Search Results (14)

Earth fill dams are susceptible to internal erosion and instability when founded over cavity-prone formations such as gypsum or karstic limestone. Subsurface voids can significantly compromise dam performance, particularly under seismic loading, by altering seepage paths, raising pore pressures, and inducing structural deformation. This study examines the influence of cavity presence, location, shape, and size on the behavior of zoned earth dams. A 1:25 scale physical model was tested on a uniaxial shake table under varying seismic intensities, and seepage behavior was observed under steady-state conditions. Numerical simulations using SEEP/W and QUAKE/W in GeoStudio complemented the experimental work. Results revealed that upstream and double-cavity configurations caused the greatest deformation, including crest displacements of up to 0.030 m and upstream subsidence of ~7 cm under 0.47 g shaking. Pore pressures increased markedly near cavities, with peaks exceeding 2.7 kPa. Irregularly shaped and larger cavities further amplified these effects and led to dynamic factors of safety falling below 0.6. In contrast, downstream cavities produced minimal impact. The excellent agreement between experimental and numerical results validates the modeling approach. Overall, the findings highlight that cavity geometry and location are critical determinants of dam safety under both static and seismic conditions. Full article

This study investigates highway pavement subsidence along Road 431, Israel, using an integrated geophysical framework that combines Interferometric Synthetic Aperture Radar (InSAR), Ground Penetrating Radar (GPR), and Electrical Resistivity Tomography (ERT). These methods address the limitations of standalone techniques by correlating surface subsidence patterns with subsurface anomalies. InSAR identified surface subsidence rates of up to −2.7 cm/year, pinpointing subsidence hotspots, while GPR detected disintegrated fill layers and air voids, and ERT revealed resistivity anomalies at depths of 50–100 m linked to karstic cavities and water infiltration. Validation through borehole drilling confirmed structural heterogeneity, specifically identifying karstic voids in limestone layers and weathered chalk layers that align with the geophysical findings. The findings highlight the complex interplay of geological and hydrological processes driving ground instability, exacerbated by groundwater fluctuations. This study demonstrates the novelty of combining surface and subsurface monitoring methods, offering a detailed diagnostic framework for understanding and mitigating geotechnical risks in transportation infrastructure. Full article

An important geological risk to which many towns in Puglia are exposed is sinking cavities in urban areas. For urban centers, studying, mapping, providing geological and speleological descriptions, classifying, and cataloging the forms and types of cavities is essential because cavities are linked to past local anthropic and natural processes at different sites. These circumstances could lead to the enhancement of existing underground cavities in urban areas through conservation and continuous monitoring. Unfortunately, in many cases, these underground cavities have been used as landfills and subsequently abandoned. In late March 2007, one of these cavities collapsed inside Gallipoli’s inhabited center, causing damage to the structures but fortunately not human lives. In the area surrounding the collapsed cavity, a series of geophysical investigations were undertaken using ground penetrating radar in an attempt to delimit the area of collapse and develop possible interventions for restoration. In the same area, these measures were repeated 16 years later in December 2022 due to another collapse. The comparison between data acquired in these two periods shows that there were no strong changes apart from an increased presence of subsoil moisture in 2022. Full article

The coconut crab, Birgus latro, has black protrusions on the tops of its walking legs and claw fingers. In addition, there are regularly aligned small black protrusions on parts of the exoskeleton surface of the claws and leg. In this study, the elemental composition, crystal structure, tissue structure, and mechanical properties of these protrusions were studied using a materials science approach, and the results were compared with those of mineralized cuticle. These leg tips were found to be a non-calcified fibrous tissue of α-chitin connected to the mineralized cuticle. The tip of the second walking leg was elongated and had a pointed shape with an oval cavity at its center that was more than 1000 times larger than the pore tubes (100–350 nm) of the mineralized cuticle. It was very soft, with a hardness of 0.4 GPa, corresponding to 11–12% of the hardness of the hard exocuticle and 55–57% of the hardness of the soft endocuticle. The elastic modulus of 8.0 GPa obtained by means of nanoindentation testing was consistent with that of α-chitin fibers of shrimp shells obtained by means of tensile testing. These soft protrusions provide a secure grip on the surfaces of trees or rocks and protect the claw fingertips. It was concluded that the black protrusions are related to a unique ecological (engaging in vertical movements, entering and exiting limestone caves, and escape behavior) aspect of the coconut crab, the largest terrestrial crustacean. Full article

