Soluble Rocks Research Articles

COMPARISON OF THREE APPROACHES TO CALCULATING DIAMETER OF A DROPOUT SINKHOLE

The possibility of sinkhole size prediction in the areas, where soluble rocks are covered by impermeable clay layer is considered. Such sinkholes are named by English-speaking authors as “dropout sinkholes” or “cover collapse sinkholes”, because the process of their formation includes collapse (dropping) of clay covering soluble rocks into a karst cavity. Triggers of this effect are: (1) widening of a cavity below the clay due to dissolution of a soluble rock by groundwater; (2) lowering of hydraulic head in confined karst aquifer, primarily caused by groundwater pumping, which results in decreased support of the overlying clay layer; (3) a dynamic load on the clays, which can have either natural or man-made origin. Fresh dropout sinkholes generally have configuration similar to vertical right circular cylinder, but sometimes their shape can be dome-like with very unstable ground “cantilevers”. The appearance of these forms under foundations can lead to deformation and even to destruction of buildings, structures, and infrastructure facilities. Two concepts exist, which can be used as basis for creating models of soil mechanics to calculate diameter of a dropout sinkhole. The first one is based on a viewpoint that clay collapse into a cavity after a trigger action is displayed immediately at the ground surface as a collapse sink. According to the second concept, the preliminary subsurface collapse of clay occurs as fall of ground block resembling a circular paraboloid. As a result, a dome-like cavity appears in the clay layer and above-lying clay fall into it to form a collapse sink. There are no prediction methods based on the two above-mentioned conceptions. The developed approaches to prediction of a dropout sinkhole diameter are adequately comparable, as they use the same input calculation parameters. The prediction results based on these approaches have been compared to an actual diameter of fresh dropout sinkhole. This verification have allowed us to infer that most adequate is the approach based on concept of initial subsurface clay’s collapse preceding the final collapse sink formation.

Karst hazard assessment in the design of a residential complex in Moscow

The composition and content of necessary engineering-geological research providing accident-free operation of buildings and constructions in karst areas are considered. These studies include karst hazard assessment and rational selection of karst protection measures. The results of the prognostic assessment of karst sinkhole formation possibility on the territory of about 4 hectares, allocated for construction of the first stage of the complex of residential buildings of different numbers of floors in the northwest of Moscow, are presented. The basis was the results of site investigations, during which, in particular, several dozen boreholes were drilled to uncover soluble rocks. Karst hazard assessment included an in-depth analysis of engineering-geological conditions of the future construction site and adjacent territories and took into account the possibility of the occurrence of karst sinkholes of different genetic types in this city area. When building forecasts and karst risk assessment, calculated methods of probabilistic and deterministic character were used, allowing to determine the necessary conditions and parameters of karst sinkhole formation in quantitative terms. The results of the karst hazard assessment were considered when selecting karst protection methods.

Clustered stone forest in Pu Dou Chun (Yunnan, China)

One of the unique examples of the development of subsoil karren into a stone forest on the varied geological bedrock of the Lunan surface is revealed to us. Originally of subsoil formation and later denuded, the rounded hills that dissect the karst surface have transformed into a clustered stone forest whose central part usually consists of a larger dissected rock mass with individual stone pillars and teeth at the edge. The geologic profile contains beds of dense, homogeneous and compact fine-grained limestones that alternate with beds of mostly coarse-grained and just as compact dolomitised limestones. These bed properties are also reflected in the exterior of the rock as a diverse relief. The average calcium carbonate content in both types of rocks combined is 97.3%. The rock is thickly bedded to massive; beds are mainly positioned subhorizontally. The contacts between the beds of limestone and dolomitised limestone are sharp and clearly visible, especially in the bottom part of the geologic profile, whereas in the central part, they are often blurred and one type of rock grades continuously into the other. In the areas containing limestone, individual bedding planes are especially visible. As can be inferred, the slightly more porous dolomitised rock, made up of larger particles, disintegrates faster in a more permanently waterlogged acid subsoil environment, where the moisture penetrates it deeper. However, as it takes longer to dissolve, it protrudes from the surface of the dolomitic limestone rock when exposed to moisture from occasional rain. The composition and fracturing of the diverse rock strata decisively influences the shape of the pillars and their rock relief. Larger subsoil rock forms (channels, notches, half-bells) have developed on all rock strata. The diversity of the rock is also reflected by the notches that have formed under the soil along the more rapidly soluble partly dolomite rock strata. Denuded subsoil-shaped pillars are reshaped by rainwater and trickling water. Smaller rock forms carved by rainwater have formed mostly only on evenly composed, fine- grained limestone rock. The tops on such rock are more distinctly conical and blade-like and wider on more slowly soluble rock.

