This work investigated the behavior of embankment models resting on soft soil reinforced with ordinary and encased stone columns (ESCs). Model tests were performed with different spacing distances between stone columns and two length-to-diameter ratios (L/d) of the stone columns, in addition to different embankment heights. A total of 39 model tests were performed on soil with an undrained shear strength of ≈10 kPa. The system consisted of a stone column–supported embankment at different spacing-to-diameter ratios (s/d) of stone columns. Earth pressure cells were used to measure directly the vertical stress on the column for all models, and another cell was placed at the base of the embankment between two columns to measure directly the vertical stress in reinforced soft soil. For embankment models constructed on soft clay reinforced with ESCs, it was found that whether a column was floating or end bearing (resting on a rigid stratum), encasement of the column by a geogrid was most effective in i...

The type of soil known as expansive soil is capable of changing its volume through swelling and contracting. These types of soils are mostly composed of montmorillonite, a mineral with the capacity to absorb water, which causes the soil to heave by increasing its volume. Due to their capacity to contract or expand in response to seasonal fluctuations in the water content, these expansive soils might prove to be a significant risk to engineering structures. Many studies have dealt with swelling soils and investigated the behavior of these soils, as well as their improvement. In this study, three percentages of lime, cement, and silica fume (5, 7, 9%) are used to stabilize the expansive soil, and the work is divided into two sections: the first is using a consolidation test to record the free swell and swell pressure for the untreated and treated soils; in the second part, the grouting technique is utilized as a process that can be applied in the field to maintain the improvement in the bearing capacity. It is concluded that the soil stabilized with different percentages of lime, cement, and silica fume exhibits a decrease in both free swell and swelling pressure by approximately 65% and 76%, respectively, as compared with untreated soil. The soil grouted with silica fume increases the bearing capacity of footings resting on the grouted soil by approximately 64% to 82% for the soil treated with 5% and 9% silica fume, respectively, as compared with untreated soil.

Studies on chemically stabilised soils have shown that the effectiveness of treatment is largely dependent on the soil’s natural environment. This type of soil can be categorised as problematic due to its weak properties. At the preliminary stage, soft clay soil does not meet the requirements necessary for construction purposes because the entire load from the top of the building will be transferred to the underlying soil. This research considers the soil stabilisation of a soft clay soil (Kaolin S300) stabilised with various percentages of lime and 4% silica fume. The percentages of lime vary at 3, 5, 7 and 9%, while the percentage of silica fume is fixed at 4%. The main objective in this research is to improve the undrained shear strength of soft clay soil mixed with various percentages of lime (L) and 4% silica fume (SF). The properties of the soils were compared for kaolin only and for different percentages of lime mixed with 4% silica fume. The results showed that the optimum percentages of lime and silica fume with respect to the maximum shear strength occurred at 5 and 6%, respectively. The soil–L–SF mix increased the shear strength and angle of internal friction compared to soil–lime and soil–SF mixes because the pozzolanic reaction between lime and SF was more effective with soil particles. The optimum percentage for enhancing the shear strength and the angle of friction was 7–4% L–SF.

In this work, laboratory experiments have been carried out to study the value of the stress concentration ratio, n, which is defined as the ratio of vertical stress acting on the stone column to that acting on the surrounding soil. A laboratory setup was manufactured in which two proving rings are used to measure the total load applied to the soil-stone column system and the individual load carried directly by the stone column. The foundation steel plates have 220 mm diameter and 5 mm thickness. These plates contain 1, 2, 3, and 4 holes. The spacing between all the holes equals twice the stone column diameter, D, center to center. The stone columns made of crushed stone were installed in very soft clays having undrained shear strength ranging between 6 and 12 kPa. Two length to diameter ratios L/D were tried, namely, L/D=6 and 8. The testing program consists of 30 tests on single, two, three, and four columns to study the stress concentration ratio and the bearing improvement ratio (qtreared/ q untreated) of stone columns. The experimental tests showed that the stone columns with L/D=8 provided a stress concentration ratio n of 1.4, 2.4, 2.7, and 3.1 for the soil having a shear strength cu=6 kPa, treated with single, two, three, and four columns, respectively. The values of n were decreased to 1.2, 2.2, 2.5, and 2.8 when the L/D=6. The values of n increase when the shear strength of the treated soil was increased to 9 and 12 kPa.