Lanslide hydrogeological susceptibility of Maierato (Vibo Valentia, Southern Italy)

A large landslide occurred at Maierato (Vibo Valencia District), Southern Italy, on 15 February 2010, when rapid failure was produced after several days of preliminary movements. The landslide can be classified as a rotational slide with flowing of the mass. It occurred within a larger deep-seated gravitational movement area and was preconditioned for failure by the intrinsic geological weakness of the area. Actually, the in situ survey showed the presence of several ancient movement surfaces all around the urban area. The landslide-triggering factor was the increase in the groundwater flow, consequent to a period of heavy and prolonged rainfall. The aim of the paper is to explain the mechanism of occurrence of the February 2010 composite landslide, in order to assess the landslide hydrogeological susceptibility in the whole urban area of Maierato. For this reason, the present paper deals with: (1) identification of the landslide mechanism and triggering factors (2) slope stability back-analysis using a finite-difference-based shear strength reduction method, and (3) 3D groundwater flow modelling extended to the whole urban area both in pre- and post-failure conditions. The results show that the February 2010 composite landslide was triggered by a water table increase of about 15 m uphill the landslide scarp. This hydrogeological condition could be reached after the period of heavy and prolonged rainfall preceding the landslide event. Finally, based on the groundwater modelling in post-failure condition, a landslide hydrogeological susceptibility map was drawn for the all urban area of Maierato, showing the presence of extended areas exposed to hazard.     

Analysis of the Maierato landslide (Calabria,Southern Italy)

On 15 February 2010, a landslide of great dimensions occurred at Maierato (Calabria, Southern Italy) after a long rainy period. Although the zone was continuously affected by ground movements especially during the wet seasons, no monitoring system was installed before the occurrence of the landslide. However, many photos and two videos were taken during the failure process of the slope. In the present study, the available images are used to reconstruct the kinematics of the landslide. In addition, a finite element analysis is performed to define the main factors of triggering and to interpret the failure mechanism of the slope. This analysis is also based on the data from a site investigation carried out after the landslide to characterise the involved soils from a geotechnical viewpoint. The analysis also accounts for the strain-softening behaviour of some soils. The results have shown that the Maierato landslide was the reactivation of a pre-existing landslide body, which was caused by a significant increase in groundwater level.     

Hydrogeological characterization of carbonated Jurassic aquifers in the Gijón-Villaviciosa basin (Asturias,N Spain) by means of geochemical and isotopic techniques

Chemical and isotopic analyses of groundwater from the carbonated Jurassic aquifers in the Gijón-Villaviciosa basin (Asturias, northern Spain) were carried out. Nine springs were sampled to determine major cations and anions, as well as the stable isotopes of the water molecule (δ²H and δ¹⁸O) and sulphate (δ³⁴S) values. Also, δ³⁴S values from gypsum coming both from Triassic rocks and bottom of Jurassic sequence were also determined. The results obtained were used to classify the waters with a genetic criteria in three groups: (1) waters with a high gypsum influence, with sulphate coming from Jurassic gypsum, (2) waters without gypsum influence, where sulphate source could be atmospheric deposition from industrial processes and marine aerosol, and (3) waters with some gypsum influence, in which sulphate origin could be a combination of different sources. In relation to recharge, δ²H and δ¹⁸O values were close to those of Global Meteoric Water Line and fit a local line that suggests a meteoric origin. The estimated elevations for spring recharge are in agreement with those obtained from hydrogeological maps.     

基于反向地球化学模拟的地下水形成作用: 以安徽省泗县为例

在了解安徽省泗县水文地质条件基础上,分析了区域水文地球化学特征及类型,探讨了其空间分布特征。根据开采条件下的地下水动力场条件,选择了3条模拟路径,采用PHREEQC软件进行了水文地球化学模拟研究,定量分析了地下水的形成机理及演化。结果表明,路径Ⅰ发生了岩盐、石膏以及伊利石的溶解,高岭土、石英、白云石、萤石发生了沉淀;钙蒙脱石、方解石不参与反应,NaX解吸,CaX_2被吸附;路径Ⅱ发生了岩盐、石膏、伊利石、石英等的溶解以及钙蒙脱石、方解石的沉淀,NaX解吸,CaX_2被吸附;路径Ⅲ发生的反应基本与路径Ⅰ相同,不同之处在该路径上的白云石发生了溶解,其原因可能是地下水在径流过程中溶解CO_2,使其继续溶解白云石以及受沉淀滞后的影响。研究结果表明地下水开采条件下,泗县地下水化学组分主要受到了岩盐和石膏等矿物的溶解作用、钙钠离子交换作用以及钙蒙脱石、方解石沉淀作用的控制。     

