Study on Formation Mechanism of Advance Grouting Curtain in Ore-Rock Contact Zone in Water-Rich Roadway

Abstract

During tunnel development in metal mines, there are situations where a zone of contact between the ore and the surrounding rock is reached. Nevertheless, there is a notable disparity in the mechanical characteristics between the ore and the surrounding rock, leading to a specific response of grouting in the contact area between the ore and rock. This response differs from the typical diffusion and curtain formation effects observed when using grouting slurry. This study investigates the effects of grouting curtain creation when implementing highly advanced curtain grouting in a water-rich highway, utilizing the engineering conditions of Zhongjiu Iron Mine as a reference. At first, Darcy’s law and the Navier-Stokes equation are used to control the flow of fluid in the area where the ore-rock meets the rock around it. COMSOL, a multi-physical field coupled analysis software, is employed for the numerical simulation of slurry plane diffusion, single-hole, and group-hole curtain grouting. Two optimization strategies for group-hole grouting parameters are subsequently suggested and proven using numerical simulation. Finally, the project implements the research to assess the influence of curtain grouting by employing the water influx of the exploratory apertures as the standard of comparison before and after grouting; the results demonstrate that the slurry forms a highly efficient grouting curtain, effectively impeding water infiltration. The findings indicate that slurry diffusion in the contact zone between the ore and rock follows a spherical motion pattern, resulting in a considerable decrease in the flow rate compared to the previous stage. The force of gravity visibly affects the spreading of the slurry in the area where the ore and rock come into contact, causing the slurry to mostly spread downwards. This inclination intensifies as the rate of grouting is elevated. To successfully address the inadequate distribution of the slurry, one can either increase the rate at which grouting is performed or decrease the distance between the grouting holes.

1. Introduction

Metal mine tunneling is often faced with a complex hydrological environment, weak and broken surrounding rock, and other adverse geological conditions, which will bring challenges to tunneling construction and subsequent production safety hazards. If the roadway development process needs to cross the mine rock contact zone or water-rich environment, it usually adopts advanced curtain grouting technology for water-blocking construction to ensure the roadway is safe and smooth digging [1]. An overrun grouting curtain can form an effective water-blocking barrier, improve the strength of the roadway, reduce the risk of water surges, and reduce the deformation capacity of the surrounding rock. Curtain grouting is frequently incorporated into cement slurry water glass to expedite slurry solidification because the dynamic water environment is not conducive to the formation of an effective curtain cement slurry. Additionally, the rheology and plasticity of concrete can be significantly enhanced by the addition of a small amount of water-reducing agent. Due to the significant difference in the mechanical parameters of the ore-rock in the contact zone, the slurry may show different diffusion patterns when it passes through the contact zone of the two rock bodies, which will directly affect the final curtain body water-blocking effect [2]. Moreover, under water-rich conditions, water pressure will make it more difficult for the slurry to form a continuous curtain body. Many researchers have carried out studies on the curtain grouting problem.

