Cave Roof Research Articles

Study on formation and expansion condition of hidden soil cavity under condition of groundwater exploitation in karst areas

This paper uses an analytical method to analyze soil cavity forming conditions and the associated mechanics. On this basis, the paper studies the soil cavity expansion rule and reveals the nature of the soil cave collapse from the mechanism angle. The results show the following: (1) the spalling force caused by pumping at different points around a soil cavity varies. The nearer the point to the pumping well, the easier it is for the soil cavity to expand. (2) The nearer the point to the soil cavity roof, the greater the spalling force, indicating that the roof is easier to expand outward than a wall. (3) The expansion condition of a soil cavity is that the spalling force is greater than the cohesive force of the soil mass. With the expansion of the soil cavity, the spalling force increases. When the soil cavity begins to expand outward, the soil cavity shows trends of development due to the increasingly larger spalling force. (4) The spalling force influencing the expansion of the soil cavity is proportional to the pump drawdown and hydraulic gradient. Thus, the water level drawdown and flow must be controlled while pumping to control generation of soil cavities. The research results of soil cavity forming processes can be used as a theoretical reference for controlling karst collapse in the region.

Inventory, classification and genesis of the ground collapses in the groundwater body of the Western Mancha I

This paper presents one of the first detailed studies about the ground collapses that have taken place in recent years in the central area of the groundwater body of the Western Mancha I, in the province of Ciudad Real. The main source of the collapses is the breakdown of the roof of the karst cavities, as a result of a rapid and unusual increase in the groundwater due to the widespread and intense rainfall, such as those that took place in the wet period (2009-2013). This brought about a washing of the karstic system, the movement of water through sinks and preferential channels, which had been dry for decades, as well as the dissolution of the chalky material itself. This ascent phase of the groundwater was preceded by a steady decrease in the piezometric levels, caused by prolonged drought and over-exploitation through pumping. To obtain an optimum knowledge of the area of study, important research has been done to localize, measure, and classify each of the collapses. Along with this, we have compiled, expanded, and updated the data of the piezometry, to a high level of detail. We have been able to distinguish four types of ground collapses: alluvial collapses, collapses in areas of dolines, lagoon collapses, and intermediate types of collapses. It is also evident that with the passage of years, the collapses that have been produced are of lesser dimensions. Finally, we have deduced the areas which have a greater susceptibility for new collapses, in places such as the river Guadiana, the lagoon areas, and some areas of dolines.

Karst collapse susceptibility assessment: A case study on the Amalfi Coast (Southern Italy)

This paper presents a study to evaluate the collapse susceptibility of a karst cave located along a slope on the Amalfi coast (southern Italy) and the presumable geomorphological evolution of the whole slope as a result of cave roof collapse. In the study area, several natural karst caves with volumes varying between 1000 and >10,000m3 were inventoried and the most likely genetic processes were identified. Some of them proved to be remnants of already collapsed caves, while others were in precarious stability conditions. The caves are usually located upslope or very close to the main populated resorts. A detailed geological, geomorphological and geostructural study was performed on a very wide, deep cave (called the “Saraceno” cave), on which the resort town of Conca de' Marini has been built. The study was carried out through a multidisciplinary approach, which included classical field geological observations, sometimes requiring the support of rock-climbing geologists, experts in photogrammetric surveys and terrestrial laser scanning techniques (TLS). TLS surveys allowed the reconstruction of an accurate geometric and geostructural model of the cave and its relationship with the upslope Conca de' Marini resort. Furthermore, it allowed the thickness of the cave overburden to be determined in detail; ground surfaces most susceptible to collapse were also identified. In the event of possible widespread collapse, several buildings and transportation infrastructures could be involved. As the cave is located on a very steep slope, a debris avalanche could be triggered in the event of a catastrophic failure, and the landslide debris, characterized by a presumably high magnitude and velocity, could involve a wide slope area down to the coast. The failure evolution could be very similar to that which took place in Amalfi in the late 19th century.

Geologic Evaluation of Kirkuk Underground Storage Project

Geologic evaluation of the Kirkuk underground was conducted by comparison of the geometric properties of the cavities derived from two surveys running during 1989 and 2015. The vertical cross sections of the cavities show that most cavities have shown that most cavities have irregular shape because of the presence of impurities in the salt bed that cause different leaching velocities in different directions. The relationship of the cavity roof with tilted salt bed was studied, that shows some of the cavities are not safe to store LPG.