间歇型降雨对堆积层斜坡变形破坏的物理模拟研究

为研究间歇型降雨作用下缓倾堆积层斜坡的变形破坏特征,以樱桃沟滑坡为例,进行了降雨作用下斜坡变形破坏的物理模拟研究。试验结果表明：前期降雨作用下坡体变形特征表现为前缘滑移沉陷、中部滑移、后缘沉陷、坡体裂缝生成,且前缘裂缝扩张明显,后期降雨作用下坡脚区域首先发生滑塌,然后依次向后缘传递发生逐阶滑塌破坏;降雨入渗易在基岩面上储存,形成暂态地下水位、高孔隙水压力区域和坡向渗流场,基岩面附近土体饱水时间长,软化程度高,抗剪强度弱化显著,边坡易沿基覆界面土层发生滑坡;坡体滑动易发生在降雨间歇期,触发特征表现为雨后坡体暂态饱和区水分和坡表积水持续下渗,导致地下水位上升滞后于降雨,造成坡体内浮托力、渗透力和孔隙水压力增大,有效应力降低,诱发滑坡。     

Parametrical landslide modeling for the hydrogeological susceptibility assessment: from the Crati Valley to the Cavallerizzo landslide (Southern Italy)

The article deals with a tool for landslides susceptibility assessment as a function of the hydrogeological setting at different scales. The study has been applied to a test area located in Southern Italy. First, a 3D groundwater flow model was implemented for a large-scale area. The simulation of several groundwater conditions compared with the landslide activity map allows drawing a hydrogeological susceptibility map. Then, a slope scale analysis was carried out for the Cavallerizzo landslide. For this purpose, a 2D groundwater parametrical modeling was coupled with a slope stability analysis; the simulation was carried out by changing the values of the main hydrogeological parameters (recharge, groundwater supply level, etc.). The results enabled to connect the slope instability to some hydrogeological characteristics that are easy to survey and to monitor (e.g., rainfall, piezometrical level, and spring discharge), pointing out the hazard thresholds with regards to different triggering phenomena.     

Tank模型在模拟滑坡地下水位中的应用

季节性的降雨及其所引起的地下水状态的变化是促使日本大型结晶片岩滑坡活动和诱发灾害发生的重要原因。基于对一典型结晶片岩滑坡、降雨和地下水位的长期观测,利用Tank模型建立了一种模拟滑坡地下水位变化的方法。通过对滑体内不同观测点地下水位实际观测数据与模拟结果的对比分析,证明所采用的模拟方法能够很好地再现地下水位随降雨的变化形态,从而为预测和评价降雨型滑坡的地下水状态变化提供了依据。     

Ennoyage des mines de fer lorraines : impact sur la qualité de l'eau

The flooding of the abandoned iron mines of Lorraine leads to a degradation of the groundwater quality. Laboratory experiments allowed us to build a kinetic chemical model based on simple chemical mechanisms. During mining operations, pyrite oxidation and carbonate dissolution lead to the precipitation of gypsum. The local decrease of pH favours local dissolutions of minerals and releases ions that are fixed on cationic exchange sites. During the flooding of the mine workings, the dissolution of the newly precipitated gypsum, the precipitation of carbonates and cationic exchange reactions are responsible for the increase of the concentrations of sulphate, magnesium, sodium, potassium and strontium in water. Thereafter, these concentrations would decrease with the natural leaching of the mining reservoir. To cite this article: P. Collon et al., C. R. Geoscience 336 (2004).     

基于概率方法的滑坡稳定性分析

本文概述了滑坡破坏概率分析的基本原理.以三峡库区的龙王庙滑坡为例,论述了地下水对滑坡的作用,进行了滑坡的破坏概率分析,分析结果表明,该滑坡在库水位骤降初期有较高的破坏概率,必须进行治理.     