Liu J et al. [1,2,3] introduced the grouting design methods and construction procedures, proposed the values of the main grouting parameters and composite materials that are applicable to various flowing water environments, adopted curtain grouting technology for tunnel pre-strengthening, and employed the seepage model to determine the safe thickness of the curtain body under stratigraphic conditions. They also proposed empirical equations between the safe thickness of the curtain body and the BQ. Zhang G et al. [4] utilized physical probe and borehole exploration methods to identify the tunnel’s eroded areas. They then implemented full-section curtain grouting and pipe shed reinforcement measures to significantly reinforce the geotechnical body during construction. Physical detection and drilling exploration methods are employed to identify the erosion area of the tunnel. During the construction process, the geotechnical body is fortified by the installation of a curtain grouting pipe enclosure and other reinforcement measures. Zhou J [5], Zhang P [6], and others established a monitoring system and, by observing the development of fractures and the formation of the mechanism, summarized the four mechanisms of local infiltration channel formation. They also proposed a method for evaluating and analyzing the seepage channel. In order to guarantee the safety of mining and the stability of the roadway surrounding the rock, Li Z et al. [7] utilize single-row annular curtain grouting to surround the surrounding rock and ore, thereby forming a complete and dense curtain body with specific strength, to address rock damage, fissure development, and other geological issues. Shi H et al. [8] employed numerical analysis to simulate the construction process of the curtain grouting section, evaluate the effects of various curtain grouting parameters, select the optimal grouting parameters, and subsequently apply them to the grouting construction. Xu C et al. [9,10] proposed a method of curtain formation and stability (FSC) for overtopping curtain grouting projects. They analyzed the mathematical equations and simplified the model from the engineering problems. The two-phase flow equations of motion proposed by Bourgeat [11], Chen J [12], and others can be applied to a variety of porous media and authenticated through numerical simulations. In order to investigate the mechanical properties of the composite rock, Wang Q et al. [13] implemented uniaxial compression experiments in the vicinity of the iron ore-marble contact zone. The composite rock body exhibited a lower strength than the rock body, and the mechanical properties were found to be correlated with the contact angle of the rock samples. The establishment of a comprehensive prediction technology system, which encompasses the principles of distance and proximity, qualitative analysis, quantitative identification, structural localization, and water-bearing tectonic identification, enabled Lin Bu et al. [14] to successfully construct curtain grouting in the water-rich zone of Sichuan karst tunnels. Using curtain grouting technology for engineering treatment, Tang Z et al. [15] analyzed the grouting effect by monitoring the change in water influx before and after the grouting operation at the quarry’s water intake site. In order to reduce the water volume to less than 85% of the initial volume, Wu Q et al. [16] implemented curtain grouting and infill in a water-rich mine voided area. Yuan J et al. [17] conducted an analysis of the causes of the cement surge disaster, proposed the use of curtain grouting for disaster management, and evaluated it based on the inspection hole survey and P-Q-t analysis. The study of the variation of grouting pressure, grout flow rate, and the law of grout diffusion, as well as the analysis of the factors affecting grout diffusion, was conducted by Jiang D et al. [18] using a self-developed grout diffusion visualization platform and a three-dimensional grouting experimental system. Du X et al. [19] summarized the factors that must be considered during the fissure grouting process, investigated the diffusion mechanism of the slurry under the influence of the grout, and proposed an optimization method for grouting parameters and a grout quality assessment technique. Methods for optimizing grouting quality and techniques for evaluating grouting quality were suggested. Using numerical simulation, Huang Y et al. [20] investigated the spatial evolution characteristics of plastic damage and grout diffusion in the presence of mining disturbances. The findings indicated that the diffusion range of the grout in each spatial direction in the surrounding rock increased as the ratio of lateral pressure coefficients perpendicular and parallel to the axial direction of the roadway increased. Nevertheless, the same porous media slurry diffusion is the focus of past scholars’ research on the slurry diffusion law, and there are fewer distinct media between the slurry diffusion law studies. Concurrently, the majority of the aforementioned studies pertain to rock mechanical differences in the ore-rock contact zone or the curtain grouting diffusion mechanism in a specific aspect. Relatively few scholars have conducted research on curtain grouting in the ore-rock contact zone.

In this paper, we utilize the theoretical equations of Darcy’s law for the mutually incompatible seepage of slurry water in porous media and the Navier-Stokes equations for laminar two-phase flow, in conjunction with level set functions to conduct exhaustive research on the planar diffusion law of the slurry in the contact zone of the mine rock under the water-rich condition. The context of the actual engineering conditions of the 2# vein-piercing channel at the −380 m level of the air shaft of the Zhongjiu Iron Mine of Anhui Ma Steel is in view. Numerical simulation was employed to investigate the slurry diffusion pattern in the ore-rock contact zone under water-rich conditions, as well as the impact of single-hole and group-hole grouting curtain formation. Two optimization methods for the group-hole grouting parameters were proposed based on the simulation results. Ultimately, this research will be implemented in the field of engineering to evaluate the impact of grouting on the change in water influx in exploratory openings prior to and following curtain grouting.

2. Project Overview

Zhongjiu Iron Mine is a subsidiary of the Ma Steel Group Gushan Mining Limited Liability Company (Maanshan, China). It is situated 7.5 km south of Dangtu County, Anhui Province. The administrative division falls under the jurisdiction of Zhongshan Village, Nianpian Town, and Dangtu County. The mine region has a well-established surface water system consisting primarily of ditches and ponds. The saturated area covers around 15% of the total area. The Qingshan River flows past Dangtu and the Yangtze River, about 1.3 km east of the mine. The Qingshan River flows from south to north in the eastern part of the mine. The riverbed has a minimum elevation of −2 m and a maximum flow rate of 568 m³/s. The greatest recorded flood level is 12.36 m. The stratigraphy of the Zhongjiu Iron Ore Mine exhibits a high level of complexity, characterized by variations in lithology and the presence of numerous faults and fissures. The primary aquifer in the mine consists of robust water-rich rock formations, namely the fourth series gravel and pebble layer, as well as the sand and shale fissure layer located beneath the ore body of the Huangmaqing Group. The water recharge mechanisms in the ore deposit are complex, with the main factors being the infiltration of pore water and water flowing through fractures, while karst fissures contribute as secondary factors. The upper and lower layers of the deposit are primarily composed of the Gushan Group and the Zhouchong Village Group. The surrounding rocks in the mining area consist mainly of class IV bedrock, which has low structural integrity. The rock hardness coefficient ranges from 2 to 9, indicating that it belongs to a soft and weak rock formation. The rock hardness coefficient ranges from 2 to 9, classifying it as a weak type of rock. The lithology of the stratum between the depths of 308 m and 438 m is a little worn sodium long diorite. The mining region contains one primary ore body and fifty-three smaller ore bodies. The primary ore body is situated in the contact zone between the Zhouchongcun Group’s tuff and the Gushan Group’s varied volcanic clastic sedimentary rocks.

