高速远程崩滑动力学的研究现状及发展趋势

高速远程滑坡具有体积大、速度高、运动距离远等特点,严重威胁着山区居民生命安全和重大工程建设。滑坡的碎屑化作用是滑坡高速运动过程中非常普遍且十分重要的现象,是滑体运动与堆积过程中特殊内部结构形成的前提条件,也被认为是可能促进高速远程滑坡超强流动性的物理力学机理。尽管滑坡碎屑化机制已经成为滑坡动力学机理研究的热点科学问题,然而对于滑坡碎屑化过程是促进滑坡运动还是阻碍滑坡运动,目前仍存在极大的争议,争议的焦点在于岩石破碎本身是耗能过程,如何能促进滑坡整体的远程运动？本文首先详细总结高速远程滑坡碎屑化作用的沉积学特征,包括反粒序、拼贴构造和局部剪切带等碎屑化堆积结构特征方面的研究,论述这些碎屑化沉积结构对于滑坡动力学的指示;其次,讨论与分析了滑坡碎屑化过程的影响因素、碎屑化过程的减阻机制研究进展;最后,归纳并阐述了高速远程滑坡动力破碎耗能和滑坡减阻这一争议性问题,提出今后高速远程滑坡碎屑化运动机理研究所面临的关键科学问题。     

A mass movement origin for cirques

The glacial process of cirque initiation, whereby small initial hillslope hollows grow by nivation until snow can form glacier ice, and ice motion then enlarges the hollow to a fully developed cirque, appears to have difficulty explaining the creation of large cirques in the time available during Quaternary glaciations, at the rates at which glaciers are reported to erode rock, and in rapidly uplifting mountain ranges. It also has difficulty explaining the striking proliferation of cirques in Fiordland, South Island, New Zealand, an area of harder rock and less glaciation than the nearby cirque‐poor area of South Westland. Here we show that cirques can be initiated as large, deep‐seated, often coseismic rock slope failure source area depressions in which snow may accumulate to form cirque glaciers, which can then remove detritus from, smooth, and enlarge the cirque. We present an example of a classically shaped cirque that has never held a glacier. We show that many similarities between the locations, sizes and shapes of rock slope failure source area depressions and cirques are understandable on this basis, as is the occurrence of cirques in presently aseismic intraplate locations and their relative paucity in actively uplifting ranges. The extent to which cirques may be of mass movement origin has implications for their value as palaeoclimatic indicators. Copyright © 2006 John Wiley & Sons, Ltd.     

高速远程滑坡裹气流态化模型试验研究

为分析高速远程滑坡运动过程中碎屑流的裹气流态化特性,以汶川地震触发的谢家店子滑坡为原型,运用自行设计的流化床试验装置,开展了一系列高速远程滑坡碎屑流裹气流态化特性的试验研究。结果表明：(1) 对于颗粒粒径变化范围广(0.1～7 mm者均有)、颗粒形状极不规则、且底部细颗粒含量高的类滑坡碎屑,其床层压降随着供风量的增加并非呈线性增长趋势,而是表现出明显的气泡控制性特征,随堆积体内部气泡和气垫层位置的不同,堆积体各部位床层压降相差较大;(2) 当供风量较低时,碎屑堆积体整体稳定性较好,在堆积体表面仅可见有限气体逸散孔的分布;当供风量达到一定值后,堆积体内部流态化特性增强,可见砂质密云、气孔、纵向脊等一系列与高速远程滑坡实例中相类似现象的出现;(3) 对于滑坡类不规则颗粒,其间容易形成架桥现象,增强碎屑流整体稳定性,使气流不易扩散,在堆积体下方形成高压气垫层,产生空气擎托现象。     

Qualitative Analysis of Rock Avalanches Propagation by Means of Physical Modelling of Non-Constrained Gravel Flows

Summary This paper presents an experimental study of rock avalanches run-out and propagation carried out with a small-scale physical model at the EPFL Rock Mechanics Laboratory. Fall height, volume, releasing geometry and materials used for testing have been varied and their influence on deposit characteristics (such as length, width, height and morphology) and run-out has been studied. The experiments have shown that deposit morphology is dependent on the type of material used: sand or gravel. Sand deposit shape, regular and compact, is in accordance with many tests described in the literature, while Aquarium gravel deposit is closer to real cases such as the Six des Eaux Froides event (Switzerland). There is also a considerable difference in deposit morphology and dimensions when the event is the consequence of one large volume released at once or when the same volume is released at different times. In this latter case the final deposit characteristics do not depend on the entire failed volume but on the individual smaller ones. This behaviour is in agreement with the Randa event (Swiss Alps) which occurred over several hours. For all-in-once releases, run-out distance depends primarily on the volume. Fall height and releasing geometry have a small influence on run-out, but on the other hand a higher fall height leads to a different lateral spreading and to the development of two different propagation mechanisms of the sliding mass. Author’s address: Irene Manzella, Rock Mechanics Laboratory, Swiss Federal Institute of Technology, Lausanne, Switzerland     

Disentangling the impacts of exogenous disturbances on forest stands to assess multi-centennial tree-ring reconstructions of avalanche activity in the upper Goms Valley (Canton of Valais,Switzerland)

