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The current regulatory requirement for cover soils in landfills and surface impoundments is that the soils attain, upon compaction, a very low hydraulic conductivity of 10−7 cm/s or less. Although the influence of the interaction between waste chemicals and clay soil on waste migration has been extensively studied, attempts to incorporate as design components the effects of sulfidic (sulfide-bearing) clays on the integrity of clay caps have largely been ignored. These influences may include increasing the permeability of the cover to percolating moisture, enhancing erosion of clay covers, and killing of vegetation on downslopes of the cover. Consequently, it is suggested that clay cap designers test the acid-generating capabilities of potential clay cap materials before exploiting these earth formations. This can be done by incubating a sample of the candidate capping material (with pH > 3.5) under moist aerobic conditions (field capacity) at room temperature. The soil will be said to contain sulfidic materials if it shows a drop in pH (1 ∶ 1 by weight in water) of 0.5 or more units to a pH value of 4.0 or less within eight weeks. Decisions should then be made as to whether the soil should be avoided or used with amendments to the cap design.

The increasing human engineering activities and frequent extreme weather events have caused extensive reactivation of ancient landslides, which are widely developed in the east margin of Tibetan Plateau. The Shangyaogou landslide, as a typical ancient landslide example in this area, was investigated to reveal the reactivation characteristics, and its stability was calculated under the continuous rainfall condition with the intensity 30 mm/day using the finite element software Geo-Studio. The whole movement process and hazard prediction under the different triggering conditions were simulated using the numerical software DAN3D. The study results showed that: (1) under the joint influence of Mw 7.9 Wenchuan earthquake, toe erosion and intensive rainfall, multi-stage deformations occurred to the front part of the Shangyaogou landslide in multiple periods and also indicated a significant potential instability; (2) under the continuous rainfall condition, when the single effective total infiltration reached about 65 mm, the reactivation part will become unstable. While the single effective total infiltration reached about 120 mm, both reactivation part and posterior part became instability; (3) the maximum run-out distance of the reactivation part was calculated to be 350 m, and the forefront of the accumulation deposit would not reach the residential area; When both parts failed simultaneously, the maximum run-out distance was calculated to be 550 m by considering the thickness and dynamic energy of the accumulation deposits, and the vulnerable elements inside the fan area with radius of 150 m would be severely threatened; (4) abundant earthquake-triggered landslides have been developing in history or in recent years in the eastern margin of Tibetan Plateau. Some of them have been partly reactivated due to the increasing human engineering activities and extreme rainfall events, and they have a potential for further deformation and failure. The presented study methods can provide guidance for local disaster prevention and mitigation, and can be used as a reference for the hazard prediction of the similar ancient landslides which have been reactivated.

Sinkholes are a common geological hazard around the world. However, it is difficult to carry out the associated indoor simulation experiments because of the complicated factors involved. Our previous research showed that sinkholes in the aerated zone caused by soil disintegration exhibit accurate critical conditions. Therefore, the kind of sinkhole formation is simulated in the paper. Before the simulate experiment, the critical value of the disintegration of clay samples is tested, which helps to control the simulation conditions. With a designed simulation apparatus, soil disintegration was conducted 70 times from October 23, 2017, to June 1, 2018, and a sinkhole formed. This experiment results indicate two developmental laws of sinkholes forming in the aerated zone. One is the forming process which has three stages, soil-void formation, soil-void expansion, and roof collapse. Second is that the two conditions water content is less than the critical value and contact between water and soil, causing the sinkhole formation. At the forming, two conditions are clear, and can easily be monitored by the associated factors in the field where sinkholes have occurred or are about to occur. According to the principle, another simulation experiment was carried out. As a result, an advanced prediction of a sinkhole is achieved in the aerated zone.