According to the roadway development plan, the Zhongjiu Iron Mine air shaft −380 m level 2# alley in the roadway development process will pass through the mine rock contact zone. The geological conditions of the 2# vein-piercing lane of Zhongjiu Iron Mine are shown in Figure 1. In the previous roadway excavation, Zhongjiu Iron Mine adopted the “steel bracket + anchor” joint support form of support, but the two sides of the roadway inward-contraction, cracking, bottom drum and steel frame deformation, and other safety issues in the palm face of the drenching, rock collapse, and other issues. The ore body exposed during the tunneling of #2 through the vein is black, has a powdery mud structure, is easy to muddy in contact with water, and has serious rock fragmentation. In view of the roadway excavation through the contact zone of the ore and rock, the Zhongjiu Iron Mine decided to adopt the technique of over-curtain grouting and water-blocking to achieve the purpose of water control and control the stability of the surrounding rock.

After on-site core drilling and sampling, according to the “engineering rock test method standard GB/T50266-2013 [21]” will be processed into 12 samples of size Φ50 m × 100 mm and six samples of size Φ50 mm × 25 mm standard specimen for the uniaxial compression test, full stress-strain infiltration test, and Brazilian cleavage test. The average of the test results for the enclosing rock physical–mechanical parameters will be used in subsequent numerical simulations. The physical and mechanical parameters of the adjacent rock were determined by averaging the test results, which served as the foundation for the subsequent numerical simulations. The mechanical parameters of the surrounding rock are shown in

Table 1. The physical and mechanical parameters of surrounding rock.

Parameter	Density (kg·m−3)	Modulus of Elasticity (GPa)	Poisson’s Ratio (v)	Internal Friction Angle (°)	Tensile Strength (MPa)	Permeability (m2)
Diorite	2654.37	16.27	0.23	42.6	8.55	3.78 × 10−13
Magnetite	3677.37	15.15	0.29	50	5.85	0.89 × 10−13

.

3. Control Equation Selection

3.1. Control Equations for Grouting of the Surrounding Bedrock

This paper adopts Darcy’s law theory to analyze the movement and diffusion of slurry in water-rich situations. The theory assumes that the seepage of slurry water in porous media is mutually incompatible, and the following assumptions are made: The rock body is a uniform and consistent porous medium with equal permeability in all directions. Grouting slurry and water are both incompressible Newtonian fluids, but they do not mix with each other. The effects of changes in viscosity over time and the viscosity of the slurry are not considered. The slurry is also not compatible with other substances. The impact of viscosity, which changes over time, is not taken into account. The governing equations to be adhered to for the numerical simulation are as follows:

3.1.1. Equations of Motion

Denoting the slurry and water by the subscripts ‘g’ and ‘w’, respectively, the system of equations is

$$\left\{\begin{array}{l}{V}_{\mathrm{g}}=-{\displaystyle \frac{K_{\mathrm{g}}}{{\mu }_g}}\nabla p_g\\ V_w=-{\displaystyle \frac{K_w}{{\mu }_w}}\nabla p_w\end{array}\right.$$

(1)

where $V_{\mathrm{g}}$, $V_{\mathrm{w}}$ are the velocities of the slurry and water in the porous medium, m/s, respectively; $K_{\mathrm{g}}$, $K_{\mathrm{w}}$ are the effective permeabilities of the porous medium for the slurry and water, m², respectively; $P_g$, $P_{\mathrm{w}}$ are the pressures of the slurry and water, Pa, respectively; ${\mu }_g$, ${\mu }_w$ are the kinetic viscosities of the slurry and water, Pa·s, respectively.

3.1.2. Continuity Equation

The continuity equations for the slurry and water are given by the following tables ‘g’ and ‘w’, respectively:

$$\left\{\begin{array}{l}{\displaystyle \frac{\partial \left(s_g{\rho }_g\varphi \right)}{\partial t}}+\nabla \left({\rho }_g{V}_g\right)={\rho }_g{q}_g\\ {\displaystyle \frac{\partial \left(s_w{\rho }_w\varphi \right)}{\partial t}}+\nabla \left({\rho }_w{V}_w\right)={\rho }_w{q}_w\end{array}\right.$$

(2)

included among these,

$$s_g+s_w=1$$

(3)

where, $S_g$, $S_w$ are the saturation of slurry and water, respectively; ${\rho }_g$, ${\rho }_w$ are the densities of slurry and water, respectively, kg/m³; $q_g$, $q_w$ are the source-sink strengths of slurry and water, respectively, 1/s; $\varphi$ is the porosity of the rock mass; t is the time, s.

