Soluble Rocks Research Articles

Karst Groundwater Vulnerability and Risk to Pollution Hazard in the Eastern Part of Gunungsewu Karst Area

Karst landscape generally has a high vulnerability to pollution. Karst landscape is a landscape that forms from soluble rock. The solution processes results many holes which connecting the surface to underground river networks. Soil and vegetation are generally thin and sparse. The increasing of the population and they various activities can add pressures to the landscapes such as in the eastern parst of Gunungsewu. The karst groundwater management and protection effort need its intrinsic vulnerability and risks to the groundwater pollution hazard characteristics information. The aim of the study are to assess the level of vulnerability and risk of groundwater in the eastern part of Gunungsewu karst area against pollution hazards, as well as making maps of land use directives in the area. Vulnerability and risk to pollution was based on budiyanto’s model. The model was based on remote sensing data of Landsat 8 OLI and GDEM ASTER. The result of this study indicate that most of the study area has a high level of vulnerability to pollution hazard. However, this area mostly has a low level risk to pollution hazard. It is in line to the lack of sources of groundwater pollutants hazard, the presence of soils on karst rocks, and the presence of vegetation cover. Land use direction maps produced based on the level of vulnerability and risk to pollution. It shows that most of these areas are designated as protected areas. However, there are areas for the maintenance of land functions that vulnerable and high risk to pollution.

Seismic attribute method for concealed collapse column identification in coal fields

A collapse column is a geological structure formed by the dissolution of a soluble rock layer under certain hydrogeological conditions. This forms a cavity, which is filled by the overburden. Collapse columns have a great impact on coal mining safety. In this work, a model of a concealed collapse column is constructed according to its diameter, and the finite difference method is used to simulate it using an acoustic equation. The seismic record characteristics of the collapse column are analyzed. In the seismic section, the attributes of the reflected wave of the concealed collapse column in the coal seam are small and undetectable, and the reflected wave of the auxiliary horizon (the upper interface of Ordovician limestone) is in-phase axis. It is difficult to artificially identify concealed collapse columns with small diameters when twisting or dislocation occurs. However, the reflected wave properties clearly indicate an annular anomaly on the horizon property plane, which helps to identify the concealed collapse column. Finally, the seismic attributes of reflected waves at the interface between the 10# coal seam and Ordovician limestone roof in the BY mining area of TY mine are identified using high-density three-dimensional seismic data to verify the effectiveness of the proposed method in identifying concealed collapse columns.

Modelling speleogenesis in soluble rocks: A case study from the Permian Zechstein sequences exposed along the southern Harz Mountains and the Kyffhäuser Hills, German

