Sample preparation method for large scale shear testing of soft-clay and granular-column composites

Cihan Cengiz,Erol Guler

doi:10.1016/j.mex.2020.100939

Abstract

This article is aimed at giving an overview of the testing equipment and sample preparation techniques for large scale shear testing of granular column enhanced soft clays. A novel testing device, designated Unit Cell Shear Device, is produced to enable clay bed consolidation and subsequent granular column installation within the clay bed. The device allows for studying the shear resistance of unit cells enhanced with slender vertical inclusions such as stone columns, geosynthetic encased stone columns, grouted piles, and conventional piles. The present study illustrates the novel clay slurry consolidation method, sample preparation sequence, testing device features, and the details of the actuators that shear the specimen. The strength parameters of the consolidated clay and the spatial distribution of engineering properties of clay are studied with different testing methods. The techniques prescribed herein present a viable method of clay bed preparation for laboratory testing purposes with the following advantages:• Homogeneous clay beds for testing• Reduced drainage path and accelerated consolidation time• Consolidation around a vertical inclusion to allow for column placement

Highlights

Ordinary Stone Columns (OSCs) and Geosynthetic Encased Columns (GECs) are utilized as a cost effective soil improvement technique where the bearing capacity of the foundation soils are not sufficient to support the vertical loads imposed by the superstructure
- The device allows for consolidation of clay specimens around a vertically oriented shaft which has provisions to shorten drainage path of the pore water thereby accelerating the consolidation process
- Shear strength of the clay determined with different methods are in reasonable agreement where the Thor Vane tests conducted at the topmost layer of the clay beds yielded similar results to that of the (Field) Vane tests

Summary

Introduction

Ordinary Stone Columns (OSCs) and Geosynthetic Encased Columns (GECs) are utilized as a cost effective soil improvement technique where the bearing capacity of the foundation soils are not sufficient to support the vertical loads imposed by the superstructure. Engineering benefits of granular column inclusions as described by Indraratna et al [9] include: (i) transmission of foundation loads to a greater depth by a combination of side resistance and end bearing, (ii) reduction in the total and differential settlements, (iii) reduction of liquefaction potential of fine grained soils, and (iv) decreased drainage path for rapid consolidation of soft soil through radial consolidation under foundation loading. Granular columns are proposed as a foundation system to mitigate seismic loads in rocking foundation applications [11] Design scenarios as such necessitate a thorough understanding of the granular column enhanced soft soil behavior under lateral loads

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Conclusion