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The rock uniaxial compressive strength (UCS) is the basic parameter for support designs in underground engineering. In particular, the rock UCS should be obtained rapidly for underground engineering with complex geological conditions, such as soft rock, fracture areas, and high stress, to adjust the excavation and support plan and ensure construction safety. To solve the problem of obtaining real-time rock UCS at engineering sites, a rock UCS forecast idea is proposed using digital core drilling. The digital core drilling tests and uniaxial compression tests are performed based on the developed rock mass digital drilling system. The results indicate that the drilling parameters are highly responsive to the rock UCS. Based on the cutting and fracture characteristics of the rock digital core drilling, the mechanical analysis of rock cutting provides the digital core drilling strength, and a quantitative relationship model (CDP-UCS model) for the digital core drilling parameters and rock UCS is established. Thus, the digital core drilling-based rock UCS forecast method is proposed to provide a theoretical basis for continuous and quick testing of the surrounding rock UCS.

Warm ice at temperatures close to the pressure melting point is often encountered in deep ice-core drilling. The heat generated by rotary cutting can melt ice chips, which seriously threatens the safety of drilling if the chips refreeze on the drill bit or barrel. Lowering the cutting heat is an effective method to reduce the melting of ice chips. In this study, a general theoretical model was established based on heat transfer theory and the cutting mechanism to calculate and analyze the cutter temperature during the circulation of the drilling fluid. The model was validated by a series of experiments, which demonstrated reasonable agreement between the calculated data and experimental results, with a maximum error of <16%. The factors that contribute to the rise in the cutter temperature during warm ice drilling were investigated. Results suggest that the drilling fluid has excellent cooling performance, and its type and flow rate have minimal impact on the cutter temperature. To mitigate the cutter temperature rise, maximizing the rake angle and thermal conductivity of the cutter, while minimizing the rotation speed of the drill bit, cutting depth, cutter width and friction coefficient between the ice and cutter is recommended.

A deep ice core was drilled at Dome A, Antarctic Plateau, East Antarctica, which started with the installation of a casing in January 2012 and reached 800.8 m in January 2017. To date, a total of 337 successful ice-core drilling runs have been conducted, including 118 runs to drill the pilot hole. The total drilling time was 52 days, of which eight days were required for drilling down and reaming the pilot hole, and 44 days for deep ice coring. The average penetration depths of individual runs were 1 and 3.1 m for the pilot hole drilling and deep ice coring, respectively. The quality of the ice cores was imperfect in the brittle zone (650−800 m). Some of the troubles encountered are discussed for reference, such as armoured cable knotting, screws falling into the hole bottom, and damaged parts, among others.

A new type of ice core drill bit, designed with a vane swirler, was developed for ice core drilling with air reverse circulation. An orthogonal experimental design method was employed to investigate the effects of the swirler structure parameters on the reverse circulation performance of the drill bit including helical angle, number of blades, blade length and blade central angle, etc. The entrainment ratio was used to evaluate the reverse circulation effectiveness of the drill bit. The results show that the helical angle is the dominant factor regardless of whether or not the flushing nozzles are part of the design of the drill bit. The number of blades is the least important factor for the drill bit designed with the flushing nozzles (referred to as drill bit I ), while the outlet area of the swirling slot is the least influential factor for the drill bit without flushing nozzles (referred to as drill bit П ). In addition, the appearance of the ice core has a certain effect on the air reverse circulation for both drill bits. Within the ranges of this study, the optimal structure of the drill bit was determined based on the range analysis of the orthogonal design.

Basal melt in the Dome A region will influence the deep-ice-core drilling at Kunlun Station. The melting point (wet bedrock) has a higher reflectivity than the surrounding area, which can be assessed using radar echoes from the bedrock. This paper uses a linear absorption model to determine wet and dry ice–bedrock interfaces around the Kunlun drilling site. In the determination process, an artificial intelligence model was applied to extract the ice–bedrock interface for inferring the ice thickness. Additionally, the various depth-averaged attenuation rates were used to identify the maximal range of basal melting. We mapped the patterns of the wet points on the bottom of the ice sheet and the modeled basal temperature to verify the results of the wet bed conditions. According to these maps of wet bed conditions, the areas with basal melting around the drilling site primarily appear in valley walls with low basal temperatures and are linked with hydraulic potential and bedrock elevation. Identifying the ice–bedrock interface is challenging in the valley bottom area, where the melting points are less than at the valley walls. Additionally, the melting proportions of 11.8% and 3.62% were calculated from two ice-penetrating radar data in this research. The mapped melting points around the site of Kunlun ice core drilling suggest complex ice flow effects and can be used to better interpret archives of old ice for paleoclimate research.

