Search

The soils found abundantly along the Konkan belt in peninsular India are lateritic soils and lithomargic clays. The locally available lithomargic clayey soils are problematic in the sense that their strength reduces drastically under saturation conditions, which is typical behaviour of the dispersive type of soil. Most foundations are placed on this soil layer. This paper presents results from a series of laboratory plate load tests carried out in unit cell tanks to investigate the behaviour of granular columns in these weak (lithomargic clay) grounds. Tests are carried out with two types of loading: with the entire area in the unit cell tank loaded, to estimate the stiffness of the improved ground; and with only the granular column area loaded, to estimate its limiting axial capacity. Investigations were carried out by varying the area ratio (or spacing), diameter of granular columns, end condition and column configuration. The load-settlement behaviour, stiffness and bulging behaviour of granular columns are analysed. It is found that the ground treated with granular columns exhibits a high load-carrying capacity and stiffness, and a significant reduction in settlement, compared with the untreated ground. [ABSTRACT FROM AUTHOR]

Geotechnical engineers often encounter problems in designing foundations of structures on soft clayey soil. There may be a need for ground treatment to improve the bearing capacity of the soil. In the case of mediumrise buildings in and around Kolkata, a common practice has been to provide closely spaced 150-200 mm diameter timber piles of 5-6 m length. These timber piles have helped the structures to stand on soft clayey soil with little or negligible distress over the years. The present investigation includes the study of bearing capacity and settlement behaviour of model footings resting on small-diameter timber piles. Model footings were tested on an artificially consolidated kaolin bed with small-diameter timber piles inserted into the clay bed. To supplement the results of laboratory model tests, prototype tests were also carried out in the field. In order to obtain a parametric study, the length and spacing of timber piles as well as the extent of piles around and below the footings were varied. The study shows that the use of small-diameter timber piles produced beneficial effects for pile lengths greater than the width of the footing. An appreciable effect on bearing capacity is observed when area ratio (i.e. pile area/soil influence area) becomes more than 10%. The extent of these timber piles beyond twice the width of the footing results in a marginal increase in the bearing capacity. Considerable reduction in settlement occurred when timber piles were used. A semi-empirical method of calculating settlement has been presented for foundations with small-diameter timber piles. [ABSTRACT FROM AUTHOR]