3.1.3. Equation of Control for Two-Phase Flow Interface

The transport equation is introduced to better represent the diffusion pattern of the slurry as follows:

$${\displaystyle \frac{\partial \varphi c_g}{\partial t}}+\nabla \left(c_{g}V\right)=\nabla \left(D_c\nabla c_g\right)$$

(4)

included among these,

$$V=-{\displaystyle \frac{K}{\mu }}\nabla P$$

(5)

$${\displaystyle \frac{1}{\mu }}=s_g{\displaystyle \frac{k_{rg}}{{\mu }_g}}+s_w{\displaystyle \frac{k_{rw}}{{\mu }_w}}$$

(6)

where, $c_g$ is the content of the slurry; $D_c$ is the capillary diffusion coefficient, m²/s; $V$ is the integrated Darcy velocity, m/s; $K$ is the absolute permeability of the porous medium, m²; $\mu$ is the dynamic viscosity at the interface of the two phases, Pa·s; $k_{rg}$, $k_{rw}$ are the relative permeabilities of the slurry and the water, m², respectively.

3.2. Grouting Control Equations for Ore-Rock Contact Zone

When studying the diffusion of slurry in the contact zone between ore and rock under conditions with high water content, the regulating equation used is the Navier-Stokes equation, based on the theory of laminar two-phase flow. This work makes the following assumptions when using this theory: The slurry remains continuous and incompressible throughout its movement, and its density remains constant. The shear rate of the slurry always follows a linear relationship with the shear stress during its movement. The velocity of the slurry is zero relative to the velocity of the wall, meaning that the no-slip boundary condition is met. The numerical simulation must adhere to the following control equations:

3.2.1. Equations of Motion

$$\rho {\displaystyle \frac{\partial u}{\partial t}}+\rho \left(u\cdot \nabla \right)u=\nabla \cdot \left[-pI+\mu \left(\nabla u+{\left(\nabla u\right)}^T\right)\right]+\rho \mathrm{g}$$

(7)

included among these,

$$\rho ={\rho }_g+\left({\rho }_w-{\rho }_g\right)\phi$$

(8)

$$\mu ={\mu }_g+\left({\mu }_w-{\mu }_g\right)\phi$$

(9)

where, $\rho$ is the fluid density, kg/m³; $\mu$ is the fluid velocity, m/s; $t$ is the time, s; $p$ is the fluid pressure, Pa; $\mathrm{I}$ is the unit vector; $\mu$ is the hydrodynamic viscosity, Pa·s; $\phi$ is the horizontal set of variables; ${\rho }_g$, ${\rho }_w$ are the densities of the slurry and the water, respectively, kg/m³; and ${\mu }_g$, ${\mu }_{\mathrm{w}}$ are the hydrodynamic viscosities of the slurry and the water, respectively, Pa·s.

3.2.2. Continuity Equation

The continuity equation for slurry diffusion in the ore-rock contact zone under water-rich conditions is as follows:

$$\rho \nabla \cdot \left(u\right)=0$$

(10)

3.2.3. Equation of Control for Two-Phase Flow Interface

The laminar two-phase flow interface is described using the level set method. A contour line with a level set function value of 0.7 defines the two-phase flow interface, where the value of pure water is equal to 0, the value of pure slurry is equal to 1, and the value of the layer close to the two-phase flow interface smoothly transitions from 1 to 0. The two-phase flow interface moves with the fluid velocity $\mu$, then the following equation describes the motion model of the reinitialized level set function:

$${\displaystyle \frac{\partial \phi }{\partial t}}+u\cdot \nabla \phi =\gamma \nabla \cdot \left[{\zeta }_{1s}\nabla \phi -\phi \left(1-\phi \right){\displaystyle \frac{\nabla \phi }{\left|\nabla \phi \right|}}\right]$$

(11)

where $\phi$ is the level set variable; $\gamma$ is the reinitialization parameter, m/s; and ${\varsigma }_{1\mathrm{s}}$ is the interface thickness control parameter, m.

4. Numerical Simulation of the Formation Effect of Grout Curtain in Ore-Rock Contact Zone

4.1. Slurry Plane Diffusion Law

This paper centers on the utilization of the multi-physical field coupling analysis software COMSOL Multiphysics (v.6.1), which is founded on the finite element method. It conducts numerical simulation calculations of physical science processes by solving partial differential equations (sets), thereby enabling the resolution of coupling problems involving multiple physical fields. The key modules in the COMSOL Multiphysics software include porous media and groundwater flow modules, flow-solid coupling modules, and partial differential equation interface modules.

