Modelling vibrated stone columns in soft clay

Abstract

The vibrated stone column technique is an economical and environmentally friendly process that treats weak ground to enable it to withstand low to moderate loading conditions. The performance of the treated ground depends on various parameters such as the strengths of the in-situ and backfill materials, and the spacing, length and diameter of the columns. In practice, vibrated stone columns are frequently used for settlement control. Studies have shown that columns can fail by bulging, bending, punching or shearing. These failure mechanisms are examined in this paper. The study involved a series of laboratory model tests on a consolidated clay bed. The tests were carried out using two different materials: (a) transparent material with ‘clay like’ properties, and (b) speswhite kaolin. The tests on the transparent material have, probably for the first time, permitted visual examination of deforming granular columns during loading. They have shown that bulging was significant in long columns, whereas punching was prominent in shorter columns. The presence of the columns also greatly improved the load-carrying capacity of the soft clay bed. However, columns longer than about six times their diameter did not lead to further increases in the load-carrying capacity. This suggests that there is an optimum column length for a given arrangement of stone columns beneath a rigid footing.

Numerical modelling of stone columns beneath a rigid footing

“…The bearing capacity of those groups of stone columns has predominantly been the focus of previous studies [5][6][7][8]. However, stone columns are installed in soft soils that can undergo large displacements at relatively low loads and the serviceability limit state may be critical for their design.…”

The settlement performance of stone column foundations

“…Laboratory-based research, together with analytical modelling, numerical modelling and field observations, is well documented, and has contributed to improvements in efficiency and quality control (Hughes & Withers, 1974;Hughes et al, 1975;Aboshi et al, 1979;Balaam & Booker, 1981;Barksdale & Bachus, 1983;Charles & Watts, 1983;Alamgir et al, 1994;Hu, 1995;Balaam et al, 1977;Raju, 1997;Slocombe et al, 2000;Watts & Serridge, 2000;McKelvey, 2002;McKelvey et al, 2004;Pulko & Majes, 2005;Black, 2007;Black et al, 2007aBlack et al, , 2007bMcCabe et al, 2009). Stone columns are typically employed to support large raft foundations at relatively low or moderate loading conditions.…”

Modelling helical screw piles in soft clay and design implications

“…The transparent soil used in this investigation consisted of 6% fumed amorphous silica aggregates (Lehane and Gill, 2004;McKelvey et al, 2004) and 94% pore fluid. This fluid was a blend of paraffinic solvent (N-paraffin C10-13 supplied by Aztec Oils, Chesterfield, UK) and white oil (Baylube WOM 15 supplied by Bayford Oils, Leeds, UK) mixed to volumetric proportions of 77:23 and giving a refractive index matched to the silica aggregates at 208C.…”

“…A significant drawback with these two investigations was that model size was limited by imperfect transparency of the soil, introducing boundary effects. Hird and Stanier (2010) reported that using fumed rather than precipitated silica (following McKelvey et al, 2004) in conjunction with the laser-aided PIV technique allowed larger models to be used, thereby reducing boundary effects. Later Stanier et al (2012) proposed a photogrammetric correction framework to improve the reliability of the PIV measurements made in their transparent soil, alongside an example analysis of the failure mechanism of a doublehelix screw pile loaded in tension.…”