Towards hydrological triggering mechanisms of large deep-seated landslides

It is a widely accepted idea that hydrologically triggered deep-seated landslides are initiated by an increase in pore-water pressure on potential slip surface induced by rising groundwater level after prolonged period of intense rainfall although the process is not fully understood. In order to contribute to better understanding, the rainfall–groundwater relationships, hydrogeological monitoring and repeated geoelectrical imaging were carried out from March 2007 to April 2011 in large deep-seated landslide near ?ubietová (Western Carpathians) catastrophically reactivated at the end of February 1977. Based on our observations, groundwater level (GWL) response to precipitation differs considerably with respect to both overall hydrological conditions and GWL mean depth. While the rate of GWL increase up to 25 cm/day were measured after some rainfall events during wet periods, noticeably lower recharge rate (up to 1–2 cm/day) and delayed GWL response to rainfall (usually from 2 weeks to 2–4 months) were observed at the beginning of the wet season after considerable depression of GWLs due to previous effective rainfall deficit. Likewise, slow GWL fluctuations without short-term oscillations are typical for deeper GWLs. Thus, long-term (several seasons to several years) hydrological conditions affect markedly groundwater response to rainfall events in the studied landslide and can be crucial for its behaviour. Comparison of hydrological conditions characterising the analysed period with those that accompanied the landslide reactivation in 1977 allow us to assume that slightly above-average rainy season following the prolonged wet period can be far more responsible for movement acceleration (and possibly failure initiation) in deep landslides than the isolated season of extreme precipitation following a longer dry period. This is true especially for landslides in regions with significant seasonal temperature changes where potential effective precipitation (PEP), calculated as excess of precipitation (P) over potential evapotranspiration (PET), may be efficiently used for estimation of slope saturation condition.     

Groundwater flow and residence time in a karst aquifer using ion and isotope characterization

In order to identify the origin of the main processes that affect the composition of groundwater in a karstic aquifer, a hydrogeochemical and isotopic study was carried out of water from numerous observation wells located in Sierra de Gador, a semiarid region in SE Spain. Several natural and anthropogenic tracers were used to calculate groundwater residence time within this complex aquifer system. Analysis of major ions enabled the principal geochemical processes occurring in the aquifer to be established, and the samples were classified into four distinctive solute groups according to this criterion. Dissolution of carbonate rocks determines the chemical composition of less mineralized water. In another group, the concurrent dissolution of dolomite and precipitation of calcite in gypsum-bearing carbonate aquifer, where the dissolution of relatively soluble gypsum controls the reaction, are the dominant processes. Marine intrusion results in highly mineralized waters and leads to base exchange reactions. The groundwater enrichment of minor and trace elements allowed classification of the samples into two classes that are linked to different flow patterns. One of these classes is influenced by a slow and/or deep regional flow, where the temperature is generally elevated. The influence of sulphate reduces by up to 40 % the barium concentration due to the barite precipitation. Isotope data (T, ¹⁴C) confirm the existence of recent local flows, and regional flow system, and ages of ground water may reach 8000 years. The importance of gypsum dissolution in this aquifer is proved by the δ³⁴S content.     

The 2015 Shenzhen catastrophic landslide in a construction waste dump: analyses of undrained strength and slope stability

The 2015 catastrophic landslide in a 110-m-high waste dump in Shenzhen is recognized as one of the largest landfill failure worldwide. An earlier comprehensive field investigation revealed that the dominant component of the fill was completely decomposed granite (CDG), and the dumping operation was accompanied by a rise of the groundwater level. In this paper, the complex stress paths for the initially unsaturated fill materials being subjected to both rapid filling and wetting were investigated. A simplified method was proposed for estimating the gain of undrained shear strength under the complex stress paths. Soil samples were taken from the site to a laboratory to measure the undrained shear strength and validate the estimation method. Total stress-based stability analyses were carried out to calculate the factor of safety of the dump at failure. The triggering mechanism of the landslide is clarified as follows: The gain of shear strength with the surcharge loading for the wet layer in the lower part of the waste dump was limited by a build-up of excess pore-water pressure. The gain of shear strength for the relatively dry fill material was attenuated with the rise of groundwater level. When the shear strength was not enough to resist the increasing slip force with the surcharge loading, a deep-seated translational failure took place in the lower wet layer of the waste dump. The proposed method for analyses of undrained strength and slope stability are proven to be applicable to the waste-dumping operation with rapid filling and rising groundwater level.

