Comparative analysis of contributing parameters for rainfall-triggered landslides in the Lesser Himalaya of Nepal

In the Himalaya, people live in widely spread settlements and suffer more from landslides than from any other type of natural disaster. The intense summer monsoons are the main factor in triggering landslides. However, the relations between landslides and slope hydrology have not been a focal topic in Himalayan landslide research. This paper deals with the contributing parameters for the rainfall-triggered landslides which occurred during an extreme monsoon rainfall event on 23 July 2002, in the south-western hills of Kathmandu valley, in the Lesser Himalaya, Nepal. Parameters such as bedrock geology, geomorphology, geotechnical properties of soil, and clay mineralogy are described in this paper. Landslide modeling was performed in SEEP/W and SLOPE/W to understand the relationship of pore water pressure variations in soil layers and to determine the spatial variation of landslide occurrence. Soil characteristics, low angle of internal friction of fines in soil, medium range of soil permeability, presence of clay minerals in soil, bedrock hydrogeology, and human intervention were found to be the main contributing parameters for slope failures in the region.     

不同降雨条件下黄土高原浅层滑坡危险性预测评价

黄土地区浅层滑坡发育非常广泛,由于其具有分布规律性差、前期变形迹象小、分布范围大、面小点多等特征,目前还无法进行有效预测,因此给黄土地区工程安全带来严重威胁。根据无限边坡模型,结合降雨入渗-土体强度衰减规律和GIS（地理信息系统）技术,构建了不同降雨条件下黄土地区浅层滑坡发育危险性评价模型,并将该评价模型应用到延河一级支流幸福川流域,预测在有效降雨量30、50、100、200 mm条件下,该流域浅层滑坡发育程度,并与当前较为流行的SINMAP模型(地形稳定性模型)进行对比。结果表明：①不稳定和潜在不稳定浅层滑坡主要分布在末级河流的两侧和源头,稳定和较稳定区域主要分布在一级河流河道两侧和塬面上;通过对比分析,SINMAP模型计算的结果与本文建立的模型在降雨强度30 mm时的计算结果较为一致。②在本文建立的模型评价结果中,随着有效降雨量的增加,F_s（稳定性系数）<1.00的不稳定区域所占比例逐渐增加,从30 mm的1.12%到200 mm的4.79%;相反,稳定区域则出现逐渐减少的趋势。③根据已发生灾害点的分布,随着有效降雨量的增加,研究区域已发生的灾害点分布在F_s<1.25的比例明显增加,从30 mm的62%到200 mm的88%,在SINMAP评价模型中,研究区域已发生的灾害点的64%分布在不稳定和潜在不稳定区域内,说明本文所建立的评价模型具有一定的精度。通过与SINMAP评价模型对比,本文建立的模型主要采用基于降雨入渗规律,而SINMAP评价模型主要基于降雨汇流过程,因此在利用过程中应根据区域特征选择利用。     

典型滑坡监测点优化布置

利用数值模拟技术与模糊模式识别算法提出了滑坡监测点优化布置的基本方法。以链子崖危岩体为例,以Ⅳ-Ⅳ′剖面作为滑坡监测点优化布置的典型剖面,根据监测变量（位移）对外界干扰因素作用下的灵敏度大小与监测信息量获取大小之间的关系,对该危岩体的监测变量（位移）进行了灵敏度分区研究,进而对该典型剖面的监测点进行了优化设计。研究结果表明,链子崖危岩体地表位移监测点宜布置在位移量明显和状态变化灵敏度较高的部位,深部位移监测钻孔宜穿越所有水平位移变化的灵敏区域。     

Erosional power in the Swiss Alps: characterization of slope failure in the Illgraben

Landslides and rockfalls are key geomorphic processes in mountain basins. Their quantification and characterization are critical for understanding the processes of slope failure and their contributions to erosion and landscape evolution. We used digital photogrammetry to produce a multi‐temporal record of erosion (1963–2005) of a rock slope at the head of the Illgraben, a very active catchment prone to debris flows in Switzerland. Slope failures affect 70% of the study slope and erode the slope at an average rate of 0.39 ± 0.03 m yr¯¹. The analysis of individual slope failures yielded an inventory of ~2500 failures ranging over 6 orders of magnitude in volume, despite the small slope area and short study period. The slope failures form a characteristic magnitude–frequency distribution with a rollover and a power‐law tail between ~200 m³ and 1.6 × 10⁶ m³ with an exponent of 1.65. Slope failure volume scales with area as a power law with an exponent of 1.1. Both values are low for studies of bedrock landslides and rockfall and result from the highly fractured and weathered state of the quartzitic bedrock. Our data suggest that the magnitude–frequency distribution is the result of two separate slope failure processes. Type (1) failures are frequent, small slides and slumps within the weathered layer of highly fractured rock and loose sediment, and make up the rollover. Type (2) failures are less frequent and larger rockslides and rockfalls within the internal bedded and fractured slope along pre‐determined potential failure surfaces, and make up the power‐law tail. Rockslides and rockfalls of high magnitude and relatively low frequency make up 99% of the total failure volume and are thus responsible for the high erosion rate. They are also significant in the context of landscape evolution as they occur on slopes above 45° and limit the relief of the slope. Copyright © 2012 John Wiley & Sons, Ltd.     

