Rock Excavation Research Articles

Experimental and numerical research on fracture behaviors of sandstone under different loading rates

The macroscopic deformation process of rock is the external performance of microscopic damage in essence, and research from the macro and micro perspectives can effectively reveal the failure mechanism of rock. To further investigate the fracture behaviors of yellow sandstone disc specimens under different loading rates, seven groups of Brazilian disc splitting tests with different loading rates from 1 × 10–6 to 1 × 10–4 s–1 were carried out. A systematical investigation of loading rate effect on macroscopic mechanical responses and microscopic damage characteristics has been conducted from the stress–strain relationship obtained from material testing system, from damage three-dimensional localization based on acoustic emission techniques, and from fracture morphology by scanning electron microscope. In addition to laboratory experiment, parallel bond models of different grain size distribution indexes based on particle flow code were established. The coupling effect of loading rate and grain size distribution index was further analyzed. The results interpret that the effect of loading rate on rock fracture behaviors is determined by the process of crack initiation, propagation and coalescence, and it is also affected by distribution of different size grains. The differences of rock fracture behaviors under different loading rates were discussed from the mechanism of energy input and dissipation. The research have actual significance for stability design and evaluation of rock excavation engineering.

A Numerical Investigation of TBM Disc Cutter Life Prediction in Hard Rocks

There is a direct relationship between the efficiency of mechanized excavation in hard rocks and that of disc cutters. Disc cutter wear is an important effective factor involved in the functionality of tunnel boring machines. Replacement of disc cutters is a time-consuming and costly activity that can significantly reduce the TBM utilization and advance rate, and has a major effect on the total time and cost of the tunneling projects. When these machines bore through hard rocks, the cutter wear considerably affects the excavation process. To evaluate the performance of the cutters, first, it is essential to figure out how they operate the rock cutting mechanism; secondly, it is important to identify the key factors that cause the wear. In this work, we attempt to introduce a comprehensive numerical method for estimation of disc cutter wear. The field data including the actual cutter wear more than 1000 pieces and the geological parameters along the Kani-Sib transmission tunnel in the northwest of Iran are compiled in a special database that is subjected to a statistical analysis in order to reveal the genuine wear rule. The results obtained from the numerical method indicate that with an increase in the wear of disk cutter up to 25 mm, the applied normal and rolling forces can be multiplied by 2.9 and 2.7, respectively, and by passing the critical wear, the disk cutters lose their optimal performance. This method also shows that confining pressure will increase the wear of the disc cutter. By the proposed formulation, the cutter consumption rate can be predicted with a high accuracy.

Direct shear test on the interface between concrete and bedrock of dam foundation of a reservoir

The weak failure surface of the dam body and the bedrock cementation surface is one of the key points of dam safety research at home and abroad. The direct shear strength of the contact surface between the dam foundation concrete and the bedrock is used as the current research on whether the dam will “slip” along the contact surface. Based on this, many different methods are used at home and abroad to determine the direct shear strength. In this paper, through the excavation of the dam foundation rock and on-site rock structure samples, 5 sets of 25-point in-situ direct shear tests on the interface between concrete and bedrock were carried out on the medium-thick-thick feldspar quartz sandstone of the main rock mass of the dam foundation to determine the dam foundation. Mechanical parameters of rock mass. Based on the results of field experiments, some reference opinions for field direct shear tests and direct shear strength selection in engineering design are put forward, which also provide a basis for subsequent numerical simulation calculations.

Development of selenium insolubilized material eluted from tunnel excavation rock

Development of selenium insolubilized material eluted from tunnel excavation rock

