Integrity Of Rock Mass Research Articles

Research on the Water Inrush Mechanism and Grouting Reinforcement of a Weathered Trough in a Submarine Tunnel

Based on the structural and geological characteristics of the F1 weathering trough of a submarine tunnel and its spatial relationship with the cavern, a simplified calculation model of the weathering trough water inrush was established, and the formation, development process and influencing factors of the water inrush channel in the water-resistant rock layer were carried out by a numerical simulation of particle flow. It shows that the integrity and stability of the critical water-resistant rock mass is the key to preventing water inrush, and the identification and positioning of the water inrush channel is the basis for the grouting reinforcement design of the weathering groove of the submarine tunnel. Based on above research results, the F1 weathering trough was blocked and reinforced by the composite grouting method, and the engineering reinforcement effect was good.

A new approach for 3D structure characterization of rock mass using an improved elliptical discrete fracture network model

Fracture structures in rock masses profoundly affect the stability of deep rock engineering, whereas conventional methods utilizing local surface fracture data on rock mass and disk models are limited in characterizing complex three-dimensional (3D) fractures. This raises two critical inquiries: How to enhance the comprehensiveness of fracture parameter collected on-site? And how to improve the accuracy of 3D fracture reconstruction? Hence, we proposed an approach for characterizing 3D fractures of rock mass by optimizing on-site acquisition techniques and discrete fracture network model. By integrating unmanned aerial vehicle (UAV) and borehole TV imaging techniques, we extracted comprehensive fracture parameters (e.g., trace length, orientation, and spacing) from the surface to the interior of the engineered rock mass. Leveraging the capability of the non-similar elliptical discrete fracture network model to more accurately represent fracture shapes, we introduced a dual-parameter correction method that integrates rotation angle and volume density adjustments into Monte Carlo simulation, resulting in an improved comprehensive parameter elliptical discrete fracture network (CPE-DFN) model. This model exhibited a substantial improvement in accuracy compared to previous disk models, achieving enhancements ranging from 11.2% to 24.9%. Finally, we validated the applicability and precision of this new method for 3D fracture characterization using comprehensive fracture data collected from a deep tunnel in western Sichuan, China, with an error of less than 8%. This work holds potential applications in investigating preferential flow paths as well as evaluating rock mass integrity and fractured zones in rock masses.

Prediction of brittle rock failure severity: An approach based on rock mass failure progress

This study presents the classification and prediction of severity for brittle rock failure, focusing on failure behaviors and excessive determination based on damage depth. The research utilizes extensive field survey data from the Shuangjiangkou Hydropower Station and previous research findings. Based on field surveys and previous studies, four types of brittle rock failure with different failure mechanisms are classified, and then a prediction method is proposed. This method incorporates two variables, i.e. Kv (modified rock mass integrity coefficient) and GSI (geological strength index). The prediction method is applied to the first layer excavation of the powerhouse cavern of Shuangjiangkou Hydropower Station. The results show that the predicted brittle rock failure area agrees with the actual failure area, demonstrating the method's applicability. Next, it extends to investigate brittle rock failure in two locations. The first is the k0+890 m section of the traffic cavern, and the second one is at K0-64 m of the main powerhouse. The criterion-based prediction indicates a severity brittle rock failure in the K0+890 m section, and a moderate brittle rock failure in the K0-64 m section, which agrees with the actual occurrence of brittle rock failure in the field. The understanding and application of the prediction method using Kv and GSI are vital for implementing a comprehensive brittle rock failure prediction process in geological engineering. To validate the adaptability of this criterion across diverse tunnel projects, a rigorous verification process using statistical findings was conducted. The assessment outcomes demonstrate high accuracy for various tunnel projects, allowing establishment of the correlations that enable valuable conclusions regarding brittle rock failure occurrence. Further validation and refinement through field and laboratory testing, as well as simulations, can broaden the contribution of this method to safer and more resilient underground construction.