4.1.1. Planar Modeling of Porous Media

The slurry fluid will disperse evenly within the same medium, but its path will alter while dispersing through two distinct porous media. A 2D planar model of porous media measuring 5 m × 5 m is created. The contact zone in the paper uses a customized “Fracture “node in COMSOL software. The contact zone extends 1 m from the upper right endpoint and 0.5 m from the bottom left endpoint. Additionally, a grouting hole with a radius of 2 cm is positioned in the center of the model, as depicted in Figure 2. The model is partitioned into a free triangular mesh consisting of 3364 triangular cells. The average quality of the mesh cells is 0.89, indicating a high-quality mesh. The model is enclosed by a border with constant pressure. The initial water pressure in the porous medium is set at 2 MPa, and the numerical simulation parameters are obtained from Table 1.

4.1.2. Slurry Diffusion Law under Different Grouting Rates

Typically, in engineering applications, the rate at which grouting is performed ranges from 0.2 m/s to 0.3 m/s. To study the changes in the shape of the stone body under different grouting rates, simulations were conducted at rates of 0.1 m/s, 0.2 m/s, and 0.3 m/s. The results are presented in Figure 3, where $V_{\mathrm{g}}$ represents the grouting rate. It is evident that when the grouting rate gradually increases, both the spreading distance of the slurry and the morphology of the stone body also increase. Using a grouting time of 60 s as the reference point, the slurry diffusion distance is 0.62 m when the grouting rate is 0.1 m per second. Similarly, the slurry diffusion distance is 0.87 m at a grouting rate of 0.2 m per second and 1.1 m at a grouting rate of 0.3 m per second.

The slurry pressure and rate were simulated under different grouting rates of 0.1 m/s, 0.2 m/s, and 0.3 m/s. The findings are displayed in Figure 4. It is evident that the maximum slurry pressure increases as the grouting rate increases. There is a direct relationship between the slurry flow rate and the grouting rate, meaning that when the grouting rate increases, the slurry flow rate also increases. At a consistent grouting rate, the slurry flow rate decreases as the distance from the grouting hole increases. Furthermore, after passing through the ore-rock contact zone, the flow rate decreases dramatically compared to its prior value.

4.1.3. Slurry Diffusion Law under Different Water Pressures

The stone body’s morphology was simulated under water pressure settings of 0 MPa, 1.5 MPa, and 3 MPa. The corresponding results are displayed in Figure 5, where ${\mathrm{P}}_w$ represents the grouting rate. It is evident that when the water pressure gradually increases, the spreading distance of the slurry and the shape of the stone body diminish. Using a time node of 60 s for grouting, it can be observed that when the water pressure is 0 MPa, the slurry diffuses to a distance of 1.67 m. At a water pressure of 1.5 MPa, the slurry diffusion distance decreases to 1.34 m. Finally, at a water pressure of 3 MPa, the slurry diffusion distance further decreases to 1.09 m. This indicates that a higher water pressure results in stronger dispersion and transportation of the slurry by groundwater. Within the area surrounding the boundary between the ore and rock, the movement of the slurry is also impeded and redirected, resulting in a much shorter distance of diffusion in magnetite compared to syenite substances.

The slurry pressure and rate were simulated under different water pressures of 0 MPa, 1.5 MPa, and 3 MPa. The corresponding findings are displayed in Figure 6. Based on the aforementioned findings, it is evident that there exists a negative correlation between the slurry flow rate and the water pressure. Specifically, when the water pressure increases, the slurry flow rate experiences a large decrease. At the same water pressure, the slurry flow rate decreases as the distance from the grouting hole increases. Furthermore, the flow rate decreases more significantly after passing through the ore-rock contact zone, and the rate of change in the flow rate is higher.

4.2. Single-Hole Grouting Curtain Body Formation Effect

4.2.1. Single-Hole Grouting Calculation Model

To investigate the impact of the curtain body’s creation, a 3D porous medium model measuring 10 m × 10 m × 40 m is created. The ore-rock contact zone is situated between y = 15 m and y = 25 m, with a dip angle of 45°. The grouting holes, which have a diameter of 10 cm and a depth of 30 m, are positioned in the center. The model may be seen in Figure 7. The model is partitioned into 295,091 cells using a quadrilateral meshing technique. The exit borders define the upper and lower boundaries of the model, while the no-flow boundaries define the left and right boundaries. The model parameters are displayed in Table 1, while the model itself is depicted in Figure 7.

4.2.2. Curtain Body Morphology at Different Grouting Rates

The morphology simulation of the curtain body under the slurry injection rate of 0.1 m/s, 0.2 m/s, and 0.3 m/s were carried out, respectively, and the results are shown in Figure 8. The blue part of the figure indicates the slurry volume fraction, which is used to describe the diffusion pattern of the slurry in the ore-rock contact zone and the yellow part of the contact zone indicates the groundwater. From the figure, it can be seen that a better curtain body morphology can be formed at different grouting rates. As the grouting rate increases, the radius of the curtain body increases significantly, and the morphology of the curtain body surface becomes smoother. The curtain body in the contact zone before and after the two surfaces can be better fit to form a whole. In the ore-rock contact zone, the slurry diffusion is obviously affected by gravity, and the downward diffusion trend of the slurry occurs, and the trend increases with the increase in the grouting rate.

