Rock Mass Excavation Research Articles

Study on transient unloading loosening simulation test of excavation of jointed rock mass

Based on the abrupt displacement of a jointed surrounding rock mass during blasting excavation of deep underground caverns, a set of transient unloading loosening simulation tests was designed for multi-joint rock masses. Through the linear regression analysis of the unloading displacement of jointed rock masses, the opening displacement of a joint is determined to be proportional to the square of the initial unloading stress. The numerical simulation method is used to apply horizontal and vertical in situ stresses to the jointed rock mass model to study the opening displacement in the jointed rock mass at different lateral pressure coefficients of in situ stress. The results indicate that, with the unloading of the horizontal stress, a larger lateral pressure coefficient of the in situ stress leads to a larger opening displacement in the jointed rock mass. When the vertical stress is unloaded after the horizontal stress is totally unloaded, a lower lateral pressure coefficient of the in situ stress leads to a larger opening displacement. The influence of the stress lateral pressure coefficient on the open deformation of the jointed rock mass is obviously higher than that of the unloading rate on the rock mass.

A flexible system for selection of rock mass excavation method

The excavation of rock masses has a crucial importance for the safety and cost of construction of engineering projects. In this study, a flexible excavation assessment (EXCASS) system was developed with two components, the geological strength index (GSI) and the point load strength index (Is50). In order to develop the system, artificial neural network (ANN) analysis were performed using datasets from surface excavations (12 sites in Turkey and 61 sites in Greece reported by Tsiambaos and Saroglou (2010)). The EXCASS system in this study includes two parameters, namely the excavation power index (EPI) and the excavation performance rating (EPR) ranging between the value of 0 and 100. The optimum excavation power index (EPIopt) can be determined theoretically by using ( $$ {\mathrm{GSI}}^2\times \sqrt{{\mathrm{Is}}_{50}} $$ ) as an input when EPR is equal to 0, for the selection of the optimum excavation method. EPR is a rating which provides relative information on the ease or difficulty of the excavation method. Although the value of EPR varies between 0 and ± 100 in the EXCASS system, the use of the excavation method for “normally classes” is recommended in order to achieve costly and efficient excavation. The EXCASS system, on the other hand, has an ability to respond to possible technological developments by associating the excavation method with the EPI rating.

Mechanical properties of limestone from Maixi tunnel under hydro-mechanical coupling

The hydro-mechanical coupling often leads to both mechanical properties and stability deterioration during excavation of water-rich tunnel rock mass. Deformation and mechanical, fracture, and strain energy characteristics of limestone from Maixi tunnel in Guiyang (China) are investigated by hydro-mechanical coupling tests in this paper. Results show that the water pressure has a significant influence on the stress-strain curve, strength characteristics, and macro-fracture degree. The compaction stage is relatively prolonged and elastic phase is shortened. With increasing water pressure, average peak strength decreases exponentially and both average elastic modulus and deformation modulus decrease linearly. The larger the water pressure, the better the fragment uniformity, and fragment uniformity increases exponentially but decreases logarithmically with peak strength. Mercury-injection curve shows a rapid increase then develops gently; the pore volume per unit mass increases exponentially revealing that water pressure has a significant effect on the dissolution pores. Strain energy dissipation characteristics show that total strain energy, dissipation strain energy, and releasable strain energy decrease exponentially with increasing water pressure. Energy ratio Ud/Ut experiences a slow increase, then dramatic rise, and finally develops gently, but Ue/Ut goes through a negative development tend and its boundary points of water pressure are both 2 MPa and 4 MPa. Ud/Ut has a typical logistic function with water pressure reflecting the damage degree and sensitivity of dissipation strain energy to water pressure.

