Mechanical properties and dynamic breaking mechanism of plateau frozen soil

AbstractThis work studies and evaluates the mechanical properties of frozen soil, FS, from Yulong mine in Tibet, under different freezing temperatures ranging from −12 °C to −1 °C, using experimental tests. In addition, the effects of temperature and time on the freezing depth of FS were investigated. Based on the cantilever beam theory, the mechanical model of FS breaking under blasting stress wave was established, and the theoretical formula for the fracture length (FL) of FS was deduced. Moreover, the major influences on FL were analyzed. The results showed that the frozen depth curves at different temperatures were approximately linear in single or double segments, and the lower the temperature, the greater the early freezing rate. Additionally, the uniaxial compression strength, elastic modulus, and tensile strength of FS were found to decrease with the increase in temperature. The findings highlight that the shear strength, cohesion, and internal friction angle decreased first and then increased with the increase in temperature. It was shown that the thickness, friction coefficient, weight density, and tensile strength of FS are positively correlated with the FL, while there is an inverse proportionality with respect to the pressure of the detonation wave

Insight on the Void Ratio–Suction Relationship of Compacted Bentonite during Hydration

Investigation on swelling characteristics of buffer/backfill materials during hydration is an important issue in the design of artificial barriers in high-level radioactive waste (HLW) disposal repositories. In this work, for clarifying the characteristic of void ratio–suction relationship for compacted bentonite on hydration path, suction-controlled swelling deformation tests under constant vertical stresses 0.001~40 MPa were carried out on compacted bentonite specimens. Four different types of void ratio-suction curves indicated that swelling-collapse behavior under hydration depends on suction and over-consolidation ratio (OCR), based on which the swelling index was defined. Then, equations were proposed for describing the swelling-collapse characteristic of void ratio–suction curves. Simulation results of suction-controlled swelling deformation tests show that the different types of the hydration deformation curves could be well described by the proposed equations. Obviously, the proposed equations could be used for description and prediction of swelling characteristics of compacted bentonite during hydration, which is also of great importance for the safety assessment of the HLW repositories

Role of Tectonic Coal in Coal and Gas Outburst Behavior During Coal Mining

Coal and gas outbursts are small-scale geological disasters controlled by tectonic movement, and tectonic coal is widespread in outburst zones. In this study, we compare tectonic and intact coal specimens to examine the basic properties of tectonic coal. We estimate the different energies and limits of the crushing work ratio of coal from five typical outburst cases using on-site outburst data, and discuss the relationship between outbursts and tectonic coal. The results show that tectonic coal is a product of tectonic movement and its original primary structure is destroyed during the tectonic process. Compared with intact coal, tectonic coal shows low strength properties and a crushing work ratio of 22.11 J/m2. The specific surface area and total pore volume of the minipores, mesopores, and macropores of the coal strongly increase under conditions of intense tectonism, which indicates that tectonic coal has a very high capacity for rapid initial gas desorption. An adequate supply of gas is required to transport outburst coal, such that the existence of coal particles smaller than the critical diameter is important. Our calculations indicate that the crushing work ratio of coal from the five outburst case ranges from 22.19 to 78.67 J/m2. Only the crushing work ratio of tectonic coal satisfies the requirement for these cases. Therefore, the properties of the tectonic coal and crushing work ratio for the five cases indicate that the widespread occurrence of tectonic coal plays a crucial role in outbursts

The Experimental Study of Dynamic Response of Marine Riser under Coupling Effect of Multiparameter

