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Wu J.T.H.,University of Colorado at Denver | Pham T.Q.,Institute of Geotechnical Engineering IGE IBST | Adams M.T.,Turner Fairbank Highway Research Center
International Journal of Geotechnical Engineering | Year: 2011

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. © 2011


Wu J.T.H.,University of Colorado at Denver | Pham T.Q.,Institute of Geotechnical Engineering IGE IBST
International Journal of Geotechnical Engineering | Year: 2010

When an earth fill is subject to loading and subsequent unloading, it will bring about an increase in the lateral stress, provided that there is sufficient constraint to lateral deformation of the soil mass. The increase in lateral stress is commonly known as the "residual" or "lock-in" lateral stress. The residual stress resulted from compaction operation, which involves a series of loading and unloading onto a soil mass, is referred to as "compaction-induced stress" (CIS). The CIS will increase the stiffness and strength of the soil mass, and is an important factor to be considered in the behavior of compacted soil. A number of studies have been conducted on the CIS in an unreinforced soil mass. With a reinforced soil, the CIS is likely to be much more pronounced because there is a higher degree of constraint to lateral deformation in a reinforced soil mass due to soil-reinforcement friction. An analytical model, referred to as the CIS model, is developed for evaluation of compactioninduced stress in a reinforced soil mass. Correlations for determination of model parameters are given so that the parameters can be estimated through reinforcement spacing and stiffness, and common soil parameters, such as the angle of internal friction (Φ), and overconsolidation ratio (OCR). In addition, the stress paths of typical fill compaction operation are discussed, including compaction with a plant moving toward and away from a section under consideration, and compaction with multiple passes. The CIS model presented in this paper is found to give CIS values very close to those obtained from sophisticated finite element analysis of a 6-m high GRS mass under different values of compaction pressure. The CIS in the reinforced soil mass is significant under compaction pressures typically used in actual fill compaction. J. Ross Publishing, Inc. © 2010


Wu J.T.H.,University of Colorado at Denver | Pham T.Q.,Institute of Geotechnical Engineering IGE IBST
International Journal of Geotechnical Engineering | Year: 2010

Current design methods for Geosynthetic-Reinforced Soil (GRS) walls consider only the stresses and forces in the wall system. A GRS wall with modular block facing is inherently a fairly "flexible" wall system; hence it can be of critical importance to include the lateral movement of the wall in design. This paper presents an analytical model for estimating the lateral movement of a GRS wall with modular block facing. Derivation of the analytical model is given in this paper. In addition, an equation for determining the connection forces in the reinforcement immediately behind the facing is provided. The equation for the lateral movement can be readily used in design of a GRS wall, whereby the required reinforcement strength can be determined for a prescribed value of maximum allowable lateral movement. The analytical model was verified through comparisons with Jewell-Milligan method for GRS walls constructed with negligible facing rigidity. Comparisons were also made with a full-scale experiment of GRS wall with modular block facing. It is shown that the analytical model offers a simple and improved tool for estimating lateral movement of a GRS wall with modular block facing. J. Ross Publishing, Inc. © 2010


Wu J.T.H.,University of Colorado at Denver | Pham T.Q.,Institute of Geotechnical Engineering IGE IBST
Journal of Geotechnical and Geoenvironmental Engineering | Year: 2013

In current design methods for reinforced soil walls, it has been tacitly assumed that reinforcement strength and reinforcement spacing play an equal role. This fundamental design assumption has led to the use of larger reinforcement spacing (≤0.3-1.0 m) in conjunction with stronger reinforcement to reduce construction time. Recent studies, however, have clearly indicated that the role of reinforcement spacing is much more significant than that of reinforcement strength. With closely spaced (reinforcement spacing #0:3m) reinforcement, the beneficial effects of geosynthetic inclusion is significantly enhanced, and the load-deformation behavior can be characterized as that of a composite material. A reinforced soil mass with closely spaced geosynthetic reinforcement is referred to as geosynthetic-reinforced soil (GRS). In this study, an analytical model is developed for predicting the ultimate load-carrying capacity and required reinforcement strength of a GRS mass. The model was developed based on a semiempirical equation that reflects the relative roles of reinforcement spacing and reinforcement strength in a GRS mass. Using measured data from field-scale experiments available to date, it is shown that the analytical model is capable of predicting the ultimate load-carrying capacity and required reinforcement strength of a GRS mass with good accuracy. © 2013 American Society of Civil Engineers.


Jonathan T.H.W.,University of Colorado at Denver | Adams M.,Turner Fairbank Highway Research Center | Pham T.Q.,Institute of Geotechnical Engineering IGE IBST | Lee S.H.,Kyungpook National University | Ma C.Y.,M Group LLC
International Journal of Geotechnical Engineering | Year: 2012

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. © 2012

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