Dynamic response of existing tunnel under cylindrical unloading wave

When an underground tunnel is excavated suddenly in the high-stress rock mass, the unloading wave will generate from the tunnel boundary and propagate into the surrounding rock mass, which can induce strong dynamic vibrations and even damage to the adjacent existing tunnel. This study aims to investigate the dynamic response of existing tunnel induced by cylindrical unloading wave resulting from neighboring tunnel excavation. A two-dimensional mathematical physical model was first constructed based on the superposition principle of coupled static and dynamic loads, in order to derive the formulas for calculating the dynamic stress, velocity and displacement around existing tunnel induced by cylindrical unloading wave. A two-dimensional numerical model established by particle flow code (PFC) was then implemented to verify the theoretical analysis, and further to investigate the failure characteristics of existing tunnel under coupled static in situ stress and dynamic unloading wave. A series of parametric studies were conducted in the theoretical and numerical models to investigate the influence of unloading rate, unloading path, in situ stress and excavation radius on the dynamic response of existing tunnel. The results show that the unloading wave induced by tunnel excavation in high-stress rock mass can induce strong dynamic response in the surrounding rock mass of adjacent existing tunnel, and the increase of stress level and unloading rate will aggravate the dynamic effect. The peak value of velocity induced by nonlinear unloading is larger than that induced by linear unloading. In addition, the excavation-induced unloading wave can induce dynamic failures in the surrounding rock mass of existing tunnel under high in situ stress. Therefore, the unloading wave induced by adjacent tunnel excavation should be taken into consideration when evaluating the stability of deep tunnels.

Excavation damaged zone division and time-dependency deformation prediction: A case study of excavated rock mass at Xiaowan Hydropower Station

Rock mass excavation is accompanied by rock deformation during unloading, which degrades the quality of rock mass and significantly affects the safety and stability of rock mass engineering. Taking the excavated rock mass from the dam foundation of Xiaowan Hydropower Station as the study object, long-time single hole acoustic tests (SHAT) were conducted in the dam abutment rock mass, with the changes in the acoustic wave velocity recorded. Then, a new method quantifying the excavation damaged zone (EDZ) was proposed according to the cumulative degradation rate of acoustic wave velocity, and a time-dependency model for evaluating the evolution of the excavation heavily damaged zone (EHDZ) was established. The results indicated that the cumulative degradation rate curves of the wave velocity along the boreholes exhibited significant differences in time and space. The depth corresponding to the inflection point on the curve can be regarded as the bottom boundary of the EHDZ, which could be used to generate time-dependency curves, and demonstrate the spatiotemporal evolution process for the EHDZ. The time-dependency curves can be classified into three categories. The differences between the classified curves are related to the depth of the initial EHDZ (EHDZ0), rock mass elastic modulus (E), and unloading stress (σu). The time-dependency model for the EHDZ evolution process follows a negative exponential function. The EHDZ0 depth, E, and σu can determine the coefficients of the model. The model provides an effective method to predict EHDZ depths at different times after rock mass excavation. The prediction results are of considerable significance for researches on the unloading failure and the selection of rock mass reinforcement, which would ensure the stability and safety of the rock mass engineering during construction and operation.

Analytical Solutions for Deep-Buried Lined Tunnels Considering Longitudinal Discontinuous Excavation in Rheological Rock Mass

AbstractFor tunneling in a deep, soft rock mass, rock deformation and lining pressure, which are time-dependent behaviors, are mainly affected by rock rheology and longitudinal excavation processes...

Artificial neural network with a cross-validation approach to blast-induced ground vibration propagation modeling

Given their technical and economic advantages, the application of explosive substances to rock mass excavation is widely used. However, because of serious environmental restraints, there has been an increasing need to use complex tools to control environmental effects due to blast-induced ground vibrations. In the present study, an artificial neural network (ANN) with k-fold cross-validation was applied to a dataset containing 1114 observations that was obtained from published results; furthermore, quantitative and qualitative parameters were considered for ground vibration amplitude prediction. The best ANN model obtained has a maximum coefficient of determination of 0.840 and a mean absolute error of 5.59 and it comprises 17 input parameters, 12 neurons in a one-layer hidden layer, and a sigmoid transfer function. Compared with the traditional models, the model obtained using the proposed methodology demonstrated better generalization ability. Furthermore, the proposed methodology offers an ANN model with higher prediction ability.

