The root reinforcement on the slope under the condition of colonization of various herbaceous plants.

This study assessed root reinforcement on slopes influenced by various herbaceous species. The study examined the distribution, structural traits of these species, and their root systems, as well as their biomass. We established a quantitative model for evaluating root reinforcement at the soil interface influenced by different herbaceous colonizers. The focus was on a mining environment, specifically measuring root reinforcement at a dumpsite slope. The results showed that the herbaceous plants in the dumpsite included Candian fleabane (Conyza canadensis), Annual bluegrass (Poa annua), and Suaeda (Suaeda glauca), and the weights of the three herbaceous plants in descending order were Annual bluegrass, Candian fleabane, and Suaeda. Notably, the tensile strength of annual bluegrass roots peaked when diameters were less than 0.4 mm. Statistical analysis revealed significant variations in root tensile strength (p < 0.05, ANCOVA), root area ratio, and reinforcement (average values from 0 to 10 cm, p < 0.05, ANOVA) among the species. Canadian fleabane demonstrated the greatest root area ratio and reinforcement throughout the soil profiles. The integration of these herbaceous species increased the surface layer's stability of the slope by 21.6 % and marginally expanded the cross-sectional area of the landslide mass.

Investigation on acoustic emission characteristics of fault stick-slip under different lateral pressures.

To explore the effect of different stress environments on fault-slip rockbursts. Bidirectional shear friction experiments with different lateral pressures were conducted on precracked syenogranites buried at 800 m. The macroscopic statistical parameters (cumulative number of AE events, magnitude and b value) and local characteristic parameters (amplitude and dominant frequency) of acoustic emission during the stick-slip process under different lateral pressures were investigated. In addition, based on fractal theory, the nonlinear characteristics of AE spectrum were analyzed. On this basis, the microscopic mechanism of fault stick-slip was discussed. The results show that the lateral pressure influences the friction strength of the fault and stick-slip motion characteristics. With increasing lateral pressure, the proportion of transgranular shear fractures increases, which leads to an increase of cumulative number of AE events and magnitude. The periodic decrease in the b value is more significant at high lateral pressure. There is a good correlation between a high-magnitude AE event and a stress drop. The AE frequency with phased response characteristics can be used to effectively identify the evolution of fault stick-slip instability at the laboratory scale. A sharp increase in the amplitude of the dominant frequency can be regarded as one of the precursory features of fault stick-slip instability. The AE frequency spectra have multifractal characteristics, that differ among the different stages. The maximum multifractal dimension and spectral width can reflect the difference in energy released during fault stick-slip motion.

Study on the pressure relief energy dissipation law of variable-diameter boreholes in roadway surrounding rock under dynamic and static loads.

To address the conflict between pressure relief and support effectiveness caused by large-diameter boreholes in roadway surrounding rock, this paper proposes a method involving variable-diameter boreholes for pressure relief and energy dissipation. With a typical rock burst coal mine as the engineering context, the study establishes a mechanical model for variable-diameter boreholes through theoretical analysis to examine the elastic stress distribution around boreholes within the coal body. Physical similarity simulation tests are conducted to investigate the influence of conventional borehole and variable diameter borehole on the transmission pattern of dynamic load stress waves. Furthermore, numerical simulations are employed to explore the effects of reaming diameter, depth, and spacing on pressure relief, energy dissipation, and attenuation of dynamic stress wave transmission in roadway surrounding rock. The results demonstrate that stress within the coal surrounding the variable-diameter borehole correlates with the borehole radius, lateral pressure coefficient, and distance from the point to the borehole center, the extent of the plastic zone is influenced by borehole diameter, spacing, and depth. Increased diameter, reduced spacing, and greater depth of deep reaming holes exacerbate the transfer of stress concentration from the surrounding rock of the roadway to the deeper regions, facilitating the formation of stress double peak areas. Moreover, the variable diameter position should be within the original stress peak position of the surrounding rock in the roadway, with deep reaming passing through the stress concentration area for optimal results. This study offers guidance on the prevention and control technology for rock bursts in deep coal mining operations.

Study on the size effect of rock burst tendency of red sandstone under uniaxial compression.

