Borehole Rock Research Articles

DEVICE FOR CREATING SLOTS-VOLTAGE CONCENTRATORS IN THE BOUNDARY AREA OF WELLS IN FINE ROCKS

It is shown that in order to expand the field of practical application of directional measuring hydraulic fracturing, it is necessary to create technical means that provide cutting of initiating slots on the walls of boreholes in rock masses of different strength. A new slotter design is proposed, the distinctive feature of which is using carbide cutters that are extended during cutting slots along the normal to the device axis. The device is brought into operation due to its normalized movement tagging the bottom. The slotter dimensions allow using it in diamond drill holes of 76 mm diameter. The device is designed to create stress concentrator slots in adjoining zones of boreholes in hard rocks with a coefficient of 5-8 according to M. M. Protodyakonov’s scale.

NUMERICAL SIMULATION OF THE BROKEN ROCK MASS TRANSPORTATION IN A ROTATING PIPELINE

The impact of the angular velocity of a horizontal pipe rotating around its longitudinal axis and the shape of its cross-section on the efficiency of pneumatic conveying of bulk material in it has been numerically investigated by the discrete elements method. The maximum number of non-contact particles, that is, particles being not in contact with other material particles and with the pipe, in the cross section of the pipe during one its revolution, is assumed the condition for effective pneumatic conveying. A method for searching for non-contact particles is proposed, which makes it possible to calculate their number at fixed pipe position angles during its rotation. For various cross-sectional shapes, the optimal angular velocities are determined at which the average number of non-contact particles in the cross-section is maximum. The results of the study can be used to increase the productivity of the removal of products of destruction when drilling horizontal boreholes in rocks and soils.

Rock mechanics and wellbore stability of deep shale during drilling and completion processes

The seepage coupling effect between the borehole rock mass and borehole fluid and the effective stress field distribution around the wellbore are obviously different under different working conditions of drilling, fracturing and completion, which affect the stability of horizontal borehole of shale gas reservoir. The physical, chemical, and mechanical properties of the shale in Longmaxi formations in a block of China immersed with different working fluids were tested experimentally. Combined with the experimental data, a theoretical model was established to evaluate and analyze the wellbore stability of Longmaxi formations shale under different working conditions of drilling, fracturing and completion. The results show that the shale of the Longmaxi Formation is a typical hard and brittle shale, the bedrock is dense, with high mechanical strength and weak hydration and expansion ability. The immersion effect of different working fluids has little influence on the expansion and mechanical properties of shale bedrock. However, the mechanical strength of shale with relatively developed bedding fractures is low, and the immersion effect of different drilling fluid further weakens the mechanical strength, resulting in obvious anisotropy of mechanical strength of underground rock. The coupling effect of seepage between wellbore and formation has obvious influence on the dynamic distribution of borehole pore pressure and wellbore stability under different working conditions. The effective fluid column pressure at the bottom of the hole is the highest during the fracturing process, which leads to the increase of pore pressure near the wellbore, and then to the increase of collapse pressure around the borehole wall. The equivalent density of collapse pressure rises to the maximum of 1.93 g/cm3, and the wellbore stability is the worst in the fracturing process. The wellbore stability is secondary in the drilling process, and the wellbore stability is good when drilling along the direction of the maximum horizontal principal stress, and the equivalent density of collapse pressure is 1.69 g/cm3. During the completion process, the formation fluid flows into the wellbore, the pore pressure in the borehole is relieved, and the equivalent density of the collapse pressure is reduced to approximately 1.35 g/cm3, the wellbore stability is the best and open hole completion can be attempted in the horizontal well section. The results provide a certain theoretical reference for the selection of the drilling and completion schemes in shale formation.

Methods and technical solutions for keeping the path of a geotechnological borehole

With increasing depth of exploration and process boreholes (at small drilling diameters), the probability of deviation of the borehole path from design trajectory increases many times; i. e. zenith curvature and azimuth deviation of the borehole path occur. Therefore, developing methods for keeping vertical path of the borehole when drilling deeper horizons of ore bodies is a very topical issue. The paper presents the results of developing a new bottom-hole assembly for drilling boreholes in soft rocks using screw casing centralizers, which provide good stabilizing and centering effects to mitigate horizontal departure of the hole axis from the design direction and minimize vertical curvature of the hole path (zenith angle) while maintaining sufficient drill string flexibility. The developed technical solutions provide simplicity of design and ability to adapt to wide range of mining, geological and technological drilling conditions. The feasibility of manufacturing the centralizers by own efforts and the technological feasibility of quick and easy connecting the centralizer with other elements of the bottom-hole assembly have been substantiated. The manufacture efficiency is proved by the use of inexpensive and wear-resistant materials in the centralizer armouring, for which tungsten-cobalt or titanium-cobalt hard-alloy inserts were used. In addition, prevailing volume of borehole drilling in soft rocks allowed using replaceable centering elements, as well as their repair and restoration to increase their service life. The manufactured centralizer has a low production cost due to the design simplicity and the use of inexpensive wearresistant material and will compete in the market of drilling tools and technical devices for drill string stabilization. The economic effect from the introduction of the self-produced centralizers amounted to more than 170,000 tenge per a borehole.