A Rock Mass Classification Method for Tuff Tunnel Based on the High-Pressure Gas Expansion Method

A precise rock mass grade result is crucial for directing the tunnel excavation engineering design. A novel rock mass classification method for tuff tunnel based on the high-pressure gas expansion method (HPGEM) was proposed, which was primarily built on field test data previously acquired by the research team. The main achievements are as follows: combined with field data and the HPGEM rock-breaking theory, analyzing the rock uniaxial compressive strength, rock mass integrity index, and the relationship between the gas generator unit consumption and fitted the relevant equations. After that, the rock optimal uniaxial compressive strength (about 150 MPa) and the rock integrity factor (about 0.85) were obtained. With reference to the BQ rock mass classification method, a new rock mass classification method that applied to HPGEM was proposed. This study fills the gap of the appropriate rock mass classification method requested on HPGEM.

Rapid Evaluation of Rock Mass Integrity of Engineering Slopes Using Three-Dimensional Laser Scanning

Rapid Evaluation of Rock Mass Integrity of Engineering Slopes Using Three-Dimensional Laser Scanning

Experimental Investigation on Anisotropy of Rocks Using Digital Drilling Technology

Accurate determination of rock anisotropy is of great significance for analyzing the safety and stability of engineering rock mass. In this paper, uniaxial compression tests are carried out on four kinds of rocks: slate, gneiss, sandstone and shale, to obtain the uniaxial compressive strength of each rock in the different directions. Digital drilling tests are carried out on four kinds of rocks to study the anisotropy of drilling parameters. According to the working principle of the drill bit, its force balance analysis model is established, and the concept of cutting strength ratio is proposed. Using the drilling parameters (drilling depth, drilling time, torque and thrust, etc.) in the different directions for each rock, the interrelationships between them are analyzed. The anisotropy index of rock is defined according to the ratio of cutting strength in different directions of drill parameters, and a new method for judging rock anisotropy is proposed. The results show that the thrust and torque in all directions of the rock increase with the drilling depth. The torque in all directions of the rock has a positive linear relationship with the thrust. The ranking of the anisotropy degree for the four types of rocks is as follows: gneiss > slate > shale > sandstone. The anisotropy results have been validated by an alternative method utilizing uniaxial compressive strength. The determination results are verified by the uniaxial compressive strength of the rocks, and the degree of anisotropy of the four rocks is consistent with the determination results. This method can help engineers analyze the anisotropy of rock, and provide a new idea for studying the integrity and stability of rock mass.

Evaluation of rock mass units using a non-invasive geophysical approach

Thorough and accurate assessment of rock mass units is important for development of engineering infrastructures and groundwater resources assessments. Rock mass units are widely evaluated by reliable geomechanical parameters namely rock quality designation (RQD) and rock core index (RCI). Conventionally, these parameters are acquired via an extensive number of geotechnical tests. Such tests, however, suffer efficiency for data coverage, cost, equipment and topographic constrictions, and hence cause ambiguity in geological models for a detailed evaluation of rock mass integrity. Conversely, geophysical surveys offer fast, more user-friendly, less invasive, more cost-effective and less time-consuming approach for geological investigations. The past research confirms a useful link between geophysical and geotechnical parameters. But, none of the past studies provides a suitable and generalized relation between these parameters which can reduce geotechnical model uncertainty mostly caused by inadequate data and subsurface heterogeneity. This paper proposes a meaningful and feasible method to obtain geomechanical parameters using a certain number of drillings and geophysical data of four different sites. Based on electrical resistivity obtained from electrical resistivity tomography (ERT) and controlled-source audio-frequency magneto telluric (CSAMT), this research provides the general and adaptable formulas for geotechnical parameter estimation and reduces geological model uncertainty for more detailed 2D/3D imaging of RQD and RCI covering the whole sites where even no drilling data exists. Thus, the investigated sites are assessed laterally and vertically along each geophysical profile via distinct value ranges of geological parameters for a thorough and reliable evaluation of rock mass units in highly heterogeneous setting. Our research reduces the ambiguity caused by structural heterogeneities and scarce data, fills the gap between inadequate well tests and the true geological models, and gives new insights into the rock mass units for proper engineering design and groundwater exploitation.

