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Copyright of World Nuclear Geoscience is the property of World Nuclear Geoscience Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Low permeability coal makes methane control in underground coal mines difficult. Drilling tree-type boreholes is a new method for improving the permeability of coal seams to stimulate cross-measure boreholes drainage. This paper presents an analysis of the permeability enhancement and methane drainage capacity of tree-type boreholes based on data from a coal mine in China. After applying the proposed method, numerical models show that a large area of enhanced permeability is created between the tree's sub-boreholes. Compared with conventional drainage programs, tree-type boreholes increase the average rate of methane extraction by a factor of 13.9 and the effective influence radius of the borehole by a factor of 4.9. The simulated methane production rates from both types of boreholes are verified against field data from the Shoushan mine, China. This paper presents a quantitative analysis of the relationships between different tree-type borehole properties and methane drainage performance. Longer and more numerous sub-boreholes result in logarithmic drainage increases in the enhanced-permeability areas. Orienting the initial tree-type borehole angle parallel to the direction of maximum horizontal stress maximizes borehole stimulation. During drainage, the effective influence radius of tree-type boreholes expands logarithmically with sub-borehole length; cumulative methane production increases linearly with the length and number of sub-boreholes. These results can provide reliable scientific guidance for optimizing the layout of tree-type boreholes in field test. [ABSTRACT FROM AUTHOR]

Mahu Oilfield is the largest tight glutenite oilfield in the world, and the upper Wuerhe formation is an important succeeding exploration horizon. However, the upper Wuerhe formation in the Mahu 1 zone has a high clay content, which can lead to serious wellbore collapse. Meanwhile, the horizontal well logging is not corrected. These factors lead to the inconsistency between the logging interpretation results and the oil test results. The interpretation precision of the clay content, water saturation, and porosity, which are crucial to reservoir evaluation, is very low. In this paper, a workflow of logging curve correction using multiple methods is proposed. The multiple linear fitting is used to correct boreholes, and then histogram frequency distribution matching is used to standardize multi-well logging curves. Finally, the optimization method is used to build a volume model based on skeleton analysis, and the results are calibrated with core analysis results. Horizontal well density logs are corrected using adjacent vertical well logs. The interpretation results of clay content, water saturation, and porosity with high precision are obtained. The reservoir interpretation is more in line with the oil test results than the original interpretation. The clay content distribution is more reasonable. [ABSTRACT FROM AUTHOR]

Copyright of Natural Gas Industry is the property of Natural Gas Industry Journal Agency and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Large-diameter drilling is an effective method for preventing rock burst disasters in coal mines. In this paper, the roadway stability of the W1123 fully mechanized caving work face of the Kuangou coal mine, located in northwest China, is investigated. A set of numerical modelling techniques were carried out to study the characteristics of stress, displacement, strain energy and the plastic zone of the roadway side rock with different parameters, including the large-diameter drilling hole diameter, depth and spacing. The results showed that: (1) after drilling, the peak values of the stress and strain energy are reduced and transferred to a deeper location, and the control effect presents a positive correlation with the diameter of the drilling hole; (2) when Lh < LP, there are no pressure relief and energy release effects, which may induce impact, whereas when LP < Lh ≤ 2.5LP, with the increase of the hole depth, the effects of pressure relief and energy release are enhanced, and further extension is not conducive to the long-term stability of the roadway; and (3) when the hole spacing decreases, the plastic zone and the broken zone between the holes are gradually penetrated, and the stress pattern transforms from a double peak to a saddle shape and then to single peak. Reducing the hole diameter reduces the efficiency of the plastic zone, failure zone and the stress form transformation between the boreholes, and weakens the pressure relief effect. Therefore, the main factor affecting the pressure relief effect is the hole diameter, and the secondary factor is the hole spacing. The engineering practice employed here showcases how a larger-diameter hole is an effective way of enhancing the effect of pressure relief and controlling the occurrence of rock burst. These research results are of great significance for guiding engineering practice. [ABSTRACT FROM AUTHOR]

Borehole cataloguing is an important task in geological drilling. Traditional manual cataloguing provides the stratification of underground boreholes based on changes in core lithology. This paper proposes a novel borehole cataloguing method using a drilling process monitoring (DPM) system. This DPM cataloguing method stratifies a borehole according to the drilling speed through the rock. A 102 m borehole was drilled and cored in Baota district, Yan'an city, Shaanxi Province, China. The rock-breaking response parameters of the drill bit displacement, drill rod rotation speed and inlet pipe and outlet pipe oil pressures were monitored throughout the drilling process, and the drilling depth-penetration rate curve during the net drilling process was obtained. The changes in drilling speed show that the DPM cataloguing can identify the depths of the layer interfaces of the borehole and describe the stratification. The interface depth values obtained by DPM have little difference from the interface depth values obtained by manual cataloguing, and the errors are between −0.04% and 4.29%. From the DPM stratification results, the engineering quality evaluation of the rock mass can be realized without coring. DPM is fast, convenient, accurate, can greatly improve the efficiency of existing catalogues, and can be applied to scientific research in any underground space. DPM is a measurement-while-drilling technology. According to DPM data, the operating state of a drilling rig and the parameter changes while drilling can be obtained in situ and in real time throughout the drilling process. [ABSTRACT FROM AUTHOR]

The working face is seriously threatened by limestone aquifer with high-water pressure in coal seam floor when Permo-Carboniferous coal is mined in North China Coalfield. Mine water control has become one of the major technical problems in coal mine production. Grouting transformation for limestone aquifer is an effective means to guarantee mining safety. A case of the 16,104 working face of the Luxi coal mine was studied in this paper. The results by the method of water-inrush coefficient (WIC) showed that there was a great risk of water inrush in 16,104 working face. There were differences between water-rich areas of floor aquifer obtained by geophysical methods and the areas with large water inflow by drilling exploration. The geophysical methods were performed again in the water-rich areas using traditional grouting method, results showed that the water-rich areas changed places, indicating that the effect of traditional grouting was not obvious. Grouting of areas of high-water inflow has reduced the water inflow. However, the grouting also has changed the water flow paths. What's more, the drill holes sealed poorly will also lead to the change of the position of the water-rich areas. To enhance overall grouting efficiency and cut down the repeated grouting times, a secondary grouting-reinforcement method was proposed to ensure amount grout injected into aquifer. The results showed that the grouting reinforcement was successful, which can provide reference for the treatment of floor confined water of North China Coalfield. [ABSTRACT FROM AUTHOR]

Featured Application: The obtained kinds of borehole camera images of long or deep holes in the tunnels of the building Sichuan-Tibet Railway. Digital panoramic borehole imaging technology has been widely used in the practice of drilling engineering. Based on many high-definition panoramic borehole images obtained by the borehole imaging system, this paper puts forward an automatic recognition method based on clustering and characteristic functions to perform intelligent analysis and automatic interpretation researches, and successfully applied to the analysis of the borehole images obtained at the Wudongde Hydropower Station in the south-west of China. The results show that the automatic recognition method can fully and quickly automatically identify most of the important structural planes and their position, dip, dip angle and gap width and other characteristic parameter information in the entire borehole image. The recognition rate of the main structural plane is about 90%. The accuracy rate is about 85%, the total time cost is about 3 h, and the accuracy deviation is less than 4% among the 12 boreholes with a depth of about 50 m. The application of automatic recognition technology to the panoramic borehole image can greatly improve work efficiency, reduce the time cost, and avoid the interference caused by humans, making it possible to automatically recognize the structural plane parameters of the full-hole image. [ABSTRACT FROM AUTHOR]

