Search

Deep mining of resources has destroyed the stress balance of original rock, formed water gushing channel, and caused the outburst of confined water, thus causing disaster. At present, "Ground Controlled Directional Bedding Branch Drilling (GCD-D)" grouting has achieved remarkable results in controlling water disasters. However, "what is the scientific design principle of GCD-D?" This key scientific question has not yet been answered by systematic science. According to the regional engineering geology and hydrogeological conditions of North China-type coalfields, this study uses the methods of analogy, theoretical analysis, and model analysis to demonstrate and analyze and obtains six basic principles for the selection of the target layer for the layout of "GCD-D." The design principle of "GCD-D" was put forward for the first time. The results can provide a scientific theoretical basis for the control of confined water disaster in deep mining of North China coalfields. [ABSTRACT FROM AUTHOR]

To solve the problem of a rapid attenuation of gas concentration along with drainage borehole collapse in the tectonic coalbeds of South China, a constant pressure grouting technology with inorganic, noncondensable material was proposed. Firstly, the slurry fluidity, water separation rate, and sealing performance of the inorganic sealing materials were tested under different water-cement ratios. The seepage model of slurry in a layer-through borehole was built with COMSOL Multiphysics simulation software, to explore the scopes of loose circles around drainage roadway and borehole, and to analyze the seepage capacity of the slurry under different grouting pressures. Eventually, the sealing performance of the slurry was investigated in the field. The results showed that the inorganic, noncondensable material with the water-cement ratio of 5 : 1 has a strong fluidity, low water retention, high permeability, and good sealing performance. After the excavations of No.2164 drainage roadway and layer-through borehole, there are obvious stress concentrations both at the shoulder corners of the roadway and at the borehole bottom, and the scope of the loose circle around the roadway is about 6.2 m. The effective seepage radius of the inorganic slurry gradually increases with a rising grouting pressure, and the slurry seepage range in the sandstone section is broader than that in the mudstone section. Adopting the constant pressure grouting technology with the slurry, the average drainage concentration of boreholes in Puxi coal mine is 51.5%, and the average gas flow rate is 0.005 m3/min, which are 1.35 times and 1.67 times than those with the cement grouting method. [ABSTRACT FROM AUTHOR]

Floor grouting reinforcement and aquifer reform can effectively improve the water barrier performance of fractured rock mass, which is widely used to prevent water inrush from a confined aquifer in theClean Utilization and SDUST Research Fund floor. In order to reveal the mechanical and strain energy characteristics of fractured rock mass after grouting with different grouting parameters, the discrete element numerical simulation software PFC is used to study the mechanical and strain energy characteristics of limestone after filling the fractures with cement stones with different parameters. The numerical test results show that the displacement of the limestone grouting stone bodies with a longer prefabricated crack length decreases more obviously after grouting, and the strain energy, dissipation energy, and total input energy increase when the strengthened limestone sample is destroyed. The greater the stiffness of the cement stone, the easier the limestone grouting stone bodies will be destroyed from the position of the prefabricated crack. The internal friction angle of cement stones has little effect on the strength, deformation, and energy characteristics of limestone. Under the same cohesion, the number and the distribution range of secondary cracks of limestone grouting stone bodies with smaller prefabricated crack length are larger. However, with the increase of the tensile strength of the cement stones, the number, distribution range, and strength of the secondary fractures of the limestone grouting stone bodies are increasing. The longer the prefabricated crack is, the greater the influence of grouting parameters on the rock. The study provides a reference for the selection of reinforcement material parameters during grouting reinforcement. [ABSTRACT FROM AUTHOR]

To predict and prevent the collapse and mud inrush caused by the deep karst trough in tunnels, an engineering case is studied. Firstly, a comprehensive identification method for the hazard-causing structure of the deep karst trough in tunnels is proposed and successfully applied. Secondly, the morphological characteristics and developmental mechanism of the deep karst trough are studied. The hazard-causing structure is mainly developed at the entrance section of the karst tunnel, which is funnel-shaped, mostly filled with clay and a small amount of gravel. The development scale is affected by the geological structure, tectonic movement, formation lithology and inclination, sunshine and precipitation, and surface soil. Thirdly, four hazard-causing modes of the collapse and mud inrush are proposed, i.e., rock mass failure of tunnel face, direct exposure of tunnel face, direct exposure of tunnel roof, and rock mass failure of tunnel roof. Finally, a treatment technology for collapse and mud inrush is put forward. The treatment technology is to "remove the mud, fill the karst cave, conduct advance grouting, strengthen the support, waterproof the collapse area, backfill the collapse pit." The collapse and mud inrush of Qiyueshan Tunnel was successfully treated by using the above technology. [ABSTRACT FROM AUTHOR]

The slurry diffusion radius is an important parameter in grouting engineering. In some cases, injection into partial overburden is needed in grouting engineering, and it is thus critical to control the slurry diffusion so as to reduce unnecessary grout take. In an effort to solve such issues in longwall overburden grouting, we proposed the addition of cement as a means of modifying fly ash slurry in order to reduce grout diffusion and grout take. The characteristics of the modified slurry were determined under different water-ash ratios and cement-blending ratios. The cement-blending ratio was found to have a small effect on the density of the slurry but a significant effect on the slurry's precipitation rate and viscosity. The slurry diffusion experimental system was established to study the diffusion radius and consolidation. Results for both the fly ash slurry and the modified slurry revealed a circular diffusion pattern centered around the grouting borehole. The diffusion radius of the modified slurry made with 10% cement was 19.4% lower than that of the fly ash slurry, but its solidification thickness appeared to increase. The modified slurry diffusion had a two-stage effect: a "stability control stage" and a "consolidation control stage." In the consolidation control stage, the diffusion radius of the modified slurry was smaller than that of the fly ash slurry, and this stage was the key to control the diffusion radius of the slurry. Field trials were conducted based on the results of the study, and grout take was reduced effectively. This research provides a theoretical basis for slurry diffusion radius control in longwall grouting. [ABSTRACT FROM AUTHOR]

Based on the failure of the initial grouting scheme in tunnel engineering, an integrated geological forecasting system incorporating an industrial endoscope was used to detect watery karst areas in this tunnel. Numerical simulations were used to analyze the change patterns of arch top settlement, arch bottom bulge, and water surge in the tunnel under different grouting thicknesses. Compared to the displacement of the support structure, curtain grouting thickness is mainly reflected in reducing the amount of water surge. When the grouting thickness exceeds 5 m, the water-stopping effect of the tunnel is almost unchanged. Finally, a grout thickness of 5 m and a grout length of 25 m were selected as the grouting range for this project. During grouting, the combination of the three grouting techniques can effectively solve the problems of high water surges and difficult hole formation. The principle of "combination of exploration and injection" was followed to obtain real-time geological information and optimize the subsequent grouting plan. After the grouting, the grouting evaluation results and the field construction conditions showed that the grouting effect was good. [ABSTRACT FROM AUTHOR]

Grouting is a common method used in reinforcing fractured rock, and it is important to study the crack evolution and mechanical properties of fractured rock after grouting under the influence of different excavation rates and crack geometries. Therefore, a set of grouting molds for small-sized specimens with fully penetrated cracks were designed. The crack formation location and penetration mechanism of grouted bodies with different crack inclinations using uniaxial compression tests with different loading rates were investigated. The crack extension process and energy concentration areas of the grouted plus solid specimens at different stages were revealed from the acoustic characteristic. The results show that the peak strength of crack-grouting sandstone decreases with the increase of crack inclination under the same loading rate. Comparisons of the crack inclination in slurry specimens under different loading rates imply that there is a critical value of crack inclination at 45° which concentrates the damage and cracking of the grouted body under compression within the grouted solidified body. When the crack inclination is small, the specimen is mainly extended from the crack of the rock block at the upper end of the grout consolidation to the lower end of the crack surface, and the acoustic emission ring count data mainly show a rising trend throughout the whole process, when the crack inclination is large, cracks are mainly produced around the surface subjected to grout consolidation and gradually expand to the interior of the grouted body, and there is almost zero growth in the ringing count in the elastic stage (II) and a larger growth in the ringing count in the yielding stage (III) and postpeak stage (IV). This research work can provide disaster prediction and theoretical guidance for the corresponding engineering construction of crack-grouting sandstone. [ABSTRACT FROM AUTHOR]