On the Failure Mechanism of Brittle Granite in 2-D Rock Indentation

Abstract Rock indentation is one of the main mechanical rock breaking approaches, in which the indenter moves perpendicular to the rock surface. A detailed understanding of the failure mechanism of brittle granite is of great importance to achieve high efficiency in rock breaking and to optimize the cutting parameters during deep hard formation drilling. In the present study, a rock indentation simulation model of Ya’an granite is carried out, using the grain-based model (GBM), which is based on the discrete element method of Particle Flow Code (PFC2D), to reproduce the crack initiation, propagation, and coalescence processes in intact rock. This study also includes an experimental program to examine the crack initiation, propagation, and the acoustic emissions in rock specimens. The results show that the microcracks generate gradually in intact rock with respect to penetration depth, and some of the microcracks coalesce with the crack number increasing, eventually resulting in the macrofracture formation. Four types of microcracks will generate during the indentation: intragrain tensile crack, intragrain shear crack, intergrain tensile crack, and intergrain shear crack. Among these four types of cracks, the intergrain tensile crack and intragrain shear crack are the two main crack types generated in indentation, especially the intergrain tensile crack. The rock failure mechanisms are different with the variation of grain size, and the lateral fragmentation of rock is restricted because of the chip hold-down effect of hydrostatic pressure. This study leads to an enhanced understanding of rock breaking mechanisms of Ya’an granite and provides the basis for improving the rock excavation machine design.

Reduction of tunnel blasting induced ground vibrations using advanced electronic detonators

Blasting has been widely used for economical and rapid rock excavation in civil and mining engineering but has great loads, such as vibrations and noises, on the surrounding environment in the case of urban areas near dwellings and important structures. In this study, for the purpose of environmental load reduction, blasting tests were conducted at a tunnel construction site using advanced electronic detonators in which arbitrary ignition times could be set. The test results showed that the peak amplitude of the vibration waveform from each of the blast holes follows the Weibull distribution and that the wave propagation time depends on the location of the blast hole on the tunnel face. The superposition method proposed from these findings reproduced the vibration waveforms in delay blasting from the seed waveform recorded in single-shot blasting. The optimum delay interval determined accurately from the superposition method was almost equal to the one simply estimated from the method with the autocorrelation coefficient or a frequency analysis of the vibration waveform in single-shot blasting. These simple methods were validated at another tunnel construction site and found to be useful for estimating the optimum delay interval from single-shot blasting at each tunnel face on each day. This study is based on the practical consideration of actual tunnel blasting and construction, and these proposed methods will be widely applied to other tunnel construction sites.

Experimental and numerical study on crack development characteristics between two cavities in rock-like material under uniaxial compression

The understanding of failure mechanisms of rocks containing multiple cavities is important for stability assessment of rock excavations in rock engineering applications. However, published research is still limited on the failure mechanism between cavities and quantitative assessment of the crack development characteristics for different cavity configurations. In this research, specimens containing two cavities were investigated for their displacement characteristics and failure mechanisms under uniaxial compression. Digital image correlation (DIC) was used to measure the displacements of the specimens in experiments, while the failure process was modelled using the Particle Flow Code (PFC) software. A density-based clustering method was used to detect micro-crack clusters and the well-known statistical tool of Principal Component Analysis (PCA) was applied innovatively in this work to define the macro-cracks. The clustering method was further developed in this work for vector analysis so that the displacement vectors around macro-cracks could be classified into different types based on the failure mechanism to understand the crack development characteristics. The crack development between two cavities and failure mechanism for different geometrical configurations were subsequently studied in detail using experimental and numerical results.

Study on Energy Release of Surrounding Rock under the Multiple Unloading Disturbance during Tunnel Excavation

During excavation of deep rock, the release of strain energy plays an important role in geologic hazards caused by excavation. However, in the previous studies, the influence of transient unloading of in situ stress caused by blasting excavation has been ignored, and the blasting excavation of a tunnel is regarded as a single blast process. In this paper, the dynamic adjustment process of strain energy and the energy storage limit of surrounding rocks caused by transient unloading of in situ stress under elastic conditions were firstly analyzed. Then, the brittle-ductile-plastic transition model based on the Hoek–Brown strength criterion was simulated in FLAC3D. Finally, the dynamic release process of strain energy of surrounding rocks caused by multiple unloading disturbances was analyzed during the excavation of 2# Underground Laboratory of Jinping II Hydropower Station employing the newly proposed index, energy release coefficient (ERC). Results show that the strain energy of surrounding rock masses firstly decreases, then increases, next reduces, and finally stabilizes under the transient unloading of in situ stress. In the process of dynamic change of strain energy, when the strain energy exceeds its storage limit, a large amount of strain energy will be released and thus will lead to damage of the surrounding rock masses. Because the cut holes and the first circle of breaking holes are far away from the final excavation boundary, the unloading disturbance to the strain energy of surrounding rock masses is small. Furthermore, the energy release of surrounding rock masses is mainly caused by the unloading of the last circle of breaking holes and perimeter holes, and the closer to the final excavation boundary, the more intense the energy release.