A rainfall-induced catastrophic landslide occurred at UTC + 8 03:50 local time on August 21, 2020, in Zhonghaicun village (N 29°20′30″, E 102°41′40″), Hanyuan County, Sichuan Province, China, resulting in damage to 6 buildings and 9 casualties (7 fatalities and 2 missing). In this paper, multitemporal remote sensing images, comprehensive field investigations, drilling holes, deformation monitoring, and numerical simulations are used to identify the main characteristics and the formation mechanism of the event. The results showed that long-term intensive rainfall in 2020 played an essential role in the failure of the Zhonghaicun landslide and that strong earthquakes in Wenchuan County (Ms 8.0, on 12 May 2008) and Lushan County (Ms 7.0, on 20 April 2013) also exerted a negative influence on the evolution process of this catastrophic landslide. Several traction zones appeared after the occurrence of the landslide. Fortunately, no evident deformation was observed and these slopes were in a stable state. In addition, a large-scale potential sliding slope, four small-scale landslides, and a debris flow were found in the study area. [ABSTRACT FROM AUTHOR]

This paper describes a recent landslide event, which occurred at Liucheng village in Tianquan County, Sichuan Province, China, on July 15, 2018. The Laochang landslide described in this research is an outstanding and valuable reference for understanding the characteristics of such kind of landslides that are geologically similar to the landslide. The deformation characteristics of the landslide are investigated based on field investigations, drilled boreholes, and exploratory trenches. The 225 residents of 64 households living on the flat platform were threatened by the landslide. Therefore, to guarantee the safety of human life and property becomes the primary emergency task. The anti-sliding piles were taken to stabilize the landslide and mitigate impacts caused by the landslide. Based on the analysis of the monitoring data, the effectiveness of anti-sliding piles is evaluated. The results indicate that the anti-sliding piles are effective in increasing the stability of the landslide, and this work can provide a reference for similar slope engineering projects. [ABSTRACT FROM AUTHOR]

Coal gangue hills are prone to spontaneous combustion, thereby polluting the environment of mining areas such as the soil, groundwater, and atmosphere, and the frequent occurrence of gangue hill collapses, landslides, explosions, and other accidents can even endanger the lives and property of residents. To realize the safety management of coal gangue spontaneous combustion and evaluate its present risks, this paper selects the Dongzhou Kiln gangue hill in Zuoyun County, Datong City, China, as the research object to conduct a risk assessment study. The Dongzhou gangue hill fire area is relatively large, with a total area of 183,039 m2. Smoke emission commonly occurs at the site, and the surface temperature reaches 50 °C, while the CO concentration exceeds 10−3. A radon detection scheme for concealed fire zones verified with borehole temperature measurements is applied. The high-temperature area is delineated with relevant data obtained by infrared thermal imaging, radon concentration, and borehole temperature detection technologies, and a coal gangue spontaneous combustion risk assessment method is established, while the gas toxicity and explosion risks of the construction area and fire trends are analyzed. The research results indicate that there are 6 likely high-temperature regions in the test area, 4 high-toxicity areas in the drilling construction area, 1 area with a high explosion risk, and 3 areas with a high risk of spontaneous combustion. Among these areas, platform 2 is a high-risk area and needs to be carefully considered. The construction of the entire area is at high risk, including toxicity, gas explosion, and spontaneous combustion risks, and measures must be implemented to reduce the overall risk. [ABSTRACT FROM AUTHOR]

Tree-type borehole drilling (TTBD) is a novel stress relief method for stimulating methane drainage from coal in underground coal mines. This paper is a report on studies that analyzed the permeability enhancement capabilities of tree-type boreholes in coal seams and presents a precedent-setting industrial trial of this new method in a 200-m section of a drainage roadway in a coal mine, the Shoushan coal mine in Henan province, China. Detailed simulation results indicated that after coal seams were stimulated using the TTBD method, a large number of fractures were initiated around the tree-type boreholes. These fractures propagated along the direction of maximum horizontal stress and formed highly permeable flow channels for methane transport from the coal into the tree-type sub-boreholes. The fractures gradually became shorter along the length of the sub-boreholes. As the sub-boreholes were shortened, the area fractured and the number of induced fracture decreased rapidly. Conversely, the fracture density and the value of homogeneity coefficient, β, increased. The industrial trial showed that compared with gas drainage from a conventional borehole in the Ji15−17 coal seams, the gas production rate from a single tree-type borehole was 4.7 times faster and the percentage of methane in the gas produced was 1.7 times higher. In addition, the borehole drainage attenuation time was 2.5 times longer for the tree-type boreholes. The total volume of gas production produced from 238 tree-type boreholes in a 200-m section of roadway was over 70,000 cubic meters, 1.4 times the methane extracted by 938 conventional boreholes in an adjoining 200-m section of the same roadway. In addition, the number of boreholes required to drain 1.4 times as much gas was 75% smaller. These results have provided support for the appreciation and application of this new technique for improving underground coal mine methane drainage. [ABSTRACT FROM AUTHOR]

The effective extraction radius of borehole is the main parameter for determining the design and layout for coalbed methane extraction. This paper is aimed at the problem that the criteria and calculation methods for the effective extraction radius of coal seams are not comprehensive. With Wudong Coal Mine in China taken as an example, the critical gas pressure (0.441 MPa) for the calculation of effective extraction radius is first defined. Next, the gas seepage unit model around the borehole is developed, and the theoretical mathematical expression to calculate the effective extraction radius is derived. Then, the numerical simulation of gas extraction is carried out through a computational fluid dynamics program, and the effective extraction radius is obtained numerically. Furthermore, the influence of original gas pressure, borehole diameter, and negative pressure of gas extraction on gas extraction is analyzed. Finally, the results from the theoretical calculation and numerical simulation are validated by the field engineering measurement and the average relative error is small (less than 10%). The results indicate that the effective extraction radius has a linear relationship with the extraction time. Moreover, it is found that the original gas pressure is the main factor affecting the effective extraction radius and the effective extraction radius is proportional to the borehole diameter and negative pressure through analysis. Therefore, the above findings can provide a theoretical basis for determining parameters such as borehole spacing and extraction time of gas extraction in coal mines. [ABSTRACT FROM AUTHOR]

This paper reports on a typical slow-moving landslide that occurred in Shuitianba village in Wanyuan County, Sichuan Province, China, on September 16, 2017. The landslide in Wanyuan County is regionally outstanding for its features and well-developed landslide morphology. Hence, this event can provide a good case study for understanding the possible triggering conditions of the occurrences of all the landslides examined in Wanyuan County. The 225 residents of Shuitianba village did not flee the village because the deformation of the landslide was extremely slow. However, the primary emergency tasks are still necessary to reduce the landslide risk that may affect the residents. Detailed field investigations, boreholes, and exploratory trenches were performed to investigate the characteristics and triggering factors of this landslide. Rainfall and anthropogenic activities (such as informal, unplanned settlements and deforestation) were revealed to be the main triggering factors. The main engineering control measures, including anti-sliding piles, an anti-sliding retaining wall, and intercepting ditch, were applied to stabilize the landslide. However, landslide mitigation measures have not been finished, and hence, some interim measures are suggested to effectively reduce landslide risk. [ABSTRACT FROM AUTHOR]

• Established a model for measuring in-situ stress in horizontal boreholes (HF). • Fracture initiation position is observed in the middle section of the wellbore. • Breakdown, reopening and shut-in pressures are presented successively in the test. • Formulas for conservative calculation in practical engineering. Horizontal directional investigation is an alternative method different from traditional (vertical) geotechnical investigation, which can effectively reflect geological conditions along the axis and evaluate the engineering characteristics of tunnels in mountainous areas with super long distances and depths. However, the absence of effective methods to measure in-situ stress in horizontal boreholes hinders the promotion of horizontal directional investigation. This paper relies on the thorough horizontal directional drilling geotechnical investigation of the Tianshan Shengli tunnel in China, based on the method of hydraulic fracturing in-situ stress measurement, the relationship between the direction and magnitude of in-situ stresses and the parameters of the hydraulic fracturing was established in a horizontal borehole by enhancing the previous model of inclined boreholes. The interpretation principles of horizontal boreholes by hydraulic fracturing method are further explored through experimental and numerical study. The conclusion of this paper provides theoretical and empirical support for in-situ stress measurement in horizontal boreholes by hydraulic fracturing method. [ABSTRACT FROM AUTHOR]