In the Vitulano area, Upper Cretaceous bauxite bodies fill small depressions and karst cavities within Cretaceous shallow-water limestones. These bauxites were studied to understand the processes that led to their formation. Geochemical, mineralogical, and petrographic analyses were carried out on the bauxite samples, together with image analysis providing geometric parameters. The texture of Vitulano bauxite consists of ooids and sub-circular aggregates dispersed in a predominantly Ca-rich matrix. Ooids are generally formed by a single large core, often surrounded by an alternation of different aggregates of boehmite and Al-hematite reflecting different climate periods. The composition is dominated by the major elements Al₂O₃ and CaO with lower concentrations of Fe₂O₃ and SiO₂. Boehmite, calcite, hematite, and anatase are the main mineralogical phases identified. Image analysis provided values of fractal dimension D that gives information on carbonate platform exposure times since it is linked to long-lasting sub-aerial events and diffusion-limited cluster aggregation processes. The tectonic evolution of the area played an important role in the genesis of the Vitulano bauxites since it favored the erosion, transport, and re-deposition of pre-existing bauxite material from the surrounding Campania bauxites. Based on this hypothesis, Vitulano bauxites are defined and classified as para-autochthonous, and this was supported by Eu/Eu* vs. Sm/Nd and Eu/Eu* vs. TiO₂ Al₂O₃ indices displaying a similarity between Vitulano and the other Campania bauxites. Full article

The pulverized lime/limestone injection by top oxygen blowing lance during the basic oxygen furnace (BOF) process has gained much interest in recent years due to its advantages in helping slag formation and consequently in promoting refining reactions such as dephosphorization. In this pneumatic process, understanding the motion behavior and distribution of the powder particles in the furnace is of importance for regulating and designing this refining system reliably and efficiently. In this study, limestone powder top blowing through a novel nozzles-twisted oxygen lance during a BOF process is proposed and the process is simulated by establishing a multi-fluid flow model. The coupled fluid flow of gaseous oxygen and liquid steel is predicted by the volume of fluid (VOF) method, and the motion of the limestone particles is tracked by the discrete phase model (DPM). The results show that the powder injection has little effect on cavity depth of the oxygen-powder mixture jets of the nozzles-twisted lance, but decreases cavity width. During the blowing process, most of the powder particles gather around hot spots while the rest are taken out of the furnace by the reflecting oxygen stream or penetrate into the molten bath. The generated swirling flow of the nozzles-twisted oxygen lance enables a decrease in the amount of the powder particles carried by the reflecting stream and going into the molten bath, through changing the motion paths of the powder particles. As a result, the concentration distribution of the powder particles in the molten bath varies. It could be suggested that for the limestone powder injection the preferred nozzle twist angle of the oxygen lance is 10° due to the favorable conditions for dephosphorization. Full article

After the destructive earthquake in Petrinja measuring M6.2 occurred on 29 December 2020, which was followed by a series of foreshocks and aftershocks in the area of the rural settlements in Mečenčani and Borojevići, cover-collapse sinkholes suddenly appeared. The investigated area is located 20 km southeast of the epicentre. Some months later, more than 90 cover-collapse sinkholes appeared, jeopardising local infrastructure and residential buildings. The sinkholes appear in the area of covered karst, where there are clastic deposits 2–10 m thick on the fractured and weathered limestone bedrock. There are two geological models located in the investigated area: GM-1, where the base consists of clastic strata covering comprising Lithothamnium limestone, which in turn leads to the formation of underground cavities and cover-collapse sinkholes, and the GM-2, where the base comprises clay deposits without any cover-collapse sinkholes. These models can be effectively distinguished due to tomographic resistivity models; hence, numerous measurements were undertaken using two-dimensional electrical tomography in several phases. An estimate of the threat to infrastructural facilities was conducted, and the boundaries of the geological models were precisely determined according to which underground cavities and cover-collapse sinkholes did not develop. Tomographic measurements were also conducted over the largest cover-collapse sinkhole measuring 25 m in diameter and helped to more precisely define the entire hydrogeological model and the mechanisms involved in the formation of cover-collapse sinkholes. Full article

The existence of karst cavities has an important impact on the safety of foundation pit excavation projects. It is of engineering guiding value to study the influence of karst cavities on the blasting process of foundation pits and how to optimize the stiffness of cement mortar to improve the blasting effect. Based on the karst foundation pit bench blasting project of Shenzhen Dayun Foundation Pit Project, this paper adopts the SPH-FEM coupling calculation method to study the influence of karst cavities, cavity-filling water and cavity-filling silt clay on the rock-blasting process of bench blasting. We analyzed the development process of blasting damage of rock when the stiffness of karst cavity grouting filling changes under the conditions of slightly weathered, moderately weathered and strongly weathered limestone. The calculation results show that the karst cavity near the blasthole changes the direction of the minimum resistance line, which leads to the release of blasting energy; the rock breaking effect is improved when the karst cavity is filled with water medium and clay medium. Under the three limestone conditions, after the karst cavity is pretreated by cement grouting, the increase in the stiffness of the cement mortar makes the rock damage area first increase and then decrease after the karst cavity implosion, and There is a critical cement mortar stiffness that makes the best rock breaking effect. The critical cement stiffness of micro-, medium- and strongly weathered limestone is 2.2%, 6.1% and 27% of the blasted rock mass, respectively, which makes the karst cavity wall stress reach the peak value, and the rock-breaking effect is the best at this time. Full article