Soluble rocks such as limestone, dolomite, gypsum, anhydrite, and salt can be dissolved by water flowing through voids in the rocks. The removal of the dissolved material from fissures and bedding partings by physical and/or chemical dissolution enlarges the permeability of the soluble rocks within geologically short periods of time, ranging from 100,000 years down to decades. This geologically short evolution time of voids in soluble rocks poses a substantial risk of mechanical instability of the enlarged voids, and possible surface deformation, when enlarged voids start to collapse. We describe karst and cave features in the rock sequence exposed along the southern part of the Harz Mountains and the Kyffhauser Hills in Germany, where limestone/dolomite and anhydrite/gypsum are exposed along a kilometer-wide strip following the foothills of the Harz Mountains. The rocks have been deposited during the Permian Zechstein period, buried, and exposed later through tectonic uplift. The exposed part of this soluble sequence is dominated by karst features. But there are also substantial cave voids deeper in the rock, with no obvious entrance to the surface, which have been discovered by chance through mining activities. Often, the sub-surface void evolution is closely linked to surface deformation, creating collapse sinkholes and subsidence. In the city of Bad Frankenhausen at the foothills of the Kyffhauser Hills, the evolution of sub surface voids is responsible for the tilting of the church tower of the Oberkirche. We explore the evolution of such a karst system composed of limestone and anhydrite by numerical means, describing flow and transport in a rock mass composed of soluble and insoluble rock sequences, with limestone and anhydrite responsible for the evolution of secondary porosity. Key words: soluble rocks, karst, mine-cave evolution, collapse sinkholes, numerical modelling. Modeliranje speleogeneze v topnih kamninah: primer zechsteinskih kamnin v južnem delu gorovja Harz in v hribovju Kyffhauser Voda, ki tece skozi pore in razpoke v topnih kamninah, kot so apnenec, dolomit, sadra, anhidrit in sol, raztaplja stene prevodnih poti. Ucinkovito odnasanje raztopljene snovi lahko mocno poveca hidravlicno prevodnost vodonosnika v geolosko kratkem casu, ki je v izjemnih primerih dolg vsega nekaj desetletij. Hiter razvoj prevotljenosti lahko povzroci mehansko nestabilnost nastalih votlin in posledicno ugrezanje povrsja. Tak primer najdemo v kilometer sirokem pasu apnenca, dolomita, sadre in anhidrita, ki se razteza vzdolž južnega dela pogorja Harz in hribovja Kyffhauser. Sedimenti, ki so se odložili v permskem Zechsteinskem morju, so bili kasneje globoko pokopani in ponovno tektonsko izdani na povrsje. Izdanki teh kamnin so izrazito krasko preoblikovani, prevotljenost pa je velika tudi v globlje pokopanih kamninah, ki nimajo ocitne povezave s povrsjem in so bile odkrite pri rudarskih delih. Velikokrat se razvoj votlin pod povrsjem izrazi tudi na povrsju, kjer nastajajo udornice in grezi. V mestu Bad Frankenhausen ob vznožju hribovja Kyffhauser se je zaradi razvoja votlin pod povrsjem nagnil cerkveni zvonik. V clanku raziskujemo razvoj kraskih sistemov v apnencu in anhidritu z numericnimi modeli. V modelu upostevamo tok, raztapljanje in prenos snovi v kamninskem masivu, sestavljenem iz topnih in netopnih kamnin, kjer raztapljanje poteka v apnencu in anhidritu. Kljucne besede: topne kamnine, kras, razvoj jam v rudnikih, udorne doline, numericno modeliranje.

Decadal trends in water chemistry of Alpine lakes in calcareous catchments driven by climate change

High mountain lakes are considered sensitive indicators of the effects of natural and anthropogenic drivers, including atmospheric deposition and climate change. In this study, we assess long-term trends in the chemistry of a group of high altitude lakes in the Western Alps, Italy, lying in bedrock with a relevant presence of basic, soluble rocks. An in-depth investigation was performed on two key-sites (Lakes Boden Inferiore and Superiore) for which continuous chemical data are available for a period of 30 years. A group of 10 additional lakes in the same area was also considered; these lakes were sampled at the end of the ice-free period during irregular surveys in the period 1980–2017. Water samples were analysed for the main chemical variables, including pH, electrical conductivity, major ions (Ca2+, Mg2+, Na+, K+, HCO3−, Cl−, SO42−, NO3−) and algal nutrients (phosphorus and nitrogen compounds, reactive silica).A steep increase in conductivity and ion concentrations was detected at the key-sites: conductivity increased from 40–45 to 60–70 µS cm−1 over the period 1984–2017; sulphate concentrations more than doubled over the same period (from 50–60 to 120–180 µeq L−1) and base cations increased from 400–500 to 600–750 µeq L−1. An increase in the solute content was also detected in the survey lakes (average conductivity from 39 ± 20 to 57 ± 23 µS cm−1). The analysis of meteorological data revealed a significant increase of air temperature (0.019 °C y−1 over the period 1950–2017), mainly in spring and summer (0.033 °C y−1), and a decrease of snow cover depth and duration. Meteo-climatic drivers were identified as the responsible for the chemical changes occurred in the lakes. Climate-driven effects on weathering rates were mainly indirect and occurred by affecting the flow paths of water at both surface and subsurface level. Cryosphere modification (reduced snow cover and permafrost thawing) also played a role.

