Rock Support Research Articles

The effectiveness of epoxy coating for preventing microbially induced corrosion of rock bolts

In the past two decades, the corrosion failures of rock reinforcement bolts in underground coal mines have been increasingly reported. Preliminary studies have shown that these failures were predominantly related to pitting and stress corrosion cracking. The analyses in affected mines indicated microbially induced corrosion (MIC) as one of the primary corrosion causes. As such, there is an urgent demand from industries to develop methods to mitigate MIC-associated failures of rock bolts in underground coal mines. This study examined epoxy coating to determine its effectiveness in preventing biofilm formation on steel surfaces and, in turn, averting MIC. The corrosion-causing bacteria were isolated and enriched from groundwater samples collected from the affected mine sites. Coated and uncoated rock bolt samples were prepared from the bolts and incubated in media in the absence and presence of the corrosion-causing bacteria. Fluorescence microscopy imaging found no evidence of bacterial biomass growth on the surface of the epoxy-coated steel surfaces after 30 days, while the non-coated surfaces were colonised by biomass. The observations suggest the potential of epoxy coating for bolt MIC prevention. Future studies to assess the applicability of epoxy coating in the underground mine environment are recommended.

WALL STABILIZATION IN MINES BY SPRAY-ON LINERS

AbstractThin spray-on liners (TSLs) have been found to be effective for structurally supporting the walls of mining tunnels and thus reducing the occurrence of rock bursts, an effect primarily due to the penetration of cracks by the liner. Surface tension effects are thus important. However, TSLs are also used to simply stabilize rock surfaces, for example, to prevent rock fall, and in this context crack penetration is desirable but not necessary, and the tensile and shearing strength and adhesive properties of the liner determine its effectiveness. We examine the effectiveness of nonpenetrating TSLs in a global lined tunnel and in a local rock support context. In the tunnel context, we examine the effect of the liner on the stress distribution in a tunnel subjected to a geological or mining event. We show that the liner has little effect on stresses in the surrounding rock and that tensile stresses in the rock surface are transmitted across the liner, so that failure is likely to be due to liner rupture or detachment from the surface. In the local rock support context, loose rock movements are shown to be better achieved using a liner with small Young’s modulus, but high rupture strength.

Research of strength and features of deformations of rocks in uranium deposits

The subject of the research was physical and mechanical properties of rocks from uranium deposits in Ukraine. The purpose of the work was to study the strength characteristics and features of deformation of rocks of uranium deposits beyond their strength limit to ensure the stability of mine workings at great depths. Research methods were experimental with using stationary laboratory equipment and special recording equipment. The studies were carried out within and beyond the strength limits. The rock specimens were made of material taken from a uranium mine. The complex of the studies included determination of general physical properties of rocks (density, specific gravity, porosity, humidity and adhesion coefficient); basic strength parameters (compressive and tensile resistance depending on humidity and layering, angle of internal friction, elastic modulus, Poisson's ratio, modulus of decrease and residual strength) and deformation characteristics. Calculations of the scale strength factor were made. The results were analyzed. It is shown that the rocks of uranium deposits in Ukraine are considered strong and very strong, according to the Protodyakonov scale. However, structural and textural features lead to the occurrence of a scale effect of strength of rocks. The complex structure of uranium deposits, the steep angle of dip of the rocks, their lamination, as well as the significant size of the mine workings further reduce the strength of the massif. It is also shown that when calculating stability of mine workings and choosing parameters for their support, the strength of rocks in the massif should be reduced by half from the value obtained by standard laboratory tests. The characteristics of rock samples within and beyond their strength limit indicate that they have almost no plastic properties. The ratio of the modulus of decrease to the static elastic modulus for all studied types of rocks of uranium deposits is greater than one. This indicates the tendency of rocks to accumulate potential energy and cause brittle failure of the massif beyond its compressive strength. That is, at great depths, the main problems in mine workings associated with rock deformation processes will manifest themselves in the form of rock bumps, collapses or other dynamic phenomena. This does not exclude the possibility of deformation or destruction of rock support due to static loads. Keywords: uranium deposit, rock, laboratory research, extreme stress, physical properties, strength, elasticity, scale factor.