In underground engineering, the fracture dip angle and three-dimensional stress have great influence on the permeability and mechanical properties of fractured rock mass. Firstly, single-fracture samples with similar three-dimensional fractal dimensions and different dip angles were selected by using CT scanning technology. Then, the grouting material seepage tests under different dip angles and different three-dimensional stresses were carried out by self-developed single-fracture stress-seepage coupling true triaxial test system. The experimental data of stress-strain curve, grouting pressure, and grouting material flow rate of single-fracture specimen under different fracture dip angles and three-dimensional stress were obtained. The results show that the three-dimensional fractal dimension can be used as an index to measure the influence of fracture factors on grouting seepage test. The third principal stress σ 3 had a greater influence on the fracture width than the first principal stress σ 1 . The larger the fracture inclination, the lower the strength of the single-fracture specimen. As the third principal stress σ 3 increases, the grouting pressure increased while the grouting flow decreased. With the increase of the fracture inclination angle, the influence of σ 1 on the hydraulic conductivity became larger, while the influence of σ 3 on the hydraulic conductivity became smaller. Moreover, the expression of hydraulic conductivity of single-fracture specimen with different dip angles under three-dimensional stress was obtained by nonlinear fitting of hydraulic conductivity data. [ABSTRACT FROM AUTHOR]

At present, polyurethane (PU) has been extensively used as a grouting material in civil engineering. The mechanical properties of PU are the key to achieving the desirable grouting effect. This study presents the research results of the mechanical behavior of PU matrix under tensile, successive cyclic tensile, and stress relaxation at the nanoscale, using the coarse-grained molecular dynamics simulation method. The influences of the number of molecule chains and strain rate on the tensile mechanical properties are discussed, and the tensile deformation mechanism of PU matrix is revealed. The tensile strength of PU matrix is independent of loading path, and after yielding, the strain of PU matrix contains the elastic strain, plastic strain, and viscous strain. In the stress relaxation process, the evolution of the axial stress is mainly caused by the varied van der Waals interactions. The stress relaxation behavior of PU matrix can be described by the viscoelastic model consisting of one elastic element in parallel with one Maxwell element. [ABSTRACT FROM AUTHOR]

The geostress in deep coal roadway is high and affected by mining frequently; under the influence of water-rock interaction, the bearing capacity of coal continues to deteriorate. Based on the characteristics of short water absorption process and low moisture content of deep coal samples in this experiment, the threshold range of quantitative division of water absorption stage of coal samples is given, and the structural characteristics of deep coal samples that are more susceptible to cracks are analyzed. The actual loading process is simulated through uniaxial stepwise high stressed loading and unloading experiments, the gradual development of cracks was the root cause of instability of coal, and saturated water mainly aggravates the instability process through these cracks; the stepwise high stressed loading and unloading path makes cracks more likely to occur in the sample. After each level of loading and unloading, the average stiffness is approximately linear trend degradation. By calculating the energy density of deep coal samples in each stage before the peak, the change of energy density indexes between saturated and dried samples is different from relative shallow samples, and the energy density indexes do not decrease but increases instead. However, the proportion of each energy is generally positive and inverted "U"-type distribution. The change trend of plastic energy in proportion to dissipation energy can be used as the judgment feature of coal sample instability. The instability of deep coal samples is mainly caused by the gradual dissipation of plastic energy to generate cracks and divided into fragments with large and long edge, resulting in low mass fractal dimension. In engineering practice, the loading times should be reduced and the suitable pressure grouting should be conducted timely to delay the deterioration process of crack development in deep water-bearing coal under high stress disturbance. [ABSTRACT FROM AUTHOR]

It is of great engineering significance to study the seepage characteristics and flow field distribution of rough fractured rock masses for grouting to stop leakage. Through the visual fracture seepage test device we developed, the visual seepage characteristics of tension fractures under vertical angles and different stress paths of grout and water were studied. Through silica gel secondary mould turning technology, the fracture morphology is accurately reprinted; based on GIS simulation technology, the visualization of the fracture surface spatial data is realized; the actual seepage area and flow path of the fluid are measured accurately by using digital image self-recognition technology, and the variation law of the grout and water seepage area under the coupling of normal stress and water pressure is obtained. Through visualization, it is pointed out that, with the increase of normal stress, the fracture water can be divided into three stages, archipelago flow, transition flow, and groove flow, while the grout has no capillary permeability and no archipelago flow effect because of its high viscosity. The critical point of grout antiseepage is defined and calibrated by data. Based on the analysis of the cross-sectional velocity of the groove flow, it is pointed out that the relationship between the velocity on the flow path and JRC is an exponential function. The main flow path is mainly distributed in the area where the JRC is relatively small. As the normal stress increases, the first deflection point of the grout flow path appears in the maximum region of JRC (6.42); the secondary deflection point appears in the second largest region of the flow path JRC (4.53), and the fluid of deflection point has the maximum kinetic energy on the main flow path. The current study can accurately obtain the relevant parameters of vertical fracture grouting seepage characteristics and provide theoretical guidance for solving the key scientific problems in grouting engineering, such as invisible flow paths and unmeasurable velocity vectors. [ABSTRACT FROM AUTHOR]

Taking China's first application of domestic shield tunneling in a water-rich sand layer for crossing a high-speed railway as research background, the influence of changes in the shield tunneling parameters on ground settlement is analyzed based on field tests, and a construction control method suitable for shield tunneling under a risk source in a water-rich sand layer is proposed. The test results show that the use of 10% sodium bentonite as the soil modifier for soil pressure balance shield tunneling into the water-rich sand layer has advantages, while adding 50% loess into the bentonite slurry in the gravel sand layer can greatly improve the impermeability of the soil; the settlement of soil can be effectively reduced by using the special segment with grouting holes for deep grouting and applying the adaptive transformation of the shield cutter. Based on the statistical analysis results, a reasonable range for the cutter head torque, cutter head speed, chamber pressure, bentonite injection volume, and advanced speed in the water-rich sand layer can provide a construction control basis for similar projects and provide data support for the compilation of relevant specifications. [ABSTRACT FROM AUTHOR]

Grouting treatment is the main technology to reduce or eliminate the residual deformation and activation deformation of foundations in the goaf sites. Under the influences of the overburden of the mining, the distribution of grouting in goaf foundation is quite different from that of conventional grouting mechanism in porous media. In this paper, considering the time-dependent viscosity and diffusion path of the slurry, the conventional permeation diffusion mechanism of Bingham fluid is derived based on the seepage motion equation in porous media. The theoretical formula is modified according to the fracture distribution characteristics of caving zone and fault zone of the goaf foundation and the superposition effect of porous grouting. Combined with the laboratory test, the theoretical formulas for four working conditions ((i) only considering the time-dependent viscosity, (ii) considering the time-dependent viscosity and diffusion path, (iii) combining the fracture distribution characteristics of goaf foundation, and (iv) combining the fracture distribution characteristics and the superposition effect of porous grouting) are verified, respectively. The results of theoretical formula are used to compare with the design scheme of an engineering example. The research results have an important engineering significance for revealing the mechanism of seepage grouting in goaf foundation and designing the optimal spacing between grouting holes. [ABSTRACT FROM AUTHOR]

