Grout Diffusion Research Articles

Grouting theories and technologies for the reinforcement of fractured rocks surrounding deep roadways

AbstractGrouting is an effective method to improve the integrity and stability of fractured rocks that surround deep roadways. After years of research and practice, various theories and a complete set of grouting technologies for deep roadways with fractured rocks have been developed and are widely applied in Chinese coal mining production. This paper systematically summarizes and analyzes the research results concerning the theory, design, materials, processes, and equipment for the grouting and reinforcement of fractured rocks surrounding deep roadways. Specifically, in terms of grouting methods, pregrouting, grouting‐while‐excavation, and postgrouting methods are explored; in terms of grouting theory, backfill grouting, compaction grouting, infiltration grouting, and fracture grouting theories are studied. In addition, this paper also studies grouting borehole arrangement, water‐cement ratio, grouting pressure, grouting volume, grout diffusion radius, and other grouting parameters and their determination methods. On this basis, this paper explores the physical and mechanical properties of organic and organic‐inorganic composite grouting materials, and assess grouting reinforcement quality testing methods and instruments. Taken as the field cases, the application of pregrouting in front of heading faces, grouting‐while‐excavation, and postgrouting in the Kouzidong coal mine are then introduced, and the effects of the grouting reinforcements are evaluated. This paper proposes a development direction for grouting technology based on problems existing in the grouting reinforcement of fractured rocks surrounding deep roadways.

Grouting slurry diffusion range based on active heating fiber optics monitoring

To quantify the diffusion range of slurry in grouting engineering, an active heating optical fiber (AHFO) monitoring method is proposed. The AHFO is arranged on the coal seam floor. The temperature is taken as the monitoring parameter to monitor the diffusion range and state of slurry in the injected medium. Considering the time-varying characteristics of slurry rheological parameters, the theoretical calculation formula of spherical diffusion radius based on the power-law fluid is deduced. The relationship between the void ratio and grouting diffusion radius is discussed. Considering the influence of the seepage effect, the "water cement ratio change matrix" in the process of mud seepage is derived, and the influence of the space–time change of the slurry water cement ratio on the temperature gradient of the injected medium is studied. According to the factors affecting grouting diffusion, four groups of small three-dimensional simulation tests and one large three-dimensional grouting test are designed to verify the feasibility of the proposed method. The results show that the relative error of the AHFO monitoring radius is between 3.00 and 14.67%, based on the actual diffusion radius. In the large-scale three-dimensional grouting test, the data from AHFO is used to generate the two-dimensional surface of the grouting diffusion form, and the grouting diffusion range is asymmetric oval. Compared with the theoretical calculation results, the maximum relative error of grouting diffusion radius is 9.6%, and AHFO shows prediction accuracy. With the decrease in the water-cement ratio of slurry, the temperature gradient of the injection medium monitored by AHFO increases, showing an obvious space–time effect. The application of AHFO in the grouting simulation test can effectively analyze slurry diffusion in the injected medium.

Theoretical Research on Diffusion Radius of Cement-Based Materials Considering the Pore Characteristics of Porous Media.

In engineering, loose sandy (gravelly) strata are often filled with cement-based grout to form a mixed material with a certain strength and impermeability, so as to improve the mechanical properties of sandy (gravelly) strata. The tortuosity effect of sandy (gravelly) strata and the time-varying viscosity of slurry play a key role in penetration grouting projects. In order to better understand the influence of the above factors on the penetration and diffusion mechanism of power-law slurry, based on the capillary laminar flow model, this research obtained the seepage motion equation of power-law slurry, the time-varying constitutive equations of tortuosity and power-law fluid viscosity were introduced, and the spherical diffusion equation of penetration grouting considering both the tortuosity of porous media and time-varying slurry viscosity was established, which had already been verified by existing experiments. In addition, the time-varying factors of grouting pressure, the physical parameters of the injected soil layer, and slurry viscosity on penetration grouting diffusion law and the influencing factors were analyzed. The results show that considering the tortuosity of sandy (gravelly) strata and the time-varying of slurry viscosity at the same time, the error is smaller than the existing theoretical error, only 13~19%. The diffusion range of penetration grouting in the sandy (gravelly) strata is controlled by the tortuosity of sandy (gravelly) strata, the water-cement ratio of slurry, and grouting pressure. The tortuosity of sandy (gravelly) strata is inversely proportional to the diffusion radius of the slurry, and the water-cement ratio of slurry and grouting pressure are positively correlated with the diffusion radius. In sandy (gravelly) strata with a smaller particle size, the tortuosity effect of porous media dominates the slurry pressure attenuation. When the particle size is larger, the primary controlling factor of slurry pressure attenuation is the tortuosity effect of porous media in the initial stage and the time-varying viscosity of slurry in the later stage. The research results are of great significance to guide the penetration grouting of sandy (gravelly) strata.

