Water-saturated Rocks Research Articles

Comparison of Torsional and SH Waves in Isotropic and Anisotropic Media Based on Laboratory Measurements

Abstract Utilization of the torsional wave signal has been reported in medical testing and engineering detection. A torsional wave is a shear-wave train whose vibrating direction (polarization) forms a torsional motion. However, there are a lack of understanding of its characteristics and potential for subsurface investigations. Here, compressional (P), shear (S) and torsional (T) transducers are constructed using different piezoelectric-transformer (PZT) chips in the laboratory and the characteristics of the torsional (T) wave propagating in isotropic and fracture-induced anisotropic media are analyzed in line with conventional P- and S-waves, covering waveform, amplitude, arrival time and velocity at different propagating angles. The results indicate that the velocity and anisotropy values measured using the T transducer are almost the same as the SH wave. For propagation in isotropic and anisotropic media, the wavefield generated by the T transducer is very simple with no mode conversions and source-generated interferences, which is similar to the SH wavefield, whilst the SV wavefield comprises of a series of complex events from mode conversions and interferences. For propagating in fluid- saturated fractured rocks, the torsional wavefield also comprises of a fast and slow wave train, which is referred to as torsional-wave splitting, and is similar to the shear wave splitting from S transducers. Furthermore, the anisotropy parameters measured using P, S and T transducer show a good correlation with the fracture density, and the P wave anisotropy is higher in air saturated rocks than water saturated rocks, while the shear wave anisotropy measured by S transducer and T transducer are sensitive to fracture density. Similar to the P transducer, the T transducer is polarization-independent, or directional invariant. Therefore, utilizing the T transducer may simplify the field logistics during 3D shear-wave surveys. However, field torsional wave generation is a major issue that needs further study.

Effects of fluid saturation and viscosity on seismic dispersion characteristics in Berea sandstone

Despite additional availability of laboratory data from water-saturated sandstone at seismic frequencies, measurements of rock samples saturated with high viscous fluids, particularly at partial saturation, are still rare. To quantify the effects of fluid viscosity and saturation levels on seismic dispersion and attenuation characteristics, we conducted two comparative forced-oscillation measurements in partially saturated sandstone with varying fluid viscosity (e.g., water, glycerin) at seismic frequencies (2–400 Hz). The results demonstrate that fluid viscosity and saturation levels substantially influence the dispersion and attenuation characteristics at the measured frequencies. Significant dispersion and attenuation are observed in the presence of a relatively small amount of gas (approximately 6%–8%) for glycerin and water saturation cases but vary in their magnitudes and characteristic frequencies. Specifically, the maximum extensional attenuation (approximately 0.024) occurs at approximately 200 Hz for water-saturated rock at 94% saturation, whereas at approximately 30 Hz with a peak of 0.032 for glycerin-saturated rock at 92% saturation. Based on theoretical modeling analysis, we suggest that mesoscopic fluid flow might be a dominant mechanism accounting for the observed attenuation in partial water or glycerin saturation, while the microscopic (squirt) flow mechanism possibly dominates the fully saturated cases.

Effect of cyclic loading level on mechanical response and microcracking behavior of saturated sandstones: Correlation with water weakening phenomenon

Rocks frequently endure water environments and diverse cyclic loading from natural and anthropogenic sources across various damage stages. Understanding the mechanical and fatigue behavior of saturated rocks under different cyclic loading levels is crucial for the intelligent design and long-term stability of the slope. Here, we report several monotonic and cyclic compression tests conducted on red and cyan sandstones under dry and water-saturated conditions, coupled with acoustic emission (AE) monitoring. We analyzed key mechanical parameters such as peak stress and peak strain, as well as AE parameters including count and energy, and dominant frequency in AE spectra. Our findings reveal that elevated cyclic loading levels significantly reduce peak stress and increase peak strain in both dry and water-saturated rocks, with more pronounced effects observed under water-saturated condition. The cumulative AE count correlates positively with increasing cyclic loading levels but decreases due to water saturation. Under cyclic loading with varying levels, dry rocks often experience shear cracking and exhibit AE waveform with high dominant frequency, while saturated rocks tend toward tensile cracking and AE waveform with low dominant frequency. Higher cyclic loading intensifies the occurrence of tensile cracking and AE waveform with low dominant frequency, which are constrained during the elastic deformation stage but become more pronounced beyond the crack initiation threshold. Moreover, cyclic loading enhances the water weakening effects in saturated rocks, closely associated with ongoing crack propagation within the rocks.

