Frictional characteristics of the submarine sediments in the Shenhu Canyons, South China Sea

The frictional characteristics of sediments control the development of landslides in submarine landslide areas. They are the basic parameters for the evaluation of submarine slope stability, and the study of the geothermal-pressure field evolution, and the law of gas hydrate hosting during the landslide process. The continental slope areas of the northern South China Sea are not only rich in gas hydrate resources, but also have many landslides in geological history. They are still potential submarine landslide areas. In order to understand the in situ frictional characteristics of the sediments in the landslide areas of the northern South China Sea as much as possible, we carried out the triaxial quasi-static frictional sliding experiments for four sediment collected from the Shenhu Canyons, under the conditions of confining pressure P-c = 20 MPa, pore pressure P-p =10 MPa and temperature T approximate to 20 degrees C. The experimental results show that: (1) all the four shallow sediments show the characteristics of velocity strengthening and displacement strengthening. (2) The maximum static friction coefficient (mu(max)) and steady-state friction coefficient (mu(ss)) of these four sediments range from 0. 460 to 0. 510, and from 0. 455 to 0. 554, respectively. Moreover, there is a positive relationship between mu(max) and mu(ss). (3) The ranges of cohesion (c) and friction angle (phi) are 0. 30 similar to 0. 57 MPa and 24. 5 degrees similar to 27. 0 degrees, respectively. In fact, the topographic slope usually lower than 6. 8 degrees in the Shenhu Canyons. It means that the unstable slip could not be induced only by the sediments weight in this area. In addition, based on the multi-stage landslide characteristics of the Shenhu Conyons, the spatial distribution relationship between the landslide bodies and the bottom boundaries of the hydrate stability domain which usually overlap with the bottom simulating reflectors (BSRs), gas chimneys and other structures, we infer that the landslides are predominantly caused by the increase of pore pressure which reduces the formation strength near the BSRs. The increase of pore pressure may be caused by the accumulation of the thermogenic free gas from deep, or/and the hydrate decomposition near the BSRs due to the disturbance of geothermal-pressure fields after the sudden geological events, such as earthquakes.