The main aim of this paper is to develop a new hybrid method to assess landslide susceptibility mapping (LSM) in neighboring provinces of Alborz Mountains in Iran. In the last centuries, this region has experienced a large number of landslides due to its location on earthquake belt, with high precipitation in some parts and having varied topography. Besides, the largest city of Iran (Tehran), a lot of important infrastructures, congested roads and a large population are located in this region. Therefore, determining the spatial outlines of the regions which are prone to future landslides is a critical issue. To reach this goal, the LSM is provided by applying a hybrid model of statistical index (Wi) and adaptive neuro-fuzzy inference system (ANFIS) in a Geographic Information System. In the first step, landslide inventory map was divided into two groups randomly. These groups are training dataset including 70 % recorded landslides and the remaining 30 % was used to test the model output. The first and second groups are used to determine the weights in model and validation of results, respectively. Then, 12 landslide conditioning factors are selected and categorized into two groups which are continuous numerical and nominal. After that, each factor is classified and the weight of each class is determined using Wi. The outputs of Wi and Wi-ANFIS were employed to determine nominal and continuous numerical data, respectively. In the Wi-ANFIS approach, the calculated weights of each class is allocated to the center of each class, and the rest weights of values are determined by ANFIS which is an artificial algorithm using training data (in this paper, the weights were calculated by Wi) in terms of predicting and interpolating. The results are evaluated using receiver operation curves including success rate curve and predicted rate curve. The validation results of the proposed hybrid method shows that the area under the curve of success rate curve and predicted rate curve are 0.90 and 0.89, respectively, which have been improved in comparison with Wi. The results pr oved that the suggested model applied in this study generated reliable LSM which can be applicable for primary land use planning and infrastructure site selection.

 The aim of this paper was to study the weathering mechanism of marbles and granites exposed to the marine environment at the Delos archaeological site. Alterations, as granular disintegration, contour scaling and alveolus formations, can be observed either at the base of blocks and columns, or at the median-high zones of monuments. A white marble, which originated from Naxos Island, had a weak porosity (0.2%). Its porous network was organized into two subnetworks of rectilinear and sinuous cracks, which limited capillary transfer to ∼10 cm. The granite, which originated from Delos Island, had a relatively high porosity (2.15%), and had a well-connected system of cracks and microporous zones of weathered minerals. This homogeneous network allowed good capillary transfer for long distances (1–2 m). For the marble, as for the granite, evaporation occurred mainly at depth in the stone, and encouraged its deterioration. This damage depends on the dissolution and crystallization of salts, which occur in cycles. First, by the capillary transfer of water and salt from the ground, when the stones are located near the sea. This processes can explain the deterioration of the marble and the granite bases, and the decay of granite on all its surfaces. Second, by fixation of water vapor by sea salt deposited on the stone by wind. This phenomenon can explain the degradations observed on the median-high parts of monuments in marble and granite, even though, for the granite, the first mechanism was more active.

Hydrological and geochemical studies performed on Lake Specchio di Venere on Pantelleria island (Italy) indicate that this endorheic basin has been formed through upwelling of the water table, and that it is continuously fed by the thermal springs situated on its shores. The lake is periodically stratified both thermally and in salinity, albeit this stratification is rather unstable over time, since meteorological events such as strong rain or wind can determine the mixing of its waters. Periodical analyses of the lake water chemistry show large variations of the salt content due to the yearly evaporation-rain dilution cycle. These processes are also responsible for the saline stratification during steady meteorological conditions. The mineralogical characterisation of the bottom sediments shows the almost exclusive presence of neoformation minerals, mainly carbonates, formed in response to the pH gradient between spring- (pH ≈ 6) and lake-waters (pH ≈ 9). Finally, the CO2 partial pressures in the lake water slightly exceeding the atmospheric one, are due to the large amounts of CO2 brought to the lake through the bubbling free gas phase of the thermal springs. Nevertheless the high pH value of the lake water, its small volume and its periodical mixing prevent dangerous built up of this gas.