Fast perception of rock mass strength and integrity in TBM tunnelling using in-situ penetration test

Tunnel boring machine (TBM) is the preferred method in the construction of long-distance and deep-buried tunnel due to its advantages in safety and high efficiency. However, the TBM method is very sensitive to the condition of the surrounding rock. The strength and integrity characteristics of rock mass have great influence on the safe and efficient tunnelling. To provide a fast perception method for these characteristics during the TBM tunnelling process, an in-situ penetration testing system is proposed in the present study. The development and testing procedure of the system are elaborated. The system is applied to a TBM-excavated water conveyance tunnel to continuously perceive the strength and integrity characteristics of the surrounding rock. Firstly, the force-penetration (F-P) responses of the surrounding rock under penetration are qualitatively studied. Then, series of penetration indices are summarized to quantify the characteristics of the F-P responses. Finally, the quantitative relationships between the rock strength and the penetration indices are studied. The results indicate that the in-situ penetration testing system can perceive the rock mass strength and integrity characteristics qualitatively and quantitatively. On the qualitative aspect, the F-P responses can be categorized into four types (Type I to Type IV), which correspond to the level of rock mass strength and integrity. On the quantitative aspect, a single penetration index cannot represent the complete information of the F-P response. The descriptive classification of the rock mass strength (class I to III) is established through multiple penetration indices. The in-situ penetration testing system can be used as a method to quickly perceive the strength and integrity characteristics of the surrounding rock in TBM tunnelling.

Mapping the integrity of rock mass with GPR: case study in decommissioning mining

Slopes are built for the purpose of extracting ore, in the case of mining, or access roads in civil works. The excavation of slopes in tropical countries is facilitated by the thick layer of soil formed from the more intense weathering when compared to other countries. However, the residence time of water in the soil is relatively longer and consequently allows the accumulation and percolation of water through rock fractures even in the dry period. These factors induce a greater probability of occurrence of ruptures. Mines in the decommissioning phase must guarantee slope stability conditions even after closure in order to comply with legislation and environmental safety. In this work, the slopes of a decommissioning mine were investigated using geophysical methods (GPR) and structural analysis of the rock mass. The results were presented in the form of radargrams that correlate distance and depth of investigation. Structural data served as the basis for the execution of kinematic analyzes for planar and wedge ruptures. The analysis of the results allowed the correlation between electromagnetic signal attenuation zones, with the presence of water and the occurrence of ruptures. Thus, the GPR results allowed the recognition of structural discontinuities, accumulation zones and water flow.

Influence of the assisted kerf depth on cracks pattern and cutting performance of TBM cutter

Kerfing on the working face of tunnel boring machine (TBM) can reduce the integrity of intact rock mass, it's one of feasible methods to improve the TBM performance. When the TBM cutter cut along the midline of two kerfs, the chipping mechanism changed to the interaction between the cutter and adjacent kerfs, the lateral cracks generated from the cutter tip could propagate to the bottom of adjacent kerfs. To study the effects of kerf depth on the cracks pattern and the cutting performance of the TBM cutter, a series of full-scale linear rock cutting tests were conducted. In addition, conventional cutting tests without kerfs were also performed to make a comparison. The cutter force and rock muck were collected, and the rock samples were sectioned after the tests. The cracks patterns beneath the cutter tip were observed by fluorescent dye. The results show that the dip angle of the lateral cracks increase with the increasing kerf depth, the vertical cracks become shorter and less. Besides, the area of the crushed zone decreases. The required normal force and rolling force are much reduced even for the large cutter penetration compared with the conventional cutting. The cutter forces decrease, while the characteristic grain diameter and coarseness index of the rock muck increase with the increasing kerf depth. The specific energy of kerf-assisted cutting is lower than that of the conventional cutting, and it declines as the kerf depth increases. A critical kerf spacing to depth ratio is found to efficiently reduce the specific energy. The results are useful for the rational parameter design of the kerfing system installed on the new generation TBM. The kerf spacing could be enlarged to save energy if the kerfs are deeper than 12 mm. However, it's still a challenging task to create deep kerfs on site.

