Borehole Rock Research Articles

Electrical resistivity tomography data inversion using prior information for tunnel prospecting: A case study from southwestern China

AbstractThe direct current (DC) resistivity method is extensively used to predict water‐inrush disasters in tunnel prospecting. However, during DC resistivity inversion, different initial models can significantly affect the inversion results, often resulting in convergence at a local optimum. To overcome these challenges, we propose a new method for DC data inversion that uses prior information as a reference model. First, the resistivity distribution of the surrounding rock mass was estimated based on detailed geological analysis. Next, an initial homogeneous resistivity model was constructed by averaging the observed tunnel resistivity values. Finally, the initial model was developed by incorporating borehole rock samples and water content data. The effectiveness of the method' was assessed using a series of synthetic models of typical water‐bearing structures. We then applied this approach to the Laomacao Tunnel in the Yunnan Central Water Diversion Project (southwestern China), where drilling data were used as a priori information to optimize the initial model together with the average tunnel resistivity values, successfully identifying the water‐bearing structure ahead of the tunnel face. Overall, the proposed method enhances the understanding of sudden surges, aiding in the prevention and control of water disasters in tunnels.

Probing subtle alterations of smectite layer charge by the spectroscopic O[sbnd]D method in bentonite from the Alternative Buffer Materials tests in Äspö, Sweden

The recent and efficient spectroscopic, “O-D (using D2O water) method”, for layer charge (LC) determination of materials containing smectitic, wettable surfaces was used to identify subtle LC changes of thermally reacted samples (between ∼80 and 250 °C) from the Alternative Buffer Material (ABM) tests 2 and 5 conducted at the Äspö Hardrock Laboratory (HRL), Sweden. The tests were in situ intermediate-scale field experiments designed to simulate an engineered barrier around canisters containing radioactive waste within a deep geological repository. The tests consisted of several different bentonites compacted into 31 (ABM2) and 30 (ABM5) discs, stacked vertically around a central heater, and emplaced in a crystalline rock borehole in the HRL. Previous investigations of the ABM2 and 5 bentonites did not reveal specific mineralogical reactions of smectites, which may be observed at temperatures above 100 °C. The data presented in the present study, however, showed LC changes, in the ABM5 test, within the individual bentonite discs along a thermal gradient from the outside edge of the discs toward the heater contact, at which the temperature reached a maximum of 250 °C. Considerably less LC changes were observed for the bentonites in ABM2, in which heating reached a maximum of only ∼140 °C. Moreover, the LC data presented in the present study were found to be consistent with previously obtained cation exchange capacity (CEC) results and explained the observed changes in CEC along the thermal gradients across the discs. Both CEC and LC displayed a strong decreasing trend toward the heater contact in ABM5, and very weak increases toward the heater contact in ABM2. Of the several bentonites used in the tests, those with an initially higher LC, generally showed the greatest decrease of apparent LC after being reacted at high temperatures in the ABM5 package. The bentonites with an initially low to medium smectitic LC, appeared to undergo the least changes at the high temperatures achieved in the ABM5 package. The observed decrease of apparent LC is interpreted as resulting from the adsorption of interlayer cations at the siloxane surface, possibly in the ditrigonal cavity of the tetrahedral sheet, causing partial neutralization of the negative charge of the 2:1 layer. The minute increase in LC in the ABM2 package also showed a correlation with CEC but was within the measurement uncertainty.

Electromagnetic signal analysis and recognition of coal and rock properties during the borehole pressure relief process: Simulation and experiment