Rock Breaking and Dynamic Response Characteristics of Carbon Dioxide Phase Transition Fracturing Considering the Gathering Energy Effect

Carbon dioxide phase transition fracturing has been widely used in rock mass excavation under complex environments, and its special rock breaking process shows obvious gathering energy effect. In this paper, the gathering energy effect of this technology is considered and then the impact reduction coefficient is defined and determined. Eventually, a combined method of field tests and numerical simulations is used to study the crack propagation characteristics and spatiotemporal changes of dynamic response. The results show that the cracks grow more and more slowly as time goes by; the peak displacement and peak point velocity in the primary impact direction are both greater than those in the secondary impact direction. The peak point velocity in different directions decreases as the distance from borehole increases and it decays more and more slowly. With the increase of distance from the borehole, the peak effective stress in the primary impact direction constantly decreases. However, it increases first and then decreases in the secondary impact direction. The results mentioned above can provide effective guidance for later experimental research and engineering.

Instability mechanism of shallow tunnel in soft rock subjected to surcharge loads

The tunnel instability accidents caused by surcharge loading could even lead to ground settlement or collapse, damage to the existing municipal pipelines or inclination of the surgical buildings. Series of large-scale physical model test was conducted in this paper to reveal the failure mechanism of tunnel in soft rock subjected to surcharge loading. The non-contact full-field displacement measurement (i.e. Digital Image Correlation, DIC) was employed to obtain a detailed deformation of surrounding rock after excavation. A coupled numerical method combing the continuum (Finite Difference Method, FDM) and dis-continuum (Discrete Element Method, DEM) analysis was used to deal with the failure mechanism of tunnel excavation in rock mass. Good agreements between physical model test and numerical analysis approve the accuracy of the proposed FDM-DEM numerical model. It is found that the collapse mainly occurred in tunnel roof rather than in tunnel sidewall. The collapse zone shows a step-type increase with the increase of surcharge loads. The stress loosening zone (SLZ) in tunnel roof is larger than that in tunnel sidewall. The thickness of SLZ in tunnel roof can be used to design the length of the formed pressure anchors. The proposed large-scale model test with DIC method is applicable to the tunnel engineering study. Moreover, the results in this paper give some insights to secure excavation works and optimize supporting structures.

Study on Influence of Slope Blasting Excavation on Stability of Adjacent Dangerous Rock Mass

Through mechanical analysis, combined with the instability mode and failure mechanism of dangerous rock mass, taking into the consideration of the influence of blasting excavation of the dangerous rock mass on the dynamic characteristics of it based on the limiting equilibrium method, the stability equations of dangerous rock mass at adjacent side slope with blasting and excavation under explosion load are derived. The engineering practice shows that the slope blasting has obvious influence on the stability of the adjacent dangerous rock mass, and the distance R between the blasting point and the dangerous rock mass and the explosive quantity Q are the key factors affecting the stability coefficient of the dangerous rock. The stability of the dangerous rock mass increases with the increase of the distance R, and decreases with the increase of the explosive amount Q. It is suggested that the impact of the blasting vibration force on the adjacent dangerous rock mass should be considered when the slope blasting is excavated.

Prediction Model for Deformation Risk Grade of the Soft Rock Tunnel Based on GRA - Extension

The soft rock tunnel is affected by geological factors and construction factors and it is easy to produce large deformation, which leads to cracking and spalling of the primary support, distorting the steel frame, uplifting the tunnel bottom, and cracking of the secondary lining, and has a serious impact on the safety of tunnel construction and operation. In this paper, the surrounding rock strength, rock mass integrity, groundwater condition, tunnel depth, excavation method, support strength and primary support closure time were chosen as the main factors affecting the deformation of soft rock tunnels. According to the actual monitoring and measurement data of the tunnel, the factor weights were calculated using GRA. Extension theory is used to establish the prediction model for the soft rock tunnel deformation risk. According to the comparison between actual deformation and model prediction deformation, the prediction model of tunnel deformation risk grade has high applicable performance in tunnel deformation risk assessment, which provides a reference for construction optimization of soft rock tunnel.

Suggestions, Methods and Examples of Monitoring of Rock Structures and Excavation of Rock Mass

Rock mechanics projects, excavations and rock mass monitoring are day-by-day concerns of professionals and scientists of rock engineer. Technological advances observed in the 20 and 21 centuries provided high precision equipment capable of establishing deformation and estimating the rock mass stress remotely and in real time. In addition, in order to confirm and study the data obtained with theses equipment, numerical programs of modeling became more accessible to schools, research centers and private companies. Monitoring an excavation requires, besides understanding fully the rock structure, precise definitions and goals: why, how, where. This article discusses concepts of monitoring, modeling and calibration, as well as presents examples of applications where these questions were successfully answered.