In recent years, a large number of bank destruction occur in the reservoir area under the effect of water fluctuation, which may be lead to reservoir accumulative landslide geological hazards finally. The paper conducted the bank destruction forecasting study for accumulative landslides in the Three Gorges Reservoir Region, China utilizing back-propagation (BP) neural network approach. A representative scenario of Jinle landslide is then taken for analysis purposes. On the basis of the existing data sets of bank destruction cases, the BP neural network forecasting model and the corresponding programs for bank destruction are both presented, whose forecasting result is validated by two independent approaches, namely empirical method and numerical modeling method. Furthermore, the BP neural network model had obvious advantages over the convention approaches in the aspects of the fast calculation speed and high convenience. According to the bank destruction forecasting scale presented above, the corresponding revetment measures can be proposed to prevent the occurring of the bank destruction, whose effectiveness has been further validated by the actual engineering practice. [ABSTRACT FROM AUTHOR]

A complete stress determination has been performed by hydraulic tests on pre-existing fractures conducted in two inclined boreholes for a railway cavern in Hong Kong, China. A total of ten complete tests including normal stress and fracture plane orientation determination have been successfully carried out in the zone where the cavern is located. The test depth in two holes varies from 101 to 120 m beneath the ground surface. After a brief introduction to the test system, procedures, and results in this paper, the inversion method for in situ stress field, neglecting both the vertical and horizontal stress gradient, is reported. Moreover, the genetic algorithm is applied to search for the optimal solution, which minimizes the misfit function, and the misfit associated with this solution is used to evaluate the 90 % confidence level domain with the Monte Carlo Technique. The results of this study are useful for a better understanding of the stress level of the planned railway cavern and also helpful for the safety design of the cavern. [ABSTRACT FROM AUTHOR]

The low permeability of coal seams is the primary difficulty for gas production. Hydraulic cutting is one of the most effective technologies for increasing permeability and stimulating gas production. This paper investigates the hydraulic cutting styles in boreholes and the optimal equivalent borehole diameter after discharging the pulverized coal particles. This paper introduces the hydraulic cutting equipment and cutting styles and determines that the cutting cylinder is the most suitable style for a soft coal seam that is prone to gas outburst. The numerical simulation suggests that the radius of the stress-relaxed range increases quickly when the equivalent borehole radius is small, and the rate slows when the borehole radius becomes large. Then the result was verified by a field experiment in Pingmei coalfield. The gas drainage flowrate and stress-relaxed range greatly increased after initially outputting 2 tons of coal from the borehole, whereas the second outputting 2 tons of coal did not appreciably increase the stress-relaxed range and the flowrate. Too much or too little coal discharge is not optimal, and the borehole radius is recommend to be between 0.3 m and 0.4 m after the hydraulic cutting considering the pros and cons in Pingmei coalfield. The results are helpful for the engineering application of the hydraulic cutting technology, for increasing coal seam permeability, and for stimulating gas production. The method for finding the optimal coal discharge in this paper is also helpful for other coal mines. [ABSTRACT FROM AUTHOR]

Coal mine methane (CMM) drainage is an effective method to curb the occurrence of coal and gas outburst and gas explosion, to reduce the amount of greenhouse gas emission, and to make full use of the clean energy(methane). Sealing in-seam horizontal boreholes plays a vital role in CMM drainage. Reasonable sealing length is an important factor to achieve high extraction efficiency and reduce the cost of construction. To determine the minimum reasonable sealing length of drainage boreholes, the radius of the fracture zone was obtained based on the ideal elastoplastic model, and this radius was taken as the minimum sealing length. The influencing factors of the minimum sealing length were analyzed and engineering verification test was taken in Zhongmacun mine in Henan province, China. The research results show that the minimum reasonable sealing length should be longer for a larger radius of the coal roadway and the coal seam with a deeper buried depth, while the minimum reasonable sealing length can be shortened with the increase of uniaxial compressive strength and the supporting stress of the coal roadway. The 11.07 m of sealing length calculated by theories was basically consistent with the 12 m of sealing length verified by the method of drilling cuttings. The reasonableness of sealing length (12 m) was verified by the test results of methane concentration and flux within 40 days. All those outcomes can provide references for other mines to determine the minimum reasonable sealing length of in-seam boreholes for CMM drainage. [ABSTRACT FROM AUTHOR]

The South Jingyang tableland, located in Shaanxi Province, China, is composed of loess deposits. Agricultural irrigation in this area has caused the continuous rise of the groundwater table, which triggered a series of loess landslides. Although extensive research has been conducted on the effect of rising groundwater tables on induced loess landslides, less is known about the groundwater table distribution. This study jointly investigated the distribution of the groundwater table in the South Jingyang tableland using boreholes, electrical resistivity tomography (ERT), and laboratory tests. A qualitative analysis between the apparent resistivity and the water content was estimated at different depths, using the borehole data and ERT inversion data. A quantitative relationship between the resistivity and the water content was established in the laboratory tests. A combination of the qualitative analysis of the inversion results and the quantitative relationship was used to determine the distribution of the groundwater table. The groundwater table is present at the depth where the water content of the loess is 30% (liquid limit of loess) and the resistivity is 28.35 Ω m. The groundwater table elevation in the southern study area is higher than that of the northern study area and decreases in a stepwise gradient from south to north. This study not only identified the distribution of the groundwater table in the South Jingyang tableland, but also makes up for the limitation and inaccuracy in determining groundwater tables by relying solely on the borehole information or inversion results of ERT. The ascertained distribution characteristics of the groundwater table provides a basis for the analysis of the formation mechanism of landslides. [ABSTRACT FROM AUTHOR]

Rock Quality Designation (RQD) is among the widely used measures of the quality of rock masses and can be derived through Monte Carlo stochastic process-based fracture network simulations. However, repeated simulations can yield variable RQD results. Here, we introduce a four-step approach that incorporates class ratio analysis to estimate the representative RQD, which includes (1) extracting the mean and confidence interval of the RQD sample, in terms of the Confidence Neutrosophic Number Cubic Value (CNNCV), (2) employing class ratio analysis to determine the thresholds of the number of virtual boreholes and that of the number of models for a given size D, beyond which the CNNCV remains substantially unchanged, (3) accepting the CNNCV at the thresholds of the number of models as the representative RQD for the model of size D (RQD(D)) and (4) determining the representative RQD (rRQD), defined as the specific value which, once D exceeds, the RQD(D) does not change significantly. The introduced approach is illustrated with a case study of an open-pit slope in China, and it was tested for its performance. The RQD calculation results of the proposed method and the traditional single-model approach exhibit differences, which diminish with increasing model sizes. At the 95% confidence level, the stable size of the RQD determined by the proposed method is 13 m, compared to 25 m for the single-model approach. This method enhances the accuracy of representative elementary volume predictions by accounting for the diversity in the simulation results of RQDs for the same size. Overall, the introduced approach offers a reliable method for obtaining RQD estimates. [ABSTRACT FROM AUTHOR]

An abandoned gypsum mine has been discovered beneath the route of a highway construction in Hunan province, south China. Due to the highway construction and operations safety, there is an urgent need for a comprehensive stability analysis of the abandoned mining area. The 3D laser scanning detection technique has been adopted, and over 400 drillholes were strategically placed near the highway to capture the spatial information of the abandoned gypsum mine. The ore body has an average mining thickness of about 3 m, and the depth of the mining roof ranges from 40 to 60 m, with an average span of 16 m. Based on the research achievements in the engineering geological investigation, rock mass quality assessment, and geometry information, a simplified numerical model has been established for stability analysis. The numerical model employed the IMASS rock mass constitutive model to conduct a stability analysis of the abandoned gypsum mine during the excavation process and in the medium to long term. The IMASS constitutive model can effectively reflect the entire process of rock mass from microscopic damage to macroscopic instability, and the numerical simulation of current and long-term stages provides a much greater understanding of the mining room stability and the effect of various geo-mechanical parameters not considered in traditional empirical methods. The abandoned gypsum mine stability is guaranteed in the mining and current stages. However, the numerical results showed that a 0.4 m spalling thickness of the sidewalls can cause an overall instability and failure of the abandoned mine, and reinforcement measures must be taken for long-term safety. The stability of the abandoned gypsum mine with filling solutions was also evaluated numerically. [ABSTRACT FROM AUTHOR]