Borehole pressure relief is an important measure to prevent and control rock bursts for high stress mine. However, the complex and changeable coal and rock properties cannot be effectively identified during the borehole pressure relief process, resulting in instability phenomena such as drill pipe jumping, drill sticking, and drill holding in the borehole system, which seriously affects the borehole pressure relief efficiency and operation safety. To perceive the drilling status of coal and rock in real time, this paper provides an in-depth analysis of the electromagnetic signals of coal and rock during drilling through simulations and experiments, so as to accurately identify the coal and rock properties. First, a small-size coaxially fed microstrip antenna that can be used on a specific drill pipe is designed, and some simulations are performed to analyze the propagation characteristics of electromagnetic signals under different drilling conditions. The electromagnetic signals of different coal and rock properties are significantly different in the range of 4–8 GHz, and the frequencies corresponding to the S11 extremes are 5.432 GHz, 5.436 GHz, 5.532 GHz, 5.552 GHz, 5.516 GHz, and 5.468 GHz, respectively. Then, the electromagnetic signals are mapped into time–frequency diagrams through continuous wavelet transform to provide training samples for coal and rock properties recognition model. Subsequently, the MobileNetV3-EACS model is proposed by embedding the efficient multi-channel attention mechanism and modifying the classification network structure to improve the detection accuracy and classification adaptability, achieving the effective recognition of coal and rock properties. Finally, an experimental platform of coal and rock borehole system is built and multiple sets of comparative experiments are conducted. The experimental results show that the MobileNetV3-EACS has a prediction accuracy of 99.11%, which is increased by 1.78% compared to the classical MobileNetV3, verifying the effectiveness and superiority of the proposed coal and rock properties recognition method.

Simulation Study on Rock Crack Expansion in CO2 Directional Fracturing

In underground construction projects, traversing hard rock layers demands concentrated CO2 fracturing energy and precise directional crack expansion. Due to the discontinuity of the rock mass at the tip of prefabricated directional fractures in CO2 fracturing, traditional simulations assuming continuous media are limited. It is challenging to set boundary conditions for high strain rate and large deformation processes. The dynamic expansion mechanism of the 3D fracture network in CO2 directional fracturing is not yet fully understood. By treating CO2 fracturing stress waves as hemispherical resonance waves and using a particle expansion loading method along with dynamic boundary condition processing, a 3D numerical model of CO2 fracturing is constructed. This model analyzes the dynamic propagation mechanism of 3D spatial fractures network in CO2 directional fracturing rock materials. The results show that in undirected fracturing, the fracture network relies on the weak structures near the rock borehole, whereas in directional fracturing, the crack propagation is guided, extending the fracture’s range. Additionally, the tip of the directional crack is vital for the re-expansion of the rock mass by high-pressure CO2 gas, leading to the formation of a symmetrical, umbrella-shaped structure with evenly developed fractures. The findings also demonstrate that the discrete element method (DEM) effectively reproduces the dynamic fracture network expansion at each stage of fracturing, providing a basis for studying the CO2 directional rock cracking mechanism.

Mechanisms and experimental study of directional thermal shock fracture of granite under bidirectional horizontal loading

The study of the mechanism of thermal shock directional fracture of rocks under bidirectional horizontal stress is important for the application of directional thermal shock fracture technology. With the engineering background of the thick igneous roof overlying the coal seam, we conducted high temperature thermal shock directional fracture tests on granite under different horizontal loads to investigate the fracture mechanism. The results show that during the directional thermal shock of granite, the heating rate of borehole surrounding rock experienced three stages of rapid increase, rapid decrease and slowly decrease. AE tests were used to characterize the typical features of rocks during thermal shock fracture: the appearance of macrocracks in the specimen was accompanied by sharp increases in the cumulative AE count and the sudden drops in b-value. The experimental results show that thermal shock can create macroscopic directional fractures within the rock. Within a certain range of horizontal stress difference, the expansion direction of thermal shock cracks could be released locally from geological stress control, i.e. expanding along the direction of the minimum horizontal dominant stress. This provides completely new thinking for the cutting of hard roof and the directional fracturing of rock. In addition, directional thermal shock caused modifications in the distribution of stress in borehole surrounding rocks. We have established a model for stress distribution around the borehole rock and given the calculation formula for the initiation stress of the rock. The studies provide significant theoretical guidance for the industrial application of directional thermal shock fracturing technology.

