Ziwei Qian

Ordinary cement slurry suffers from drawbacks such as rapid settling, low filling efficiency in micro-fractures, and poor injectability. To meet the requirements of grouting engineering applications, modification of the performance of ordinary cement slurry holds significant research value. This study aims to enhance the suspension properties, stone formation rate, and impermeability of the slurry by modifying it with sodium-based bentonite. Through basic performance testing and microscopic structural observation of the slurry, the study ultimately determined the optimal addition range of bentonite. Injection tests were conducted using a transparent pore channel model and a 3D-printed transparent rough single-crack model to validate the superiority of the modified slurry. The research results show that: adding approximately 3 % sodium-based bentonite to ordinary cement slurry significantly improves the slurry’s suspension properties, reduces water separation rates, and increases stone formation rates; in grouting experiments conducted using a transparent pore channel model, the optimal modified slurry (water-cement ratio of 1, bentonite content of 3 %) had a higher filling rate and longer grouting distance than ordinary cement slurry; in grouting experiments conducted on rough single-fissure models produced by 3D printing, the optimal modified slurry exhibited greater activity, diffusion speed, and diffusion area; in seepage tests conducted in the filled fissures formed by grouting experiments, the modified grout resulted in a 15 % increase in the Darcy factor and a 31.5 % decrease in permeability compared to ordinary cement slurry.

To address the challenges of water hazard control in the thick water-rich sandstone aquifer of the roof under monoclinal structure conditions at Panel 110504 of Wangwa Coal Mine, as well as the problems of excessive ineffective drainage and high cost associated with the traditional full-face pre-drainage method, a study on the coordinated technology of mining progress and roof water drainage was carried out. By analyzing the geological and hydrogeological conditions of the panel, it was determined that the height of the water-conducting fracture zone reaches 228 m, which has penetrated the Yan’an Formation and entered the sandstone aquifer of the Zhiluo Formation, forming a unified composite water-filling source from the two aquifers. Based on calculations using the Theis equation and field drainage tests, the stable drainage time was determined to be 95 d and the advance drainage distance 300 m. Accordingly, a coordinated technical scheme of “sectional drainage while mining” was proposed, optimizing the layout parameters of drainage boreholes and the division of drainage sections. Field application results show that this technology reduced the average water inflow of the panel by 255.94 m³/h compared with the traditional mode, cumulatively saved 5.1413 million m³ of drainage water, cut drainage costs by 20.5652 million CNY, and no water hazard occurred. The research results can provide a technical reference for mining coal seams with water-rich roof under similar monoclinal structure conditions.

In mining, the large amount of slurry used in grouting may harm groundwater quality and cause pollution. Therefore, researching the pollution effects of common grouting materials on regional groundwater is vital. A dynamic percolation reaction system was set up, and three sets of percolation tests were conducted for the ungrouted control (W), cement slurry (C), and cement-sodium silicate slurry (CS) groups. Their leachates were analyzed. The study found the following: (1) the slurry’s hydration reactions greatly affect ionic contamination in the leachate. (2) After grouting, most ions in the leachate had high initial concentrations but decreased as percolation continued. The ionic concentration trends varied. Cement grouting caused metal ion contamination like Ca²⁺, while CS grouting led to high SO2- 4 levels. The main pollutants’ degradation mostly follows an exponential decay model. (3) The leachate was alkaline after grouting, with increased total dissolved solids and reducing properties. Its hydrochemical type changed and gradually shifted towards that of the control group as percolation continued.

It is of practical significance to carry out a study on the pollution effect of typical chemical grouting materials on the regional groundwater quality. A dynamic seepage reaction system was developed, and constant-flow, long-term percolation tests were conducted on two groups: no grouting and urea-formaldehyde resin grouted group. The study found that UF slurry and its reaction products can cause significant pollution damage to groundwater quality, and grout contamination can last for quite some time before completely degrading. UF slurry can affect conventional water quality indicators of groundwater and can alter the water chemistry type of groundwater. The UF grouting process has a significant effect on the ionic content of groundwater. In the process of continuous infiltration, the hydrochemical type of groundwater gradually converges to that of the control group. The water quality indicators and ion content also gradually converge to the values measured in the control group. At the same time, the degradation of the main pollutants from the grouting process shows an exponential decay pattern.

