Stability monitoring and bearing pressure capacity of waterproof sealing wall in underground goaf

Underground water storage in goaf is one of the important means of water conservation and mining in the western ecologically fragile area. The stability of waterproof sealing wall is related to the safety of water storage in goaf. In view of the key problem that the stability of the waterproof sealing wall in the goaf is difficult to monitor and the water pressure resistance ability is difficult to predict, under the background of underground mining end sealing in Chahasu Coal Mine, by means of theoretical analysis, numerical simulation and field measurement, the mechanical properties of coal seam and roof and floor are tested, and the minimum compressive strength of coal body and roof and floor is obtained. Considering the stress characteristics of the sealing wall structure, the maximum bearing capacity of the waterproof closed wall without the influence of mining is calculated and deduced. The numerical model of waterproof sealing wall is established, and the stress state, deformation and damage of sealing wall under the influence of advanced mining and different water head heights (6, 9, 12 and 15 m) were analyzed. The stress and displacement monitoring systems of the waterproof sealing wall in the underground goaf has been developed. Based on the theoretical analysis, the monitoring points had been reasonably arranged and applied in the field. On this basis, combined with theoretical analysis and numerical simulation results, the maximum safe head height of the waterproof sealing wall and the head height of the warning water line are determined. The results showed that the advance mining has a certain impact on the damage of the waterproof sealing wall, and the water pressure increases the sliding range of the cracks between the sealing wall and the coal pillar contact surface. The maximum water head height borne by the waterproof sealing wall at the end of mining is 12 m, and the water head height of the warning water level line of the waterproof sealing wall is 9.6 m. The contact surface between the wall and the coal pillar as well as the top and bottom corners of the closed wall are structural weak surfaces, which are prone to damage. Attention should be paid to strengthening the monitoring or observation of the position of the sealing wall embedded in the coal and rock mass and the top and bottom corners of the sealing wall. If necessary, grouting and plugging can be used to reinforce the weak surface or leakage part of the structure. The research results can provide theoretical basis and application reference for stability monitoring and water pressure resistance evaluation of similar mine waterproof sealing walls

Enhanced removal of dissolved effluent organic matter in wastewater using lignin-based biochar supported Fe–Cu bimetallic oxide catalyst

The effluent discharged from wastewater treatment facilities frequently enters the ocean, posing a considerable threat to the health of marine life and humans. In this paper, an alkali lignin-based biochar-loaded modified Fe–Cu catalyst (FeCu@BC) was prepared to remove soluble microbial products (SMP) from secondary effluent as disinfection by-products precursors at ambient temperature and pressure. The humic acid (HA) was taken as the representative substance of SMP. The results showed that the maximum removal efficiency of HA reached 93.2% when the FeCu@BC dosage, pH, initial HA concentration, and dissolved oxygen concentration were 5.0 g/L, 7, 100 mg/L, and 1.75 mg/L, respectively. After three cycles, the removal efficiency of HA could be maintained at more than 70%. The quenching experiments and electron spin resonance (EPR) results showed that •OH and 1O2 were involved in the degradation of HA in the FeCu@BC catalyst reaction system, with 1O2 playing a dominant role. Theoretical calculations confirmed that •OH and 1O2 were more prone to attack the C=O bond of the side chain of HA. After processing by the FeCu@BC catalyst, the yield of chlorinated disinfection by-products from secondary effluent had decreased in an obvious manner. This study provides a new solution to efficiently solve the problem of chlorinated disinfection by-products from HA

Study on the Effect of Demulsification Speed of Emulsified Asphalt based on Surface Characteristics of Aggregates

Aggregate is an indispensable raw material for emulsified asphalt construction. For the purpose of explaining the influence of aggregate characteristics on the demulsification speed of emulsified asphalt, the surface energy and specific surface area (SSA) characteristics of aggregates were calculated based on the capillary rise method and the BET (Brunauer-Emmett-Teller) adsorption test. Afterwards, the effect of the surface energy and specific surface area of the aggregate on the emulsified asphalt demulsification speed was systematically studied by using ultraviolet spectroscopy as well as the orthogonal test. Experimental results indicate that the specific surface energy parameter of the aggregate is certainly related to the particle size of the aggregate. That is, the surface free energy of the unit system is proportional to the surface area A and the density of the interface unit. The specific surface area parameter of aggregates increases with the decrease of particle size, when the particle size is reduced to 600 mesh, the specific surface area parameters of the three aggregates selected in this paper tend to be consistent. Orthogonal experimental analysis demonstrates that the surface energy and specific surface area have an impact on the emulsion breaking speed and they are proven to be positively correlated. Meanwhile, in the case of small particle sizes, there is no statistically significant correlation between the physical properties of aggregates and the demulsification speed of emulsified asphalt, and the physical property of aggregates is not the main factor that affects the demulsification speed of the emulsified asphalt. On the contrary, the material properties of the aggregate, such as acid-base property and chargeability, are the dominant factors

An overview of methane emissions in constructed wetlands: how do plants influence methane flux during the wastewater treatment?