Numerical modelling of inflatable steel-tube rock bolt considering non-linear contact behaviour

Inflatable steel-tube rock bolts are useful as they can introduce a pull-out resistance immediately after installation and do not cause a loss of frictional force under the existing groundwater environment. The anchoring mechanism and pull-out resistance of the inflatable steel tube has been basically explained through theoretical studies. The contact behaviour between the tube and borehole rock is essentially geometrically non-linear and elasto-plastic, which cannot be properly considered in theoretical approaches. In this study, the contact behaviour of inflatable steel-tube rock bolts was investigated through a novel modelling based on the contact theory. A validating representative model test for an inflatable steel-tube rock bolts was performed and successfully reproduced through the contact modelling method. It was revealed that the contact behaviour differs significantly differ from theoretical assumptions. Parametric analyses were carried out to investigate the effect of influencing factors such as the diameter ratio, the elastic modulus and maximum installation pressure, which cannot be considered in the theoretical model. It was found that the state of full inflation is the stress turning point where the general tube behaviour changes from mainly plastic to elastic. The maximum contact stress was obtained immediately before full inflation.

Investigation on radial fracturing around borehole under combined static stress and blasting

Blast-induced radial fracturing is generally subjected to geo-stress. This study experimentally, theoretically and numerically investigates the radial fracturing behaviours around a rock borehole under combined static stress and blast loading by combining blast testing, elastic mechanics analysis and finite element modelling. The study begins with 11 blast tests on 100 mm cubic granite samples under various uniaxial and biaxial stress states based on a biaxial hydrostatic loading system. The fracture networks are subsequently image-processed in ImageJ where the morphology and fractal characteristics of radial fracturing in the rock surface are examined. Then, the variations in fracture patterns are analyzed using elastic mechanics, and the corresponding crack extension is numerically simulated in LS-DYNA. The mechanisms of the influence of static pressure on blast-induced radial cracking are revealed. The results demonstrate that the static stress greatly suppresses the blast-induced radial fracturing, resulting in fewer and shorter radial cracks with lower propagation velocity. This leads to a reduction in the fractal dimension of fractures and rock damage, which is attributed to the initial stress offsetting the blast-formed tangential tensile stress. Meanwhile, uniaxial pressure governs the propagation direction of radial fractures, as the cracks initiate at the borehole wall where the maximum hoop tensile stress presents and propagate along a path with the smallest circumferential compression. At last, the implications of the current results for practical blasting are discussed. It is advisable to leverage the directional cracking advantage offered by blasting under anisotropic in-situ stress to achieve a smoother excavation profile.

Coupled TMD modeling of cryogenic treatment of borehole in coal under confinement

Cryogenic fracturing using liquid nitrogen (LN2) is a waterless fracturing technology that is under extensive research nowadays given the high demand of environmental-friendly development of unconventional oil and gas resources. Excluding the exerted hydraulic pressure, the initiation and propagation of cryogenic fractures in rock materials largely depend on thermal stress generated by LN2 and the rock properties. So far, there are quite a few experimental studies elaborating on the cryogenic fracturing process of coal rocks; however, modeling studies on the topic are still very preliminary with no damage quantification. This study first set up a coupled thermo-mechanical (TM) modeling procedure by solving the heat conduction and rock mechanics equations in a serial manner and incorporating the maximum principal stress failure criterion. Then the numerical stability of this modeling procedure was examined through time step and grid resolution tests, and the model accuracy was corroborated by analytical solutions. Furthermore, the damage criterion was quantitatively validated against our experimental observations. Using this thermo-mechanical damage (TMD) modeling procedure, a systematic examination of the effects of key factors on cryogenic circulation treatment of coal rock borehole was carried out using realistic parameters. Trends and patterns of the cryogenic damage upon key factors, including realistic temperature boundary with the Leidenfrost effect, Young's modulus, thermal expansion coefficient, Poisson's ratio, specific heat capacity, density, thermal conductivity, in-situ stresses, and initial temperature of the coal rocks have been revealed and discussed. The modeling results herein are of great significance to understand the mechanisms of cryogenic fracturing of coal rocks, and this TMD modeling procedure could be further expanded to evaluate and optimize cryogenic treatment process of coal seams in field pilot tests.