Multiple episodes of dolomitization of the shallow marine carbonates of the Late Kingriali Formation resulted in regional scale mappable dolostone geobodies in the Kohat and Potwar sub-basins. With the exception of few unaltered patches of the host limestone, more than 90% of the carbonates of the studied formation are diagenetically altered by replacive dolomites with associated dolomite cementation. Petrographical and geochemical data interpretation reveals that during the initial stage of dolomitization, the precursor limestone was significantly modified by the fabric-retentive replacive dolomite (RD-I) and produced bulk dolostones with non-planar-a to planar-s crystals. Neomorphic recrystallization (RD-II) was observed as an overgrowth of the already formed RD-I dolomite crystals during progressive dolomitization. The seawater at shallow depths is enriched with Fe-ions due to its interaction with Fe-rich beds within the studied formation. The modified seawater actively participated in the formation of ferroan replacive dolomites (RD-III). Stable isotopic composition of the unaltered Echinoderm plates, calcite cement (CC-I), and RD-I demonstrates signatures of δ¹⁸O and δ¹³C within the limit of late Triassic marine seawater or modified seawater. Depletion in the stable oxygen isotopic composition (from −0.99‰ to −3.75‰ V-PDB) demonstrates that RD-II and RD-III were formed in a sequence with progressively higher temperature fluids than normal seawater. Precipitation of dolomite cements as cavity filling rhombs (DC-I) and crystal overgrowth (DC-II) with highly depleted δ¹⁸O values (−5.44‰ to −7.45‰ V-PDB) illustrates dolomite cementation at higher temperatures and greater depths. The highly depleted values of δ¹⁸O (up to −9.16‰ V-PDB) and (up to 0.42‰ V-PDB) for δ¹³C of saddle dolomite (SD-I) indicate the precipitation of SD-I as a cavity filling dolomite at considerable depth. Calcite cementation and calcitization actively participated in the early, middle, and late diagenetic modifications as interpreted from their petrographic and stable isotopic studies. Porosity enhancement is clearly demonstrated by dissolution, stylolization, fracturing, and replacement dolomitization. Dolomite and calcite cementation had a negative impact on the reservoir character and occluded the dolostone porosity to a greater extent. Full article

This paper reviews the site investigation field data and access work performed between 2016 and 2019 in the study area located close to Gun-dong mine. The research was aimed at defining the cause of sinkholes and their relationship with the underlying karstic limestone bedrock and nearby mining activities. Only a limited number of small sinkholes appeared in 2014, 2016, and 2018 in the agricultural land close to the limestone mine. The previously open pit mine started its underground operations in 2007. Since then, the mine has developed, and is now comprised of, large underground excavations at several levels below the surface. The studies carried out concluded that the appearance of sinkholes may be related to a general lowering of the groundwater table because of nearby agricultural and mining activities and also due to over-extraction of water due to increased urban use. Whilst these are the best determinations, this paper identifies missing elements of the previous investigations mentioned above, some issues with the interpretation of poorly prepared borehole logs and the improper preservation of borehole cores. The authors make recommendations for a systematic approach for implementation of an investigation strategy. This paper concludes that the appearance of sinkholes is a natural phenomenon, developing over geological time. However, human intervention contributes to sinkhole formation, which in urban areas may result in human, property, and economic losses. A better understanding, based on a methodical approach and suitable technologies, can determine the causes of sinkholes and can lead to the formulation of solutions and the implementation of economically and socially acceptable mitigation measures. Full article

Karst cavities and caves are often present along fractures in limestone reservoirs and are of significance for oil and gas exploration. Understanding the formation and evolution of caves in fractured carbonate rocks will enhance oil and gas exploration and development. Herein, a reactive transport model was established considering both the matrix and fractures. Different factors affecting the dissolution along fractures were considered in the simulation of matrix–fracture carbonate rocks, including the magnitude and characteristic length of the matrix porosity heterogeneity, intersecting fractures, and complex fracture network. The results show that a strong heterogeneity of the matrix porosity significantly affects the cave formation along the fracture and the existence of fractures increases the heterogeneity due to the high permeability as well as the dissolution area. The characteristic length of the matrix porosity heterogeneity affects the cave location and shape. The larger permeability of intersecting fractures or the matrix greatly increases the cave size, leading to the formation of large, connected cave areas. A complex fracture network leads to more developed karst dissolution caves. The topology of the fracture network and preferential flow dominate the distribution of caves and alleviate the effect of the matrix heterogeneity. Full article

