Shear Strength of a Sand Under Plane Strain Conditions

Laboratory tests are performed to simulate, in the best way, the observed field conditions. These conditions assist in the choice of the test to be performed for the determination of the relevant geotechnical parameters. Among the tests used in Geotechnical Engineering, simple shear stands out. This test is known and used to measure shear strength and soil stiffness. Further, it is the only laboratory test capable of imposing on a sample plane strain conditions under constant volume and allowing rotation of principal stresses. A few of the most common applications of the simple shear testing are the vertical shear wave propagation through a soil column, the mode of shearing to a pile shaft and under an offshore gravity base platform. In this context, simple shear apparatus was developed with the purpose of analyzing the behavior of materials under such loading conditions. The study was conducted in a fine uniform sand from the city of Osorio, Brazil. The Osorio sand showed a behavior typical of medium dense sands with stress envelope with the angle of 35 degrees. Results presented a peak of shear stress followed by reduction of resistance. Furthermore, the three initial effective stress carried on this research showed a normalized behavior during shear strain. The cyclic tests presented the same stress envelope as the monotonic test, reaching also the angle of 35 degrees. As expected, a stiffness degradation for a wide range of shear strain was observed.