settlement analysis Granular columns Geosynthetics Soft clay Encasement & Rajagopal Karpurapu [email protected] Jayapal Jayarajan [email protected] 1
Department of Civil Engineering, Indian Institute of Technology Madras, Chennai 600036, India
List of Symbols as Area replacement ratio Ag Area of the intervening soil in the unit cell Acell Area of the unit cell C Constant applied for a given granular column arrangement Cu Undisturbed undrained shear strength of the soft clay D Diameter of the granular column m Deformability ratio Mor J Modulus of the geosynthetic encasement K0 At-rest earth pressure coefficient in the soft clay soil S Spacing of the granular column at c/c qsafe Safe bearing pressure of the foundation soil Q Overall safe load on each column and its tributary soil rv Limiting axial stress in the column rv Limiting axial stress in the column after geosynthetic encasement rrL Limiting radial stress Dr3 Additional confinement offered by the geosynthetic encasement Drr0 Increase in mean radial stress rv0 Average initial effective vertical stress uc Angle of internal friction of the granular column material us Angle of internal friction of the foundation soil b Settlement reduction ratio b1 Improvement factor ea Allowable axial strain in the geosynthetic Abbreviations OGC Ordinary granular column EGC Encased granular column
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PVD
Prefabricated vertical drain
Introduction Ra
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