Analysis of Damage and Permeability Evolution for Mudstone Material under Coupled Stress-Seepage.

Mudstone material in a deep roadway is under the coupled stress-seepage condition. To investigate the permeability change and damage development during rock excavation in roadways, a stress-seepage damage coupling model has been proposed. In this model, damage capacity expansion of mudstone material is considered as the initiation and propagation of micro-cracks and the fracture penetration. A damage variable is introduced into the proposed model based on the principle of minimum energy consumption. As a result, an elastoplastic damage constitutive equation is established. Then, the permeability evolution equation describing the micro-macro hydraulic behavior of mudstone is deduced via percolation theory, which can describe the characteristics of sudden permeability change after rock capacity expansion. Furthermore, a finite element model is established based on commercial finite element software-ABAQUS. The numerical model was firstly verified by comparison between experimental and simulation results. On the basis of it, numerical investigation of the temporal and spatial evolution law of pore pressure, damage and permeability coefficient during roadway excavation is undertaken. The numerical results indicate that with increase of construction time, pore pressure first increases and then decreases, while the damage zone and permeability coefficient increase gradually and finally nearly keep constant. The proposed coupling model and finite element method can describe damage and permeability evolution for mudstone material under coupled stress-seepage well.

Study of influences of rock hardness on crack evolution rule under hydraulic fracturing

In order to study the crack evolution rules of hydraulic fracturing rock with different hardness, a numerical model of hydraulic fracturing rock was established. It explored the expansion length, expansion width, propagation rate of crack and initiation pressure of hydraulic fracturing different hardness rocks. The results show that the expansion length, the propagation rate along length and the initiation pressure of crack were positively correlated with the rock hardness, and the expansion width and propagation rate along width were negatively correlated with the rock hardness. In addition, considering the effect of in-situ stress difference, it took granite as an example, and studied the effect of in-situ stress difference on crack propagation. It is found that as the in-situ stress difference increases, the initiation pressure of the crack decreases, and the crack expansion length and the propagation rate along length shows a linear increase, but it has little effect on the crack expansion width. The results can provide theoretical references for improving the application of hydraulic fracturing technology in hard rock excavation, such as the coal roadway excavation, the tunnel excavation and so on.

Predictive plots for conical pick performance using mechanical and elastoplastic properties of rocks

Abstract Conical picks are by far the most widely used drag type cutting tools employed on partial face rock excavation machines. The cutting force and specific energy are two important design parameters for the conical pick performance, and the rock cutting testing is considered as the promising tool for determining these parameters. In the absence of an instrumented cutting rig, researchers generally rely on empirical predictive plots. For this, this paper suggests predictive plots for estimating the cutting force and specific energy, in consideration of the cutting depth to define the cuttability with conical picks. In this context, rock cutting tests were carried out on six volcanic rock samples with varying cutting depths using the unrelieved and relieved cutting modes. The cutting force and specific energy were correlated with the uniaxial compressive strength, Brazilian tensile strength, elasticity modulus, and plasticity index. Predictive plots were proposed for different cutting depths in the unrelieved and relieved cutting modes and exponential relationships were obtained among the cuttability parameters, and mechanical and elastoplastic properties of rocks.

Understanding the Impact of Test Configuration on Welded-Wire Mesh Laboratory Test Results

Underground mines use a combination of rock reinforcement and surface support elements to maintain the structural integrity of excavations in rock. The design of an effective ground support system requires an understanding of the mechanical behaviour of individual ground support components and how they interact under load. This paper reviews the mechanical behaviour of welded wire steel mesh routinely used in underground mines. It further reviews the advantages and limitations of using testing rigs used to quantify the performance of mesh. In particular, it illustrates the impact of rig configuration and testing parameters on mesh performance. The main focus of this work is the development and calibration of 3D discrete element method of numerical models capable of reproducing mesh behaviour under specific testing configurations. The developed models successfully reproduced the load redistribution on the mesh wires, the load–displacement response, and failure mechanisms observed in laboratory tests. The calibrated models were subsequently used to determine the impact of testing rig configurations, including loading plate dimensions and orientation, and mesh dimensions on the performance of mesh under load. This work has significant practical implications on how to interpret results obtained from different testing rigs. Furthermore, the results of this work can provide guidance towards designing new testing rig configurations as well as demonstrating the need for the development of testing methods and procedures. Finally, it illustrates the challenges that have to be overcome if the explicit modelling of mesh will be a reliable part of the ground support design process.