Experimental investigation on the anisotropy of friction property for dry and water-saturated rock

Friction properties of rock are closely connected with the anisotropy. The anisotropy of rock friction can provide a valuable assessment for geotechnical and geological engineering. In this study, the rotary friction tests were conducted to analyze the water effect on the friction property and the friction anisotropy of the four types of rock. The drilling response model (DD-model) was employed to characterize the rotary friction behavior of the rocks. The parameters of this model include the three types of friction parameters: 1/ς, μ, and f, where 1/ς and μ are constant, and f is a variable. A quantitative method is proposed for assessing the anisotropy of rock friction. The results of the rotary friction tests indicate that the relation between torque force and thrust force conforms to the DD-model. The changes of two friction constants 1/ς and μ from dry state to water-saturated state suggest that the water effect on the friction strength of the rocks exhibits significant anisotropy. The friction strength determined by the friction variable f increases first, then decreases, and finally stabilizes with the increasing of depth. AIf is an anisotropy index calculated by the proposed method. The percentage difference of the average value of AIf between water-saturated and dry states shows the degree of the water effect on the friction anisotropy of the rocks, mudstone (MU) > granite (GR) > fine sandstone (FS) > argillaceous siltstone (AS). The quantitative model is hopefully constructed for characterizing the relation between the anisotropic friction strength of rock and the moisture state in future.

Experimental study on fractal dimension of energy dissipation and crack growth in saturated tuff at different strain rates

In order to investigate the effects of strain rate and water saturation on the energy dissipation and crack growth of tuff, uniaxial compression tests were carried out on dry and water saturated tuff with different strain rates using an electro-hydraulic servo press and a 50 mm diameter split Hopkinson pressure rod (SHPB) device. High-speed camera and Image J image analysis software were used to obtain the crack growth process of the specimen under impact load, and fractal dimension was introduced to quantitatively study the crack growth degree. The results show that more than 90% of the energy is stored in the specimen as elastic energy when it reaches the peak stress under static load. The average total energy of water-saturated specimens is 67.55% of that of dry specimens. The average energy dissipation density of water-saturated specimens under 0.3 MPa, 0.4 MPa and 0.5 MPa air pressure is 0.79, 0.91 and 0.92 times of that of dry specimens, respectively. Water-saturated specimens will deteriorate and thus reduce their energy storage and energy absorption effects. The reflected energy, transmitted energy, absorbed energy and incident energy are linear, logarithmic and linear functions, respectively, and the energy absorptivity and specific energy absorptivity of water-saturated specimens are lower than those of dry specimens. Due to the existence of “stefan” effect, the increase of energy dissipation density of water-saturated specimen at high strain rate is greater than that of dry specimen. The mean fractal dimension of water-saturated specimens under 0.3 MPa, 0.4 MPa and 0.5 MPa is 1.09, 1.05 and 1.16 times that of dry specimens. At the same strain rate, the number and width of cracks in water-saturated specimens are larger than that in dry specimens. Water-saturated behavior reduces the energy absorption capacity of tuff, increases the fractal dimension of crack growth, and significantly reduces the resistance of water-saturated rock to external loads.

An improved model for discrete element method simulation of spatial gradient distributions of freeze-thaw-induced damage to sandstone

The investigation into the freeze-thaw (F-T) damage holds paramount theoretical significance in comprehending the mechanisms underlying F-T disasters, predicting catastrophes, and devising engineering protection systems. F-T damage in rock evolves progressively from the surface towards the interior, however, current models exhibit conspicuous deficiencies in simulating such progressive damage. Drawing upon experimental findings concerning the evolution of F-T damage in water-saturated rock, an improved discrete element model (DEM) for rock F-T damage is developed. In this model, thermal conduction model and volume expansion theory are integrated to describe the volumetric expansion characteristics during the freezing of internal pore water, thus effectively simulating the initiation and progression characteristics of frost heave cracks. We validated this model through comparisons with theoretical analyses and experiments, exploring the effects of model parameters. Employing moment tensor, the spatial gradient distribution patterns of F-T damage in water-saturated rock from the vantage point of fracture energy was analyzed. The results reveal that at −20 °C, 20 F-T cycles are requisite for the propagation of damage from the outer layer to the center of the Sichuan sandstone samples. The extent of damage in the outer layer exceeds that of the center, with the maximum fracture energy density of the outer layer being approximately 38.7 times that of the center. This model aptly delineates the progressive development of F-T damage characteristics and holds promise for further applications in identifying and delineating F-T damage zones in cold region rock engineering.