The purpose of dendrogeomorphic analyses is to amplify the signal related to the geomorphic process under investigation, and to minimize the noise induced by other signals in the tree-ring series. Yet, to date, no study accounts specifically for interferences induced by climate conditions or exogenous disturbances and which can, potentially, affect the quality of tree-ring based process reconstructions. In this paper, we develop a specific procedure allowing evaluation of the quality of reconstructions in five avalanche paths at Oberwald (Swiss Alps). The study is based on possible interferences between snow avalanches, climatic conditions and ecological signals in the tree-ring series. Analysis of past events was based on tree-ring series from 564 heavily affected, multi-centennial European larch trees (Larix decidua Mill.) growing near or next to the avalanche paths. A total of 2389 growth disturbances, such as scars, tangential rows of traumatic resin ducts, compression wood as well as abrupt growth suppressions or releases, were identified in the samples, indicating 43 destructive snow avalanches since AD 1780. At the same time, 31 potential events, which were detected with the conventional Shroder index value, were rejected from the final reconstruction due to potentially strong interferences between the different signals. This high rejection rate underlines the necessity to systematically–and carefully–discriminate ecological and climatic noise from avalanche-related disturbances. This discrimination is even more so crucial as a significant proportion of dendrogeomorphic studies in the Alps are based on L. decidua trees which are cyclically affected by larch budmoth outbreaks.     

1556年陕西关中华县特大地震地质灾害遗迹发育特征

1556年陕西关中华县8 1/4 级特大地震造成地表强烈变形破坏,灾害群发,伤亡惨重,是史载灾害极端严重的具有世界对比性的特大地震。地表现存的华县特大地震地质遗迹清晰完整,具有重要的地震灾害比较学意义和地震地质学研究价值。本文在深入调查关中盆地东部的渭南、华县、华阴、潼关等高烈度区地震地质遗迹的基础上,重点对发震断层、地震裂缝、地震山崩与地震滑坡等4类典型地质遗迹的发育特征进行了调查分析。结果表明,华县特大地震的典型地震地质遗迹的形成机理是地震动力与区域构造应力场、场地岩土体性质、地形地貌特征、水文地质等要素和作用的耦合结果。华县地震地质遗迹具有重要的科考科普价值和开发应用前景,应积极开展评价和保护工作,发挥地质遗迹的社会和经济效益。     

Landscape and sedimentary response to catastrophic debris avalanches, western Taranaki, New Zealand

Catastrophic volcanic debris avalanches reshape volcanic edifices with up to half of pre-collapse cone volumes being removed. Deposition from this debris avalanche deposit often fills and inundates the surrounding landscape and may permanently change the distribution of drainage networks. On the weakly-incised Mt. Taranaki ring-plain, volcanic debris avalanche deposits typically form a large, wedge shape (in plan view), over all flat-lying fans. Following volcanic debris avalanches a period of intense re-sedimentation commonly begins on ring-plain areas, particularly in wet or temperate climates. This is exacerbated by large areas of denuded landscape, ongoing instability in the scarp/source region, damming of river/stream systems, and in some cases inherent instability of the volcanic debris avalanche deposits. In addition, on Mt. Taranaki, the collapse of a segment of the cone by volcanic debris avalanche often generates long periods of renewed volcanism, generating large volumes of juvenile tephra onto unstable and unvegetated slopes, or construction of new domes with associated rock falls and block-and-ash flows. The distal ring-plain impact from these post-debris avalanche conditions and processes is primarily accumulation of long run-out debris flow and hyperconcentrated flow deposits with a variety of lithologies and sedimentary character. Common to these post-debris avalanche units is evidence for high-water-content flows that are typically non-cohesive. Hence sedimentary variations in these units are high in lateral and longitudinal exposure in relation to local topography. The post-collapse deposits flank large-scale fans and hence similar lithological and chronological sequences can form on widely disparate sectors of the ring plain. These deposits on Mt. Taranaki provide a record of landscape response and ring-plain evolution in three stages that divide the currently identified Warea Formation: 1) the deposition of broad fans of material adjacent to the debris avalanche unit; 2) channel formation and erosion of Stage 1 deposits, primarily at the contact between debris avalanche deposits and the Stage 1 deposits and the refilling of these channels; and 3) the development of broad tabular sheet flows on top of the debris avalanche, leaving sediments between debris avalanche mounds. After a volcanic debris avalanche, these processes represent an ever changing and evolving hazard-scape with hazard maps needing to be regularly updated to take account of which stage the sedimentary system is in.     

Effects of Release Conditions Uncertainty on Avalanche Hazard Mapping

Dynamical models for calculating snow avalanche motion have gained growingimportance in recent years for avalanche hazard assessment. Nevertheless, inherentuncertainties in their input-data specification, although well acknowledged, areusually not explicitly incorporated into the analysis and considered in the mappingresults. In particular, the estimate of avalanche release conditions is affected bystrong uncertainties when associated to a return period. These sources of error arenormally addressed through sensitivity analysis or conservative parameters estimate.However, each of these approaches has limitations in assessing the statistical implications of uncertainties.In the present paper the problem of release scenarios randomness is looked at following a Monte Carlo procedure. This statistical sampling-analysis method allows the evaluation of the probability distributions of relevant variables for avalanche hazard assessment – such as runout distance and impact pressure – once the release variables – essentially releasedepth and release length – are expressed in terms of probability distributions, accounting explicitly for inherent uncertainties in their definition. Both the theoretical framework of this procedure and its application to a real study case are presented. As initial step of this research in the present work the attention is mainly focused on flowing avalanches descending on open slopes. Therefore, the one-dimensional version of VARA dynamic models is usedfor avalanche simulations.     

Quickbird卫星影像在汉源县小堡乡崩塌群识别中的应用

高分辨率的Quickbird卫星影像,在地质灾害的调查中有着广泛地应用。本文采用Quickbird卫星影像,通过正射校正后,获得高精度的遥感影像图,作为地质灾害遥感解译的数据源,准确、快速地识别了小堡乡崩塌群,判定了其规模、稳定性和危害程度,取得了较好的应用效果。