Deep boreholes represent a source of clean energy. Therefore, effective calculations of potential extraction of heat from boreholes for realistic models of the Earth's crust with variable thermal conductivity and diffusivity are needed. We deal with heat extraction in a quasi-steady state from coaxial boreholes where downward and upward flows of pumped fluid (water) are separated by an inner pipe and connected only at the bottom. We first obtain theoretical estimates of heat extraction for a thermally isolated inner pipe and a model of the ground with constant thermal diffusivity and conductivity. Then, we develop a new analytical matrix method for a general layered ground model that enables us to include depth-dependent ground properties as well as heat exchange between the downward and upward flows of fluid in the borehole. Our straightforward and fast approach is thus suitable for various parametric studies or as a tool for benchmarks of numerical software. A key role in heat extraction from coaxial boreholes is played by the inner-pipe thermal resistance. We apply our method to the parametric study showing the dependence of pumped water temperature and total heat extraction from the borehole on realistic borehole geometries under different amounts of water pumping. The calculations are performed for a 3 km deep borehole as the representative of present deep boreholes used for extraction of geothermal energy and for a 10 km deep borehole. Drilling of such a  superdeep borehole has just started in China and our results demonstrate potential limits of geothermal energy extraction from such great depths. [ABSTRACT FROM AUTHOR]

The Hobq Desert (HD) locates at the northern margin of the Ordos Plateau, China and the transition zone to the Hetao Basin. It is one of the main proximal deserts of the Loess Plateau, and its formation was controlled by the evolution of the Yellow River and the Ordos Plateau. It is still worthy of discussing the regional structure to enhance the understanding of the desert formation and paleoenvironment, especially with the additional works in the eastern part. Geophysical methods including gravity, magnetic, EM (electromagnetic) are often used to analyse the regional and near-surface structure. As for drilling records, they could show the lithology sequence directly and be applied for the environmental study (e.g., OSL dating). Therefore, in this paper, we used the satellite gravity data, GPR (Ground Penetrating Radar), TEM (Transient electromagnetic method) and drilling records with borehole resistivity data to analyse the desert structure from different scales and the paleoenvironment. Trough the upward continuation and Park-Oldenburg calculation for the gravity data, the thickness of Quaternary deposits is 0.85–1.55 km. The inferred faults indicated the performance of the Hetao Basin and the Ordos Plateau's uplift in Pleistocene, which also contributed to HD's formation and existing topography. A three-part structure within 350 m was revealed in the profile at eastern HD by EM data. The upper layer within 80–90 m was the aeolian dry sand, the middle one was mainly fluviolacustrine saturated sand with the occurrence of clay and grey calcareous root tubes, and the lower one might be the aeolian sand. This near-surface structure was consistent to the western part, and the forming period for the sand in the upper zone was thereby estimated no earlier than 80 Ka. Moreover, during this period, millennial-scale changes in paleo-effective moisture occurred although it was dominated by the arid climate. [ABSTRACT FROM AUTHOR]

Evaluation of groundwater quality has an important role in groundwater management and conservation. Addressing the uncertain characteristics of groundwater quality as affected by multiple interacting factors – and the factors being changeable, random and fuzzy – sample test data from 20 hydrogeologic boreholes in a study area in Fenggang town, Zunyi city, China were collected and a groundwater quality evaluation model was built based on set pair analysis. Through expressions of the connection degree and decomposition of the degree of discrepancy and calculation of the comprehensive fuzzy connection degree, results of groundwater quality evaluation in the study area were obtained. The reliability and validity of the model were proved by comparing the results with the actual situation. This new groundwater quality evaluation method reflects the characteristics of groundwater quality controlled by multiple factors and factor uncertainty. [ABSTRACT FROM AUTHOR]

The buried depth of coal seams in China gradually increases as shallow resources decrease. The purpose of this article is to reveal the effect of buried depth on gas extraction boreholes. Firstly, we analyzed the shortcomings of the Mohr–Coulomb (M-C) constitutive model for simulating excavation problems and introduced the strain-softening (S-S) model and its advantages. Subsequently, we constructed the gas extraction models with different buried depths based on the S-S model and combined them with the evolution equations for permeability and the equations for gas migration. Then, we studied the difference between the M-C and S-S models using numerical simulations. We found that the influence of the S-S phenomenon in the surrounding rock of boreholes is more significant as the buried depth increases—that is, the strain-softening has a significant buried depth effect. When the buried depths were 300, 500, and 700 m, the maximum ratios of permeability to the initial permeability obtained from the Mohr–Coulomb model were 1.37, 6.88, and 97.56, respectively; the maximum ratios of permeability to the initial permeability obtained from the strain-softening model were 2.06, 291.23, and 3629.66. The differences in the increase zone of permeability from the two models also increased with the increase in the buried depth. The distribution curves of gas pressure in the surrounding rock of boreholes obtained from the S-S model were below those of the M-C constitutive model at the same buried depth, and the zones with slowly increasing gas pressure with the increase in buried depth were more obvious in the S-S model compared with the M-C constitutive model. The differences in borehole effective extraction radius also increased gradually between the S-S and M-C models as the buried depth increased. Through the analysis of the research results, we found that S-S of the surrounding rock has a lesser influence on the gas extraction boreholes, and the S-S phenomenon in the surrounding rock of boreholes can be ignored when the buried depth is relatively shallow. It is increasingly necessary to consider the S-S phenomenon in the surrounding rock of boreholes with the gradual increase in the buried depth. [ABSTRACT FROM AUTHOR]

Directional long drilling on the roof is an effective gas control measure in the goaf, but there is little research on the stability of the surrounding rock. In this study, the geological conditions of the #4 coal seam in the Tingnan Coal Mine, Shaanxi Province, China taken as the application background, and the deformation characteristics of boreholes under four typical coal and rock conditions were first analyzed based on the Universal Distinct Element Code (UDEC) numerical simulation. Secondly, the stress, strain, and plastic deformation of the rock surrounding the borehole with different diameters were carried out using the Fast Lagrangian Analysis of Continua 3D (FLAC 3D). The effect of the casing on the stability of the borehole was also simulated. The results showed that the borehole stability of coal and mudstone was lower than that of fine-grained sandstone and coarse-grained sandstone. The larger the borehole diameter, the lower the stability. The borehole tended to be unstable, especially when the diameter was 160 mm and 200 mm. Traditional pipes can provide some protection, but for large boreholes, the protection is poor. Based on the above research, uniaxial compression tests were carried out on various internal support tubes, such as 'line-shaped', 'Y-shaped', and 'cross-shaped'. The results showed that the cross-shaped pipe had the highest compressive strength, which was 4–5 times that of the other types of protective pipe and had a good protective effect. The research results can provide reliable technical support for the protection of directional boreholes on roofs through strata and have important implications for the popularization and application of the directional long borehole technique. [ABSTRACT FROM AUTHOR]