4.2.3. Curtain Body Morphology under Different Water Pressures

The shape of the curtain body was simulated under water pressure conditions of 0 MPa, 1.5 MPa, and 3 MPa. The corresponding results are displayed in Figure 9. At a water pressure of 0 MPa, the slurry is able to spread into a larger area without being dispersed or transported by groundwater. In the zone where the slurry contacts the ore-rock, it has already spread to the lower edge of the model. As the grouting time increases, the slurry will completely fill the entire contact zone. At water pressures of 1.5 MPa and 3 MPa, the groundwater disperses and carries the slurry diffusion. As the water pressure increases, the shape of the curtain body decreases to varying extents, and the range of slurry diffusion at the contact zone is significantly reduced.

4.3. Group-Hole Grouting Curtain Body Formation Effect

4.3.1. Group-Hole Grouting Calculation Model

An engineering-scale three-dimensional porous media model is created to investigate the formation effect of the curtain body. The model has dimensions of 30 m × 30 m × 40 m and considers circular arrangements of the grouting holes. Eight grouting holes are set up to prevent overflow. The center of the working face is used as the starting point, and the grouting holes are positioned at equal intervals along a specific inclination and tangential angle, as illustrated in Figure 10. To ensure the quality of the curtain body formation, a grouting sequence is followed. First, the bottom plate, top plate, and two gangs are grouted in a specific order. This process involves grouting eight holes in the bottom plate to form a first-order curtain body. Next, a second-order curtain body is formed in the top plate, followed by a third-order curtain body in the two gangs at the end. This sequence helps reinforce both the top plate and the bottom plate.

4.3.2. Group-Hole Grouting Curtain Body Formation Effect

A simulation is conducted to analyze the morphological changes in slurry diffusion during the established grouting sequence. The findings are presented in Figure 11. The final curtain body takes the form of bundles as a result of the reciprocal influence of the slurry dispersion between the surrounding grouting holes. By drilling grouting holes at a specific angle into the working face, the slurry can be spread effectively near the working face, filling the pores and fissures in the surrounding rock to achieve water plugging. However, as the grouting holes are spaced farther away from the working face, the slurry may not spread adequately near the center, resulting in the formation of a hollow stone body. At the end of the grouting holes, the stone body takes on a bundle-like shape. The presence of circular formations at the ends of the grouting holes can hinder the effectiveness of the grouting process. This prevents the slurry from properly bonding with the surrounding rock, hence failing to produce the desired water-sealing effect. Thus, in the subsequent construction section, a portion of the grouting curtain body formed in the previous construction section can be utilized as a grout-stopping pad. This serves the dual purpose of reinforcing the weak curtain body by injecting additional material, preventing slurry leakage and other issues during grouting in the upcoming construction section.

4.3.3. Changes in Curtain Morphology for Different Cross-Sections

Figure 12, Figure 13 and Figure 14 illustrate the variations in the shape of the curtain body’s cross-section at different positions. During the construction of the first sequence of holes, it is evident that the slurry spread at the working face will gradually form an almost elliptical stone body. Additionally, the slurry can also have a cementing effect on the two groups of rocks surrounding the base plate. However, at the end of the curtain body, due to the wide spacing of the grouting holes, only a small portion of the slurry spread will come into contact with the slurry from the adjacent grouting holes. As a result, a complete stone body fails to form, leading to poor grouting effectiveness. Upon construction of the second series of holes, it was observed that the spreading of the slurry both at the working face and at the end encountered the same issue. During the construction of the third sequence hole, it was observed that after the first two processes, the grouting holes were closely arranged at the working face. This resulted in the formation of a more complete curtain body. The grouting carried out by the two gangs also reinforced the top and bottom plates by filling the pores created during the first two construction processes. This further led to the formation of a complete and nearly rounded nodular body. The diagram in Figure 14c shows that the slurry diffusion at the two gangs forms a curtain that connects the top plate and the base plate. However, due to the disadvantage of insufficient slurry diffusion in the first two sequences of grouting holes with large spacing, a complete nodular body fails to form. Therefore, improvement measures need to be implemented in the subsequent stages to ensure that the bottom of the grouting holes forms a complete and dense curtain body, which will effectively plug water and provide waterproofing.

5. Optimization of Group-Hole Grouting Parameters

Based on the aforementioned study, it is evident that as the distance from the grouting working surface increases, the spacing between the stone bodies in various sections also increases. This results in an inability to form a cohesive and compact curtain body at that distance from the working surface. Additionally, the dispersion of the slurry at the bottom of the grouting holes is particularly severe. With increasing grouting rate, the slurry’s spreading distance and the stones’ morphology also increase under the same water pressure condition. Additionally, reducing the spacing of the grouting holes can decrease the spacing of the rocks at the bottom of the holes. Therefore, optimizing the grouting parameters can be achieved by increasing the grouting rate and reducing the spacing of the grouting holes.