Қарнақты бекітпелермен жоғары кернеулерден контурға жақын массивінің геомеханикасын бақылау арқылы қайта пайдаланылатын дайындау қазбаларының тұрақтылығын арттыру

An analysis of existing methods and means to improve the sustainability of reused development workings has been made. to protect the workings on the border with the goaf permanent artificial fences should be used: organ rows, bushes of racks, bonfires made of sleeper timber filled with rock, bonfires with an organ row, organ rows with a rubble strip, supports of high strength and limited compliance, etc. and portable protective supports made of metal friction struts, hydraulic struts, etc. The following factors are accepted as influencing factors: the presence of zones of increased rock pressure; strength characteristics of the rocks of the roof and soil of the formation and their thickness; structure and water saturation of rocks; landing step of the main roof; the presence of disjunctive geological disturbances; lava movement speed; power characteristics of the lining of the excavation. The output parameters are: the magnitude of the heaving of the formation soil, the deformation of the elements of the lining of the mine working; breaks in the interlocks of the support, displacement of the working contour in the vertical and horizontal plane, displacement of the side arched legs into the working cavity, etc. All these parameters were considered from the point of view of the need to invest in the development of material and labor costs to bring it into an acceptable operational condition. The nature of the pressure distribution depends on the extracted thickness of the reservoir, for example, the displacement and convergence of roof and soil rocks with an increase in reservoir thickness from 1.0 to 2.0 m increase, on average, by 10-20%. The results of the analysis indicate more "heavy" conditions for maintaining the workings, formed behind the lava by 1.3-2.5 times and reused 1.7-3.5 times compared to the undercut and workings made in the coal massif.

Microstructure Imaging and Characterization of Rocks Subjected to Liquid Nitrogen Cooling

Liquid nitrogen (LN2) fracturing is a potential stimulation method in unconventional hydrocarbon recovery, showing its merits in being water free, creating low formation damage and being environmentally friendly. The microstructure evolution of rocks subjected to LN2 cooling is a fundamental concern for the engineering application of LN2 fracturing. In this paper, pore-scale imaging and characterization were performed on two rocks, i.e., tight sandstone and coal specimens subjected to LN2 cooling using computed tomography scanning. The digital core technique was employed to reconstruct the microstructures of rocks and give a quantitative analysis of the pore structure evolution of both dry and water-saturated rocks. The results indicate that LN2 cooling has a great effect on the pores’ morphology and their spatial distribution, leading to a great improvement in pore diameter and aspect ratio. When compared to the sandstone, coal is more sensitive to LN2 cooling and thermal stresses, having a more noticeable growth in pore–throat size. The porosity growth of coal is 291% higher than that of sandstone. There is a growing trend in the irregularity and complexity of pore structures. After LN2 cooling, the fractal dimensions of the pores of sandstone and coal grow by 11.7% and 0.87%, respectively, and the proportion of pores with a shape factor > 100 increases. More bundle-like and strip-shape pores with multiple branches are generated, which causes a significant growth in the throat size and the proportion of connected pores with a coordination number ≥ 1, enhancing the complexity and connectivity of pore structures dramatically. Additionally, pore water plays an important role in aggravating rock damage during LN2 cooling, enhancing the pore space and connectivity. The porosities of the saturated sandstone and coal samples grow by 22.6% and 490.4%, respectively, after LN2 cooling, which are 5.6% and 186.6% higher than dry samples. The generation of macropores ≥ 70 μm is the primary contributor to porosity growth during LN2 cooling, although such pores account for only a small proportion of the total. These findings contribute to our understanding of the microscopic mechanism of LN2 cooling on rock damage and may provide some guidance for the engineering application of LN2 fracturing.