Soil Column Experimental Study on the Effect of Soil Structure Disturbance on Water Chemistry.

The changes in soil/rock structure caused by engineering disturbance or earthquakes could affect water chemistry by increasing the reaction surface, enhancing the oxidation condition, or exposing soluble rocks. However, the details of the mechanisms of the disturbance of soil/rock are little known. Based on the soil column experiment, this study analyzed the concentrations of sulfate (SO4), sulfur, and oxygen isotopic composition of SO4 (δ34S-SO4 and δ18O-SO4) in effluent water. The water-rock interaction mechanisms in the disturbed soil and the contribution of this interaction to the SO4 in groundwater were studied. The results suggest that the concentration of SO4 in the first effluent water sample can reach up to 97 mg/L, much higher than that in natural groundwater (6.8 mg/L). The isotopic composition of SO4 further suggested that SO4 in the first effluent water sample was mainly derived from the dissolution of SO4-containing evaporites. The proportion was estimated to be 93%. SO4-containing evaporites accounted for 23% of the SO4 content in all effluent water samples during the experiment. The disturbance of soil structure led to the exposure and dissolution of SO4-containing evaporites, which were initially insoluble under natural conditions. This study is essential to the clarification of the water-rock interaction mechanisms following the changes in soil/rock structures.

Geophysical analysis of an area affected by subsurface dissolution – case study of an inland salt marsh in northern Thuringia, Germany

Abstract. The subsurface dissolution of soluble rocks can affect areas over a long period of time and pose a severe hazard. We show the benefits of a combined approach using P-wave and SH-wave reflection seismics, electrical resistivity tomography, transient electromagnetics, and gravimetry for a better understanding of the dissolution process. The study area, “Esperstedter Ried” in northern Thuringia, Germany, located south of the Kyffhäuser hills, is a large inland salt marsh that developed due to dissolution of soluble rocks at approximately 300 m depth. We were able to locate buried dissolution structures and zones, faults and fractures, and potential fluid pathways, aquifers, and aquitards based on seismic and electromagnetic surveys. Further improvement of the model was accomplished by analyzing gravimetry data that indicates dissolution-induced mass movement, as shown by local minima of the Bouguer anomaly for the Esperstedter Ried. Forward modeling of the gravimetry data, in combination with the seismic results, delivered a cross section through the inland salt marsh from north to south. We conclude that tectonic movements during the Tertiary, which led to the uplift of the Kyffhäuser hills and the formation of faults parallel and perpendicular to the low mountain range, were the initial trigger for subsurface dissolution. The faults and the fractured Triassic and lower Tertiary deposits serve as fluid pathways for groundwater to leach the deep Permian Zechstein deposits, since dissolution and erosional processes are more intense near faults. The artesian-confined saltwater rises towards the surface along the faults and fracture networks, and it formed the inland salt marsh over time. In the past, dissolution of the Zechstein formations formed several, now buried, sagging and collapse structures, and, since the entire region is affected by recent sinkhole development, dissolution is still ongoing. From the results of this study, we suggest that the combined geophysical investigation of areas prone to subsurface dissolution can improve the knowledge of control factors, hazardous areas, and thus local dissolution processes.

