Wael M. Albadri

Bio: Wael M. Albadri is an academic researcher from Universiti Teknologi MARA. The author has contributed to research in topics: Triaxial shear test & Shear strength (soil). The author has an hindex of 2, co-authored 6 publications receiving 16 citations.

Mechanical response of saturated and unsaturated gravels of different sizes in drained triaxial testing

Abstract: During the construction of pavements, gravelly soil is used as the main material in the base and sub-base layers. Predicting the deformation behaviour of gravelly soil has been increasingly important, and this may require comprehensive knowledge about both the mechanical and microstructural behaviours of gravelly materials. This study evaluates the saturated and unsaturated behaviours of 200-mm-high remoulded gravelly soil samples under a large-scale consolidated drained triaxial test. The laboratory tests included physical, mechanical, and microstructural testing on gravelly soil and different sizes of gravel. A series of drained triaxial tests were conducted on gravelly soil under both saturated and unsaturated conditions and on 5 mm, 10 mm, 14 mm, 20 mm, and 25 mm sizes of gravel. The results indicated an increase in the mechanical properties with increasing gravel size. The shear strength parameters were also improved with increasing gravel size. When comparing the results of the gravelly soil under both saturated and unsaturated conditions, the soil had an apparent shear strength that decreased beyond the residual suction during the unsaturated condition. The deviator stress and axial and volumetric strains were significantly dependent on the confining pressure. The microstructural studies confirmed the presence of calcite minerals with granular structures and crystalline textures as the main mineral in the gravelly soil. Therefore, the particle breakage when confining pressure is applied will be minimal, which enables the use of this soil in the base and sub-base layers of the pavement.

The relationship between the shear strength and water retention curve of unsaturated sand at different hydraulic phases

Abstract: This technical paper focuses on evaluating the shear strength of unsaturated sand at drying, wetting and alternate drying–wetting cycles, as well as the correlation between the strength and the water retention curve (WRC) at different hydraulic phases. Results of stress–strain curves and WRCs were obtained from conducting numerous tests using suction-controlled triaxial test. Although the maximum shear strength was obtained from the specimens under drying conditions, the difference between the drying and wetting shear strength was relatively small for the tested soil. Based on analysis of the test results, a multi-surfaces envelope model was proposed to fit the experimental shear strength data under drying conditions and to predict the shear strength under wetting conditions (or any subsequent drying–wetting cycle) based on the drying fitting parameters. The fitting and prediction performance of the proposed equations were checked using experimental data from previous studies, and very good agreement was reported. Moreover, the WRC was found to be capable of not only estimating unsaturated soil property functions but also anticipating the soil shear strength behaviour under different hydraulic phases.

Membrane penetration effects on shear strength and volume change of soil during triaxial test

Abstract: In a triaxial test of soil, a specimen in the cell is enclosed by a rubber membrane to separate soil particles from the surrounding water that represents the confining pressure. Upon increasing the confining pressure, this membrane penetrates the voids between the particles of the specimen and cause errors in triaxial test results, these errors lead to changes in shear strength and volume change measurements. Therefore, the results need to be corrected for membrane penetration. This paper emphasizes the importance of correcting triaxial test results for membrane penetration by presenting the influence of membrane penetration on shear strength and volume change measurements. It was concluded that the rubber membrane can produce apparent increase in volume change and shear strength either due to membrane penetration (when the test is at drained condition) or due to membrane compliance (when the test is at undrained condition).

The importance of incorporating hysteresis effect in determining shear strength of unsaturated soil

Abstract: Soil water characteristic curve (SWCC) can be defined as a graphical representation for the relationship of matric suction - water content of a soil. SWCC demonstrates soil's ability to retain water (capacity of the soil for water storage), thus, it shows the water content corresponding to each matric suction. SWCC can be measured either by drying or wetting the soil mass. The soil that has undergone drying and wetting exhibits two different curves, therefore there is no unique SWCC, the difference between these curves is referred to as hysteresis of soil. SWCC is used to identify several soil properties such as shear strength, the coefficient of permeability and grain size distribution. Most of the researchers consider only drying SWCC as it is easy to measure compared to wetting SWCC. This paper highlights the hysteresis effect and the significance of incorporating wetting SWCC in identifying soil properties such as shear strength and stress-strain response.

Direct shear testing on unsaturated silty soils to investigate the effects of drying and wetting on shear strength parameters at low suction

Abstract: A modified conventional direct shear device was used to measure unsaturated shear strength of two silty soils at low suction values (0 ~ 50 kPa) that were achieved by following drying and wetting paths of soil water characteristic curves (SWCCs). The results revealed that the internal friction angle of the soils was not significantly affected by either the suction or the drying wetting SWCCs. The apparent cohesion of soil increased with a decreasing rate as suction increased. Shear stress-shear displacement curves obtained from soil specimens subjected to the same net normal stress and different suction values showed a higher initial stiffness and a greater peak stress as suction increased. A soil in wetting exhibited slightly higher peak shear stress and more contractive volume change behavior than that of soil in drying at the same net normal stress and suction.

Application of hybrid intelligent systems in predicting the unconfined compressive strength of clay material mixed with recycled additive

Abstract: A reliable prediction of the soil properties mixed with recycled material is considered as an ultimate goal of many geotechnical laboratory works. In this study, after planning and conducting a series of laboratory works, some basic properties of marine clay treated with recycled tiles together with their unconfined compressive strength (UCS) values were obtained. Then, these basic properties were selected as input variables to predict the UCS values through the use of two hybrid intelligent systems i.e., the neuro-swarm and the neuro-imperialism. Actually, in these systems, respectively, the weights and biases of the artificial neural network (ANN) were optimized using the particle swarm optimization (PSO) and imperialism competitive algorithm (ICA) to get a higher accuracy compared to a pre-developed ANN model. The best neuro-swarm and neuro-imperialism models were selected based on several parametric studies on the most important and effective parameters of PSO and ICA. Afterward, these models were evaluated according to several well-known performance indices. It was found that the neuro-swarm predictive model provides a higher level of accuracy in predicting the UCS of clay soil samples treated with recycled tiles. However, both hybrid predictive models can be used in practice to predict the UCS values for initial design of geotechnical structures.

Effect of density on the soil-water-retention behaviour of compacted soil

Abstract: This paper presents a series of experimental results obtained from wetting and/or drying cyclic tests and constant suction triaxial tests on unsaturated compacted clay with different initial densities using two suction-controllable triaxial apparatus. The primary objective of this research is to investigate the influence of the soil density on the soil-water-retention behaviour. The initial density and initial degree of saturation were controlled by changing the compaction energy using clay powders with almost the same water content. The test results contain the water-retention curves and deformation behavior at different initial densities using different specimens and one specimen before and after collapse. The test data indicate that the measured water-retention curves vary with the current specimen density. A denser specimen results in a higher degree of saturation at the same imposed suction, which implies that the water-retention curve shifts to the right in the ln s-S r plane.