Ahmed M. Al-Mahbashi

Effect of Vertical Stress on the Soil Water Characteristic Curve of Highly Expansive Soils

This study investigates the effect of vertical loading and sample saturation procedure on the drying soil water characteristic curve (SWCC) of expansive clay from Al-Qatif area in Saudi Arabia. An experimental program is conducted on remolded samples using Fredlund SWCC device with simultaneous application of vertical stress and suction. Samples are tested under vertical stresses of 4, 300, and 600 kPa and over a range of suction up to 1400 kPa. During the test, volume changes experienced by tested samples are evaluated using image processing method for the determination of SWCC in terms of degree of saturation. Results indicate that sample saturation have a significant effect on the shape and air entry value of SWCC of expansive clay. Furthermore, at specific suction level, the combined application of vertical stress and suction cause a reduction in gravimetric water content and degree of saturation.

Effect of polypropylene fibre reinforcement on the consolidation, swell and shrinkage behaviour of lime-blended expansive soil

In this article, synthetic fibres in the presence of lime stabilisation are proposed as an alternative to overcome the issues related to shrink-swell distress in expansive soils. Two types of synthetic fibres, Fiber Cast® (FC) and Fiber Mesh® (FM), were studied by conducting one-dimensional fixed ring Oedometer swell-consolidation and bar linear shrinkage tests. Three dosages (0.2, 0.4 and 0.6% by weight of soil) and two lengths of the fibres (6 and 12 mm) were evaluated with and without lime treatments. The results indicated that FC fibres had better swell restricting performance in the absence of lime treatment, while in the presence of lime both fibres had similar performance in reducing swelling. Shrinkage tests results showed that irrespective of dosage levels, both the fibres had pronounced effect in reducing the linear shrinkage strains up on lime treatment. Non-linear best fit equations have been proposed to relate compression index (C c ) and recompression index (C r ) of expansive clay deposits with and without lime treatment to amount and dosage of FC and FM reinforcements. The proposed non-linear fit provides a mean for recognising, more efficiently, the patterns in the experimental data and predicting the compression indices, C c and C r reliably.

Effect of compaction state on the soil water characteristic curves of sand–natural expansive clay mixtures

Proper understanding and interpretation of the performance of sand–clay liners requires the consideration of its unsaturated behaviour. A cornerstone in the understanding of the unsaturated hydraulic efficiency is the soil water characteristic curve (SWCC). This study discusses the results of an experimental programme performed to investigate the influence of clay content and compaction state on the SWCCs of a proposed sand–natural clay liner. The proposed liner is a mixture of sand and natural expansive clay obtained from the city of Al-Qatif, Saudi Arabia. Experimental results revealed that the SWCC of sand–natural clay mixture is mainly dependent on the sand–clay composition and compaction state. The influence of clay content on the SWCC of sand–natural clay mixtures was marked by an increase in water retention capacity with increase in clay content ranging between 0% and 60%. This increase in water retention capacity was attributed to the formation of micropores due to the addition of clay. In addition, compacted specimens simulating optimum, dry-of-optimum and wet-of-optimum conditions showed two forms of SWCCs: unimodal and bimodal SWCC. The unimodal SWCC was observed to be dominant for sand–clay mixtures with low clay content (less than 5%) and for specimens compacted at wet-of-optimum conditions. The bimodal SWCC was observed for optimum and dry-of-optimum water content specimens. These forms of SWCCs were used to interpret mixture structure and pore size distribution arising from different clay content and compaction conditions.

Trends of Moisture and Electrical Conductivity in Clay Liners

This research is aimed at investigating the influence of ambient air temperature on the moisture content and electrical conductivity of clay sand mixtures. Volume changes as a result of shrinking or swelling are very much related to the moisture content and the electrical conductivity for liners consisting of sand and clays. The laboratory tests carried out for clay sand mixtures subjected to drying indicated a bilinear trend for 15, 20, 25, and 30% clay content. Moisture content measurements are influenced by the ambient temperature and exposure time. Watering a clay sand layer at a regular frequency in a field site revealed useful information on the trends of moisture gain and loss. Suction fluctuation associated with these changes is responsible for absorbing variable amounts of water. Moisture/Temp/EC sensors (5TE) were utilized to survey a sand clay liner section over 30 day’s period. A metrological station installed within the site was used to observe temperature, humidity, and rain fall. The drop of moisture and electrical conductivity was found to be nonlinear with temperature changes and reflecting the bimodal nature of the soil. The general trends of repeated wetting and drying were found similar in shape.