Experimental investigation on pneumatic pre-fracturing grouting in low-permeability soil

Effective injection of grout into low-permeability soil is difficult in the process of soil reinforcement. To address practical problems, this study proposes a pneumatic pre-fracturing grouting method comprising model experiments to analyze the initiation and propagation of fractures, earth pressure, soil displacement, and the characteristics of grouting consolidation. In the pneumatic fracturing experiment, the fractures exhibited larger effective radii under gradual pneumatic loading compared with those created due to instant loading, providing more initial channels for grout diffusion. Meanwhile, the higher the pneumatic pressure, the greater the residual height of the fractures after pneumatic fracturing, yielding a predominant condition for grout injection. Compared with conventional grouting, the effective injection amount, effective diffusion radius, and height of grout consolidation of pneumatic pre-fracturing grouting were much larger. The results prove the feasibility and superiority of pneumatic pre-fracturing grouting in low-permeability soils.

Experimental Investigation on the Diffusion Law of Polymer Slurry Grouted in Sand.

Polymer slurry is widely used in underground engineering treatment, but due to the concealed nature of underground projects, the diffusion pattern of slurry in the sand has been little studied. In this study, the basic physical properties of water-based polyurethane, oil-based polyurethane, and acrylate and epoxy resin were compared, and the performance of chemical grouted sands with different polymer slurry/sand mass ratios (PS/S) was tested. The higher the PS/S, the better the mechanical and impermeability properties of the chemical grouted sands. In this paper, water-based polyurethane was selected to carry out orthogonal tests on the diffusivity of slurry in sands. This experiment investigated the degree of influence of sand quality, grouting pressure and sand compactness on the diffusion of slurry in sands. The test results show that, in terms of factors affecting the final pressure of grouting, the sand density has the greatest influence, followed by the sand quality, and the grouting pressure is the smallest. In terms of slurry diffusibility, grouting pressure has the greatest influence, followed by sand compactness, and the sand quality is the smallest. The diffusion mechanism of slurry in the sand was deduced from the morphology of chemical grouted sands. Water-based polyurethane showed splitting-compression-penetration diffusion in sands of different grades, and the diffusion pattern of the slurry was not the same in low-pressure (1–1.5 MPa) grouting and high-pressure (2 MPa) grouting, and lateral splitting occurred in the case of high-pressure grouting diffusion.

Study on the Influence of Back-fill Grouting Parameters in Unsaturated Strata on the Seismic Performance of Shield Tunnels

In this study, based on unsaturated soil theory, the diffusion behavior of shield tunnel back-fill grouting in unsaturated strata was considered, and Van Genuchten equation was introduced for deriving calculation formula for grouting diffusion radius. Then, an analysis flow for the influence of back-fill grouting parameters on seismic performance of shield tunnel was proposed, and the analysis was carried out with an actual project example. The results show that, compared to the saturated state, owing to the existence of matrix suction in the unsaturated soil, the permeability of the stratum is reduced, resulting in a slower increase in the grouting diffusion radius and smaller ultimate grouting distance. In this project, after using asphalt-cement grouting material, increasing the grouting time and grouting pressure, as well as reducing the elastic modulus of the material can decrease the seismic response of the tunnel. When the grouting time t = 60 min, grouting pressure P0 = 0.5 MPa, elastic modulus E = 49.1 MPa, the seismic-reduction rate of the structure can reach 25.65%. Finally, the fitted equations for the grouting time, pressure, and elastic modulus of the grouting material with the relative displacement and seismic-reduction rate of the tunnel were obtained.

