The settlement performance of stone column foundations

Abstract

Vibrated stone columns are frequently used as a method of reinforcing soft ground as they provide increased bearing capacity and reduce foundation settlements. Their performance in relation to bearing capacity is well documented, but there is also a need for enhanced understanding of their settlement characteristics, particularly in relation to small-group configurations. This paper presents results obtained from physical model tests on triaxial specimens 300 mm in diameter and 400 mm high. Parameters investigated include column length to diameter ratio, area replacement ratio and single/group configuration. The findings of the work are as follows. The design is flexible: settlement can equally be controlled using short columns at relatively high area replacement ratios, or longer columns at smaller area replacement ratios. An optimum area replacement ratio of 30-40% exists for the control of settlement. The settlement performance of a small column group is highly influenced by inter-column and footing interaction effects.

Numerical modelling of stone columns beneath a rigid footing

“…The load-settlement curves of different groups of stone columns show the small influence of column diameter and position. That is confirmed by a review of small-scale laboratory test data available in the literature [6,9]. The finite element results also offer some guidance for the design, provide some background for homogenization techniques (e.g.…”

“…A reanalysis of a set of high-quality laboratory experiments performed by Black et al [9] shows the small differences caused by the number of columns beneath the footing and by the L/dc ratio ( Figure 14). The settlement performance of a small group of 3 columns was very similar to that of an isolated column for the same values of ar, L/H and L/B.…”

“…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. Black et al [9] identified the lack of information regarding the settlement performance and conducted small-scale laboratory tests. Similarly, Shahu and Reddy [10] performed laboratory tests and their numerical simulation.…”

Experimental and Numerical Analysis of Geosynthetic-Reinforced Floating Granular Piles in Soft Clays

“…However, the displacement technique is difficult to implement in a small scale laboratory model tests. Black et al [40] conducted trial tests and concluded generation of suction during removal of the poker which caused collapse of the cavity whereas the replacement technique is known to produce the granular piles of excellent consistency. With the help of auger guide, a thin seamless steel pipe, of outer diameter equivalent to granular pile diameter, was inserted smoothly in the centre of clay bed up to the desired height of granular pile (Fig.…”

Creep improvement factors for vibro-replacement design

“…Ambily and Gandhi, 2007;Barksdale and Bachus, 1983;Black et al, 2011;Mitchell and Huber, 1985;Watts et al, 2000). Stone columns accelerate consolidation, meaning that creep may contribute a significant proportion of post-construction settlement.…”