The heading face in soft and low-permeability coal seams is one of the most high-risk areas for Chinese coal and gas miners because of the number of outburst-related accidents. To prevent and control these disasters, the in-seam borehole gas extraction technology is widely used because of its low construction cost. Unfortunately, few studies consider its gas extraction efficiency. Thus, a new in-seam borehole hydraulic flushing (ISBHF) gas extraction technology is proposed in this paper, where the hydraulic flushing technology is used to enhance the gas extraction of in-seam boreholes. Based on the engineering background in the Xinjing coal mine, a detailed study of this new technology is conducted. First, we model the permeability-increasing mechanism of this technology and the gas flow characteristics of the hydraulic flushing boreholes using a finite-element method. During this process, the strain-softening behavior of the coal mass and the effect of the coal mass failure on the permeability evolution are considered. Second, a reasonable gas extraction scheme is designed, which considers the divergent characteristics of boreholes in the heading face and the interactions among multiple boreholes in the gas extraction process. Finally, the gas extraction scheme is implemented at the S5 intake airflow roadway to verify the simulation results and to evaluate the efficiency of this technology. The field test results are consistent with the simulation results, which validates our model. Moreover, using this new technology, the number of gas extraction boreholes in the heading face decreased by 50%. Conversely, the gas extraction-based concentration and flow increased 10- and 6-fold, respectively, which results in a 65% decrease in gas extraction time and a 100% increase in monthly excavation length of the coal mine roadway. These results indicate that this new technology is a promising method to achieve efficient gas extraction and rapid excavation in the heading face of soft and low-permeability coal seams. [ABSTRACT FROM AUTHOR]

Through integral studies on cores, seismics, well-logs and laboratory sediment analysis a new sequence stratigraphic framework of the Late Cretaceous first member of the Yaojia Formation in the Songliao Basin, in China's Zh ao y uan- T ai p ing ch uan (Zhy-Tpch) region, has been reconstructed. In this study, the first member of Yaojia Formation is divided into 3 three-order depositional sequences, each composed of three systems tracts, i.e. the lowstand systems tract (LST), the transgressive systems tract (TST) and the highstand systems tract (HST). Using a dense network of cored boreholes data and data acquired from a combination of spontaneous potential and electric resistivity logging methods, the paper studies the characteristics and distribution of sedimentary environments within the cyclic patterns (systems tracts) of the major depositional sequences, and ascertains that deposition of sediments in a predominantly shallow lake delta environment which prevailed in the region during the Late Cretaceous period was responsible for the creation of the first member of the Yaojia Formation. Results show that this formation is mainly composed of three sub-facies namely, the delta plain, delta front and prodelta (the shore shallow lake). Each sub-facies is further subdivided into eleven sedimentary environments including distributary channels, natural levees, crevasse splays, inter-distributary channels, flood plains, subaqueous distributary channels, inter-distributary bays, subaqueous crevasse splays, mouth bars, distal bars and sheet sands. The delta plains and delta fronts are widely developed. Deposited with frequent bifurcations, the distributary channels gradually moved towards the center of the lacustrine basin where prodelta sedimentation had hardly occurred. Meanwhile, subaqueous channels were frequently developed within the shallow water areas of the delta fronts. Sandstone facies in the distributary and subaqueous distributary channels mutually interacted and stacked up to form dendritic-like sands. Distributary channel sands formed the most favorable reservoirs available today and are considered to be the most important exploration targets for the oil industry. Overall, this study is crucial for improving the understanding of the geological and paleo-geographic record in the Zhy-Tpch region including the facies types, relationships and cyclicity in response to changes in depositional environments (i.e. sedimentation and base-level changes) that prevailed in the region during the Late Cretaceous period and hence important for the predictive aspects of the economic petroleum exploration and development in the Songliao Basin. [ABSTRACT FROM AUTHOR]

Agricultural irrigation of the South Jingyang tableland in Shaanxi Province, China has led to a continuous rise of the groundwater level and has triggered a series of loess landslides, thereby seriously affecting the life and property safety of local residents. Research shows that the major cause of the landslide in the loess layer of the South Jingyang tableland is the rising groundwater level. Therefore, the research on the formation mechanism of landslide in this area should include the investigation of the stratigraphic structure and groundwater level distribution characteristics. On this basis, a series of approaches, such as electrical resistivity tomography (ERT), borehole, and laboratory tests, was carried out on the South Jingyang tableland, and the groundwater level distribution and stratigraphic structure in the study area were determined. The qualitative relationship between resistivity value and water content at different depths was detected using the inversion results of ERT and borehole data. Through laboratory tests, the quantitative relationship between resistivity values under different water contents was established. The precise depth of the groundwater level was inferred by connecting the qualitative relationship with the quantitative relationship, and then a detailed 3D geological model was established by linking the inversion results of ERT with the field borehole lithology data and geological survey data. The detection results show that when the qualitative and quantitative analyses of the ERT inversion results were combined, the distribution of the groundwater level was accurately judged. The ERT is effective in reflecting the stratigraphic structure and hydrological characteristics of the Loess Plateau, and its potential as a supplementary technology for detecting the groundwater level is reasonable. This study addresses the limitation and inaccuracy in determining the stratum structure and groundwater level by solely relying on borehole information or ERT. The established 3D geological model not only provides a basis for the study of groundwater table fluctuation, but also a technical guidance for the stability evaluation of loess slope, landslide prediction, and early warning in the study area. [ABSTRACT FROM AUTHOR]

The Wenchuan earthquake Fault Scientific Drilling project-hole 1 (WFSD-1) offers a unique opportunity for studying the faulting behavior and the thermal regime of the Longmen Shan fault zone (LMFZ), east margin of Tibetan Plateau. Thermal conductivity of fault rocks within main fault zone shows strong negative interrelations with the porosity, the gamma ray and the P-wave slowness, as well as a positive interrelation with the density. Here we attribute these correlations to the fractures and the rock-fluid reaction generated from the earthquake, which will increase the porosity, the radioactivity and the P-wave slowness as well as decrease the density and the thermal conductivity, synchronously. 15 continuous temperature profiles were summarized in this paper. Based on integrated studies of temperature variations and thermal gradients, local temperature anomalies were detected at three depth ranges of 480–510 m, 580–610 m and 625–755 m, respectively. These anomalies seem to correspond to different fracture zones and may be attributed to fluid flow in the fractures. In addition, the non-uniform vertical distribution of these temperature anomalies was observed across the co-seismic slip surface at 589.2 m. In the below ∼200 m borehole depth, a prominent thermal anomaly zone was developed, implying more factures were generated in the footwall than the hanging wall during the Wenchuan earthquake. The heat flow ranges from 69 mW/m 2 to 72 mW/m 2 for different logs. The persistence of elevated heat flow in the LMFZ appears to rule out frictional heating on the Yingxiu-Beichuan fault (YBF) as the source of the WFSD-1 value, but is probably related to the regional tectonic evolution. [ABSTRACT FROM AUTHOR]

The basin sediment provides an important means of studying regional tectonic actives; however, regional climate factors, overlaying tectonic actives, affect the sedimentary process in the basin. Because of the lack of long-term scales data, the research on climate change in the arid and semi-arid region is limited. The PL02 core, located in the center area of deposition in the Yinchuan Basin, has a thick deposit with a higher resolution and sedimentation rate, making itself practical for the reconstruction of the paleoclimate and the coupling relationship between regional tectonic activities and climate change. The study of the 720-m borehole near Pingluo County is presented in this paper. The chronostratigraphic sequence of the core is established by palaeomagnetic dating. The magnetostratigraphic correlation to the geomagnetic polarity timescale shows that the PL02 core recorded the Brunhes, Matuyama, Gauss, Jaramillo, Olduvai, Kaena and Mammoth polarity chron or subchron. The sedimentation rate and the magnetostratigraphic of the core indicate that the onset of the PL02 core in this section occurred at ∼3.4 Ma BP. The analysis of the core established a detailed chronological framework for regional geological research. At the stage of 3.22–3.04 Ma, 2.581–1.95 Ma and after 0.012 Ma, the sedimentation rate increases gradually, which archive three regional tectonic subsidence events. The frequency-dependent susceptibility of the sediment is used to reconstruct the paleoclimatic change. The frequency-dependent susceptibility is more effective than the magnetic susceptibility on reflecting regional climate change in the basin. From 3.4 to 0.467 Ma, the gradual decrease of frequency-dependent susceptibility reflects the regional climate change from warm and humid to cold and dry. Since 0.467 Ma, the gradual increase of the frequency-dependent susceptibility corresponds to the climate becoming warm and humid again. [ABSTRACT FROM AUTHOR]