The deep coal mining in the North China type of coalfield is generally threatened by the underlying limestone water of Taiyuan Formation and Ordovician. The occurrence of water inrush can be avoided effectively by applying grouting reinforcement technology to the coal floor. However, the reinforcement treatment of the coal floor belongs to underground concealment engineering, and it is of great significance for the safe production of the coal mine by scientifically and comprehensively evaluating the technical method of the grouting effect on the working face floor. In this study, the optimal transfer matrix is used to construct the judgment matrix that meets the consistency requirements; the analytic hierarchy process is improved; and the grouting effect of the working face floor is evaluated by fuzzy comprehensive evaluation based on several factors of the grouting effect. Taking the grouting engineering of the 15092 working face of the Guhanshan Mine as an example, the evaluation of the grouting effect based on four evaluatory indices have been refined: dynamic hydrological features, grout amount, grouting inspection hole, and geophysical prospecting have been refined. Based on the improved analytic hierarchy process (AHP), the result of the grouting effect can be divided into four levels: distinction, good, average, and poor. The study would play a very important role in the evaluation of the grouting reinforcement of the working face floor and the practice of coal mine production safety. [ABSTRACT FROM AUTHOR]

In order to improve and restore the strength and stability of broken overburden caused by coal seam mining in underground, the grout containing aggregate is employed to backfill specific fracture space in rock strata, which is an important method to prevent the mine water leakage and roof collapse in working face. Therefore, the migration characteristics and restoration mechanism of grout containing aggregate in overburden fractures based on the CFD-DEM coupling model are researched in this paper. Specifically, the mechanical constitutive model of aggregate migration is obtained by mechanical analysis of particles and flow field, and the mechanism of aggregate flow and transport with grout in rock fracture is put forward. Besides, the coupled CFD-DEM model is built by numerical simulation software, and the transport process of grout containing aggregate in the fracture is numerically calculated. On this basis, the transport law and deposition characteristics of aggregate transport with grout are studied, and the inner mechanism of the change law is obtained. The research results indicate that the aggregate is gradually deposited by various "settlement forces" during the migration process. The smaller the particle size and density of aggregate are, the slower the deposition rate of aggregate particles and the longer the migration distance are. The aggregate with particle size of 3 mm and density of 3250 migrates 1.25 m to reach the maximum solid ratio of 12.9%. The settlement ratio reaches 100% after migration of 1.5 m, and the longest migration distance is 1450 mm. In addition, the solid ratio of each aggregate firstly increases and then decreases with its migration, which is analyzed from the perspective of aggregate deposition and concentration change. When the aggregate density of two particle sizes changes from 3500 to 3750, the aggregate migration distance is significantly reduced. The research results provide an important guiding significance for reasonably selecting aggregate parameters and optimizing the design of grouting holes in mining engineering. [ABSTRACT FROM AUTHOR]

Synchronous grouting is the key factor causing segment floating during the construction of shield tunnel, especially the grout ratio and the control of the grouting pressure. In this paper, the ratio of grout material was optimized through multiple groups of physical and mechanical tests. The results showed that 0.3% content of water reducing agent in grout could improve the ability of water resistance significantly. 2.9% content of bentonite could reduce bleeding rate of grout and grout setting time and improve the fluidity in the meantime. Then, the distribution law of grout along the segment ring in the filling stage was studied based on a typical underwater tunnel in China. The results showed that the theoretical calculation of grouting pressure was between 0.15 MPa and 0.18 MPa, which were in good agreement with the measured data. The grouting pressure distribution is affected by four parts including the lateral earth pressure, foundation reaction, grout shear stress, and gravity. [ABSTRACT FROM AUTHOR]

In slurry pipe jacking, lubricant slurry is commonly used to sustain against the displacement and pressure of the overcut area and reduce the interface friction of pipelines. Therefore, a reasonable grouting pressure should ensure the stability of surrounding soils, which is raised as a new method in this study. Not only ensure the grouting pressure is not too small to support the stratum effectively and reduce the frictional resistance but also ensure that the grouting pressure will not be too large to produce excessive deformation and affect the surrounding environment. First of all, the influence of grouting pressure on the stability of surrounding soil is analyzed, and the mechanical model of slurry grouting expansion is established. Then, the minimum grouting pressure is designed from the critical balance between radial expansion tension by grouting and loose earth pressure by jacking excavation, and the maximum grouting pressure is designed from the critical expansion pressure caused by grouting splitting. Finally, the rationality of grouting pressure design is proved by the engineering example of a slurry pipe-jacking project near Haikou Meilan Airport and on-site GPR detection test. All these work aims to raise a new theoretical solution of grouting pressure and provide theoretical reference for similar projects. [ABSTRACT FROM AUTHOR]

This paper presents a prediction method of mining-induced surface subsidence due to longwall mining with overburden grouting, which has been proven an effective method to mitigate the overburden failure. This paper proposes a partial overburden grouting (POG) mining method based on surface subsidence basin inversion and innovative longwall panel layout to mitigate overburden failure and subsidence. A prediction model of surface subsidence with overburden grouting, namely, overburden grouting equivalent calculation model (OGECM), is proposed. In this study, an engineering design process and method of POG was established, the strike and dip excavation length and grouting quantity combined as critical indicators for determining the key parameter in surface basin control. In applications at the field grouting test, the surface subsidence characteristics of POG on the side of the opening line of longwall panel were investigated through surface observation station and estimated surface subsidence reduction ratio based on OGECM with grouting compared with those without. The field measurement validated the new subsidence calculation method. POG technology applied to subsidence control has effectiveness in controlling the surface subsidence to less engineering cost but expanding the applications. [ABSTRACT FROM AUTHOR]

As the problems of serious bottom drum and roadway broken surrounding rock are influenced by repeated mining in multiple coal seams, the factors affecting the surrounding rock deformation of a +980 m roadway in Faer coal mine by analyzing the rock composition and obtaining borehole video data are investigated. The mechanism of the overburden caving affected by repeated mining of multiple coal seams is analyzed theoretically, and the numerical simulation is conducted to evaluate the deformation mechanism of roadway bottom drum. A combined support technology is proposed consisting of bolts, anchor cables, grouting, and pressure relief grooves. The measurements obtained during a 50 d monitoring period indicate that the deformations of the roof, floor, and both sides of roadway in the repaired and reinforced section are only 26, 56, and 26 mm, respectively. The fissures filled with slurry in the rock surrounding roadway can prevent further deformation of the rock mass. [ABSTRACT FROM AUTHOR]

The fractured limestone aquifers under coal seams bring great threat to coal production, and grouting engineering before mining is usually used to seal the fractures and prevent water inrushes. However, the grouting mechanism is still a difficult issue since the hidden fissures cannot be observed. In this paper, two characteristics of fractures filled with high-pressure water, deformation, and stiffness are studied to seek some good explanations for grouting. First, an ideal flow model composed of a borehole and a fracture is established with the fracture aperture as the main variable. The estimation methods for the aperture of fractures with high-pressure water before grouting and the stiffness of the fracture filled with slurry consolidating body during high-pressure grouting are proposed, and the millimeter-scale solution of deformation is obtained by using hydrological data and slurry consolidating body. Then, the methods are used for the field grouting practice, and its applicable conditions are given. The estimated apertures of the fractures with high-pressure water range from 2.08 to 2.56 mm. Under the grouting pressure of 15 MPa and the designed slurry diffusion radius of 30 m, the normal stiffness of the fracture filled with slurry consolidating body ranges from 0.5 to 14.4 GPa/m. The results meet the positive relationship between normal stiffness and fracture aperture got by the literature data and can be used for the study of grouting effect of the hidden fractures, including the evaluation of strength and water resistance of the slurry consolidating body. Our method of estimating the aperture and stiffness of fractures is applicable when grouting is used in the fractured limestone aquifers with high water pressure under coal seams before mining. [ABSTRACT FROM AUTHOR]