Research on 3D virtual simulation of geology based on GIS

A simplified method based on GIS combined with virtual reality modeling language (VRML) to achieve real time and fast 3D geological modeling is proposed. By calling the borehole rock and soil information stored in the GIS database, it is automatically created using spatial interpolation technology. The spatial interpolation technology is used to automatically create the side map of the model, and automatically output this information as a VRML script according to the standard format. The created model can be displayed independently without relying on the modeling software platform and can realize functions such as free rotation, flying, and zooming. Successfully developed a 3D geological modeling system based on the introduced design ideas, and used the system to achieve 3D geological modeling of a certain bridge site. This method has the characteristics of simple operation, fast modeling speed, less manual intervention, and visual interactive operation and can be used as an auxiliary decision-making method for engineering surveys.

Advanced monopole and dipole sonic log data processing — Part 1: Real time

Real-time open-hole wireline sonic logging data processing becomes a nontrivial task to accurately, automatically, and efficiently evaluate the compressional and shear slowness of a borehole rock formation when human interaction is not possible and the signal processing time is limited to the elapsed time between different transmitter excitations. To address real-time sonic data processing challenges, we have developed self-adaptive, data-driven methods to accurately measure the formation P- and S-wave slowness from monopole and dipole waveforms in all types of formations. These new real-time processing techniques take advantage of the fact that advanced wireline sonic logging tools have wide frequency responses and little to no detectable tool body arrivals. These technology improvements provide an opportunity to implement a first-motion-detection technique that detects the onset of P-waves in the monopole array waveforms. The knowledge of compressional arrival time and corresponding slowness are then used to project an appropriate slowness-time window to identify the monopole refracted S-wave and its slowness based on the range of possible compressional to shear velocity ratio ([Formula: see text]/[Formula: see text]) for earth rock formation. To process the borehole dipole flexural waves, we develop a new, data-driven frequency-domain method that enables the evaluation of the full flexural-wave dispersion response and its corresponding low-frequency shear slowness asymptote. Field data processing results indicate that our methods provide high-quality compressional slowness (delta-T compressional) and shear slowness measurements that are not affected by other borehole modes or dispersion complications in most formation types.

Experimental Investigation of Cuttability Improvement for Hard Rock Fragmentation Using Conical Cutter

Stress conditions and preflaws are prominent conditions influencing the cuttability of deep hard rock. This study aims to investigate the cuttability of intact, prefractured, and drilled rocks under biaxial confining stress, uniaxial confining stress, and stress-free conditions using a conical cutter in rock fragmentation tests on true triaxial loading apparatus. Peak cutter force and penetration depth at rock initial fracture and final failure of the rock specimen were used to reflect rock cuttability. The results show that the rock cuttability increases with stress in one direction decreasing under biaxial confining stresses, and presents a decreasing trend followed by an initial increase as uniaxial confining stress increases. The prefractures and boreholes in rock can further improve the rock cuttability, compared with intact rock. A series of cuttability improvement measures were proposed to provide a suitable condition for the application of nonexplosive mechanized mining in hard rock. Finally, comparative field tests were performed on a single-face entryway and a peninsula-shaped pillar, in which the mean value of cutting efficiency increased from 32.6 to 107.7 t/h, and the dust production and cutter wearout failure reduced significantly.