Geochemical Features of Potentially Ore-Bearing Mafic Intrusions at the Eastern Norilsk Region and Their Relationships with Lavas (NW Siberian Traps Province)

The problem of the world-class PGE-Cu-Ni Norilsk deposits’ origin has attracted geologists for several decades. The main goal of this study is to determine the specific features of ore-bearing intrusions in comparison with thousands of similar barren intrusions widespread within the Siberian igneous province, and to establish their genesis. As a result of statistical processing of previously published isotope-geochemical data and obtained by the authors, systematic differences were found in the distribution of the isotopic ratio of Nd in ore-bearing and barren intrusions, as well as in volcanic rocks at the Norilsk region. Thus, ore-bearing rocks in ten deposits (Talnakh, Kharayelakh, Norilsk 1, South-Maslovsky, North-Maslovsky, Norilsk 2, Chernogorsky, Zub-Mrksheydersky, Pyasino-Vologochansky, Imangdinsky), different in Ni and PGE reserves, show a very narrow range of Nd isotopic ratio, ԐNd(T) = 1.0 ± 1.0 (2σ, N = 139), whereas barren and volcanic rocks are characterized by a rather wide ԐNd(T) range, from −10 to +7 units (N = 256). Furthermore, ore-bearing intrusions are characterized by reduced and compact variations of the La/Lu ratio due to lower concentrations of light lanthanides. For the first time the authors studied two new intrusions penetrated by MD-48 and MD-60 boreholes drilled by Norislkgeologia LLT at the eastern part of the Mikchangda area. Their economic values are still unclear and should be estimated using geochemical methods. Both intrusions lie in the Devonian rocks, have similar thickness and mineral composition, but differ in textural and structural features, which indicate a rapid crystallization of the MD-48 intrusion. According to the contents of the major oxides, the rocks in MD-48 and MD-60 are identical, but they differ in U/Nb, La/Sm, and Gd/Yb ratios. It is important that the rocks in the MD-60 borehole are characterized by ԐNd(T) = 1.0 ± 0.6 (2σ) and fall into the range of ore-bearing intrusions, whereas the rocks in MD-48 have ԐNd(T) 2.4 ± 0.9, and, thus, are outside of ore-bearing intrusions. Therefore, ԐNd(T) values can be used as a local criterion for the estimation of economic potential of mafic intrusions, which is demonstrated for the Mikachangda area.

LogRegX: An Explainable Regression Network for Cross-Well Geophysical Logs Generation

Geophysical logging instruments continuously measure multiple geophysical properties of borehole rocks, thus providing a feasible way to fine borehole geology modelling. Since the missing problem of well logs is inevitable, it is essential to generate the missing logs by the available ones. Recently, a large body of interdisciplinary studies has demonstrated the effectiveness of applying machine learning to solve the missing logs generation problem, under which the training and testing datasets obey the independent and identical distribution (iid) assumption. This assumption, however, is not satisfied in the case of the cross-well missing logs generation task. A standard method to solve the non-iid issue is to map source and target data to a common feature space and then employ Mean Maximum Discrepancy (MMD) to measure domain differences. However, this method suffers from high computational complexity and poor feature explainability when dealing with logs generation tasks. To solve the above problems, we propose an explainable regression network for cross-well geophysical logs generation named LogRegX. LogRegX integrates single-well feature extraction, cross-well feature alignment, and missing logs prediction while maintaining the explainability of logging features. Specifically, LogRegX leverages the gating mechanism to fuse multi-scale logging features to capture the response characteristics of well logs. The learned source and target feature representations are subject to domain discrepancy constraints, measured by Random Fourier Feature transform induced MMD. Additionally, target-domain information retaining mechanism is introduced to maintain the structure of target data so that the transferred features are explainable. Experiments on real-world field data demonstrate the superiority and the explainability of LogRegX over the existing methods.