For non-directional drilling cores, selection of samples and the test methods for in situ stress measurements to evaluate the Kaiser effect (KE) were proposed, and the magnitude and direction of the principal stresses were derived from first principles. Based on this approach, the KE for 423 samples in the Burtai and Baode coal mines in the northern Ordos Basin (NOB), China, have been investigated. The results show that the maximum horizontal principal stress ( σ H ), the minimum horizontal principal stress ( σ h ) and the vertical stress ( σ v ) varied with depth and location, and the values increase with increasing depth. Generally, the horizontal stresses play a leading role. For the main stress regimes in the NOB, σ H  >  σ h  >  σ v (Burtai Mine, < 172 m; Baode Mine, < 170 m) and σ H  >  σ v  >  σ h (Burtai Mine, 170–800 m; Baode Mine, 170–400 m), and the σ v  >  σ H  >  σ h stress regimes are mainly distributed in moderately deep to deep coal mines. For rock masses with a depth of 350 m, k (( σ H  +  σ h )/2 σ v ) tends to 1, indicating that a deep critical state will gradually emerge. The test results are compared with those for the overcoring (OC) method, the anelastic strain recovery (ASR) method and micro-hydraulic fracturing (HF). The relative errors for σ H , σ h and σ v were 14.90%, 19.67%, 15.47% (Burtai Mine) and 10.74%, 22.76%, 19.97% (Baode Mine), respectively, and the errors are all within an acceptable range, thus verifying the reliability of the KE method. The dominant orientation for the σ H (Burtai mine, NE-NNE; Baode Mine, NEE) is obtained via paleomagnetic technology, and the data are consistent with those (NE-NEE) of the earthquake focal mechanism solutions for the area. Based on the Byerlee–Anderson theory, a discussion is given on the levels of stress accumulation in the rock mass of the mines. For dry rocks or hydrostatic pressure rocks, the friction coefficients of the faults are low for both locations, and the values are less than the lower limit (0.6) of the strike-slip faults slip, indicating that the stress fractures at a low level around the study areas are lower than the friction limit stress. The stress accumulation levels in the Baode Mine are slightly larger than those in the Burtai Mine.

Using an anti-icing coating to prevent ice accretion on the drill surface is a feasible solution to address the drilling difficulties in warm ice. In this study, four types of commercially available hydrophobic coating materials were tested to evaluate their water repellency and anti-icing properties, namely, a mixture of silica and fluorocarbon resin with polytrifluoroethylene, modified Teflon, silica-based emulsion and an acrylic-based copolymer. Their water contact angles are ~107°, 101°, 114° and 95°, respectively. All these hydrophobic coatings can significantly reduce the strength of the ice adhesion within a temperature range of −10 to −30°C on a planar or curved surface. The coating of an acrylic-based copolymer, in particular, can reduce the average tensile strength and the shear strength of the ice adhesion by 87.08 and 97.11% on planar surfaces at −30°C, and by 98.06 and 96.15% on a curved surface, respectively. The main challenge in the practical application of these coatings is their durability. An acrylic-based copolymer coating will lose its water repellency performance after 140 cycles of abrasion. The shear strength of ice adhered on curved surfaces coated with this material will approach that achieved on uncoated surfaces after 11 cycles of icing and de-icing tests.