Numerical and experimental study of diffusion law of foamed polymer grout in fracture considering viscosity variation of slurry

As a new type of chemical grouting material, polymers have been widely used in fractured rock masses, but the understanding of the diffusion characteristics of polymers still needs to be further improved. Due to the expansion of polymer slurry, the change of grouting pressure is not synchronized with the time change of diffusion radius, leading to the diffusion law of polymer slurry more complicated. Therefore, based on the rheological properties of the slurry and the theory of viscous hydrodynamics, a polymer fracture grouting diffusion model was established. Through the finite element level set method and adjusting the liquid level according to the fluid velocity, it can be obtained the diffusion interface of the fluid at the corresponding point in time and the change law of the pressure at the corresponding diffusion interface with time. Finally, the validity of the model is verified by the polymer slurry parallel plate grouting diffusion experiment. The research results indicated that: (1) The diffusion mode of the polymer fracture grouting diffusion model is basically consistent with the test results. (2) The grouting pressure gradually decreases along the direction of the diffusion radius, increases with the decrease of the crack width, and increases with the time, but the change of the grouting pressure lags behind the change of the diffusion radius. (3) The results are consistent with the pressure field curve measured by the experiment, indicating that the main factor causing the hysteresis effect of the pressure field change is the time-varying viscosity of the polymer slurry.

The Characteristics of Grout Diffusion in Reduce Subsidence Mining with Abscission Layer Grouting

The Characteristics of Grout Diffusion in Reduce Subsidence Mining with Abscission Layer Grouting

Backfill grouting diffusion law of shield tunnel considering porous media with nonuniform porosity

Current studies usually do not consider the effect of spatially inhomogeneous distribution of formation parameters on grout diffusion caused by shield tail voids. To solve the above problem, this study proposes a nonuniform pore model for porous media formation and establishes a one-dimensional penetration grouting diffusion model considering the spatial nonuniformity of formation pores under the condition of constant grouting pressure. This model was used to analyze the penetration diffusion behavior of grout in the strata and the influence of parameters such as grouting pressure, water-cement ratio, and formation displacement. The numerical solution was provided by the finite element software COMSOL. According to the degree of cement particle blockage, it is pointed out that there is an injectability control zone in the grouting process. A one-dimensional visualized penetration grouting diffusion simulation system considering the shield tail gap was designed, and a grouting diffusion test was carried out with cement slurry. The results show that grouting pressure, water-cement ratio, and soil displacement have a significant influence on the grout deposition process. The higher the grouting pressure, the lower the water-cement ratio, the faster the formation turns into the non-injectable state. The grouting pressure has little influence on the injectable control zone, while the larger the water-cement ratio, the greater the displacement of the formation, and the farther the injectability control zone is from the grouting hole. By comparing the nonuniform pore model with grouting test, the rationality of the nonuniform pore model is verified, which provides guidance and a basis for backfill grouting.

Actively heated fiber optics method to monitor grout diffusion range in goaf

The invisibility of grouting has always been one of the most challenging problems related to the research of grouting theory, but it has not been solved. An actively heated fiber optics (AHFO) method is proposed in this paper to realize the visualization of slurry diffusion morphology. The grid installation method of AHFO is designed, and the calculation formula of grid size is deduced. Based on the self-developed spatial positioning algorithm and Kriging spatial interpolation algorithm, the temperature anomaly in the AHFO temperature profile is used to locate and quantify the range of grouting diffusion in goaf. To verify the applicability of this method, a large-scale three-dimensional grouting model test was carried out. The test results show that the grouting diffusion mode is elliptical, consistent with the previous research results. Compared with the theoretical calculation results, the maximum relative error of the monitored grouting diffusion radius is 18 %. Therefore, the monitoring method can monitor the grouting diffusion.

