Study on grouting reinforcement mechanism and experiments in fractured rock mass for underground engineering

Mechanism and experiment of self-stress grouting reinforcement for fractured rock mass of underground engineering

Development of cement-based self-stress composite grouting material for reinforcing rock mass and engineering application

Effect of fissure water on mechanical characteristics of rock mass

Numerical determination of deformability and strength of 3D fractured rock mass

Grouting reinforcement is an effective method for controlling fractured rock in the deeply buried roadways of coal mines. However, quantitatively evaluating the strength of grouted rock masses remains a challenge. The design of grouting reinforcement is primarily based on empirical knowledge. Consequently, this study proposes a real-time in-situ method for evaluating grouting quality using measure while drilling (MWD) based on a roofbolter. Initially, we validated the method through a numerical study using the discrete element method. Several 3D rock samples with varying crack densities were established and drilled numerically, demonstrating that the strength of fractured rock masses can be better estimated using the rock drillability index rather than drilling specific energy. Therefore, a model, known as the Pd–Rc model, was established to estimate rock strength based on the rock drillability index. Subsequently, an in-situ validation was conducted using a self-developed MWD testing system to assess the grouting quality in fractured rock masses. The results show that the strength of the rock mass increases by 38%, 56.0%, and 49.7%, respectively, after grouting, as observed in three boreholes. This method allows for quantitative estimation of grouting quality.

Cracking propagation in elastic and porous media is still challenge topics in mechanical, energy, and environmental engineering. In this paper, the phase field method will be used to model the cracking propagation at the small scale for elastic media. This method is doing well in DEAL.II with the help of local refinement technique which allows studying the tensile strength of fractured rock mass behavior without prior knowledge of cracking propagation path and reduction of computational consumption. This implementation is applied to model a fractured rock mass in which a plenty of explicit fractures are distributed though total energy released by Griffith's criterion. Through these applications, we demonstrate and highlight the performance of the phase field method with local refinement technique in modeling crack propagation as well as investigate the tensile strength of fractured rock mass dependency its crack orientation

Investigating the scale effects in strength of fractured rock mass

Cracking propagation in elastic and porous media is still challenge topics in mechanical, energy, and environmental engineering. In this paper, the phase field method will be used to model the cracking propagation at the small scale for elastic media. This method is doing well in DEAL.II with the help of local refinement technique which allows studying the tensile strength of fractured rock mass behavior without prior knowledge of cracking propagation path and reduction of computational consumption. This implementation is applied to model a fractured rock mass in which a plenty of explicit fractures are distributed though total energy released by Griffith's criterion. Through these applications, we demonstrate and highlight the performance of the phase field method with local refinement technique in modeling crack propagation as well as investigate the tensile strength of fractured rock mass dependency its crack orientation

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.

The equivalent strength parameters of fractured rock masses are prerequisite for stability analysis of geotechnical engineering projects constructed in fractured rock masses which are encountered frequently in western china. Based on generated mesh of fractured rock masses, combined with statistic damage constitutive model of intact rock and damage model of structural plane, progressive failure of fractured rock masses is studied using finite element method (FEM). Furthermore, Scale effect and anisotropy of compressive strength of fractured rock masses are studied. Study results show that the strength decreases and tend towards stability rapidly from intact rock to fractured rock masses, and the anisotropy of strength of fractured rock masses is not significant. At last, based on numerical simulation conducted on 10 m scale rock masses under different confining pressures, the equivalent strength parameters of fractured rock masses are gained and the results are compared with Hoek-Brown criteria. The method developed is helpful for determination of strength parameters of fractured rock masses.

The analysis of jointing in a rock mass is a critical step in any rock engineering project as the extent of fracturing in the rock mass is the dominant factor controlling the rock mass strength. Uncertainties in the characterisation of a rock mass are very rarely considered. Historically, the assessment of jointing has been a largely empirical process and a project may proceed when in the opinion of the geotechnical staff 'enough' data has been collected. For example, the number of fractures in a length of core is used to calculate the RQD or the fracture frequency, but the direction of the core axis may be ignored even though it is known that the fracture frequency is a function of direction when the jointing is not isotropic and thus the fracture frequency may be incorrectly assessed. The orientation distribution of joint sets in a rock mass can be analysed quite easily as conventional scanline mapping of the rock mass provides a reasonably precise estimate of the dip and dip direction of every joint logged. However, to make a three-dimensional estimate of the extent of fracturing in a rock mass, it is necessary to determine joint persistence in three dimensions. To do this requires the assumption of a model of the geometry of the joints and flat disks are usually chosen as this is the simplest possible two-dimensional shape, requiring the least amount of information to describe the joints. The estimation of the size distribution of the joints in a joint set is a statistical estimation process that is in principle well defined, once a model for the joints has been adopted. If the estimation process has a sound mathematical basis, it is possible to estimate the uncertainty in the parameters. These estimates of the uncertainties in the nature of the joints can be propagated through to arrive at a range of values for the rock mass indices of interest rather than a single value of unknown reliability. Once these ranges are known, an objective decision can be made regarding the state of knowledge of the rock mass. This paper introduces the new paradigm of quantification of uncertainty in the assessment of the extent of fracturing in jointed rock masses and provides some examples of how estimates of rock mass indices are affected by the quantity of data available for analysis.