A Preliminary Evaluation of The Karst Flora of Brazil Using Collections Data

Karst is defined as landscapes that are underlain by soluble rock in which there is appreciable water movement arising from a combination of high rock solubility and well-developed secondary (fracture) porosity. Karsts occupy approximately 20% of the planet’s dry ice-free land and are of great socioeconomic importance, as they supply water to up to 25% of the world’s population and represent landscapes of cultural and touristic importance. In Southeast Asia karst is associated with high species-richness and endemism in plants and seen as priority areas for the conservation of biodiversity. There has been little research into the floras associated with karst in South America, most of which occurs in Brazil. We therefore sought to evaluate the importance of Brazilian karst with respect to its species-richness and endemism. We sought to do so using curated plant specimen data in the Botanical Information and Ecology Network (BIEN) dataset. We show that, except for Amazonia, the BIEN dataset is representative of the Brazilian flora with respect to the total number of species and overall patterns of species richness. We found that karst is under-sampled, as is the case for much of Brazil. We also found that whilst karst represent an important source of plant diversity for Brazil, including populations of approximately 1/3 of the Brazilian flora, it is not significantly more species-rich or richer in small-range and endemic species than surrounding landscapes. Similarly, whilst important for conservation, comprising populations of 26.5–37.4% of all Brazilian species evaluated as of conservation concern by International Union for Nature Conservation (IUCN), karst is no more so than the surrounding areas. Whilst experimental error, including map resolution and the precision and accuracy of point data may have under-estimated the species-richness of Brazilian karst, it likely represents an important biodiversity resource for Brazil and one that can play a valuable role in conservation. Our findings are in sharp contrast to those for Southeast Asia where karst represents a more important source of species-richness and endemism. We also show that although BIEN represents a comprehensive and curated source of point data, discrepancies in the application of names compared to current more comprehensive taxonomic backbones, can have profound impacts on estimates of species-richness, distribution ranges and estimates of endemism.

Subsidence rings and fracture pattern around dolines in carbonate platforms – Implications for evolution and petrophysical properties of collapse structures

Abstract This work focuses on the study of collapse dolines, which are the most expressive collapse structures in carbonate rocks, and their relations with preexisting and syn-collapse fractures. The study area has two fracture sets that were formed before folding, early N-S/E-W- and late NE-SW/NW-SE-striking sets, which concentrate most of the dissolution in the region and allow the formation of the dolines. We define subsidence rings as the circular and ellipsoidal concentric zones around collapse structures, which are subjected to subsidence due to major collapses and represent locations where new fractures are formed. In these subsidence rings, the downfaulted topography plunges towards the doline center and reaches more than 10 m in relation to unaffected areas away from dolines. The topographic data indicate that the mean radius of the combined rings is ~twice the radius of the collapse, which corresponds to the closed depression due to failure and downfall of blocks. The subsidence process enlarges, links preexisting fractures, and forms a new set of semicircular concentric opening mode fractures, here named collapse fractures. Increases in the apertures and densities of these fractures occur towards the dolines, which increases fracture porosity around collapse structures. Fractures are reactivated as normal faults close to the main collapse at the doline edge. This increase in fracture intensity could represent an indicator of permo-porous quality improvement in these areas. Further, this fracturing increases structural instability, raising the risk of accidents in areas built on soluble carbonate rocks, since the affected area may be much larger than previously predicted. Subsidence rings around collapse dolines could merge with other rings from neighboring collapse structures and potentially increase porosity and permeability, as well as linking areas in carbonate reservoirs.

Modelling long-term and short-term evolution of karst in vicinity of tunnels

Tunnel construction offers unique insights into the interior structure of rock massifs. Soluble rocks encountered during tunnel construction, however, pose a substantial challenge. Especially classical karst rocks such as limestone, dolostone, gypsum, and anhydrite are unpredictable during tunnel excavation. The enlarged voids created by the long-term dissolution of the soluble rocks in contact with water pose risks because of possible uncontrollable water inflow and of instability of the encountered cave voids, which often requires expensive remediation measures. We model the long-term development of karst features and the evolution of phreatic and epi-phreatic caves below the Schalkau Plateau in the Triassic limestone with a numerical karst evolution model. With hydrological boundary conditions derived from local meteorological data and karst springs, and a simplified model of the local lithology, our model predicts the increase in secondary permeability in the karst aquifer. Enlarged fracture zones develop at locations, where cave systems have been explored. Thus our long-term evolution model can successfully predict karst features in the Schalkau Plateau. Applying the karst evolution model on a short-term period, we assess the effect of consolidation measures taken to stabilise the tunnel cross section in vicinity of the Bleßberg Cave and its longer-term stability. Our model results suggest that flow through the cave section beneath the tunnel, which has been filled with concrete and blocks, is blocked and that during flood events the impounded water will accelerate the development of by-passes around the artificial infill.

