Patrick J. Fox

Contaminant Transport through a Compacted Clay Liner with the Consideration of Consolidation Effects

Professor, Institute of Geotechnical and Underground Engineering, Huazhong Univ. of Science and Technology, Wuhan, Hubei 430074, China. E-mail: puh@hust.edu.cn Shaw Professor and Head, Dept. of Civil and Environmental Engineering, Pennsylvania State Univ., University Park, PA 16802. Email: pjfox@psu.edu Professor and Head, Dept. of Civil and Environmental Engineering, Colorado State Univ., Fort Collins, CO 80523. Email: shackel@engr.colostate.edu

SEISMIC TESTING PROGRAM FOR LARGE-SCALE MSE RETAINING WALLS AT UCSD

Mechanically stabilized earth (MSE) retaining walls have steadily grown in popularity due to their low cost, ease of construction, and excellent performance record. Observations from post-earthquake reconnaissance efforts have also indicated that these retaining wall systems exhibit excellent performance under seismic loading, often exceeding the performance of conventional rigid and semi- rigid walls. However, significant questions remain with regard to seismic design procedures for MSE walls, due in part to lack of sufficient test data under dynamic loading. The objective of this paper is to describe a new research program at the University of California-San Diego (UCSD) to conduct dynamic tests of large-scale (5 to 7 m tall) MSE retaining walls using a large outdoor shake table. The advantage of this approach is that test specimens can be constructed using realistic materials and methods, and yet still be shaken to accelerations approaching 0.7g. The research program is expected to provide benchmark data that researchers can use to develop improved design methods for MSE walls and to refine numerical models for assessment of their seismic performance.

Effect of Consolidation on VOC Transport Through a GM/GCL Composite Liner System

This paper presents the results of a numerical investigation of the transport of a volatile organic compound (VOC) through a composite liner system comprising a geomembrane (GM) overlying and in intimate contact with a geosynthetic clay liner (GCL), which is commonly used as an engineered barrier for containment of solid waste. The simulations were performed using the established CST2 model (i.e., Consolidation and Solute Transport 2). The results are presented in the form of VOC mass flux, cumulative VOC mass outflow, and distribution of VOC concentration within the GCL. Consolidation of the 10-mm-thick GCL is shown to result in a decrease in the thickness, void ratio, and effective diffusion coefficient of 41%, 49%, and 72%, respectively, such that the steady-state TCE mass flux and cumulative TCE mass outflow at the bottom of the GCL decreased by 47% and 43%, respectively, relative to results for traditional diffusive simulations that ignore the effect of consolidation. Thus, despite the thinness of the GCL, the effect of consolidation on the transport properties of the GCL can result in a significant decrease in VOC transport through a composite GM/GCL liner system.

Large-Scale Combination Direct Shear/Simple Shear Device for Tire-Derived Aggregate

This paper describes a novel large-scale device capable of performing both direct shear and simple shear tests to evaluate shear deformation and strength properties of Type B tire-derived aggregate (TDA). The device consists of stacked tubular steel members that can be locked as upper and lower rigid sections to displace relative to one another in direct shear or pinned at the ends to translate in simple shear. For both configurations, the TDA specimen has a length of 3,048xa0mm, a width of 1,220xa0mm, and an initial height up to 1,830xa0mm. The upper rigid section of the device can also be used to conduct interface direct shear tests. Vertical stress is applied to the top surface of the specimen using deadweights and horizontal shearing force is applied using two hydraulic actuators in displacement-control mode. Typical results from internal direct shear, concrete interface direct shear, and cyclic simple shear tests are presented. In direct shear mode, the device allows for mobilization of peak shear strength and, in simple shear mode, for evaluation of shear stiffness and damping ratio under large strain conditions for TDA with large particle size.

Shaking Table Test of a Half-Scale Geosynthetic-Reinforced Soil Bridge Abutment

This paper presents an experimental study on the dynamic response of a half-scale geosynthetic-reinforced soil (GRS) bridge abutment system using a shaking table. Experimental design of the model specimen followed established similitude relationships for shaking table tests on reduced-scale models in a 1-g gravitational field, including scaling of model geometry, geosynthetic-reinforcement stiffness, backfill soil modulus, bridge load, and characteristics of the earthquake motions. The 2.7-m-high GRS bridge abutment was constructed using well-graded sand backfill, modular facing blocks, and uniaxial geogrid reinforcements with a vertical spacing of 0.15xa0m in both the longitudinal and transverse directions. A bridge beam was placed on the GRS bridge abutment at one end and on a concrete support wall resting on a sliding platform off the shaking table at the other end. The GRS bridge abutment system was subjected to a series of input motions in the longitudinal direction. Results indicate that the testing system performed well, and that the GRS bridge abutment experienced small deformations. For two earthquake motions, the maximum incremental residual facing displacement in model scale was 1.0xa0mm, and the average incremental residual bridge seat settlement in model scale was 1.4xa0mm, which corresponds to a vertical strain of 0.7 %.

Full-Scale Seismic Test of MSE Retaining Wall at UCSD

Mechanically Stabilized Earth (MSE) retaining walls have been designed and constructed for over 40 years and their popularity has steadily grown due to low cost, ease of construction, and excellent performance record. Observations from post-earthquake reconnaissance efforts have also indicated that these retaining wall systems exhibit good performance under seismic loading, often exceeding the performance of conventional rigid and semi-rigid retaining wall systems. However, significant questions remain with regard to seismic design procedures for MSE walls, due in part to lack of sufficient test data for dynamic loading conditions. Data from centrifuge and 1-g shake table tests on small- to moderate-size specimens have been limited by scaling effects and use of non- standard materials and methods. The objective of this paper is to describe an ongoing research program at UCSD to conduct dynamic tests of full-scale (up to 7 m tall) MSE retaining walls using an outdoor shake table. The resulting data will provide important new information for the development of design standards for seismic regions and assessment of numerical models used to analyze the dynamic response of MSE walls.