Loose Media Research Articles

Feasibility experimental study on plugging leakage in goaf based on two-phase foam

Air leakage in goaf often leads to coal spontaneous combustion (CSC), which not only directly affects the safety production of mines but also causes significant environmental damage. Therefore, effectively sealing the airflow in goaf is crucial for preventing CSC. Feasibility experiments on using two-phase foam to seal air leakage in goaf were conducted, leveraging the advantages of large flow rate, wide diffusion range, and good accumulation characteristics of two-phase foam. The research results indicate that continuous injection of foam into loose media with maintained ventilation can completely seal the air leakage, with the foam capable of withstanding wind pressures of nearly 600 Pa. When the foam is used for one-time sealing with a length of 2 m, it remains effective for 60 min, and the sealing effectiveness improves with longer distances sealed against air leakage. Numerical simulation analysis and field measurements of airflow leakage in mine working faces reveal that effectively sealing the airflow passage in the goaf behind the corner of the return airway is crucial for preventing CSC. Two methods are proposed for sealing external airflow during coal mining: foam injection using a point drilling method near the heading and an incremental buried pipe injection method. Finally, the feasibility of two-phase foam sealing technology for goaf airflow leakage is analyzed from multiple perspectives including sealing effectiveness, practicality, economy, foaming process, and engineering implementation. The research findings provide new insights into goaf sealing technology, aiding in addressing safety and environmental issues caused by spontaneous combustion in goaf areas.

An investigation into the morphological distribution of the temperature field in loose media and its underlying principles of evolution

The spontaneous combustion of coal in goaf has important implications for the safe mining of working faces; hence, it is crucial to prevent and control such occurrences. Here, we establish an experimental system to investigate the morphological distribution, evolution, and migration process of the temperature field of the thermal core area in systems with various particle sizes. Furthermore, we propose a high-temperature-region inversion method based on the morphological evolution model of the temperature field. Our experimental results demonstrate that particle size is a critical factor influencing the temperature field morphology under a given heating condition. During the heating stage, the isothermal surface within the thermal core area forms an ellipsoidal shape, with a transverse section comprising concentric circles, and a longitudinal section comprising ellipses. During the heat dissipation stage, the isothermal surface of the small-particle-size system encircles the thermal core area from the upper direction downwards, while the isothermal surface of the large-particle-size system encircles the thermal core area from the lower direction upwards. Moreover, the thermal core area of the large-particle-size system migrates upwards, while the thermal core area of the small-particle-size system migrates a shorter distance. Finally, we used a geometrically simplified temperature field in loose media to propose a high-temperature-region inversion method, which was verified by experiments. This study is crucial for understanding the distribution and evolution of temperature fields in loose media and predicting the formation and development of high-temperature regions.

Experimental study on the migration and expansion of liquid nitrogen in loose media with different dip angles

ABSTRACT The goaf is the main disaster area for natural fires in mines, and liquid nitrogen has become an essential medium for fire prevention in goafs due to its excellent cooling and inerting properties.At present, there is no in-depth research on the transport and vaporization of liquid nitrogen after injection into the goaf, and it is impossible to quantitatively evaluate the cooling inerting effect after liquid nitrogen injection. To address the above problems, this project proposes to carry out the following research: to study the effects of different inclination angles on the transport and vaporization of liquid nitrogen and temperature distribution in the loose medium in confined space by monitoring the temperature field changes during the pressure injection of liquid nitrogen in the loose medium in confined space.The results show that the temperature field distribution is very uneven after liquid nitrogen is injected into the loose medium in the restricted space.It is found that the vaporization rate of liquid nitrogen decreases with the increase of diffusion time and diffusion area, and the instantaneous vaporization rate of liquid nitrogen decreases with the larger inclination angle under the same injection position. Compared with the horizontal state, the maximum vaporization rate decreased 84.79% when the maximum inclination angle was 15°, which indicates that the vaporization rate was greatly affected by the inclination angle of the surface. In the vertical direction of the experimental box, the cooling area of liquid nitrogen in the experimental box is mainly concentrated within 0.05 m height from the bottom of the experimental box, and the changes of the “cooling restricted zone” after liquid nitrogen injection into the goaf are further explained during the experiment.It is found that the “cooling restricted zone” mainly exists in the upper part of the goaf, under the inclined condition, and the area increases with the increase of the inclination angle, so the increase of the angle is not conducive to the effective cooling effect of liquid nitrogen.The research results of the project will help to improve the theory of liquid nitrogen fire prevention in mines and provide theoretical support for the fire prevention technology of liquid nitrogen direct injection in goafs.