Grouting technology is widely used to improve the mechanical properties and reduce the permeability of the rock in underground engineering. Fluidity is important to promote the grout to be injected into longer fractures, so chemical grouts with low viscosity and adjustable gel time are usually chosen to increase this property. However, the high temperature in some deep engineering leads to a faster hydration rate of the chemical grout than that in the room temperature environment, resulting in the decrease of fluidity. The heat exchange between the grout and the environment is usually ignored in the existing researches, so the aim of the numerical study is therefore to analyse the seepage process of chemical grout in the temperature field, where heat exchange between the grout and environment is considered. A sandstone model with a fracture is established in COMSOL, which is validated using laboratory experiments to confirm the accuracy of the results. The grouting time rises exponentially with the increasing of the flow distance in a single fracture, and a higher environmental temperature leads to a larger grouting time because the gap in the viscosity of the grout at different temperatures enlarges with the increasing hydration time. The effect of the temperature field on the grouting time becomes more significant when the temperature is higher and the hydration time is longer because the viscosity of the grout rises more slowly. The grouting time reduces dramatically when injection pressure is raised because an increasing pressure results in a larger aperture and less hydration time, which is one of the best ways to improve the efficiency of the grouting. The findings of this study can help for better understanding of the seepage process of chemical grout in fractures under high temperature and provide guidance for the selection of chemical grout in grouting engineering. [ABSTRACT FROM AUTHOR]

Cement-based grout has been widely used in various civil engineering applications. However, the filtration behaviors of it when grouting the porous geological masses vary a lot under different grouting conditions, which significantly influences its penetration and the enhancement effect. The purpose of this work was to better understand the filtration of cement-based grout in porous sand by conducting a series of visualized laboratory tests and EDTA titration tests. The experimental results show that the cement filtration, including the penetration, retention, and formation of cement filter cake above the grouting body, is collectively influenced by different grouting factors. With the increase of the soil samples' pore size and the cement slurry's water-cement ratio, the penetrated distance and amount of cement in sand increase. However, the penetration does not increase monotonically with the grouting pressure. Too excessive grouting pressure (e.g., 300 kPa in this study) accelerates the formation of cement filter cake and thus stops the subsequent cement infiltration. The mechanisms of different filtration behaviors were explained from microscopic particle clogging in the pore throat of the porous media. Furthermore, the reduced permeability of the sand column with the retained cement due to filtration was discussed, and the dewatering phenomenon of the cement slurry after filter cake formation was first revealed. [ABSTRACT FROM AUTHOR]

Reasonable determination of the water pressure on the shaft linings is the key to the optimization design of the vertical shaft of mining. The traditional water pressure calculation model is not suitable for the stratum conditions in western China. A new shaft-surrounding rock seepage model is proposed based on the coordinated seepage conditions of surrounding rock and shaft linings. In the model, the seepage within the shaft depth is assumed happening in a unit thickness confined aquifer. Thereby, the water pressure on the shaft linings is derived by the steady seepage theory, and the water pressure reduction coefficient is defined by normalizing the hydrostatic pressure. The influences of shaft diameter and shaft depth, the permeability coefficient of the surrounding rock, and the seepage flow on the water pressure reduction coefficient are analyzed. After that, the mechanism of reducing water pressure by grouting the surrounding rock is studied by considering the stratum conditions in western China. Finally, a practical equation, which only relating to the depth of the shaft, is fitted on account of the averaged water pressure reduction coefficient from the theoretical model. The effectiveness of the theoretical model and the fitted equation are verified by the measured data and data in the literature. [ABSTRACT FROM AUTHOR]

In this study, the role of the pedrail powered (PP) support produced in China in the Wongawilli short-wall mining was explored, and the process from its import and introduction to its localization and use effect were detailed. The influences of the gob side and the solid-coal side on the pillar pressure were numerically simulated by exploring the working resistance of PP support at different locations and under different widths of pillar between mining caves (PMC) of the same branch lane during mining and investigating the pressure distribution and variations of each single pillar. The main influencing factors and their relationships with the working resistance were derived accordingly. Finally, key processing technologies to solve the problem of PP support crushing in the crushed zone were analyzed. The results suggest that the rated working resistance of PP support satisfies the requirement for use, and the roof of the branch lane behind the cutting roof line does not collapse, which ensures the safety of short-wall mining. The gob-side pressure is notably higher than the solid-coal-side pressure. When the PP support undergoes a support crushing accident, it can be pulled out by jointly adopting four key technologies, i.e., reinforced support to the roof, reinforcing rib support and ground bolt support for caving gangue piles, roof and loose body reinforcement by grouting, and traction by a prop-pulling winch. [ABSTRACT FROM AUTHOR]

Grouting in deep, loose layers are a complex process in which many modes such as infiltration, splitting, and compaction coexist. It is of great significance to establish a realistic, simplified physical model to study the law of slurry diffusion. Herein, a cylindrical diffusion model of radial tube flow is established, and the control differential equations of both the Bingham slurry diffusion velocity in a single tube and the diffusion velocity of the radial tube flow are deduced. Additionally, the calculation formulas for the diffusion radius and slurry pressure distribution function are obtained. The rationality of the theory is verified by combining our results with those of the field grouting test of the Guotun coal mine. The results show that the cylindrical diffusion model of radial tube flow can successfully characterize the slurry diffusion law of grouting in a deep, loose layer. The slurry pressure attenuation shows distinguishable stages: within the first 30% of the diffusion radius, the slurry pressure decreased sharply by approximately 70%, and the slurry pressure decreases slowly in the later stages. Furthermore, the diffusion radius has a nonlinear, negative correlation with the height of the grouting section and the comprehensive injection rate of formation; the change rate is relatively more gradual, and there are no distinguishable stages. The research results provide a theoretical basis for reasonably determining the grouting parameters of deep, loose layers in the future. [ABSTRACT FROM AUTHOR]

During downward mining of a bifurcated coal seam, the roof of the lower coal seam is relatively broken and difficult to control due to the mining influence of the upper coal seam. Roof accidents occur frequently during mining of the lower coal seam, reducing mining efficiency. How to ensure safe and efficient mining of the lower coal seam is a significant issue. In this paper, overlying strata migration and fracture characteristics of the lower coal seam, the structure and stability of the regenerated roof, and porosity and permeability characteristics of the overlying strata under the mining influence of the upper coal seam are studied by using similar simulation tests. Results show that the overburden structure of the lower coal seam is altered due to the mining influence of the upper coal seam, and the regenerated roof of the lower coal seam is divided into three structural types from top to bottom, namely: intact rock mass+block fracture rock mass+loose rock mass (type I structure); intact rock mass+block fracture rock mass+loose rock mass+cataclastic rock mass (type II structure); and intact rock mass+block fracture rock mass+loose rock mass+cataclastic rock mass+slab-rent rock mass (type III structure). The stability of each type of rock mass structure is evaluated, and the stability of three types of rock mass structures is III > II > I. The overburden porosity and slurry permeability coefficient are relatively large at the cutting hole and stopping line. The porosity of the caving zone within 70 m of the cut hole and stopping line is greater than 5%, and the permeability coefficient is greater than 0.1 m/s. Based on differences in the surrounding rock porosity and permeability characteristics, the grouting difficulty of overburden is divided into three types of areas: extremely easy grouting areas, easy grouting areas, and difficult grouting areas. The results of this paper can provide reference for the stability evaluation of the regenerated roof and the selection of grouting treatment parameters for the broken roof under similar conditions. [ABSTRACT FROM AUTHOR]

