23-25 September 2013
GEOMAR East shore
Europe/Berlin timezone
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Back Analysis of the Strength Parameters of the Offshore Sediment from an Earthquake-triggered Submarine Landslide

Presented by Prof. Huai-Houh HSU on 23 Sep 2013 from 17:15 to 19:15
Type: Poster presentation
Session: Poster session

Content

The strength parameters of marine sediments play an important role in the assessment of seabed slope stability. Laboratory and in situ tests are usually utilized to determine the sediment strength for engineering purposes. However, for marine sediments in water depth over hundreds of meters, it becomes difficult to carry out in situ tests and obtain undisturbed sediment samples for laboratory tests. Back analysis of the failed slope is then usually adopted to obtain the representative shear strength of the sliding surface. Occurred in the offshore of SW Taiwan on 26 December 2006 with a magnitude of 7.0, the Pingtung earthquake had triggered numbers of submarine landslides (Hsu et al., 2008). This event provides an excellent opportunity to incorporate the back analysis approach to evaluate the representative in situ strength. In this study, two chirp sonar images of the seabed near the SW Xiaoliuqiu before (OR1-809, 29 Step. 2006) and after (OR1-820B, 8 Jan. 2008) the Pingtung earthquake are adopted to identify the location of sliding surface. It is indicated that the studied landslide resulted in a circular sliding surface. The dimensions of the landslide body are 330m in length and a maximum thickness of 30m. Utilizing the widely used software for slope stability (SLIDE 5.0; limit equilibrium method), the strength parameters under the critical condition (i.e. safety factor = 1) can be back calculated. The input parameters included unit weight (ϒ=17 kN/m3, the sediments sampled near the landslide site) and seismic coefficient for pseudo-static analysis (kh=0.067, and kv=0.033) related to the Pingtung earthquake (Central Weather Bureau, Rec. No. 95107). The results indicate that the friction angle (ϕ) of the sliding surface is 14∘with a cohesion (c) of 6 kPa. According to the infinite slope stability theory, the landslide with a thickness of 30m yields an undrain shear strength (Cu) of 37kPa under the critical condition. These evaluated strength parameters are close to the results obtained from the triaxial tests. Key words: submarine landslide, sediment strength, back analysis, Pingtung earthquake, SW Taiwan.

Place

Location: GEOMAR East shore
Address: Wischhofstr. 1-3 / D-24148 Kiel
Room: Lithothek

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