     

云南小江流域滑坡关键影响因子研究

确定诱发滑坡失稳的关键因素是滑坡研究的一个重要内容。采用不同影响因子图层进行危险性分区结果存在明显差异,这是由于第一因子对于滑坡变形失稳的贡献程度不同,即不同影响因子与滑坡的相关性不同。在进行滑坡灾害分析时,必须首先确定影响滑坡的关键因子以建立准确的统计分析模型。采用滑坡确定性系数的合并检验方法,在GIS中对云南小江流域进行了滑坡影响因子分析,并确定了影响滑坡的关键性因子。据此建立的多元统计分析预测模型经检验具有较高精度,要以为小江流域的灾害防治、规划建设提供科学依据。     

鬃岭高位滑坡带地下水补径排特征及致灾作用研究

本文以贵州省纳雍县鬃岭崩塌滑坡带两个滑坡区为例,通过水文地质调查、水动力场分析、水化学和流量动态对比分析,得出结论（1）天然条件下,崩塌滑坡带存在3个相对独立的地下水系统,采煤活动改变了局部地下水径流排泄方向,使上部基岩裂隙水、中部岩溶水补给到下部基岩裂隙水中,最后从坑道或泉排泄出地表。（2）流量动态和钙离子含量变化表明,雨季中部岩溶水灌入式补给到了采空区坑道中,同时也表明老鬃岭镇滑坡区山体浅部垂直裂缝发育,左家寨滑坡区山体浅部至深部垂直裂缝均有发育。（3）鬃岭崩塌滑坡体内部地下水以非饱和水下渗运动为主,不存在饱和地下水流场,故而不存在水动力驱动滑坡影响作用。（4）在鬃岭崩塌滑坡孕灾或灾害触发过程中,地下水对垂直裂缝、滑动结构面的发展和岩体破坏、失稳主要起到加速和促进作用。本文对岩溶石山地区类似滑坡机理研究有一定意义。      

强度折减法在高含水滑坡稳定性分析中的应用

文章依据滑坡体岩体破碎、地下水丰富、坡体含水量高、滑坡面积大、厚度小、稳定性差等特点,选取青海省麦秀山1^#滑坡为例。结合麦秀山地区的工程地质特点,利用FLAC-3D有限差分程序,基于强度折减法对该滑坡进行了稳定性分析。通过对滑体岩土体强度指标的折减,模拟地下水对岩土体的影响,当边坡的塑性区由坡脚贯通至坡顶、坡体上特征点的位移值产生突变,且无限制的增长时,认为边坡达到临界破坏状态,此时的强度折减系数即为滑坡的稳定系数,同时可得到滑坡失稳破坏的潜在滑动带,以揭示滑坡的失稳破坏机理。分析计算表明：强度折减法不仅能够模拟出滑坡渐进破坏的过程,而且所求得的稳定系数更符合滑坡的实际状态,在滑坡稳定性分析中具有明显的优势。     

四川省盐源玻璃村特大型玄武岩古滑坡复活机制

受前期14 d持续累计350.6 mm降雨影响,2018年7月19日盐源玻璃村一巨型玄武岩古滑坡体发生大规模复活,复活体积为1 390×104 m3,损坏房屋186间,造成重大经济损失。基于现场调查、无人机航测、钻探揭露、物理力学试验及数值模拟分析,在查明滑坡体地质结构、失稳特征基础上,对其影响因素及复活机制进行了探讨。研究结果表明,破碎岩土体及地形地貌是滑坡复活的孕灾基础,持续降雨及其引起的地下水位升高是滑坡复活的诱发因素。复活滑坡可分为主滑区和侧滑区两种破坏模式不同的区域。降雨作用下滑坡体内渗流场明显变化,孔隙水压力增大,导致7月13日古滑坡体开始发生变形,稳定性系数逐渐降低。受微地貌约束,主滑区具有多级、多次失稳,渐进破坏的特点。侧滑区斜坡前缘临空条件受坡脚主滑坡控制,在主滑坡运动过程中,侧滑区坡体位移量、最大剪切应变增量逐渐增大,塑性区扩展,破坏过程表现出与主滑坡一定的关联性和滞后性。分析表明,受地下水长期影响,滑带土体强度逐渐削弱,降雨导致坡体渗流作用加剧,抗剪强度降低,从而诱发滑坡复活。     

Rise in seawater sulphate concentration associated with the Paleoproterozoic positive carbon isotope excursion: evidence from sulphate evaporites in the ∼2.2–2.1 Gyr shallow‐marine Lucknow Formation,South Africa