Background At present, it is not known whether hip effusion/synovitis affects the therapeutic effect of multiple drilling core decompression (MDCD) in patients with bone marrow edema syndrome of hip (BMESH). The aims were to assess hip effusion/synovitis and its relationship with results of MDCD in patients with BMESH. Methods The data of undergoing arthroscopic-assisted MDCD for treatment of BMESH with hip effusion/synovitis by one surgeon were retrospectively reviewed from the associated medical records at the Affiliated Hospital of Zunyi Medical University (2016–2019). Seven patients (9 hips) participated in this study. Patients were followed up at 1, 2, 3, 6, 12 and 24 months. Data included demographics and clinical outcomes. The pre- and postoperative pain and functional outcomes were measured with the visual analogue scale (VAS), Harris Hip Score (HHS), Hip Outcome Score Activities of Daily Living subscale (HOS-ADL), International Hip Outcome Tool-12 (iHOT-12) and range of motion (ROM). Results Seven patients (9 hips) were followed up. Disappearance of hip pain immediately obtained at rest after surgery. All of 7 patients returned to their former activity level at postoperative 3 months, bone marrow edema had disappeared on Magnetic Resonance Imaging (MRI). The VAS, HHS, HOS-ADL, iHOT-12, and ROM at postoperative 1 month had a significant difference ( P < 0.05 ) compared with preoperative. It was also statistically significant ( P < 0.05 ) when compared with other time points. At the final follow-up, all patients had no limited ROM, which was symmetrical with the contralateral of hip joint. Hip effusion/synovitis were observed in 9 hips. Labral tears, cartilage fissure, and loose bodies were observed in 1 hip, respectively. Kirschner wire tracks bleeding occurred in 1 hip. No other complications occurred. Conclusions Hip effusion/synovitis could affect the clinical outcomes after MDCD in patients with BMESH. Arthroscopic procedure of hip effusion/synovitis can shorten postoperative pain relief time, disappearance time of bone marrow edema on MRI. It can simultaneously diagnose and treat other concomitant intraarticular pathologies, and be a safe operation with fewer complications.

The study of pulse flushing impact on weakening of rock formation in the course of diamond core drilling using diamond bits. Theoretical research of rock formation softening processes under transient thermal impact is based on the theory of thermoelasticity. Comparative analysis of thermal stress condition of rock formation in the course of diamond core drilling using both the pulse and continuous flushing modes was carried out in the course of the research. The process of rock formation breaking in the course of diamond core drilling using stationary and transient (pulse) flushing with drilling fluid was studied herein. Conditions for transition of rock formation fractures to movable state and strength reduction have been defined. The estimated relation between the fracture development rate and delay of rock formation decomposition are obtained herein. The study revealed that under the pulse mode of drilling fluid supply conditions appear for thermal decomposition of rock formation. Owing to a greater, as compared to the continuous flushing mode, amplitude of temperatures in the borehole working area., strength reduction of the rock formation surface occurs. When boring granitic rocks, its strength reduction is 12 % on average. The analysis of thermal stress condition of the rock formation was carried out for the first time along with grounding of the possibility to employ the thermal cycle effect to enhance the efficiency of rock decomposition in the course of the core drilling using diamond bits. For the first time ever the characteristics of thermal decomposition of rock formation were determined as follows: minimum dimensions of fractures and minimum delay time of decomposition commencing; the evaluation of rock formation strength reduction for the diamond core drilling process. The study revealed that the technique of pulse supply of the drilling fluid stipulates for notable reduction of energy consumption of the rock formation decomposition process. The outcomes of the study can be applied to develop pulse techniques of wells boring, as well as to establish efficient and cost saving parameters of the process.

Due to its high mechanical penetration rate and lack of pollution of the environment, air reverse circulation drilling is considered to be a promising method for ice drilling. The air reverse circulation is caused by the combination of the ejector and the flushing nozzles in the drill bit. In this paper, CFD software was used to simulate the influence of the structure of the swirler on the effect of air reverse circulation in the swirling drill bit, and a testing stand was established for the testing of air reverse circulation. The results show that for drill bits without flushing nozzles, the smaller the helical angle is, the larger the entrainment ratio will be, meanwhile the smaller the area ratio is, the larger the entrainment ratio will be. In contrast, for drill bits designed with flushing nozzles, the larger the helical angle is, the larger the entrainment ratio will be, and the larger the area ratio is, the larger the entrainment ratio will be. In addition, the presence of the ice core sharply reduces the effect of air reverse circulation. When the ice core’s height exceeds that of the outlet of the swirler, the reverse circulation effect is slightly improved.