The Non-Agriculturalization of Cultivated Land in Karst Mountainous Areas in China

When used for agricultural production, karst mountainous areas are susceptible to soil degradation due to the effects of soluble rocks and the climate. To mitigate the risk, the Grain for Green Project, a sizable initiative, was commenced to transition cultivated land away from agricultural use. This conversion of cultivated land to non-agricultural land has been significant. The study area considered in this research included four small towns in southwest China in karst mountainous areas with various morphologies. The investigation of the non-agriculturalization of cultivated land in the four sample areas revealed that the non-agriculturalization rate of cultivated land as a result of the Grain for Green Project has reached between 21.36% and 51.43% each decade. Thus, the Grain for Green Project has been advantageous for lowering the landscape ecological risk. Furthermore, because an increasing number of agricultural production materials have been introduced to the cultivated land, the conversion from cultivated land to non-agricultural land has not caused a staple food crisis on the national scale. However, it is impossible to observe all the potential drawbacks of the non-agriculturalization of cultivated land from satellite photos alone, and further social data collection is required. The findings of this study can offer precise information for policymaking in relation to the protection of rural cultivated land and rural spatial optimization in karst mountainous areas.

Study on the Microstructure Evolution and Strength Damage Mechanism of Dolomite under Dissolution Condition

Dolomite is a common type of natural soluble rock. The strength of rock decreases under the action of corrosion, which has a significant impact on the self-stability and long-term safety of the tunnel surrounding the rock. To reveal the microscopic structure evolution and strength-damage law of carbonate rock caused by chemical corrosion, a series of tests such as rock chemical corrosion test, rock uniaxial compression test and electron microscope scanning test are conducted at different pH values on the dolomite of the Doushantuo Formation. The rock dissolution at different pH values exhibits four typical stages: the initial dissolution stage, secondary dissolution acceleration stage, stable dissolution rate stage and dissolution attenuation stage. During the dissolution process, the initial dissolution rate is 25.91 times that of the stable stage, and the maximum strength attenuation is 76.2% after 21 days of dissolution. For macroscopic failure, the rock is developed from 1 to 2 external fractures to multiple internal and external fractures and penetrated, and the specimen transforms from brittle to flexible. For microstructure, the sample exhibits corrosion characteristics along the joint surface, intensified corrosion at the edge, etc. The porosity increase rate is 0.6%/d; however, the length–width ratio of the pores is maintained at 1.7–1.85, indicating that the development rate of pores in different directions is similar. The results of this study have enriched the study of the dolomite dissolution mechanism and, in addition, have important reference value for the stability evaluation of tunnel surrounding rock in karst environments.

Caves in clastic rocks (Muğla, SW Türkiye)

Caves evolution is controlled by lithological properties, discontinuities, water, climate, and physico-mechanical properties of soluble rocks, vegetation and human impact. This study investigates the cave formation in Upper Miocene-Pliocene clastic rock in Menteşe town of Muğla. The lithology, physico-mechanical properties and hydrogeologic factors of host rocks and morphology of the caves in Asar Hill and Damlam stream valley were examined. The caves are 1.47-9.71 m long, 2.24-19.36 m wide and 1.38-27 m high. Four joint sets and bedding planes affect the clastics in the Asar Hill area. Mudstones (low plasticity clay, sandy clay) are in soft-very soft rock, while conglomerate is in moderate-hard rock class. The mudstone removal has started the formation of the caves. The vegetation roots act as groundwater circulation paths in the Damlam stream area. Water has eroded mudstone and muddy matrix of conglomerate following cracks and led to the formation of the caves. Water infiltration may have led to stalactite, flowstone and travertine formation in Damlam stream caves. Possible cave collapse could threaten life and property in the Asar Hill area, and may cause the destruction of internal structures of the caves in the Damlam stream. Thus, precautionary measures such as continuous monitoring and protection must be taken in both cave areas.

Alcoves as Havens From a Harsh Martian Environment

AbstractFuture missions to Mars will undoubtedly be directed toward sedimentary terrains in search for evidence of past life and geologic history. Astronauts will need to find shelter from harsh surface conditions. Natural underground voids provide a readily adaptable habitat for crews to shelter from radiation. Naturally formed caves would be desirable habitat sites, but thick deposits of limestone or other soluble rocks in which karst topography would form have not been identified by current observations. Alcoves, arched recess in steep escarpments, should be widely distributed across the planet and provide an adaptable shelter for astronauts operating on the surface of Mars. Alcoves provide a more stable thermal environment, a reduced radiation environment, shielding from macro‐ and micro‐meteorite impacts, and protection from atmospheric disturbances.

