Underground Systems (United States)

True triaxial compression experiments were conducted on jointed rock with different Joint Roughness Coefficient (JRC, JRC = 4.78, 9.57, 14.74 and 19.47) or inclined angle (α = 30°, 45°, 60° and 90°) firstly. Then, the adaptive transform a Lagrangian solid element to Discrete Element Sphere particles (adaptive Solid to DES) method was employed to realize the true triaxial compression simulation on jointed rock with various JRC and α. The results show that: (1) The maximum equivalent stress and cracks are firstly concentrated at the joint asperities and develop into the rock matrix with increasing axial stress, resulting in joint-matrix coupled fracture mode. (2) The strength and peak strain of the jointed rock show a decreasing (30 ° ≤ α ≤ 60°) then increasing α = 90°) tendency as the α increased. Increasing JRC weaks the influence of α on strength but amplify on peak strain. (3) When the joint strike parallels to intermediate principal stress, the failure mode are matrix shear (α = 30°), matrix shear-joint sliding (α = 45°), joint sliding (α = 60°), to matrix shear failure (α = 90°), respectively. When the joint strike parallels to minor principal stress, the larger stress on the inclined side inhibits the influence of the joint, resulting in all jointed rock matrix shear fracture.

Geophysical investigations were conducted utilizing Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) to assess a Non-Aqueous Phase Liquid (NAPL) contaminated site in the southeast of China. Traditional drilling and sampling methods combined with geochemical analysis are limited in deriving reliable spatial interpolations due to low sampling density and high heterogeneity of shallow groundwater. Variations in soil physical properties, such as conductivity and dielectric properties, resulting from NAPL infiltration, provide the physical basis for geophysical detection. While the combined use of ERT and GPR is established in geophysics, its effective application to NAPL sites remains challenging due to complex site conditions and ambiguous signatures. Our ERT results reveal high resistivity anomalies potentially indicative of NAPL contamination, and overlaying GPR attribute analysis (including amplitude, phase, coherence, and texture) onto these results enhances subsurface characterization and anomaly discrimination. The integrated approach demonstrates its capability to clarify subsurface contamination patterns under heterogeneous conditions, providing a spatially continuous interpretation framework that complements sparse direct sampling.

The Huainan–Huaibei mining area is widely covered with calcareous clay layers, characterized by low freezing points, high frost heave, easy disintegration upon water exposure, and low strength. Its mechanical properties are complex and variable, posing significant challenges for the construction of frozen walls. To optimize the design of frozen walls in calcareous clay, this study examined remolded calcareous clay from deep layers in the Huainan–Huaibei area, utilizing equal-stress ratio true triaxial loading tests to systematically analyze the stress–strain behavior of frozen calcareous clay under varying confining pressures and temperatures. The results indicate that variations in confining pressure and the intermediate principal stress ratio significantly affect the mechanical properties of frozen calcareous clay. The stress–strain curves of frozen calcareous clay reveal typical nonlinear characteristics: the material exhibits an elastic response in the small-strain stage and gradually transitions into plastic deformation with increasing strain, showing significant strain hardening during the plastic deformation phase. Based on a hyperbolic model and fractional calculus, a fractional hyperbolic model was developed to suit complex stress conditions, with relevant model parameters derived. The study’s findings provide a theoretical basis for rational shaft frozen wall thickness design and serve as valuable references for improving artificial ground freezing construction techniques.

ABSTRACT In light of the decreasing availability of high-grade ore reserves, enhancing the flotation efficiency of fine low-rank coal has become increasingly crucial. This study aims to introduce an innovative two-stage turbulent micro-bubble mechanical flotation cell (TMFC) designed to overcome these limitations. We employed kinetic tests and CFD analysis to assess the performance of the TMFC in comparison to traditional flotation techniques. The kinetic tests demonstrated that the TMFC achieved a remarkable increase in combustible recovery, reaching 91.23%, and noticeably accelerated the flotation rate to 1.6868 min−1, thereby considerably surpassing the performance of conventional methods. CFD analysis further illustrated that the TMFC generates enhanced turbulence within the impeller zone. This turbulence facilitates the formation of smaller vortices and bubbles, which improve particle surface cleaning and promote increased collisions among finer particles, collectively enhancing flotation efficiency. Photographic evidence supported the production of smaller bubbles by the TMFC. This study not only demonstrates the superior performance of the TMFC but also makes a valuable contribution to the broader field of mineral processing by offering a more effective approach for refining coal amidst an era of limited ore availability.

A search for the processes of double beta decay of 82Se into excited states of 82Kr is conducted using the OBELIX setup. The measurements are conducted using a 600 cm3 HPGe detector. The detector is surrounded by 6.5 kg of enriched selenium (the content of 82Se was ~92.5%). The data collected over 17 572.2 h of measurements are given. As a result, a world-record sensitivity is reached for transitions of this type. Specifically, we have found an indication of the existence of two-neutrino 82Se decay into the first 0+ 82Kr excited state with a half-life of $$4.4_{{ - 0.9}}^{{ + 1.6}}$$ × 1022 years.

The CO2-enhanced shale gas recovery (CO2-ESGR) technique is a promising method for enhancing shale gas production and sequestering of CO2. In this study, a two-component gas flow model in shale reservoirs considering the stress–strain–sorption behavior of shale during the CO2-ESGR process was developed. Using this model, the impact of the parameters of the ratio of Langmuir volume of CO2 (VL,CO2) to Langmuir volume of CH4 (VL,CH4), initial reservoir pressure, CO2 injection rate (Ri), and the staring time of CO2 injection (Ts,i) on the CO2-ESGR process was analyzed by numerical simulation. The results indicate that the sustained reduction in reservoir porosity and permeability during primary production is dominated by the effect of effective stress changes. Following CO2 injection, reservoir porosity and permeability decrease rapidly in the CO2 sweep region mainly due to the CO2/CH4 adsorption-induced differential swelling, while it is still dominated by effective stress changes outside the CO2 sweep region. CH4 production is negatively related to VL,CO2/VL,CH4 and Ts,i, while positively related to the initial reservoir pressure and Ri. The CO2 storage volume is positively related to VL,CO2/VL,CH4, Ri, and Ts,i, while shows no significant correlation with the initial reservoir pressure. These findings offer valuable insights for parameter optimization of the CO2-ESGR process.