重庆缙云山森林火灾干扰边坡的滑坡易发期预测  

Prediction of landslide prone period for forest fire disturbed slope in Jinyun Mountain,Chongqing of China

作　　者：李通 王云琦[1,2] 祁子寒 何相昌 李克文 LI Tong;WANG Yunqi;QI Zihan;HE Xiangchang;LI Kewen(Three-gorges Reservoir Area(Chongqing)Forest Ecosystem Research Station,School of Soil and Water Conservation,Beijing Forestry University,Beijing 100083,China;Chongqing Jinyun Mountain Three Gorges Reservoir Area Forest Ecosystem Positioning Observation and Research Station,School of Soil and Water Conservation,Beijing Forestry University,Beijing 100083,China)

机构地区：[1]北京林业大学水土保持学院重庆三峡库区森林生态系统教育部野外科学观测研究站,北京100083 [2]北京林业大学水土保持学院重庆缙云山三峡库区森林生态系统国家定位观测研究站,北京100083

出　　处：《农业工程学报》2023年第9期131-141,共11页Transactions of the Chinese Society of Agricultural Engineering

基　　金：国家自然科学基金项目“降雨条件下植物根系动态固土护坡效应研究”(31971726);北京林业大学热点追踪项目“重庆缙云山森林火灾调查和灾后植被恢复重建研究”(2022BLRD11)。

摘　　要：为明确缙云山火灾后边坡的失稳机制并预测未来滑坡风险,该研究通过对火林地根-土体物理性质勘测和试验,借鉴森林砍伐与根系强度预测模型-SIDLE曲线模型预测了根系强度的衰减和恢复动态,并采用COMSOL模拟了未来40 a林地边坡在正常状态和极端降雨事件后的稳定性动态。结果表明:(1)缙云山林缘边坡为约1.5 m厚的砂质壤土-砂质泥岩双层土坡结构,上下层渗透性和土体强度差异悬殊;(2)林缘边坡在自然状态下处于稳定状态,潜在滑动面位于深层(稳定系数FOS>2);极端降雨条件下,潜在滑动面位于土层结构面上,该处易出现带状积水,正孔隙水压力约10 kPa,极端降雨后无根系状态临界FOS为1.13,根系固土状态下临界FOS为1.32;(3)火灾发生后对自然状态下边坡深层稳定性影响较小,而极端降雨后边坡浅层稳定性随火灾后的年动态呈现快速降低而后缓慢恢复的趋势,期间FOS谷值处便出现长达数年的浅层滑坡易发期。缙云山林缘边坡的失稳机制为降雨过程中土层界面处正孔隙水压力积累弱化了有效应力。结合文献已有灌木根系数据和本区植物根系固土特性和土层特征,保守估计该次火灾发生后6~9 a为滑坡易发期,FOS为1.22~1.32,至少18~24 a后才可完全恢复至火灾前的稳定条件。研究结果有助于了解区域浅层滑坡形成机制,为火后森林恢复和边坡风险评估提供初步参考。The Jinyun Mountain forest fire event in August 21 to 26,2022 has attracted extensive attention in China.The forest fire hazard has a long-term impact on the nature soil of forest plant and soil.In addition to the mechanism and prevention measures of forest fire,the safety prediction for post-hazards(such as landslide)can also be one of the most urgent tasks at present.But now,the main challenge is the long-term estimation of dynamical root reinforcement for the lack of monitoring data on plant root death and regrowth post fire.This study aims to clarify the mechanism of forest slope failure,and then to predict the landslide risk post fire.The field and lab tests were performed on the physical properties of root soil in the burned woodland in the Hutou Village near Jinyun Mountain.The SIDLE curve model was selected to predict the dynamics of root reinforcing strength after forest timber harvesting.Finally,the simulation was conducted for the post-40 years slope stability using COMSOL.Specifically,a double-layer slope model was assembled,according to the surveyed slope size and soil property.A systematic analysis was made on the root strength time inflection points of common trees and shrubs in published literature and according to which the SIDLE parameters of shrub in this work were inversed and dopted for simulation work of slope deformation and stability in the future.Both the general and extreme rainfall conditions with an intensity of 80 mm/d were considered in the simulation.The results show that:(1)The common type of forest margin slope in Jinyun Mountain was characterized by the double-layer soil slope structure consisting of sandy loam and deeper sandy mudstone.There was a significant difference in the magnitude of average conductivity and shear strength parameters between the upper sandy loam and lower layer sandy mudstone.The conductivity of the surface layer was 5.2×10^(−6) m/s on average,3.47 times that of the lower layer.The cohesion and internal friction angle of the surface layer were 5.5 kPa a

关 键 词：边坡失稳 降雨 入渗 森林火灾 根系固土 流固耦合 边坡稳定 

分 类 号：S152.7[农业科学—土壤学]