Elastic-plastic analysis and shrinkage properties study of swelling rock borehole in coalmine

The borehole shrinkage of swelling rock in coalmine is a complex problem affected by the combination of multiple fields, such as humidity field and stress field. By establishing the equilibrium equation of swelling rock borehole in coalmine, considering the expansion and softening properties, an elastic-plastic mechanics analysis was carried out, and the plastic zone radius and radial displacement of swelling rock borehole in coalmine were determined under the combination of humidity field and stress field. Taking the floor rock roadway in the 8# coal seam of Songzao Coalmine in Chongqing as an example, the influence laws of water content, ground stress, and water pressure in the hole on the borehole shrinkage were studied. The results show that, with the increase of water content of the surrounding rock, the radius of plastic zone and radial displacement of borehole wall gradually increase. Both the humidity expansion and softening have an important influence on borehole shrinkage in coalmine, and the radial displacement of borehole wall under the combination of swelling and softening is greater than that of only considering expansion or softening. With the increase of ground stress, the radius of plastic zone and radial displacement of borehole wall gradually increase, showing a nonlinear increasing relation. The larger the water pressure in the borehole, the smaller the radius of plastic zone and radial displacement of borehole wall, and properly increasing the water pressure in the borehole can effectively control the borehole shrinkage. The accuracy of theoretical analysis was further r verified by similar model tests. The results can provide a theoretical basis for solving the problem of borehole shrinkage in the swelling rock of coalmine.

Probability Density Function of Rock Mass Discontinuity Distances

Rock masses are presenting an enduring challenge since the first authors began trying to model these natural structures. This modelling needs a parametrisation and a latter value assignment for those parameter value series, which show high variability, and a lack of clear patterns, in nature. Understanding the statistical nature of these values is an essential goal of rock mechanics, searching for the most appropriate probability density function (pdf) for fitting each one of those parameter values. The identification of those pdf is an aid for a better understanding of the rock mass nature and a need for correct discrete fracture network generation, or any probabilistic calculation. The parameter studied in this work is the degree of fracturing, in particular: the distances between fractures in a borehole rock core, which determines the Rock Quality Designation (RQD) value. The most accepted hypothesis is that these values fit a negative exponential pdf, however, with some criticism. Through the analysis of 1985 m of borehole rock core from five lithologies from two rock masses, this work shows the lognormality of the data series. The negative exponential does not fit correctly; however, the old approach for RQD based on this hypothesis offers satisfying results. Furthermore, it has been observed that schist presents the unclearer random pattern.

Lithospheric extension in response to subduction of the Paleo-Pacific Plate: Insights from Early Jurassic intraplate volcanic rocks in the Sk2 Borehole, Songliao Basin, NE China

Subduction of the Paleo-Pacific and Mongol–Okhotsk oceanic plates is widely believed to have caused extensive Mesozoic magmatism and lithospheric deformation in East Asia. However, it remains unclear how the two tectonic domains affected NE China, and whether a boundary exists between them, because the Songnen Block in central NE China is covered by sedimentary rocks and the related mafic magmatism has been rarely discovered. Here we report a suite of Early Jurassic (ca. 175 Ma) mafic volcanic rocks (including basalt and basaltic andesite) from the Sk2 Borehole, Songliao Basin, NE China. The Sk2 mafic rocks are characterized by high Th/U, Zr/Y and Ti/Y ratios, and their geochemical signatures are consistent with formation in a back-arc extensional setting, rather than an arc setting. The rocks show depleted zircon εHf(t) and whole-rock εNd(t) values, which are comparable to mafic rocks located on the east of the Songliao Basin. This suggests that they both have a depleted mantle source, unlike the mafic rocks on the west of the Songliao Basin with relatively enriched Nd and Hf isotopes. Early–Middle Jurassic mafic rocks are distributed in the Erguna Block, >500 km to the west from the Sk2 Borehole, whereas coeval mafic rocks are widely distributed in the nearby eastern Heilongjiang and Jilin provinces. These intraplate-like mafic rocks and the Early Jurassic bimodal rocks within the Lesser Xing'an and Zhangguangcai ranges likely formed in response to lithospheric extension that was triggered by subduction of the Paleo-Pacific Plate. The Early Jurassic mafic rocks directly underlie the oldest sedimentary rocks (the Huoshiling Formation) in the Songliao Basin, which suggests that basin formation was probably initiated by lithospheric extension.

