Rock Mass Grouting Research Articles

Characteristics of slurry-water mixing region in fractured rock mass grouting process: Experimental study

Grouting is one of the most commonly used methods to control water inrush disasters in fractured rock mass. At present, most of the research on the diffusion process of fracture grouting is carried out on the hypothesize that the groundwater was completely displaced by the slurry, which is lack of sufficient theoretical basis. Therefore, a one-dimensional visual fracture grouting experimental system was developed and a new characterization method of slurry concentration based on the image gray level was proposed in this paper in order to characterize the variation law of slurry-water mixing region during the grouting process. Results show that there exists slurry-water mixing region at the frontal surface of the diffusion slurry in the grouting process in fractured rock mass. The slurry-water mixing region can be characterized by the gray level of the images captured by cameras. The relationship of water to cement ratio of slurry (w/c) and image gray level of slurry (G) conforms to linear function, which can be expressed by G = 19.17 w/c when w/c is between 0.8 and 10. In addition, slurry concentration decreased linearly along the diffusion flow path in the slurry-water mixing region. The size of slurry-water mixing region is positively related to grouting flow rate, the mass ratio of water to cement (w/c) and fracture aperture when the grouting flow rate is between 0.6 L/min to 2.4 L/min, w/c is between 0.8 and 1.6 and fracture aperture is between 1 mm to 5 mm. Furthermore, the ratio of slurry-water mixing region size to hypothetical diffusion radius (RSR) was proposed to characterize development degree of slurry-water mixing region. The stable value of RSR was between 0.04 and 0.24 under the experimental conditions in this paper. The index of RSR can be used to provide theoretical basis for the simplification of the interface between slurry and water. The distribution rules of the slurry-water mixing region can be applied to predict the diffusion range more accurately and perfect the grouting theory.

Evaluating rock mass groutability at shallow depths: a novel approach based on geo-structural surveys and permeability tests

The study describes the geological and geo-structural setting of an unstable sea arch in a very attractive landscape of Southern Italy. It evaluates the applicability of some reinforcement work designs consisting of rock mass grouting at shallow depths along the arch vault and abutments. To this aim, the hydraulic conductivity of the rock mass and its groutability were evaluated in detail, integrating field geo-mechanical surveys, boreholes, Lugeon tests, and grouting tests with different grout compositions. Results from site tests were compared with grout take values calculated by applying classical empirical approaches available in the literature, based on rock mass permeability, or by using a novel deterministic approach based on geo-mechanical field surveys. Considering the shallow depths of the tests, the results suggest that the former gave high values, inconsistent with grout tests. On the contrary, the novel deterministic approach provided grout take values consistent with the results of grouting tests, resulting in the most reliable approach for the arch’s thin, shallow, and highly fractured structure.The use of different grout compositions in the site tests proved that extensive use of highly dense and viscous slurries is required (bentonite-cement grout) due to the high-grade weathering and karstification of joint surfaces, which deeply increases their hydraulic conductivity. However, the rock mass grouting must be considered complementary to other reinforcement measures such as bolting, especially along the arch vault.

Experimental research on mechanical performance of grouting plugging material with large amount of fly ash

In order to achieve the purpose of long-term stable mining of roadway, the strength and stability of rock mass are improved by means of grouting of fractured rock mass. In this paper, orthogonal test and numerical simulation methods were used to study the plugging performance of large amount of fly ash grouting slurry. The fluidity, water separation rate, compressive strength, setting time, stone rate and viscosity of the slurry were analyzed, and the optimal slurry ratio scheme was obtained. Under the optimal ratio scheme, the slurry transport process of the fractured rock mass was simulated, and the dynamic evolution law of the permeability of the slurry in the fractured rock mass was obtained. The study shows that the proportions of fly ash, ordinary Portland cement, loess, accelerant, expansion agent, bentonite water reducer and solidifying agent were 52.65%, 27.70%, 13.85%, 3%, 0.7%, 0.8%, 0.6% and 0.7% in the slurry ratio scheme, respectively. The slurry migration in the fractured rock mass experienced three stages, namely the filling and diffusion stage, the percolation and deposition stage and the sealing stage. The initial permeability was 971.9 mD and decreased to 45.79 mD after 1800 s, with a decrease of 95.3%. The slurry sealing performance was significantly improved, which has certain guiding significance for the application of underground grouting reinforcement engineering.