基于加卸载响应比理论的降雨型滑坡预警研究

在建立边坡远程实时监测系统并获得变形与降雨量连续监测数据的基础上,运用加卸载响应比理论的基本原理,提出以一用为加卸载周期、将日降雨量及其变化作为边坡的加卸载参数、相应的日平均变形速率及其变化值为加卸载响应参数,建立了基于加卸栽响应比的降雨型滑坡短周期预警模型。以某公路边坡为例,运用加卸载响应比预测模型对边坡的2个监测点进行了加卸载响应比计算,发现2个点的加卸载响应比时序曲线与其稳定性动态演化规律相吻合。研究结果表明,可以运用该模型进行降雨型滑坡短周期预测预警。     

金沙江水电站工程区典型单体滑坡风险评价探讨

在对金沙江流域内的部分大型水电站工程区内的滑坡分析基础上,以两个滑坡为例,针对水电站工程区讨论了单体滑坡的风险评价方法。选取滑坡稳定性,规模和可能造成的涌浪高度3个指标进行危险性评价;并且定性地将大坝的易损性确定为高、中、低三个等级。在此基础上,对研究区的牛滚函滑坡和东岳庙滑坡进行了危险性分析和易损性评价,得出这两个单体滑坡的风险分析结果：牛滚函滑坡为低度风险,东岳庙滑坡为中度风险。研究成果为水电站工程区滑坡减灾防灾与风险管理提供了科学依据。     

基于数值模拟的三峡库区典型堆积层滑坡变形预测方法

目前对堆积层滑坡的变形预测大多基于数学模型或方法,忽略了引起滑坡位移显著变化的动力外因及滑坡自身的地质特征,因此,预报准确度和可信度较低。以三峡库区典型堆积层滑坡--鹤峰场镇滑坡为例,通过4组主要控制因素科学组合构建了滑坡的基本地质模型;以此为基础,重点考虑引起滑坡发生变形的库水作用动力因素,建立滑坡的数值-力学模型。通过实际监测点的变形监测结果与数值-力学模型中模型监测点的变形进行拟合分析,获取了实际时间与数值-力学模型中时步的等效关系;基于时间-时步等效关系及三峡水库设计水位调度曲线,得到了不同时步水位的波动特征;通过时步的外延,并在相应的时步段对数值-力学模型施加等效时间的库水作用,预测了滑坡在未来库水位变动条件下的变形。该预测方法既考虑了滑坡的工程地质模型又考虑了地下水作用效应,克服了纯数学方法预测的不足。     

滑坡降雨阈值模型的应用

在数字高程模型（DEM）的基础上,运用滑坡降雨阈值模型,以楚雄丁家坟一斜坡作为试验研究工点,结合现场勘察、监测数据以及斜坡岩土体主要特性、地形地貌、降雨强度与降雨持续时间、地下水位等因素,模拟斜坡单元产生潜在滑动时的临界降雨量,研究降雨对滑坡发生、分布的影响。研究结果表明：各斜坡单元产生潜在滑动时的临界降雨量各不相同,在不同的降雨量及地下水位条件下滑坡降雨阈值模型模拟的潜在滑坡位置主要位于楚勐公路下边坡处,与实际发生滑坡的位置吻合率达80%以上,滑坡降雨阈值模型可实现对斜坡稳定性进行可视化分析与预测,为降雨型滑坡提供一种有效的预测与分析方法。     

Gigantic low-gradient landslides in the northern periphery of the Crimean Mountains (Ukraine)

Large-scale, low-gradient ancient landslides estimated at 5.4–18.9 km² in area and  0.2–1.2 km³ in volume have been studied in the northern hilly periphery of the Crimean Mountains (Ukraine). They originated on slopes along wide water gaps of rivers (Belbek, Kacha, Alma and Biyuk–Karasu) crossing the cuestas of the northern foothills. The slopes generally consist of slightly northward tilting Miocene (mainly Sarmatian) limestones overlying weak, clay-rich Lower Neogene–Palaeogene substratum with a significant content of smectite. Although the region is characterised by the least active contemporary morphodynamics within the Crimean Mountains, the landslides which were studied are of the same size or even larger than various types of landslides occupying active geomorphic domains of the highest mountain range in the southernmost part of the peninsula. The landslides are generally a spreading type, but the sliding mechanics were probably very complex, involving toppling, rotational slides, gravitational folding and translational block slides. All the landslides which were studied are located in the vicinity of regional faults and three of them have headscarps aligned along faults. A common feature is also a location close (within several km) to the Mesozoic suture zone which is the most important tectonic feature in the northern periphery of the Crimean Orogene. This suture was formerly classified as aseismic; however, evidence of strong, low-frequency palaeoearthquakes was collected during the last decade within both the Mesozoic suture and the low-lying northern part of the Crimean Peninsula. Radiocarbon dating of deposits associated with the landslides has revealed at least two phases of increased landslide-activity during the Late Glacial chronozone and Holocene epoch. The main landslide phase presumably took place at some time between the Late Glacial and Atlantic chronozones. Minor reactivation of landslide toes occurred during the Subatlantic chronozone and some of them have been active up to recent times. The first major landslide phase was possibly triggered by an earthquake, whereas late Holocene activity can be attributed both to seismic and hydroclimatic factors.     

激光雷达测量技术在地学中的若干应用

对激光雷达测量技术在全球冰川监测、局部断裂带提取、滑坡监测和稳定性评价以及海岸线提取和海岸侵蚀等方面的应用做了较为全面的综述.作为一种新型的对地观测手段,激光雷达(含星载、机载、车载和地面)的应用已经从传统的测绘扩大到包括文物保护在内的诸多其他应用领域.所综述的激光雷达技术在地学研究中的4个应用方面,是传统地学研究中与全球变化和人居环境最为密切的方向.分析表明,激光雷达技术在这些研究方向中的应用大有作为.