An ANN-adaptive dynamical harmony search algorithm to approximate the flyrock resulting from blasting

Blasting is the cheapest and most common method of rock excavation. The basic purpose of blasting is to breakage and displacement of rock mass and, on the other hand, it has some undesirable and inevitable effects such as flyrock. In this study, a novel hybrid artificial neural network (ANN) based on the adaptive musical inspired optimization method is proposed for accurate prediction of blast-induced flyrock. The dynamical adjusting process was adaptively introduced to enhance the ability of harmony search algorithm to obtain the optimum relationship between input variables, i.e., spacing, burden, stemming, powder factor and density of rock and output variable, i.e., flyrock. Two adjusting processes were used to update the new position of particles. The statistical information of the harmony memory was implemented in the proposed hybrid ANN coupled with adaptive dynamical harmony search (ANN-ADHS). The capacity for agreement, tendency, and accuracy of the proposed ANN-ADHS was compared with that of the ANN and two hybrid ANN models coupled by harmony search (ANN-HS) and particle swarm optimization (ANN-PSO) models using comparative statistics such as root mean square error (RMSE). The results confirmed viability and effectiveness of the ANN-ADHS model (with RMSE = 17.871 m and correlation coefficient (R2) = 0.929) and showed its capacity for better predictive performance compared to ANN-HS (with RMSE = 22.362 m and R2= 0.871), ANN-PSO (with RMSE = 24.286 m and R2= 0.832), and ANN (with RMSE = 24.319 m and R2= 0.831).

Methods for reducing the environmental impact of rock mass excavation

Many engineering projects and interventions have negative effects on the environment. Rock excavation in civil engineering, either in mining or in construction, often is unthinkable without the use of explosive. However, blasting can have extensive adverse environmental impacts, like vibrations, noise, dust and chemical contamination. Therefore, it is better to avoid blasting activities near urban areas, protected animal habitats, sensitive historic buildings, water protection zones, pipelines, etc. While mechanical excavation is often longer lasting and more expensive, in some cases it may adequately replace blasting, where the applicability of mechanical excavation methods greatly dependent on the rock mass characteristics which should excavate. This paper provides practical examples of using existing methods for the assessment of the applicability of excavation technologies. In order to minimize the project impact on the environment, mechanical excavation was applied in some cases. In one case, the blasting could not be avoided, but controlled careful blasting techniques were applied.

Experimental investigations on thermal behavior during pick-rock interaction and optimization of operating parameters of surface miner

Operation of surface miner has significantly expanded in mines because of its mass production ability and eco-friendly way of rock excavation. Optimal utilization of operating parameters ensures better cutting efficiency and longer machine life. Elevated temperature of a pick developed during the rock cutting process affects its life. It especially influences the wear rate of the cutting pick. During the present study, operating parameters of a surface miner were examined using the Taguchi method. In the process, an appropriate parametric combination was developed facilitating the use of optimal cutting power, higher production and minimum pick consumption. The role of operating parameters, i.e., depth of cut (DOC), cutting speed (CS) and drum speed (DS) with temperature (T) was analyzed statistically. Empirical models were also developed for studying temperature variations in cutting picks using Taguchi method, multiple linear regression (MLR) and artificial neural network (ANN). Confirmation test revealed that optimized temperature was achieved at a significance level of 0.05 and the Taguchi method enabled better outcomes with minimum deviation and a high degree of optimization of operating parameters of surface miner.

A 3D synthetic rock mass numerical method for characterizations of rock mass and excavation damage zone near tunnels

In practice, a damage zone is generally formed after tunnel excavation in jointed rock mass. This damage zone is closely related to rock mass properties and requires careful examination in order for cost effective supporting designs. In this research, a synthetic rock mass (SRM) numerical method is applied for characterizations of the jointed rock mass and excavation damage zone (EDZ) near underground tunnels in 3D. The SRM model consists of bonded particles and simulates deformation and crack propagation of the rock mass through interactions between these particles. The effects of joint stiffness and distribution on the rock mass properties are systematically examined by comparing the numerical data with an empirical geological strength index (GSI) system and an associated Hoek-Brown strength criterion. The numerical results suggest that rock mass properties are comparable to the empirical GSI/Hoek-Brown system only when inclined joints are simulated in the rock mass subjected to axial loading. The rock mass is strengthened and the empirical GSI/Hoek-Brown characterization becomes inappropriate when the joints are less favorable to shear sliding. The SRM method is then applied for characterizations of tunnel EDZ. It appears that the depth and location of the EDZ are a function of the tunnel orientation, joints, and in situ stresses. The EDZ depth is expected to be higher when inclined joints are simulated. The EDZ area is reduced when the joints in the rock mass are horizontally and vertically distributed.