Energy Action Mechanism of Reinforced Sandstone under Triaxial Cyclic Loading and Unloading

In underground engineering, reinforcement is a necessary means to ensure the stability of surrounding rock. Due to the stress redistribution caused by excavation disturbances, the reinforced rock mass is frequently subjected to loading and unloading, and its mechanical properties change accordingly. Based on the above engineering practice, using pasted circular CFRP, an approximate simulation of the rock reinforcement effect of bolt and shotcrete support was performed. Triaxial cyclic loading and unloading tests of reinforced sandstone were carried out, and the influence of different reinforcement schemes on the mechanical properties was compared and analyzed. Furthermore, the strengthening mechanism, damage evolution, and energy transformation mechanism of CFRP are discussed. The results showed that the peak strength increased about 14.2% and 23.8% with the two reinforced schemes, and the residual strength increased about 27.3% and 52.8% with the increase in the area reinforced by CFRP. Under the same confining pressure and strain conditions, the characteristic energy density and elastic energy ratio increased with an increase in the reinforcement area, but the damage variable decreased. It is proved that CFRP can improve energy absorption efficiency, enhance the energy storage limit, and reduce dissipation efficiency. By inhibiting the propagation of internal fissures and limiting the energy dissipation during fractures, the rock mass can be restrained and strengthened.

Mechanical characteristics and stability analysis of surrounding rock reinforcement in rectangular roadway

The stability of surrounding rock with bolt support depends on the stability within the reinforcement range. To understand the reinforcing mechanism of a rectangular roadway bolt fully and accurately, a quantitative method for evaluating the stability of the surrounding rock of a rectangular roadway must be developed. First, a roof beam model of a rectangular tunnel is established according to the deformation law of surrounding rock. Based on the elastic–plastic theory, the deflection calculation formula can be derived, and the ultimate load of the roof beam can be obtained under the plastic state without support. Second, based on the reinforcement effect of bolts, a model of a surrounding rock reinforcement body is established, the physical and mechanical properties of this body are deduced, and a method for evaluating the stability of surrounding rock is derived. Finally, by considering actual engineering cases, the theoretical calculation results of surrounding rock deformation are compared with the numerical simulation and field monitoring results. Moreover, the influence of different parameters of the bolt support on the mechanical characteristics and stability of reinforcement is investigated. The results show that the theoretical calculations approximate the numerical simulation and field monitoring values, thus verifying the rationality of the theory. The physical and mechanical properties and stability of the surrounding rock reinforcement body are considerably affected by changes in bolt length and spacing. The anchor design must apply the following principle: the bolt must either be long and sparsely spaced or short and densely spaced. The theory presented in this paper provides a relatively simple and fast quantitative calculation method for the study of the surrounding rock stability of bolt-supported rectangular roadways.

Investigating the Influence of Embedment Length on the Anchorage Force of Rock Bolts with Modified Pile Elements

The embedment length (EL) of full-grouting rock bolts is a core factor in rock bolt reinforcement. Therefore, understanding the influence of EL on the reinforcement performance of rock bolts benefits the rock reinforcement quality. To realise this purpose, this paper adopted the numerical modelling method. In this numerical modelling method, the structural elements of modified piles were used. The elastic debonding law was incorporated into the modified pile elements to model the debonding behaviour of the surface between rock bolts and grout. The results showed that the sliding of modified pile elements had a marginal influence on the reinforcement performance of rock bolts. Moreover, the EL has a paramount influence on the reinforcement performance of rock bolts. Before the rock bolts reached the largest anchorage force, there was a linear relation between the largest anchorage force and the EL. It was effective to use the linear regression analysis method to predict the critical EL of rock bolts. This finding was also applicable to fibre-reinforced polymer (FRP) rock bolts. Additionally, the rock bolt type had a paramount influence on the reinforcement performance of rock bolts. Before the rock bolts reached the largest anchorage force, metal rock bolts showed much larger initial stiffness than FRP rock bolts.