The thermal state of permafrost in the present and future is fundamental to ecosystem evolution, hydrological processes, carbon release and infrastructure integrity in cold regions. In 2011, we initiated a permafrost monitoring network along the China–Russia crude oil pipeline (CRCOP) route at the eastern flank of the northern Da Xing'anling Mountains in Northeast China. We compiled an integrated dataset of the ground thermal state along the CRCOP route consisting of meteorological data near the southern limit of latitudinal permafrost, ground temperature (GT) data in 20 boreholes with depths of 10.0–60.6 m, soil volumetric liquid water contents (VWCs) and 2D electrical resistivity tomography (ERT) data at different sites. Results demonstrate a permafrost warming during 2011–2020 in the vicinity of the southern limit of latitudinal permafrost, as manifested by rising GTs at almost all depths in response to climate warming. Local thermal disturbances triggered by the construction and operation of CRCOPs have resulted in significant permafrost warming and subsequent thawing on the right-of-way (ROW) of the pipelines. This permafrost thaw will persist, but it can be alleviated by adopting mitigative measures, such as an insulation layer and thermosyphons. The in situ observational dataset is of great value for assessing the variability of permafrost under the linear disturbances of the CRCOPs and related environmental effects, for understanding hydro–thermal–mechanical interactions between the buried pipelines and permafrost foundation soils, and for evaluating the operational and structural integrity of the pipeline systems in the future. The dataset is available at the National Tibetan Plateau/Third Pole Environment Data Center (10.11888/Cryos.tpdc.272357; Li, 2022). [ABSTRACT FROM AUTHOR]

Northeast China has experienced rapid and substantial climate warming over the past 60 years, and permafrost is degrading rapidly. In this study, permafrost distribution and extent in Northeast China were estimated from monitored ground surface temperatures using the temperature at the top of permafrost (TTOP) model and geographically weighted regression method. Using the TTOP model, the computed mean annual ground temperatures (MAGT@TOP) at the top of permafrost of Northeast China increased significantly from 1961–1990 (1.8°C) to 1991–2020 (3.0°C). The areal extents of permafrost defined by a subzero MAGT@TOP (MAGT@TOP ≤ 0°C) in Northeast China in the period 1961–1990 and 1991–2020 were estimated at 461.5 × 103 and 365.8 × 103 km2, respectively, indicating a decline of 95.7 × 103 km2. On average, the simulated MAGT@TOP values were 2.07°C lower than the observed MAGT@TOP values in boreholes. The linear correlation coefficient between the simulated and measured MAGT@TOP values was 0.63. Compared with the simulation results of other previous models, the result of this research is more reliable and accurate. The compiled maps of permafrost distribution can serve as an important reference for the study of permafrost changes in Northeast China. [ABSTRACT FROM AUTHOR]

Reducing gas content via cross-measure boreholes is one of the primary gas control technologies in China, where most outburst-threat coal seams are soft and highly gassy. Regardless of the significant costs associated with drilling boreholes, the gas drainage rate remains low because of the low permeability of the soft coal seam and the small influence zone of a single borehole. In this paper, the effect of increasing borehole diameter on coal seam permeability is discussed and a new method for drilling large diameter cross-measure boreholes by using the water-jet technique is proposed. Numerical modeling results indicate that the plastic zone and the effective influence zone of one borehole expand as borehole diameter increases, and the interaction between adjacent boreholes is strengthened. The field test shows that when the borehole diameter is 1.0 m, the effective influence zone radius reaches 4 m which is 2.67 times larger than that of an ordinary borehole. After using the new method, the number of cross-measure boreholes per hundred meters and the length of cross-measure boreholes per meter can reduce by 32.5% and 42.9%, respectively. In addition, the gas drainage rate reaches 52.1%, and the monthly excavation length of coal roadway increases from 50–70 m to 109 m. [ABSTRACT FROM AUTHOR]

A water curtain system consists of many boreholes arranged in a systematic manner. To maintain tight seals when storing substances (e.g., crude oil), water curtain systems are usually employed for underground storage in hard rock. With the aid of these systems, stable seepage fields develop around storage caverns, and hydrodynamic containment is achieved in the storage caverns. In this paper, several issues regarding the design and testing of a water curtain system in underground oil storage caverns in China were investigated. Regarding the design of these systems, natural and artificial containments were compared, and the role of hydrogeology in the selection of containment was explored. A literature review on the geometrical parameters of these systems used in storage caverns was performed and provided reference for the design of the proposed water curtain system. The influence of rock joint orientations on the arrangement of boreholes in the curtain system was addressed; it was concluded that the boreholes should be arranged perpendicularly to the dominant joints to obtain a system with good performance. Regarding the testing of these systems, a procedure used to evaluate the performance of the proposed water curtain system was developed. A method used to determine the interconnectivity of the system was also developed, and an improved test procedure was proposed based on the test results. A curtain system injection test was performed, and the groundwater flow rates into both the water curtain system and the storage caverns were measured. It was shown that the groundwater flow rates were dominated by the groundwater flow in the rock joints and the areas where high groundwater flow rates around the cavern surfaces coincided with those where high groundwater flow rates appeared at water curtain boreholes. [ABSTRACT FROM AUTHOR]

Filling of the modern coastal-zone portion of the Qiantang River (QR) in eastern China was initiated by marine inundation during the transgression after the Last Glacial Maximum and has continued during the Holocene sea-level stillstand. The early part of the fi ll is transgressive in character, while the younger part is regressive. This paper deals with the sedimentary facies, surfaces, architecture, and depositional model of the QR incised-valley fi ll based on the detailed analysis of the newly drilled core SE2 and its correlation with more than 800 boreholes. The incised-valley deposits are grouped into fi ve stacked facies: amalgamated channel, floodplain and channel, paleo-estuary, offshore shallow marine, and present-day estuary. A paleo-estuary facies had never been identifi ed before, making these observations novel. This facies is characterized by a sedimentary succession and sediment distribution that are distinct from those of the present-day estuary because of a change in sediment supply from the sea fl oor beyond the estuary mouth. It also contains large numbers of tidal-channel sand bodies that are signifi cant reservoirs for shallow biogenic gas. Since the last glaciation, there have been three stages in the development of the QR incised-valley fi ll sequence: (1) a formation stage associated with sea-level fall, (2) a fi lling stage during the early transgression with rapid sea-level rise, and (3) a burial stage corresponding to the slowing of sea-level rise and the onset of progradation. This fill consists of four longitudinal segments, each of which is distinguished by a distinct stratigraphic succession and different degrees of marine and fluvial influence. The basal erosion surface and sidewalls of the incised valley, the top of stiff clay on the interfl uves, and the top of falling-stage fluvial-terrace deposits compose the sequence boundary. The initial flooding surface and maximum flooding surface are located with in the amalgamated channel and offshore shallow-marine sediments, respectively. These observations indicate that: (1) relative sea-level changes determine the stratal stacking patterns, but local environmental factors, such as physical processes, accommodation, sediment supply, and coastal confi guration control the nature of the facies, surfaces, and sediment-distribution patterns; and (2) the tripartite facies organization and wave ravinement surfaces typifying wavedominated or mixed-energy (wave and tide) incised-valley fi lls are absent in the macrotidal QR succession, and the tidal ravinement and erosion surfaces of the macrotidal QR incised valley are more extensive and numerous than those of the wave-dominated or mixed-energy succession. [ABSTRACT FROM AUTHOR]