Karst Brackish Springs of Albania

The territory of Albania presents wide outcrops of soluble rocks, with typical karst landforms and the presence of remarkable carbonate aquifers. Many karst areas are located near the coasts, which results in a variety of environmental problems, mostly related to marine intrusion. This paper focuses on the brackish springs of Albania, which exhibit temperatures approximately equal to the yearly air temperature at their location. Total dissolved solids of the springs are higher than 1000 mg/L, their waters are not drinkable, and they are rarely used for other purposes. The groundwater of the alluvial aquifers of Albania, particularly those of Pre-Adriatic Lowland, are often brackish too, but these will not be addressed here. Brackish springs of Albania are mainly of karst origin and can be classified into two groups: springs in evaporitic rock, mainly gypsum, and springs in carbonate rock. The hydro-chemical facies of the first group are usually Ca-SO4, locally with increased concentrations of Na-Cl, whereas springs belonging to the second group usually exhibit Na-Cl facies. The largest brackish springs of Albania are described in detail, including their hydro-chemical correlations.

Multi-hazard susceptibility assessment using analytic hierarchy process: the Derwent Valley Mills UNESCO World Heritage Site case study (United Kingdom)

Many of the UNESCO World Heritage Sites face geological threats which could have negative effects on the value, integrity and accessibility of their heritage assets. A relevant example is the Derwent Valley Mills UNESCO World Heritage site, one of the key sites of Britain's industrial revolution of the 18th century and located along the Derwent River Valley. Individual susceptibility scenarios of natural hazards in the area like collapsible deposits, compressible ground, debris flow, landslide, running sands, shrink-swell, soluble rock and flooding (both riverine and groundwater) are available, but a comprehensive product able to support disaster mitigation measurement and land planning still does not exist. On this basis, a multi-hazard susceptibility analysis was completed with the added benefit of reducing the complexity and providing a methodological framework for multi-hazard estimation. The analysis was completed in a GIS environment through an Analytical Hierarchy Process (AHP) multicriteria decision-making process. Since the AHP method is affected by a user selection bias, a quantitative Relative significance index was derived to rank the AHP factors during the susceptibility estimation. This index suggests that flooding is the principal natural hazard for the Derwent Valley Mills UNESCO World Heritage site. The multi-hazard susceptibility map also indicates that most of the areas where the mills are located are subject to significant susceptibility to natural hazards.

KARST OF THE SOUTHERN URALS AND THE CIS-URALS, THE CURRENT ACTIVITY OF IT’S DEVELOPMENT

Recent studies have established a close relationship of surface karst manifesta-tions and deformations of buildings and structures with buried forms of paleohy-dronet. The development of territories previously considered unsuitable for construc-tion purposes is inevitably accompanied by a serious human impact on the geological environment and, as a result, karst processes are activated. The technogenic modern activity of sulfate and sulfate-carbonate karst is most pronounced within the industri-ally urbanized territories of the Belaya — Ufa (“Ufa Peninsula”) interfluve and areas of oil-producing technogenesis (Tuymazinsky, Shkapovsky, etc.).
 The authors created a GIS database project “Karst of the Southern Urals and the Cis-Urals”, which contains geospatial data on the manifestations of the karst pro-cess in soluble rocks in the South Urals and Cis-Urals. The database is managed using the “Karst” classifier.

ИЗМЕНЧИВОСТЬ СВОЙСТВ РАСТВОРИМЫХ ОТЛОЖЕНИЙ ВБЛИЗИ ПОВЕРХНОСТНЫХ КАРСТОВЫХ ФОРМ В ОБСТАНОВКАХ РАЗВИТИЯ КАРБОНАТНО-СУЛЬФАТНОГО КАРСТА

The properties of soluble rocks in the karst area within the Dobryanskiy district of Perm Krai are studied. The research area is located in the region of carbonate-sulfate karst development with a wide distribution of surface karst forms. The change in the content of carbonates, gypsum and anhydrite in the soluble rocks depending on the distance from the surface karst forms is evaluated. The change in the carbonate softening coefficient, that is characterized the ability of soils to reduce their strength after water saturation, is analyzed, as well. The tendency of the research parameters changes depending on the distance from the surface karst forms was determined and the conclusion about the presence of non-linear functional dependence between the research parameters was made. The dependences were approximated to get predictive equations. With the use of the equations on the raster models, that were built by interpolation of the special values of the studied parameters, the potentially karst susceptibility intervals are selected. These zones are also recommended to outline during the territory zonation as areas unfavorable with respect to the karst.