Accumulation capacity of soluble rocks as the main stability index in covered karst areas

For an engineering geologist, covered karst areas are of special interest, not only because these are the most widespread on the Earth. More important, unlike the areas of bare karst, these areas are more favorable and suitable for economic development and human life as a whole. And the study shows that the greater is the thickness of the cover series, the more true is this statement.
 The local forecast of sinkholes appears to be the most important and difficult engineering geological problem in these areas. It is especially acute there, where collapses and subsidence are absent, not registered, or poorly expressed in the relief, that is, in the areas of unrealized (potential, expected) sinkhole hazard. One of the possible approaches to solving this problem is discussed in the paper. It is based on comparing the volume of incoherent and fractured rock removed from the cover deposits with the accumulation capacity of the karst massif, i.e., the volume of hollow space in the karstic massif capable of receiving and accumulating clastic material.
 The most common result of soils outflow in fissure-karst reservoirs is their loosening in the deformed-destructed area of the overburden. For the three canonical schemes of this area structure, the critical values of clastic matter volume were obtained from the equation for soil mass balance before and after loosening, the further removal of which will lead to the failure of the earth's surface. Some techniques and methods for assessing the accumulation capacity of soluble rocks are considered and serious differences in the use of the discussed approach in predicting the stability of karstified and undermined territories are revealed. In particular, it is shown that in karst areas, when performing calculations, one should be guided by the maximum values of the coefficient of primary loosening of soils. Otherwise, the predicted stability of the overburden will prove to be unjustifiably underestimated. The results obtained and the procedure for assessing the stability of covered karst terrains by the proposed method are exemplified by the construction site of the main buildings of the Nizhny Novgorod NPP (3.25 km2), where there are no collapse and subsidence sinkholes. However, the entire construction site (20 km2) is located in the area of active sulphate-carbonate karst. From the engineering-geological point of view, this is the main feature of the facility design.

The role of N form supply for PGPM‐host plant interactions in maize

AbstractThe form of nitrogen (N) supply has a significant impact on rhizosphere chemistry and root growth responses of higher plants. The respective effects are also employed as management options to improve nutrient acquisition and to minimize nutrient losses in cropping systems. However, surprisingly little is known concerning the interactions with rhizosphere biota. In this study, we investigated the effects of selected bacterial and fungal inoculants with proven plant growth‐promoting and phosphate (P)‐solubilizing potential (plant growth‐promoting microorganisms, PGPM) in maize with nitrate or stabilized ammonium supply, on soils with limited P availability and sparingly soluble rock phosphate (Rock‐P) applied as P fertilizer. The combination of the bacterial inoculants Pseudomonas sp. DSMZ 13134 (Proradix) and Bacillus amyloliquefaciens FZB42 with ammonium sulphate fertilization, stabilized with the nitrification inhibitor 3,4‐dimethylpyrazole‐phosphate (DMPP), resulted in a superior shoot biomass production (79–111%) and shoot P accumulation (109–235%) as compared with nitrate supply. This effect could be partially attributed to (1) ammonium‐induced rhizosphere acidification via increased root extrusion of protons, (2) promotion of root hair elongation, and (3) increased shoot concentrations of hormonal growth regulators (indole‐3‐acetic acid, zeatin, gibberellic acid). The effects, induced by the microbial inoculants were mainly related to increased root length development (43–44%), associated with a 60% increase in auxin production potential. No inoculant effects were detected on root hair elongation or on chemical modifications of the rhizosphere involved in P solubilisation, such as rhizosphere acidification, release of carboxylates or secretory phosphohydrolases. However, the ammonium‐induced stimulation of root hair elongation increased preferential sites for root colonization by the selected inoculants, which may explain the increase in rhizosphere abundance of PGPMs, exemplarily recorded for the fungal inoculant Trichoderma harzianum OMG16 (210%). The presented data suggest a network of positive interactions between stabilized ammonium fertilization and plant growth‐promoting functions of various bacterial and fungal PGPM inoculants. This offers perspectives to increase the efficiency and the reproducibility of PGPM‐assisted fertilization strategies.