SINKHOLE DEVELOPMENT MODEL PART I. MODELING

This paper includes the basic results of sinkhole modeling wish use special analogue materials. Natural and experimental investigations of sinkhole development have been carried out since 1982. Experimental investigations are based on selection of special analogue materials. These materials have enabled to simulate the process of sinkhole development from the karst cavity roof destruction to sinkhole formation on the earth surface. It has been determined that the karst cavity roof destruction leads to the first intermediate cavity formation in the cover ground. Then arch destruction of the first intermediate cavity leads to the second intermediate cavity formation, etc., include sinkhole formation on the earth's surface.

Numerical analysis of the stability of abandoned cavities in bench blasting

When open-pit bench blasting approaches a site with underground cavities, concerns arise regarding the safe blasting distance to prevent collapse of the cavities because such collapses may induce other secondary problems related to the safety and workability of the site. It is therefore necessary to estimate the stability of underground cavities in the proximity of bench blasting. In this paper, blasting tests of small scale were carried out in a site with cavities and field blasting test data were measured to obtain the site-specific attenuation relations of PPV and principal frequency of stress waves. A numerical model is then developed based on these relations to calculate bench blasting induced stress wave propagation. The accuracy of the numerical prediction is verified by the field measured data. The verified numerical model is used to perform a series of simulations. The results are then used to assess the roof stability of cavities adjacent to upper bench blasting. Based on the numerical results, the response characteristics of cavity roof with respect to different explosive charge mass are also studied.

Bypassing and tightening of an underground water retention system in permeable karst: case study of the hydropower plant (HPP) Bribin, Indonesia

In the framework of the Integrated Water Resources Management (IWRM) joint research project in the karst area of Gunung Kidul, Province of Yogyakarta Special Region on the Java Island, Indonesia, an underground hydropower driven water extraction facility in the cave “Bribin” was developed using pump-as-turbine-driven systems for freshwater supply of the rural area. As numerous other caves in the Gunung Kidul area, Bribin is part of a ramified system of all-season water-bearing subterraneous rivers and natural caves in karstic limestone. The elliptic cross section of the cave was completely closed with a concrete barrage, thus creating a year-round underground retention volume with an operational storage level of approx. 15 m. This contribution highlights the geotechnical and geohydraulic challenges handled within the sub-project “Short-time and long-time behaviour of karst rock surrounding pressure-bearing underground water-retaining structures”. One key to the feasibility of an artificial water retention scheme in a natural cave is to ensure the mechanical stability of the cave roof and sidewalls. The necessary geotechnical investigations are described. Another key to the effectiveness of such a water retention concept is the control and minimization of “lost” seepage water bypassing the barrage structure through the karst rock mass. Measures to monitor and to explain the seepage phenomena are presented as well as grouting efforts to minimize them. The limitations of improving the overall tightness will be discussed. Interpretation includes the use of analytical and numerical methods.

A process model for underground coal gasification – Part-I: Cavity growth

In underground coal gasification (UCG), a cavity is formed in the coal seam due to consumption of coal. The irregular-shaped cavity consists of a spalled-rubble on the cavity floor, a cavity roof and a void zone between the two. Depending on the cavity growth pattern, UCG process can be divided into two distinct phases. In phase-I, coal/char near injection well gets consumed and cavity grows in a vertical direction and hits the overburden. Phase-II starts thereafter, in which the cavity grows in the horizontal direction toward the production well. This paper presents an unsteady-state model for gas production during phase-I for a coal under consideration for UCG. The non-ideal flow patterns in the cavity are determined using computational fluid dynamics (CFD). The CFD results and residence time distribution (RTD) studies show that the complex UCG cavity can be reduced to a computationally less time consuming compartment model consisting of a radial plug flow reactor (PFR) followed by a continuous stirred tank reactor (CSTR). The developed compartment model incorporates reaction kinetics, heat-transfer, mass-transfer, diffusional limitations and thermo-mechanical failure effects for the coal of interest. The model is tested on a lab scale UCG; it can predict the location of reaction and drying fronts, profiles of solid and gas compositions, exit gas calorific value and cavity growth rates. Further, the model predictions show an excellent match with the cavity growth rate and exit gas quality observed during laboratory-scale UCG-like experiments on the coal of interest. Therefore, the model can potentially be used to determine feasibility of UCG for any other coal for the known kinetics and spalling parameters.