The study of rock burst tendency of rock masses with different sizes plays a key role in the prevention of rock burst. Through theoretical analysis, it is proposed that uniaxial compressive strength and deformation modulus ratio are the key mechanical parameters affecting rock burst occurrence. In order to find out the size effect of uniaxial compressive strength and deformation modulus ratio, theoretical analysis and uniaxial compression experiment are carried out on rock samples with different heights, different cross-sectional areas and different volumes. The results show that the smaller the uniaxial compressive strength is, the larger the deformation modulus ratio is, and the more likely rock burst are to occur. On the contrary, rock burst is still not easy to generate. The uniaxial compressive strength of rock samples with different heights, different cross-sectional areas and different volumes increases with the increase of rock sample size. The deformation modulus ratio of rock samples with different heights and different volumes shows an upward trend on the whole, while that of rock samples with different cross-sectional areas shows a downward trend on the whole. The fracture forms of rock are analyzed using the energy conversion law in the process of deformation and failure for three kinds of rock with different shapes and sizes.

Analysis of size effect and its influencing factors of brittle red sandstone with different heights.

We carried out uniaxial compression tests on brittle red sandstone with different heights. The test results show that the uniaxial compressive strength of rock sample increases first and then tends to be stable with the increase of the size, which is approximately stable between 75 and 81 MPa. Both elastic energy and dissipated energy increase with the increase of rock sample size. In order to further analyze the mechanism behind these phenomena, we combined advanced numerical simulation and theoretical analysis to explain these phenomena, and systematically analyzed the end face effect as one of the key factors affecting the uniaxial compression characteristics of brittle red sandstone for the first time. Small sized rock samples are very sensitive to end effect. The middle of the large sized rock samples is in a uniform compression state, and the effect of end effect is weakend. When there are rigid pads at both ends of the rock sample, there is an obvious elastic vertebral body during the loading process of the rock sample. The bearing capacity of rock samples with rigid pads is greater than that of rock samples without rigid pads, and the energy released during instantaneous failure of rock samples without rigid pads is greater than that of rock samples with rigid pads. The findings of this paper make a valuable contribution to establishing optimal study sample sizes and advancing the utilization of laboratory test mechanics parameters in engineering applications.

Experimental Study on Carbon Dioxide Displacement by Coal Seam Water Injection.

Using water to displace carbon dioxide adsorbed in coal can prevent coal and gas outbursts. However, the mechanism of continuous water injection replacing adsorbed gases in coal has not been well studied. An experiment with the same water injection pressure and different adsorption equilibrium pressures for displacing carbon dioxide was conducted. The variation patterns of the amount of displaced carbon dioxide, time, and water displacement rate, displacement ratio, and water action ratio were analyzed. The modes of water injection displacing carbon dioxide are discussed. The results show that the change in the amount of displaced carbon dioxide consists of three stages: rapid, slow, and stop growth stages. For the same displacement time, as the adsorption equilibrium pressure rises, more carbon dioxide is displaced. The time displacement rate and water displacement rate can be divided into three stages: rising, peak, and dropping stages. As the adsorption equilibrium pressure increases, the duration of the peak stage decreases, while the time and water displacement rates increase. At different adsorption equilibrium pressures, the carbon dioxide displacement ratio ranged from 45% to 54%, less than the natural desorption ratio. But the water action ratio containing the gas dissolution amount was close to or greater than the natural desorption ratio. Thus, the displacement effect of flowing water accelerated the desorption of carbon dioxide in coal. The modes of carbon dioxide displacement by water injection include water-displacement, gas-dissolution displacement, and gas-diffusion-dissolution displacement. The findings of this study provide novel suggestions for preventing and controlling coal and gas outbursts.

Study on time-frequency features of induced charge signals during the damage and failure process of coal medium.

Monitoring and preventing coal-rock dynamic disasters are vital for safe mining. To investigate the time-frequency features of induced charge signals with coal damage and failure of roadways, the generation mechanism of free charge in loaded coal is analyzed and the induced charge monitoring test is conducted. According to the stress-induced charge-time curves, the time-domain features of charge signals at each loading stage are obtained. The wavelet threshold denoising approach and generalized Morse wavelet transform method are applied to denoise the raw signals and study the frequency-domain features. Further, the quantitative relationship between the de-noised induced charge signals and the degree of coal damage is established. The results show that the event number, amplitude and fluctuation degree of available induced charge signals are all at a low level in the compaction and elastic stages of the coal, which are mainly generated by the piezoelectric effect and predominantly represent discreteness. When entering the plastic and failure stages, the available signals are primarily produced by the crack propagation and triboelectric effects, with a significant increase in the event number, amplitude, and fluctuation degree. Then the induced charge signals gradually transit from discrete to continuous. Generally, the dominant frequency of the available induced charge signals during the coal damage process is concentrated at 0 ~ 11 Hz. The available induced charge is positively correlated with the degree of coal damage, which can perform the damage degree of coal mass, providing a new approach to evaluate the stability of roadway surrounding rocks.

