含水率及坡度对红壤丘陵区崩岗崩壁重力侵蚀影响规律的有限元分析

花岗岩崩岗区崩壁的坍塌、崩落，主要是由于崩壁岩土体存在裂隙，在雨水作用下，由重力作用引发崩壁失去稳态而崩塌，含水率和坡度是影响崩壁重力侵蚀( 稳定性) 的重要因素。为系统探索不同坡度的崩岗崩壁剖面在降雨或干旱环境下的稳定性情况，结合对湖北省通城县室内浸泡或风干不同时间的崩壁土体进行直剪试验得出的强度初始参数，选取 8 种分析坡度，采用 Abaqus 有限单元强度折减法计算了不同坡度的崩壁在不同含水率下的安全系数和潜在滑动面。结果表明: 在同一含水率下，随着崩壁坡度的增大，坡度对临界滑动面位置变化的影响程度减小，安全系数非线性降低; 在同一坡度下，随着崩壁含水率的增大，安全系数先增大后减小，含水率对临界滑动面的影响程度先减小后增大再减小，且影响比较显著。通过数据描点发现安全系数与整体含水率之间存在三次函数关系，与坡度之间呈对数型函数分布，并建立了安全系数与整体含水率和坡度之间的一般定量关系式。综合分析崩壁的破坏方式可知，当崩壁较缓时，崩壁滑动面呈圆弧滑移状，失稳类型属于滑移破坏型; 当崩壁较陡( 尤其＞60°) 时，滑动面近似直线状，失稳属于崩塌破坏型。坡度越大，张拉破坏区向土体内部延伸的深度越大，越易崩塌。通过查阅文献并与前人的研究成果做对比，来验证数值计算结果的合理性与适用性。成果可为崩岗灾害的防治体系建设提供借鉴。

Analysis on influence of water content and slope gradient on gravitational erosion of collapsing gully wall in red soil hilly region with finite element method( FEM)

The instabilities of the collapse wall profiles in granite collapse region are mainly due to the infiltration of rainwater in to the cracks in the back edge of the headwall in the early stage，which softens the mechanical strength of surface soil mass of caved wall，and then the collapse of collapsing gully wall will occur under the action of gravity. The slope gradient has a certain effect on the collapsing mound gravitational erosion，and water content is one significant factor affecting the stability of the collapse wall as well. In order to comprehensively explore the relationship between moisture content or slope gradient and gravitational erosion ( stability) of collapse gully profiles，we design eight kinds of analysis slope gradients combined with field investigation and conduct natural air drying or water immersion tests for different periods on the collected soil mass of collapsing gullies in Tongcheng County，subsequently，obtaining finite element calculation parameters through geotechnical tests of soil samples. By means of SＲM based on ABAQUS software platform，we calculate the safety factor ( denoted as Fs) and potential sliding surface of collapse mound profiles respectively under forty-eight working conditions. The results demonstrate that: ( 1) when controlling water content remains unchanged， the influence level of slope gradient on the change of critical sliding surface position of the collapsing gully profile decreases gradually along with the increase of slope gradient，while a logarithmic function relationship is there between the Fs of collapse wall and slope gradient; ( 2) under the condition that slope gradient is maintained at a constant value， the influence degree of moisture content on sliding surface decreases with the increase of moisture content of the collapsing gully wall， then increases and finally reduces，which is obvious to some extent. Based on discovering the existence of cubic function distribution between Fs and integral moisture content via fitting the data，we further establish the general quantitative formula for estimating Fs utilizing integral moisture content and slope gradient through careful deduction; ( 3) by probing further into the failure types of collapse wall comprehensively thus come to conclusion that when slope gradient is less than a certain value，potential sliding surface of collapsing mound profile appears a circular arc shape， instability mode belongs to the sliding failure type;when the collapsing gully wall is steeper comparatively ( especially when slope gradient exceed 60 degrees) ，sliding surface exhibits approximately linear sliding surface， instability mode belongs to the collapsing type. The greater the slope gradient is， the greater the depth of the tensile failure zone to the interior of the soil is，and the more likely it is to collapse. At last， the reasonableness and practicability of the numerical results are identified by comparative analyses between the previous research findings and measured data through referring to related academic articles. The study achievements shows clearly an unambiguous direction and technical guidance for the prevention and control measures of collapsing gullies.