Grouting reinforcement technology is a vital component of geotechnical engineering, which plays a crucial role in repairing surrounding rock that is damaged and improving its strength. To analyze the impact of grouting on the mechanical properties of rock fractures, specimens of mudstone fractures were selected before and after grouting reinforcement for direct shear tests. The purpose was to investigate the changes in mechanical properties under normal and tangential loading conditions. Furthermore, the microscopic–mesoscopic and macroscopic aspects of grouting reinforcement were discussed to explore its influence on the interface structure, deformation resistance, and strength of the fractured rock mass. By analyzing the test results of the fracture’s mechanical properties before and after grouting, a constitutive model and strength criterion were proposed to accurately describe the mechanical behavior of the fracture surface. Building on a numerical software platform, the custom model was compiled with the VC++ integral programming environment and embedded in UDEC software. Finally, these findings were successfully applied to a typical deep roadway surrounding rock grouting reinforcement project, which showcased the practical implications of this paper. The results demonstrate that grouting reinforcement significantly impacts the normal and tangential mechanical properties of the fracture surface and the shrinkage and dilatation mechanical behaviors. The grout filling and cementation process enhances the rock mass fracture’s resistance to deformation, effectively preventing the gradual weakening and slip in the fracture field. This improves the overall integrity and stability of the rock mass. The proposed mechanical model effectively captures the compression, shear, shrinkage, and dilatation mechanical behaviors before and after grouting. Similarly, the custom fracture grouting mechanical model could be a useful tool to simulate the behavior of grouting reinforcement in engineering rock masses.

It is very important to investigate the forces applied on the rock mass by the fluid flow through fractured rock mass, which is one of the issues for analyzing the stability of rock mass. The forces applied on the fissure walls by the fluid flow include the hydrostatic seepage pressure and the dynamic seepage pressure, i.e., the drag force. Based on the cubic law of the single fissure flow, the equations of the drag forces applied on the fissure walls by the single fissure flow are deduced by means of the momentum law of fluid mechanics. The equations are designated for the cases of no-filled fissure, filled fissure and the combined flow of fluid and the fillings, respectively. The equations have important values for analyzing the effect of fluid flow on the behavior of deformation and strength of fractured rock mass, and are the foundation of the interaction mechanism between stress and fluid flow. Based on the equations, the two kinds of forces applied on the fracture wall of fracture network in rock mass are studied, which include the normal hydrostatic seepage pressure and the tangent drag force. The equivalent node force of joint element is deduced under the two-dimensional and three-dimensional conditions. A numerical computation example is also given to indicate the effect of seepage through fracture network on the stress of rock mass.

Because of large number of discontinuities existing in rock mass, the mechanics and failure modes are controlled by the rock mass structure characteristics. The numerical test method, integrating the results of in-situ investigations, laboratory and in-site tests, can provide a new approach to study the mechanical behavior and failure theory of fractured rock mass. The fractured sandstone rock masses in the west area of Hubei Province were chosen as a case study. Based on the statistic analyses of discontinuities, the structure models of rock masses are founded with Monte-Carlo method. Then a series of numerical compress tests using Distinct Element Method were carried out to discuss the failure strengths and failure modes in rock masses. The study shows that, the failure strengths and failure modes have a strong dependency on model size, confining pressure and loading orientation. In addition, the fractured rock mass shows anisotropic behavior, but this behavior is insignificant with the increase of confining pressure and the side length of rectangle model. The failure modes in fractured rock masses can be generalized into two types. One occurs in a complex way in small models under high confining pressures, i.e., combining sliding and bursting of discontinuities and shear bands in the rock matrix. Another takes place with slide of discontinuities in small models under low confining pressures or in large models. However, the pathways of these two failure modes both have an angle of 30° to 40° to the loading orientation.

IntroductionUndertaking engineering tasks such as tunnel construction, dam construction, mine development, the abstraction of petroleum, and slope stabilization require the estimation of hydraulic conductivity for fractured rock mass.The understanding of hydraulic properties of fractured rock mass, which involves the fluid flow behaviour in fractured consolidated media, is a critical step in support of these tasks.To obtain hydraulic properties of fractured rock mass, double packer systems can be adopted (NRC 1996).They can be used to determine the hydraulic conductivity in a portion of borehole using two inflatable packers.Although this type of test can directly measure the hydraulic parameter, costs of the testing are fairly high.Several studies (Snow, 1970;Louis, 1974;Carlsson & Olsson, 1977;Burgess, 1977;Black, 1987;Wei et al., 1995;) have proposed the estimation of rock mass hydraulic conductivity using different empirical equations, which were based on the concept that rock mass permeability decreases with depth, as shown in Table 1.These empirical equations provide a great feature for characterizing rock mass hydraulic properties quickly and easily.However, the applicability of these equations is very limited because depth is not the only significant variable on the prediction of rock mass permeability.Hydraulic properties of rock mass may vary with geostatic stress, lithology and fracture properties, including fracture aperture and frequency, fracture length, fracture orientation and angle, fracture interconnectivity, filling materials, and fracture plane features (Lee & Farmer, 1993;Sahimi, 1995;Foyo et al., 2005;Hamm et al., 2007).Thus, a more applicable empirical equation for estimating hydraulic conductivity of rock mass possibly must include the aforementioned factors.This chapter proposes two empirical models to estimate hydraulic conductivity of fractured rock mass.The first empirical model was based on the rock mass classification concept.The study developed a new rock mass classification scheme for estimating hydraulic conductivity of fractured rocks.The new rock mass classification system called as "HCsystem" based on the following four parameters: rock quality designation (RQD), depth index (DI), gouge content designation (GCD), and lithology permeability index (LPI).HCvalues can be calculated from borehole image data and rock core data.The second empirical model was simply based on results of borehole televiewer logging, flowmeter logging and packer hydraulic tests.Three borehole prospecting techniques for fractured rock mass hydrogeologic investigation were performed to explore various hydrogeologic characteristics, such as fracture width, fracture angle, flow velocity and hydraulic www.intechopen.com