Plants play an essential role in methane (CH4) production, transport and release processes of constructed wetlands but as yet there has been no consistent and clear consensus of their impacts on CH4 emissions. In this study, we used plant presence, species richness, plant species-specificity, and harvesting activity information obtained by reviewing papers published from 1993 to 2018 to elucidate the key factors that drive CH4 emission from constructed wetlands. Although it was not statistically significant, plant presence increased the CH4 emissions compared to unvegetated conditions and relatively lower values were observed for constructed wetlands planted with Acorus calamus, Cyperus papyrus or Juncus effusus. The use of a single plant species not only changed the production and consumption of CH4 by affecting the functioning of roots but also influenced the process of CH4 entering the atmosphere under different transport capacities. The CH4 flux reached 1.0686 g CH4 m−2 d−1 from the Zizania latifolia system, which is eight times larger than that of the Phalaris arundinacea system. The mixed systems exhibited a positive increase in CH4 flux with plant species richness due to the complementary effects of the root exudates excreted from different plants. The minimum CH4 value (−0.0084 g CH4 m−2 d−1) was observed in the three-species system (Oenanthe javanica, Phalaris arundinacea and J. effusus). These results demonstrate that selecting several species with lower methane fluxes such as Typha latifolia and C. papyrus and suitably regulating harvesting in constructed wetlands can be more effective for mitigating the potential of CH4 emissions while maintaining the efficiency of sewage purification

Corn Straw as a Solid Carbon Source for the Treatment of Agricultural Drainage Water in Horizontal Subsurface Flow Constructed Wetlands

Agricultural drainage water with a low C/N ratio restricts the nitrogen and phosphorus removal efficiencies of constructed wetlands. Thus, there is a need to add external carbon sources to drive the nitrogen and phosphorus removal. In this study, the effects of the addition of corn straw pretreated with different methods (acid treatment, alkali treatment, and comminution) on treating agricultural drainage water with a low C/N ratio were investigated in constructed wetlands. The results showed that soaking the corn straw in an alkaline solution was the most suitable pretreatment method according to the release rule of chemical oxygen demand (COD) and the dissolution of total nitrogen (TN) and total phosphorus (TP). The average removal efficiency of TN and TP in constructed wetlands increased respectively by 37.2% and 30.5% after adding corn straw, and by 17.1% and 11.7% after adding sodium acetate when the hydraulic retention time (HRT) was 3 days. As an external carbon source, straw was cheap, renewable, and available. In contrast, the sodium acetate demanded high costs in a long-term operation. Therefore, corn straw had a great advantage in treatment effect and cost, which improved the treatment efficiency of agricultural drainage water using a byproduct of agricultural production as a slow-release carbon source

Study on reasonable width of coal pillar under water-rock interaction

The water accumulation in goaf and coal rock interaction will weaken the strength of the coal pillar in the section and cause gradual destruction and failure of the coal pillar. The interaction of water and rock is the key factor that must be considered in the design of the reasonable width of the coal pillar. The uniaxial compression experiment and theoretical analysis are carried out based on the engineering background of the coal pillar design between mining area 31 and 33 of a mine in Xinjie mining area, Ordos, Inner Mongolia. The results show that water-rock interaction has a significant impact on the weakening of coal strength parameters. The width of the plastic zone at the side of the water accumulation in the section coal pillar expands with the increase of the weakening degree of the coal body strength. Based on the basic conditions for the stability of the section coal pillar, the reasonable theoretical width of the section coal pillar is 53.62 m. Using FLAC3D to simulate the process of water-rock interaction, the paper analyzes the stability characteristics of coal pillar with different widths. The results show that when the width of the coal pillar is small, the weakening effect of water accumulation in goaf has stronger destructive capability to the elastic core area with higher stress concentration. With the increase of coal pillar width, the stress concentration degree in the elastic core area decreases. The area where the vertical stress at the water accumulation side of the goaf is lower than that of the original rock increases. The stress concentration distribution on both sides of the coal pillar tends to be uniform, and the weakening effect of water accumulation in the goaf on the elastic core area is no longer significant. Based on the results of theoretical calculation and numerical simulation, the width of coal pillar is determined to be 70 m. The engineering application results show that the coal pillar with width of 70 m can effectively bear the roof pressure. The deformation of the roadway surrounding rock is small, the stress of the anchor cable is stable, and the safety production of the mine is guaranteed