Synthesizing Geologically Coherent Cave Networks

AbstractWe present a geologically‐based method to generate complex karstic networks. Karsts are a type of landscape formed by the dissolution of highly soluble rocks (generally limestones). In particular, they are characterized by complex underground networks made of varieties of tunnels and breakout chambers with stalagmites and stalactites. Our method computes skeletons of karstic networks by using a gridless anisotropic shortest path algorithm according to field data of the underground system (such as inlets and outlets), geomorphological features and parameters such as faults, inception horizons, fractures, and permeability contrasts. From this skeleton, we define the geometry of the conduits as a signed distance function construction tree combining primitives with blending and warping operators. Our framework provides multiple levels of control, allowing us to author both the structure of the karstic network and the geometric cross‐section shapes and details of the generated conduits.

Physical and analytical modeling of rhythmic karst springs

Rhythmic Karst Springs (RKSs) are rare geologic features that rhythmically outflow water. A mechanical model for the rhythmic flow with rhythmic spill-over configuration was constructed in this work. The evolution of the RKS was revealed by using geological process analysis. The analytical model can directly explain the existence of RKSs in soluble rock regions and their formation mechanism in nature. Visual observations and flow measurements were performed using a laboratory physical model of RKS. The physical model components included a soluble rock simulation area, karst pipes, cave-reservoir, karst depression terrain, water tank, rhythmic spring, and the outflow measurement system. Groups of tests were carried out to recreate the process of RKS functioning and to confirm the rhythmic cycle duration and the threshold of replenishment intensity. This research helped to interpret the behavior of rhythmic springs using the recharge and evacuation of the subsurface cave-reservoir by means of fluid mechanics and groundwater hydraulics theories.

Conceptual engineering designs on resumption of mining operations and flooding protection in Mir Mine

Selection of a geotechnology for underground mining in Mir Mine, in challenging hydrogeological conditions has been the point under hot discussion for a few decades. An associate issue is protection of underground excavations from flooding. The latter problem is critical at interfaces of kimberlite and freely soluble host rock salt. After termination of surface mining operations, out of two variants of underground mining systems with cemented backfill or with bulk caving, the scenario with backfilling and with dry conservation of the open pit was selected. Dry conservation means fill of dolerite layer on the pit bottom, placement of water-proof film on this layer and outlet of all inflows via a drainage day drift and vertical boreholes. No other activities on protection of the mine from halite-undersaturated brine inflows from the pit were provided by the adopted design solutions. In the chosen scenario, above the impermeable film, a water body generated had varied volume subject to the ratio of water inflows in the pit and flow rate of discharge boreholes. Water inflows in the mine resulted in uncontrollable growth of salt karst at the kimberlite–rock salt interface, and in the subsequent degradation of the interface due dissolution of salt in the contact zone and owing to filling of fractures with dissolved salt inside the ore body. Based on the implemented research, the authors assess prospects for the resumption of operations in the mine by stoping with caving. Such technology seems to be most advisable in the given hydrogeological conditions. In this case, it is required to start with catchment of ground water inflows in the pit by means of arrangement of internal and external drainage loops.