In order to investigate the dynamic response of a marine riser under the coupling effect of multiparameter, a model experiment of a marine riser was designed and carried out. The main parameters of the model test were divided into riser design parameters and flow field parameters. The riser parameters included the elastic modulus, boundary conditions, and top tension forces, and the flow field parameters were the velocities and wave parameters (wave height and period). The riser materials were aluminum (Al) and polymethyl methacrylate (PMMA), representing the metal riser and fiber-reinforced composite marine riser, respectively, which differ greatly in modulus. Two types of boundary conditions were considered, which were simple supports at both ends (S-S) and simple and fixed supports at each end (S-F). The top tension forces were chosen as 10 N and 30 N, respectively. In terms of the flow velocities, 0.3 m/s and 0.7 m/s were used. For the wave types, the small wave had a period of 1.0 s and a wave height of 5 cm while the large wave had a period of 2.0 s and a wave height of 15 cm. The dynamic response of the riser under 32 different working conditions was studied experimentally, and through the analysis of the experimental data, the effects of various parameters on the dynamic response of the risers were obtained. The results show that the amplitude of the riser was negatively correlated with the elastic modulus, the number of constraints, and the magnitude of the top tension, while it was positively correlated with the flow velocity and wave size. Moreover, the sequences of importance were b3 (flow velocity) > b6 (modulus) > b1 (number of constraints) > b2 (top tension force) > b5 (wave height) > b4 (wave period) for the vibration of the riser in the in-flow direction and b3 (flow velocity) > b1 (number of constraints) > b6 (modulus) > b2 (top tension force) > b5 (wave height) > b4 (wave period) for the vibration of the riser in the cross-flow direction, respectively, according to the multiple linear regression calculation

Separation and physicochemical properties of residual carbon in gasification slag

Gasification slag is the solid waste produced in the coal gasification process, and its treatment and disposal problems are becoming more and more serious. In this study, the gasification slag produced in a chemical base in northern China and its residual carbon obtained by gravity separation of water medium were taken as the research objects, and their physicochemical properties were analyzed comprehensively. The residual carbon products, ash-rich products and high-ash products were obtained from the gasification slag after gravity separation. Under the optimal structure, the ignition loss of residual carbon products was reduced from 79.80% to 16.84%, and the yield was 11.64%. The high content of amorphous carbon and developed pores in the residual carbon provide the possibility of manufacturing high value-added materials. Raman spectrum showed that the residual carbon had lower aromaticity, higher content of small and medium aromatic ring structures, lower structural stability and easier combustion. Thermogravimetric combustion kinetics showed that the average combustion rate of residual carbon was 0.325(dm/dt)mean/%•min−1, the comprehensive combustion characteristic index was 1.41•10−9%2•min−2•°C−3. It has excellent performance and can be used as a raw material for mixed combustion in a circulating fluidized bed. The analysis of physical and chemical properties of residual carbon is of great significance for follow-up exploration of the resource utilization and high-value utilization of the residual carbon

Experimental investigation on the formation and transport mechanism of outburst coal-gas flow: Implications for the role of gas desorption in the development stage of outburst

As the one of the most catastrophic hazards in underground mining, coal and gas outburst seriously threatens the safe mining of collieries. To understand the formation and transport mechanism of outburst coal-gas flow in roadway as well as evaluate the effects of gas desorption on its development, a new apparatus was developed to conduct simulated experiments with different gases of CO 2 and N 2 . Results indicated that the outburst coal-gas flow was a high-speed (up to 41.02 m/s during tests) gas-solid two phases flow with extreme complexity, its transport/destructiveness characteristics were significantly influenced by a number of factors including the outburst pressure, coal sample composition, ejection distance and so on. Among these factors, the gas desorption showed the greatest impact when compared to the controlled tests which only considered the effect of free gas expansion. With the effect of gas desorption, especially the rapid gas desorption from powdered coal, the total outburst energy could be promoted by 1.30-2.43 times; the peak values of outburst shockwave could be enhanced by at least 13.67%-63.22%; the transport type of coal-gas flow could be changed from dynamic pressure pneumatic conveying to the static pressure conveying which providing higher capability for outburst coal/rock conveying; the motion of ejected coal flow could have higher speed, longer transport duration and could suffer secondary acceleration. As the result, the destructiveness of outburst coal-gas flow would be remarkably intensified. A further analysis for the energy consumption during the outburst coal-gas flow transport indicated that the free gas expansion energy was insufficient for the conveying of ejected coal (only accounting for less than half of the total energy), the difference of which was made up by the gas desorption, especially the rapid gas desorption from powdered coal (the average contribution ratio reached 56.0%, while the maximum reached 64.1%). Thus, it can be concluded that the rapid gas desorption from powdered coal played a decisive role on the promotion of outburst