Macroscopic fracture mechanism of coal body and evolution characteristics analysis of impact force in deep coal and gas outburst.

With the increase of mining depth and intensity, coal and gas outburst dynamic disasters occur frequently. In order to deeply study the macroscopic fracture mechanism of coal body and evolution characteristics analysis of impact force, taking the outburst coal seam of Pingmei No. 11 Coal Mine and Sunjiawan coal seam of Hengda Coal Mine as the research objects, the simulation roadway test system of self-developed true triaxial coal and gas outburst is applied to carry out the simulation test of deep coal and gas outburst with buried depths of 1000 m, 1200 m, 1400 m and 1600 m. During the test, the overlying strata stress is simulated by axial compression, the surrounding rock stress is simulated by confining pressure, the gas pressure is simulated by pore pressure, the impact force and acoustic emission monitoring technology are introduced, and the coal seam gas pressure is simulated by mixture pressure of 45% CO2 and 55% N2. From the viewpoint of fracture mechanics, the crack propagation mechanism of coal in the outburst launching area is discussed, the evolution characteristics of impact force and gas pressure are analyzed, and the influence law between acoustic emission signal and impact force is revealed. From the viewpoint of energy conversion, the transformation character of gas internal energy to impact kinetic energy (gas pressure to impact force) are analyzed. The results show that the generation of I-type crack is a prerequisite for outburst catastrophe. With the crack propagation, I-type and II-type cracks intersect and penetrate, resulting in internal structural damage and skeleton instability of coal. Gas wrapped fragmentized coal body thrown, outburst occurs. There is obvious negative pressure in the roadway after outburst. The occurrence of negative pressure is greatly affected by the physical and mechanical properties of coal, ground stress and gas pressure. Impact kinetic energy is mainly provided by gas internal energy. Part of the gas pressure is converted into impact force. The strength and duration of the impact force are determined by the gas pressure. Under the condition of deep working conditions (high ground stress and low gas pressure), the propagation of impact force in the roadway is more hindered. Both impact force and acoustic emission signals can monitor the occurrence of outburst. The peak point of acoustic emission ringing count is earlier than the impact force. The acoustic emission signal can monitor the outburst hazard earlier. The impact force can more specifically reflect the coal fracture.

Slip instability behavior of block rock masses on dynamic-static combined loads.

A rock mass is a system of various scale blocks embodied into one another. Inter-block layers are usually composed of weaker and fissured rocks. On the action of dynamic-static loads, it can induce slip instability between blocks. In this paper, the slip instability laws of block rock masses are studied. Based on theory and calculation analysis finding that the friction force between rock blocks varies with block vibration and the friction between rock blocks can drop sharply, resulting in slip instability. The critical thrust and occurrence time of block rock masses slip instability are proposed. The factors affecting block slipping instability are analyzed. This study has significance to the rock burst mechanism induced by slip instability of rock masses.

Research on the comparison of impact resistance characteristics between energy absorption and conventional hydraulic columns in fluid-solid coupling.

Rock burst disaster affects underground mining safety. The energy-absorbing hydraulic support for preventing tunnel impact has been implemented in rock burst mines. In order to compare the impact resistance characteristics of conventional columns and energy-absorbing columns, based on the derivation of energy theory, the CEL fluid-solid coupling simulation algorithm is used to simulate the process of static load 1000 kN superimposed impact load 1500 kN on φ180 mm type conventional column and energy-absorbing column. Combined with the static-dynamic combined test of the 6500 kN impact testing machine on the column, the accuracy and reliability of the CEL simulation column impact response are verified. The results showed that compared with conventional columns, the reaction force of energy-absorbing columns is reduced by 32.55%. The stress and expansion of the cylinder are significantly reduced. The acceleration of the mass movement has been reduced by 59.46%. The addition of the energy-absorbing device enhances the system's energy absorption by 33.46%, thereby reducing the energy absorption of the column itself to 23.58%. Additionally, the deformation of the energy-absorbing device increases the effective displacement by 239.45%. This also prolongs the impact duration, ensuring sufficient time for the safety valve to open, safeguarding the support from damage, and enhancing the overall integrity of the tunnel.

