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.
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.
The technique of sand or stone columns is widely used to improve the load carrying capacity and reduce the settlement of soft soils. The technique consists of excavating holes of specific dimensions and arrangement in the soft soil and backfilling them with either stone or sand particles. The efficiency of the technique depends primarily on the type of the backfill material (sand or stone) and gradation as well as the placement relative density. In the present research, holes 50 mm in diameter and 300 mm in length were excavated in a bed of soft soil, 400 mm in thickness, of undrained shear strength between 16-19 kPa. The holes were backfilled with either sand or stone particles at loose and dense states. Each column was loaded gradually through a circular rigid footing 64.6 mm in diameter up to failure with continuous monitoring of the settlement. The outcomes of the model tests revealed that for both floating and end bearing types, the sand columns at low relative density exhibited higher bearing improvement ratios and lower settlement reduction ratios compared to stone columns. On the other hand, a reverse behavior was noticed, when the backfill material was placed at "dense state". The results shed the light on the importance of placement relative density of both backfill materials. The results are thoroughly analyzed in terms of the stress concentration ratio and stiffness ratio.
Geotechnical design and execution of civil engineering structures on soft to very soft soils are usually associated with substantial difficulties. These soils are sensitive to deformations and possess low shear strength values. Geotechnical properties of such soil stabilization are improved by various methods. Admixtures improve soil properties in order to form strong foundation capable of bearing loads of such structure. Clay soils cause cracking and fracture of pavement, rail ways, highways, embankment, foundations… etc. The main objective of this study is to discuss and evaluate the effect of addition of fly ash on shear strength of soft soil and bearing capacity of these soils by adding clay columns stabilized with fly ash in soft soils. The essential idea represents in investigation of possibility of using fly ash to reduce compressibility to find solution for some problems of failure in soft soils in Iraq. This will encourage the use of fly ash as stabilizer especially as it is an economic material and for its local availability. Soil used in the study was obtained from Al-Nahrawan City 35 km east of Baghdad. According to the Unified Soil Classification System, it is classified as (CL) soil. The soil consists of 3% sand, 35% silt, and 62% clay. The tests were carried out using a steel container with internal dimension of (400×350×300 mm). The steel container is made of steel plates that are 4mm in thickness. The thickness of the bed of clay was 300 mm, and 400 mm for (L/D) 4 and 6, respectively. The depth of the column was 200 mm and 300 mm for (L/D) 4 and 6, respectively, at 50mm diameter of column (D). Square steel foundation of 4mm thickness and width 60 mm was used in all the tests. The length to diameter ratio (L/D) which was used in this study was 4 and 6. The results of curing days in 14 days and 28 days are close to each other. The incensement ratio is about 5% between 14 and 28 days for the two (L/D) 4 and 6. (L/D) 6 has shown more improvement than L/D 4, the improvement in bearing ratio failure is about 30%.
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