Plant ecology of tropical and subtropical karst ecosystems

AbstractSubstantial areas of tropical forests, including those within nine tropical biodiversity hotspots, contain karst landscapes that have developed on soluble carbonate rocks. Here, we review how the ecology of karst forest trees is influenced by hydrological, edaphic, and topographic factors that exhibit fine spatial heterogeneity. Comparative analysis of drought tolerance traits including wood density contributes to the assessment of whether karst tree species are more drought‐tolerant compared to non‐karst trees. Although karst ecosystems are generally considered to have low phosphorus availability, foliar nitrogen‐to‐phosphorus ratios exhibit wide variation across karst regions without a clear difference from non‐karst ecosystems. According to the analyses of leaf phenology, stem water storage, and isotopic signatures from xylem sap, water use strategies of karst trees can be classified into five types: (a) soil water dependent, (b) epikarst water dependent (mainly use water stored in fine pores and gaps within the epikarst rock during the dry season), (c) groundwater dependent, (d) fog water dependent, and (e) drought‐deciduous (shed leaves during the dry season). Overall, published data suggest that only a subset of karst tree species are exclusively distributed within karst hilltops where water availability is limited. The diverse resource acquisition and utilization strategies of karst plants across edaphic habitats must be considered when developing effective strategies to conserve and restore biodiversity in karst landscapes, which are under increasing anthropogenic pressure.

Karst map of Georgia (Caucasus region) scale: 1:1,500,000

Karst landscapes develop in soluble rocks, such as carbonates and evaporates, but also in various types of rocks that develop pseudokarst features. The main aim of this work is to introduce a new karst map of Georgia (scale: 1:1,500,000) presenting karst and pseudokarst features, which occupy about 17.9% (12,454 km2) of the entire territory of the country and include over 1500 known caves. We distinguish two types of karst features—karst (developed in carbonate rocks) and pseudokarst, and also five subtypes, mainly based on their lithology. About 10.2% (7120 km2) of the country is occupied by karst (carbonate rocks), and about 7.7% (5334 km2) of the country is occupied by pseudokarst features. This karst map of Georgia will provide important assistance to local and foreign researchers interested in studying Georgian karst features.

Morphological indications of hypogene speleogenesis in caves of the Urals (Russia)

Approximately all types of surface and underground karst elements are represented in the Urals. Rock formations are elongated in the longitudinal direction, which allows for a comparative analysis of the processes in karst landscapes in different latitudinal geographic areas. During the long geological history of the Urals, karst development occurred in conditions of extensive occurrence of soluble rocks in the territory and in the geological section in cratons, folded zones and depressions. The most intense karstification occurs in Paleozoic sediments. Sulfate rocks (gypsum and anhydrite) located on the eastern margins of the East European Craton and adjacent parts of the Ural Foredeep are the most karstified. These deposits are also intercalated with thin layers of limestone and dolomite of the Irenskaya Suite, and to a lesser extent—limestones and dolomites of the Filippovsky Unit of the Kungurian Stage and limestones of the Artinskian Stage of Lower Permian. Salt-bearing and sulfate deposits are mainly found in the Ural Foredeep. Karst development in the Devonian, Carboniferous, and Permian carbonate strata with a total thickness of more than 2000 m is typical for the folded zone of the West Ural and Central Ural uplifts. The western slope of the South Urals is the most intensely karstified. Hypogenic karst cavities occur from the Polar to the Southern Urals on the western and eastern slopes. The article presents the most interesting examples of hypogenic speleogenesis in the Ural.

