In this study, the chemical stabilization of moderately to highly plastic expansive soil using calcium chloride with added cement is introduced as an effective alternative to the conventional approaches using a single additive such as lime, cement, or a by-product of industrial processes. Using only calcium chloride may lead to its leaching or dissolution over time, leaving a collapsing skeleton with weak bonds. The chemical effect produced by additives is dependent on the constituents of the stabilized soil and the curing period considered. Herein, calcium chloride concentrations of 2%, 4%, and 8% with the addition of 2% cement by dry weight of the soil were considered. The main objective of this study is to investigate the addition of a low amount of cement as a binder to improve the strength and durability of a chemically treated expansive soil. The engineering properties were investigated at 3 curing times: 3 days, 7 days, and 28 days. A laboratory investigation was carried out to investigate the effect of the addition of calcium chloride with cement on the swell potential, swell pressure, compression index, suction, and unconfined compressive strength. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX) testing was conducted. The X-ray diffraction patterns were recorded to observe the mineralogy of the material. The results confirmed that calcium chloride with cement is very effective for stabilizing the expansive soil. A reduction in the swell potential by 8% and 25% and a reduction in swelling pressure by 28% and 37.4% were observed for 4% and 8% calcium chloride with cement addition. The compression index decreased with the increase in the calcium chloride content.

Expansive clays present serious issues in a variety of engineering applications, including roadways, light buildings, and infrastructure, because of their notable volume changes with varying moisture content. Tough weather conditions can lead to drying and shrinking, which alters expansive clays’ hydro-mechanical properties and results in cracking. The hydro-mechanical behavior of Al-Ghatt expansive clay and the impact of wetting and drying cycles on the formation of surface cracks are addressed in this investigation. For four cycles of wetting and drying and three vertical stress levels, i.e., 50 kPa, 100 kPa, and 200 kPa, were investigated. The sizes and patterns of cracks were observed and classified. A simplified classification based on main track and secondary branch tracks is introduced. The vertical strain measure at each cycle, which showed swell and shrinkage, was plotted. The hydromechanical behavior of the clay, which corresponds to three levels of overburden stress as indicated by its swell potential and hydraulic conductivity was observed. It was found that at low overburden stresses of 50 kPa, the shrinkage is high and drops with increasing the number of cycles. Al-Ghatt clay’s tendency to crack is significantly reduced or eliminated by the 200 kPa overburden pressure. The results of this work can be used to calculate the depth of a foundation and the amount of partial soil replacement that is needed.

The hydraulic properties of expansive soils are affected due to the formation of visible cracks in the dry state. Chemical stabilization coupled with fiber reinforcement is often considered an effective strategy to improve the geotechnical performance of such soils. In this study, hydraulic conductivity tests have been conducted on expansive clay using two different types of fibers (fiber cast (FC) and fiber mesh (FM)) exhibiting different surface morphological properties. The fiber parameters include their dosage (added at 0.2% to 0.6% by dry weight of soil) and length (6 and 12 mm). Commercially available lime is added to ensure proper bonding between clay particles and fiber materials, and its dosage was fixed at 6% (by dry weight of the soil). Saturated hydraulic conductivity tests were conducted relying on a flexible wall permeameter on lime-treated fiber-blended soil specimens cured for 7 and 28 days. The confining pressures were varied from 50 to 400 kPa, and the saturated hydraulic conductivity values (k_sat) were determined. For FC fibers, an increase in fiber dosage caused k_sat values to increase by 9.5% and 94.3% for the 6 and 12 mm lengths, respectively, at all confining pressures and curing periods. For FM fibers, k_sat values for samples mixed with 6 mm fiber increased by 12 and 99.2% for 6 and 12 mm lengths, respectively for all confining pressures at the end of the 28-day curing period. The results obtained from a flexible wall permeameter (FWP) were compared with those of a rigid wall permeameter (RWP) available in the literature, and the fundamental mechanism responsible for such variations is explained.

The hydraulic conductivity is known as the soil properties that mostly vary over an order of magnitude. There are many laboratory test methods to determine the hydraulic conductivity of the soil. Each test has its own merits, drawbacks and limitations. One of these methods is the measurement using a rigid wall permeameter (RWP), which is a common practice to obtain the fluid transmissibility characteristics of the soil matrix. This type of permeameter has the advantages of low cost, simplicity of test equipment, and adaptability to many different types of permeant liquids. Another method is the measurement through a flexible wall permeameter (FWP). The hydraulic conductivity measured using the FWP is conducted in a confined cylinder in which water flow is forced into one direction. The main disadvantage of this type is being relatively more expensive and needs more time to perform the test compared to the RWP. This study is aimed at comparing three testing conditions to obtain an adjustment factor for the hydraulic conductivity test normally carried out in practice in order to cut down the time needed to perform the test as well as its cost. Different mixtures of sand and expansive clay addition were considered to examine the effect of expansive clay content on the values of the hydraulic conductivity. Tests results revealed that the clay content had a significant effect on the swelling potential, which was attributed to structural changes in the mixtures. The hydraulic conductivity of mixtures decreases with the increase in clay content. The hydraulic conductivity of mixtures tested using FWP was observed to be lower than that of mixtures tested using RWP at similar clay contents. The tests conducted enabled establishing a correction factor to adjust the hydraulic conductivity normally obtained in practice using rigid wall cells.

The washout of fine materials from liners consisting of clay–sand mixtures is expected to influence the hydraulic conductivity. Clay sand liners must be assessed for efficiency when initially subjected to flood or standing water as the wetting under a hydraulic gradient can cause fine material to move and migrate away from the mixture. During wetting and drying complex expansion and shrinkage, changes take place. These changes affect the hydraulic conductivity and are likely to go out of the design range set out for the facility. The research covers the behavior of two clay sand liners tested over an extended time. The hydraulic conductivity measured under a specific hydraulic gradient was measured continuously following the establishment of the test set-up. Self-recording sensors were used to measure the temperature during the tests. The results indicated that the hydraulic conductivity reduces after an initial period of increase and fluctuation caused by the loss of mass because of fine material migration and swelling initiated due to the high content of smectite minerals. The testing and monitoring continued for more than 400 days. The permanent reduction in the hydraulic conductivity occurs after the initial period of repeated rise and fall. The extent of the initial period for the two tested mixtures is subject to the fine content mass and the clay mineralogy. The continuous reduction in the hydraulic conductivity after the initial period is due to the rearrangement of particles and compression in the sand–clay mixture.