A multi-PMT optical sensor for IceCube-Gen2

A new long optical module (LOM) is under development for IceCube-Gen2, the proposed expansion to the IceCube neutrino observatory at the South Pole. The module is housed in an elongated borosilicate-glass pressure vessel, the size of which is constrained by the borehole diameter, which impacts drilling economy. The designs under consideration use either 16 or 18 4-inch PMTs, conditional on future performance tests, mounted so as to guarantee full angular coverage. Modular electronics have been custom-designed to fit into the available space and to minimize cost and power requirements for the ∼10000 modules to be installed. We will provide an overview of our approach to these design considerations and summarize the results of our tests and simulations. Prototype modules will be installed in the upcoming IceCube Upgrade.

Numerical Simulation of Borehole Parameters for Coal Seam Gas Pre-Drainage

Borehole parameters are quite important for gas drainage. This paper studies the impact of borehole diameter and time on gas drainage and performs numerical simulation on the distribution of gas pressure under the conditions of different borehole diameters and drainage times. The simulation results reveal that, as the borehole diameter increases, the gas drainage volume increases along with it and the gas pressure decreases, but such effect on gas drainage is limited. In terms of drainage time, the longer the drainage time, the greater the drainage impact scope. Taking a gas pressure drop of 51% as the indicator of the effective pre-drainage radius, the distance from the point with a gas pressure drop of 51% to the position of the borehole is the effective pre-drainage radius. When the pre-drainage reached the 30th, 45th, 60th, 75th, and 90th day, the effective pre-drainage radius was 1.04m, 1.29m, 1.51m, 1.68m, and 1.82m respectively. According to the numerical simulation results, the effective pre-drainage radius varies with the pre-drainage time, and the fitting analysis of the two indicates that the relationship between the two can be described by a power function.

Study on Pressure Relief Effect and Rock Failure Characteristics with Different Borehole Diameters

Rock burst is a common tunnel and mine dynamic disaster, especially for deep buried tunnels, which often leads to tunnel construction delay and even induces tunnel collapse and subsidence of strata. Rock drilling is one of the effective pressure relief methods to prevent these disasters. In order to study the influence of borehole diameter on rock mass pressure relief effect, indoor acoustic emission characteristics and numerical simulation of rock samples with different borehole diameter were studied. The research result shows that with the increase in borehole diameter, the effect of borehole pressure relief is better. Different borehole diameters do not change the overall trend of acoustic emission evolution, but it will lead to different acoustic emission count characteristics of rock damage and failure, especially the maximum acoustic emission count characteristics and corresponding strain values. The existence of drilling will lead to the failure stress of rock in advance. Moreover, the existence of drilling causes a great change in the failure mode of the specimen.

Study on the Radial Displacement Law and Permeability Enhancement Effect of Coal Body around Hydraulic Flushing Drilling

Hydraulic flushing drilling technology can not only improve the efficiency of high-pressure and low-permeability geological reservoir coalbed methane drainage but also effectively reduce the probability of coal and gas outburst disasters through pressure relief. The main mechanism of this technology is to expand the borehole diameter through hydraulic flushing measures, increase the strain of the coal around the borehole, and increase the development of cracked pores, to improve the permeability of the coal seam and realize the dual reduction of ground and gas pressure. However, in the actual application process, the interaction mechanism among the stress field, the structure field, and the seepage field is still not clear, and there is no clear method to accurately determine the pressure relief range based on the pressure relief mechanism in order to carry out reasonable drilling arrangements. Therefore, this article comprehensively uses laboratory experiments, numerical simulations, and field practices to fully explain the hydraulic flushing pressure relief mechanism and proposes a method to accurately determine the pressure relief range based on the radial line strain law. The results based on radial line strain showed that the effective relief radius expands to 0.86 m once adopting the Φ579 mm hydraulic flushing borehole compared to Φ160 mm; the borehole’s equivalent diameter of drilling field #11 is 2 to 3 times than that of #10 and 1.2 times the average CBM extraction amount. Therefore, as the borehole diameter increases, the permeability and radial line strain of the coal around the borehole increase significantly, but the tendency of the increase in permeability decreases with increasing vertical stress. The findings of this study can help for a better understanding of the pressure relief and permeability enhancement mechanism of hydraulic flushing, and the method of determining the pressure relief range based on radial strain can also provide a new way for other mines to practice ideas.

