Precise grading of surrounding rock based on the numerical calculation of the jointed rock mass

In this study, grading of surrounding rock was based on rock mass basic quality (BQ) values according to the specifications in China. Numerical approach was to construct synthetic rock mass (SRM) model to represent the jointed rock mass, and obtain the strength of the rock mass. It represented intact rock by the bonded particle model (BPM), and represent joint behaviour by the smooth joint model (SJM) to construct the discrete fracture network (DFN). In the Hongtuzhang Tunnel, the micro properties of granite cores with different weathered degrees were determined by the validation process, and the calculation representative elementary volume (REV) of surrounding rock was 15 m×15 m. Five slightly weathered, three slightly to moderately weathered, and two moderately weathered granite surrounding rock mass models were established based on the probability distribution of joint sets in each borehole, the conversion BQ value was acquired according by the calculated strength of rock mass model. It was discussed the differences of surrounding rock grades between the geological survey method and the numerical calculation method, and then found that the geological survey report is higher than the numerical calculation method predicted. And the numerical calculation is consistent with the actual excavation of rock mass at borehole A1388.

Thermal Process of Rock Crystal: Cause of Infrared Absorption Band at 3585 cm−1

Synthetic rock crystals often show a typical infrared (IR) absorption band at 3585 cm−1. However, the authors recently found this band in a natural rock crystal with blue coating. The origin of this IR band is controversial as yet. In this paper, the infrared spectra of several natural and synthetic rock crystal samples which were heated to 673 K and 1073 K were measured after these samples returned to room temperature. Comparing the infrared spectra of samples before and after heating, we found the absorption band at 3585 cm−1 was induced by the thermal process, which indicates that this band cannot be used as diagnostic evidence for synthetic rock crystal alone. In addition, the LiOH bands decreased while AlOH bands increased upon thermal processing. And the negative correlation between the LiOH bands and the 3585 cm−1 band was also distinct. The above results reveal that the thermal process destroyed the LiOH defects, leading to the formation of a new AlLi defect. And the isolated OH− defect inside dislocations generated upon thermal processing is considered to be the exact cause of the 3585 cm−1 band.

Numerical Analysis for the Caving Characteristics of Rock Mass with Inclined Joints in Caving Mining

In caving mining, the successful initiation and propagation of caving require one low-dip joint set. However, not every mine has a low-dip joint set. The Hemushan Iron Mine in China was taken as the engineering background, and the caving characteristics of rock mass with inclined joints were analyzed based on the synthetic rock mass (SRM) model. First, the inclined joints were investigated in the Hemushan Iron Mine. Second, model parameters were determined based on the geological conditions of the mine, and seven models were established. Third, the caving process was simulated, and caving characteristics were monitored. For rock mass with inclined joints after undercutting, the research showed that the crack zone was significant, and the crack zone existed not only around the undercut area but also further away in the model. The stress concentration areas dispersed in the model except for the top of the undercut area. The caving line was not a standard arch, and the highest point of the caving line was biased towards the direction of the undercut. Under the same undercut width, with the decrease of joint length in the joint system, the number of cracks decreased, the degree of stress concentration became weaker, and the height of the caving line decreased.

Effect of Gap Geometries on the Crack Initiation Stress of Synthetic Rock Material

<p>The cracking phenomenon of the brittle rock and rock-like materials (concrete, gypsum) have been widely researched. Such long-standing intensive research requirement is due to the fact that crack initiation, propagation and coalescence are some of the most important parameters for evaluating the rock failure behavior and strength properties. Especially defining the crack initiation stress is a fundamental part of crack propagation that leads to the rock material's final failure. However, due to the nature of rocks, they may have complex inherit structures containing various gaps and void with different sizes and numbers. Rocks mostly tend to have circular and ellipsoidal voids as a result of long and complex geological processes. Owing to this limitation, it is always hard to understand and assess the crack initiation stress comprehensively. Especially for a couple of decades, with the help of developing computer science and technology, numerical models were used on this subject. In this study, various two-dimensional numerical rock models created using Distinct Element Method (DEM) based Particle Flow Code (PFC) were used to understand the effect of different gap geometries over crack initiation stress values of rock materials under uniaxial loading conditions. A base numerical model was calibrated using laboratory test results belonging to basalt rocks. In order to calibrate the numerical model, uniaxial, conventional triaxial and in-direct tensile test results were used. A flat-jointed contact model was chosen to create bonded material during the calibration process. Seven different numerical models were used to investigate the gap geometry effect on crack initiation stress under uniaxial conditions. The base model has a circular gap with 5.40 mm diameter. The other models created to understand the effect of geometry on crack initiation stress have different ellipsoidal geometry depending on the initial circular gap, 1.5 (8.10 mm), 2.5 (13.50 mm) and 3.5 (18.20 mm) times the diameter in the vertical and horizontal direction, respectively. The results of numerical models reveal that the crack initiation stress value decreases with the increase of the gap's vertical length while the width of gaps remains constant. Based on numerical models' results, the crack initiation stress value decreases with the increase of the gap's vertical length while the diameter of gaps remains constant.</p>