Determination of rock mass integrity coefficient using a non-invasive geophysical approach

Determination of rock mechanical parameters is the most important step in rock mass quality evaluation and has significant impacts on geotechnical engineering practice. Rock mass integrity coefficient (KV) is one of the most efficient parameters, which is conventionally determined from boreholes. Such approaches, however, are time-consuming and expensive, offer low data coverage of point measurements, require heavy equipment, and are hardly conducted in steep topographic sites. Hence, borehole approaches cannot assess the subsurface thoroughly for rock mass quality evaluation. Alternatively, use of geophysical methods is non-invasive, rapid and economical. The proposed geophysical approach makes useful empirical correlation between geophysical and geotechnical parameters. We evaluated the rock mass quality via integration between KV measured from the limited boreholes and inverted resistivity obtained from electrical resistivity tomography (ERT). The borehole-ERT correlation provided KV along various geophysical profiles for more detailed 2D/3D (two-/three-dimensional) mapping of rock mass quality. The subsurface was thoroughly evaluated for rock masses with different engineering qualities, including highly weathered rock, semi-weathered rock, and fresh rock. Furthermore, ERT was integrated with induced polarization (IP) to resolve the uncertainty caused by water/clay content. Our results show that the proposed method, compared with the conventional approaches, can reduce the ambiguities caused by inadequate data, and give more accurate insights into the subsurface for rock mass quality evaluation.

A probability prediction method for the classification of surrounding rock quality of tunnels with incomplete data using Bayesian networks

The classification of surrounding rock quality is critical for the dynamic construction and design of tunnels. However, obtaining complete parameters for predicting the surrounding rock grades is always challenging in complex tunnel geological environment. In this study, a new method based on Bayesian networks is proposed to predict the probability for the classification of surrounding rock quality of tunnel with incomplete data. A database is collected with 286 cases in 10 tunnels, involving nine parameters: rock hardness, weathering degree, rock mass integrity, rock mass structure, structural plane integrity, in-situ stress, groundwater, rock basic quality, and surrounding rock level. Moreover, the Bayesian network structure is built using the collected database and quantitatively verified by strength analysis. Then, the accuracy, precision, recall, F-measure and receiver operating characteristic (ROC) curves are utilized for model evaluation. The average values of accuracy, precision, recall, F-measure, and area under the curve (AUC) are approximately 89.2%, 91%, 92%, 91%, and 0.98, respectively. These results indicate that the established classification model has high accuracy, even with small sample size and imbalanced samples. Ten additional sets of tunnel cases (incomplete data) are also used for verification. The results reveal that compared with the traditional Q-system (Q) and rock mass rating (RMR) classification methods, the proposed classification model has the lowest error rate and is capable of using incomplete data to predict sample results. Finally, sensitivity analysis suggests that the rock hardness and rock mass integrity have the strongest impact on the quality of tunnel surrounding rock. Overall, the findings of this study can serve as a useful reference for future rock mass quality evaluation in tunnels, underground powerhouses, slopes, etc.

A novel approach to determine rock mechanical parameters using non-invasive geophysical methods

Engineering design of the major infrastructures mainly relies on determination of rock mechanical parameters. However, such indexes are traditionally acquired from the borehole tests of the construction site. The drilling test is generally time-consuming and costly procedure. Further, such tests provide geology information only at some specific points, need more equipment, are hardly carried out in the high topographic sites, and often leave ambiguity in the subsurface interpretation. Alternatively, geophysical research of ERT (electrical resistivity tomography) is swift, user-friendly, inexpensive and non-destructive, and can provide a bridge between the limited drilling tests and a true geotechnical model of the subsurface. In the present research, we introduce a novel geophysical approach to estimate rock mass integrity index (Kv) via integration between the ERT-based electrical resistivity and the limited borehole-based Kv. The obtained Kv offers 2D and 3D evaluation of rock mass integrity along all ERT profiles for large coverage of the project site where even no borehole data exist. Furthermore, uncertainty in the evaluation of water-clay distinction was removed by the integration of IP (induced polarization) with ERT. Our research, compared to the conventional geotechnical investigations, removes uncertainties in the geotechnical model and offers more accuracy in rock mass quality classification for various types of rock units. This approach removes the extensive drilling tests and offers a comprehensive assessment of rock mass integrity to achieve the proper design of engineered infrastructures in the highly heterogeneous terrains.