Thermal properties of the hanging wall of the central Alpine Fault, New Zealand

ABSTRACT Samples of schist, protomylonite, mylonite and ultramylonite from the hanging wall of New Zealand’s Alpine Fault were measured using a transient plane source, yielding mean bulk thermal conductivity of 2.04 ± 0.33 W m–1 K–1 in a dry state and 2.78 ± 0.51 W m–1 K–1 in a wet state at room temperature. Corresponding thermal diffusivity is 1.35 ± 0.32×10–6 m2 s–1 in a dry state and 1.72 ± 0.27×10–6 m2 s–1 in a wet state. Thermal conductivity and diffusivity calculated from the mineralogical composition of cuttings from the DFDP-2B borehole in Whataroa Valley and previously published thermal properties of minerals are 3.26 ± 0.16 W m–1 K–1 and 1.56 ± 0.08×10–6 m2 s–1, respectively. We attribute the significant difference in thermal conductivity to regional mineralogical variations in composition of rock samples versus borehole cuttings. Anisotropy of thermal properties is inferred to exist on a centimetre scale, due to competing effects of aligned quartz veins, minerals, and microfractures; but our measurements do not confirm significant anisotropy. Radiogenic heat productivity calculated from geochemical data and a gamma log in DFDP-2B (1.8–2.1 μW m–3) falls within the previously reported range for greywacke and schist.

Influence of water-based drilling fluids on the performance of the fluidic down-the-hole hammer

Fluidic down-the-hole (DTH) hammer is a recently explored percussion drilling tool for the production of boreholes in hard rock. It has been proven efficient for exploration core drilling, geothermal drilling, and oil and gas drilling. Previous studies of this hammer have concentrated on its performance operating with clear water rather than water-based drilling fluids with additives. As the first step to filling the gap of knowledge in this area, this study was designed to explore only the performance of an SC86–H fluidic DTH hammer driven by water-based drilling fluids with various temperatures and different contents of bentonite and barite. Such performance was characterized in terms of output power, motion characteristic and operating pressure drop, and compared with that driven by water. The results showed that the output power of the SC86–H type hammer driven by drilling fluids with bentonite content <3% was better than that driven by water thanks to the lubrication effect in the fit clearance, whereas with bentonite content ≥3%, its output power was in the range or below that driven by water due to the elevation of the hydraulic losses and the frictional drag. Its operating pressure drop is only insignificantly influenced by the bentonite content. As the weighting agents in the drilling fluids, the barite particles impeded the smooth motion of the piston. However, the increased impact energy and output power can entirely offset the disadvantage mentioned above. Temperature affects the performance of the SC86–H type hammer by influencing the viscosity and density of the drilling fluids. Some optimal schemes are suggested for the rational design and application of the fluidic DTH hammer in practice. In summary, the SC86–H type hammer operated well in the drilling fluids with realistic fluid power levels. It means that the fluidic DTH hammer has good adaptation and robustness, which is favorable to practical application.

Distributed Acoustic Sensing as a Distributed Hydraulic Sensor in Fractured Bedrock

AbstractDistributed acoustic sensing (DAS) was originally intended to measure oscillatory strain at frequencies of 1 Hz or more on a fiber optic cable. Recently, measurements at much lower frequencies have opened the possibility of using DAS as a dynamic strain sensor in boreholes. A fiber optic cable mechanically coupled to a geologic formation will strain in response to hydraulic stresses in pores and fractures. A DAS interrogator can measure dynamic strain in the borehole, which can be related to fluid pressure through the mechanical compliance properties of the formation. Because DAS makes distributed measurements, it is capable of both locating hydraulically active features and quantifying the fluid pressure in the formation. We present field experiments in which a fiber optic cable was mechanically coupled to two crystalline rock boreholes. The formation was stressed hydraulically at another well using alternating injection and pumping. The DAS instrument measured oscillating strain at the location of a fracture zone known to be hydraulically active. Rock displacements of less than 1 nm were measured. Laboratory experiments confirm that displacement is measured correctly. These results suggest that fiber optic cable embedded in geologic formations may be used to map hydraulic connections in three‐dimensional fracture networks. A great advantage of this approach is that strain, an indirect measure of hydraulic stress, can be measured without beforehand knowledge of flowing fractures that intersect boreholes. The technology has obvious applications in water resources, geothermal energy, CO2 sequestration, and remediation of groundwater in fractured bedrock.

Experimental Investigation of Drilling Lateral Boreholes in Chalk Rocks with High-Pressure Jets