Deep-buried tunnel at high-ground temperature is prone to the sudden surge of water when crossing the water-rich formation, resulting in casualties and economic losses. Slurry injection is a common and effective method of governance for addressing this issue. However, there has been little research into pulping at high-ground temperature, with most of the existing research focusing on room temperature conditions. We studied two kinds of slurry commonly used in grouting, cement slurry and cement-sodium silicate slurry. Indoor testing was used in this paper to clarify the effect of temperature on slurry viscosity, and numerical simulation was used to study slurry diffusion in flat cracks at different temperatures. The results showed that in a hydrostatic environment, the spread rate of slurry was independent of temperature and type of slurry. For the same kind of slurry, the higher the temperature, the greater the maximum slurry pressure. The higher the temperature in a flow environment, the faster the slurry diffusion. As the temperature rised, the grouting pressure required for crack sealing decreased at first then rises. In a flow environment, the sealing effect of cement-sodium silicate slurry was superior to that of cement slurry. [ABSTRACT FROM AUTHOR]

In the treatment of goafs in traffic engineering, technical problems such as those related to large-volume grouting and the precise control of material properties are often encountered. To address these issues, we developed a new composite material comprising cement-fly ash-modified sodium silicate (C-FA-MS). The setting time, fluidity, unconfined compressive strength, and microstructure were varied for different proportions of cement-sodium silicate (C-S) slurry, cement-fly ash-sodium silicate (C-FA-S) slurry, and C-FA-MS slurry, and their performances were compared and analysed. The experimental results showed that the initial setting time of the slurry was the shortest when both the original sodium silicate volume ratio ( V S ) and modified sodium silicate volume ratio ( V MS ) were 0.2. The final setting time of the C-S and C-FA-S slurries tended to decrease but then increased with decrease in V S , while that of the C-FA-MS slurry increased with lower V MS . The fluidity of the C-FA-S and C-FA-MS slurries decreased with decrease in V S or V MS at different fly ash admixture ratios. The consolidation compressive strength of C-S increased with decreasing V S , while that of C-FA-S showed a considerable increase only when V S decreased from 0.4 to 0.2. Meanwhile, the compressive strength of the C-FA-MS concretions first increased and then decreased with decrease in V MS . Microstructural analysis revealed that there were more cracks in the C-S agglomerate, the fly ash in the C-FA-S agglomerate reduced the relative density of the skeletal structure, and the stronger cross-linking in the C-FA-MS agglomerate improved the strength of the agglomerate. Under the condition of unit grouting volume, the cost of the C-FA-MS slurry was approximately 44.7% and 31.3% lower than that of the C-S and C-FA-S slurries, respectively. The new C-FA-MS material was applied for the treatment of the goaf in the Wu Sizhuang coal mine. Core drilling detection and audiofrequency magnetotelluric survey revealed that the goaf was sufficiently filled. [ABSTRACT FROM AUTHOR]

The rheological properties of cement grouts are significantly affected by the changes of the time and the water-cement ratio, which determine the diffusion state of grouts in rocks and soils and influence the outcome of projects. In this study, Portland cement grouts with water-cement ratios of 0.50, 0.55, 0.60, 0.65, 0.70, and 0.75 at six moments, including 0 minutes, 5 minutes, 10 minutes, 20 minutes, 30 minutes, and 60 minutes, were evaluated to figure out the comprehensive effect of the time and the water-cement ratio on the rheological properties of power-law cement grouts. The results showed that the water-cement ratio had a great influence on both the consistency coefficient and the rheological index of the power-law cement grouts. The former appeared to have a downward trend with the increase of the water-cement ratio, and the latter appeared to have an upward trend. There was a rising tendency between the time and the consistency coefficient, while the rheological index was less affected by time. The difference between its maximum and minimum values was within 5%. Combined with the perspectives of statistical theory, practical applicability, and accuracy, the exponential model was the optimal model for showing the relationship between the comprehensive effects of the time, water-cement ratio, and consistency coefficient of the power-law cement grouts. The linear model was the optimal model of the rheological index based on the comprehensive effect of time and the water-cement ratio. Based on this, a power-law rheological equation with consideration of the comprehensive effect of time and water-cement ratio was established. The research results could not only improve the rheological theory of power-law cement grouts but also provide technical support for engineering practice. [ABSTRACT FROM AUTHOR]

In this study, the deformation characteristics and mechanical properties of coal and rock mass in the S2N5 working face of the Xiaokang coal mine are analyzed to address the problem of large deformation of soft rocks with high in situ stress surrounding roadways. Through a newly developed grouting pipe, a double-shell grouting technology, consisting of low-pressure grouting and high-pressure split grouting, is proposed for the Xiaokang coal mine. In addition, the effect of grouting is evaluated by borehole peeping and deformation monitoring. The results show that the double-shell grouting technology can effectively improve the overall mechanical properties of the surrounding coal and rock mass, preventing the large deformation and failure of the roadway. This technology can be useful when analyzing and preventing large deformation of soft rock roadways. [ABSTRACT FROM AUTHOR]

Diffusion radius is an important construction parameter, because it can significantly influence the grouting effectiveness. Theoretical models in predicting diffusion radius have been practiced, but there are still significant discrepancies between theoretical calculations and realistic results in the practical construction. One of the critical reasons for the misprediction is the time-dependent behavior of the cement grout, which is significantly affected by the water-cement ratio (W/C). Therefore, this paper experimentally and numerically studies the influence of W/C on the viscosity variation of the grout and grouting process. Firstly, the apparent viscosity of the cement grout under different W/C is tested by a rotational viscometer in a laboratory experiment. Subsequently, based on the laboratory tests, numerical models are established to investigate the influence of W/C on the diffusion process of cement grout in sand layers. According to the laboratory results, the apparent viscosity of cement grouts decreases with the increase of W/C. Besides, the apparent viscosity increases with time, while the increasing range of apparent viscosity firstly increases and then decreases as W/C increases. Based on the simulated results, when W/C changes from 0.8 to 1.1, the diffusion radius at 60 min experiences a less and less obvious increase under the given grouting pressure for permeation grouting in the sand layer. When W/C is 0.9, the relative error reaches to 37.65% at 60 min, which is slightly lower than that of 0.8. However, when W/C changes from 0.9 to 1.0, the relative error becomes very narrow (21.36%), and this figure is much lower than that of 0.8 or 0.9. The simulation results are verified by field test, and the relative error is 6%, which proves the effectiveness of the analysis. Therefore, the cement permeation model considering viscosity variation of the grout is a reasonable alternative in the real project. At the same time, the time-dependent behavior of cement grouts should be considered, especially when using cement grouts with a low water-cement ratio in the practical engineering. [ABSTRACT FROM AUTHOR]