Grouting in mining operations can potentially cause environmental pollution. The significant volume of slurry used in grouting can adversely affect groundwater quality, potentially resulting in groundwater pollution. In light of this, researching the pattern and mechanism of the impact of common grouting materials on regional groundwater quality is crucial. Based on the hydrogeological conditions of the study area, a dynamic seepage reaction system was established. Three sets of constant-flow, long-duration percolation tests were conducted for the ungrouted control (W), cement slurry (C), and cement-sodium silicate slurry (CS) groups. The leachate from each group was thoroughly analyzed to determine the water quality. The study found: (1) The hydration reactions of the phases present in the slurry have a significant influence on the nature and degree of ionic contamination in the liquid phase of the leachate. (2) After grouting, the leachate exhibited high initial concentrations of most ions. However, as infiltration progressed, the concentrations of these ions decreased significantly. Additionally, the concentration trend of some ions in the grouted leachate samples has a differentiated pattern. Cement grouted resulted in the contamination of metal ions, such as Ca²⁺, whereas CS grouted led to high levels of SO2- 4 contamination. (3) After grouting, the leachate was alkaline, with elevated total hardness and total dissolved solids, and exhibited reducing properties. The hydrochemical type of the leachate underwent significant changes after the grouting process. As the percolation continued, the hydrochemical characteristics of the leachate gradually shifted towards that of the control group. (4) The ionic concentrations in the leachate exhibit a trend of attenuation or rebound under percolation action, generally showing a dynamic recovery towards the control group concentrations. The degradation trends of the main pollutants for both types of grout largely conform to an exponential decay model.

The grouting operations have the potential risk of causing pollution to the environment during the mine management process. The large volume of slurry may have an impact on groundwater quality and even lead to groundwater pollution. Given this, it is of vital significance to carry out research on the pattern and mechanism of the impact of typical grouting materials on regional groundwater quality, in order to assess the degree of grouting pollution, and the degradation cycle, as well as to attenuate, prevent and control the adverse impacts brought about by it. Based on the hydrogeological conditions of the study area, a dynamic seepage reaction system was established. Constant flow long-term percolation tests were conducted for three groups: a control group without grout (W), a cement-grouted (C), and a (cement-sodium silicate)-grouted (CS). Comprehensive water quality analyses were performed on the corresponding leachate samples. The study found: (1) In the later stages of the experiment, white flocculent precipitates were observed in the cement-grouted leachate (C group), while the leachate from the cement-sodium silicate grouted (CS group) initially appeared yellow. (2) In the C group, the leachate led to the formation of Ca(OH)₂ (CH) crystals on the surface of the sand grains, whereas the leachate in the CS group altered the surface morphology of the sand grains. (3) After grouting, the initial leachate exhibited high concentrations of most ions. However, as infiltration progressed, the concentrations of these ions decreased significantly. Additionally, the concentration trend of some ions in the grouted leachate samples has a differentiated pattern. (4) After grouting, the leachate was slightly alkaline, with elevated total hardness and total dissolved solids, and exhibited reducing properties. The hydrochemical structure underwent significant changes. (5) Different patterns of pollution degradation due to the ring-band structure of the grouting stone body. (6) The ionic concentrations in the leachate exhibit a trend of attenuation or rebound under seepage action, generally showing a dynamic recovery towards the control group concentrations. The degradation trends of the main pollutants for both types of grout largely conform to an exponential decay model.

The study of fissure seepage and grouting diffusion, seepage reduction law is of great significance for the prevention and control of water damage in fissured rock bodies. To this end, a visualization test model based on the morphology of real rock fissures was prepared in bulk using 3D scanning and 3D printing technology, and tests were carried out to realize the visualization of seepage flow in a single fissure, grouting with different water-cement ratios, and seepage flow after the fissure grouting was consolidated and filled. The test results show that: compared with grouting diffusion, the seepage of water injection into the fissure is different in activity and coverage; the rough single fissure seepage shows nonlinear flow characteristics, and is a composite flow form of laminar and turbulent flow; the grouting into the fissure has the effect of climbing and swooping, and the diffusion rate and filling rate of the grout are obviously different under different water-cement ratio conditions; after the grout is filled and consolidated in the fissure, the permeability coefficient of the fissure is greatly reduced, and the seepage performance is significantly different. After the slurry is filled and consolidated in the fissure, the permeability coefficient is greatly reduced, and the seepage flow is nonlinear, which conforms to the Forchheimer's equation, and with the decrease of the water-cement ratio of the cement slurry, the coefficient of the linear term decreases, and the coefficient of the nonlinear term increases and accounts for a larger proportion in the binomial.