The coal‐bearing Yan'an Formation in the Ordos Basin of the Middle Jurassic was deposited in a river delta–lacustrine sedimentary environment with relatively stable accumulation rates. Spectral analysis and wavelet transform analysis of the natural gamma‐ray (GR) curves from several boreholes through the Yan'an Formation yielded five main sedimentary cycles with wavelengths of 34–57, 10–18, 8–14, 2.9–4.1, and 2–3 m. These cycles were controlled by orbital cycles of eccentricity (405, 128, and 97 kyr), obliquity (35 kyr), and precession (22 kyr), and the long‐eccentricity period of 405 kyr was the most significant cycle. Filtering the sedimentary records for the long‐wavelength cycle and short‐wavelength cycle implies that there are 11 long‐eccentricity cycles and 35 short‐eccentricity cycles preserved in the Yan'an Formation. Assigning the 405 kyr long‐eccentricity cycle to the filtered 11 primary long‐wavelength cycles implies that the Yan'an Formation spanned 4.4 Myr. The orbital–climate cycles were critical factors in the sediment facies changes and episodes of coal formation within the basin. The long‐eccentricity cycles of the Milankovitch cycle are the predominant control factors of the coal seams deposited in the Middle Jurassic Yan'an Formation. [ABSTRACT FROM AUTHOR]

The upper corner gas overrun caused by goaf gas gushing in the high-gas mine can be mitigated by roof positioning of long boreholes in the goaf fracture zone, creating an artificial gas migration channel and achieving safe comining of coal and gas. This study numerically simulated the fracture evolution in the coal rock overlying goaf in workface #2-104 of the Detong Mine, China. Using the O-shaped circle theory and the FLAC3D commercial software package, the range parameters of goaf fracture zone gas-concentrated areas were obtained by defining the pressure relief coefficient, which provided a basis for the arrangement of holes in the goaf located at 15 m from the workface goaf collapse zone to the workface floor and 15–60 m from the structure zone to the workface. According to the obtained goaf parameters, the distribution and migration law in the goaf under the conditions of initial state and extraction with different roof borehole parameters were simulated by the FLUENT software. The optimal borehole location was 30 m from the floor and 25 m from the return airway. The field experiment with three boreholes arranged in the optimal extraction position provided the extraction concentration in the borehole above 30%, the gas extraction volume of 12 m3·min−1, and the concentration at the upper corner below 1%, which ensured safe coal and gas comining. [ABSTRACT FROM AUTHOR]

To better understand water inrushes originating from shaft-freezing holes, the hydrogeological conditions and water source were analyzed for a typical inrush case in the Yingpanhao coal mine in western China. The mechanism of this new type of water inrush was identified by considering the stratum movement caused by mining, the concentric annular channels of freezing holes, and the dynamic recharge of multiple aquifers. A new risk assessment model and corresponding grouting method were developed and the problems involving the prediction of water inrush and selection of the optimum grouting position were described. Detailed guidelines for grouting, including the layout of injection boreholes, slurries, grouting pressure and stopping criteria, were proposed. A grouting case targeting this type of water inrush in the Yingpanhao coal mine was introduced. Field studies indicated that open, concentric annular freezing hole channels provide favorable conditions for groundwater migration. The proposed method may effectively inhibit groundwater migration in multiple aquifers and prevent water inrushes through shaft freezing holes and provides an appropriate framework for water inrush prevention for similar mining areas in western China. [ABSTRACT FROM AUTHOR]

Abstract: As a paradigm of greenhouse climate in Earth's history, the Cretaceous provides significant rock records of global climate changes under conditions of greenhouse climate. The Songliao Basin, among the longest duration (85–90m.y.) of continental sedimentary basins, provides an excellent opportunity to recover a nearly complete Cretaceous terrestrial sedimentary record. Extensive lake deposits, ten-kilometers deep and covering an area of 260,000km2 of the Songliao Basin, provide unique, detailed records that can be tied to the global stratigraphic time scale, thereby improving our understanding of the continental paleoclimate and ecological system. The two coreholes at SKIs and SKIn sites were drilled into this basin and completed with a total length of 2485.89m of recovered core that spanned the complete middle-to-Upper Cretaceous strata in the basin. The unique geological setting of long-term continuous subsidence within the largest Cretaceous landmass in the world — makes the Cretaceous Songliao Basin of northeastern China an ideal place to study Cretaceous climate change on the continent. This paper reviews the literature on the paleogeography and paleoclimate of the northern East Asia and the Songliao Basin during the Cretaceous. Based on the climatologically sensitive deposits, oxygen isotope studies, and paleontology, the climate during the Cretaceous in the Songliao Basin was temperate and humid with relatively abundant rainfall. During the period, significant changes – four cooling, three warming, and three semiarid events – are generally consistent with the oxygen isotope data from East Asia, and the four cooling events, in Berriasian–Valanginian, Aptian–Albian, early Santonian, and Campanian–Maastrichtian, may be related to potential glaciations in Cretaceous. [Copyright &y& Elsevier]

Anti-slide piles are economical and effective slope-retaining structures that are widely used in highway subgrade protection, and the mechanism of these piles has been attracting increasing attention. In this study, a cutting loess slope in Shaanxi Province, China, was excavated during the construction of a highway, and a row of anti-slide piles was used in the field to stabilize the slope. The results of in situ surveys and drilling indicated that a landslide had previously occurred. To ensure the safety of the slope, detailed monitoring measures were applied. Soil boreholes and pile monitoring holes were drilled to investigate the horizontal displacement. The pile length was 40 m with a cross section of 2 m × 3 m and a pile spacing of 6 m. To explore the interaction between high slopes and long anti-slide piles, a three-dimensional numerical model was established. Thereafter, the stress and deformation characteristics of a single pile were studied, and factors such as the pile length, embedment ratio, pile spacing, and cross section were considered. A comparison of the simulation and measurement results demonstrated that increasing the pile length may cause a shallow landslide, leading to a lower safety factor of the slope. It was found that s = 4b can be thought of as the most cost-effective arrangement and the soil arching effect in the vertical direction of 8–20 m is stronger; the earth pressure behind the pile will decrease due to the friction between the bedrock and soil near the sliding surface. It was also found that rectangular piles are more suitable for stabilizing high slopes. This study provides optimization choices for the slope and has reference value in the application of stabilizing piles. [ABSTRACT FROM AUTHOR]

Coal and gas outbursts can lead to serious disasters in coal mines. The drilling of boreholes to predrain the gas is an effective measure for preventing such accidents. However, due to the complexity of the geological situation, the drilling trajectory often deviates from the design trajectory, resulting in poor gas extraction. To solve the problem of gas drainage borehole deflection, an analytic hierarchy process (AHP) model is established based on geological factors, technical factors, and human factors. The AHP model is used to rank the weights of various influencing factors, and the analysis is combined with a drilling model and engineering examples. Finally, the results show that soft and hard interlayers are the most important factors affecting the deflection of the borehole. The rock drilling model is mainly affected by the formation forces. The regularity of the change in the azimuth angle during drilling is not obvious when the angle of the encountered layer is less than some critical value. When the borehole is skewed downward, the deflection angle ranges from 0 to 4°, and the deflection of the borehole occurs mainly at the interface of the rock layers. When the angle of the encountered layer is greater than the critical value, the borehole is skewed upward, with a deflection angle of 0–6°, and the deflection occurs at the rock interface. The trajectory curve obtained by theoretical predictions from field data is found to be consistent with that of an actual project. [ABSTRACT FROM AUTHOR]

