Hillslope–channel sediment transfer in a slope failure event: Wet Swine Gill,Lake District,northern England

This paper describes and analyses a hillslope–channel slope failure event that occurred at Wet Swine Gill, Lake District, northern England. This comprised a hillslope slide (180 m³, c. 203 ± 36 t), which coupled with the adjacent stream, resulting in a channelized debris flow and fluvial flood. The timing of the event is constrained between January and March 2002. The hillslope failure occurred in response to a rainfall/snowmelt trigger, on ground recently disturbed by a heather moorland fire and modified by artificial drainage. Slide and flow dynamics are estimated using reconstructed velocity and discharge values along the sediment transfer path. There is a rapid downstream reduction in both maximum velocity, from 9·8 to 1·3 m s^?1; and maximum discharge, ranging from 33·5 to 2·4 m³ s^?1. A volumetric sediment budget quantified a high degree of coupling between the hillslope and immediate channel (～92%: 167 m³), but virtually all of the sediment was retained in the first‐order tributary channel. Approximately 44% (81 m³) of the slide volume was retained in the run‐up deposit, and termination of the debris flow prior to the main river meant that the remainder did not discharge into the fluvial system downstream. These results suggest poor transmission of sediment to the main river at the time of the event, but importantly an increase in available material for post‐event sediment transfer processes within the small upland tributary. Copyright © 2007 John Wiley & Sons, Ltd.     

Effects of forest harvesting on the occurrence of landslides and debris flows in steep terrain of central Japan

Landslides and debris flows associated with forest harvesting can cause much destruction and the influence of the timing of harvesting on these mass wasting processes therefore needs to be assessed in order to protect aquatic ecosystems and develop improved strategies for disaster prevention. We examined the effects of forest harvesting on the frequency of landslides and debris flows in the Sanko catchment (central Japan) using nine aerial photo periods covering 1964 to 2003. These photographs showed a mosaic of different forest ages attributable to the rotational management in this area since 1912. Geology and slope gradient are rather uniformly distributed in the Sanko catchment, facilitating assessment of forest harvesting effects on mass wasting without complication of other factors. Trends of new landslides and debris flows correspond to changes in slope stability explained by root strength decay and recovery; the direct impact of clearcutting on landslide occurrence was greatest in forest stands that were clearcut 1 to 10 yr earlier with progressively lesser impacts continuing up to 25 yr after harvesting. Sediment supply rate from landslides in forests clearcut 1 to 10 yr earlier was about 10‐fold higher than in control sites. Total landslide volume in forest stands clearcut 0 to 25 yr earlier was 5·8 × 10³ m³ km^?2 compared with 1·3 × 10³ m³ km^?2 in clearcuts >25 yr, indicating a fourfold increase compared with control sites during the period when harvesting affected slope stability. Because landslide scars continue to produce sediment after initial failure, sediment supply from landslides continues for 45 yr in the Sanko catchment. To estimate the effect of forest harvesting and subsequent regeneration on the occurrence of mass wasting in other regions, changes in root strength caused by decay and recovery of roots should be investigated for various species and environmental conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

降雨作用下碎石土滑坡解体变形破坏机制研究

为了揭示碎石土滑坡的变形解体破坏机制,结合工程实例,通过资料搜集整理和分析、现场工程地质调查与勘探和室内外的物理力学试验,采用不平衡推力法、数理统计分析方法和三维弹塑性接触有限元算法,以及运用碎石土边坡地下水管网状排泄系统理论,分析降雨作用下碎石土滑坡的变形解体破坏过程,揭示了降雨作用下中深层碎石土滑坡变形解体破坏的主要机制和一般的力学机制。结果表明,一定强度的长时间连续降雨或强降雨是中深层碎石土滑坡发生失稳的主要触发因素;采用考虑降雨作用的弹塑性接触有限元算法,可以更好地反映该类型滑坡在降雨作用下所处的实际状态及滑坡的滑动过程,可以为该类型滑坡稳定性的准确评价和预测预报提供可资借鉴的方法。     

清江水布垭库区大堰塘滑坡涌浪分析

2007年6月15日位于水布垭水库巴东县清太平镇的大堰塘滑坡发生滑动,激起高达50 m的巨大涌浪,造成了沿岸的人员伤亡。为了解决大堰塘滑坡引起的涌浪问题,把滑坡引起的涌浪分为体积涌浪和冲击涌浪两部分。根据体积守恒原理及块体水下运动的位移公式求出了初始涌浪的计算公式。把滑坡涌浪衰减过程分为急剧衰减和缓慢衰减两个阶段来考虑,并认为急剧衰减阶段的涌浪的衰减符合指数衰减规律,缓慢衰减阶段符合明槽水流的沿程水头损失规律,对其涌浪的传播和爬坡进行了深入探讨,并与实际调查结果进行了对比分析,该成果对水库库岸滑坡的涌浪传播的研究具有一定的参考意义。     

