Numerical Simulation on the Effect of Rock Joint Roughness on the Stress Field

In view of the influence of Joint Roughness Coefficient (JRC), which is for quantitative description of the joint surface roughness, on the stress field of the rock mass, compression test and shear-compression test were simulated on models with different joint roughness. The photoelasticity technique is applied to examine the feasibility of numerical simulation. The results show that numerical simulation results are in agreement with the results of photoelastic experiments. The stress concentration area is distributed near the joint plane. Thus, the joint plane controls the shear strength of the rock. In compression test, the maximum shear stress of the model is proportional to JRC and the normal pressure. In shear-compression test, when the ratio of the axial shear to the normal pressure is small, the maximum shear stress is nonlinearly positively correlated with JRC. When the ratio of the axial shear to the normal pressure is relatively large, the relationship curve between the maximum shear stress and JRC is parabolic. When the JRC is small, as the ratio of the axial shear force to the normal pressure increases, the maximum shear stress changes abruptly, and the maximum shear stress after the mutation decreases significantly. The reason is that the upper and lower parts of the model have slipped, resulting in a redistribution of stress. In addition, when the JRC is 6 to 12, it is more likely to cause stress concentration.

Kajian pengaruh faktor batuan terhadap fragmentasi batuan overburden hasil peledakan berdasarkan model Kuz-Ram

Distribusi fragmentasi hasil peledakan dipengaruhi oleh beberapa faktor ialah massa batuan, jenis bahan peledak, jumlah bahan peledak yang digunakan, deskripsi massa batuan didalam faktor batuan pada daerah penelitian yaitu powdery dan blocky. Penelitian ini berfokus pada pengaruh factor batuan terhadap fragmentasi hasil peledakan overburden.Metode yang digunakan pada penelitian ini adalah pengamatan secara langsung dilapangan untuk mendapatkan gambaran mengenai kondisi situasi aktual seperti keterdapatan rock mass description (RMD), joint plane spacing (JPS), joint plane orientation (JPO), specific gravity (SGI), hardness. Pada penelitian faktor batuan hanya nilai RQD yang memiliki pengaruh sangat besar dalam peledakan. Analisis faktor batuan terhadap fragmentasi batuan menggunakan perangkat lunak Split Desktop 2.0 untuk menghitung hasil fragmentasi aktual hasil peledakan sedangkan untuk teoritis menggunakan metode model Kuz-Ram. Berdasarkan kajian nilai rock quality designation terhadap fragmentasi batuan hasil peledakan didapatkan nilai fragmentasi 80 cm ≥ 80% dikatakan ideal, hasil fragmentasi pada 2 lokasi penelitian dengan kegiatan peledakan 6 kali ialah 93,61%, 87,68%, 90,91% (powdery) dan 72,68%, 74.56%, 76.04% (blocky) untuk perhitungan model Kuz-Ram. Jadi pada satu lokasi penelitian masih di jumpai hasil distribusi fragmentasi yang kurang bagus dengan ukuran saringan 80 cm ≤ 80%, yaitu pada deskripsi massa batuan blocky. Kata Kunci: factor batuan, fragmentasi batuan, hasil peledakan, massa batuan

Numerical Investigation on the Hydraulic Fracture Evolution of Jointed Shale

Joints are a common structure of heterogeneous shale rock masses, and in situ stress is the environment in which heterogeneous rock masses can be found. The existence of joint plane and confining pressure difference influences the physical properties of shale and propagation of fractures. In this study, jointed shale specimens were simulated under different confining pressures to explore the failure patterns and fracture propagation behavior of hydraulic fracturing. Different from the common research of hydraulic fracturing on signal parallel joint rock mass, the simulations in this study considered three points (parallel joint, multi-dip angle joint, and no-joint points). The effects of the single-dip angle joint, multi-dip angle joint, and confining pressure difference on the hydraulic fracture evolution and stress evolution of the jointed shale were studied comprehensively. The confining pressure difference coefficient proposed in this study was used to accurately describe the confining pressure difference. Results indicate that the larger is the confining pressure difference, the stronger is the control of the maximum principal stress on fracture evolution; by contrast, the smaller is the confining pressure difference, the stronger is the control of the joint plane on fracture evolution. Under the same confining pressure difference, the hydraulic fracture propagates more easily along the small dip angle joint plane. As the value of the confining pressure difference coefficient moves closer to zero, the hydraulic fracture propagates randomly, the tensile stress region around the fracture tip widens, and the joint planes fractured by tensile increase. This study can offer valuable guidance to the design of unconventional reservoir reconstruction.

