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The influence of the moisture content of woody biomass on the mechanisms of its ignition and combustion. Research was carried out on an experimental setup under conditions corresponding in temperature to the combustion chamber of typical boiler units (873-1273 K). It was found that ignition occurred in the gas phase at a distance depending on the ambient temperature. The higher the air temperature, the larger the distance from the particle surface to the combustion zone of gaseous pyrolysis products of wood. Based on the results of experiments, the influence of the type of woody biomass on the characteristics and conditions of ignition of fuel particles was established. An analysis of the influence of wood fiber orientation in space relative to the direction of the heat flux vector on the ignition characteristics and conditions.

A numerical simulation of the ignition of a structure made of wood material by a set of “hot” particles was performed. The problem is considered in Cartesian coordinates in a three-dimensional formulation. It was found that the ignition of the initial reagent is determined by the processes of heat exchange with the fire, drying, pyrolysis of dry wood, and oxidation reactions of carbon monoxide, methane and hydrogen. The dependences of the ignition delay time of wood material on the initial temperatures of the reagent, heated particles and the number of “hot” particles at which ignition conditions are realized have been established. A qualitative comparison of the calculation results with known data is provided.

The article focuses on formulation and substantiation of a problem of safe subsoil management in view of the more and more difficult geological and climatic conditions, as well as growing depth and scale of mineral mining. It is shown that the current basic and applied research has created prerequisites for a successful solution of this problem. In Russia these prerequisites are connected with finding energy-based mechanisms of origination and growth of high-stress concentration and destruction zones in rock masses and geomaterials which feature a hierarchical block structure and many phases, and show properties of open self-organizing geosystems in the tectonic stress and strain field. Using advances in nonlinear geomechanics and geophysics, and cloud technologies of Big Data, a new methodology, technologies and software systems are developed for shaping a multilayer geoinformation and monitoring system for diagnostics, control and prediction of the industrial and ecological safety of mining regions in Russia.

In order to clarify the relationship between the mechanical properties of coal-rock composite and the loading rate and rock-coal strength ratio, uniaxial compression tests were carried out on coal-rock combinations with three different rock-coal strength ratios at four different loading rates. The rock-coal strength ratio λ is a ratio of the compression strength of rock to the compression strength of coal. The test results indicate that the relationship between the mechanical properties of coal-rock composite and loading rate is influenced by both the strong and weak components in the composite. The peak stress and elastic modulus mainly depend on the weak component, while the peak strain is determined by both the strong and weak components. For peak stress and elastic modulus, when the weak body is the same, the relationship with loading rate is the same, otherwise it is different. The relationship between the mechanical properties of coal-rock combination and λ is not affected by the loading rate. The weak body in the coal-rock combination is the main body of damage, and the greater the value of λ, the more severe the damage. At the same time, the failure mode shows a gradual transition from weak body failure inducing strong body failure to only weak body failure.

This article experimentally investigates the characteristics of P-wave propagation in block rock mass when blocks fracture transversely and longitudinally. The velocity of P-wave, rock block acceleration, kinetic energy, displacement response, and the time-frequency response of rock block were analyzed. The results show that when the rock block fractures, the P-wave velocity decreases, the acceleration response duration time increases, and the maximum acceleration and kinetic energy decrease. However, transverse fractures show a more evident decrease in the acceleration and kinetic energy near the fracture area, and longitudinal fractures show a more evident decrease in the displacement amplitude far from the fracture area. On transverse fractures, the dominant frequency of acceleration and kinetic energy leads to a low value near the fracture area, but the dominant frequency of displacement-to a high value. Longitudinal fracture leads to a dominant frequency of block response occurrence time delayed far from the fracture area.

This article studied the biomechanical properties of salix root sampled from arid and semi-arid regions of China. The damage law of root in the process of stretching was analyzed by acoustic emission technique. The fractal dimension of root failure section was calculated by digital image processing technology. The results show that salix root tensile strength and ultimate elongation decreases with the diameter increasing, while ultimate tensile resistance and diameter are positively correlated. Damage variable characterized by cumulative AE energy can not only help research the rule of root damage quantitatively, but also allows determining the critical elongation when root became inactive. The optimal mining depth values are proposed, which enable reduction of ground surface deformation, elimination of root system damage, protection of planting on ground surface and, thus, decrease of possibility of bench convergence.

Taking working face 8006 of a coal mine in North China as the engineering background, the contact stress of each rock stratum interface is calculated based on the principle of composite beam to predict the development position of the separation layer. The distributed fiber optic sensing technology monitors the horizons where the abscission develops. The test results can accurately reflect the deformation characteristics of the overlying strata in the field, which provides an important theoretical basis and guiding role for the design of the overlying strata grouting scheme in this coal mine. The results show that when the working face is fully mined, the separation layer is mainly developed between the coarse-grained sandstone and the lower sandy mudstone at a distance of 265 m from the coal seam roof. The grouting scheme is effective, which can provide a useful reference for similar grout injection in overburden separation projects.

A large number of cases of tunnel bottom deformation occur in nearly horizontally layered strata. This article analyzes the common characteristics of such tunnel bottom deformation through case studies, and introduces the limitations and requirements for bottom designs for China’s high-speed railway tunnels. The deformation mechanisms of the tunnel bottom were studied through the physical model experiment which revealed the interaction characteristics between the layered surrounding rock and the tunnel bottom structure. Through the numerical simulation study, the effect of different elevated arch curvatures on deformation of the tunnel bottom was investigated, and the effectiveness of elevation arch deepening in deformation control of the tunnel bottom was verified. The classified control countermeasures for deformation at the bottoms of the tunnels in nearly horizontally layered strata are provided.

In response to the engineering problem of severe damage to tunnels caused by coalburst, which leads to support failure and personnel casualties, a method of preventing coalburst through the support and energy-absorbing effects of supports has been proposed. An energy-absorbing hydraulic support is designed for circular or arched tunnels: it is called gantry energy-absorbing hydraulic support. The support mainly consists of three parts: an arched top beam, a micro-arc base, and an energy-absorbing hydraulic column. Through experiments, two types of the energy-absorbing components were compressed and tested. The results show that the average yield strength of a single anti-impact component is 1840 kN, and the energy absorption is 180 kJ when compressed by 100 mm. The average yield strength of the double section anti-impact component is 2460 kN, and the energy absorption is 410kJ when compressed by 100 mm. Both of these energy-absorbing components with a total energy absorption capacity of over 700 kJ are used in actual gantry energy-absorbing hydraulic support.

Ground-penetrating radar is used to study defects in the form of internal layers in concrete structures. It is found that modulus of deflection coefficient of GPR signals changes as function of the layer thickness and electromagnetic properties of the material filling the layer (sand, wet sand or air). The experimental and numerical research used the method of peak-to-peak amplitude ratio, which enabled determining the Fresnel coefficients for the upper and lower boundaries of a layer. The minimal layer thickness recorded by GPR was 2 mm.