Increasing reservoir connectivity to the wellbore and bypassing the damaged area is crucial in improving the productivity of the wells and enhancing the swept area. This has become feasible by a new technology called radial jet drilling (RJD), in which relatively long, small-diameter laterals can be drilled radially from the main wellbore. In this study, the authors attempt to gain a better understanding of the efficiency of a high-velocity jet drilling on chalk destruction, and also identify parameters controlling the jet drilling. For this purpose, two distinct outcrop chalks from Austin, Texas (US) and Northern Province, Welton (UK) are used in this study, which are analogs to the reservoir chalk in the North Sea. In conjunction with the jet drilling experiments, basic rock mechanics testing is carried out in order to correlate the rock strength and stiffness properties to the jet drilling performance. Jet drilling of boreholes is evaluated not only by varying the fluid and nozzle type and the fluid pressure at the nozzle, but also varying the jet drilling setup under unconfined and also confined stress fields resembling reservoir condition. Results of our study show a clear correlation of the rock strength (and stiffness) on the threshold pressure and specific energy required to break the rock. Tight chalk requires more than 30% higher pump pressure than used in soft chalk for breaking the chalk, having more than twice the strength properties. Soft chalk presents larger borehole size and better rate of penetration, both with water and acid-aided fluid, owing to its higher matrix permeability value, as well as lower mechanical properties that favor diffusion of the jet drilling fluid into the rock and faster erosion/breakage compared with tight chalk. Static nozzles create a larger surface area compared with rotating nozzles. The penetration rate of the nozzle is improved significantly under stress confinement. In addition, jet drilling in the direction of minimum principal stress (σ3) appears to be faster owing to localization of shear failure around the drilled hole induced by the differential stresses compared with the jet drilling in the direction of maximum principal stress (σ1) under isotropic stress or ambient conditions.

Morphological Feature Description Method of Structural Surface in Borehole Image During In-Situ Instrumentation

It is of great significance to obtain the high precise structural surface properties of rock mass during the process of deep geotechnical engineering investigation by in-situ instrumentation, especially for preventing disasters and reducing damages. To obtain more detailed features of the structural surface in the image obtained by digital panoramic borehole imaging technique, this paper describes and analyzes the morphological feature of structural surface in the borehole image during in-situ instrumentation, and the feature is used to describe joint roughness coefficient (JRC) and analyzed the anti-sliding ability of borehole rock mass. We use a digital panoramic borehole imaging system to obtain the camera image and related data of borehole rock mass, extract the profile line of structural surface in the image, analyze the dip direction and dip angle, and transform the circular profile line of structural surface into three-dimensional feature. Finally, the statistical parameters of three-dimensional feature from the profile lines in each direction are calculated and used to form a roughness coefficient rose diagram according to related JRC theory. Results show that the rose diagram can well describe the actual three-dimensional morphology of the structural surface and its anisotropy of borehole rock mass structures. This paper provides a novel way to describe the morphological feature of structural surface in borehole image and can be applied to determine the dominant anti-slip direction of rock structure, which can solve the difficulty of obtaining the morphological features and mechanical properties of structural surface in deep rock mass.

Design and applications of drilling trajectory measurement instrumentation in an ultra-deep borehole based on a fiber-optic gyro

Abstract. The working environment in hot dry rock boreholes, encountered in deep geothermal investigation drilling and ultra-deep geological drilling (up to 5000 m), is very difficult at the present stage. We have developed a drilling trajectory measuring instrumentation (DTMI), which is based on the interference fiber-optic gyro (FOG). This can work continuously, for 4 h, in an environment where the ambient temperature does not exceed 270 ∘C and the pressure does not exceed 120 MPa. The DTMI is mainly divided into three parts: an external confining tube, a metal vacuum flask, and a FOG measurement probe. Here, we focus on the mechanical design, strength, and pressure field simulation analysis for the external tube, the structural design and temperature field simulation analysis for the vacuum flask, and the FOG Shupe error analysis and compensation in the temperature field. Finally, through the engineering applications of the SK-2 east borehole of the China Continental Scientific Drilling (CCSD) project and the geothermal well of Xingreguan-2, the data measurements of the drilling trajectory were used to analyze the stability of the DTMI. The instrument realizes long-duration, high-stability work in the process of making trajectory measurements in an ultra-deep hole. The instrument has the characteristic of anti-electromagnetic interference and enables work to be carried out in the blind zone of existing technologies and instrumentation. Therefore, DTMI has great potential in the promotion and development of geological drilling technology.

Analysis of Dynamical Heat Conductivity of the Reservoir and Fluid Evacuation Zone on the Gas Condensate Well Flow Rate

This study shows that the thermal conductivity of the rock borehole adjacent to the wells varies depending on the operation of the well. This is due to the fact that the actual temperature and temperature difference affect the humidity and other thermal properties of the rocks, which in turn affect the heat transfer coefficient across the section between the moving gas and the rocks. The static temperature field of primitive geothermal gradients acquires changes in a dynamic form. Theoretical consideration of changes in the thermal conductivity of rocks near the face and the wells is proposed to improve the prediction of gas condensate wells production. The result is achieved by introducing the specified equations of the thermal energy balance in the radial filtration and lifting of well products, which contain the coefficients of heat exchange and throttling. The refinement bias estimation of the 10%–15% level of gas condensate well extraction is shown using proposed methodological approach to relatively well-known (traditional in the field development practice) methods for estimating the extraction of a “medium well” from a particular oil and gas field evaluation. The results of this work demonstrate important scientific, applied, educational and methodological significance of using the methodology presented by the authors.