Time-lapse gravity and levelling surveys reveal mass loss and ongoing subsidence in the urban subrosion-prone area of Bad Frankenhausen, Germany

Abstract. We present results of sophisticated, high-precision time-lapse gravity monitoring that was conducted over 4 years in Bad Frankenhausen (Germany). To our knowledge, this is the first successful attempt to monitor subrosion-induced mass changes in urban areas with repeated gravimetry. The method provides an approach to estimate the mass of dissolved rocks in the subsurface. Subrosion, i.e. leaching and transfer of soluble rocks, occurs worldwide. Mainly in urban areas, any resulting ground subsidence can cause severe damage, especially if catastrophic events, i.e. collapse sinkholes, occur. Monitoring strategies typically make use of established geodetic methods, such as levelling, and therefore focus on the associated deformation processes. In this study, we combine levelling and highly precise time-lapse gravity observations. Our investigation area is the urban area of Bad Frankenhausen in central Germany, which is prone to subrosion, as many subsidence and sinkhole features on the surface reveal. The city and the surrounding areas are underlain by soluble Permian deposits, which are continuously dissolved by meteoric water and groundwater in a strongly fractured environment. Between 2014 and 2018, a total of 17 high-precision time-lapse gravimetry and 18 levelling campaigns were carried out in quarterly intervals within a local monitoring network. This network covers historical sinkhole areas but also areas that are considered to be stable. Our results reveal ongoing subsidence of up to 30.4 mm a−1 locally, with distinct spatiotemporal variations. Furthermore, we observe a significant time-variable gravity decrease on the order of 8 µGal over 4 years at several measurement points. In the processing workflow, after the application of all required corrections and least squares adjustment to our gravity observations, a significant effect of varying soil water content on the adjusted gravity differences was figured out. Therefore, we place special focus on the correlation of these observations and the correction of the adjusted gravity differences for soil water variations using the Global Land Data Assimilation System (GLDAS) Noah model to separate these effects from subrosion-induced gravity changes. Our investigations demonstrate the feasibility of high-precision time-lapse gravity monitoring in urban areas for sinkhole investigations. Although the observed rates of gravity decrease of 1–2 µGal a−1 are small, we suggest that it is significantly associated with subterranean mass loss due to subrosion processes. We discuss limitations and implications of our approach, as well as give a first quantitative estimation of mass transfer at different depths and for different densities of dissolved rocks.

Alluvial karstification and paleodoline development in Eocene limestones, a case study from west Sohag City, Egypt: implications for causes and impacts

The Late Oligocene pre-Eonile paleoriver flows northwesterly over the Eocene Limestone Plateau in the east central Western Desert, west of the Nile Valley (Sohag), building an alluvial plain and leading to the karstification of the limestone bedrock, as paleoerosional surfaces and paleodolines. Knowledge of this alluvial karstification is completed with the detailed studies of the sedimentary evolution of the fluvial system and its contemporary deposition. Analysis of the sedimentological and geomorphological features allows discussing the natural environmental conditions that favored karst in the past and its main genetic mechanisms. The architectural elements of the fluvial deposits indicate that they were deposited in a gravel-dominated braided fluvial system, characterized by high availability of water and sediment supplies. The current study proves that genesis of paleodolines was mainly related to this high water supply. Some of them were progressively filled by syn-sedimentary deformed unconsolidated deposits. Such deformation is due to dissolution of the underlying sagging synclinal limestone, conditioning the location of sinking waters where preferential dissolution and later suffosion took place. A model for the evolution of the paleodoline fills is proposed and interpreted in three different stages: (1) gravitational processes developed and disorganized gravels were remobilized and dragged toward the created paleodolines; (2) flooding of the paleodolines acted as lakes where Gilbert-type deltas and gravel slope deposits accumulated, exhibiting several unconformities interpreted as a result of continued subsidence of the paleodoline related to dissolution; and (3) nondeformed fluvial facies sealed the whole deposits, marking the end of the karstification process. Combinations of different types of factors that could cause karstic subsidence and associated hazards include soluble rock lithology, paleoclimate, and deformational structure.