Real-time characterization of the grouting diffusion process in fractured sandstone based on the low-field nuclear magnetic resonance technique

Investigations of the flow and diffusion mechanism of grout slurry in underground fractured rock mass are of critical significance to guarantee the grouting reinforcement of deep soft rock tunnel and to ensure the construction safety. This paper reports a series of permeation grouting tests in fractured sandstone samples based on the low-field nuclear magnetic resonance (LF-NMR) technique. During the grouting process, the NMR signal characteristics of the grout were monitored in real-time, and the parameters such as the slurry injection volume, effective grouting time and grout filling speed were comprehensively analyzed under various temperatures, confining pressures, flow velocities and numbers of fractures. The results show that the final injection amount of the grout decreases with increasing temperature and confining pressure. The effective grouting time is inversely proportional to the flow velocity, while it is positively related to the temperature. The filling speed decreases with increasing the temperature and confining pressure, while it increases with increasing the grout flow velocity. Compared to the single fractured sample, the sample with more fractures is injected with more grout slurry in a shorter effective grouting time and a higher filling speed. Under the conditions of high confining pressure (e.g., 15 MPa) or high flow velocity (e.g., ≥5 ml/min), the grout slurry preferentially transports into the micropores, and then the mesopores and macropores. However, the temperature and number of fractures have equal effects on the grout flow and diffusion in the three types of pores. The grouting filling performance becomes worse when the temperature and confining pressure are higher. The findings in this study provide meaningful guidance for the grouting reinforcement of deep soft rock tunnel.

Permeation grouting diffusion mechanism of quick setting grout

Quick setting grout is used in permeation grouting projects to control the grouting diffusion range effectively and reduce the waste of grout. Owing to the double-component injection method and quick setting property of the grout, the viscosity of the quick setting grout is non-uniformly distributed in the grouted region, which has a significant influence on the grouting diffusion process. In this study, the permeation grouting process of a quick setting grout was studied. A 2-D cylindrical permeation grouting diffusion model was developed considering the non-uniform distribution of grout viscosity. A visible permeation grouting diffusion simulation test system was designed and established. A series of tests were carried out to verify the correctness of the theoretical model, in which cement–sodium silicate grout, a typical quick setting grout, with two water–cement ratios (W/C = 1, 2) and gravel sand with two different ranges of particle size (2–5 mm, 5–20 mm) were used. The results show that (1) when the size of the void space in the sand stratum exceeds a certain value, the permeation diffusion of grout is completely controlled by grout gravity, and the influence of the quick setting characteristics can be ignored. Otherwise, the quick setting characteristics have the most important effect on permeation diffusion. (2) The calculated results agree well with the test results. The calculated injection pressure result is 1.0–1.4 times the experimental result, and the calculated diffusion radius is 95.7% –98.5% of the test value with the same final injection pressure. (3) It is necessary to consider the non-uniform distribution of viscosity in the calculation of the permeation grouting process of a quick setting grout. For a quick setting grout, if the non-uniform distribution of viscosity is not considered, the injection pressure would be overestimated by more than 10 times the actual value, and the diffusion radius would be underestimated by 30%–50% of the actual value.

Spatial Distribution Characteristics of Plastic Failure and Grouting Diffusion within Deep Roadway Surrounding Rock under Three-Dimensional Unequal Ground Stress and Its Application

To explore the bolt-grouting method of the deep roadway under three-dimensional unequal ground stress, a unidirectional coupling model of surrounding rock plastic failure and grouting diffusion considering the influence of excavation disturbance stress was established. Spatial evolution characteristics of plastic failure and grouting diffusion, and the impact of the spacing and row spacing of grouting bolts/cables on grout diffusion, were simulated by using the numerical method. The results revealed that the horizontal ground stress perpendicular to the axial direction of the roadway was the main factor inducing roadway damage. Moreover, the more significant the difference of the ground stress in three directions, the larger the plastic zone of the roof corner and floor corner of the roadway. Under different lateral pressure coefficients, the grout diffused can be approximate ellipsoid and cylinders. Furthermore, the larger the ratio of lateral pressure coefficients perpendicular to and parallel to the axial direction of roadway, the larger the diffusion length of grout in each spatial direction in the surrounding rock. In bolt-grouting support, the length of the grouting bolts/cables should be greater than the plastic zone of the surrounding rock, and the optimal relationship between their spacing and row spacing and diffusion length of grout is determined. The research results were applied in the bolt-grouting engineering for the three-level main roadway in the Haizi Coal Mine, and a good support effect was achieved. This can provide technical guidance and a method of reference for the design and parameter optimization of bolt-grouting support for roadways under deep high ground stress.

