Fast shear behavior of granular materials in ring-shear tests and implications for rapid landslides

Surface roughness plays an important role in estimating the shear strength of granular materials. A series of ring shear tests with different surface roughnesses (i.e., smooth and rough surfaces) were performed. A large-sized ring shear device, which is applicable for fine- and coarse-grained sediments, was developed to examine the shear strength of large particle sizes (i.e., commercial gravels with a mean grain size of 6 mm). In terms of surface roughness, the drainage- and shear-velocity-dependent shear strengths of the granular materials were examined. In this study, different shear velocities of 0.1, 0.5, and 1 mm/s were applied under drained and undrained conditions. The test results clearly show that shear stress is affected by drainage, shear velocity, and surface roughness. In particular, a typical strain-hardening behavior is exhibited regardless of the drainage and shear velocity condition. The measured shear strength obtained from both drained and undrained conditions increased with increasing shear velocity. All tests showed a large fragmentation using rough surfaces compared to the smooth surfaces of the device. The grain crushing was significant during shearing, even when normal stress was not applied. For a given shear velocity, surface roughness is an important feature in determining the shear strength of granular materials.

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Mechanical behaviour of granular materials used in analogue modelling: insights from grain characterisation, ring-shear tests and analogue experiments

Journal of Structural Geology ◽

10.1016/j.jsg.2006.05.004 ◽

2006 ◽

Vol 28 (9) ◽

pp. 1710-1724 ◽

Cited By ~ 84

Author(s):

Marion Panien ◽

Guido Schreurs ◽

Adrian Pfiffner

Keyword(s):

Granular Materials ◽

Mechanical Behaviour ◽

Shear Tests ◽

Analogue Modelling ◽

Ring Shear ◽

Ring Shear Tests ◽

Analogue Experiments ◽

Materials Used

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Post-failure mobility of saturated sands in undrained load-controlled ring shear tests

Canadian Geotechnical Journal ◽

10.1139/t02-032 ◽

2002 ◽

Vol 39 (4) ◽

pp. 821-837 ◽

Cited By ~ 58

Author(s):

Gonghui Wang ◽

Kyoji Sassa

Keyword(s):

Shear Strength ◽

Steady State ◽

Stress State ◽

Initial Stress ◽

Shear Behavior ◽

Shear Tests ◽

Grain Crushing ◽

Ring Shear ◽

Ring Shear Tests ◽

Undrained Shear

The undrained shear behavior of soils with progress of shear displacement is essential to the understanding of liquefied slope failures with long travel distance. In this paper, using a newly developed ring shear apparatus, a series of ring-shear tests were conducted on a silty sand to examine the undrained behavior of sand subjected to long shear displacement. Based on the test results, the undrained shear behavior of sands with a wide range of densities is discussed. A very low effective stress corresponding to liquefaction was observed at the steady state in all of the tests on loose, medium, as well as dense sand. The effects of stress state and shear history on the undrained shear behavior were examined by performing tests on a sample with different initial stress states and shearing the same specimen repeatedly (three times) at each initial stress state. The tests at different initial stress states proved that the initial stress state has an influence on static liquefaction resistance but has no effect on the steady-state shear strength. Repeated shear tests on the same specimen showed that with increasing shear times, both the peak shear strength and the steady-state shear strength for each specimen became greater. Detailed examination of the shear deformation revealed that the liquefaction phenomena in ring shear tests are localized in the shear zone, irrespective of the initial state of the sand. Grain crushing within the shear zone was examined. Finally, it was found that there was an optimal density at which the undrained brittleness index had a minimum value; meanwhile, the undrained brittleness index became greater with increasing initial normal and shear stresses, but decreased with shear times. These findings offer some basic understanding in assessing the postfailure mobility in landslides.Key words: excess pore pressure, localized liquefaction, shear resistance, ring-shear tests, grain crushing, silty sands.

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