Intrusion rheology in grains and other flowablematerials.

The interaction of intruding objects with deformable materials arises in many contexts, including locomotion in fluids and loose media, impact and penetration problems, and geospace applications. Despite the complex constitutive behaviour of granular media, forces on arbitrarily shaped granular intruders are observed to obey surprisingly simple, yet empirical 'resistive force hypotheses'. The physics of this macroscale reduction, and how it might play out in other media, has however remained elusive. Here, we show that all resistive force hypotheses in grains arise from local frictional yielding, revealing a novel invariance within a class of plasticity models. This mechanical foundation, supported by numerical and experimental validations, leads to a general analytical criterion to determine which rheologies can obey resistive force hypotheses. We use it to explain why viscous fluids are observed to perform worse than grains, and to predict a new family of resistive-force-obeying materials: cohesive media such as pastes, gels and muds.

Rolling Friction in Loose Media and its Role in Mechanics Problems

Rolling friction between particles is to be set in problems of granular material mechanics alongside with sliding friction. A classical problem of material passive lateral pressure on the retaining wall is submitted as a case in point. 3D method of discrete elements was employed for numerical analysis. Material is a universe of spherical particles with specified size distribution. Viscose-elastic properties of the material and surface friction are included, when choosing contact forces. Particles' resistance to rolling relative to other particles and to the boundary is set into the model. Kinetic patterns of medium deformations are given. It has been proved that rolling friction can significantly affect magnitude and nature of passive lateral pressure on the retaining wall.

Research on Chamber Earth Pressure of EPB Shield Considering Soil Arching Effect

Chamber earth pressure is one of the significant parameters during the Earth Pressure Balance (EPB) shield construction processing. The soil arching effect is existence when the tunnel depth is enough. It is significant to consider the influence of arching effect to analyze the pressure in soil chamber in shield tunneling. In this paper, the influence of arching effect is considered to calculate the chamber earth pressure. Firstly, the soil is supposed as loose media, and the necessary buried depth of producing arching affects is deduced according to the loose media theory. Then, based on the characteristic of proper arching axis, the equation and the height of proper arch are obtained. At last, the calculation formula of minimum chamber earth pressure of EPB shield tunnel is deduced which can consider the effect of arching effect.

Investigations into the influence of wave oscillations on highly dispersed loose media using the wave mixer-activator to produce modifying additives

The results of investigations of wave processes in dispersed media for application of wave effects in the development of a new class of wave machines, including the mixer-activator to produce modifying additives, are presented. The results of experimental investigations into the wave effect on various types of dry multicomponent dispersed systems to apply similar wave machines and aggregates in various branches of industry are presented.

Penetration of rigid bodies into loose and layered media

Penetration and motion of rigid bodies in ground media attracts the researchers’ attention because of various problems arising as the technology evolves. In fact, there are two independent directions of studies in this field: (1) the problem of earth excavation when a rigid body of a definite shape slowly moves along a given trajectory in the ground; (2) an impact of a rapidly flying free rigid or deformable body against the ground. In the latter case, to which the proposed studies pertain, it is sometimes of interest to study the medium behavior and the motion of the free body, which moves in the medium after the impact owing to the kinetic energy of itself. In this field, a majority of studies deal with collision and penetration of bodies of various shapes into clay media. An extensive survey of these studies is given in [1]. After this survey appeared, numerous paper dealing with complicated collision conditions have been published [2]. Penetration in loose media has been studied much more rarely. The direct collision with fractured rock was studied in connection with the expected landing of spacecraft on other planets [3, 4]. In this case, the influence of grain dimensions and the density of the filling and vacuum on the penetration was studied for the initial velocities in the range of 1.7–10 m/s. On the other hand, in [5], the results of investigating the penetration of conic bodies in sand at entry velocities of 700–900 m/s are given; these velocities significantly exceed the speed of sound in this medium, which lies in the range of 100–200 m/s for dry sand. Analyzing the experimental results, the author came to the conclusion that it is necessary to use different representations of the drag force in the supersonic and subsonic modes. In the present paper, we do not consider the influence of the grain distribution, sand density, and filling methods on the penetration. But, as follows from the experiments whose results are described in [6] and [7], to represent the results of penetration of rigid bodies at velocities up to several hundreds of meters per second, in addition to the characteristics listed above, it is also required to describe the technology of the experiment preparation, because such media have the property of shape “memory.”