Dynamic Failure Model of Thin Coal and Rock Mass under Uniform Impact Load

During the excavation of deep coal and rock mass, the radial stress of the free face changes from three-dimensional compression state to two-dimensional stress, bearing the combined action of dynamic disturbance and static load at the same time. With that, many mines suffer from dynamic disasters, such as coal and gas outburst, rock burst and rock caving during deep mining excavation, which is often accompanied by plate crack, spalling and other disasters, seriously affecting the stability of stope and roadway. Taking thin rectangular coal and rock mass as the research object, the dual equation of the free vibration was derived and the exact solution model of the free vibration was established with the use of Hamilton dual system. Based on the action characteristics of the uniform impact load, the effective mode of the forced vibration was obtained by using the Duhamel integral principle and the orthogonality of the mode function. Based on the third strength theory and the numerical simulation results, the dynamic damage process and development trend of coal and rock mass were analyzed under uniform impact load. It was concluded that the starting position of dynamic damage can be judged by the first order main mode, and the development direction and trend of the damage can be judged by the fifth and sixth order main modes. It was concluded that the vibration mode functions of coal and rock mass with four side fixed (C-C-C-C), the two sides fixed and simply supported on the other (S-C-S-C) are mainly composed of three modes that are the first order (dominant frequency), the fifth order and the sixth order, from which the dynamic damage mechanism is preliminarily studied.

Model Test Study on Cylindrical Blasting Stress Wave Propagation across Jointed Rock Mass with Different Initial Stresses

In the drilling and blasting excavation of underground rock mass, the stress wave produced by the blasting holes usually propagates in the form of cylindrical wave, while the rock mass surrounding the underground engineering is initially subjected to the in situ stress. To explore the propagation and attenuation law of cylindrical stress wave in the in situ stressed rock mass, a model test of cylindrical blasting stress wave propagation across the intact and jointed rock mass under different initial stresses was carried out. First, the attenuation law of the cylindrical stress wave in the intact rock mass under different confining pressures is analysed, and then the influence of the confining pressure scales, the angle, and the number of joints on the propagation law of the cylindrical blast wave in the jointed rock mass is studied. The experimental results show that the physical attenuation of the cylindrical wave in the intact rock mass decreases and then increases as the confining pressure increases from zero. Under zero confining pressure, the transmission coefficient of the cylindrical wave in the jointed rock mass decreases with the increase of joint angle, and the transmission coefficient increases with the increase of the joint angle under confining pressure. As the confining pressure increases from zero, the transmission coefficient shows a trend of increasing firstly and then decreasing.

Modelling the coupled fracture propagation and fluid flow in jointed rock mass using FRACOD

Water inrush is a major hazard for mining and excavation in deep coal seams or rock masses. It can be attributed to the coalescence of rock fractures in rock mass due to the interaction of fractures, hydraulic flow and stress field. One of the key technical challenges is to understand the course and mechanism of fluid flows in rock joint networks and fracture propagation and hence to take measures to prevent the formation of water inrush channels caused by possible rock fracturing. Several case observations of fluid flowing in rock joint networks and coupled fracture propagation in underground coal roadways are shown in this paper. A number of numerical simulations were done using the recently developed flow coupling function in FRACOD which simulates explicitly the fracture initiation and propagation process. The study has demonstrated that the shortest path between the inlet and outlet in joint networks will become a larger fluid flow channel and those fractures nearest to the water source and the working faces become the main channel of water inrush. The fractures deeper into the rib are mostly caused by shearing, and slipping fractures coalesce with the joint, which connects the water source and eventually forming a water inrush channel.

Research on the Layered Rock Mass Excavation Relaxation Stability of Underground Caverns

In order to compare the influence of rock mass parameters weakening on the deformation and stability of excavation caverns in layered rock mass, based on power generation system caverns of a hydropower station, the stability and deformation of the caverns is analyzed. The results show that the mechanical characteristics of the structure surface play a major role in controlling the stability of caverns. And the displacement and yield zone value of plan 3, which adopt elastic-plastic softening model, are significantly larger than other two. The method which consider the residual strength of structure surface is more suitable for the excavation calculation of layered rock mass cavern.