This study is aimed at better understanding the deformation and failure mechanism of surrounding rock during excavation unloading of a high-stress rock mass and determining the reasonable reinforcement time for the surrounding rock. To fulfill this aim, true triaxial tests were carried out on different loading and unloading paths during the unilateral unloading of a high-stress rock mass. The variational condition for minimization of plastic complementary energy is obtained, the optimal reinforcement time is determined, and the range of the plastic zone in the surrounding rock reinforced by anchor mesh-cable-grouting is compared and analyzed. The results are as follows: (1) Based on the Mohr-Coulomb yield criterion and the deformation reinforcement theory of surrounding rock, the stable state with the minimum reinforcement force is obtained. (2) After the true triaxial tests on the unilateral unloading of the third principal stress were carried out under different confining pressures, loading continued to be performed. Compared with rock failure without confining pressure, in the conventional uniaxial compression test, the failure of samples is dominated by composite splitting-shear failure; the unilateral unloading stress-concentration failure is a progressive failure process of splitting into plates followed by cutting into blocks and then the ejection of blocks and pieces. (3) The relationship between the time steps of the surrounding rock stability and the excavation distance is obtained. The supporting time can be divided into four stages: presupport stage, bolt reinforcement stage, anchor cable reinforcement stage, and grouting reinforcement stage. (4) In the range of within 5 m behind the tunneling face, the plastic zone of the surrounding rock with support is reduced by 7 m as compared with that with no support. In the range of over 5 m behind the tunneling face, the plastic zone of the roadway floor with support is reduced by 2.6 m as compared with that without support, and the deformation is reduced by 90%. These results can serve as a reference for controlling the behavior of surrounding rock during excavation unloading of high-stress rock masses. [ABSTRACT FROM AUTHOR]

Grouting is an effective technical way for the construction of deep tunnels in unfavorable geological conditions. The fluid-solid-chemical coupling mechanism of grouting process is analyzed from the following three aspects: influence of physical properties of silica sol on permeability coefficient, dynamic changes of porosity and permeability of geotechnical media with seepage pressure, and governing equations for flow and mass transfer characteristics. A dynamically changing model for nanosilica sol grouting in deep tunnels is established, considering the changing physical properties of grout and surrounding rock. Based on the Xianglushan Tunnel of Yunnan Water Diversion Project, the temporal and spatial evolution of silica sol grout is studied. The effect characteristics of grouting pressure and initial permeability are clarified. The rationality of this model is verified by classical Newtonian fluid grouting theory. The main conclusions: with the molar concentration as the index, the grout range can be divided into the raw grout region and the transition region; with the decrease of the grouting pressure, the growth rate of the normal grouting radius and the axial grouting radius will gradually decrease; due to the mechanical dispersion and molecular diffusion, the range of the transition region will gradually increase with time. The ratio of the transition region to grouting radius fluctuates slightly with time under the initial permeability of 5 D. The fluctuation increases with the decrease of initial permeability, and the average ratio increases with the decrease of grouting pressure. This study can provide theoretical guidance for grouting design of deep tunnel engineering. [ABSTRACT FROM AUTHOR]

Grouting reinforcement is one of the most effective methods to enhance the stability of the goaf, and its scheme selection, hole location, and parameter determination directly affect the success or failure of goaf treatment. On the basis of discussion of the deformation mechanism and evolution law of the longwall goaf, this article comprehensively analyzed the grouting reinforcement mechanism of the goaf combined with filling theory, permeability theory, and fracturing theory and studied the physical and chemical reaction principles of two commonly used filling materials, cement-fly ash slurry and cement-clay slurry. Three grouting models have been established: whole grouting, local grouting in fracture zone, and strip grouting, and then simulated the grouting effect of the two more common methods of whole grouting and strip grouting by numerical simulation software (FLAC3D, tecplot, Surfer). Simulation analysis is carried out from the perspectives of settlement deformation, horizontal movement, vertical stress, and horizontal stress. Finally, the feasibility of grouting treatment in the goaf is verified by engineering example. The results show that a reasonable grouting scheme can effectively reduce the residual deformation of the goaf and its overlying rock and improve the poor stress state, so as to achieve the purpose of effective grouting. [ABSTRACT FROM AUTHOR]

It is very important to determine the seepage behaviour of fractured rock mass infilling to evaluate the stability of the surrounding rock. The joint transfixion rate is the ratio of the unpenetrated length to the penetration length of a joint in a sample. Samples of the fractured rock mass infilling using different transfixion rates were prepared, and a TCQT-III low-permeability coal-rock triaxial seepage device was used to conduct three cycles of confining pressure-seepage coupling tests. Results show that the permeability is a power function in the confining pressure of the sample, and the permeability changes most significantly with the confining pressures. The permeability of the sample increases exponentially with the joint transfixion rate. The permeability loss is positively correlated with the plastic deformation of the sample; the permeability changes most significantly during the first cycle loading. There is over 60% recovery of the permeability of the sample under cyclic loading for loads that do not exceed the strength of the infilling. The stress sensitivity coefficient decreases as the confining pressure increases and is higher during the unloading stage than that during the loading stage for samples with an incomplete transfixion rate. The conclusions obtained in this study can serve as a reference for grouting applications. [ABSTRACT FROM AUTHOR]

The tunnel passing through the loess stratum with high moisture content can easily lead to the seepage and mud burst accident and the instability and collapse of the tunnel face. Under the condition of high groundwater level, the seepage situation is more complicated, it is difficult to control the groundwater seepage, and the excavation progress is very slow. In order to solve the various disasters when the tunnel passes through the water-rich loess stratum, taking a water-rich loess tunnel in Gansu Province as an example, the method of comprehensive prevention and control of seepage and mud inrushing disaster by basement grouting and curtain grouting was introduced. Firstly, the basic situation of the Yulinzi tunnel is introduced, including site conditions, seepage collapse accident, and its cause analysis. On this basis, the design and construction methods of basement grouting and curtain grouting are introduced, and the effect of grouting reinforcement is evaluated in detail through on-site monitoring. The results show that the basement grouting and curtain grouting can effectively control the deformation of surrounding rock and the surface settlement, the decrease of the deformation of surrounding rock can reach 36%-71%, and the decrease of the surface settlement can reach 55%. After grouting, the deformation of the surface and surrounding rock can be controlled within the allowable value in the code. Grouting plus solid can effectively block the seepage of groundwater and prevent the surface cracks, water gushing, mud gushing, collapse, and other disasters in the process of tunnel excavation. It can be seen that the basement grouting combined with curtain grouting technology has a good reinforcement effect, which has significant engineering value for quickly and efficiently passing through high moisture content loess strata. [ABSTRACT FROM AUTHOR]

It is of great significance for the improvement of grouting technology and engineering practice to master the flow law of grout between parallel plates. However, the traditional calculation model ignores the influence of the inertia term and only considers the stable flow of slurry, so there is a big error in some cases. It is difficult to solve the motion equation of a Bingham fluid considering the inertial force term directly. Combined with the relationship between the steady-state flow equation of a Bingham fluid and a Newtonian fluid, the approximate unsteady-state flow equation of a Bingham fluid suitable for describing slurry flow is constructed. In addition, according to the unsteady flow equation, the relationship between the time and distance of slurry flow in parallel plate fractures can be obtained, and the simplified conditions of the Bingham fluid unsteady flow model are given. Finally, the accuracy of the flow equations and the simplified conditions are verified by experiments and numerical calculations. [ABSTRACT FROM AUTHOR]

Based on laboratory experiments, the paper researches the effect of polyvinyl alcohol (PVA) content on the performance of fly ash-based cement grouting materials. The test results show that the addition of PVA has limited effect on the initial and final setting time and brings a certain but minor delay on the appearance of the hydration peak period. It enhances cement hydration during the hydration slow down period. The impermeability of PVA to the grouting material is obviously improved, and it increases with the growing amount of PVA content. PVA improves the flexural strength and compressive strength of the sample block to varying degrees, and the improvement on flexural strength is more obvious than that on the compressive strength. It has a significant effect on the mechanical properties of the grouting material and can effectively improve the rock mass's hydraulic coupling characteristics. It also has great application value and practical significance for the prevention and control of water hazards in deep coal stopes. [ABSTRACT FROM AUTHOR]