Study of changes in the induced wave field in mining waste storage facilities

An integrated approach to analyzing changes in the induced wave field in mining waste storage facilities for mineral waste is considered to localize potentially dangerous zones in the body of bulk structures using georadar sounding. It has been established that the zone of possible water saturation of rocks is perceived by the georadar signal as a transition to a medium with a higher dielectric constant and is reflected by the maximum amplitude of the signal. The boundaries of water saturation zones are not always sharply defined, but change smoothly depending on the degree of water saturation from a natural state unsaturated with moisture to complete saturation of soil pores. During GPR sounding, below the expected zone of water saturation, the soil structure is noticeably smoothed out, where, due to increasing attenuation, the signal amplitude sharply drops, which manifests itself in a noticeable decrease in the contrast of the wave pattern of the radargram. The use of intra-method integration by profiling on a permanent base and a common depth point with simultaneous synchronization of groundwater level measurements in a piezometer made it possible to identify and identify zones of increased water saturation in the dam body.

Theoretical Simulation of the Resistivity and Fractured–Cavernous Structures of Carbonate Reservoirs

Recently, theoretical modeling based on rock physics has emerged as a pivotal approach to studying the resistivity of complex fractured–cavernous microstructures. In this work, to study the effects of fractured–cavernous structures on carbonate reservoir resistivity, electrical conductivity models were developed based on the effective medium theory and Ohm’s Law, and theoretical simulations were performed to examine how the porosity and resistivity of the rock matrix, the formation water resistivity, and the parameters of the fractured–cavernous microstructure affect the resistivity of rocks saturated with petroleum or water. Furthermore, the modeling results revealed the specific relationships between these factors in petroleum-saturated and water-saturated rocks. For vuggy reservoirs, a significant negative correlation between throat diameter and resistivity was revealed when variations in the rock matrix and formation water resistivity were negligible. Furthermore, the pore shape—especially the extension of pores in the direction of the current—severely reduced the resistivity of petroleum-saturated rocks. For fractured reservoirs, the porosity and resistivity of the rock matrix were the primary factors affecting resistivity, with the fracture inclination angle and width also exhibiting pronounced effects on the resistivity of water-saturated rocks. The rock cementation exponent was much smaller when the matrix pores were interconnected through fractures than when they were interconnected through throats. The findings reveal that the effects of the structural parameters of fractured–cavernous carbonate reservoirs on reservoir resistivity differ between petroleum-saturated and water-saturated rocks. The conventional Archie’s equation is insufficient for evaluating fluid saturation in carbonate reservoirs. A saturation evaluation model with a variable rock cementation exponent tailored to the specific reservoir type should thus be developed.

The influence of water-saturation on the strength of volcanic rocks and the stability of lava domes

The rocks forming a volcanic edifice or dome are typically saturated or partially-saturated with water. However, most experiments aimed at better understanding the mechanical behaviour of volcanic rocks have been performed on dry samples, and therefore most large-scale models designed to explore volcano stability have used parameters representative for dry rock. Here, we present a combined laboratory and modelling study in which we (1) quantified the influence of water-saturation on the mechanical behaviour of variably altered dome rocks from La Soufrière de Guadeloupe (Eastern Caribbean) and (2) used these new data to investigate the influence of water on dome stability. Our laboratory data show that the ratio of wet to dry uniaxial compressive strength (UCS) and Young's modulus are ∼0.30–0.95 and ∼0.10–1.00, respectively. In other words, the dome rocks were all mechanically weaker when water-saturated. Further, the ratio of wet to dry UCS decreased with increasing alteration (the wt% of secondary minerals in the rocks). Micromechanical modelling suggests that the observed water-weakening is the result of a decrease in fracture toughness (KIC) in the presence of water. The ratio of wet to dry KIC also decreases with increasing alteration, explaining why water-weakening increased as a function of alteration. To explore the influence of water-saturation on lava dome stability, we numerically generated lava domes in Particle Flow Code using the experimental data corresponding to unaltered and altered rock under dry conditions. The strength of the dome-forming rocks was then reduced to values corresponding to wet conditions. Our modelling shows that, although the stability of the unaltered dome was not influenced by water-saturation, larger displacements were observed for the wet altered dome. Additional simulations in which we modelled a buried alteration zone within an otherwise unaltered dome showed that higher displacements were observed when the dome was water-saturated. We conclude that (1) the water-saturation reduces the UCS and Young's modulus of volcanic rock, (2) larger decreases in UCS in the presence of water are observed for altered rocks, and (3) the stability of a dome can be compromised by the presence of water if the dome is altered, or contains an altered zone. These conclusions highlight that the degree of alteration and water-saturation should be mapped and monitored at active volcanoes worldwide, and that large-scale models should use values for water-saturated rocks when appropriate.