Study on Zonal Cooperative Control Technology of Surrounding Rock of Super Large Section Soft Rock Chamber Group Connected by Deep Vertical Shaft

Aiming at solving the problem of asymmetric deformation, failure, and stability control of surrounding rock caused by the excavation of deep super large section soft rock chamber group passing through multilayer strata, taking super large section soft rock chamber group connected by deep vertical shaft in Wuyang Coal Mine as the engineering background, the deformation development mode of surrounding rock, the expansion situation of loosening range, and the plastic failure response characteristics in chamber group under the disturbance influence are monitored and numerically analyzed. On this basis, the super large section chamber group is divided into four maintenance control areas: area I (severe deformation area), area II (stable deformation area), area III (medium deformation area), and area IV (small deformation area), and the asymmetric deformation and failure mechanism of the surrounding rock of the chamber group is analyzed. The influence mechanism of specific support technologies on the deformation control effect of surrounding rock of chamber group is systematically studied, including high‐strength prestressed bolt (cable) mesh shotcreting coupling support technology, reinforced concrete wall subarea brickwork support technology, and hollow bolt (cable) grouting reinforcement technology of fragmented coal and rock mass. The basic control ideas and technical methods of surrounding rock of deep large section soft rock chamber group are formed. The subarea collaborative control technology of “high‐strength prestressed bolt (cable) mesh shotcreting coupling + reinforced concrete wall brickwork support technology + high‐strength bolt (cable) grouting of fragmented coal and rock mass” is proposed. The field application shows that this technology realizes effective control of surrounding rock of super large section chamber group.

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.

Experimental study on grouting of elliptical fractured rock mass at various temperatures

Experimental study on grouting of elliptical fractured rock mass at various temperatures

Drill Monitoring for Rock Mass Grouting: Case Study at the Stockholm Bypass

In tunneling, rock mass grouting is a method applied to reduce water ingress. Grouting is influenced by rock mass conditions, especially apertures, frequency, and continuation of fracturing. These rock mass conditions can partly be determined by rock mass classification systems. At the Stockholm bypass, the Measurement While Drilling (MWD) Fracturing Index was applied to characterize the rock mass for grouting purposes, with a focus on adjusting the grout hole drill plan to minimize environmental impact. This study divided the rock mass in a 1.9 km tunnel into six categories based on rock mass conditions, identifying rock mass quality, apparent fracturing, and grout consumption. These categories were then compared with the mean fracturing index based on the coefficients of penetration rate and rotation pressure variations, as well as grout consumption at each grout umbrella. The fracturing index was 93% successful in assessing favorable and unfavorable rock mass conditions in the studied tunnel and 85% successful in determining grout consumption. Finally, a conceptual method was developed to reduce the grouting activities using the MWD fracturing index and water loss tests. The introduction of this conceptual method for grouting decisions could potentially reduce 59% of the umbrellas found in the case study.

Extension of grouting-induced splitting fractures in materials similar to coal rocks containing prefabricated fractures

Abstract To reveal the influence of prefabricated fractures (PFs) with different parameters on the extension of grouting-induced splitting fractures, a combination of numerical simulation and physical experiments were used to carry out grouting trials on similar materials to coal rock. The RFPA software was used to simulate the whole process of fracture initiation and expansion of coal rock with PFs during grouting. In the experiment, acoustic emission (AE) technology was used to monitor the extension process of grouting-induced splitting fractures. The results demonstrated that when the PFs do not intersect with the grouting holes, the extension of grouting-induced splitting fractures in rocks containing PFs experienced four stages: splitting and penetrating, slurry filling, fracture splitting and splitting extension. PFs have an orienting effect on the direction of grouting fracture extension and the size of the PFs influenced the extension of the grouting-induced splitting fractures: the larger the size, the easier the surrounding rocks were ruptured, the easier the connection was formed of channels between the grouting-induced splitting fractures and the PFs were formed, and the more complex the secondary splitting pattern in the PFs. This indicated that the angle of PFs played a decisive role in determining the extension direction of grouting-induced splitting fractures. The extension of grouting-induced splitting fractures during grouting of rock mass with different parameters is revealed by numerical simulation and experimental results.

Tools for optimizing rock mass grouting

AbstractOptimization of rock grouting procedures during construction is necessitated when sparse data sets and incomplete geologic understanding form the basis of initial design. Relying on geologic investigation findings that often have limited budgets, initial designs typically consider data from only a small volume of the entire rock mass to be grouted. During construction, thousands of production boreholes may be drilled and grouted, and each of these boreholes has the potential to provide valuable information for modifying the injection materials and construction means/methods. Implementation of procedural changes is greatly facilitated by the ability to efficiently assemble, query, visualize and interpret vast amounts of 3D data in near real‐time.This contribution summarizes the main targets of rock mass characterization in the context of grouting works, along with investigative tools that provide valuable information: (1) regarding the distribution and properties of in situ permeability features; (2) for modifying and optimizing grouting procedures; and (3) for verifying grouting results in situ. Three dimensional modeling approaches that are amenable to data visualization are reviewed, including the workflow for near real‐time model updating as construction proceeds.

Method for Measuring Rock Mass Characteristics and Evaluating the Grouting-Reinforced Effect Based on Digital Drilling

Various types of broken rock masses, such as those in fault-fracture zones and fracture zones, which form as a result of disturbance from tunnelling, are often encountered during underground engineering construction. These rock masses have low self-supporting capacity and poor stability, which can easily cause damage to surrounding rock, such as large deformation features, collapse and falling blocks, etc., posing a threat to construction safety. During a field project, reinforcement by grouting is a primary means for addressing the aforementioned problems. The effective measurement of rock mass characteristics (e.g., rock layer interfaces and the broken area of surrounding rock) provides a basis for the reasonable design of a grouting scheme. The quantitative evaluation of the effect of rock mass grouting is essential for optimizing the grouting scheme. In view of this, in this study, a multi-functional rock mass digital drilling test system and a special polycrystalline diamond compact drill bit for digital testing were developed and were applied to conduct digital drilling tests on intact, broken and grouted rock masses. In addition, a digital drilling test (DDT) technique-based method for measuring rock mass characteristics in real time and rapidly evaluating the grouting effect was proposed. The proposed method is capable of identifying rock layer interfaces, determining the broken area and obtaining the equivalent strength of grouted rock masses. This method is advantageous for obtaining quantitative and rapid test results, which can provide a theoretical basis and technical means for optimizing the grouting parameters and designing support schemes for underground engineering construction.

