贺兰山水土保持功能乔木根系锚固土壤作用与数值模拟研究

Helan Mountain is a geological hazard prone area and ecological shelter in Yinchuan plain. Plants have been widely used for controlling shallow landslides and soil and water loess in this area. In order to reveal the mechanisms of soil reinforced by plant roots and built a finite element numerical model to simulate root reinforcement mechanism on slope stability, Picea crassifolia, Pinus tabuliformis and Populus davidiana root system were selected as the research object. These are the most important soil and water conservation trees in Helan Moutain. In this study, several representative test pits were excavated in the field to survey the morphology of the root system and a series of laboratory tests were carried out to evaluate the anchorage resistance of roots. The single root specimens for each species were tested for tensile strength measurement and root-soil composite shearing tests were also performed to determine roots-soil interaction. Based on the numerical simulation of root-soil interaction, this paper will develop a three-dimensional finite element model to analyse the stability of forested slope. In the model strength reduction method was used to calculate the Factor of Safety (Fs) of the different slope types under extreme conditions. The Relative Factor of Safety (RFs) was introduced to quantify the reinforcement effect of the different forest root sysytem on the stability of slope. The successful implement of this research could play a key role in understanding the nature of root reinforcement, promoting the numerical simulation study on root-soil interaction and preventing the shallow landslides and soil and water loess in Helan Mountain.

贺兰山是银川平原重要的生态屏障和风景名胜区，也是滑坡等地质灾害多发区，目前植物措施已逐渐成为该地区主要的浅层滑坡和水土流失防治技术。为了揭示贺兰山水土保持功能乔木根系锚固土壤的作用机理和建立贺兰山造林边坡稳定性分析的有限元数值模型。本研究选取青海云杉、油松和山杨3种贺兰山最重要的固土、护坡乔木根系为研究对象，将试验研究与数值模拟相结合，从而更深入的探索乔木根系与土壤相互作用的力学机制和过程；尝试将构建的根-土相互作用有限元数值模型应用到贺兰山造林边坡稳定性分析实践中，利用强度折减法计算不同类型边坡在极端条件下的安全系数（Fs），并引入相对安全系数（RFs）量化不同林木根系对边坡的锚固作用。本项目的实施对于解释林木根系锚固土壤作用的本质、推进根-土相互作用的数值模拟研究、防治贺兰山浅层滑坡灾害及水土流失具有重要意义。

贺兰山是银川平原重要的生态屏障和风景名胜区，也是滑坡等地质灾害多发区，目前植物措施已逐渐成为该地区主要的浅层滑坡和水土流失防治技术。山杨、青海云杉、油松是贺兰山地区最主要的3种水土保持乔木树种，为了揭示这3种乔木树种在降雨条件下的固坡机理和科学评价3种乔木的固坡能力，本项目通过对3种乔木根系的单根生物力学特性研究、根土复合体的抗剪强度研究、根土复合体的渗透特性研究、贺兰山水土保持林边坡稳定性有限元模型构建和计算等研究结果，综合分析了山杨、青海云杉、油松3种乔木根系锚固土壤和在降雨条件下稳定边坡的作用。结果表明：（1）3种乔木的单根力学特性（最大拉力、抗拉强度、杨氏模量）存在极显著差异。平均最大拉力排序为：山杨（0.38 kN）＞青海云杉（0.25 kN）＞油松（0.17 kN）；平均抗拉强度排序为：山杨（33.39 MPa）＞青海云杉（27.79 MPa）＞油松（18.45 MPa）；平均杨氏模量排序为：山杨（0.17 GPa）＞青海云杉（0.12 GPa）＞油松（0.11 GPa ）。（2）3种乔木根土复合体的黏聚力存在显著差异，但摩擦角没有显著差异。山杨根土复合体的黏聚力（10.65±1.03）kPa ＞青海云杉（8.97±1.36）kPa）＞油松（7.13±1.02）kPa；3种乔木根土复合体的渗透性存在显著差异，相同条件下根土复合体的饱和渗透系数：山杨（26.87 mm/h）＞油松（26.57 mm/h）＞青海云杉（10.99 mm/h）。（3）根据有限元模型的模拟结果，3种乔木固坡能力大小与降雨强度和边坡坡度有密切关系；随坡度增大乔木的固坡能力有相对增加的趋势，但随降雨强度增大，乔木的固坡能力有相对减弱的趋势。除了用降雨条件下的边坡破坏时间，还可用边坡破坏时的平均位移反映乔木的固坡能力，两者的结果可以相互参照。（4）从3种乔木单根生物力学特性、根土复合体力学特性、降雨条件下的边坡稳定性等方面综合评价结果为：山杨的固坡能力＞云杉＞油松。本项目的实施对于揭示林木根系锚固土壤作用的本质、推进根-土相互作用的数值模拟研究和防治贺兰山浅层滑坡灾害及水土流失具有重要意义。