Analysis of Soil Erosion on Mine Area

Mining activities disturbing large areas of land may increase erosion rate up to several hundred times greater than from undisturbed areas. The erosion process occurs in stripping overburden, excavation of rocks and minerals, dumping in stock file and waste dump, and mine reclamation. Since the eroded material/sediment becomes a big problem to the environment and for mining operations, estimation of soil erosion need to be carried out to create a good mine planning. For the early stage, a study of soil erosion was performed to classify erosion hazard level and to estimate soil erosion size. This study uses the Revised Unified Soil Loss Equation (RUSLE) method supported with Geographic Information System application for study area in the Block D1-D3 of Petea Mine Area. The study result showed that the research area can be classify into four erosion hazard level namely; low, medium, heavy, and very heavy with estimated material losses is 116,146.43 tons/year.

Numerical Modeling of a Punch Penetration Test Using the Discrete Element Method

Abstract Understanding the brittleness of rock has a crucial importance in rock engineering applications such as the mechanical excavation of rock. In this study, numerical modeling of a punch penetration test is performed using the Discrete Element Method (DEM). The Peak Strength Index (PSI) as a function of the brittleness index was calculated using the axial load and a penetration graph obtained from numerical models. In the first step, the numerical model was verified by experimental results. The results obtained from the numerical modeling showed a good agreement with those obtained from the experimental tests. The propagation path was also simulated using Voronoi meshing. The fracture was created under the indenter in the first step, and then radial fractures were propagated. The effects of confining pressure and strength parameters on the PSI were subsequently investigated. The numerical results showed that the PSI increases with enhancing the confining pressure and the strength parameter of the rock, including cohesion and the friction angle. A new relationship between the strength parameters and PSI was also introduced based on two variable regressions of the numerical results.

The dnỉ-Measure in Ancient Egyptian Tomb Construction Projects

When constructing the rock-cut tombs in the Theban necropolis, the ancient Egyptian builders kept track of the progress by recording the amount of rock that was excavated. This is clear from Eighteenth Dynasty ostraca from the tomb chapel of Senenmut, TT 71, which record stages of excavation and measure the production output in units of dnỉ. The current article reconfirms the observations of J. Černý on the dnỉ-unit and its usage as a measure exclusively for capacity, particularly in building projects involving excavation of rock. From this, the article outlines the implications for the understanding of other tomb construction terminology, in particular the ȝʿʿ, the šʿd and the dḳr. The consequence is to acknowledge that the tomb builders of Senenmut only recorded progress of excavation, and not different stages of decoration. In addition, the article suggests that baskets filled with stone flakes at Deir el-Bahri from the Middle Kingdom may represent a practical use of the dnỉ-unit.

Numerical Research on Cutting Force and Fracture Morphology of Rock Plate with Two Sides Fixed and Two Sides Free

Conical pick is a diffusely applied cutting tool in rock excavation in the coal-mining industry. In order to enhance the capability of conical pick, a new rock cutting method based on increased free surface is proposed. To research the peak cutting force and fracture morphology, ANSYS/LS-DYNA is used to establish the conical pick and rock interaction model. To obtain the fracture morphology of rock plate, eroding contact, erosion element failure, and damage constitutive are considered in the numerical model. Mechanical properties test and rock plate cutting experiment are carried out to guarantee and verify the correctness of the numerical model. The width and height of rock plate influencing peak cutting force and fracture morphology are studied, and the stable peak cutting force is defined. Lower width and height contribute to more fragments in smaller dimension produced during the rock plate cutting process. Besides, higher skew angle leads to more fragments. The peak cutting force decreases with the increasing width and height of rock plate while reaching stable peak cutting force, and it reduces and then remains stable with the increasing cutting position and symmetrical with skew angle of zero degree.