Permeation grouting estimation is important for the design of grouting engineering. Filtration effects and rheological behavior play a key role in permeation grouting diffusion of cement-based grouts. To better understand the effect of filtration and grout rheological behavior on the grouting diffusion mechanism, one-dimensional permeation grout injections in sand columns under constant flow rate were performed by a self-developed experimental procedure. Experimental results showed that there were dramatic variations in rheological parameters and porosity along the diffusion distance. However, the rheological parameters changed slightly with time for each position. Based on the experimental results, a numerical model considering the filtration effect and grout rheological behavior was established to describe the mechanism of grout flow in porous media. In addition, numerical solutions from the proposed model are compared with the experimental results. The comparative results showed that the proposed numerical method can match the laboratory tests well. Finally, the effects of the grout flow velocity and the water/cement ratio of the grout on the diffusion mechanism are also discussed. [ABSTRACT FROM AUTHOR]

It is very extraordinary for the success of coal mine roadway grouting with the following factors of high early strength, good fluidity, and convenient pumping, but the existing grouting materials make it difficult to achieve the above characteristics at the same time. Therefore, a modified grouting material is developed, which is composed of two kinds of dry materials A and B, which are mixed with water and in equal amounts. The physical and mechanical properties of modified grouting materials under different ratios were tested by laboratory orthogonal test, and the optimal ratio of grouting materials and additives was obtained: (1) the water-cement ratio is 0.8 : 1; (2) base material: the mass ratio of cement, fly ash, bentonite, and water is 1 : 0.3 : 0.1 : 1.44; (3) admixture: the mass ratio of water reducer C, accelerator D, and retarder E is 1.5% : 0.05% : 0.3%. The basic properties of the modified grouting materials were studied from the aspects of slurry flow state, diffusion range, and grouting parameters by using the numerical simulation method, and the reinforcement mechanism of slurry to the broken surrounding rock properties of the roadway was revealed: (1) the grouting pressure is the main factor affecting the slurry diffusion radius; (2) the mechanical properties of the roadway surrounding rock are improved, the plastic zone and deformation of surrounding rock are reduced, and the active support function of the anchor and cable is enhanced through grouting reinforcement; (3) the control effect of the roadway is improved, and the balanced bearing with anchorage structure of the roadway surrounding rock is realized through grouting reinforcement. On this basis, the modified grouting material is applied to roadway repair and reinforcement engineering practice. The field monitoring data show that the production practices were guided by roadway repair and reinforcement technology with the modified grouting material, as the core of the roadway surrounding rock control effect is good, and the modified grouting material has a wide range of application prospects. [ABSTRACT FROM AUTHOR]

Gas extraction from coal seams in China faces various middle-term and long-term problems, such as the poor sealing quality and low extraction rate. The mean gas extraction concentration is only 30%. Studying the flowing laws of the grout and fracture plugging mechanism is of important significance to improve the sealing quality and increase the gas extraction efficiency. For this reason, a new coal-based grouting material was prepared in this study, and its parameters such as viscosity were tested. Moreover, a grouting theoretical model with considerations of the flowing of the grout and coal fracture plugging by migration and deposition of slurry particles was constructed. The crack distribution before and after the grouting of fractured coal samples was scanned with an industrial CT, and the fracture distribution of coal samples was reconstructed using an independently compiled MATLAB program. Meanwhile, the variations of the coal permeability before and after the grouting were tested. On this basis, this study built a numerical calculation model of the grouting in fractured coal samples to simulate the leakage stoppage and permeability reduction mechanism of the coal-based sealing material grouting. Results demonstrate that (1) according to the experimental test results, the new coal-based grouting materials achieve a good fracture plugging effect, and the fractures in coal samples after the grouting are filled densely by the grouting particles. (2) According to the simulation results, the permeability of grouting coal samples declines quickly and then tends to be stable. The overall permeability of coal samples and the fracture permeability are decreased by 93.5% and more than 99.9% in average, respectively. (3) Influences of the grouting pressure on the permeability variation of coal samples were investigated through a numerical simulation. It was found that a reasonable grouting pressure for coal samples is about 0.3 MPa. (4) The numerical simulation reproduces the whole process of the grout flowing and the fracture filling. The variation laws of the diffusion and the permeability of the grout which are calculated through a numerical simulation agree well with the experimental results, which verifies the reasonability of the model. Research conclusions can provide important significance in theory and practice to disclose the leakage stoppage and the permeability reduction mechanism of the borehole grouting during the gas extraction and strengthen the sealing effects of extraction boreholes. [ABSTRACT FROM AUTHOR]

Grouting is always used in mine water plugging, reinforcement, and other disaster prevention projects. The diffusion mechanism of slurry in fractured rock is affected by geological environment and slurry performance, which should be revealed and characterized better. Based on the two-phase flow diffusion theory, a slurry diffusion model considering flowing water condition was established for a blocking area of a fracture zone in one case from China. The feasibility of two-phase flow model in grouting diffusion calculation was analyzed. The diffusion model in dynamic water environment was studied, and the diffusion range varying with time in the grouting area of Zhangji Coal Mine was explored. The optimization method of multi grouting holes was put forward, and the influence of water flowing was discussed. The results show that the slurry diffusion calculated by the two-phase flow model was feasible and consistent with the experimental study. The dynamic water can change the conventional circular diffusion state of slurry, but its pattern was oval and leaf type. There were different penetration distances in directions, and typical grouting voids were made on the side and upstream. When the single-hole grouting was carried out, the predetermined value can be achieved in the height range, but it was only about 15 m on the side because of the water flowing, which cannot meet the requirements. The optimization scheme of grouting was put forward, which adopted multiple grouting holes in the long side, and grouting in different directions and periods to avoid the possible problems of multihole intersection. The rationality and effectiveness of the proposed optimization method were verified through the calculation of water yield and analysis of cement composition from the drilling core in the grouted zone. In the grouting process, the water flowing has double effects, which has a significant role in promoting and scouring along the flow direction, but there is a significant weakness in the side diffusion. It is very important to realize the rational use of the dynamic water through the optimization scheme. This study is an important basic work of grouting mechanism, and it is expected to promote the development of grouting technology and application of two-phase fluid-solid coupling theory. [ABSTRACT FROM AUTHOR]

In coal mines, under high in situ stress and strong mining activity, roadway surrounding rock commonly contains large amounts of larger fractures and microfractures. Along with the large deformation and continuous rheology of the soft rock roadway, the fractures in the surrounding rock are likely to be compressed and closed, forming undeveloped microfractures, which hinder conventional grouting support methods. Based on the fluid-solid coupling between slurry seepage and microfracture deformation, a theoretical model of microfracture grouting seepage is established. A program for the analysis and calculation of microfracture grouting is developed to quantitatively describe the variation in slurry seepage distance and fracture opening. Numerical experiments are carried out to study the grouting seepage of microfractures under different grouting pressures and fracture opening conditions, and the variation rules for the spatial distribution of fracture opening and slurry seepage distance during grouting pressure are obtained. Fluid-solid coupling has a significant influence on grout seepage characteristics. The grouting pressure and the fracture opening changes are nonlinearly attenuated along the grout seepage direction. [ABSTRACT FROM AUTHOR]