Burial and thermal history of the eastern transform boundary of the central western carpathians based on 1D basin modeling

This paper represents the first data on the thermal and burial history of Mesozoic and Cenozoic sedimentary rocks in the Maruszyna IG-1 deep borehole from the transpressional shear zone of the Western Carpathians. Representative, organic-rich mudstone and claystone samples were selected to determine thermal maturity using mean random vitrinite reflectance (Ro) and thermal alteration index (TAI) data. The reconstruction of the thermal history of fold-and-thrust units was carried out using 1D modeling. This study uniquely distinguishes various thermal maturity levels in the deep profile determined by strata repetition, different absorption of clay and carbonate mineral settings and structural thermal changes in humic particles and palynomorphs. Reflectance of autochthonous vitrinite varies from 0.77 to 1.95% indicating thermally mature to overmature organic matter. Different subsidence-uplift models were tested during modeling in order to find a plausible scenario of tectonic development and heat flow history. The thermal maturity of the individual thrust sheets was modeled separately allowing their individual thermal histories to be investigated before and after the main and final thrusting phase. The best-calibrated scenario assumes a low paleo heat flow ranging from 45 to 54 mW.m-2, affecting the eastern part of the Western Carpathians. The maximum temperature which lead to maturation of the organic matter seems to be related to its successive burial during Cretaceous due to compressional deformation. Individual thrust sheets reached thermal maturity prior to the final thrusting phase. The overthrust was accompanied by 3000–4000 m burial/erosion resulting in different thermal pathways during wedge growth.

Exploring the roles of sediment provenance and igneous activity on the development of synrift lacustrine source rocks, Pearl River Mouth Basin, northern South China Sea

Lacustrine mudstones developed in the synrift Wenchang and Enping formations are the major source rocks of the Pearl River Mouth Basin (PRMB) and vary in both richness and quality of hydrocarbons generated. While organic productivity is known to have played a role in the development of these rocks, it has been mostly neglected in prior research. In this study, new zircon geochronological data from igneous intrusive and volcanic rocks in boreholes of the PRMB are used alongside compiled detrital zircon U-Pb ages from Paleogene sandstones to decipher the roles of sediment provenance and volcanic activity in the development of source rocks. The result suggests that during deposition of the Wenchang Formation (49-39 Ma), sediments were mainly derived from intrabasinal structural highs dominated by Yanshanian igneous rocks (180-90 Ma). Similarities in young ages (42–45 Ma) in volcanic and clastic units of the Wenchang Formation suggest volcanic activity concurrent with its deposition. Chemical weathering of the proximal source area together with volcanic materials provided abundant nutrients for the basin and enhanced the primary organic productivity, resulting in the development of high-quality lacustrine source rocks, derived mainly from plankton. In contrast, the detrital zircon provenance of the Enping Formation (39-33 Ma) suggests sediments were derived from the South China Block (SCB), far to the north, with complicated lithologies and more older zircon grains. The long-distance transport of SCB sediments diluted the productive nutrition conditions of the larger and shallower lakes, and introduced organic matter derived from higher terrestrial plants. This study provides a new approach to evaluating the lacustrine source rocks especially for the deep-water areas with limited mudstone samples.

Study on the Weak Interlayer Identification Method Based on Borehole Photo-Acoustic Combined Measurement: Application to a Landslide Case Study

A weak interlayer is the key factor in controlling slope stability. It is of great significance to effectively identify the weak interlayer in the study of spatial and temporal distribution law and the internal structure characteristics of a landslide. Considering the limitations of traditional optical imaging and wave speed test methods, this paper presents a weak interlayer identification method based on borehole photo-acoustic combination measurement. By using the combination of optical imaging and acoustic wave scanning, the multi-source data collection of borehole rock wall and borehole surrounding rock is realized, which effectively captures the comprehensive response characteristics of the weak interlayer. This paper first constructs a multi-source data acquisition technology based on the borehole photo-acoustic combination measurement to realize the visualization of the image information and acoustic data of the target area on the borehole rock wall. Subsequently, the optical image features and the acoustic response characteristics of the weak interlayer are clarified based on the optical image and the acoustic scanning data. The hole wall texture characteristic response function, hole wall integrity characteristic response function, hole wall acoustic characteristic response function and hole wall contour characteristic response function are constructed. Finally, the landslide weak interlayer identification method considering the texture characteristics, complete characteristics, acoustic response characteristics and contour characteristics of the borehole rock wall is proposed, which effectively distinguishes the types of rock mass structural surface and realizes the automatic identification of the weak interlayer. Combined with the case analysis, the correctness and reliability of the present method are verified. The results show that the method can identify the weak interlayer and provide scientific basis for landslide management, which can provide a feasible and effective new way to identify the landslide weak interlayer in practical engineering, with a good application prospect and promotion value.