Hysteresis soil-water characteristic curves of highly expansive clay

The main objective of this study is to evaluate the hysteresis of soil–water characteristic curves (SWCC) of highly expansive clay subjected to wetting and drying cycles. Variables considered included hysteresis suction range (i.e. low and high suction ranges), suction determination technique (vapour equilibrium technique, axis translation technique and contact filter paper technique) and initial specimen condition. Experimental results revealed that the degree of SWCC hysteresis was higher in the low hysteresis suction range (less than 1.5 MPa) than the high hysteresis suction range (greater than 1.5 MPa). The results further revealed notable difference between matric and total SWCCs of this expansive clay. Furthermore, a hysteresis was observed that is inherent to suction determination technique and is independent of soil characteristics. Also, it was concluded that initial specimen condition (i.e. as-compacted and saturated) had a significant impact on degree of hysteresis, especially in the low suction range. Plausible explanations of observed trends in view of soil–water retention mechanism were provided. Finally, volumetric strains during drying and wetting paths were evaluated and its impact on SWCC was assessed.

Effect of Unit Weight on Porosity and Consolidation Characteristics of Expansive Clays

This study investigated the relationship between pore characteristics and unit weight of clayey soils. This relationship was particularly important in case of expansive soils, as the pore characteristics determine moisture flux boundaries, which in turn represent volume change behavior. Current research tried to evaluate the effect of compaction unit weight on the pore size and pore volume along with consolidation and swell characteristics on two expansive clays from semi-arid environment. The two selected clays represent soils with different degrees of expansion, particle size and mineralogy. Pore size characterization for these two soils was performed using Mercury Intrusion Porosimetry, while swell and consolidation characteristics were determined using a conventional oedometer test. Samples for both tests were compacted at different unit weights including, 100, 95, 90, 80, 75, and 70 % of maximum dry unit weight (MDUW) obtained from standard proctor. The compaction water content was kept constant for all unit weight levels. Both pore volume and pore size distribution was analyzed with varying unit weight characteristics and particle sizes. In addition, swell strains and compression indices were studied with varying unit weight of compacted specimens. It was observed that, in the case of samples compacted at 100 % MDUW, about 50 % of the pores were larger than 0.1μm, and this value increased with reduction in unit weight. Current research is of practical importance, especially in the wake of microbial treatments for clayey soils where the passage of microbes depends on the pore size and more specifically pore throat size.

Effect of Moisture Hysteresis on the Resilient Modulus of Lime-Treated Expansive Clay

Several studies have asserted that seasonal moisture variation of unsaturated subgrade has a significant impact on its resilient modulus and, consequently, on the pavement performance and longevity. In regard to unsaturated lime-treated expansive subgrade, little research has addressed the influence of moisture variation on resilient modulus (MR). In this context, this study aims at evaluating the effect of the drying and wetting cycle on the resilient behavior of lime-treated expansive clay at optimum lime conditions. Initially, the effects of lime content and curing period on the MR of lime-treated expansive clay were investigated to evaluate the optimum lime content. This involved conducting a series of repeated load tests under different lime contents and curing periods. In addition, a complementary series of tests were conducted to evaluate the unconfined compression strength along the same drying and wetting paths. Test data indicated that lime treatment resulted in a 370 % increase in the MR after 28 days curing. On the other hand, the effect of the wetting and drying cycle, depicted as the relationship between MR and suction (or water content), showed a hysteresis phenomenon. Further examination of the MR along the drying path indicated a positive contribution of suction to the resilient behavior of lime-treated samples up to a specific suction value (>20 MPa), after which this contribution is considered negligible. Hysteresis phenomenon was also observed for unconfined compression strength because of wetting and drying; however, with a different trend. The discrepancy between hysteresis trends were attributed to differences in loading characteristics.

Expansive Soil Foundation Practice in a Semiarid Region

AbstractExpansive soils are known to be a serious hazard to buildings and the infrastructure industry. Saudi Arabia is located in a semiarid region where extremely dry expansive formations are freq...