| Citation: |
SHI Xingxing, CUI Shenghua, PEI Xiangjun, ZHU Ling, YANG Qingwen. A study of the pro-water pressure for initiation of a large landslide triggered by a strong earthquake based on fluid-structure coupling[J]. Hydrogeology & Engineering Geology, 2022, 49(2): 102-114. doi: 10.16030/j.cnki.issn.1000-3665.202104052
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A study of the pro-water pressure for initiation of a large landslide triggered by a strong earthquake based on fluid-structure coupling
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Abstract
The Daguangbao landslide is the largest co-seismic landslide with a volume of approximately 12×108 m3, which triggered by the Wenchuan earthquake (Ms 8.0) occurred on May 12, 2008. The slide zone is located in the Paleozoic carbonate strata and it is an interlayer structural dislocation zone with a depth of 400 m and a maximum thickness of 5 m inside the slope. A previous study concluded that the shear failure of the Daguangbao landslide developed within the bedding fault. Our latest investigation showed that this bedding fault was under the water table, and its rock mass was saturated before the landslide. To reveal the initiation mechanism of the Daguangbao landslide related to the groundwater, a simplified model of a hard carbonate slope with an inter-weak layer is given. The response characteristics of the model are stimulated by a fluid-structure coupling algorithm using the FLAC3D. The results show that significant differences in deformation patterns during the earthquake, such as response time, wave shape, and amplitude exist between the upper and lower hard layers. Three uncoordinated deformation patterns, i.e., tension, compress, and shearing coming from the upper layer to the weak layer, are identified. The deformation pattern results in the amplification of compress and shear forces within the weak layer. The stress amplification subsequently induces excess pore water pressure with instant amplification and accumulation features. It is reasonably inferred that the excess pore water pressure essentially reduces the effective stress of the bedding fault. Our simulation confirms that the excess pore-water pressure can be generated within a saturated bedding fault deep situated in a slope during a strong earthquake. We propose that the excess pore water pressure within the saturated fault at 400 m underground is the cause of the Daguangbao landslide.
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References
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SHI Xingxing, CUI Shenghua, PEI Xiangjun, ZHU Ling, YANG Qingwen. A study of the pro-water pressure for initiation of a large landslide triggered by a strong earthquake based on fluid-structure coupling[J]. Hydrogeology & Engineering Geology, 2022, 49(2): 102-114. doi: 10.16030/j.cnki.issn.1000-3665.202104052
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Figure 1.
Geological map profile of the Daguangbao landslide[14]
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Figure 2.
Water-saturated interlayer structural dislocation zone
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Figure 3.
Diagram showing the model size and free field boundary
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Figure 4.
Distribution map showing the model monitoring points
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Figure 5.
Dynamic triaxle test (the confining pressure is 100 kPa and the cyclic deviatoric stress is 100 kPa)
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Figure 6.
Vertical stress field before the earthquake
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Figure 7.
Pore water pressure field before the earthquake
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Figure 8.
Oscillation curve of the model displacement
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Figure 9.
Dynamic load applied by the model
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Figure 10.
Acceleration response curves without groundwater level
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Figure 11.
Acceleration response curves with groundwater level
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Figure 12.
Instantaneous displacement responses curve without groundwater level
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Figure 13.
Instantaneous displacement response curves with groundwater level
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Figure 14.
Stress response curves without groundwater level
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Figure 15.
Stress response curves with groundwater level
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Figure 16.
Response curves of pore water pressure in a slope body
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Figure 17.
Pore water pressure distribution under vertical wave action
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Figure 18.
Uncoordinated deformation
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Figure 19.
Response mechanism of pore water pressure in the weak zone
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Figure 20.
Vibration stamping effect of the weak zone results in the accumulation of pore water pressure (11.5 s)
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Figure 21.
Vibration tensioning effect of weak zone results in the dissipation of pore water pressure (4.5 s)
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Figure 22.
Simplified mechanical model
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Figure 23.
Effective stress response curves of the weak zone
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Figure 24.
ZX-direction shear stress of seismic acceleration in both directions (groundwater conditions are not considered)
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Figure 25.
ZX-direction shear stress of seismic acceleration in both directions (groundwater conditions are considered)