Direct shear tests on reinforced sand

Abstract

New data are presented from internal measurements in direct shear tests on sand. An interpretation is given for the plane strain angle of friction and the angle of dilation of sand in a direct shear test. The direct shear angle of friction deduced from the conventional analysis is shown to underestimate the frictional shearing resistance of sand by about 20%. Results are presented from direct shear tests on reinforced samples and these are fitted by a limit equilibrium analysis in which all the parameters are independently measured. Plastic incremental strains cause dilation in dense sand and dominate the deformation with increasing stress ratio. The rate of increase of the reinforcement force in shearing sand is shown to depend on the angle of dilation. The maximum bond angle of friction between sand and the rough surface of reinforcement is also determined by plastic deformation in the sand. A theoretical analysis for the bond is supported by the test results which show that the maximum bond angle of friction for rough reinforcement equals the direct shear angle of friction. Thus the modiied direct shear test is a good way to measure bond strength parameters for design.

Evaluation on Failure of Fiber-Reinforced Sand

“…This was first revealed by direct shear tests in which the measured strength of a fiber-reinforced soil was found to be dependent on the fiber orientation in the composite (Gray and Ohashi 1983;Jewell and Wroth 1987;Palmeira and Milligan 1989). More recent studies using triaxial compression and extension tests with varying fiber orientations have repeatedly supported the aforementioned observations (Li 2005;Diambra et al 2010;Ibraim et al 2010).…”

“…Centrifuge tests by Tei et al (1998) also demonstrated that using soil nails at around 10°of inclination to the horizontal provides more effective prevention of horizontal movement of the slope. In biotechnical slope stabilization, root orientation is also an important factor affecting the reinforcing efficiency (Gray and Ohashi 1983;Jewell and Wroth 1987;Sonnenberg et al 2010). Direct shear tests by Gray and Ohashi (1983), Jewell andWroth (1987), andPalmeira andMilligan (1989) have shown that the reinforcement is the maximum when fiber inclination q 2 with respect to the vertical is around 30°(see Fig.…”

A behavioural framework for fibre-reinforced gravel

“…Diambra et al, 2013). Depending on the fibre orientation relative to the applied stresses, the fibre tension may also contribute to carrying the shear stress directly (Jewell and Wroth, 1987). The first approach has pragmatic practical merit, while the second offers a more fundamental insight into the mechanics of the interactions between the grains and the fibre reinforcements.…”

“…The sand matrix was assumed to obey its own constitutive laws, with the fibres considered as discrete forces with defined orientations. Here, we develop the model proposed by Jewell and Wroth (1987) in which the tension generated in the fibres as the material strains "increases the normal effective stress….., allowing additional frictional shearing resistance to be mobilised".…”

“…In their analysis of direct shear tests, Jewell and Wroth (1987) also allowed for a reduction in the shear stress carried by the granular matrix as a result of the component of the fibre tension tangential to the shear plane.…”