This technical note discusses the load–settlement response from two steel plate load tests (0.3 m diameter, 25 mm thick) carried out on a thick homogeneous stratum of compacted sandy soil, reinforced with polypropylene fibers, as well as on the same soil without the reinforcement. In addition to the field test program, laboratory triaxial compression tests were performed to determine the static stress–strain response of the compacted sandy soil reinforced with randomly distributed polypropylene fibers. The laboratory test results showed that the reinforcement changed dramatically the stress–strain behavior at very large strains. The strength was found to increase continuously at a constant rate, regardless of the confining pressure applied, not reaching an asymptotic upper limit, even at axial strains as large as 25%. The plate load test on the soil–fiber stratum was performed to relatively high pressures, and gave a noticeable stiffer response than that carried out on the nonreinforced stratum.

The aim of this research was to study the behaviour of polypropylene-fibre-reinforced sand under large shear strains. The experimental study consisted of ring shear tests on a sand, with and without randomly distributed fibrous reinforcement. The behaviour of the fibre-reinforced sand mixtures was investigated at large distortional strains, examining the effects of fibre length, fibre content, effective normal stress, and relative density. The effects of reinforcement were found to be more pronounced for longer fibres, higher fibre contents and denser fibre-reinforced sand composites. The results showed the great potential of this kind of fibre reinforcement, because the increase of strength does not deteriorate even at very large strains. The fibres were exhumed after testing and it was found that they had both extended and broken at all normal stresses and for all initial fibre lengths studied, and that the fibre performance depended on the shear displacement that had occurred.

High-pressure isotropic compression tests were carried out on samples of a uniform fine sand at different initial specific volumes, reinforced with randomly distributed polypropylene fibers (0.5% by weight, 24 mm in length and 0.023 mm thick), as well as on a nonreinforced sand specimen. Analysis of the results identified changes in the isotropic compression behavior due to the random inclusion of fibers into the sand. Two distinct and parallel normal compression lines were observed for the fiber-reinforced and nonreinforced sand. The fibers were exhumed after testing and it was found that fibers had both extended and broken, indicating that the fibers tend to suffer large plastic tensile deformations before breaking and that the fibers act under tension even in isotropic compression.

The results of drained triaxial tests on fiber reinforced and nonreinforced sand (Osorio sand) specimens are presented in this work, considering effective stresses varying from 20 to 680 kPa and a variety of stress paths. The tests on nonreinforced samples yielded effective strength envelopes that were approximately linear and defined by a friction angle of 32.5° for the Osorio sand, with a cohesion intercept of zero. The failure envelope for sand when reinforced with fibers was distinctly nonlinear, with a well-defined kink point, so that it could be approximated by a bilinear envelope. The failure envelope of the fiber-reinforced sand was found to be independent of the stress path followed by the triaxial tests. The strength parameters for the lower-pressure part of the failure envelope, where failure is governed by both fiber stretching and slippage, were, respectively, a cohesion intercept of about 15 kPa and friction angle of 48.6 deg . The higher-pressure part of the failure envelope, governed by te...

The behavior of a polypropylene fiber-reinforced bentonite was evaluated at large shear displacements by a series of ring shear tests carried out at normal stresses varying between 20 and 400 kPa . Bentonite/polypropylene fiber composites were molded at an initial moisture content of 170%, with fiber lengths of 12 or 24 mm . The fiber thickness was 0.023 mm and the fiber content was either 1.5 or 3% by dry weight. The inclusion of randomly distributed fibers increased the peak shear strength of the bentonite, but the increase in strength deteriorated at large displacements and the residual strengths of both the nonreinforced and fiber-reinforced bentonite were similar. The peak shear strength was found to increase both with increasing fiber length and content. The fibers were exhumed after testing and it was found that the fibers had both extended and broken, with a predominance of broken fibers.

Plate load tests were carried out on un-reinforced sand and sand reinforced with fibres, compacted at relative densities (DR) of 30%, 50% and 90%. For the reinforced sand, 24 mm long polypropylene fibres were added, a concentration of 0·5% by dry weight. The analysis of the results indicates that the soil load-settlement behaviour is significantly influenced by the fibre inclusion, changing the kinematics of failure. The best performance was obtained for the densest (DR = 90%) fibre-sand mixture, where a significant change in the load-settlement behaviour was observed at very small (almost zero) displacements. However, for the loose to medium dense sand (DR = 30% and 50%), significant settlements (50 mm and 30 mm respectively) were required for the differences in the load-settlement responses to appear. The settlement required for this divergence to occur could best be represented using a logarithmic relationship between settlement and relative density. The overall behaviour seems to support the argument that inclusion of fibres increases strength of sandy soil by a mechanism that involves the partial suppression of dilation (and hence produces an increase in effective confining pressure, and a consequent increase in shear strength).