Mechanism of increasing or inhibiting laser-weakened rocks by saturated fluids and mechanical behavior of rocks after laser damage

Laser technology has a wide range of application prospects as a novel means of assisting rock breaking. The realization of efficient laser-assisted breaking of deep hard rocks is based on revealing the mechanism of the saturated fluid increase or inhibition of laser-weakened rock. The laser irradiation of basalt with different water contents was used to analyze the mechanical response characteristics and investigate the destruction law of basalt under different laser power irradiations to explore the mechanism of the influence of water on the effect of laser rock breaking. The results show that the presence of water can significantly increase the drilling depth, and a laser irradiation of 1250 W can penetrate 56.5 mm deep into the rock in 30 s. The uniaxial compressive strength of basalt was reduced by a maximum of 38.23 % and the modulus of elasticity by a maximum of 74.99 % after the laser irradiation. Under low- power conditions, water has a positive effect on the laser rock-breaking efficiency. After 30 s of a laser irradiation in the range of 250–750 W, the uniaxial compressive strength of the water-saturated rock (WSR) samples was 12.64–13.43 % less than that of the original rock (OR) samples, and that of the natural state rock (NSR) samples was 1.09–3.93 % less than that of the OR samples. Both acoustic emission events and basalt energy significantly increased after a laser irradiation, and water promoted the expansion of rock microcracks. The degree of rock fragmentation increased with an increasing laser power. Laser irradiation can significantly reduce the strength of the rock, and water can effectively promote a low-power laser to break the rock, which is effective in reducing the difficulty and improving the efficiency of rock breaking. The obtained results provide theoretical and technical support for the application of the laser technology in the effective crushing of deep hard rock, and efficient and safe exploitation of deep resources.

Assessing the impact of oil saturation on wormhole morphology in carbonate acidizing

Carbonate acidizing is a well stimulation technique used to improve oil production by acid injection into the formation, creating conductive paths through rock dissolution. Most of the acidizing laboratory experiments are conducted on water-saturated rocks, assuming no oil is present after previous drilling and completion operations. However, different saturation conditions can occur in the rock formation, affecting the acidizing process. This study aims to assess the impact of oil saturation on carbonate acidizing. Reactive flow experiments were conducted on rocks saturated with water and oil using HCl 0.5 M and HCl 15%wt. at room temperature and 45 °C at flow rates of 1 and 20 mL/min. X-ray microtomography was used to visualize the wormhole morphology and compare the pore-volume-to-breakthrough (PVBT) values for each flow condition. Oil saturation resulted in efficient propagation of the wormhole with lower acid consumption and lower PVBT values. At 45 °C, PVBT values decreased by 54% for HCl 15%wt. at 20 mL/min. Wormhole morphology showed a smaller thickness in its propagation with oil saturation than with water saturation at the lower acid concentration, but not at the higher concentration. The presented results contribute to a deeper understanding of the significance of oil saturation in reactive flow during carbonate acidizing.

