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.

Collapsible soils are soils susceptible to large volumetric strains when they become saturated. Numerous soil types fall in the general category of collapsible soils, including gypseous soil which is characterized by relatively low density, appreciable strength and stiffness in the dry state, but is susceptible to significant deformations as a result of wetting. The aim of this study is to investigate the effectiveness of curing period time of carbonation on magnesium oxide stabilization of gypseous soil. In this research, magnesium oxide is used to improve a collapsible gypseous soil by using (0, 5, 10 and 15%) with two relative densities (35 and 75%) and carbonation at different carbonation periods (0, 1, 3 and 24 hours). Conventional collapse tests, single oedometer and double odeometer and modified collapse test are used in this research to investigate the effect of carbonation periods on the improvement of the soil. The modified collapse test apparatus is used. The results illustrated that the collapse potential decreased more than 65% and 55% for the carbonated soil without treatment for conventional tests and modified collapse test, respectively. A decreased about 55% for treated soil with 10% magnesium oxide and carbonated for 3 hours for both of conventional tests and modified collapse test. The carbonation period time is used to accelerate the improvement of the soil as well as decreased the collapse potential and the results showed that no clear change in collapse potential for the period time more than 3 hours.

The soft soil's poor tensile strength requires reinforcing to increase bearing capacity, improve stability, and reduce settlements. This study assessed the efficacy of using geogrid layers to enhance and secure the soil surrounding tunnels. enabling the tunnel to endure pressure, particularly during excavation. The utilization of geogrids in soil reinforcement has experienced a substantial rise as a result of their consistent dimensions and exceptional tensile strength. To quantify the exerted force transferred to the tunnel, during this study utilized various testing tools, including a soil container, a steel loading frame, data loggers, a 0.5-ton load cell, and a miniature pressure cell. The vertical loads are applied by utilizing a hydraulic jack. A series of eleven tests were conducted on the tunnel at two depths of 1.5D and 2.5D, where D is the tunnel's diameter. The different models of geogrid layers showed that using two layers of geogrid at the first dimension, 0.5B and 1B from the base, led to a significant increase in tunnel stability. Two layers of reinforcement were used in both directions, giving the soil a high bearing capacity for the loads applied to the tunnel. This resulted in an improvement, a 1.65 in 1.5D and a 1.82 in 2.5D. The pressure above the pipe decreased by approximately 7.1kPa at the first tunnel depth and about 3.5kpa at the second depth. In conclusion, the study found the geogrid improves the stability of the tunnel by equally distributing loads and minimizing stress concentrations, hence decreasing the chances of collapses or deformations. Doi: 10.28991/CEJ-2024-010-08-04 Full Text: PDF

The clay soil is weak and unable to carry the applied loads as a result of the weight of buildings or vehicles on the load performing on the soil. In this research, clay soil was grained and mixed with different percentages of activated carbon additives to investigate its performance. One type of clay soil from Al-Taji city was used. The percentages of activated carbon 3, 5, 7 and 9% were added to the soil and the influence of the admixture was observed by comparing the results with the untreated soil. The selected properties for this comparison were specific gravity, consistency limits, compaction, static compaction, CBR, consolidation, swelling and unconfined compressive strength. The results showed that the plasticity index, maximum dry weight and specific gravity decreased as the percentage of additives increased. The unconfined compressive strength increased as the percentage of additives and curing periods (1, 7, 14 and 28)days increased. The amount of increase in soil strength was even more than 100% for the 9% activatedcarbon. The results showed that the addition of activated carbon has a positive effect to the geotechnical properties.