三峡库区溪沟湾滑坡的诱发因素及前期降雨影响

多年来的监测数据表明溪沟湾滑坡加速变形时总伴随着季节性降雨和库水位变动, 难以辨别滑坡变形的主导诱发因素, 对风险分析带来了挑战。鉴于此, 论文首先采用邻域粗糙集模型中的属性约简算法, 对溪沟湾滑坡活跃区和非活跃区日变形速率与降雨、库水位和库水位变动速率因素之间的相关性进行了系统分析, 计算结果表明溪沟湾滑坡活跃区变形主要受过去7日降雨因素影响, 并与短期库水位变化率因素存在关联性, 滑坡非活跃区的微弱变形与过去3日库水位变化率因素存在关联性。然后, 结合滑坡变形特征, 研究发现诱发溪沟湾滑坡活跃区剧烈变形的过去7天平均降雨量在20 mm左右, 库水位下降因素对其变形存在影响, 但影响较小, 而溪沟湾滑坡非活跃区的微弱变形主要受库水位波动影响。最后, 通过对溪沟湾滑坡进行渗流-力学数值计算分析, 结果揭示了溪沟湾滑坡活跃区受长历时前期降雨作用的变形机理。数值分析过程中, 当降雨强度由1 mm/d增至20 mm/d, 降雨造成滑坡体内部孔隙水压逐渐增大, 内部水位抬升并不断向滑坡活跃区延伸, 导致活跃区滑坡体由稳定状态降至欠稳定状态, 进而引发溪沟湾滑坡活跃区变形加剧。此外, 数值模拟结果也表明库水位下降因素对滑坡活跃区内部渗流场影响较小, 对其稳定性影响有限, 而库水位变动对滑坡非活跃区内部渗流场影响较大, 说明滑坡非活跃区的微弱变形主要受库水位波动影响。论文针对溪沟湾滑坡变形诱发因素的综合分析结果, 有助于对该滑坡进行风险预警, 可将过去7日平均降雨量20 mm作为诱发溪沟湾滑坡活跃区剧烈变形预警阀值之一。

Factors inducing the Xigouwan landslide in the Three Gorges Reservoir area and the influence of antecedent precipitation

Monitoring data over the years have shown that seasonal rainfall and reservoir level changes have always accompanied the accelerated deformation of the Xigouwan landslide, which makes it difficult to identify the dominant triggering factors of landslide deformation and poses a challenge to risk analysis. Given this, this paper analyzed the correlation between the daily deformation rate of the active and inactive areas in the Xigouwan landslide and rainfall, reservoir level, and the change rate of reservoir level by applying the attribute reduction algorithm of the neighborhood rough set model. The calculation results showed that the deformation in the active area was mainly affected by the rainfall in the past seven days. It was also related to the short-term change rate of reservoir water level in some ways. The weak deformation in the inactive area was related to the change rate of reservoir water level in the past three days. Then, based on the landslide deformation characteristics, it was further obtained that the average rainfall in the past seven days inducing severe deformation in the active area was about 20 mm. The decline of the reservoir water level influenced its deformation, but the effect was small. The reservoir level change affected the weak deformation in the inactive area with negligible influence, while the weak deformation in the inactive area was mainly influenced by the reservoir level change. Finally, the seepage-mechanics numerical analysis of the Xigouwan landslide reveals the deformation mechanism of the active area under long-duration early rainfall. As the rainfall intensity increased from 1 mm/d to 20 mm/d, the pore water pressure at the bottom of the landslide body gradually increased. The internal reservoir level rose and extended to the active area, which caused the landslide body in the active area to go from a stable state to an under-stable state, leading to large deformation in the active area. In addition, the numerical simulation results further showed that the decline of the reservoir level had little effect on the internal seepage field and the stability in the active area. The reservoir level change greatly influenced the internal seepage field in the inactive area, indicating that the weak deformation in the inactive area was mainly affected by the reservoir level change. The complete analysis results of factors inducing the Xigouwan landslide in this paper can help provide early warning. The average rainfall of 20 mm in the past seven days can be used as one of the early warning thresholds for severe deformation in the active area of the Xigouwan landslide.