地震引发滚石灾害及其基本特征研究

通过对已有地震资料的搜集、整理和综合分析,研究了地震滚石灾害的致灾方式、诱发环境条件及发生模式,总结得出地震引发滚石灾害的基本特征,提出了解决地震滚石灾害的可行性方法和思路,以期能为相关研究工作提供参考.     

簧式缓冲器的工作原理及其在滚石柔性防护系统中的应用

滚石是突发于人工边坡或自然边坡上的一类特殊的地质灾害,对坡下的人类活动和基础设施的安全构成极大威胁.柔性防护系统是滚石灾害防治的重要方法之一,而摩擦制动环是应用于钢绳拦石网并起到关键缓冲作用的部件.作者发现,当前使用的摩擦制动环存在着缓冲效率较低、较易损坏、成本较高等诸多不足.针对这些不足,提出了一种可应用于滚石柔性防护系统的簧式缓冲器.理论研究表明,它具有缓冲效率较高、不易损坏、价格较低等优点,可望在滚石柔性防护系统中得到广泛应用.     

Causes of rockfalls in AI-Huwayshah area, Yemen

According to topography of Yemen, most areas and villages are located at obligated crest, toe of mountain and under cliffs. Therefore Al-Huwayshah consisting of Tawilah sandstone group is characterized by steep slope reach to 90℃ in some areas. This area is affected by strong tectonic movements and faults that occurred during the geological epochs. This effect enhances to find out fractures and joints as well as the rocks become brittle and ready to slide depending on the position of area. And there are some fractures and joints on the surface of the areas due to tectonic movement associated with opening the Red Sea and Gulf of Aden. The rainfalls, fractures, joints, earthquakes, gravity, vegetations, temperatures and human activities play a big role in the processes of rockfalls and landslides in this area. All those factors are considered as the basic causes and catalyzed factors for occurrence of rockfall in the studide area. In addition, the authors carried out laboratory test for many rock samples to get the physical properties of the rocks.     

汶川地震后公路边坡崩塌灾害发育规律

震后崩塌是强烈地震造成的震裂山体在后期余震、降雨及重力作用下变形不断发展并再次发生的崩塌。基于对四川省省道S303线映秀-卧龙段震后公路边坡崩塌灾害的调查,通过空间分布、崩塌与物质组成、岩性、失稳斜坡坡度、坡高、坡形、坡向和崩塌形成机理的关系等方面的分析,得到了震后崩塌灾害的发育规律:1.震后崩塌分布规律与地震时引发的崩塌的规律一致,即地震时易发生崩塌的地段地震后仍然易发生崩塌。2.按照边坡物质组成,以岩质边坡崩塌占绝大多数,岩土组合体边坡次之;较坚硬岩石中发生的崩塌多而较弱岩石中发生崩塌少,沿线发生崩塌最多的是岩性为闪长岩、辉长岩和变质砂岩等坚硬岩石组成的斜坡。3.失稳斜坡坡度在36°～85°之间,主要分布在41°～60°之间,即震后崩塌灾害主要发生在40°以上的斜坡。映秀-耿达段和耿达-卧龙段发生崩塌的边坡坡度有明显的差别,映秀-耿达段集中在坡度为46°～60°的斜坡,而耿达-卧龙段集中在在坡度为41°～55°的斜坡。4.绝大多数崩塌发生在坡高150 m以内的斜坡上,映秀-耿达段和耿达-卧龙段发生崩塌的边坡高度有明显的差别,映秀-耿达段集中在高度为51～350 m的斜坡,而耿达-卧龙段集中在在高度<200 m的斜坡,尤以高度<100 m的最多。5.阳坡和阴坡的崩塌数量有明显的差异,阳坡发生崩塌的数量远远大于阴坡崩塌发生的数量。6.震后边坡崩塌的形成机理以滑移式崩塌和倾倒式为主。映秀-耿达段和耿达-卧龙段地处不同地质构造单元,由于岩性的差异,发生崩塌的斜坡的坡度、高度和主要形成机理具有差异性。     

Seismogeological effects on rocks during the 12 April 1998 upper So a Territory earthquake (NW Slovenia)

On 12 April 1998, the strongest earthquake (M_L 5.7), with an epicentre in Slovenia, in the last 100 years shook the upper So a Territory (NW Slovenia). Its maximum intensity was between VII and VIII according to the European Macroseismic Scale (EMS-98). Its epicentre is located in the area SE of the town of Bovec in the Krn mountain range (Julian Alps). Apart from substantial material damage to nearby settlements, the earthquake caused considerable changes to the landscape through many rockfalls and landslides. In this paper, we try to assess the effects of this event on the natural surroundings. The presented results are useful to understand the relation between “seismogeological” effects and the intensity scale EMS-98 for this particular event, but might also be a first step towards a future statistically meaningful assessment of the intensity scale on the basis of “seismogeological” effects.     