Grouting theories and technologies for the reinforcement of fractured rocks surrounding deep roadways

AbstractGrouting is an effective method to improve the integrity and stability of fractured rocks that surround deep roadways. After years of research and practice, various theories and a complete set of grouting technologies for deep roadways with fractured rocks have been developed and are widely applied in Chinese coal mining production. This paper systematically summarizes and analyzes the research results concerning the theory, design, materials, processes, and equipment for the grouting and reinforcement of fractured rocks surrounding deep roadways. Specifically, in terms of grouting methods, pregrouting, grouting‐while‐excavation, and postgrouting methods are explored; in terms of grouting theory, backfill grouting, compaction grouting, infiltration grouting, and fracture grouting theories are studied. In addition, this paper also studies grouting borehole arrangement, water‐cement ratio, grouting pressure, grouting volume, grout diffusion radius, and other grouting parameters and their determination methods. On this basis, this paper explores the physical and mechanical properties of organic and organic‐inorganic composite grouting materials, and assess grouting reinforcement quality testing methods and instruments. Taken as the field cases, the application of pregrouting in front of heading faces, grouting‐while‐excavation, and postgrouting in the Kouzidong coal mine are then introduced, and the effects of the grouting reinforcements are evaluated. This paper proposes a development direction for grouting technology based on problems existing in the grouting reinforcement of fractured rocks surrounding deep roadways.

Quality assurance considerations for friction rock stabilizers

ABSTRACT Friction rock stabilizers (FRS) are routinely used to provide rock reinforcement to excavations in hard rock. Since the expiration of the original patent taken out in 1977, FRS are now available from multiple suppliers. The expectation that all FRS are equivalent, however, is not necessarily accurate. There are inherent variations in the design configuration, material chemistry/properties, and consequently in performance. In this context, a full traceability from steel grade and heat treatment to final product is critical. This paper reports the results of a QA/QC investigation aiming to identify the material properties for three equivalent FRS from the same supplier. A series of mechanical and accelerated corrosion tests highlighted the differences in these rockbolts. This work provides a template for a more comprehensive quality assurance programme to ensure compliance of FRS. This is critical when rockbolts, due to global supply chain constraints, are outsourced from multiple sources worldwide.

Optimization Analysis on Seismic Mitigation of Building Foundation in Coastal Area

The stability of the buildings foundation in coastal areas caused by the submarine earthquake caused by the seabed plate movement has increasingly become the research focus of the engineering construction department. For the foundation under special geological conditions in coastal areas, the failure mechanism is complicated and the stress analysis is difficult. Based on the current situation of seismic design of building foundation in coastal areas, and aiming at the immature aspects of seismic treatment of foundation in coastal areas, this paper analyzes the optimization scheme of seismic design of foundation in such areas, which provides reference ideas for seismic design of building foundation in coastal seismic zones in China. In this paper, the research method is mainly through the comparative analysis of the relevant coastal engineering foundation treatment cases, the comparison of their treatment schemes and the combination of the existing foundation damping theory to summarize the suggestions on the foundation damping design under the special geological conditions in China’s coastal areas. In this paper, it is suggested that two aspects should be considered in the design of foundation vibration reduction in coastal areas: the application of dampers to reduce the vibration of foundation structures and the reinforcement of rock and soil under the foundation to meet the requirements of vibration reduction.

Rock Reinforcement by Stepwise Injection of Two-Component Silicate Resin

Our research aims to improve the efficiency of the reinforcement of loose rocks with two-component polymer resins. The standard approach consists of the injection of two pre-mixed components into a rock massive. We propose a stepwise injection of individual components of a resin into the rock and deep extrusion of the solutions into the rock by gas between the injection stages. The experimental results indicate that the proposed method provides a reduction of polymer consumption per unit volume of the rock, and an increase in the impregnation depth, area of the resin impact, and the reinforced rock volume in comparison with the conventional method of prepared resin solution injection. The cured resin partially fills the sand rock pore space, binds the grains, and acts as a reinforcing frame. The highest reinforcement is achieved with the sequential stepwise injection of the resin by separate small portions of each component. We have shown the uniaxial compressive strength is on average more than twice as high that obtained with the conventional injection method. This can be explained by higher fracture toughness of the reinforced rock with a flexible hardened network of the cured resin in the structure.