Actively Heated Fiber Optics Method to Monitor Grout Diffusion Range in Goaf

Actively Heated Fiber Optics Method to Monitor Grout Diffusion Range in Goaf

Penetration Grouting Mechanism of Time-Dependent Power-Law Fluid for Reinforcing Loose Gravel Soil

The time-dependent behavior of power-law fluid has a significant influence on the grouting effects of reinforcing loose gravel soil. In this paper, based on basic rheological equations and the time-dependent behavior of rheological parameters (consistency coefficient and rheological index), rheological equations and penetration equations of time-dependent power-law fluid are proposed. Its penetration grouting diffusion mechanism for reinforcing loose gravel soil was then theoretically induced. A set of indoor experimental devices for simulating penetration grouting was designed to simulate the penetration grouting of power-law fluid with different time-dependent behaviors for reinforcing loose gravel soil. Then, relying on the COMSOL Multiphysics platform and Darcy’s law, three-dimensional numerical calculation programs for this mechanism were obtained using secondary-development programming technology. Thus, the numerical simulations of the penetration grouting process of power-law fluid with different time-dependent behaviors for reinforcing loose gravel soil were carried out. This theoretical mechanism was validated by comparing results from theoretical analyses, indoor experiments, and numerical simulations. Research results show that the three-dimensional numerical calculation programs can successfully simulate the penetration diffusion patterns of a time-dependent power-law fluid in loose gravel soil. The theoretical calculation values and numerical simulation values of the diffusion radius obtained from this mechanism are closer to indoor experimental values than those obtained from the penetration grouting diffusion theory of power-law fluid without considering time-dependent behavior. This mechanism can better reflect the penetration grouting diffusion laws of a power-law fluid in loose gravel soil than the theory, which can provide theoretical support and guidance for practical grouting construction.

The numerical simulation of rock mass grouting: a literature review

PurposeThe purpose of this article is to understand the current research status and future development trends in the field of numerical simulation on rock mass grouting.Design/methodology/approachThis article first searched the literature database (EI, Web of Science, CNKI, etc.) for keywords related to the numerical simulation of rock mass grouting to obtain the initial literature database. Then, from the initial database, several documents with strong relevance to the numerical simulation theme of rock mass grouting and high citation rate were selected; some documents from the references were selected as supplements, forming the sample database of this review study (a total of 90 articles). Finally, through sorting out the relationship among the literature, this literature review was carried out.FindingsThe numerical simulation of rock mass grouting is mainly based on the porous media model and the fractured media model. It has experienced the development process from Newtonian fluid to non-Newtonian fluid, from time-invariant viscosity to time-varying viscosity, and from generalized theoretical model to engineering application model. Based on this, this article summarizes four scientific problems that need to be solved in the future in this research field: the law of grout distribution at the cross fissures, the grout diffusion mechanism under multi-field coupling, more accurate grouting theoretical model and simulation technology with strong engineering applicability.Originality/valueThis research systematically analyzes the current research status and shortcomings of numerical simulation on rock mass grouting, summarizes four key issues in the future development of this research field and provides new ideas for the future research on numerical simulation on rock mass grouting.