5.1. Increase Grouting Rate

Based on the group-hole grouting model, keeping the same grouting sequence and only increasing the grouting rate from 0.3 m/s to 0.5 m/s, the simulation results are shown in Figure 15.

By comparing Figure 11 and Figure 15, it can be observed that the curtain body’s final morphology remains in the shape of bundles after increasing the grouting rate. However, the thickness of the curtain body is greater than that of the previous one. By increasing the rate at which grouting is performed, it is possible to create a fully formed and compact spherical body of grouted stones in the area near the working face once the second sequence of holes is completed. The diffusion of the grouting slurry is elliptical, allowing the top and bottom plates of the slurry to come into contact with each other, resulting in a more solid grouted stone body. However, the slurry near the edges of the diffusion radius is limited, and it does not effectively reinforce the surrounding rock. Nevertheless, subsequent hole grouting in the three sequences can enhance the thickness of the curtain body between the two edges. Grouting can increase the thickness of the curtain body of the two gangs. A solid and compact stone body can be generated at the bottom of the grouting holes, reducing the hollow region significantly. This is in contrast to the previous pattern of cross-section of the curtain body, which had a grouting rate of 0.3 m/s. Increasing the grouting pace can cause the slurry to transition from a discrete state to a cohesive state, resulting in improved quality of the curtain body and increased efficiency of water plugging.

5.2. Reduce the Spacing of the Grouting Holes

The group-hole grouting model involves arranging 12 grouting holes equidistantly along the contour line of the working face. Among these holes, three near the lower part are considered first sequence holes, five on the upper part are second sequence holes, and each of the left and right gangs has two holes as third sequence holes. The optimization model for the grouting interval is depicted in Figure 16, and the simulation calculation results are presented in Figure 17.

By comparing Figure 11 and Figure 17, it can be observed that the final shape of the grouting curtain body resembles that of a round table. Additionally, the surface of the grouting curtain body is smoother, and its overall integrity is significantly improved compared to the prior form. Once the first hole grouting sequence is completed, the slurry can fully diffuse near the bottom plate due to the narrow spacing between the grouting holes. It can also diffuse into the two gangs at the grouting surface. This results in the formation of a complete and thick grouted stone body in the bottom plate as the slurry comes into contact with each other at the bottom of the grouting holes. Once the second hole grouting sequence is completed, the slurry will be evenly distributed throughout all parts, resulting in the formation of a dense interior with little porosity, creating an optimal stone structure. Nevertheless, there was a lack of contact between the slurry at the bottom of the hole grouting sequence and both the bottom plate and the top plate. Therefore, it is necessary to adhere to the third hole grouting sequence in order to reintroduce this reinforcement by injecting it again. After the third hole operations were finished, a roughly spherical mass of slurry stones formed at the working face. The slurry expands laterally, with the horizontal gap between the two clusters steadily increasing as the distance between the section and the working face increases. The ultimate shape of the slurry clusters shows a broader width on both sides. The hollow region has significantly decreased in size after optimization, while the curtain body can still maintain its complete and thick spherical shape at the bottom of the grouting holes. The improvement of the final curtain body’s quality can be achieved by effectively reducing the gap between injection holes.

6. Engineering Applications

6.1. Curtain Grouting Design

The air shaft at the −380 m level of the Zhongjiu Iron Mine, known as 2#, has a straight wall three-center arch section design for the vein lane. The roadway has a net width of 4.0 m, a net height of 3.7 m, and a net section of 14.1 m². To ensure the smooth passage of the roadway through the ore-rock contact zone, exploration and grouting for flyover curtain water are being carried out in the 2# vein lane. The exploration and injection will take place between the 46.8 m and 76.8 m points along the vein lane. The depth of exploration and injection will be 30 m. Water exploration work will be conducted on the surface at the 46.8 m position along the vein lane. The water exploration hole is positioned 500 mm inward from the contour line of the net diameter. The hole has a diameter of Φ76 mm and a depth of 30 m. The orifice pipe is made from Φ95 × 5 mm × 6000 mm seamless steel pipe. There are a total of 10 holes, with 7#, 5#, and 6# being the first sequence, 1#, 2#, and 3# being the second sequence, and 4# and 8# being the third sequence. The 9# and 10# holes are designated as inspection holes. The diagram illustrating the arrangement can be observed in Figure 18, with the measurements in millimeters.

A flow chart of the grouting process is shown in Figure 19. The primary components consist of three aspects:

• The task involves transporting materials and mixing slurry, specifically cement, water glass, and water, in accordance with a prescribed water-cement ratio to create a cement-water glass slurry. The objective is to prevent blockages and pipe clogs during the grouting process.
• The grouting pump should be controlled based on the real grouting conditions, and the pump should be promptly started and stopped as needed. It is important to continuously monitor the grouting pressure to prevent pipe blockage and pipe collapse.
• When connecting the orifice pipeline, it is important to carefully monitor the grouting situation on the working surface. It is necessary to promptly identify any leaks, pipe blockages, or other accidents and effectively control the grouting volume and pressure. Additionally, grouting valves should be promptly removed and cleaned as needed.