The electrical resistivity tomography method has been widely used in geophysics for many purposes such as determining geological structures, water movement, saltwater intrusion, and tectonic regime modeling. Karstic springs are important for water basin management since the karst systems are highly complex and vulnerable to exploitation and contamination. An accurate geophysical model of the subsurface is needed to reveal the spring structure. In this study, several karst springs in the Gökova Bay (SW, Turkey) were investigated to create a 3D subsurface model of the nearby karstic cavities utilizing electrical resistivity measurements. For this approach, 2D resistivity profiles were acquired and interpreted. Stratigraphically, colluvium, conglomerate, and dolomitic-limestone units were located in the field. The resistivity values of these formations were determined considering both the literature and field survey. Then, 2D profiles were interpolated to create a 3D resistivity model of the study area. Medium-large sized cavities were identified as well as their locations relative to the springs. The measured resistivities were also correlated with the corresponding geological units. The results were then used to construct a 3D model that aids to reveal the cavity geometry in the subsurface. Additionally, several faults are detected and their effect on the cavities is interpreted. Full article

When inner cavities of significant dimensions exist in natural rocks, problems arise when a shallow foundation for a building, bridge or other structure is builtonthem. Thus, taking one of the most representative cavity geometries in nature, the ellipsoidal horizontal shape, the main objective of this study is to obtain the ultimate bearing capacity of the foundation with cavities of different sizes and positions, on rock masses with different strengths and deformation characteristics. The study focuses on natural rocks of karst origin (in limestones, dolomites or gypsums) and of volcanic origin. The ultimate bearing capacity is determined relative to a situation without the existence of the cavity for different cavern positions and sizes, rock types (m_i), strengths (UCS), and states (GSI) of the rock mass. The results showed that the most decisive parameter is the relative eccentricity. The influence of the rock type (Hoek’s parameter m_i) is, for practical purposes, negligible (lower than 10%). The strength and condition of the rock mass (parameters UCS and GSI) have relatively little influence on the results obtained. This study aims to provide a simple design criteria for universal use, with different geometric configurations and qualities of rock masses that can be used directly without the need for sophisticated calculations by the designer. Full article

The quartz-K-feldspar-cemented breccia of Berglia-Glassberget in the Lierne municipality in central Norway forms an ellipsoid structure 250 m × 500 m in size. The hydrothermal breccia is barren in terms of economic commodities but famous among mineral collectors for being a large and rich site of crystal quartz of various colours and habits. Despite being a famous collector site, the mineralization is rather unique in respect to its geological setting. It occurs within Late Palaeoproterozoic metarhyolites of the Lower Allochthon of the Norwegian Caledonides regionally isolated from any other contemporaneous hydrothermal or magmatic event. In order to understand better the formation of the Berglia-Glassberget breccia, the chemistry, fluid inclusion petrography and age of the breccia cement were determined. Structural features indicate that the Berglia-Glassberget is a fault-related, fluid-assisted, hydraulic breccia which formed by single pulse stress released by a seismic event. ⁴⁰Ar-³⁹Ar dating of K-feldspar cement revealed a middle Triassic age (240.3 ± 0.4 Ma) for this event. The influx into the fault zone of an aqueous CO₂-bearing fluid triggered the sudden fault movement. The high percentage of open space in the breccia fractures with cavities up 3 m × 3 m × 4 m in size, fluid inclusion microthermometry, and trace element chemistry of quartz suggests that the breccia was formed at depths between 4 and 0.5 km (1.1 to 0.1 kbar). The origin of the breccia-cementing, CO₂-bearing Na-HCO₃-SO₄ fluid may have been predominantly of metamorphic origin due to decarbonation reactions (T > 200 °C) of limestones of the underlying Olden Nappe. The decarbonation reactions were initiated by deeply derived, hot fluids channelled to sub-surface levels by a major fault zone, implying that the breccia is situated on a deep-seated structure. Regionally, the Berglia-Glassberget occurs at a supposed triple junction of long-lived fault zones belonging to the Møre-Trøndelag, Lærdal-Gjende and the Kollstraumen fault complexes. These fault systems and the associated Berglia-Glassberget earthquake are the expression of rifting and faulting in northern Europe during the middle/late Triassic. Full article