Prediction of Porosity and Permeability Alteration Based on Machine Learning Algorithms

The objective of this work is to study the applicability of various machine learning algorithms for the prediction of some rock properties which geoscientists usually define due to special laboratory analysis. We demonstrate that these special properties can be predicted only basing on routine core analysis (RCA) data. To validate the approach, core samples from the reservoir with soluble rock matrix components (salts) were tested within 100 + laboratory experiments. The challenge of the experiments was to characterize the rate of salts in cores and alteration of porosity and permeability after reservoir desalination due to drilling mud or water injection. For these three measured characteristics, we developed the relevant predictive models, which were based on the results of RCA and data on coring depth and top and bottom depths of productive horizons. To select the most accurate machine learning algorithm, a comparative analysis has been performed. It was shown that different algorithms work better in different models. However, two-hidden-layer neural network has demonstrated the best predictive ability and generalizability for all three rock characteristics jointly. The other algorithms, such as support vector machine and linear regression, also worked well on the dataset, but in particular cases. Overall, the applied approach allows predicting the alteration of porosity and permeability during desalination in porous rocks and also evaluating salt concentration without direct measurements in a laboratory. This work also shows that developed approaches could be applied for the prediction of other rock properties (residual brine and oil saturations, relative permeability, capillary pressure, and others), of which laboratory measurements are time-consuming and expensive.

The initial phase of cave formation: Aquifer-scale three-dimensional models with strong exchange flow

Limestone, dolomite, gypsum, anhydrite, and salt are rocks, which can be dissolved, either by water alone, or in the case of limestone and dolomite more efficiently by water enriched with carbon dioxide. With time, the secondary porosity in these rocks increases substantially, and flow through these soluble rocks becomes very effective and fast. The time period for a substantial increase in secondary porosity ranges from years (salt) to 10,000–100,000 years (limestone, dolomite).The temporal evolution of such a soluble rock can be described by numerical models, coupling flow, transport, and dissolution. On the fracture-scale, numerous models describe fingering and wormhole formation in soluble rocks. On the aquifer-scale, numerical models predict preferential flow patterns and a strong exchange-flow component.We present results from three-dimensional numerical models describing the evolution of a karst aquifer in its early stage. Our numerical approach, which describes the large aquifer-scale, is capable to simulate the strongly heterogeneous development of secondary permeability in the aquifer. Based on irregularities in the model (e.g. geometry, chemistry, lithology, hydrology), preferential pathways evolve under a catchment-control situation, limiting the inflow into the system through the amount of water available from a catchment. We compare qualitatively our large aquifer-scale results to small fracture-scale results and show that the fingering described by the latter models is driven by similar mechanisms as the preferential growth in the former models.

KARST CHARACTERISTICS AND GOVERNANCE MEASURES IN KUNMING METRO LINE 4

The geological conditions of Dianchi Basin are complex, and soluble rocks are distributed in many parts of the basin and the edge of the basin. The Karst problem is prominent and has a great influence on metro. The investigation of Karst in metro needs to be carried out through multiple stages using comprehensive survey technology to find out its characteristics, properties and hazards. After investigation and analysis, the Karst weak development of the Dahegeng Station of Kunming metro Line 4~Datangzi Station Section, Chenggong East Station(including)~Kunming South Railway Station Section, Liandajie Station~Chenggong East Station Section, Bailongtan parking lot and the Karst middle development of the entrance and exit section line, The Karst section of Jindingshan Station~Xiaocaiyuan Station developed strongly. Line 4 is covered Karst. Karst mainly develops in the 15m range below the base rock surface, and is dominated by filled caves with a height of 0.5~3.0m. The average hole rate of boreholes is 21%, and the average line Karst rate is 3.29%.The Karst area is divided into stable area, sub-unstable area and unstable area. Karst management should adopt corresponding treatment principles and engineering measures for different engineering types and Karst characteristics. Karst treatment generally adopts grouting reinforcement measures. For Karst with a small buried depth, excavation to expose backfill grouting can be used for reinforcement treatment. The pile foundation needs to pass through the Karst and be placed in the lower stable strata. This paper has some guidance for the Karst survey and treatment of metro in Kunming.