岩土体物理力学参数对岩质滑坡稳定性的影响

采用有限元-极限平衡法研究了含软弱滑动带的岩质滑坡滑动体、滑动带和滑床的密度、弹性模量和泊松比及滑动带的抗剪强度对滑坡稳定性的影响。结果表明:滑床密度、滑体及滑动带的弹性模量、滑动带及滑床的泊松比和滑动的抗剪强度指标与滑坡稳定性系数呈正相关关系,而滑体及滑动带土体密度、滑床的弹性模量和滑体的泊松比与滑坡稳定性系数呈负相关关系;软弱滑动带的抗剪强度对滑坡稳定性的影响最显著,其次为软弱滑动带的泊松比和滑床的弹性模量,其他参数的影响相对较小。      

基于集对分析的滑坡变形动态建模研究

滑坡是一个确定-不确定的动态系统,其变形表现出复杂的非线性演化特征。为了克服传统分析方法在处理系统不确定性方面的不足,将集对分析法（SPA）引入岩土变形监测分析领域,并结合层次分析法（AHP）提出了滑坡变形动态预测模型,给出了基于概率论的最优预测算法,提出并证明了集对论中最大同一度在等势条件下存在极限解,据此提出位移势的概念。在位移势的基础上,进行SPA二次建模,提出了基于SPA的滑坡变形与水库蓄水过程相关性动态分析模型。运用上述预测模型对新近发生的刘家沱滑坡进行变形监测定量分析,实践证明：最优预测值具有良好的短期预报精度;位移势能够表征系统当前状态下位移所能达到的最大潜力,可作为短期预测的上限值,其变化能够反映系统宏观层面上的演化特征,对滑坡演变加速预警具有指导意义;运用集对分析方法进行滑坡变形响应滞后效应的定量研究是一条可行的新思路,反演结果与实际情况吻合;该方法在岩土监测分析领域有良好的应用前景。     

滑坡次生灾害损失评估方法研究

针对目前滑坡灾害破坏损失评估研究还没有涉及滑坡次生灾害破坏损失评估方面的研究,提出并建立了滑坡次生灾害破坏损失的评估模型与方法。应用故障树分析法（FTA）和事件树分析法（ETA）相结合的因果图方法对滑坡次生灾害作可靠性分析,由此对滑坡次生灾害损失进行了预测及评估。     

时间域反射法用于滑坡监测的试验研究

依据时间域反射测试技术（TDR）的基本原理,提出了TDR技术在滑坡监测中的野外工作方法。为了更好地了解电缆的变化规律,进行了室内试验。结合实际应用,给出了TDR监测滑坡的野外应用实例。通过对室内模拟试验和野外应用试验数据的分析、对比,讨论了TDR监测滑坡的实际应用效果和有效性。研究结果表明,与传统的滑坡监测方法相比较,TDR用于滑坡监测的技术方法比较新颖,具有节省时间、成本低廉、定位准确等特点。由此可见,TDR用于滑坡监测,能够实现快速、实时、连续监测。     

用FLAC-3D分析呷爬滑坡的变形特征

简单地介绍了边坡岩体变形研究的现状和FLAC-3D软件,利用FLAC-3D软件对天然状态下和蓄水条件下呷爬滑坡的变形进行数值模拟研究。根据模拟所得的计算结果,从滑坡主剖面上特征点的位移值和位移矢量图分析,得出滑坡体在天然状态下和不同蓄水高程下的变形特征,确定滑坡变形特征与滑坡稳定性之间的联系。从而为呷爬滑坡的稳定性评价提供必要的理论依据。     

万州侏罗纪红层软弱夹层特征

在万州侏罗纪红层中,连续分布多层产状稳定、厚度较大的软弱夹层。经X射线衍射分析、红外光谱分析及扫描电镜观察：软弱夹层主要矿物成分为蒙脱石、长石、α-石英、伊利石、绿泥石等;其微观结构以片状结构为主,微裂隙和微孔隙发育,有少量网格结构,局部可见粘土矿物定向排列。野外调研表明：软弱夹层曾经受较强的构造挤压作用,部分已发生层间剪切破坏,从而导致剪切强度降低。对软弱夹层的物理力学性质进行试验研究可知：软弱夹层为中等膨胀性土;且一旦遇水饱和,其剪切强度将大幅度下降。这些特征说明,在特定的条件下,软弱夹层容易成为基岩滑坡的滑动面。