Shear Rate Effect on Strength Characteristics of Sandy Soils
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SOIL MECHANICS SHEAR RATE EFFECT ON STRENGTH CHARACTERISTICS OF SANDY SOILS
M. Beren,1 I.
obanoglu,2 S.B.
.. .. .. elik,2 O. Undul1
UDC 624.131.377
1
Istanbul University-Cerrahpasa, Istanbul, Turkey; 2Pamukkale University, Denizli, Turkey, *Corresponding author Email: [email protected].
In this study, the effects of different shear rates during direct shear tests on variations in the strength characteristics were investigated for the sand samples of various particle size distribution. Direct shear tests were carried out at nine different shear rates ranging from 0.05 to 5 mm/min under normal stresses of 54.5, 109, and 218 kPa. Both sample groups were tested under a condition of defined water content and in a water-filled condition. Results show that with increasing shear rate, the internal friction angle and peak shear strength values increased. The increase in the internal friction angles and peak shear strengths were particularly evident for shear rates higher than 1 mm/min. Even though the effect of grain size on the variation in strength parameters due to shear rate is limited for the soils examined in this study, the effect should be considered. Introduction Shear strength characteristics (cohesion c, internal friction angle ϕ, peak strength T) are important soil parameters in geological and geotechnical engineering practice. Triaxial compression and shear box tests are commonly used testing methods to determine the shear strength characteristics of soils. The shear box test is commonly utilized because it is simple and practical to apply it to disturbed and undisturbed soils. This relatively simple test directly measures shear forces, as the sample is deformed at a controlled rate until failure occurs. The testing device is forced to yield the sample through a shear plane at varying shearing rates. For loess samples (i.e., sandy, clayey, silt), Horn [1] determined a loading rate of 0.15 mm/min as the maximum shear rate under drained direct shear conditions. He attributed the increase of shear stress (τf) with increasing displacement rate to pseudo-plasticity (i.e., viscosity decreases with increasing shear stress). Thermann et al. [2] used a direct shear apparatus and applied different shear rates (SR) on silty sand soils to examine the effects of SR on ϕ, c, and T. Saito et al. [3] carried out direct shear tests on silica sands with illite and bentonite at four different shear rates (e.g., 0.01, 0.1, 1 and 10 mm/min). These researchers observed that the effective residual internal friction angle of the silica sands was almost constant at 34° for all shear rates. Nakao et al. [4] carried out shear box tests on coarse grained granular backfill soils and determined that peak and residual internal friction angles varied in response to different shear rates. McCartney et al. [5] carried out direct shear tests on a geo-synthetic clay liner at low shear rates ranging between 0.0015 mm/min and 1 mm/min. It was found out that under relatively high normal stresses (e.g., 250 kPa), there was a decrease
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