Land subsidence occurrence in the Tasuj plane is becoming more frequent and hazardous in the near future due to the water crisis. To mitigate damage caused by land subsidence events, it is necessary to determine the susceptible or prone areas. This study focuses on producing and comparing land subsidence susceptibility map (LSSM) using boosted regression tree (BRT), random forest (RF), and classification and regression tree (CART) approaches with twelve influencing variables, namely altitude, slope angle, aspect, groundwater level, groundwater level change, land cover, lithology, distance to fault, distance to stream, stream power index, topographic wetness index, and plan curvature. Moreover, by implementing the Relief-F feature selection method, the most important variables in LSSM procedure were identified. The performance of the adopted methods was assessed using the area under the receiver operating characteristics curve (AUROC) and statistical evaluation indexes. The results showed that all the employed methods performed well; in particular, the BRT model (AUROC = 0.819) yielded higher prediction accuracy than RF (AUROC = 0.798) and CART (AUROC = 0.764). Findings of this study can assist in characterizing and mitigating the related hazard of land subsidence events.

 Wide karst plateaus extend in the carbonate rocks of the Grands Causses area, north of Montpellier (south of France). They are surrounded by a hard rock base that feeds important rivers, such as the Tarn River and tributaries, and crosses the plateaus creating deep gorges. The Larzac plateau, the most southern, makes a link with the Mediterranean region. It is traversed by one of the main national roads and another main road under construction from Clermont-Ferrand to Montpellier and Spain. The karst water resource of the plateau, from springs, is used as a water supply for the Millau area (30,000 inhabitants); but it also recharges surface rivers, mainly during the summer and fall when the water level is low, in a region that is well known for water recreation activities, for fish farming and, above all, for sheep farming and Roquefort cheese production. The fundamental question was should the karst and its water resource be fully protected by strict regulations (for example as a nature reservation) in land-use management of the plateau based upon the knowledge of its hydrogeological functioning and its karst structure? Decisions, concerning the ∼500-km2 area were elaborated from detailed hydrogeological studies, which included natural and artificial tracing, analysis of karst aquifer functioning, landscape analysis, and risk assessment and mapping. Recommendations were proposed to local and regional decision makers to define what were the preferences in terms of water resource protection and water quality restoration. Following such an approach in a karst area is not easy for hydrogeologists or for decision makers. In non-karstic regions, protection zones currently extend over small areas of a few square kilometers, which can be easily placed under the control of a small municipality. In the present example, the main water supplies are two springs that recharge areas that extend respectively over 100 and 110 km2. Included are several municipalities, some of which use them for their water supply, whereas others are concerned with pollution risks and land management projects. The recent French Water Act, which considers water as a common heritage, allows for general management by all the users, and it deals with the water and the terrain in which it flows. The regulation tools seem very well suited to karst region management. However, time is needed to educate users and decision makers, and with the help of karst scientists, to work together in a framework that is larger than the usual municipal limits.

Douala city, located in the littoral province of Cameroon, receives abundant rainfall quantities due to its geographical position in the Gulf of Guinea and bears considerable surface water and groundwater resources. Due to socioeconomic development and rapid demographic growth in the city and its consequences of unplanned urbanization and improper sanitation system, these water resources are poorly protected and managed. Streams in the Wouri watershed receive large amounts of wastewater discharge, and hundreds of boreholes have been drilled into the aquifer system without any management plan. A detailed hydrodynamic and hydrogeochemistry study in Douala town and its environs was conducted to get a better insight into the groundwater system functioning in order to provide information for the sustainable management and protection of the groundwater resource. Two field campaigns were carried out with 187 samples collected and analyzed for major ions, stable isotopes (18O, 2H), and tritium 3H. The results of the sampling have shown that the weathering of silicate minerals is the dominant geochemical process affecting groundwater chemistry in this system. However, acid rainfall in the humid climate has also caused carbonate mineral dissolution, amorphous silica deposition, and ion exchange reactions to occur in aquifers in the region. The various water types identified were categorized into four major clusters C1 to C4, based on the major ion composition and the local hydrogeological conditions. Environmental isotope data reveal that modern-to-submodern waters occur in the phreatic Quaternary/Mio-Pliocene and Oligocene/Upper Eocene aquifers, respectively. These results corroborate with the conceptual model built where modern groundwater types indicated silicate mineral weathering and calcite dissolution (C1 and C2), whereas submodern groundwater mostly showed silica deposition, ion exchange, and, to a lesser extent, carbonate mineral dissolution (C3 and C4). This improved understanding of the aquifer system functioning is essential to provide a reasonable basis for effective control measures and sustainable water management.