Gas pressure evolution characteristics of deep true triaxial coal and gas outburst based on acoustic emission monitoring.

Coal and gas outburst is one of the geological disasters that seriously threaten the safety of coal mines production. In recent years, with the increase of mining depth, outbursts become frequent. To further explore the occurrence mechanism of deep coal and gas outburst, a self-developed true triaxial coal and gas outburst simulation device was used to simulate the coal and gas outburst at different depths. The results show that with the increase of simulation depth, the critical gas pressure of outburst gradually decreases, and the unit outburst intensity increases sharply. The gas threshold of deep coal and gas outburst is lower. During the incubation and excitation, gas pressure has three special variation rules, namely self-increasing characteristic, stage and instantaneous. In the early incubation, acoustic emission (AE) energy is at a low level, low energy frequency is dominant; in the later incubation, AE energy increases greatly, high energy frequency is dominant. From the perspective of AE energy, a quantitative index that reflects the danger of coal and gas outburst in the incubation is defined, which provides a scientific reference for the prediction and prevention of disasters of coal and gas outburst in deep mining.

Numerical Analysis of Mechanical Characteristics of Constant-Resistance, Energy-Absorbing and Anti-Scour Bolts.

In order to improve the impact resistance mechanical properties of bolt, the requirements of rock burst roadway support must be met. Based on the requirements that the anchor should have a reasonable deformation load threshold, high stroke efficiency, constant reaction force and stable repeatable deformation damage mode. A constant resistance anti-impact device was designed, and a new constant resistance energy-absorbing impact anchor rod was designed in combination with a conventional anchor rod, and the working principle of a constant resistance energy-absorbing impact anchor rod was given. ABAQUS finite element software was used to analyze the mechanical properties of bolt and the results showed that the constant resistance energy-absorbing anti-shock anchor has a stable and repeatable deformation damage mode under both static and impact loads, and the three indexes of the constant resistance energy-absorbing anti-shock anchor, such as yield distance, impact resistance time and energy absorption, are significantly better than those of the conventional anchor. The impact energy and impact velocity have less influence on the load-bearing capacity and stroke efficiency of the impact device. The impact velocity has less influence on the indices of the rod yield load, breaking load, absorbed energy and the yield distance of a conventional anchor and constant resistance energy-absorbing anti-stroke anchor, and the impact resistance time decreases non-linearly with the increase in the impact velocity.

The financial impact of the 'zero-markup policy for essential drugs' on patients in county hospitals in western rural China.

OBJECTIVE: With a quasi-experimental design, this study aims to assess whether the Zero-markup Policy for Essential Drugs (ZPED) reduces the medical expense for patients at county hospitals, the major healthcare provider in rural China. METHODS: Data from Ningshan county hospital and Zhenping county hospital, China, include 2014 outpatient records and 9239 inpatient records. Quantitative methods are employed to evaluate ZPED. Both hospital-data difference-in-differences and individual-data regressions are applied to analyze the data from inpatient and outpatient departments. RESULTS: In absolute terms, the total expense per visit reduced by 19.02 CNY (3.12 USD) for outpatient services and 399.6 CNY (65.60 USD) for inpatient services. In relative terms, the expense per visit was reduced by 11% for both outpatient and inpatient services. Due to the reduction of inpatient expense, the estimated reduction of outpatient visits is 2% among the general population and 3.39% among users of outpatient services. The drug expense per visit dropped by 27.20 CNY (4.47 USD) for outpatient services and 278.7 CNY (45.75 USD) for inpatient services. The proportion of drug expense out of total expense per visit dropped by 11.73 percentage points in outpatient visits and by 3.92 percentage points in inpatient visits. CONCLUSION: Implementation of ZPED is a benefit for patients in both absolute and relative terms. The absolute monetary reduction of the per-visit inpatient expense is 20 times of that in outpatient care. According to cross-price elasticity, the substitution between inpatient and outpatient due to the change in inpatient price is small. Furthermore, given that the relative reductions are the same for outpatient and inpatient visits, according to relative thinking theory, the incentive to utilize outpatient or inpatient care attributed to ZPED is equivalent, regardless of the 20-times price difference in absolute terms.