Mousa F. Attom

Solutions for Soil-Pile-Soil Forces in Pile Stabilized Slopes

This paper introduces a mathematical procedure to analyze slope/pile systems. Limiting equilibrium method of slices is extended to account for the pile in the slope. Force and moment equilibrium for each individual slice is satisfied. The proposed procedure allows two separate predefined failure slip surfaces (one in the upslope side and the other in the downslope side) with a unique factor of safety for each slip surface. An illustrative example is presented to elucidate the use of the solution in comprehending the interrelationships among the pile location, the desired factor of safety of the slope/pile system, and the interactive soil/pile forces.

Numerical prediction of plane strain properties of sandy soil from direct shear test

Abstract Direct shear test is commonly used for research and geotechnical engineering design due to its simplicity and cost effectiveness. However, analysis of many geotechnical structures such as earth pressure and slope stability problems require measurement of plane strain properties of soil. Therefore, it is usually relied on empirical relationships to predict soil properties in plane strain conditions from direct shear or triaxial tests. In this study, a two-dimensional plane strain numerical model is developed using the finite difference program, FLAC to simulate the mechanical behavior of sandy soil tested in direct shear box. Results are presented in terms of stress distribution within the soil specimen at different stages of shearing process and at different locations of the failure surface. Principal stresses and their directions are also investigated and discussed. Results indicated that, the plane strain properties of the sandy soil can be back-calculated from numerical simulation of direct shear tests with reasonable accuracy. Moreover, the numerical model was able to capture the trend in the experimental results and in most cases gave reasonable estimates of the shear strength and volume change of sandy soil. Numerical results also indicated that angle of internal friction at plane strain condition is significantly larger than the direct shear friction angle. In addition, both normal and shear stresses distributions at failure plane are diverted from being uniform at initial conditions to non-uniform during shearing process and at failure. Finally, principal stresses at failure surface are non uniform and rotated significantly during shearing process.

The Use of Wastewater in Construction of Base Course Layers in Pavement Structures

Large amounts of wastewater are produced annually and treated for use in agriculture, irrigation and groundwater replenishment. The produced treated wastewater (TWW) can be used as an alternative to the millions of gallons of fresh water that are typically used in pavement construction. This study was conducted to investigate the potential of using treated wastewater in base course layer in pavements. Chemical analysis tests were conducted both on the treated wastewater samples and on tap water to determine their properties. Samples of the base course material were prepared and soaked using the two different TWW samples as well as the tap water. Proctor compaction and California Bearing Ratio (CBR) tests were conducted on the prepared samples, and the results have shown that TWW can be a suitable replacement for fresh water in base course layers in pavement construction.

Laboratory simulation of the influence of groundwater rise and drip irrigation on the settlement of a sample of collapsible desert soil

Most types of sand have low susceptibility to settlement when in dry, dense and well-graded states but certain sands, when saturated, exhibit a decrease in suction and tensile strength hence leadin...

Effect of admixture’s formulation on the damping of engineered sand

Abstract Vibrations due to dynamic loading such as machines and earthquakes are controlled by installing base isolation systems comprising of dampers. Previous study on low frequency resonant-column testing showed that damping ratio of sand increases significantly if viscoelastic admixture (Glycerine and Bentonite) is added. The study, however, did not examine the effect of formulations (Glycerine to Bentonite ratio, GBR) of admixture on damping, which is important for designing practical solutions. This study presents the effect of admixture formulation on dynamic properties of sand at different saturations (fraction of volume of voids). The dynamic properties are measured by conducting high frequency ultrasonic testing. The results indicate that wave velocity is insensitive to saturation or GBR of admixture. The damping ratio, however, changes significantly with increase in saturation and GBR of the admixture. The selection of GBR and saturation level shall be decided on the basis of desired level of vibration amplitudes.

Laboratory Simulation of Irrigation-Induced Settlement of Collapsible Desert Soils Under Constant Surcharge

The heterogeneous nature of soil as a load bearing material, coupled with varying environmental conditions, pose challenges to geotechnical engineers in their quest to characterize and understand ground behavior for safe design of structures. Standard procedures for checking bearing capacity and settlement alone may sometimes be insufficient to achieve an acceptable degree of durability and in-service performance of a structure, particularly under varying environmental conditions, whether natural or man-made. There exists a wide variety of problematic soils that exhibit swelling, shrinkage, dispersion and collapse characteristics occasioned by changes in moisture content. Specific examples are collapsible soils, which occur mainly in arid and semi-arid regions, are generally capable of resisting fairly large loads in the dry condition but suffer instability and significant strength loss when in contact with water. A number of case studies in the United Arab Emirates were examined, where lightly loaded structures such as boundary walls, pavements and footpaths had been built on ground overlying collapsible soil strata. Sustained irrigation of the dry landscapes was found to have caused uneven settlement of the collapsible soils leading to continuous distress to the structures as evident from cracking and deformation. To help address the problem, an opportunity has been taken to develop a laboratory method of simulating the loaded behavior of collapsible soils in varying situations and to measure its deformation at constant surcharge and ground water infiltration rates. Finally, relationships were developed to estimate the time and magnitude of settlement, if thickness of collapsible soil is known.

Performance of Olive Waste Ash Concrete Exposed to Thermal Cycling

This paper explores the influence of olive waste ash (OWA) on the performance of concrete to thermal cycling. The performance of concrete to thermal cycling was evaluated by measuring the compressive strength, electrical conductance, and visual inspection of cracks in concrete specimens. Three OWA replacements were utilized in the study: 7, 15, and 22 % by weight of sand. The other experimental parameters investigated in the study were aggregate type (crushed limestone and volcanic pumice), water to cement (w/c) ratio (0.4 and 0.6), and curing type (moist and autoclaving curing). After the initial moist curing, concrete specimens were exposed to thermal cycling regime in the range from 30 to 150°C during a period of 24 h using an electric furnace. The results of the study showed that thermal cycling of OWA concrete resulted in significant cracks and damage in concrete specimens. The OWA concrete was found more resistant to thermal cycling compared to plain concrete. Additionally, the resistance of OWA concrete to thermal cycling increased with increasing the OWA content. The OWA concrete containing pumice aggregate showed more resistance to thermal cycling than OWA concrete containing limestone aggregate. The resistance of OWA concrete at w/c ratio of 0.4 to thermal cycling was observed higher compared to OWA concrete at w/c ratio of 0.6. The autoclaved OWA concrete showed higher improvement to thermal cycling than the moist cured OWA concrete.