Study Interprets Electromagnetic-Wave Penetration, Absorption for Bitumen Reservoir

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 199941, “Interpretation of Electromagnetic-Wave Penetration and Absorption for Different Reservoir Mineralogy - Quartz-Rich, Limestone-Rich, and Clay-Rich - and at High- and Low-Water Saturation Values for a Bitumen Reservoir,” by Matthew Morte, SPE, Hasan Alhafidh, SPE, and Berna Hascakir, SPE, Texas A&M University, prepared for the 2020 SPE Canada Heavy Oil Conference, originally scheduled to be held in Calgary, 18–19 March. The paper has not been peer reviewed. Interpretation of logging data generated through electromagnetic (EM) waves or determination of EM-wave propagation in a medium as an enhanced-oil-recovery (EOR) method are not easy tasks. The complete paper aims to identify the role of different geological settings with different types of fluid saturations in the response of EM-wave propagation and absorption. Several correlations were created in this study and can be used to better interpret the reservoir mineralogy and fluid saturation as a response to EM-wave logging. Moreover, these results can be used to estimate the effective area (penetration depth) of EM waves as an EOR method. Experimental Procedure Complex permittivity of synthesized rock samples was recorded by means of a vector network analyzer as the source and a dielectric probe kit as the transmitter. The dielectric probe behaves as both the transmitter and receiver simultaneously by measuring the proportion of the reflected wave. The dielectric probe is capable of measuring both the solid interface, as is the case with the synthesized reservoir rock, and fluids. The output of the vector network analyzer is both the dielectric constant, defined to be the real-portion complex permittivity, and the loss index, defined to be the imaginary portion. The loss tangent is a parameter that describes the overall efficacy of the material as a microwave absorber with higher values corresponding to higher heat generation in the reservoir. Reservoir properties of interest are isolated by taking advantage of experimentally defined synthesized cores. Variable properties are achieved by introducing a known quantity of specified materials to ensure control over the outcome of representative reservoir rock. Samples are an unconsolidated mixture of both the skeletal frame (rock matrix) as well as the pore space. The rock matrix is comprised of a systematic and stepwise variability of quartz sand, limestone sand, and kaolinite clay or bentonite clay. The fraction of each introduced mineral is manipulated to isolate the contribution of the individual components. The weights of the introduced constituents are calculated to result in a synthetic rock matrix with the desired rock mineralogy. The first batch of synthesized cores consisted of 75 mixtures. The remainder of the contrived cores were limestone. A separate 20 experiments were performed to account for the presence of both pore-filling and swelling clays, namely kaolinite and bentonite, respectively. Compaction and blending of the cores were performed by hand; homogenization of the mixture was ensured by thorough mixing.

Analysis of Rock β-Dynamic Parameters and the Stability of Earthquake Dangerous Rocks Based on PFC

Mesoparameters of rock materials are the main factors affecting the macromechanical properties of dangerous rock slopes. Based on the principle of particle flow and synthetic rock mass technology (SRM), the influence of mesoparameters on macromechanical properties is investigated by calibrating mesoparameters of rock materials at depth for a rock sequence in Beichuan Qiang Autonomous County, Sichuan Province, China. By combining these parameters with conventional and dynamic cycle triaxial tests, sensitivity analysis of rock β-parameters was completed. As a result, the reliability of mesoparameters in the simulation of dangerous rocks is strengthened, providing a basis to examine the failure mechanism of earthquake dangerous rocks in this region. Results indicate that, in the triaxial test, sandstone failed in tension, and brittleness gradually weakened as confining pressure increased. Mudstone recorded shear failure, and the characteristic value of brittle attenuation showed a V-shaped change with increasing confining pressure. Under cyclic loading, cracks had a degrading effect on the damping ration (β) and the damping coefficient (C) of sandstone. Mudstone recorded relatively low β and low brittleness whilst sandstone had high β and high brittleness. In rock materials, β n is more sensitive than β s in mechanical properties. When the value of the β n -parameter was between 0.2 and 0.3 and the value of the β s -parameter was between 0.2 and 0.6, rock brittleness was more stable, and the reflected macroscopic mechanical properties were the most authentic. By using a deepened mesoparameter trial adjustment method, the failure mode of the Particle Flow Code (PFC) dangerous rock model near provincial highway 205, simulated under conditions for the Wenchuan earthquake, indicated a tensile fracture-horizontal slip failure. The simulated failure mode was consistent with that of real dangerous rocks, with the failure trend being concentrated between the first and the third layer of the rock mass.