Excess Pore Water Pressure within a Deep-seated Bedding Fault: Understanding of Earthquake Induced Large Landslide Initiation

Abstract

The 2008 Wenchuan Ms8.0 earthquake triggered a landslide (i.e., Daguangbao landslide) with a volume of near 1.2 billion m3. This landslide involved the Paleozoic carbonate strata and the geological background of the sliding zone is a pre-existing bedding fault with a maximum thickness of 5 m and depth of 400 m in the slope. The bedding fault was the groundwater channel in the slope with saturated rock mass, according to the latest survey. To reveal the initiation mechanism of Daguangbao landslide (hereinafter short for DGB landslide) related to groundwater, a kind of simplified model of hard carbonate rock-cut slope with weak layer has been proposed to generalize bedding fault to weak layer in hard carbonate rock layer. And response characteristics of the model have been simulated by fluid-solid coupling algorithm in the FLAC3D program. The results showed that the hard carbonate rocks above and below the weak layer were different in deformation during strong earthquake, which led to the dynamic behavior of vibratory stamping-tension to the weak layer. And then, the discordant deformation of the two layers resulted in the excess pore water pressure featured with instant amplification and cumulative growth in the saturated water weak layer. So it was inferred that the rapid drop of inside effective stress caused by excess pore water pressure in the weak layer during strong earthquake would give rise to the sudden shearing of stress in the front locked segment of the slope after rapid stress concentration, and consequently trigger the DGB landslide.