Analysis of the damage mechanism of strainbursts by a global-local modeling approach

Strainburst is the most common type of rockbursts. The research of strainburst damage mechanisms is helpful to improve and optimize the rock support design in the burst-prone ground. In this study, an improved global-local modeling approach was first adopted to study strainburst damage mechanisms. The extracted stresses induced by multiple excavations from a three-dimensional (3D) global model established by fast Lagrangian analysis of continua in 3 dimensions (FLAC3D) are used as boundary conditions for a two-dimensional (2D) local model of a deep roadway built by universal distinct element code (UDEC) to simulate realistic stress loading paths and conduct a detailed analysis of rockburst damage from both micro and macro perspectives. The results suggest that the deformation and damage level of the roadway gradually increase with the growth of surrounding rock stress caused by the superposition of mining- or excavation-induced stresses of the panel and nearby roadways. The significant increase of surrounding rock stresses will result in more accumulated strain energy in two sidewalls, providing a necessary condition for the strainburst occurrence in the dynamic stage. The strainburst damage mechanism for the study site combines three types of damage: rock ejection, rock bulking, and rockfall. During the strainburst, initiation, propagation, and development of tensile cracks play a crucial role in controlling macroscopic failure of surrounding rock masses, although the shear crack always accounts for the main proportion of damage levels. The deformation and damage level of the roadway during a strainburst positively correlate with the increasing peak particle velocities (PPVs). The yielding steel arch might not dissipate kinetic energy and mitigate strainburst damage effectively due to the limited energy absorption capacity. The principles to control and mitigate strainburst damage are proposed in this paper. This study presents a systematic framework to investigate strainburst damage mechanisms using the global-local modeling approach.

Amplification effect of near-field ground motion around deep tunnels based on finite fracturing seismic source model

Dynamic failure of rock masses around deep tunnels, such as fault-slip rockburst and seismic-induced collapse, can pose a significant threat to tunnel construction safety. One of the most significant factors that control the accuracy of its risk assessment is the estimation of the ground motion around a tunnel caused by seismicity events. In general, the characteristic parameters of ground motion are estimated in terms of empirical scaling laws. However, these scaling laws make it difficult to accurately estimate the near-field ground motion parameters because the roles of control factors, such as tunnel geometry, damage zone distribution, and seismic source parameters, are not considered. For this, the finite fracturing seismic source model (FFSSM) proposed in this study is used to simulate the near-field ground motion characteristics around deep tunnels. Then, the amplification effects of ground motion caused by the interaction between seismic waves and deep tunnels and corresponding control factors are studied. The control effects of four factors on the near-field ground motion amplification effect are analyzed, including the main seismic source wavelength, tunnel span, tunnel shape, and range of damage zones. An empirical formula for the maximum amplification factor ( α m ) of the near-field ground motion around deep tunnels is proposed, which consists of four control factors, i.e. the wavelength control factor ( F λ ), tunnel span factor ( F D ), tunnel shape factor ( F s ) and excavation damage factor ( F d ). This empirical formula provides an easy approach for accurately estimating the ground motion parameters in seismicity-prone regimes and the rock support design of deep tunnels under dynamic loads.

Experimental and Numerical Investigation of the Tensile Performance and Failure Process of a Modified Portland Cement

A better understanding of the tensile performance and tensile failure mechanism of cement paste is significant in preventing rock reinforcement failure. Therefore, this paper aims to reveal the tensile performance and failure mechanism of a modified Portland cement: Stratabinder HS cement. To achieve this objective, the split tensile test was conducted on specimens followed by simulating the failure mechanism numerically. The results indicated that the water–cement rate significantly influenced the tensile performance of the cement paste. When the water–cement rate increased from 0.35 to 0.42, the tensile strength declined from 1.9 MPa to 1.5 MPa. It was also observed that vertical tensile failure constantly occurred regardless of the water–cement rate. During the testing process, tensile cracks and shear cracks occurred. The increasing rate in the number of specimen cracks was dependent on the tensile stress state. Before the tensile stress reached the peak, the crack quantity increased slightly. After the peak, the crack quantity increased dramatically. During the vertical loading process, horizontal tensile stress occurred in the specimen. This horizontal tensile stress zone showed a diamond shape. The higher the tensile stress is, the larger the area of the horizontal tensile stress zone. When the tensile strength was reached, horizontal tensile stress mainly concentrated at the vertical centre of the specimen. This finally led to tensile failure of the specimen. This paper indicated that the water–cement rate was the key factor in evaluating the tensile strength of the Stratabinder HS cement.