A very challenging but meaningful task in geodynamic research is determining how to clearly disentangle and quantify the frequency-dependent barometric responses of borehole dilatometers. However, we still lack a fundamental understanding of how the Chinese TJ-2 borehole dilatometer network has responded to barometric pressure at different frequencies since the late 1990s. For this reason, we systematically analyze the transfer functions of volumetric strain changes associated with barometric pressure at 21 stations. The results demonstrate that the barometric responses for most sites are generally flat and near-flat in the low- (0.1–0.5 cpd) and high-frequency (8–30 cpd) bands, respectively, while drastically fluctuating in the intermediate-frequency band (0.5–8 cpd) due to the tidal influences. Overall, many sites exhibit strongly frequency-dependent behaviors over the whole frequency range (0.1–30 cpd), which are likely controlled mainly by the complex properties of sensor-grout-formation systems. In light of both the low- and high-frequency barometric responses of dilatometers, whether the surrounding formations are linear elastic medium can be verified. The mechanical properties of three stations, with surrounding formations that are thought to be linear elastic structures, can therefore be roughly but quantitatively estimated by utilizing barometric responses, which are shown to be consistent with the parameters tested by rock mechanics. Altogether, this work not only provides a useful method for frequency-dependent pressure correction, but also offers profound insights to advance sensor-grout-formation modeling. [ABSTRACT FROM AUTHOR]

• An effective rock damage control technique for large-diameter-hole lateral blasting. • An accurate numerical model for rock breaking extent analysis in lateral blasting. • Reasonable combination of charge structure can achieve rock damage control effect. • Most of boulders are caused by the collapse of the remaining rock mass. Controlling rock damage induced by lateral blasting excavation is a source of concern. In underground mines, large-diameter-hole lateral blasting excavation often causes engineering disasters such as large blocks falling and overall collapse of the remaining rock mass. Because of their high cost and cumbersome operation, conventional contour blasting techniques, such as smooth and presplit blasting, are unsuitable for production boreholes. In this paper, based on the large-diameter-hole lateral blasting excavation of the Shaxi underground mine in China, a field lateral blast test with a single row was initially conducted, and the sonic wave speeds and goaf boundaries were measured to evaluate the damage degree to the remaining rock mass. A numerical model with three rows of boreholes was developed and calibrated against the lateral blast test with a single row. The calibrated numerical model was used to simulate the blasting process. The blast-induced damage characteristics with different charge structures in different rows were investigated, and the optimal charge structure for each row was obtained. The results indicate that the rock damage control effect can be achieved by a reasonable combination of charge structures and number of blasted rows, and it is more satisfactory with an increasing number of blasted rows and a reasonable decrease in the charge coefficient row by row. The rock breaking pattern at Cut X2 shows that most of the boulders are caused by the collapse of the remaining rock mass under the impact of blasting excavation. The ratio of broken rock in Part 4 indicates that the blast impact of the last row plays a dominant role in the damage to the remaining rock mass. Two optimized schemes were applied to the field of large-diameter-borehole lateral blasting, and satisfactory effects were achieved in the blast-induced damage control of the remaining rock mass. [ABSTRACT FROM AUTHOR]

The Yuyao River Valley is located in the northwest of Ningbo basin, China. The confined aquifers in the study area show obvious spatial distribution characteristics, which are essentially controlled by the evolution and distribution of the paleochannel. Therefore, it is of great significance to determine the spatial geometric characteristics of the paleochannel for finding out the hydrogeological characteristics and establishing a sustainable groundwater management system. In order to confirm the geo-electric parameters (resistivity and thickness) of each geotechnical layer and the spatial geometric characteristics of the paleochannel in the Yuyao River Valley, 77 vertical electric soundings were performed on five profiles perpendicular to the valley. In addition, 13 geological boreholes distributed over the study area were collected, and the borehole-side electrical sounding measurements were carried out near the boreholes. In fact, the interpretations of borehole-side electrical sounding measurements indicate that the resistivity of each geotechnical layer in the survey area varies greatly in the vertical direction. After calibrated by the lithology of the boreholes, the results of the explication of VES and the electrical resistivity profiles demonstrated the existence of the paleochannel. The paleochannel corresponds to the sand gravel or round gravel aquifers whose particle diameter gradually increases from top to bottom. Thus, the buried depth of the paleochannel is about − 70 to − 35 m, and its width is more than 1000 m. This study corroborated the reliability of the VES method through combining electrical resistivity profiles and hydrogeological data to determine the spatial geometric characteristics of the paleochannel in terms of electrical differences. [ABSTRACT FROM AUTHOR]

Borehole pressure relief method is one of the most effective ways of rock burst prevention in coal mines. The measured results of borehole pressure relief at no. 8939 longwall face in Xinzhouyao coal mine, China, are presented here. The analyses identify the pressure relief magnitudes in coal mass around the boreholes with different diameters, spacing, and drilling time. This research has established that the best pressure relief of the rib coal can be achieved by using φ108 mm borehole with 0.7 m interval after 288 hours. The strain relief is acceptable after 288–360 hours of drilling, while the best result is achieved after 432 hours. It is also the first time to monitor the borehole pressure relief in a coal mine on-site using Brillouin optical time domain reflectometer (BOTDR) distributed fibre-optic sensing. The method implemented in this research provides new ways to improve stress relief design and minimize the rock burst occurrence for mine practitioners. [ABSTRACT FROM AUTHOR]

• Three cooling events are identified: 65-50 Ma, 33-22 Ma, 14-6 Ma. • Three cooling events led to about 1500 m denudation thickness. • The tectonic uplifts were due to the changes of the Pacific plate velocity. We conduct apatite fission-track analysis in the Songliao Basin to reveal the Cenozoic tectonic uplifts and determine how basin development was associated with the transformation from the Paleo-Pacific plate to the Pacific plate and the change of the Pacific plate velocity. Our results from the CCSD-SK1 boreholes in the northern Songliao Basin reveal three Cenozoic cooling (uplift) events:Paleocene (65–50 Ma), Oligocene (33–22 Ma), late Miocene–Pliocene (14–6 Ma) with the apparent mean exhumation rates of 0.08–0.09 mm/yr, 0.08–0.09 mm/yr and 0.11–0.24 mm/yr, respectively. The total removal of the sedimentary cover resulted from 3 cooling (uplift) events is about 1500 m, the removal by the extreme cooling (uplift) event (14–6 Ma) is about 900 m. In this paper, we infer that the transformation of the Paleo-Pacific plate (Izanagi plate) to the Pacific plate plays the first-order control on the first cooling event (65–50 Ma). The second (33–22 Ma) and third (14–6 Ma) cooling events are closely related to the steady and relatively high motion velocity of the Pacific plate. Since Oligocene, a large scale of tectonic uplifts widely happened not only in basins but also in the ranges around them in northeastern China. [ABSTRACT FROM AUTHOR]

Most serious geotechnical problems related to rock engineering are generated by the existence of faults. Detection of fault (especially active faults) is the first step to conduct any further in-depth studies in faulted rock mass or rock blocks. In this paper, we investigated the plausibility to image fault zones by passive seismic surveys using recorded ambient noise. The test site is in the north suburb of Beijing, northern China along the south bank of the northwest-southeast running Wenyuhe River, where the NNE-striking Huangzhuang-Gaoliying fault (HGF, active in the Holocene) is crossing. In general, the results are in good agreement with previous studies using active source seismics conducted in this area along the HGF and existing borehole drillings in the vicinity. Undoubtedly, Active source seismic reflection technique is the best technique to image fault in depth with high resolution. The drawback is its high cost and the necessity of using explosives, a practice usually prohibited in urban settings. In contrast, passive seismic surveys take the advantage of the ever-existing ambient noise source, and provide a low-cost technique, and fast deployment that can locate the fault effectively. Though the imaging resolution is lower compared to those obtained by active source seismic surveys, our passive seismic experiment at the Wenyuhe River site demonstrated that this approach is effective, especially for those faults with significant normal faulting component and the stratigraphy is significantly different on the two sides crossing the fault line. • Passive seismic survey using ambient noise was conducted at the Wenyuhe River site for the purpose to image the Huangzhuang-Gaoliying Fault. • The fault occurrence information deduced by passive seismic survey is in good agreement with active seismic survey results; though understandably with lower resolution. • Passive seismic survey can serve as a low-cost reconnaissance tool for those active fault detection projects merit higher resolution imaging using active seismic survey methods. [ABSTRACT FROM AUTHOR]