Footings on Weak Soils Stabilized with Encapsulated Gravel Trenches and Columns

Abstract

Shallow isolated footings are usually used to support multitude of light and medium weighted structures like low rise buildings, warehouses, fences, advertising panels and parking sheds, where the surface soil formation is strong enough to carry the structural loads safely and keep the settlement values within the allowable ranges. A very common challenge is the construction of these footings on soft and very soft clay deposits, due to their low shear strength and induced large settlement. Maybe the most common method in dealing with such soil formations is to fully or partially replace the weak soil with more competent granular fills. In this research, a series of numerical analyses are performed to study the enhancement in the load-settlement response of a square footing rested on a soft clay deposit, when stabilized with ordinary granular trenches and encapsulated granular trenches and a group of ordinary stone columns and encapsulated stone columns. The effect of combining both granular trenches and columns under the footing as an improvement technique is also studied. The impact of different factors affecting the improved soil load-carrying capacity are studied, as: trench width ratio, trench depth ratio, gravel column diameter, length, encapsulation length ratio and encapsulation stiffness. Finite element method FEM based software (ABAQUS 6.20) is utilized to model the footing-soil ensemble and study the effect of the various parameters. Results had it that introducing gravel trench and gravel column under the footing improved the soft soil settlement-response and even more improvements are gained by introducing geotextile encapsulation. The gravel trench and gravel column combination has proved to be efficient in providing a noticeable improvement in the footing load-settlement response.