Root cap specific expression of an endo-?-1,4--glucanase (cellulase): a new marker to study root development in Arabidopsis

The sloughing of root cap cells from the root tip is important because it assists the growing root in penetrating the soil. Using a promoter-reporter (GUS) and RT-PCR analysis, we identified an endo-beta-1,4-glucanase (AtCel5) of Arabidopsis thaliana that is expressed exclusively in root cap cells of both primary and secondary roots. Expression is inhibited by high concentrations of IAA, both exogenous and internal, as well as by ABA. AtCel5 expression begins once the mature tissue pattern is established and continues for 3 weeks. GUS staining is observed in both root cap cells that are still attached and cells that have already been shed. Using AtCel5-GUS as a marker, we observed that the root cap cells begin to separate at the sides of the tip while the cells of the central region of the tip separate last. Separation involves sequential tiers of intact cells that separate from the periphery of the root tip. A homozygous T-DNA insertion mutant that does not express AtCel5 forms the root cap and sheds root cap cells but sloughing is less efficient compared to wild type. The reduction in sloughing in the mutant does not affect the overall growth performance of the plant in loose media. The modest effect of abolishing AtCel5 expression suggests that there are multiple redundant genes regulating the process of sloughing of the root cap, including AtCel3/At1g71380, the paralog of the AtCel5 gene that is also expressed in the root cap cells. Thus, these two endo-1,4-beta-D-glucanases may have a role in the sloughing of border cells from the root tip. We propose that AtCel5, provides a new molecular marker to further analyze the process of root cap cell separation and a root cap specific promoter for targeting to the environment genes with beneficial properties for plant growth.

Modeling end ore discharge with incomplete similarity between the mechanical properties of the loose material in the model and prototype

mining in the field, this process is studied in the laboratory with the aid of models. To get reliable data for calculating the parameters of the discharge figures, the system of mining, and the ore discharge indices, we must maintain geometrical similarity and similarity of the mechanical properties of the loose medium between the model and the prototype. In this case, to convert the parameters of the system of mining, found from the ore discharge indices, to the prototype scale, it is enough to multiply the results by the scale factor. Whereas it is easy to maintain geometrical similarity in a model, it is very difficult to obtain similarity of the mechanical properties of the loose media. Investigators who have studied ore discharge usually recommend that the model should preserve equality or similarity of the natural angles of internal friction and repose, the coefficient of distention of the loose material, the moisture content, the grain-size composition, and other mechanical characteristics which influence the running properties of the broken-down ore [1, 2]. To determine most of these characteristics in industrial conditions is very difficult or impossible, and in the laboratory, as a rule, one cannot obtain the required combination of these indices. Therefore in a model one usually obtains equality or similarity of only a small fraction of the mechanical characteristics of the caved ore, and investigations have not infrequently led to results which differ between the model and prototype. To avoid modeling all the mechanical properties of a loose medium in laboratory experiments we can use some parameters which characterize these properties as a whole. These are the eccentricity of the discharge ellipsoid $, the indexof looseness of the ore {the radius of curvature of the vertex of the discharge diagram) P, the diameter of the caving crater on the surface of the caved ore d, etc.; on this basis G. M. Malakhov, V. V. Kulikov, and V. R. Imenitov [1-3] have developed the best-known conditions of similarity for modeling the discharge of caved ore. These similarity conditions and expressions for ~ and P were developed for platform ore discharge for which the discharge figure is a symmetric solid in the shape of an ellipsoid of revolution. In layerwise end discharge of ore in a system of subpanel caving, the discharge figure is a triaxial ellipsoid or an ellipsoid of revolution truncated by the planes of uncaved rock, and this governs its development and prevents us from using the above parameters to preserve similarity in the model. In this case a model of discharge can be made by preserving geometrical similarity alone, and the test parameters of the system of mining, calculated from the parameters of the discharge figures, can be determined by comparing the absolute values of the latter obtained in the laboratory and in the field. This preserves equality of the absolute values of the discharge indices of the ore in the model and prototype. As a confirmation of this, we will give a method of calculating the parameters of a system of mining, starting from a comparison between the parameters of the discharge figures of the model and prototype, with equality of the ore discharge indices. To simplify the calculations, we assume that the discharge figure is an ellipsoid of revolution, that the major axis of the figure lies alongthe plane of the uncaved reck, and that the caved layer of ore has the form of a parallelepiped with free dimensions in the ratio 1 : 2.