Stress Relief and Stimulation of Coal Reservoir by Hydraulic Slotting

Coal seam permeability is one of the key factors influencing the gas extraction efficiency, which is of great significance to reduce coal and gas dynamic disasters in gassy coal mines. Hydraulic slotting technique is an effective method to stimulate the coal reservoir, but the selection of slotting key parameters has great impact on gas extraction efficiency. For this reason, the hydraulic slotting model was established by using FLAC3D software to analyze the stress distribution before and after slotting. Then, the influence of borehole diameter, slotting width, and slotting length on coal seam stress relief is also discussed. The results show that the slotting width has a great influence on the stress relief of the coal seam, while the borehole diameter and slotting length have no obvious influence on that. Based on the results of numerical simulation, field tests were carried out in Sangshuping NO.2 coal mine. The results show that the coal seam stress can be fully released, resulting in the improvement of coal seam permeability. The gas extraction efficiency can be highly enhanced by hydraulic slotting. This research achievement provides the guidance basis for high-stress water jet slotting technology with adaptive selection of slotting parameters in different geological conditions.

Non-contact measurement system for hot water drilled ice boreholes

A programmable borehole measurement system was deployed in hot water drilled ice holes during the ‘Bed Access and Monitoring of Ice Sheet History’ (BEAMISH) project to drill to the bed of the Rutford Ice Stream in West Antarctica. This system operates autonomously (no live data) after deployment, and records borehole diameter (non-contact measurement), water column pressure, heading and inclination. Three cameras, two sideways looking and one vertical, are also included for visual inspection of hole integrity and sediments. The system is small, lightweight (~35.5 kg) and low power using only 6 ‘D’ cell sized lithium batteries, making it ideal for transport and use in remote field sites. The system is 2.81 m long and 165 mm in diameter, and can be deployed attached to the drill hose for measurements during drilling or on its own deployment line afterwards. The full system is discussed in detail, highlighting design strengths and weaknesses. Data from the BEAMISH project are also presented in the form of camera images showing hole integrity, and sensor data used to calculate borehole diameter through the full length of the hole. These data are used to show confidence in hole verticality and subsurface cavity development and connection.

Research on In Situ Stress Measurements in Reinforced Concrete Beams Based on the Core-Drilling Method

To increase the accuracy of the core-drilling method in measuring the in situ stresses within concrete beams, this paper developed a special core-drilling machine system, studied the surface stress release rule of concrete beams through finite element simulations, and then carried out verification tests. The effects of the borehole diameter, drilling depth, strain sensor size, and borehole position on the measurement accuracy were studied. The results showed that borehole diameters of 100 mm, 75 mm, and 50 mm can achieve stress release and that the smaller the borehole diameter was, the easier it was to release the stress. When using the smallest borehole, the stress concentration range around the borehole was narrow, and there was little damage to the original structure. The strain gauge size influenced the actual measurement results. An excessively large strain gauge will be disturbed by drilling because of the limited size of the borehole. An excessively small strain gauge will be easily influenced by the inhomogeneity and randomness of the concrete materials, resulting in large measurement error. The difference between the measured concrete stress and the theoretical value was less than 10%, and the average error was only 6.03%, indicating the feasibility of the proposed method.

INTERACTION OF A HELICAL BLADE OF A DRILLING TOOL WITH FROZEN GROUND

Introduction. Drilling of frozen and permafrost soils is one of the most complicated and energy-intensive processes of earthworks. The current drilling tools are not efficient enough to use since they implement energy-intensive drilling processes and are not always suitable for various types of soil. The use of helical working elements that implement the process of soil destruction with less energy-intensive types of deformations is advanced. The purpose of the research is to study the interaction of a helical blade of a drilling tool with frozen soil.Materials and methods. The article covers a method for conducting experimental studies of the interaction of a helical blade of a drilling tool with frozen ground and the tested models of the drilling tool. The influence of geometric parameters of a helical drill on a borehole formation process is studied.Results. The experimental research proved the hypothesis about the possibility of implementing a drilling process with tearing strain and obtaining a borehole diameter larger than a diameter of a destructive section of a helical blade. The dependence of the destroyed soil volume and the relation of an obtained borehole diameter to a diameter of a destroying section of a helical blade according to the angle of bend of a helical blade radius at which its increment occurs is determined.Discussions and conclusion. It is established that a helical drilling tool performs a borehole drilling due to the tearing strain implementation, which makes it possible to achieve more efficient drilling and obtain a borehole diameter larger than a diameter of the destroying section of a helical blade.Financial transparency: the authors have no financial interest in the presented materials or methods. There is no conflict of interest.