Control the drainage: the gospel accorded to sinkholes

Karst is a terrain distinguished by its underground drainage, natural cavities and sinkholes. New subsidence sinkholes (both dropout and suffosion) formed within the soil cover constitute the main karst geohazard. Nearly all are induced by increased drainage inputs or by water table decline, and control of the drainage is the primary means of reducing their hazard. Cave collapse and the development of collapse sinkholes in bedrock are less common, and the stability of a cave roof that is thicker than its width means that only those caves at shallow depth create any hazard. Predictions of the locations of caves or potential sinkhole sites are next to impossible, geophysical searches have severe limitations and borehole searches can incur significant costs. Consequently, controlling the drainage on construction projects is usually the most cost-effective means of minimizing the karst geohazard.

Similar cryptic behaviour during the early juvenile phase of two unrelated reef fishes: Epinephelides armatus and Bodianus frenchii

The juveniles of many reef fishes behave cryptically during critical juvenile stages in their life history and thus the microhabitats they often occupy are not well known. Comprehensive surveys of reef fishes on the temperate mid-west coast of Australia identified that juveniles of the unrelated Epinephelides armatus (Epinephelidae) and Bodianus frenchii (Labridae) < 100 mm total length both exhibit cryptic behaviour by exclusively swimming upside down under cave roofs and ledges. These individuals swam among the sponges and small algae in this microhabitat which would provide refuge from predation and also supply the dietary requirements of these two carnivores. Occupying this microhabitat would also reduce intra-specific competition, as individuals > 150 mm were only observed swimming ventrally oriented to the substrate in caves, under ledges or on open reef. Identifying the nursery habitats of fishery species, such as E. armatus and B. frenchii, is critical for understanding their life histories, but would also inform survey designs aimed at determining recruitment strength or variation.

Heat Removal Using the Hollow Roof in the Javanese House

Ventilation plays a vital role in securing optimum air quality and thermal comfort in buildings. In fulfilling this need, it touches on a wide range of building design and ventilation performance. Early attempts to minimize ventilation energy loss frequently resulted in poor indoor quality and comfort problems. This paper explains about natural air circulation, indoor and outdoor air temperature and also air velocity on the hollow roof in Javanese house, which has a specific shape of geometry and how far that roof can reduce the heat gain in the building. This method using computational fluid dynamics based program have become available to predict airflow and pollutant transport throughout a space. These approximate the space by the grid system containing many control volumes or elements to which numerical equations of flow are applied. And, the result of this research, the cavity roof in Javanese house is able to add indoor air rate velocity, with the average value of 0.5 m/s, and giving the indoor majority cooling effect average value of 0.55 ° C.

InSAR-based modeling and analysis of sinkholes along the Dead Sea coastline

Sinkholes commonly form by subsurface dissolution cavities that collapse after the overlying layers become mechanically unsupported. Sinkholes along the Dead Sea shorelines are preceded by, associated with, and followed by gradual surface subsidence that accompanies the cavities' growth. We exploit satellite radar interferometry (interferometric synthetic aperture radar) to resolve temporal and spatial relationships between gradual subsidence and sinkhole collapse. The geometry of the deflating cavity roof is determined by elastic inverse modeling of the surface displacements. A Coulomb failure stress criterion is applied to calculate the stress field induced by the deflating cavity at the ground surface. We find that the induced stress field favors generation of sinkholes at the perimeters of the subsiding areas rather than at their centers, in agreement with field observations, providing important information for sinkhole hazard assessment. Further, our analysis suggests that short-term deformation in consolidated gravel layers at shallow depths could be approximated by simple elastic modeling.

Landslide and Subsidence Potential due to the Progressive Development of Cave Network in Ella-Wellawaya Area, Sri Lanka

