Search

Mechanical excavation machines, like continuous miners and road headers, have been broadly used in tunneling and underground and surface mines. The disc cutters are seated on the different cutter heads' to cut different parts of the tunnel face. With the increase in the cutters' size and power, the cutting disc cutters' capacity has been extended to cut moderate and tough rock types. This experimental and numerical research includes the application of, "Pin‐on‐Disk" ASTM abrasion testing, in which the failure mechanism of an interface between both the rock‐like samples and (WC–Co) tungsten carbide has been investigated under different confining pressures. The research aims to investigate the wear mechanism of gypsum and concrete samples. The Particle Flow Code in three dimensions (PFC3D) was used for test simulations concurrently with the experimental setup. A drilling pin with a diameter of 0.4 m was positioned above the model. The pin was inserted into the model at speeds of 0.01 mm/s at depths of 1, 3, and 5 m. A total of nine lab tests were conducted. The tensile strength of the material was 2.5 MPa. The results show that the values of volume lost for the gypsum and concrete discs were detected as a function of sliding length, fitting to non‐linear behavior. The wearing depth increased by increasing the loading force. Under constant loading force, the gypsum sample wears more than the concrete sample because gypsum is less strong than concrete. The PFC generates useful findings that experimental tests cannot provide. [ABSTRACT FROM AUTHOR]

The effect of bedding cohesion and loading conditions on the bolting behavioral characteristics of a bedded rock mass was investigated using a self-developed artificial material and loading system. First, physical samples with dimensions of 15 cm × 15 cm × 8 cm containing both the grout and gypsum layers were prepared. The ratio of the thickness of the grout layer to the gypsum layer was 0/100, 25/75, 50/50, 75/25, and 100/0. One grouted bolt was situated in the middle of the sample. Two types of filling materials were chosen as a filling segment around the rock bolt, i.e., gypsum and grout. The tensile strengths of gypsum and grout were 1.4 and 2.4 MPa, respectively. The length and diameter of the bolt were 12 and 2 cm, respectively. The grout dimension was 5 cm × 5 cm × 8 cm. These samples were tested under two different axial loading conditions. A total of 20 distinct tests were conducted concurrently with laboratory experiments utilizing Particle Flow Code in Two Dimensions. The loading rate was 0.05 mm/s. The findings revealed a strong correlation between breakage patterns and loading conditions. Moreover, it was observed that the grout filling significantly impacts the ultimate axial load compared to gypsum filling. When loading the interface between the rock bolt and the filling segment, the final axial load remained consistently similar across all filling types. Notably, the grout filling resulted in a notably higher final axial force. The variation in grout and gypsum bedding layer thicknesses did not demonstrate any discernible effect on the final axial load. Conversely, when loading the interface between the filling and bedding layers, an increase in grout layer thickness led to an augmented final axial load. The grout filling segment also contributed to a heightened final axial force. The results of the numerical simulations exhibited a commendable agreement with the experimental outputs. This research effectively addresses two critical aspects: stability control and support design for the bedded rock mass. Practical Applications: This study used a unique artificial material and loading system to investigate how bedding cohesion and loading conditions affect bolting behavior in rock mass. The findings showed a significant difference in ultimate axial load when grout was used compared to gypsum filling around the rock bolt, emphasizing the importance of this factor in stability control. The research revealed a strong connection between breakage patterns and the specific loading conditions applied, providing valuable insights into support design in a bedded rock mass. The study also demonstrated a high level of agreement between experimental and numerical simulations, strengthening the credibility of the findings and their relevance to real-world stability control measures. [ABSTRACT FROM AUTHOR]

The mechanism of fracture propagation, interaction and coalescence inside rock masses is a highly concerned issue in geotechnical engineering. But as it is difficult to manufacture 3D internal pre-fractures and observe directly the failure evolution process inside real rocks or their opaque similar materials, most previous studies have been limited to 2D conditions. The experiment investigation on 3D rock failure is still in a preliminary stage. In this study, a resin material has been developed by extensive formula tries. It is absolutely transparent and the ratio of tension–compression strength (brittleness value) can be 1/6.6 at −10 to −15℃. It is much more brittle and rock-like than analogous materials used by former scholars. A set of preparation, casting mould, and post-processing technologies were established and specimen-making with multiple pre-fractures is enabled. In the designed scheme, specimens are made with two parallel internal fracture surfaces yet of four different stagger separations. Uniaxial tests were carried out and the stress–strain relationship is analysed. It is shown that the specimen has gone through four stages as the traditional rock test before failure. Many diverse forms of secondary fractures, such as wrapping wing crack, petaloid crack, and giant quasi-wrapping fracture surface, which were not found in 2D conditions have appeared and their evolutions were clearly seen in each stage.

The conventional uniaxial compression test is used to investigate the interaction of two preexisting cracks with an internal hole in some typical gypsum specimens in the laboratory. The gypsum specimens are specially provided with 150 mm × 150 mm × 50 mm in dimensions and containing one internal hole and two cracks of 2 cm in lengths. These notches are located at varying distances, 2 cm, 3 cm and 4 cm from the hole and their inclination angles range from 0 to 90 degrees with an increment of 30 degrees. By this procedure, 12 different specimens can be provided for the experimental tests. On the other hand, an Extended Finite Element analysis of these tests is also provided in Abaqus software by assuming a plane strain state for the same specimens and taking the model geometry dimensions as 15 cm × 15 cm. In this analysis, the length of the cracks is 2 cm and their distances with the hole changes as 2 cm, 3 cm and 4 cm. However, in the two dimensional numerical simulation of the tests, the inclination angles of the cracks ranges from 0 to 90 degrees but the increment is taken as 15 degrees to provide 21 model samples and make a more detail analysis of the geo-mechanical problem. The results of laboratory tests and numerical models are very similar as far as the failure mechanisms and fracture patterns are conserened. The failure strengths are also very close for both analyses. It is concluded that the compressive strength of the specimens is highly affected by the fracture pattern and failure mechanism of the specimens assuming different configurations of the cracks and the hole locations. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper investigates the influence of indenter shape and rock texture on the crack growth properties and rock hardness. For this purpose, two different rock specimens such as basalt and marble with various textures were prepared and tested by Vickers indentation hardness device with rhombus indenter shape under two different temperatures of 35°C and 100°C. Concurrent with the experimental test, Vickers indentation simulations have been done on three calibrated rock models with nine different indenter shapes. The tensile strength of marble was 8 MPa, while basalt had a tensile strength of 10.8 MPa. Regarding compressive strength, marble exhibited 71 MPa, whereas basalt had a compressive strength of 153 MPa. Marble and basalt had elastic moduli of 45 and 95 GPa, respectively. The physical loading was applied vertically at a rate of 0.004 mm/min. The rock's texture and temperature significantly impact Vickers indentation hardness. Penetration by the Vickers indenter creates an elastic‐plastic stress field, leading to radial cracks due to exceeding the critical stress level. Ring cracks are caused by bulging of the test material and nested cracks directly under the indentation due to high shear and bending stresses in the region. The indentation shape affected the extent of the damage zone below it, leading to increased crack growth with smaller indentation diameters. The radial fracture number increased when the cross‐section changed from circular to quadrilateral shape. The crack growth and damage zone area increased with higher rock temperature due to increased rock brittleness. [ABSTRACT FROM AUTHOR]