Recent research projects cover three main research themes:

1. Discrete Element Modeling

 a) A finite discrete element framework for the 3D modeling of geogrid soil interaction under pullout loading conditions


The behavior of a geogrid-soil system under pullout mode is known to depend on the properties of the geogrid material, the backfill soil and the interface condition. Modeling the geogrid-soil  interaction taking into account the true geogrid geometry is a challenging numerical problem that requires the consideration of the discontinuous nature of the soil and the different modes of  resistance that contribute to the pullout capacity of the geogrid layer. In this study, a coupled finite-discrete framework has been developed to investigate the behavior of a biaxial geogrid sheet embedded in granular material and subjected to pullout loading. Validation is performed by comparing experimental data and numerically calculated results using the proposed model. The detailed behavior of the geogrid and the surrounding soil is then investigated. The numerical results indicated the suitability of the coupled model to solve this class of problems.

b) An Algorithm for the Propagation of Uncertainty in Soils using the Discrete Element Method

An efficient algorithm to create discrete element samples with predefined properties incorporating the random field theory is introduced in this paper. The algorithm considerably reduces the time needed to generate a large scale domain as only a small initial sample with dynamic packing is used. Three-dimensional anisotropic random fields are generated using the Local Average Subdivision (LAS) method accounting for the spatial variability. The random fields are then mapped on the discrete element domain and uncertain parameters of each particle are obtained from the corresponding random field cell. Triaxial tests are conducted on large soil samples with the dimensions of 1.5m x 3.0m x 1.5m comprising over 150,000 spherical particles. The microscopic friction angle and stiffnesses of the particles are selected as random variables since they have a significant effect on the soil behavior under triaxial testing conditions. Monte Carlo simulation is implemented to analyze the probabilistic features of the output values.

C) Discrete Element and Experimental Investigations of the Earth Pressure Distribution on Cylindrical Shafts

Experimental and numerical studies have been conducted to investigate the earth pressure distribution on cylindrical shafts in soft ground. A small scale laboratory setup that involves a mechanically adjustable lining installed in granular material under axisymmetric condition is first described. The earth pressure acting on the shaft and the surface displacements are measured for different induced wall movements. Numerical modeling is then performed using the discrete element method to allow for the simulation of the large soil displacement and particle rearrangement near the shaft wall. The experimental and numerical results are summarized and compared against previously published theoretical solutions. The shaft-soil interaction is  discussed and conclusions regarding soil failure and the earth pressure distributions in both the radial and circumferential directions are presented.

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2. Soil Improvement

a) Measuring contact pressure distribution around rigid pipes installed using induced trenching method and subjected to repeated loading

Loads on buried conduits have been shown to be dependent on the installation conditions (trench vs. embankment methods). The vertical earth pressure on a rigid pipe installed using embankment construction is greater than the weight of the soil above the structure because of negative arching. To reduce the vertical earth pressure on rigid pipes, the imperfect ditch method has been introduced. EPS products have proven to be very successful in geotechnical applications due to their durability and light weight nature. This research project aims at studying the response of a rigid pipe installed using the imperfect trench method to repeated loading. This is achieved using experimental investigation and numerical modeling. Recommendations will be made regarding the optimum configuration for the EPS layer that leads to pressure reduction on the pipe walls.

b) Soil Reinforcement using Geosynthetics:

The use of geogrid as a soil reinforcing material has proven successful over the years for different geotechnical applications. Whether it is a single layer or several layers placed in the soil beneath the footing an improvement in the bearing capacity and the load settlement response of the soil has been reported by several researchers. In addition, the existence of geosynthetic in the soil has a positive effect on enhancing the overall system by compensating   for the lost soil particles due to void formation. In this study, an experimental investigation that combines Geosynthetics and void formation has been conducted to measure changes in the load-displacement response of strip footings. . The effect of soil reinforcement on the footing response to subgrade weakening is thoroughly examined. Preliminary results indicate the presence of a geogrid layer can improve the performance of the granular material and reduce the adverse effects of the unexpected development of local soil weakening under an existing foundation system.

3) Dams

a) Investigating the stability of earthen structures subjected to internal erosion

Adverse wildlife activities and their damage to earthen structures are observed worldwide. Animal burrows have been known to negatively impact the hydraulic performance and structural integrity of levees and earth dams. The yearly cost of failed earthen structures and their infrastructures due to animal burrows worldwide is estimated to exceed billions of dollars. Significant amount of the literature that is available in the area of wildlife focuses on the ecological and environmental impact of animal activities and habitat. However, studies related to the synthesis of failure mechanisms of earth structures due to wildlife activities appear to be relatively limited. This project is intended to make a step forward in that regard

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