Shawn Dennis McGee (smcgee@hullinc.com)

and

Dr. Brian W. Randolph, Professor (brandolp@eng.utoledo.edu)

Department of Civil Engineering

University of Toledo

Toledo, Ohio 43606

Reinforcing soil is a composite construction material that consists of alternating layers of compacted backfill and tensile reinforcing material. The theory behind reinforced soil is that the vertical normal stresses that the backfill exerts on the embedded reinforcement are a source of frictional resistance that results in tensile stress being carried by the reinforcement. The stress occurring in the reinforcement is transferred to the surrounding soil. The stress transfer, or anchorage, is caused by friction and bearing between the reinforcement and soil. Geogrids are an excellent form of reinforcement due to the large strengths and stiffness properties.

Two requirements common to the design of reinforced soil structures are that the reinforcement must not fail in tension and the reinforcement must not pull out of the soil. In many reinforced soil applications the critical mode of failure involves pullout of the reinforcement from the soil. In designing against pullout failure of geogrid reinforcement, a coefficient of friction between the soil and the reinforcement is used. It is assumed that friction along both surfaces of the reinforcement supplies the pullout resistance. However, reinforced convex curved walls present an interesting problem since adjacent geogrid panels overlap to some degree.

Previous research has demonstrated how the pullout strength has deteriorated when reinforcement materials are placed directly on each other compared to reinforcement placed solely in the soil. The primary objective of this experimental investigation was to evaluate the effects of the angle of incidence on overlapped geogrids in pullout resistance. The pullout testing generally consisted of measuring the force necessary to pull a specimen out of a soil mass. A second static geogrid was fixed at different angles of incidence across the test specimen to model the overlapping phenomenon of different size wall curvatures. The research will help in predicting an influence factor based on the angle of incidence of overlap for the design of geogrid reinforced walls.