Carbonate rocks are highly soluble. Sinkholes are formed by both the failure of solution cavities and the rapid removal of fines from solution cavities in carbonate and metacarbonate rocks. Sri Lankan landmass is composed of Proterozoic high-grade metamorphic rocks such as gneiss and metacarbonates like marble. Large caves in Sri Lanka form in both marble and gneiss. A few land subsidence events have occurred recently in Ella-Wellawaya area, which is a hilly terrain. In addition, some cases of groundwater table lowering, which has caused drying of dug wells have also been recorded within the area, apparently related to a major development project presently under way in the area. The main objective of this paper is to draw the immediate attention of local researchers and authorities whom are working on mitigation and management of disasters, groundwater and climate change, showing the importance of carrying out detail studies on potential landslides and land subsidence of Ella-Wellawaya area for avoiding and minimising loss of humans and properties. Preliminary surveys on some land subsidence cases and speleological studies including geology, hydrogeology and morphological mapping of the underground caves in the area have been actively carried out. According to the results, it is shown that the subsidence is likely to be correlated with the collapsing of cavities and weathered zones in metacarbonates, and disturbances to the groundwater table. Field explorations done during the last two years have discovered several large underground caves in the area some more than 100 m across. Most of the cave roofs have been thinned by the breakdown of bedrock along weak zones such as joints. Since the process of collapse, trigged by weathering is continuing and patches and lenses of carbonate rocks observed in the caves are still being dissolved, the expansion of the cave spaces is unending. Some of the chambers of these caves are aligned parallel to the steep slopes in the Ella-Wellawaya area and some acted as underground water conduits and storages during the rainy seasons. The Ella-Wellawaya area has been undergone a change in vegetation cover since the colonial period and hence the area is more prone to soil erosion which exposes the near surface natural cavities to the underground caves. Present human exposures and interactions within the susceptible slopes have brought lives and properties under threat. Hence future land subsidence and landslide occurrences are highly predictable with the recent conditions in the area and hence threat to human life and properties is high. The tourism industry, unique to the area could particularly be affected. Hence such hazardous should properly be identified and demarcated and the erosion triggered by present vegetation changes must properly be addressed. Keywords: Metacarbonate rocks, Subsidence, Ella-Wellawaya, Cave network, Erosion

FORMATION OF CERTAIN CRATER-LIKE LAKE BASINS: RESULTS FROM THE LAKE SVETLOE (MOSCOW REGION)

The basin of the lake Svetloe was created before the Moscow Ice Age by karst process in carboniferous rocks. Deposits of the rim surrounding the lake are similar to those of kames, which arise from accumulation of aqueglacial deposits in the cavity under the dead ice, and after the collapse of the cavity roof in the englacial lake. The part of aqueglacial deposits was accumulated in the basin of the lake, while other part formed the annular rim on its shores. After the melting of the glacier, ice shores of the lake and part of its water content disappeared. The lake deposits remain as a rim elevated above surrounded plain. Some other crater-like basins in the Moscow region could be created by periglacial processes during late Moscow or late Valdai ice ages at the places of the collapsed pingos.

KARST-SUFFUSION SINKHOLES ON THE BUGULMA HIGHLAND

Karst sinkholes located in the eastern part of the Republic of Tatarstan have a different shape and age. The morphological sequence "cone-dish-saucer" relates to their age only in areas with similar geological structure. The field investigations proved that strongly fractured and karstified Lower Permian sulphate-carbonate deposits could absorb and accumulate a clastic material practically in unlimited amount. It was shown that the processes of cavity roof collapse, loosening and destruction of the Upper Permian rocks as well as suffusion of the fine clastic product play a major role in sinkhole development. The reservoir filling and seasonal fluctuations of water level in the large rivers are the main factor of the intensification of the process.

Bubble-induced cave collapse.

Conventional wisdom among cave divers is that submerged caves in aquifers, such as in Florida or the Yucatan, are unstable due to their ever-growing size from limestone dissolution in water. Cave divers occasionally noted partial cave collapses occurring while they were in the cave, attributing this to their unintentional (and frowned upon) physical contact with the cave walls or the aforementioned “natural” instability of the cave. Here, we suggest that these cave collapses do not necessarily result from cave instability or contacts with walls, but rather from divers bubbles rising to the ceiling and reducing the buoyancy acting on isolated ceiling rocks. Using familiar theories for the strength of flat and arched (un-cracked) beams, we first show that the flat ceiling of a submerged limestone cave can have a horizontal expanse of 63 meters. This is much broader than that of most submerged Florida caves (~ 10 m). Similarly, we show that an arched cave roof can have a still larger expanse of 240 meters, again implying that Florida caves are structurally stable. Using familiar bubble dynamics, fluid dynamics of bubble-induced flows, and accustomed diving practices, we show that a group of 1-3 divers submerged below a loosely connected ceiling rock will quickly trigger it to fall causing a “collapse”. We then present a set of qualitative laboratory experiments illustrating such a collapse in a circular laboratory cave (i.e., a cave with a circular cross section), with concave and convex ceilings. In these experiments, a metal ball represented the rock (attached to the cave ceiling with a magnet), and the bubbles were produced using a syringe located at the cave floor.