Study on Granite Permeability Zoning Based on Electrical Resistivity: Take Wuyue Pumped Storage Power Station as an Example

A granite mass in Xinyang, China, was studied to better understand the features of the link between permeability and resistivity. The permeability coefficient of subsurface media has a certain correlation with electrical conductivity. The following steps are conducted in this method; first, water pressure tests were conducted on the borehole to determine the permeability of the granite mass at different depths; next, the electrical resistivity values of the borehole rock were determined using geophysical logging techniques; finally, three mathematical models were chosen to construct the relationship between the two, and their applicability in the study area was confirmed. The method has some applicability and can serve as a guide for the design of reservoir impermeability. It was discovered that the calibration permeability obtained by inverting the power function model has the greatest applicability and can be applied to the permeability zoning of two high-density logging lines to obtain the characteristic dividing line of 0.5 Lu and 1.0 Lu more clearly and that this method has certain applicability and can serve as a reference for the design of reservoir impermeability.

Experimental study on double cuneiform reamed anchorages for cable bolt boreholes in soft rock

This paper deals with the problems of the low bonding force between hardened resin and soft surrounding rock, and the rapid attenuation of anchoring forces when conventional anchoring methods are used for cable bolts. The main goal of paper is to develop methods that will take full advantage of the potentially great supporting force that can be provided by high-strength cable bolts installed in soft rock. The study described in this paper discusses cuneiform reamed anchors for cable bolt boreholes. It is proposed that increasing the number of cuneiform cavities in the boreholes (with each cavity having appropriate geometric dimensions) is an effective way to prevent cable bolt anchorage failure. The results of a comparative analysis of single cuneiform reamed anchors (SCRAs) and double cuneiform reamed anchors (DCRAs) using numerical simulations are described. The simulations show that after being deformed by tensional forces of up to 200 kN, the maximum displacement of hardened resin in a DCRA borehole and the maximum plastic strain in the rock surrounding a DCRA borehole are, respectively, 50% and 46% smaller that they are for an SCRA borehole. The DCRA provides more stability and is an effective way to access the great supporting forces that a high-strength cable bolt is potentially capable of providing. The simulations were also able to determine the appropriate reaming angles for rocks of different strength. Using the simulation data, a double cuneiform reaming tool (DCRT) was developed. A field test has verified that this tool can ream two cuneiform cavities in a borehole to enlarge a section of the borehole when the tool is rotated by the drill rod. The DCRAs guarantee that cable bolts installed in soft rock will provide high supporting forces and that the cable bolts will not suffer anchoring force attenuation under severe ground pressure. • The synergistic mechanism of DCRAs was revealed, and the optimal reaming angle for different surrounding rock strengths was determined. • The DCRT was developed, boreholes reamed with the DCRT can prevent the resin encasing the cable bolt from separating from surrounding rock. • DCRAs allow high-strength cable bolts to take full advantage of their supporting force and minimize supporting force attenuation.

Water flux profiling in fractured rock boreholes with an In-Well Point Velocity Probe (IWPVP)

