The mechanical properties and energy evolution law of dolomite under a combined action of dry-wet cycle and cyclic loading and unloading were explored. The results show that the structural damage caused by dry-wet cycles leads to the transformation of dolomite from brittle fracture to ductile fracture, which is manifested by an increase in the area of hysteresis loops and a decrease in peak strength. At the early stage of cyclic loading and unloading, a strengthening effect is observed, and then the dolomite develops into the strain-softening and damage stages. An energy analysis indicates that the total input energy is mainly stored in the form of elastic strain energy, and the proportion of dissipated energy increases slowly with the accumulation of damage. Additionally, based on the variation of the damage variable defined by dissipated energy, the damage evolution tends to be stable after a progressive and accelerated process.

Based on the characteristics of the exploration contracts approved by the International Seabed Authority (ISA), the global competition status and variation trend of the exploration contract areas are analyzed in terms of temporal changes, spatial distribution and mineral types. Based on the analysis results, strategies to cope with the variation in the situation of ISA exploration contract areas are proposed, including commercial companies acting as the main players, strengthening international cooperation with African countries and the Enterprise of ISA, giving priority to exploration of polymetallic nodules, cultivating advantageous contractors and safeguarding the rights and interests of contractors.

A 3D heterogeneous numerical model was established based on the C6^# mining area of the Bayan-Uul uranium deposit to analyze the effects of different horizontal permeability in the filter section on solute transport, pH value and uranium mineral leaching performance. The simulation results show that after 450 days, the uranium leaching rate is 13.56% at the vertical depth of 30 m in the filter section, presenting 22.71% higher compared to the leaching rate of 11.05% at the depth of 35 m. According to the sandstone permeability, grade of uranium in the stratum and heterogeneity, the vertical arrangement position and length of filter section can be optimized, so as to effectively improve the economically recoverable metal quantity.

To investigate the fracture characteristics of rocks with bent cracks under saturated condition, uniaxial compression tests were conducted for rock specimen with different inclination degrees and numbers of crack bends under saturated conditions to study load-displacement curves, peak strength, acoustic emission characteristics, crack initiation modes, and penetration modes of the rock specimen. The results show that the load-displacement curve of saturated rock specimen with bent cracks presents one-peak or double-peak shape, with peak strength increasing after an initial decreasing as the crack inclination angle becomes larger. The acoustic emission signals become stronger as the crack inclination angle becomes larger and the number of crack bends increases. Cracks mainly initiate at the tip and bends, and mainly penetrate directly or run without penetration.

To explore the impact of near-surface ore body mining on the stability of overburden and dangerous rock masses of slopes, a phosphate mine was taken as an engineering project in the study. The stability of the dangerous rock mass of the slopes was determined by on-site investigation, and the evolution of deformation, stress and plastic zone of overburden under different mining schemes were simulated with FLAC^3D software. The research results indicate that structural planes between layers of surrounding rock on the roof of stope are well-developed, probably causing falling debris in blocks or flakes. The strata are hard and brittle in lithology and have developed rock fractures. Under unloading effect of high and steep slopes, dangerous rocks are prone to be separated along the combination of fractures and strata plane, forming dangerous rock masses. The response law of the maximum stress in the overburden is similar to the law of the unbalanced force in numerical calculation. There is relatively small disturbance generated during mining process, which brings a little impact to the stability of adjacent stopes and surface. It is found that the ground surface is less affected by underground mining, with the deformation within the maximum limit value specified in the standard. If Ph2^# ore body is mined after Ph1^# ore body, the overburden can have relatively small displacement, and no connectivity in the plastic zones is occurred in the mining pillars, stopes and overlying strata.

To address the problems of poor fluidity and high viscosiy, ore rocks and higher ore losses and dilution due to the influence of moisture content on eastern stopes of Jinshandian Iron Mine, the variation laws of fluidity of ore blocks, shape characteristics of drawn ore blocks, as well as loss and dilution indices of two types of ore bodies in the eastern stopes under influence of different moisture content were analyzed by preforming physical tests and numerical simulation. A reasonable range of drift spacing for the eastern stopes was determined, which was then optimized from the perspectives of safety, technology and economy, based on the improved CRITIC-TOPSIS evaluation method. The results show that with the moisture content in a range of 0-8%, the drawn ore blocks in the eastern stopes are in a shape of an “inverted water drop”, and become shallow as the moisture content increases; with the moisture content in a range of 4%-8%, the natural angle of repose of ore rocks increases with the increase of moisture content, the recovery rates of those two ore bodies are negatively correlated with moisture content, and present an upward trend followed by a decline as the drift spacing becomes wider, while the dilution rate follows the opposite trend. With the moisture content at 6% on average, the optimal drift spacing in the eastern stopes of Jinshandian Iron Mine should be set at 15 m.