The material used is a quick-setting slurry made by mixing cement and water glass. The cement used is ordinary silicate cement of grade 42.5. The water-cement ratio is controlled between 0.4 and 0.6. A high-efficiency water-reducing agent is added to the cement in an amount of 0.7 to 1.0%. The water glass slurry has a concentration of 10 to 12°Be. The ratio of cement slurry to water glass slurry is 1:1. The speed of the slurry is 0.5 m/s.

6.2. Analysis of the Effect of Grouting Curtain

The primary objective of constructing a grouting curtain is to address the issue of flooding during tunnel excavation. The magnitude of water seepage from the surrounding rock of the tunnel can be utilized to assess the effectiveness of the curtain. To assess the effectiveness of grouting, it is important to record the changes in water volume in the drill holes before and after the grouting process. These data can then be shown for evaluation purposes.

Figure 20 displays the water inflow in the exploratory boreholes both before and after grouting. Out of the holes mentioned, holes 1 to 8 are used to probe for water and have a water influx rate of approximately 30 m³/h before grouting. Holes 9 and 10 are designated as check holes and, following the grouting process, exhibit a water influx rate of less than 1 m³/h. This is performed to ensure that the cumulative water ingress while digging does not exceed 5 m³/h. This suggests that the slurry has the ability to create a reliable barrier for grouting when used with this specific arrangement of water-probing holes, resulting in an optimal water-plugging effect.

The roadway meets the necessary conditions for resuming excavation. However, it is possible that there may be loose water in the rock body, and the rock-mineral contact zone may be exposed during excavation. Therefore, it is important to strengthen the construction process with the complementary measures of “short exploration and short injection + short excavation and short support”. Enforce the efficient execution of the brief survey and excavation process and adopt appropriate support measures based on the revealed lithology. To ensure construction safety, we adopt a method of short exploration and excavation in addition to long exploration. Each cycle involves digging 5–8 short exploration holes, with a depth of 5–8 m and a maximum excavation depth of 1.6–3 m. During construction, if the cumulative amount of water in the short exploration holes exceeds 5 m³/h but is less than 10 m³/h, the excavation will be halted. Grouting and water-blocking will be carried out before resuming construction. If the cumulative amount of water in the short exploration holes exceeds 10 m³/h, a long exploration of the working face will be conducted. If the total volume of water in the short probe hole exceeds 10 cubic meters per hour, the long probe construction will be conducted at the working face.

7. Conclusions

This paper focuses on the engineering conditions of the Anhui MaGang Zhongjiu Iron Mine. This study applies Darcy’s law equations to analyze the seepage flows of slurry water in a porous medium. It also utilizes Navier-Stokes equations to study the laminar two-phase flow theory coupled with the horizontal set function. With COMSOL Multiphysics, a program for coupled multiphysics field analysis, the formation effect of single-hole and group-hole grouting curtain bodies and the numerical modeling of the slurry plane diffusion law in the ore-rock contact zone were completed. By analyzing the simulation results, two methods to optimize the grouting parameters of group holes are proposed and verified using numerical simulations. Ultimately, the findings of this research are applied to a specific project. The following primary findings were obtained:

The results indicate that as the grouting rate increases and the water pressure decreases, the thickness of the curtain body increases, and the surface morphology becomes smoother. The curtain body in the contact zone between the front and rear surfaces fits well together, forming a cohesive unit. In the contact zone between the ore and rock, the spread of the slurry is significantly influenced by gravity, with a tendency for the slurry to diffuse downward. This tendency increases as the grouting rate increases. Increasing the grouting rate effectively addresses the issue of insufficient slurry spread. To address the issue of inadequate slurry spreading, one can either increase the rate at which grouting is performed or decrease the distance between the grouting holes. In this project, a total of 10 drill holes were set up with an arrangement based on the section’s shape. Holes 1 to 8 were designated as grouting holes, while holes 9 and 10 were designated as inspection holes. The exploratory holes discharged less than 1 m³/h of water after grouting, indicating the formation of an effective grouting curtain. This grouting curtain successfully prevented water leakage.

This work presents a study on the application of overtopping curtain grouting in the mineral-rock contact zone in a water-rich environment. This research has yielded certain outcomes, but it is important to acknowledge its limits. Several academics have already proposed a more precise model of clayey soil material in their research [22,23]. Utilizing a more exact ontological model can facilitate more comprehensive research in future articles. Furthermore, our study reveals that the slurry in the contact zone exhibits a propensity to descend as a result of gravity. Exploring ways to harness this downward movement to enhance grouting efficiency is a promising avenue for further research.