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Title: Effect of horizontal reinforcement on stability of earth masses
Authors: Al-Hussaini, Mosaid M.
Perry, Edward B. (Edward Belk)
Keywords: Membrane strips
Soil stability
Soil stabilization
Reinforced earth
Reinforcing materials
Stress-strain relations
Shear strength
Soil mechanics
Retaining walls
Publisher: Soils and Pavements Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Technical Report
Abstract: Reinforced earth consists primarily of soil whose engineering properties and performance have been improved by the introduction of small quantities of frictional material that possesses a relatively high tensile strength and modulus of elasticity. The design concept of reinforced earth is based on the assumption that the induced lateral force of a restrained soil mass under load will be resisted by frictional forces that develop between the reinforcement and the surrounding soil. This practical concept has been applied to the problem of stabilizing slopes, retaining walls, pavements, and other applications as described in the literature review. The objectives of this study were: (A.) to investigate the uncertainties concerning the stress-strain distribution and the interrelation between the reinforcement and the surrounding soil, and (B.) to evaluate the performance of neoprene-coated nylon fabric (membrane) versus galvanized steel as reinforcing material within a cohesionless soil mass. These two objectives were directed toward the feasibility of using the concept of reinforced earth in Corps of Engineers projects. The objectives were achieved by constructing two instrumented retaining walls, each 16 ft long, 12 ft high, and 10 ft deep; the first wall was reinforced with membrane ties, and the second with galvanized steel ties. The membrane ties were 4 in. wide, 0.08 in. thick, and 10 ft long, spaced at intervals of 2 and 4 ft in the vertical and horizontal directions, respectively. The galvanized steel ties had the same width and length as the membrane ties but were 0.024 in. thick and spaced 2.5 ft apart along the wall. Three galvanized steel ties along the center line of the wall and located at 1, 5, and 9 ft above the bottom of the wall were instrumented with complete SR-4 strain gage bridges on both surfaces at points 1, 2.5, 5, and 7.5 ft from the face of the wall. At the elevation of each instrumented tie and 1 ft away from the surface of the wall, two pressure cells were placed to measure the induced vertical and horizontal pressures within the backfill soil. A similar pressure cell arrangement was used for the membrane-reinforced wall. The skin element which comprised the exposed surface of the wall was made of Alcoa T11 high-strength aluminum landing mat panels similar to those used for construction of expedient airfield strips. Although the membrane-reinforced wall failed before it reached 10 ft high, the steel-reinforced wall was constructed to the full height of 12 ft and uniformly surcharge loaded, using 1- and 2-ton lead weights, to surface pressure in excess of 1500 psf. Deflection of the skin elements was measured during construction and surcharge loading. It is probable that failure of the reinforced earth retaining wall was initiated by failure of the connection which joined the reinforcing ties to the skin element or by failure of the skin element due to buckling and shear. Based on the instrumentation measurements collected during construction and during loading of the structure to failure, it appears that the Rankine earth pressure theory provides a good approximation for the measured lateral pressure when the wall is carrying little or no surcharge load. Prior to failure under a substantial surcharge loading, the measured lateral earth pressure was maximum at the middle third of the wall and varied from 1.0 to 1.2 times the earth pressure predicted by the Rankine theory for the active case. The curve connecting the points where maximum tensile stress occurred in the reinforcing ties did not coincide with the theoretical Rankine failure surface. An improved method of defining the effective length of reinforcing tie, compatible with full-scale field test results, to be used in computing tie pullout should be developed. The field test conducted at the U. S. Army Engineer Waterways Experiment Station indicated that the reinforced earth concept provides another alternative for constructing earth structures which may prove to be more economical when compared with conventional methods under certain conditions.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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