Five decades of settlement and subsidence

During the late 1960s and 1970s consideration of land instability in Great Britain was dominated by coal mining-related problems. Subsequently, as the pace of development and infrastructure has increased, there has been a greater awareness regarding collapses due to mining for resources other than coal and also due to karstic features in soluble rocks. This has been highlighted by reference to national and regional studies. In addition, there has been an improvement in the number of recorded occurrences of sinkholes and crown holes. The hazard of ground collapse in certain geological settings, together with the size of collapses and resulting damage to development and infrastructure, has become more evident as case studies have been published. Whereas a range of subsidence triggers are evident, the principal causal agency is usually water from rainfall or leaking utilities. Wider-ranging studies, both in Britain and overseas, have identified ever broader causes of land instability, including those related to glacial and periglacial features, and also uncontrolled groundwater exploitation. This review provides a useful summary of land settlement and subsidence activity to warn practitioners where caution should be applied when carrying out ground investigations and providing design advice.

A methodological approach to assess the hazard of underground cavities subjected to environmental weathering

Soft highly porous carbonate rocks, such as calcarenites, and soluble sulphate rocks, such as gypsum, are very common in the Mediterranean region and, due to their microstructure and chemical composition, are prone to water induced weathering mechanisms. Cliffs, underground cavities and other morphological features in such formations are hence affected by intense erosion phenomena and weathering processes responsible for unexpected collapses and sinkholes. Just considering the Apulian region (Italy), 150 sinkholes have been recorded since 1925, with increasing frequency since 2000 (Fiore et al., 2018). The geosystem’s failure is often the short- or long-term result of a very complex hydro-chemo-mechanical process taking place at the micro-scale which can be detected and analysed by means of field and laboratory experimental test campaigns. Therefore, stability problems are often related to changes of the mechanical properties of the rock forming the cave caused by environmental weathering processes, despite the external boundary conditions are not changing with time. The paper deals with the assessment of hazard associated with the stability of abandoned underground caves, which is nowadays frequently required for land and urban planning activities. A methodological approach for hazard assessment based on a step-by-step procedure is proposed. This includes in-situ surveys, laboratory experimental studies, theoretical analyses and finally numerical investigations. The approach derives from the experience developed from several case studies analysed by the authors. In this work, two of these are presented. The first one concerns the stability of an anthropic cavity in a calcarenite formation which is affected by a water induced short-term and long-term debonding processes. The second one regards the stability of a three-level abandoned gypsum mine, the lowest level being partially flooded by water. The methodological procedure aims to evaluate the factors controlling the change of the mechanical properties of the rock so that efficient remediation measures can be designed in order to avoid any further decay of the rock mass stability with time.The proposed methodological approach, validated on real case studies, shows the convenience of performing advanced experimental, theoretical and numerical studies to properly assess the hazard in space and time and to better design the mitigation measures if they are required. The adoption of the proposed approach reduced the remediation costs of the second case study of one order of magnitude.

Study of the Corrosion Characteristics of Tunnel Fissures in a Karst Area in Southwest China

The development of the fissures in soluble rock of karst areas directly affects the construction and operation safety of tunnel engineering. It is thus of theoretical and practical significance to study the characteristics of its corrosion and its influencing factors. Taking the Wulong tunnel as the research object, the numerical model of the study area was established to quantitatively analyze the corrosion range, corrosion ratio, and changes in the permeability and porosity of the fissures in soluble rock of karst areas of the tunnel over the past 100 years, and the simulation results were verified by field experiments. The results show that the main controlling factor of the fissure corrosion of the tunnel in the karst area is the flow rate. The corrosion range and corrosion ratio of the fissures of the tunnels in the karst area increased with temperature because the reaction rate constant increased with temperature, causing the reactions’ equilibrium to move towards the direction of the solution. The larger the initial permeability and the larger the porosity of the fissures, the faster the fissures corrode. In the same time period, the fissures with high permeability and large porosity will lead to the permeability and porosity being more enhanced, thus causing the corrosion of the fissures to exhibit secondary enhancement effects. The opening of the dead-end pores greatly enhanced the permeability and slightly increased the porosity, which caused the differential corrosion of fissures in the karst area. The protection of the tunnel should be strengthened, mainly in strong hydrodynamic conditions and in the fracture development zone.