Study on Deformation and Strength Characteristics of Hollow Cylindrical Rock Under Complex Loading Conditions

Drilling a borehole and inserting high-pressure fluid to induce rock fracture is a rock-mass pre-conditioning method in block caving mining of hard rock metal mines, and the borehole surrounding rock is under the complex loading conditions with in-situ stress and borehole inner pressure. In order to further understand the failure mechanism of borehole rock during hydraulic fracturing, a numerical model of hollow cylindrical rock sample was built with FLAC3D and the deformation and strength characteristics of this sample was studied by conducting simulation tests. The results show that oblique shear failure was found during uniaxial compression test and the uniaxial compression strength and elastic modulus of hollow cylindrical rock sample were weakened with the increasing of inner hole diameter. The rock triaxial compression strength increased linearly with the confining pressure during triaxial compression tests. The confining and internal pressure were the major factors to induce rock failure during hydraulic fracturing tests and the breakdown pressure increased linearly with confining pressure. For the rock type in this paper, the breakdown pressure was 2.28 times confining pressure plus rock tension strength.

Field test of a Combined Thermo-Mechanical Drilling technology. Mode I: Thermal spallation drilling

Accessing hydrocarbons, geothermal energy and mineral resources requires more and more drilling to great depths and into hard rocks, as many shallow resources in soft rocks have been mined already. Drilling into hard rock to great depths, however, requires reducing the effort (i.e., energy), time (i.e., increasing the rate of penetration) and cost associated with such operations. Thus, a Combined Thermo-Mechanical Drilling (CTMD) technology is proposed, which employs a heat source (e.g., a flame jet) and includes two main drilling modes: (I) Thermal spallation drilling, investigated here as a field test and (II) Flame-assisted rotary drilling, investigated as a field test in the companion paper. The CTMD technology is expected to reduce drilling costs, especially in hard rocks, by enhancing the rock penetration rate and increasing the bit lifetime. ModeI of the CTMD technology (thermal spallation drilling) is investigated here by implementing the concept on a full-scale drilling rig to investigate its feasibility and performance under realistic field conditions. During the test, the successful thermal spallation process is monitored, employing a novel acoustic emission system. The effects of thermal spallation in the granite rock are analyzed to provide conclusions regarding the rock removal performance and the application potential of the technology. The field test shows that thermal spallation of the granitic rock can be successfully achieved even when a liquid (water) is used as the drilling fluid, as long as the heat source is appropriately shielded by compressed-air jets. Thermal damage of the surrounding rock is investigated after the spallation test, employing micro-computer tomography imaging and modeling the stability of the cracks, generated by the spallation field test. This study shows that thermally induced damage is mainly confined within a narrow region close to the rock surface, suggesting that thermal spallation only marginally affects the overall mechanical stability of the borehole. Thus, this confirms that, as part of the Combined Thermo-Mechanical Drilling (CTMD) technology, thermal spallation drilling is a promising mode that has a high potential of facilitating the drilling of deep boreholes in hard rocks.

Field Experimental Study on the Broken Rock Zone of Surrounding Rock and the Rock Borehole Shear Tests of the Large Deformation Tunnel

A large deformation tunnel in LIXIANG railway, named Zhongyi tunnel is located in Southwest of China, was taken for the engineering background. The field experiments of the broken rock zone and the borehole shear test were conducted. The results show that the range of the broken rock zone of the test sections is 4.20∼4.45 meters. The cohesive force and the internal friction angle of the test sections are 221.4∼224 kPa and 14.25∼15.14°, respectively. The test results are in good agreement with the status of the surrounding rock. The surrounding rock is mainly composed of shale, which is badly broken, and the integrity and the stability are poor. In this study, the reasons for the deformation and instability of the tunnel are analyzed combined with the in situ tests and the site condition, and the suggestions for the tunnel support are put forward. This study is of great significance to ensure the safety of the constructors and can improve the service years of the tunnel. In addition, it can provide reference for the same type of the tunnel construction.