Christina Y. Ma’s scientific contributions

Geosynthetic-Reinforced Soil (GRS) mass, comprising soil and layers of geosynthetic reinforcement, is not a uniform mass. To examine the behavior of a GRS mass by a laboratory test, a sufficiently large-size specimen of soil and reinforcement is needed to produce a representative soil-geosynthetic composite. This paper presents a generic test, referred to as the Soil-Geosynthetic Composite (SGC) test, for investigating stress-deformation behavior of soil-geosynthetic composites in a plane strain condition. The specimen dimensions, 2.0 m high and 1.4 m wide in a plane strain configuration, were determined by the finite element method of analysis. The configuration, specimen dimensions, test conditions, and procedure of the SGC test are described. In addition, the results of a SGC test with nine sheets of reinforcement, as well as those of an unreinforced soil test conducted in otherwise identical conditions, are presented. In the test, the soil mass was subject to a prescribed value of confining pressure, applied by vacuum through latex membrane covering the entire surface area of the mass in an air-tight condition. Vertical loads were applied on the top surface of the soil mass until a failure condition was reached. The behaviors of the soil masses, including vertical displacements, lateral movement, and strains in the geosynthetic reinforcement, were carefully monitored. The measured data allow the behavior of reinforced and unreinforced soils to be compared directly, provide a better understanding of soil-geosynthetic composite behavior, and serve as the basis for verification of numerical models to investigate the performance of GRS structures. J. Ross Publishing, Inc.

In current design methods for geosynthetic-reinforced soil (GRS) walls and abutments, there is a fundamental design assumption that the reinforcement strength and spacing play an equal role in the performance of a GRS wall/abutment, i.e., larger reinforcement spacing can be fully compensated by using proportionally stronger reinforcement and lead to the same performance. This has encouraged designers to use larger reinforcement spacing in conjunction with stronger reinforcement for reduction in construction time. Recent studies, however, has indicated that reinforcement spacing plays a much more significant role in the performance of a GRS wall/abutment than reinforcement strength. In this paper, an analytical model that is capable of reflecting more accurately the roles of reinforcement spacing and reinforcement strength is presented. Using available data from large-scale experiments, it is shown that the analytical model provides a much improved tool for predicting reinforcement forces at failure than the current design equation. Based on the analytical model, a protocol for determination of required minimum reinforcement stiffness and strength in design is presented. J. Ross Publishing, Inc.