A semi‐elliptical surface compound diffusion model for synchronous grouting filling stage in specially shaped shield tunnelling

AbstractIn constructing super‐large section shield tunnels, it is difficult to guarantee the filling efficiency and uniformity of grouting behind the segments. Studies on grout diffusion models often simplify the grout filling process, leading to inaccurate results, especially for shield tail void with special noncircular profiles. This paper presents a theoretical study on the grout filling diffusion mechanism and its mechanical behaviour, with a particular focus on the grout actual motion process at the synchronous grouting filling stage when the shield is advancing. A semi‐elliptical surface compound diffusion model without the predetermined flowing passage was developed, and this model was used to derive the grout filling pressure and diffusion distance formulas. To address the time‐varying diffusion surface and irregular integral region issues in derived equations, a stepwise solution algorithm based on the spatiotemporal discretisation operation was proposed. Finally, the grout pressure distribution patterns and some critical influence factors were analysed using a case study in the soft silty clay area to compare the presence and absence of circumferential‐longitudinal correlations in the grout filling diffusion process. The results show that the diffusion mechanical behaviour and force transmission significantly affected the total and per‐unit‐area grout pressures, and the proposed theoretical model is more consistent with the field‐measured data. The local trend and fluctuation characteristics of grout filling pressure are clearly different from those of a circular tunnel. The grout filling diffusion mechanism was determined to be the main cause of pressure distribution changes under the premise of a certain initial grouting pressure.

Investigation of grouting diffusion in a single rock fracture considering the influences of obstructions

Grouting reinforcement was used to improve rock strength and avoid seepage in rock engineering. A self-developed visualised test platform was developed and the influences of different fracture openness on grouting diffusion modes were revealed; the Bingham rheological model was imported to simulate the grouting diffusion process in a single plate fracture, the spatiotemporal distribution of the velocity field under different obstructions was determined using the finite element method. The results indicate that (i) the grout diffuses faster with the increase of fracture openness, while a stagnation effect of the grouting diffusion velocity behind the obstruction occurs. (ii) Due to obstructions, the grouting diffusion process can be divided into four stages: circular diffusion, flat diffusion, vortex diffusion, and butterfly diffusion. (iii) The grouting diffusion area is divided into a fully reinforced zone and a semi-reinforced zone, and the area of the latter increases with the fracture openness, while being little affected by the size of any obstruction. (iv) Furthermore, some new grouting diffusion laws were revealed considering the asymmetrical arrangement of obstructions. The results presented in this work will be helpful for describing and predicting the grouting process in fracture networks.

Analysis of Grout Diffusion of Postgrouting Pile Considering the Time-Dependent Behavior of Grout Viscosity

Abstract To get an accurate bearing capacity of a postgrouting pile, the range of grout diffusion should be considered in practice. Considering the time-dependent behavior of power-law cement grout...

Fissure Grouting Mechanism Accounting for the Time-Dependent Viscosity of Silica Sol.

Subject to the complex hydrogeological environment where underground engineering is located, the grouting prevention and control of microfissure water ingress are increasingly strict. Silica sol grout has been increasingly used in field tests because of its fine particles and good injectability. Therefore, it is necessary to examine the time-dependent viscosity of silica sol grout and clarify its diffusion law in a rock fissure. In this study, the time dependence of the viscosity of silica sol grout was studied, and then the grout viscosity was subdivided into a slow growth period, accelerated growth period, and rapid curing period according to the growth rate. The effects of the concentration of colloidal silica suspension, the concentration of accelerant, and the mixing volume ratio of the two on the growth of the slurry viscosity were studied. A parameter λ was introduced to comprehensively characterize the influence of the three factors on the rheological properties of the slurry. The relationship between the gel induction time and λ and the accelerating growth stage of the slurry gel was obtained by data fitting. The time-dependent equation of the silica sol solution was established. The difference in the grouting diffusion law between silica sol grout and cement–sodium silicate grout (C-S grout) is compared and analyzed by a stepwise calculation method under two grouting modes (constant-pressure grouting and constant-rate grouting). The results show that under the condition of constant-pressure grouting, the silica sol grout migrates and diffuses continuously for a long time, while the C-S grout is close to the final diffusion form at 15–20 s, and the maximum diffusion distance is much smaller than that of silica sol grout. Under the condition of constant-rate grouting, the grouting pressure driving C-S grout increases sharply with time. Compared with C-S grout, silica sol grout has the obvious advantages of a longer effective diffusion time and lower energy consumption. The research results have certain theoretical significance and reference value for the engineering design of silica sol grouting.