Mechanisms of subglacial cavity filling in Glacier de Tête Rousse, French Alps

AbstractThe deadliest outburst flood from an englacial cavity occurred on Glacier de Tête Rousse in the Mont Blanc area, French Alps, in 1892. A subglacial reservoir was discovered in the same glacier in 2010 and drained artificially in 2010, 2011 and 2012 to protect the 3000 inhabitants downstream. The mechanism leading to the spontaneous refilling of the cavity following these pumping operations has been analyzed. For this purpose, the subglacial water volume changes between 2010 and 2013 were reconstructed. The size of the cavity following the pumping was found to have decreased from 53500 m3 in 2010 to 12 750 m3 in 2013. Creep and the partial collapse of the cavity roof explain a large part of the volume loss. Analysis of cavity filling showed a strong relationship between measured surface melting and the filling rate, with a time delay of 4–6 hours. A permanent input of 15 m3 d−1, not depending on surface melt, was also found. The meltwater and rain from the surface is conveyed to bedrock through crevasses and probably through a permeable layer of rock debris at the glacier bed. The drainage pathway permeability was estimated at 0.054 ms−1 from water discharge measurements and dye-tracing experiments.

Inferior Turbinate Flap for Nasal-side Closure of Palatal Fistula in Cleft Patients: Technical Note.

Summary:Residual palatal fistula after repair of palatal cleft is common. Repair of residual oronasal fistula is not always successful. Two-layer closure techniques that close these fistulas with soft tissue are a common practice. Turnover flaps are the most used flaps and often the sole method for nasal-side closure of fistula. Anteriorly based inferior turbinate flap can be used to provide soft tissue for nasal-side closure when turnover flaps will not provide sufficient tissue for this purpose. Under general anesthesia with nasotracheal intubation, inferior turbinate was released from posterior attachment. After removing the inferior conchal bone, mucoperiosteal flap was used for nasal-side closure of anterior palatal fistula in patients with cleft. Anteriorly based inferior turbinate flap was used for nasal-side closure of residual palatal fistula in 3 patients with cleft. Age of the patients was 14, 16, and 18, and recurrence of palatal fistula has not occurred. Anteriorly based inferior turbinate flap is an axial pattern flap with appropriate surface of the paddle and vicinity to the oral cavity roof. It can be used in large anterior, palatal fistula for reconstruction of nasal floor. Considering appropriate another flap for oral side coverage of such fistula is mandatory.

Location of microseismic swarms induced by salt solution mining

Ground failures, caving processes and collapses of large natural or man-made underground cavities can produce significant socio-economic damages and represent a serious risk envisaged by the mine managements and municipalities. In order to improve our understanding of the mechanisms governing such a geohazard and to test the potential of geophysical methods to prevent them, the development and collapse of a salt solution mining cavity was monitored in the Lorraine basin in northeastern France. During the experiment, a huge microseismic data set (∼50 000 event files) was recorded by a local microseismic network. 80 per cent of the data comprised unusual swarming sequences with complex clusters of superimposed microseismic events which could not be processed through standard automatic detection and location routines. Here, we present two probabilistic methods which provide a powerful tool to assess the spatio-temporal characteristics of these swarming sequences in an automatic manner. Both methods take advantage of strong attenuation effects and significantly polarized P-wave energies at higher frequencies (>100 Hz). The first location approach uses simple signal amplitude estimates for different frequency bands, and an attenuation model to constrain the hypocentre locations. The second approach was designed to identify significantly polarized P-wave energies and the associated polarization angles which provide very valuable information on the hypocentre location. Both methods are applied to a microseismic data set recorded during an important step of the development of the cavity, that is, before its collapse. From our results, systematic spatio-temporal epicentre migration trends are observed in the order of seconds to minutes and several tens of meters which are partially associated with cyclic behaviours. In addition, from spatio-temporal distribution of epicentre clusters we observed similar epicentre migration in the order of hours and days. All together, we suggest that the recorded microseismicity mainly represents detachment and block breakage processes acting at the cavity's roof, indicating a zone of critical state of stress and where partial fractures cause chain reaction failures as a result of stress redistribution processes.

Middle Pleistocene stratigraphy of the deposits in Za Hájovnou Cave (Javoříčko Karst, northern Moravia, Czech Republic)

Middle Pleistocene stratigraphy of the deposits in Za Hájovnou Cave (Javoříčko Karst, northern Moravia, Czech Republic)