The effect of rock hardness and integrity on the failure mechanism of mortar bolt composite structure in a jointed rock mass

The appearance of joints in the rock tunnels makes the rock mass show obvious anisotropy and discontinuity in physical and mechanical properties, which has a significant influence on the rock mass stability. As one of the normally used support structures in tunnel construction, Mortar bolts will inevitably pass through the joints during the process. Both rock hardness and rock mass integrity will directly affect the anchorage performance of mortar bolts in joint rock. Considering this, this paper designs a mortar bolt pull-out experiment to investigate the joint rock failure modes and bolt-grout composite structure failure modes under different conditions of rock hardness and rock mass integrity. By taking the two influencing factors of rock hardness and integrity into account, the calculation formulas of ultimate pull-out load and ultimate displacement of mortar bolts in joint rock are established and proposed.

Rockburst tendency prediction based on an integrating method of combination weighting and matter-element extension theory: A case study in the Bayu Tunnel of the Sichuan-Tibet Railway

The Bayu Tunnel is the most problematic tunnel project in the Lhasa-Nyingchi section of the Sichuan-Tibet Railway. Rockbursts have occurred frequently during the construction process, which has seriously threatened the safety of construction workers and equipment. Aiming at the rockburst hazard prediction problem of the Bayu Tunnel, in this paper an integrating method of combination weighting and matter-element extension theory is proposed. This method introduces the rock brittleness evaluation index BICSS, Russenes criterion and rock mass integrity coefficient as the main rockburst evaluation indexes, which characterized the control factors of rock physical and mechanical property, surrounding rock stress and rock mass integrity on rockburst tendency, respectively. Then the rockburst tendency evaluation index system is constructed. The weight of each rockburst control factor is determined by the combination weighting algorithm of triangular fuzzy number analytic hierarchy process (TFN-AHP), criteria importance though intercriteria correlation (CRITIC), and determination of comprehensive weight (MDI). The correlation degree between the rockburst sample and rockburst grade can be calculated using the matter-element extension theory, after which the prediction of rockburst grade is carried out. Finally, the applicability, superiority and the necessity of selected rockburst control factors in this method are verified and discussed further. The research results provide a new analysis method and technical means for rockburst tendency assessment of deep tunnel.

Geophysical evaluation of geological model uncertainty for infrastructure design and groundwater assessments

Uncertainty in geological models, mainly caused by natural heterogeneity and inadequate data, often leads to substantial societal risk including failures of engineered structures, geohazards, and groundwater and environmental problems. These models mainly depend on geological knowledge about evaluation of rock mass quality, fractures/faults and clay. Traditionally, geotechnical parameters of rock mass quality classification, such as rock mass integrity index (Kv) are obtained by drilling tests. However, the boreholes approaches are time-consuming and expensive, provide limited data and have topographic constraints. Alternatively, the inexpensive integrated approaches of geophysical methods can reduce geological ambiguity by bridging the gaps between accurate subsurface models and inadequate borehole data. In this work, we incorporate electrical resistivity tomography (ERT) with inadequate drilling data, and determine Kv over large area even where no borehole exists. Our results reduce a large number of wells and evaluate the subsurface thoroughly using 2D/3D imaging of Kv. The ambiguity in water-clay differentiation caused by low resistivity was resolved by integrating ERT with induced polarization (IP). The integration of ERT, Kv and IP identified several localized fractures/faults. Our novel approach, compared with the past studies, reduces uncertainty in the geological model and provides a thorough insight into the subsurface for infrastructure design and groundwater assessments. Our approach is applicable in most cases.