Hydro-Stratigraphic Conditions and Human Activity Leading to Development of a Sinkhole Cluster in a Mediterranean Water Ecosystem

Salento Peninsula (Apulia, southern Italy) is characterised by many active sinkholes, which represent the main geological hazard. The stretch of coastline between the village of Casalabate and Le Cesine wildlife reserve is highly affected, with a system of dunes separating the low beach from extensive wetlands, which were subject to uncontrolled urban development after reclamation. The overall morphology is characterized by flat topography, whilst from a hydrogeological standpoint, the mixing of inland freshwater with advancing brackish water favours the higher aggressivity with respect to soluble rocks, and the development of enhanced dissolution (hyperkarst). The relict landscapes within the protected areas still allow for the recognition of actively occurring sinkholes, which cause damage to houses, the road network and infrastructures. In this article the case of Aquatina di Frigole is described, where in the last 15 years numerous sinkholes have formed, with the processes still in rapid evolution. Detailed surveys allow for to identification of the mechanisms of sinkhole formation (suffusion sinkholes), the deriving cluster, and the main hydrogeological links among the different water bodies in the area. Acquatina di Frigole provides an excellent natural laboratory to observe development and evolution of sinkholes, and their relationships with the stratigraphic and hydrogeological elements.

Plant adaptability in karst regions.

Karst ecosystems are formed by dissolution of soluble rocks, usually with conspicuous landscape features, such as sharp peaks, steep slopes and deep valleys. The plants in karst regions develop special adaptability. Here, we reviewed the research progresses on plant adaptability in karst regions, including drought, high temperature and light, high-calcium stresses responses and the strategies of water utilization for plants, soil nutrients impact, human interference and geographical traits on karst plants. Drought, high temperature and light change their physiological and morphological structures to adapt to karst environments. High-calcium and soil nutrients can transfer surplus nutrients to special parts of plants to avoid damage of high nutrient concentration. Therefore, karst plants can make better use of limited water. Human interference also affects geographical distribution of karst plants and their growing environment. All of these aspects may be analyzed to provide guidance and suggestions for related research on plant adaptability mechanisms.

MORPHOGRAPHIC STUDY OF BOIULUI VALLEY HYDROGRAPHIC BASIN

The aim of the present paper is to determine the morphometric parameters and features of Boiului Valley hydrographic basin. The basin is located in a karst area, in Pădurea Craiului Mountains, Romania, which makes it special, as the rivers flow through soluble rocks. We selected a small basin in order to analyse its morphometric elements and check if the morphometric laws of hydrographic basins are respected in the same way by the rivers flowing in karst areas. We applied the classical working method, that is processing the information from the topographic maps and with the help of the ArcGis soft we managed to measure the major morphometric indicators: the surface of the basin, the area, the shape factor, the length and width of the basin, drainage basin asymmetry factor and sinuosity index.

P-legacy effect of soluble fertilizer added with limestone and phosphate rock on grassland soil in subtropical climate region

P-fertilization can be applied to cropped soil through two main ways, namely: by using soluble phosphates to increase P pools, rapid release and uptake by plants or by using less soluble rock phosphate powder to trigger synchronization between P solubilization and its uptake by plants. The aims of the current study were to evaluate whether there is no dissolution of P-bearing minerals in the long-term when phosphate rock is used, as well as to analyze its response associated with P-legacy and plant dry-matter production in comparison to that of fertilization based on soluble phosphate added with limestone. A 20-year-old field experiment is in progress at Pampa grassland, Southern Brazil. Two rates of phosphate rock and triple superphosphate plus limestone (118 and 250 kg ha−1 of P), as well as a P-free control, were tested. The P-legacy effect of fertilizers were analyzed by phosphorus lability and apatite minerals recalcitrance. Additionally, a historic data set of dry matter production was considered to access phosphorus use efficiency. The use of soluble P source and limestone (triple superphosphate at rate of 250 kg ha−1 of P add with limestone at rate of 3.2 Mg ha−1) resulted in greater nutrient use efficiency (42 kg kg−1 - five times greater than that of phosphate rock) and in higher dry matter yield (22 %). In addition, the use of phosphate rock (at rate of 250 kg ha-1 of P) has led to higher total P and moderate-lability P levels in the soil due to low apatite dissolution (even under favorable soil thermodynamics conditions). P-apatite minerals were found in sand and silt soil fractions subjected to phosphate rock treatment, which presented up to 6-year P dissolution and promoted low P bioavailability. Agronomic use of soluble phosphate added with limestone is the most suitable technique used to increase grassland yield and P-use efficiency.