Effect of Water Content on the Impact Propensity of White Sandstone

Impact ground pressure is one of the most common dynamic disasters induced by mining activities, and water content is an important factor affecting such dynamic disasters. In this paper, uniaxial compression test, cyclic loading and unloading test, and acoustic emission test were conducted on white sandstone using RMT-150B rock mechanics test system and DS5 acoustic emission test system. The influence law of water content was analyzed on the strength characteristics, energy change characteristics, and impact propensity of white sandstone. The results showed that (1) the internal structure of the sandstone gets softened with the increase of the water content. The cohesive effect within the rock also begins to weaken, which in turn reduces the stiffness of the material and enhances its plasticity. The ability of the rock to resist elastic deformation becomes weaker, resulting in lower compressive strength and elastic modulus when the rock is subjected to external forces, making it more prone to deform and fail. The decrease in compressive strength of the water-saturated rock is 33.3%, and the decrease in its elastic modulus is 28.1% compared to the dry rock. (2) As the water content increases, the cohesion of the rock decreases and the internal structure of the rock fails more easily, which ultimately makes the energy needed for rock destruction lower. As a result, the total energy, elastic energy, and dissipative energy of the rock are reduced. The accumulated AE energy also decreases with the increase of the water content, indicating that rocks with higher water content gather less elastic energy before damage and accumulate less energy when deformation damage occurs. (3) The impact energy index and elastic energy index are negatively correlated with the water content. The impact energy index is reduced by 28.6%, and the elastic energy index is reduced by 20.9% for the saturated rock compared to the dry rock. The elastic energy index and impact energy index both decrease with the increase of rock water content, indicating that the less elastic energy is stored before the destruction of the rock and no excess energy is transformed into energy in rock crushing when the rock breaks, and therefore, the impact propensity of the rock is smaller. The results of the study can provide a theoretical basis for underground construction as well as rock fracture destabilization.

DEVELOPMENT OF ZEOLITE-CONTAINING LAYERS IN WESTERN SIBERIA DEPOSITS

Often, during the development of wells that have come out of drilling, these wells do not reach the design operating modes, since when the aqueous filtrate of the drilling fluid penetrates into the bottomhole formation zone (BFZ) and comes into direct contact with clay minerals, the pores narrow, the formation of insoluble sediments and creates insurmountable barriers. for the movement of reservoir fluids in the reservoir to the perforation interval, resulting in a decrease in the productivity of production wells. If the clayey cement of the reservoir rock contains zeolite, then its role in reducing the porosity and permeability properties (PPP) of rocks in the bottomhole zone of wells will be insignificant, since its presence does not lead to an increase in the water saturation of rocks in the bottomhole zone of wells and does not affect the reduction well flow rate. The article presents the results of experimental work on core samples of zeolite-containing rocks and geological and field studies in order to establish the effect of zeolites on obtaining potential well flow rates. Acid solutions are proposed for the development of wells when they exit from drilling.

Fracture behavior of yellow sandstone under freeze–thaw cycles with varied saturation states: An investigation of mode I fracture

In cold regions, the behavior of fissured rock in rock engineering is significantly affected by freeze–thaw (F–T) cycles. To investigate the impact of freeze–thaw cycles on rock fracture behavior, freeze–thaw cycle treatment, and fracture tests were conducted on Cracked Straight Through Brazilian Disc (CSTBD) specimens. The freeze–thaw treatment notably degraded the physical and mechanical properties of the rock, marked by a downward trend in fracture load, toughness, and energy. A considerable volume of data suggests that the impact of freeze–thaw (F–T) on yellow sandstone was predominantly during the initial stages of cycling, with this trend stabilizing as the number of cycles increased. Microscopic analysis via Scanning Electron Microscopy (SEM) uncovered the patterns of freeze–thaw damage in yellow sandstone. Dry rocks exhibited crack propagation, while water-saturated rocks displayed pore and crack expansion. The Digital Image Correlation (DIC) method illuminated the evolution of the high strain zone during the fracturing process. The mode I fracture process revealed a gradual expansion of the high strain zone originating from the crack tip, intensifying with increased load. As freeze–thaw cycles progressed, damage accumulation was gradual, and the path of mode I crack propagation grew increasingly intricate from a macroscopic perspective. Additionally, the quantification of fractal dimensions, achieved through the analysis of binarized SEM images, corroborates these observations at a microscopic level.

Methanogenic conversion of hydrogen to methane in reservoir rocks: An experimental study of microbial activity in water-filled pore space

Underground hydrogen storage can lead to the activation of methanogenic Archaea, demanding to quantify microbial activities within the pore space to evaluate potential hydrogen conversion rates. This study presents a method to determine microbial activities within various water-saturated reservoir rocks, inoculated media containing sand particles and rock fragments as well as bulk solution, by monitoring pressure and gas composition. Measured activities in water-saturated rock specimens with identical bulk volumes varied between 0.15 and 1.28 mM H2/h correlating with pore volume. Additionally, the results reveal that activities within intact rocks are 8–10 times higher than in corresponding bulk solutions. This observation demonstrates that the surface area available for microorganism colonization is another potential factor controlling microbial activity when the substance amount is held constant. This notion is supported by activities measured in inoculated media containing sand particles and rock fragments, as well as in rocks with similar pore volumes.