Aimed at the problem to plug the main ore pass with the large collapse at Xingshan Iron Mine, the viscosity-time test and the heap perfusion test of cement-silicate grout in a loose rock mass are carried out. The relationship between the vertical diffusion distance of cement-silicate grout and setting time of grout is studied, and research results are applied to the design of plugging engineering of the main ore pass in -330 m. Based on the numerical simulation of the plugging structure and the long-term stress monitoring of the cable sensors, the stability of the plugging structure itself and the control for the movement of shafts nearby are comprehensively evaluated. The test results show that for a specific loose rock mass, the vertical diffusion distance of cement-silicate grout in the loose rock mass is a power function of grout setting time. Based on the design concept to plug the main ore pass with the large collapse using artificially constructed "bite-bonded arch," the plugging design and construction procedures are proposed. A numerical model and long-term monitoring of cable stress show that the plugging structure is stable and has an obvious effect on the control movement of abutment shafts. [ABSTRACT FROM AUTHOR]

The development of water-conducting fractures from underground coal mining is a geological cause of groundwater loss. Sealing mining-induced rock fracture channels through borehole grouting is an effective way to protect groundwater resources. A ground-based engineering test was conducted at the Gaojiabao coal mine that utilized horizontal directional drilling (HDD) to grout and seal water-conducting overburden fractures. This study carried out a theoretical and experimental exploration using HDD to evaluate the development characteristics and grout hydraulic conductivity of these mining-induced fractures. The results showed that, as a result of varying fracture morphologies in different zones of the mining overburden, multiple fracture types were sequentially exposed as the HDD borehole advanced from the original rock mass outside the mining area towards the mining-induced fractured rock mass. The fracture types were exposed in the following order: compressive shear fractures, tensile failure fractures, and bed separation fractures. Moreover, the void characteristics of the exposed fractures in the borehole were significantly different at different drilling horizons, which affected the flow behavior and sealing performance of the injected grout. Lastly, three typical orders in which the different types of fractures were sequentially exposed by the borehole were summarized, and further analysis of the orders led to a scheme for determining drilling horizons favorable for efficient fracture sealing. The results of this study will enable efficient grout sealing of the fractures caused by mining and reduce groundwater loss. [ABSTRACT FROM AUTHOR]

Based on the systematic study on the characteristics of water and mud inrush during the excavation of Jingzhai tunnel, the mechanism of water inrush seepage transformation caused by excavation disturbance is analyzed. By means of electromagnetic geophysical prospecting, the potential water bearing area of the tunnel was analyzed. The constitutive model of rock mass and grouting parameters are considered in the numerical simulation. The law of tunnel crack initiation and expansion under different curtain grouting parameters is proposed. The characteristics of seepage water inrush caused by excavation are described. It is considered that there are three stages in the seepage characteristics of tunnel: incubation, sudden, and stable. Numerical simulation was used to analyze the crack propagation track and water inflow characteristics under the grouting thickness of 3 m, 5 m, and 7 m. When the curtain grouting thickness was 3 m, the fracture field penetrated the curtain grouting area. The dominant seepage channel is formed, which greatly increases the probability of water inrush. When the curtain thickness is 5~7 m, the expansion of the crack zone can be controlled basically, so that the fracture and water bearing rock layer cannot form a seepage channel. At last, the grouting scheme of 6 m thick grouting and 20 m advanced grouting was selected, and the water seepage was reduced by 83%. [ABSTRACT FROM AUTHOR]

When grouting in a sand layer, the filtration of the layer on cement particles is an important aspect affecting the grout dispersion. However, few laboratory studies have been conducted to investigate the distribution of cement particles along the direction of dispersion. In this study, a group of laboratory tests were conducted by grouting in a sand layer under different levels of pressure. The distributions of cement particles in sand after curing were then measured using the EDTA titration test. The results show that, due to the filtration effect, the cement content along the radial direction of dispersion decreases nonlinearly in a reversed S shape. The filtration effect becomes more obvious when grouting with a higher grout concentration. With the decrease in grout concentration, the filtration effect becomes weak and cement particles could disperse farther in the sand layer, but the cement content in a farther location becomes lower and the improvement of the soil strength is limited. In the end, the measured results were compared with the calculated results according to an existing theoretical study and the trend reasonably matches with each other. [ABSTRACT FROM AUTHOR]

In order to realize the diffusion law of segmental grouting in muddy fault of tunnel engineering, a three-dimensional grouting diffusion simulation test has been done. Three times of grouting operation have been done for three adjacent sections in grouting pipe. Grouting pressure, injection rate, soil pressure field, and seepage pressure field have been real-time monitored in three grouting stages. The effect of segmental grouting operation on soil pressure field and effective stress field has been analyzed. Results show that previous grouting operation can affect later grouting operation. Due to previous grouting operation, the grouted stratum can be compacted and grouting diffusion will conquer greater resistance in later grouting stages. Correspondingly, grouting pressure increases and injection rate decreases in the later grouting stage. There exists a limited influence range for a single grouting operation. For every grouting stage, soil pressure and effective stress in the section which the injection hole locates in are affected effectively by grouting operation. By contrast, soil pressure and effective stress in section away from injection hole are affected relatively weakly by grouting operation. With distance to injection hole increasing, compaction degree and reinforcement effect of grouted muddy fault decay in space. Multisegmental grouting method has significant advantages over single grouting method. Ineffectively compacted area by previous grouting operation can be effectively compacted by later grouting operation from adjacent injection hole. As a result, uniformity of grouting reinforcement effect can be improved, and weakly reinforcement area can be reduced. [ABSTRACT FROM AUTHOR]

The poor impermeability of fractured rock induced by excavation and construction is improved through the application of microbial-induced calcite precipitation (MICP), but it is difficult to monitor and evaluate the permeability reduction under a confining pressure and fracture aperture. For this, the grouting ratio, permeability, and electrochemical impedance of fractured rock with MICP grouting were experimented with, considering the effects of fracture aperture and confining pressure. The equivalent circuit model of grouting-fractured rock is presented, and the corresponding ratio of the electrical resistivity and cross-sectional area of the grouted fracture (ρ / S) is indicated by an electrochemical impedance spectroscope (EIS). The relationships of the permeability coefficient, the ρ / S , and the grouting ratio are analysed. The experimental results show that the Darcy permeability coefficient of fractured rock with MICP grouting is reduced by an order of magnitude of 3 to 4. As fracture aperture ranged from 1.28 to 2.56 mm and grouting rate was 0.003 ml/s, the Darcy permeability coefficient decreased with an increase in confining pressure. The grouting ratio and fracture aperture also decreased with a reduction in ρ / S. The results also showed that the permeability reduction of MICP correspondingly increased in these conditions. What is more, the Darcy permeability coefficient of fractured rock grouted by MICP and its permeability reduction may be well predicted by confining pressure and ρ / S. This study provides a new EIS method for predicting the reduction in permeability of MICP grouting-fractured rock and further enriches the application of MICP and EIS techniques in impermeable rock engineering. [ABSTRACT FROM AUTHOR]

This research presents the grouting method of preventing rib sloughage which severely impacts mine safety and longwall retreat speed in thick coal seam with numerical simulation and laboratory tests. Based on the analysis of the plastic failure mode of five types of coal seam, roof strata ahead of the longwall face, and fractures developed in the coal seam, the following results are drawn, the range and degree of plastic failure generated in the coal seam and roof strata ahead of the longwall face gradually decreased as the coal mass strength increased; the grouting boreholes are essentially laid out within the coal rib instead of the roof. For a particular case of a coal mine in Shanxi province, a novel cement-based material was grouted, which fulfilled the reinforcement requirements under the tectonic stress regions and front abutment zones. Besides, the grouting borehole construction requested predrilled boreholes, full borehole intubation, lengthened hole sealing, and multiple-step drilling and grouting. This study can provide a theoretical framework of a design overview and practical basis for similar mining conditions in other coalfields. [ABSTRACT FROM AUTHOR]