• First field measurements with the fracture adapted IWPVP reached 38 m below ground surface. • Depth profile of water fluxes compares well with PFM, ORP, and FLUTe liner profiles. • Demonstrated calibration of probe measurements with acoustic borehole televiewer data. • IWPVP shown to be a simple, cost-effective tool for measuring flow in fractures. Flow in a fractured rock aquifer beneath the Edwards Air Force Base in California was characterized by depth profiling two wells with In-Well Point Velocity Probes (IWPVPs). The probes, which were originally designed for use in porous media wells, were optimized for use in fractured rock wells and to meet several challenges including: sampling depths up to 38 m; high background site-water salinity; and variable well construction (screened vs open borehole, and well diameters of 7.62 cm and 15.8 cm). The IWPVP measures water flux inside the probe (internal flux), which is converted to fluxes in the aquifer through calibration. At this site, the internal fluxes ranged from 3 to 53 m/d. The channeled internal design of the probe inherently provides information about general flow directions and allows further interpretation of specific flow direction within ±15°, which at this site was generally consistent with the expected regional flow direction. Notably, a significant shift in the flow system was observed following a rain event (up to 180° shift in the flow direction). The IWPVP identified highly transmissive zones in the fractured rock, which were independently confirmed by passive flux meters and oxidation-reduction potential sensors. Transmissivity profiles determined during a FLUTe (Flexible Liner Underground Technologies™) liner deployment also showed similarities in the depths of potentially high flow rates, particularly in the shallower portion of the well (<20 m). With additional information on fracture apertures provided by an acoustic televiewer, the internal fluxes were converted to water fluxes in the observed fractures, indicating seepage velocities in the rock aquifer between 3.7 m/d and 22.4 m/d.

Study on the Influence of Shear Indenter Parameters on the In Situ Shear Strength Test

Cohesion and friction angle are important indicators of shear strength in mining engineering. Indoor testing methods are detached from the actual state of the rock mass and affected by disturbances and significant dimensional effects that do not fully reflect the shear strength of the rock mass itself. In situ borehole shear testing is of great practical importance because of its low disturbance and high speed. In this paper, a new testing device based on the principle of a rock borehole shear tester was designed to simulate the shear test in the laboratory. Seven shear indenters were designed to test the effect of different tooth heights, spacing, and angles on the shear strength of rock-like specimens, and the damage surface was scanned in three dimensions and compared with conventional triaxial tests and compression shear tests. The results show that as the tooth height increases, the flatness of the press-in damage surface increases, and the results will be closer to the press-shear test. As the spacing increases, the maximum damage angle and the damage surface between the grooves gradually decrease. The tooth angle has little effect on the friction angle, but cohesion decreases significantly when exceeds 60°.

Quantification of time-varying groundwater flow in boreholes in fractured crystalline rock using long-term distributed temperature sensing

Quantification of time-varying groundwater flow in boreholes in fractured crystalline rock using long-term distributed temperature sensing

Quantification of time-varying groundwater flow in boreholes in fractured crystalline rock using long-term distributed temperature sensing

Quantification of time-varying groundwater flow in boreholes in fractured crystalline rock using long-term distributed temperature sensing

Justification of the parameters of rotary-vibration drilling of small-diameter boreholes in rocks based on a submersible cavitation hydrovibrator

The article presents the results of laboratory studies of the rotary-vibration drilling method of blast-holes and boreholes of small diameter based on a submersible cavitation hydro-vibrator. A generator that operates in the mode of intermittently stalled cavitation was used as a source of vibration load to the rock-breaking tool. The authors of this article developed and described the design of a submersible cavitation hydro-vibrator at the level of the patent of Ukraine for the invention. In addition, a bench design for laboratory studies of the parameters of a rotary-vibration drilling method was developed and described at the level of a patent of Ukraine for a utility model. It is established that the optimal mode of operation of the cavitation generator is ensured by its cavitation parameter in the range of 0.16-0.2. The geometrical parameters of the cavitation generator in the submersible cavitation hydro-vibrator are determined: the diameter of the critical section is 2.0 mm, the opening angle of the diffuser is 20º, and the outlet diameter is 10.0 mm, and the length of the post-diffuser channel is 200 mm. It is established that under the action of pressure pulses of the washing liquid, which is passed through the cavitation vibrator in the optimal mode, the additional deepening of the rock-breaking tool into the rock sample reaches up to 0.6 mm per rotation. Thus, the drilling speed of small-diameter blast-holes and boreholes (up to 55 mm) with the ЕБГП‑1М drilling rig of the Konotop Machine-Building Plant with the optimal mode of the rotation frequency of the rock-breaking tool, which equals 315 min-1 (5.25 s-1), can be increased by 3∙10-3 m/s, from 23∙10-3 m/s up to 26∙10-3 m/s, which is 13%. Keywords: the rotary-vibration drilling method, cavitation generator, submersible cavitation hydro-vibrator, mining rock.