Effective Shear Strength of Fiber-Reinforced Clays

ABSTRACT: Results from unconfined compression testing of clay soils have provided evidence that the short term total shearing strength of the soils increased with the presence of randomly distributed polypropyl-ene fiber-reinforcements. The results of a testing program are presented in which the (long term) effective shear strength of fiber-reinforced clay soils is determined utilizing both isotropic consolidated-undrained (ICU) triaxial testing with pore pressure measurement and isotropic consolidated-drained (ICD) triaxial test-ing. Unreinforced and reinforced specimens were prepared at constant water content and density so that ef-fective stress failure envelopes could be defined. The results from the testing program provide insight on the influence of the fiber inclusions on the behavior of the clay specimens during shearing, namely the pore pres-sure generation within the reinforced and unreinforced soil specimens, and the effects of strain rate and drain-age conditions on the effective shearing strength of the reinforced clay. Results from the ICU triaxial testing of fiber-reinforced and unreinforced clay specimens provides evidence that the presence of the fibers changes the behavior of the clay during shearing, which consequently alters the pore pressure generation within the specimens. Results from ICD triaxial tests are presented for the two fiber-reinforced clay soils and compared with the results from the ICU triaxial testing, which provides evidence that the effect of fibers within the clay specimens under ICU testing conditions may lead to a higher estimation of the effective shearing strength as compared to ICD testing conditions.