Diseases failures characteristics and countermeasures of expressway tunnel of water-rich strata: A case study

Various diseases failures inevitably appear in expressway tunnels in water-rich strata under the long-term erosion of water. In order to ensure the operation safety of Jizhao tunnel which is in Guizhou Province, China, the radar scanning, drilling and coring and laser scanning were employed to illuminate the diseases failures characteristics and the causes of the tunnel failures. Further, a complete set of solutions against cracks, water seepage and inverted uplift and other diseases was put forward innovatively and applied in the actual project. This case study seeks to examine the characteristics and causes of tunnel failure in water-rich strata. The results show that the water-rich strata, expansive soil and the development of surrounding rock joints are the main factors causing the failure of Jizhao tunnel. The cracking and damage of tunnel lining is dense and disorderly, the water leakage of lining is small but long-term, and only some sections have floor heave. The treatment of crack grouting, clay steel belt and low prestressed anchor bolt were adopted to ensure the integrity of secondary lining and rock mass. The method of adding inverted arch, foot locking bolt and bolt grouting taken in this tunnel is to improve the stability of the tunnel structure and alleviate the stress release in the later stage. Transverse drainage pipes and longitudinal drainage pipes were set to ensure smooth drainage. After the treatment scheme is adopted, the disease is effectively controlled and does not affect the normal operation of the tunnel, which can provide a certain reference for the failure treatment of similar tunnels projects.

Classification Method and Application of Rock Fracture Ability by Supercritical CO2 Blasting

In order to study the fracture ability classification of rock mass under the cracking action of supercritical CO2 phase transition, based on the classification theory of rock mass in blasting engineering, an analytic hierarchy process (AHP)-entropy weight method (EWM) and the cloud model classification method for rock mass cracking under CO2 phase transformation are proposed. In this method, rock density, rock tensile strength, rock wave impedance, and rock mass integrity coefficient are used as the factors to determine the level of rock mass fracturing, and the evaluation index system of rock mass fracturing is established. Through this evaluation method, the rock mass in a reconstruction project section of Nyingchi, Tibet, is classified and evaluated. The results present that this new classification method of rock mass fracture ability uses AHP–EWM to carry out the weight distribution of the classification index. In addition, it is combined with the cloud model for the classification division, overcoming the traditional classification method fixed with appraisal pattern flaw. Therefore, it has validity and feasibility. According to the characteristics of fracture ability, the rock masses in the area to be rebuilt on the Tibet Highway are divided into grade II, grade III, and grade IV, which provides scientific guidance for the construction of the project.

Application of electrical resistivity tomography (ERT) for rock mass quality evaluation

Rock mass quality evaluation is a challenging task in geotechnical investigations given the natural heterogeneity and the limited data. These investigations mainly depend on the traditional drilling tests. However, such tests are expensive and time consuming, provide point measurements, and cannot be conducted in steep topographic areas, and thus cause uncertainties in the geological model. Conversely, geophysical methods such as electrical resistivity tomography (ERT) are non-invasive, user-friendly, and fast. In this work, we establish empirical correlation between ERT and limited drilling data to obtain rock mass integrity coefficient (Kv). The estimated Kv provides 2D/3D imaging of the rock mass quality evaluation via weathered/unweathered rock and faults detection in order to cover the entire area even where no drilling test exists. Compared with the past geotechnical investigations, our work reduce the ambiguities caused by the inadequate well tests and provide more accurate geological model for infrastructures design. Our work proposes that, in case of sparse borehole data, the established empirical equations can be used to determine Kv along different geophysical profiles via 2D/3D insight of the subsurface. Our approach is applicable in any hard rock setting, and the established correlations can be used in areas even where no well test exists.

Numerical Simulation of Rock Mass Structure Effect on Tunnel Smooth Blasting Quality: A Case Study

Taking the Zigaojian tunnel, Hangzhou–Huangshan high-speed railway, China, as background, the rock mass structure effect on smooth blasting quality was studied. Four rock mass structures were determined on the basis of the information collected on the tunnel site. Smooth blasting finite element models were established using LS-DYNA. The accuracy of the numerical calculation model was verified by comparing the overbreak and underbreak between the numerical simulation and monitoring. Orthogonal numerical test was used to study the rock mass structure effect through single factor and main effect analysis methods. With the decrease in rock mass integrity, the smooth blasting overbreak of tunnels with massive integrity structure, massive structure, layered structure, and cataclastic structure increased. For massive integrity structure and cataclastic structure, the peripheral hole spacing should be emphatically considered. Meanwhile, in massive structure and layered structure, the included angle and spacing of structural planes had a great influence on the smooth blasting quality. The research results could provide a reference to improve the quality of similar tunnel smooth blasting.