Abstract Past oceanic sulphate concentration is important for understanding how the oceans’ redox state responded to atmospheric oxygen levels. The absence of extensive marine sulphate evaporites before ～1.2 Gyr probably reflects low seawater sulphate and/or higher carbonate concentrations. Sulphate evaporites formed locally during the 2.22–2.06 Gyr Lomagundi positive δ¹³C excursion. However, the ～2.2–2.1 Gyr Lucknow Formation, South Africa, provides the first direct evidence for seawater sulphate precipitation on a carbonate platform with open ocean access and limited terrestrial input. These marginal marine deposits contain evidence for evaporite molds, pseudomorphs after selenite gypsum, and solid inclusions of Ca‐sulphate in quartz. Carbon and sulphur isotope data match the global record and indicate a marine source of the evaporitic brines. The apparent precipitation of gypsum before halite requires ≥2.5 mm L^?1 sulphate concentration, higher than current estimates for the Paleoproterozoic. During the Lomagundi event, which postdates the 2.32 Gyr initial rise in atmospheric oxygen, seawater sulphate concentration rose from Archean values of ≤200 μm L^?1, but dropped subsequently because of higher pyrite burial rates and a lower oceanic redox state.     

Speleothems in gypsum caves and their paleoclimatological significance

This article highlights the relationship between speleothems growing inside gypsum caves and the particular climate that existed during their development. Speleothems in gypsum caves normally consist of calcium carbonate (calcite) or calcium sulphate (gypsum) and the abundance of such deposits greatly differs from zone to zone. Observations carried out over the last 20 years in gypsum caves subjected to very different climates (Italy, Spain, New Mexico, northern Russia, Cuba, Argentina) highlight wide variation in their cave deposits. In arid or semi-arid climates, the speleothems are mainly composed of gypsum, whilst in temperate, humid or tropical regions, carbonate formations are largely predominant. In polar zones no speleothems develop. These mineralogical details could be useful paleoclimatic indicators of climate change. The interpretation proposed is based on the fact that in gypsum karst the kind of speleothems deposited is determined by competition between the two principal mechanisms that cause precipitation of calcite and gypsum. These mechanisms are completely different: calcite speleothem evolution is mainly controlled by CO₂ diffusion, while gypsum deposits develop mostly due to evaporation. Therefore, the prevalence of one kind of speleothem over the other, and the relationship between the solution–precipitation processes of calcite and gypsum, may provide evidence of a specific paleoclimate. Additionally, other non-common deposits in gypsum caves like moonmilk, cave rafts and dolomite speleothems can be used as markers for the prevalence of long, dry periods in humid areas, seasonal changes in climate, or rainfall trends in some gypsum areas. Moreover, the dating of gypsum speleothems could contribute paleoclimatic data relating to dry periods when calcite speleothems are not deposited. In contrast, the dating of calcite speleothems in gypsum caves could identify former wet periods in arid zones.     

Landslide hazards and mitigation measures at Gangtok, Sikkim Himalaya

Landslides and other mass movements are serious geo-environmental hazards in the Himalayas. Massive landslides killing tens of thousands of people with catastrophic damages have occurred in the Eastern Himalayan State of Sikkim, which shares common borders with Tibet, Nepal, and Bhutan. This paper describes the investigations carried out on recent landslides in Gangtok, Sikkim, India, with emphasis on the triggering mechanisms that have contributed to the release and creep of natural slopes in the region. It is believed that the intense rainfall in the region not only contributes to rapid erosion and weathering of the rock mass, but also increases the groundwater level that leads to reduction in the stability of natural slopes. A landslide instrumentation programme that includes placement of settlement pillars and piezometers is underway to predict the behaviour of landslides in the area.     

Analysis of the relationship of landslide occurrence with rainfall: a case study of Wudu County,China

Landslides are a significant hazard in many parts of the world and represent an important geohazard in China. Rainfall is the primary triggering agent for landslides and often used for prediction slope failures. However, the relationship between rainfall and landslide occurrences is very complex. Great efforts have been made on the study of regional rainfall-induced landslide forecasting models in recent years; still, there is no commonly accepted method for rainfall-induced landslide prediction. In this paper, the quantitative antecedent soil water status (ASWS) model is applied to investigate the influence of daily and antecedent rainfall on the triggering of landslides and debris flows. The study area is Wudu County in Gansu Province, an area which exhibits frequent landslide occurrences. The results demonstrate a significant influence of high intensity rainfall events on landslide triggering. Still, antecedent rainfall conditions are very important and once a threshold of approximately 20 mm is exceeded, landslides and debris flows can occur even without additional rainfall. The study presented could also facilitate the implementation of a regional forecasting scheme once additional validation has been carried out.