金沙江向家坝库区崩滑灾害的环境效应

金沙江向家坝库区长约１５０ｋｍ的沿江地带，共发育１０２个变形破坏体（含滑坡、崩塌和变形体），总体积１５．６５×１０８ｍ３．据统计岸坡变形破坏密度Ｄ和模数Ｅ分别达０．３４个／ｋｍ和５２４．９３×１０４ｍ３／ｋｍ．对崩滑灾害所处的环境特征研究表明，滑坡、崩塌与所在地层岩性、地质构造、地形条件、岩体结构特征及近期河流地质作用等环境因素共同作用有关．     

Modelling Transient Ground Surface Temperatures of Past Rockfall Events: Towards a Better Understanding of Failure Mechanisms in Changing Periglacial Environments

Despite the rising interest in mountain permafrost due to climatic changes and a noticed increase of registered rockfall events in the European Alps and other mountain ranges, little is known about transient thermal conditions in the detachment areas of rockfalls. Temperature conditions prior to the rockfall events of 144 past events in the European Alps were modelled with a physically based ground temperature model. To minimise the impact that uncertainty has on interpretations, only relative values were used, that is, percentiles obtained from cumulative distribution functions of the modelled ground surface temperatures from the beginning of the meteorological measurement series up to the event dates. Our results suggest that small and mid‐sized rockfalls (volumes up to 100 000 m³) from high elevation occurred mainly during short‐term periods of unusually high temperatures. This was neither found to be a result of the seasonal distribution (most analysed events in higher elevations occurred from July to September) nor of the longer‐term temporal distribution (most analysed events occurred after 2000) only. Plausible explanations are either a destabilisation related to advective thaw or failure due to stress redistribution caused by large temperature variations. Large deep‐seated rock slope failures (≥100 000 m³) in high elevation occurred all year round.     

Controls on the geotechnical response of sedimentary rocks to weathering

Weathering reduces the strength of rocks and so is a key control on the stability of rock slopes. Recent research suggests that the geotechnical response of rocks to weathering varies with ambient stress conditions resulting from overburden loading and/or stress concentrations driven by near-surface topography. In addition, the stress history experienced by the rock can influence the degree to which current weathering processes cause rock breakdown. To address the combined effect of these potential controls, we conducted a set of weathering experiments on two sedimentary lithologies in laboratory and field conditions. We firstly defined the baseline geotechnical behaviour of each lithology, characterising surface hardness and stress–strain behaviour in unconfined compression. Weathering significantly reduced intact rock strength, but this was not evident in measurements of surface hardness. The ambient compressive stress applied to samples throughout the experiments did not cause any observable differences in the geotechnical behaviour of the samples. We created a stress history effect in sub-sets of samples by generating a population of microcracks that could be exploited by weathering processes. We also geometrically modified groups of samples to cause near-surface stress concentrations that may allow greater weathering efficacy. However, even these pronounced sample modifications resulted in insignificant changes in geotechnical behaviour when compared to unmodified samples. The observed reduction in rock strength changed the nature of failure of the samples, which developed post-peak strength and underwent multiple stages of brittle failure. Although weakened, these samples could sustain greater stress and strain following exceedance of peak strength. On this basis, the multi-stage failure style exhibited by weaker weathered rock may permit smaller-magnitude, higher-frequency events to trigger fracture through intact rock bridges as well as influencing the characteristics of pre-failure deformation. These findings are consistent with patterns of behaviour observed in field monitoring results. © 2019 John Wiley & Sons, Ltd.     

Seismically Activated Swarm of Landslides,Tension Cracks,and a Rockfall after Heavy Rainfall in Bafaka,Cameroon

A swarm of 57 landslides, tension cracks and a rockfall occurred spontaneously on September 5, 1995 killing 3 people and destroying farmlands and forests over an area of 6 k across, at Bafaka, Ndian Division, Cameroon. From analyses of field observations, eyewitness accounts, rainfall data, and soils, the principal causative factors of the disaster are interpreted as meteorological, hydrogeological, and tectonic in origin. High and continuous rainfall which lasted for 3 days prior to the event might have saturated both sedimentary shaly sandstones of Cretaceous Period, and weathered basaltic trachytes of Tertiary Period which are prone to sliding and which lie unconformably on Precambrian gneisses and migmatites. A mapped distribution of the landslides showed their concentration along two deeply incised river valleys which are probably fault zones running in a northwest-southeast direction. This is antithetic to the direction of faults in the area which are predominantly parallel to the northeast-southwest direction of the Cameroon Volcanic Line. A felt earthquake with an estimated intensity of about IV on the Mercalli Intensity Scale must have triggered the landslides, some tension cracks, and the rockfall in the already saturated sedimentary and volcanic rocks, with larger landslides observed around the possible epicenter of the earthquake. The rockfall, from a cliff of basalt, occurred simultaneously with the landslides and this is used to further confirm a tectonic force as a probable trigger to the disaster. The tension cracks which have remained unchanged in shape three years after the disaster are interpreted as aborted landslides. Although disasters of such magnitudes are rare in this volcanic area which has been considered to be dormant, the Cameroon Volcanic Line in general is still tectonically and volcanically active. This is evidenced by the last eruption of Mount Cameroon in 1982 situated about 45 kilometers southwest of the study area, the seismically activated landslide along the Santa Graben in 1982, the Tibati fault displacement with associated seismicity in 1986, and the carbon dioxide gas explosions from Lake Monoun in 1984 and lake Nyos in 1986 which killed 37 and 1746 people respectively.     

层状块体结构岩坡崩塌过程的数值模拟

本文在某实际工程地质分析的基础上，采和数值模拟方法研究了反倾层状块体结构岩体中开挖边坡的崩塌过程。通过统计分析得到岩体结构的统计性质参数及岩层厚度和节理间距分布的密度函数。采用随机参数模拟生成边坡岩体的结构，随机生成边坡开挖线切割岩体，根据岩块间的相互关系追踪每个岩块的稳定性，统计岩体崩塌的最大深度，得到破坏深度分布的概率分布曲线。模拟结果为实际开挖过程所证实。