Correction of the Koenig Formula for the Kinetic Energy of a Rotating Solid

An exact solution is obtained for the kinetic energy in the general case of the spatial motion of solids with arbitrary rotation, which differs from the Koenig formula by three additional terms with centrifugal moments of inertia. The description of motion in the Lagrange form and the superposition principle are used, which provides a geometric summation of the velocities and accelerations of the joint motions in the Lagrange form for any particle at any time. The integrand function in the equation for kinetic energy is represented by the sum of the identical velocity components of the joint plane-parallel motions. The moments of inertia in the Koenig formula do not change during movement and can be calculated from the current or initial state of the body. The centrifugal moments change and turn to 0 when rotating relative to the main central axes only for bodies with equal main moments of inertia, for example, for a ball. In other cases, the difference in the main moments of inertia leads to cyclic changes in the kinetic energy with the possible manifestation of precession and nutation, the amplitude of which depends on the angular velocities of rotation of the body. An example of using equations for a robot with one helical and two rotational kinematic pairs is given.

Dickinsonia: mobile and adhered

The classical genus of Ediacaran macroorganisms,Dickinsonia, was part of an extensive benthic marine community inhabiting the fields of microbial mats. The remains ofDickinsoniaare commonly preserved in the position of adhesion to the habitat substrate. However, these were mobile organisms. In addition to the already known feeding traces ofDickinsonia, structures described as traces of motor activity are reported. Long parallel furrows, extending from the posterior end of the body imprint, are interpreted as imprints of ridges left by an organism moving along the surface of the substrate. Groups of differently shaped grooves laying in the depression that enhalo theDickinsoniabody imprints or accompany their individual areas are interpreted as imprints of ridges and cords of mucous material. They are considered to represent structures of self-determined stretching and lift-off of the body margins from the substrate. The rings and arcs of silt- and sand-sized mineral particles bordering the body imprints are composed of material that was supposedly brushed off from the surface of the microbial mat byDickinsonia. They are considered traces of the adhesion of these organisms to the substrate. Accumulations of multidirectional pulling and tear-off structures, lacking the body imprint but accompanied by the joint plane passing into the overlying sediment and cutting through the bedding, are interpreted as escape traces. The dual modality of the behaviour (attachment and mobility) could indicate the adaptability ofDickinsoniato life in extremely shallow-water environments.

Correction of the Koenig Formula for the Kinetic Energy of a Rotating Solid

An exact solution is obtained for the kinetic energy in the general case of the spatial motion of solids with arbitrary rotation, which differs from the Koenig formula by three additional terms that take into account the change in the centrifugal moments of inertia when the body rotates. The description of motion in the Lagrange form and the superposition principle are used, which provides a geometric summation of the velocities and accelerations of the joint motions in the Lagrange form for any particle at any time. The integrand function in the equation for kinetic energy is represented as the sum of the identical velocity components of the joint plane-parallel motions. In the general case of motion with 6 degrees of freedom, the energy of rotational motion is determined by three axial moments of inertia, as in the Koenig formula, and three additional centrifugal moments, which take into account the rotation of the body. They can be calculated through 6 integral characteristics of the density distribution, determined for the initial position of the body.