The ARMR Classification System and the Modified Hoek-Brown Failure Criterion Compared to Directional Shear Strength Models for Anisotropic Rock Masses

The anisotropic rock mass rating classification system, ARMR, has been developed in conjunction with the Modified Hoek-Brown failure to deal with varying shear strength with respect to the orientation and degree of anisotropy within an anisotropic rock mass. Conventionally, ubiquitous-joint or directional shear strength models have assumed a general rock mass strength, typically estimated using the Hoek-Brown failure criterion, and applied a directional weakness in a given orientation depending on the anisotropic nature of the rock mass. Shear strength of the directional weakness is typically estimated using the Barton-Bandis failure criterion, or on occasion, the Mohr-Coulomb failure criteria. Directional shear strength models such as these often formed the basis of continuum models for slopes and underground excavations in anisotropic rock masses. This paper compares ARMR and the Modified Hoek-Brown failure criterion to the conventional directional shear strength models using a case study from Western Australia.

Automation of design for dynamic loading at the designing stage of mining machinery

Meeting the growing needs of the state’s economy for the raw materials needed for the production of ferrous and non-ferrous metals accelerates the technical re-equipment of the mining industry through the introduction of new, more powerful equipment. This circumstance determines the urgency in the automation of calculations at the design stage of mining machines. The originality of the developed software product is in consideration of the actual loads acting in the working equipment of a career excavator. Actual dynamic loads significantly exceed their calculated values, which leads to an increased number of structural element failures. At the design stage, with the use of the developed program, it is possible to establish rational cross-sectional dimensions of the handle metalwork taking into account the actual loads arising during the rock mass excavation and stress concentrators.

Modeling transient excavation-induced dynamic responses in rock mass using an elasto-plastic cellular automaton

The problem of transient excavation-induced dynamic response in rock mass is discretized on both spatial and temporal scales and is solved by using the cellular automaton (CA) technique and the Newmark scheme, respectively. Using this approach, a dynamic analysis version of 3D elasto-plastic cellular automaton (EPCA3D) is developed. The advantage of this method is it avoids the solution of large-scale linear equations since only the local CA rule is used for dynamic state updating. The Den Iseger algorithm is introduced to validate the numerical method. The evolution of stress and velocity for the transient excavation in rock mass under different conditions obtained by the EPCA3D and Den Iseger methods are in good agreement. The abilities of EPCA3D in the modeling of elasto-plastic dynamics of transient excavation in rock mass are well demonstrated. By considering different in situ stresses, excavation radiuses, unloading durations and unloading paths, the factors affecting nonlinear dynamic responses are investigated. It is found that the failure extent increases with the decrease of unloading time. When lateral pressure coefficient (σx/σy) equals to 1, the failure zone is evenly distributed around the tunnel. However, with the decrease of lateral pressure coefficient, the extent of failure localization increases. The fault around the tunnel makes the dynamic failure zone asymmetric distribution. The modeling helps to understand the major mechanism of rock mass damage for the transient excavation.

Analysis of Collapse Load and Open Hole Evaluation Based on Rock Mass Ratting (RMR) Method in Underground Mining

The excavation of a underground rock mass resulting a change in the balance of rock conditions such as the occurrence of rock collapse and changes in the dimensions of tunnel as a result of the displacement of the voltage distribution. It is desirable to have a good geotechnical analysis to provide an appropriate treatment of rocks excavated. This research was conducted to determine rock mass class, rock strength. Classification of rocks mass with RMR system And Q-System FK potential of wedge using unwedge software. From the measurement of several parameters of RMR method, RMR value of 48 ( Coal) and 60 (Sillstone) is obtained where as rock mass class III (fair rock), based on the Q-System obtained a value of 14 in class II for coal and 4 Class III for Sillstone. Based on the RMR-system classification, the value for span maximum is 3 m with a collapse time of 110 hours and the value of the load collapses is 1,56 tons / m2. Based on the Undwedge Software processing, there was an increase in FK values for both methods, Based on Support RMR Ground from 1,907 to 2,939 and Based on Ground Support Q-System from 1,907 to 2,078.