Aquifer layer in Muara Batu and Dewantara Sub-district based on resistivity cross-sectional model

This study aims to determine the depth of the aquifer layer in the Muara Batu and Dewantara sub-district as a source of groundwater that can be used continuously. The identification of this aquifer layer is based on the results of the resistivity values of subsurface rocks measured using the electrical resistivity method of the Schlumberger array. Data acquisition was carried out on 3 lines (MB1, MB3, and MB4) with a length of 330 m each. The variations in the resistivity values of the rocks obtained were modeled in the form of a 2D cross-section using the Res2DInv software, thus providing an overview of the subsurface for groundwater exploitation. The cross-sectional model obtained shows that the shallow aquifer layer is at a depth of 20-52 m (2-12 Ωm) on the MB1 and a depth of 60 m on MB3 and MB4. The low resistivity value 12 Ωm on the MB1 indicates that the subsurface is generally composed of water-saturated rock layers.

Experimental and DEM simulations of the mechanical properties of rock under freeze–thaw cycles

The investigation of the physical-mechanical properties of rock after freeze–thaw (F-T) cycles has important theoretical significance for understanding freeze–thaw disaster mechanisms, disaster prediction, and tunnel protection system design in cold regions. Physical-mechanical tests are carried out to quantify the deterioration of the physical-mechanical properties of sandstone subjected to long-term F-T cycles. The damage mechanism of sandstone subject to F-T cycles is discussed based on scanning electron microscopy (SEM) results. A new three-dimensional discrete element method (DEM) model for simulating freeze–thaw damage of water-saturated rocks is established based on the volume expansion theory. In the new method, a one-dimensional thermal conduction equation is introduced to realistically simulate the distribution of the temperature field in a cylindrical sample during thermal conduction, and the evolution equation of ice volume expansion is introduced to control the volume expansion of ice particles in the sample as the freeze point. The crack development mechanism during the F-T cycle and the correlation between the cracks generated by the F-T cycle and subsequent loading are also analyzed. The results show that approximately 80% of the frost-heave cracks are distributed in the annular column area 10–25 mm from the axis of the sample. In the radial direction, there is a significant correlation between the formatting of cracks during F-T cycles and loading. In the axial direction, due to the relatively uniform distribution of F-T cracks, the formation of cracks under subsequent loading is mainly controlled by stress concentration.

In-situ physical and elastic properties of Archaean basement granitoids in the Koyna seismogenic zone, western India from 3 km downhole geophysical well logs: Implications for water percolation at depth

The Koyna region in western India is characterized by recurrent artificial water reservoir triggered seismicity since the impoundment of the Shivaji Sagar lake in 1962. Physical and mechanical properties of the crystalline basement rock beneath the Koyna seismogenic zone are determined from the downhole geophysical logs in a 3 km research borehole. The borehole, KFD1, is located in the proximity of the Donichawadi fissure zone (DFZ), the surface manifestation of the fault associated with the 1967 M 6.3 Koyna earthquake. KFD1 penetrated 1247 m thick Deccan traps and continued 1767 m into the underlying granite-gneiss basement. Geophysical logs provide a rare opportunity to characterize the basement granitoids, which host the recurrent seismicity. Several major zones of anomalous physical and mechanical properties were delineated below a depth of 2 km from the analysis of downhole geophysical logs. High Poisson's ratio and high neutron porosity across anomalous zones imply the presence of water saturated rock. The analyses of Nuclear Magnetic Resonance log reveals the presences of clay bound and free fluid across these zones. Sharp decrease in dynamic Young's modulus with increasing Poisson's ratio imply the presence of fractures saturated with water. These hydraulically conductive fractures are potential locations for fault reactivation. Additionally, strike of major and minor fractures associated with the anomalous zones are compared with the strike of Donichawadi fault. High angle between strike of the major shear fractures in the anomalous zone and strike of the Donichawadi fault imply that borehole KFD1 may have either intersected subsidiaries of the main fault at multiple depths or a new hidden fault system.