Development of an algorithm to detect hydraulic jacking in high pressure rock mass grouting and introduction of the PF index

Pre-excavation rock mass grouting is a common procedure for reducing water ingress into tunnels during construction in Norwegian tunnelling. The level of grouting pressure is a disputed subject and the knowledge of how the rock mass responds to the high pressure and how this inflicts on the grouting results is sparse and little investigated. For this reason, it is of interest to use data from high pressure grouting performed in Norwegian projects to investigate these matters. This paper presents the development of a method for identifying hydraulic jacking during rock mass grouting and the making of an algorithm to perform computerized detection of hydraulic jacking in grouting logs. The algorithm is the base for a larger study, where screening for hydraulic jacking is performed in over hundred grouting rounds, distributed on several Norwegian tunnels excavated in rock mass. The relation between grout flow and grouting pressure has shown to be vital for the understanding of the grouting progress and events occurring during the grouting. Interpretation of pressure and flow as two separate variables, which are affected by aliasing, caused by low and irregular sampling frequency is a challenging task, and it was found to be helpful to create a parameter to represent this relationship, named the PF index (Pressure Flow index). This parameter has also shown to be useful in other applications such as monitoring the grouting progress on site.

Numerical Investigation of Grouting of Rock Mass with Fracture Propagation Using Cohesive Finite Elements

Numerical Investigation of Grouting of Rock Mass with Fracture Propagation Using Cohesive Finite Elements

Rock Mass Grouting in the Løren Tunnel: Case Study with the Main Focus on the Groutability and Feasibility of Drill Parameter Interpretation

The Loren road tunnel is a part of a major project at Ring road 3 in Oslo, Norway. The rock part of the tunnel is 915 m long and has two tubes with three lanes and breakdown lanes. Strict water ingress restriction was specified and continuous rock mass grouting was, therefore, carried out for the entire tunnel, which was excavated in folded Cambro-Silurian shales intruded by numerous dykes. This paper describes the rock mass grouting that was carried out for the Loren tunnel. Particular emphasis is placed on discussing grout consumption and the challenges that were encountered when passing under a distinct rock depression. Measurement while drilling (MWD) technology was used for this project, and, in this paper, the relationships between the drill parameter interpretation (DPI) factors water and fracturing are examined in relation to grout volumes. A lowering of the groundwater table was experienced during excavation under the rock depression, but the groundwater was nearly re-established after completion of the main construction work. A planned 80-m watertight concrete lining was not required to be built due to the excellent results from grouting in the rock depression area. A relationship was found between leakages mapped in the tunnel and the DPI water factor, indicating that water is actually present where the DPI water factor shows water in the rock. It is concluded that, for the Loren tunnel, careful planning and high-quality execution of the rock mass grouting made the measured water ingress meet the restrictions. For future projects, the DPI water factor may be used to give a better understanding of the material in which the rock mass grouting is performed and may also be used to reduce the time spent and volumes used when grouting.

The Calculation of Grouting Diffusion Radius on Based Bingham Fluid for Chunnel That Passes through Fractured Rock Mass

To conduct pro-grouting design and make the prediction of the result of grouting about the chunnel that passes through fractured rock mass, the essay adopts following theoretical formula to calculate the fractured rock mass grouting diffusion radius: Wittke and Wallner Formula、Lombadi Formula and Huang Chunhua Formula. Finally through the analysis of calculation results can conclude: (I) The diffusion radius of the slurry can meet the design requirements under the condition of 3-4 Mpa designed grouting pressure、5 cm grouting holes’ radius and 1800-3600s grouting time. (II) The calculation result of Huang Chunhua Formula is almost the same as Wittke and Wallner Formula and Lombadi Formula, but the margin of grouting diffusion radius’ change as grouting time and grouting pressure growing are different, it’s more close to the real situation.(III) The calculation of these theoretical formula only consider the breadth of fractured rock without considering the variation of its thickness and direction. So all of the calculation results of these formula are generally bigger than the standard.

Utilization of slag-alkaline cement as a grouting medium in hydrotechnical construction

One of the main factors which determine the failure-free operation of a hydrotechnical object, a dam, is reduction of water filtration through basement rocks and the dam structure. During the last ten years, slag-alkaline cement was used as a grouting medium in the creation of the antifiltration screens of selected dams built in Poland. Field as well as laboratory results have proved the rightness of accepted assumptions and high efficacy of the rock mass grouting in the basement and dam structure.