Correction of the Koenig Formula for the Kinetic Energy of a Rotating Solid

An exact solution is obtained for the kinetic energy in the general case of the spatial motion of solids with arbitrary rotation, which differs from the Koenig formula by three additional terms that take into account the change in the centrifugal moments of inertia when the body rotates. The description of motion in the Lagrange form and the superposition principle are used, which provides a geometric summation of the velocities and accelerations of the joint motions in the Lagrange form for any particle at any time. The integrand function in the equation for kinetic energy is represented as the sum of the identical velocity components of the joint plane-parallel motions. In the general case of motion with 6 degrees of freedom, the energy of rotational motion is determined by three axial moments of inertia, as in the Koenig formula, and three additional centrifugal moments, which take into account the rotation of the body. They can be calculated through 6 integral characteristics of the density distribution, determined for the initial position of the body.

Time-dependent behavior of rock-like specimen containing multiple discontinuous joints under uniaxial step-loading compression

Rock with multiple discontinuous joints widely exists in rock engineering, and its mechanical properties are complex, which greatly increases the difficulty of engineering design and construction. Time-dependent deformation characteristics and long-term strength evaluation of jointed rock masses remain poorly understood. In this work, the creep experiments of rock-like specimens with multiple discontinuous joints under uniaxial step-loading compression are carried out to explore the influence of joint geometry (rock bridge length, joint length, joint angle, and joint spacing) on creep strain, long-term strength, and failure pattern of specimens with multiple discontinuous joints. The following conclusions are drawn from the test results: 1) The deformation of jointed rock specimens has evident time-dependent effect, and the cumulative creep deformation increases as creep load increases; 2) The strength of jointed rock specimens under loading changes with time, and the ratio of long-term strength and creep peak strength ( σ∞/ σc) of the tested specimens ranges from 41% to 96%; 3) The distribution of initial joints affects the creep fracture modes of rock-like specimens. The rupture of rock-like specimens with different joints distribution is mainly caused by the growth of wing cracks and quasi-coplanar secondary cracks. Three different failure modes are observed from these specimens: i) tensile failure with cracks across the joint plane; ii) shear failure with cracks along the joint plane; and iii) tensile failure with cracks along the joint plane. Based on the principles of damage mechanics and fracture mechanics, a theoretical mechanistic model considering both the closure stage of pre-existing open joints and time-dependent propagation stage of new cracks is established. Considering the influence of joint length, joint angle and joint density, the evolution of creep strain of rock-like specimen with multiple discontinuous joints is analyzed. The theoretical model results agree well with the experimental results, which indicates that the established model can replicate the creep failure process of jointed rock mass. These theoretical and test results help us better understand the effect of multiple joints on the long-term behavior of rock mass.

Robot-Assisted Thoracoscopic Surgery of Neurogenic Tumours in the Apical Chest: A Case Series

Background: Superior posterior mediastinal tumours may arise in the apical chest. However, the removal of such tumours via conventional minimally invasive approaches remains challenging. In this paper, we demonstrate our experience of robotic-assisted thoracoscopic surgery (RATS) for patients with neurogenic apical chest tumours (ACT). Methods: We retrospectively included 15 consecutive patients who underwent the resection of posterior mediastinal neurogenic tumour wherein the upper extent of the tumour extended upwards to the sternoclavicular joint plane based on chest imaging findings. The clinical characteristics and perioperative outcomes of these patients were collected and analysed.Results: Between April 2017 and June 2020, a total of 15 consecutive cases with ACT underwent radical surgical resection through RATS by our team. These patients showed encouraging short-term outcomes after surgery and there was no conversion to thoracotomy. The median tumour size was 4.0 (2.1-10.6) cm. Five large tumours (> = 5.0 cm) were completely resected. The median overall time of surgery was 100 (range, 30–240) minutes. In only one case, a patient experienced massive bleeding (> 500 mL) with a left schwannoma (10.6*5.8*4.8 cm). This resulted in intraoperative haemorrhage because of significant adhesion around the lesion. However, this case was successfully managed by robotic manoeuvres. The median hospital stay was 3 (range, 4–7) days. The median duration of the chest tube was 2 (range, 1–3) days. One case suffered from a non-permanent Horner’s syndrome and recovered within seven months. No patients developed brachial plexus-associated complications. No death occurred during the perioperative period. Conclusions: RATS is a safe and effective alternative modality for the treatment of ACT. The technique extends conventional thoracoscopic indications for posterior mediastinal lesions including apical chest lesions.