Muawia Dafalla

The expansive soils pose significant challenges in geotechnical engineering due to their tendency to swell when wet and shrink when dry. They present serious issues and challenges to light structures and pavements. Treatment using hydrated lime is one of the stabilization techniques that is widely used to improve the performance of these soils. This study aims to examine the behavior of volume change for three types of expansive clays from three different locations in Saudi Arabia that are classified as expansive. Experimental work covered lime-treated and untreated clay. The influence of lime content and curing period is monitored. Four lime contents: 2%, 4%, 6%, and 8% by weight of dry clay were investigated. All tested samples were investigated at three different curing periods: 1, 10, and 28 days. Laboratory investigation included determining pH values, conducting one-dimensional odometer tests, and measuring suction. To achieve a 90% reduction in the swell potential of expansive clays, it was found that Tabuk clay requires at least 2–3% lime addition, while Al-Qatif clay requires 3–4% lime addition. Al-Ghatt clay requires more than 4% to reduce the swelling potential by 90%. These differences are attributed to the mineralogy of the clay and the pozzolonic reactions as a result of adding hydrated lime.

Designing environmental protection barriers requires careful consideration in the choice of coastal sand material used in clay-sand mixtures. The purpose of this study is to present a comparison and guide between two methodologies to investigate sands of different nature and shapes for the hydraulic conductivity and compressibility. Hydraulic conductivity is generally measured using the falling head test, which was carried out in a cell with a rigid lateral wall and one-dimensional water flow. The flexible wall method is another approach that simulates the natural field conditions. ASTM D5084 and BS1337-6:1990 were found appropriate to provide reliable hydraulic conductivity values. The differences in hydraulic conductivity measurements are expressed in terms of orders of magnitude. A flexible wall, falling head permeameter unit in which lateral confinement can be controlled and changed, was utilized for this study. The flow was found to assume different passages with enlarged tracks when confinement is relaxed. The sphericity of the sand grains used in this study indicated a 0.860 for rounded grains and 0.642 for the angular grains. The tests conducted enabled comparison of compressibility and geotechnical parameters for the clay sand mixtures, including sand of different shapes and angularity. The differences obtained for the hydraulic properties are influenced by the grain size and shape. Predicted hydraulic conductivity and compressibility depends to a greater extent on the shape and sand texture. The obtained results can be used as a predictive guide to liner performance and field applications.

This study investigates how adding polypropylene fibers and cement affects the strength of highly plastic clay used in clay bricks. The research looked at various curing times to improve the strength of clay bricks for effective use in the construction industry. A fiber content of 0.2% was added to the clay and compared to untreated control samples improved with varied amounts of cement (2%, 4%, and 6%). The influence of curing on strength increase was explored, as well as the profile of the stress–strain relationship. The compressive strength increased by 53% to 140% after 7 days of curing, which is almost a quarter of the strength attained after 28 days. The results showed a considerable increase in strength, illustrating the cumulative benefits of longer curing times and the suggested additions. Fiber addition was shown to be associated with a significant increase in compressive strength. This advantage is due to the particle connection established by incorporating the fibers and cement into the mixture. Improvement in tensile and shear strength was investigated. It was also found that fibers made the material more ductile. It was noted that using cement alone can increase the compressive strength but cracking and shrinkage control may not be achieved. When compared to the untreated sample, mixtures containing 0.2% fibers and treated with 2%, 4%, and 6% cement increased compressive strength by 225%, 390%, and 630%, respectively. This improvement is comparable to a 2-, 4-, or 6-fold improvement. This increase will enhance the supporting capacity of the non-load-bearing clay bricks.

In several geotechnical and geoenvironmental projects, fines containing expandable clay minerals such as expansive clay (EC) were added to sand as sealing materials to form liners or hydraulic barriers. Liner layers are generally exposed to different climatic conditions such as freeze-thaw (FT) during their service lifetime. The hydromechanical behavior of these layers under such circumstances is of great significance. In this study, the impact of fine contents of expansive soil on swelling, consolidation characteristics, and hydraulic conductivity under FT conditions is examined. Different clay liners with 20%, 30%, and 60% of EC content were designed. The specimens were initially subjected to successive FT cycles up to 15 in close system criteria. The results revealed that volumetric strains attained during successive FT cycles are proportional to the content and nature of expanding minerals (i.e., montmorillonite) and reached a 4.5% magnitude value for the liner with 60% clay. Vertical strains during wetting conditions have been reduced by about 90% after the first FT cycles, which implies significant destruction in the soil structure. The yield stress indicated a 60% change, along with increasing FT cycles. The hydraulic conductivity during an extended period of 100 days shows significant changes and deterioration due to FT actions. The outcome of this study will help to predict the lifetime behavior and performance of the liner, taking into account the stability under frost conditions.

The risk posed by expansive soils can be lessened by placing foundations at a more deep level below the surface. Structures are able to withstand uplift forces because overburden pressure partially suppresses swelling pressure. In order to transfer the forces to a sufficiently deep depth, this study suggests introducing shafts of a low-expansion overburden material. Soil improved with cement is chosen for this purpose. This study suggests using sand with added excavated natural clay and cement. The expansive clay is added to sand in ratios of 10, 20, 30, 40 and 60%. The clay–sand mixture is then enhanced by cement of 1, 2, 4 and 8% by the weight of the mixture under four curing periods of 1, 7, 28, and 90 days. This material is recommended for use under lean concrete to transfer the loads to lower levels below the foundation depth. The thickness of this material depends on the stresses exerted, the type and the properties of the subsurface soils. The cement-enhanced clay–sand shaft’s properties are examined in this work with regard to the swelling potential, compressibility, and the unconfined compressive strength for different clay contents and curing conditions. Stiff shafts were formed and found to support stresses from 600 to 3500 kPa at cement additions in the range of 1% to 8%. Clay content above 30% is found to be not suitable for Al-Qatif clay due to the compressibility and low strength of the mixture. When two percent or more of cement is added, the swelling potential is significantly reduced. This is reliant on the pozzolanic interactions of soils and cement as well as the clay mineralogy. Determining how cement affects clay–sand combinations in regions with expansive soils would facilitate the introduction of a novel, inexpensive technology to support loads applied by the superstructure.

The feasibility of using crushed limestone instead of sand in cement grout is examined in this work. This study entails performing several tests, including the Brazilian test, the compressive strength test, and the stress–strain correlation test. The curing times used were 7, 14, and 28 days for mixtures with various proportions of cement to limestone (1:1, 1:2, and 1:4). The conventional sand–cement grout laboratory tests were prepared using a similar methodology to examine the effectiveness of the suggested substitute. The findings show that the limestone-based grout has sufficient strength, but that it is less than that of the typical sand material. The values of the tensile strength and elastic modulus were determined. A focus was made on the tensile strength and stress–strain relationship. A special laboratory set-up was used to look at the progress of failure using strain gauges fitted to the cylindrical samples both vertically and horizontally. The angular shape of the particles’ ability to interlock is responsible for the material’s increase in strength. According to this study, crushed limestone can be used as a substitute for sand in circumstances where sand supply is constrained. The suggested grout can be used in the shotcrete of tunnels and rock surfaces.