Pilot trials of mine support system in decline to Level -830 m in Taimyrsky Mine

Support and reinforcement of underground excavations is one of the main processes in underground mining and construction. Considering the implemented pilot trials and based on the accumulated positive experience gained in support and reinforcement in foreign mines, it is decided to optimize the mine support systems which are in use in the mines of Norilsk Nickel’s Polar Division. The use of novel materials and equipment in mine support systems can enhance mining safety owing to unmanned operation in the unsupported part of roadways, shorten duration of operations connected with scaling and support installation, as well as reduce or totally eliminate manual labor in mine support and reinforcement. The preferable selection of mine support systems should include the modern and most economic options (different rock bolts; rockbolting+reinforcement meshing) featuring the best performance, reduced labor content and materials consumption. Regarding reinforcement of rock mass and reduction in its natural and induced jointing, the method of injection has found wide application. Injection of polymeric resins is assumed to be a promising approach in this respect. This method boasts successful implementation in many mines of Russia, including the mining production units of Norilsk Nickel. Resin injection is a process of deep-earth chemical reinforcement of rocks with synthetic resins. It is found that resin injection reinforcement of rocks makes rock mass a solid structure.The authors appreciate participation of the members of Norilsk Nickel’s Polar Division V. P. Marysyuk, Yu. N. Nagovitsin, M. P. Sergunin, A. A. Kisel, A. A. Bazin and A. A. Kabulov in this study.

Research on suitable methods of soil and rock reinforcement to stabilize mining tunnels in the Quang Ninh area

Currently, along with the economic development speed and the huge demand for activities and living in Vietnam, the demand for energy is becoming an urgent problem that needs to be solved. Among all types of energy, coal is one of the types of energy that occupies a large proportion of the energy industry in Vietnam. Therefore, it is necessary to develop mining technologies that can boost the efficiency and quality of coal. In the total annual coal production of Vinacomin, underground coal mining output accounts for a large proportion (60÷80%). At present, the design and construction units have applied many different construction methods to prevent and stabilize the mining tunnels in the Quang Ninh area. However, in some mining tunnels, are still occurred phenomenon of instability, excessive deformation and affecting the exploitation of these mining tunnels. The paper aims to synthesise, analyse and give a process of choosing suitable reinforcement methods that are suitable for mining tunnels in the Quang Ninh area. The paper also applies theoretical bases to selects an appropriate reinforcement method for a specific mining tunnel under construction in Khe Cham I mining area, Ha Long Coal Company, Vinamcomin.

Evaluation of rockburst energy capacity for the design of rock support systems for different tunnel geometries at El Teniente copper mine

Rockburst events have been a serious problem for many years in many mines worldwide, and in particular at El Teniente mine in Chile. El Teniente is the largest copper mine in the world, located in the Andes Cordillera where high stress levels are present due to intensing mining activity in addition to complex geology. Consequently, the study and management of the rockburst threat are necessary. In this work, the case of the Diablo Regimiento (DR) mine within El Teniente is studied. The energy capacity of dynamic support systems is determined for different tunnel geometries based on two kinetic methodologies, using data from DR. Initially, rockburst potential is determined by means of a stress analysis around different tunnel geometries through the boundary elements method. In the first methodology a yielding zone (YZ) is estimated for each excavation geometry using the finite element method FEM. The second methodology involves the definition and determination of a critical strain energy (SE) around each excavation geometry using a FEM numerical analysis. In both cases, peak particle velocity PPV is estimated by a scaling law, which is subsequently adjusted due to tunnel amplification effects. According to the results, and knowing the working energy capacity applied in DR mine, it was found that the values of energy capacity for the rock dynamic supports were better estimated by the YZ-PPV approach than by the SE approach.

Mechanical Characteristics Analysis and Structural Optimization of Key Component of Self-Moving Temporary Support

In order to prevent a roof fall accident of a coal mine roadway mining face, temporary support must be provided before the permanent support of the roadway. At present, the commonly used forepoling bar support has poor reliability and low efficiency, and other machine-mounted or self-moving temporary supports are also difficult to use widely due to the complex geological conditions and limited working space at the heading face. On the basis of the mechanical characteristics analysis and numerical simulation of the wall rock support system, we propose a temporary support scheme that can adapt to the uneven roof of the roadway and the complex geological conditions on site, and that can ensure the cooperative operation of multiple equipment on site. A self-moving temporary support (SmTS) is designed, and its mechanical characteristics are analyzed to meet the mechanical requirements of the wall rock support system on the mining face. The multiobjective optimization of the main beam structure based on response surface methodology (RSM) is carried out to eliminate the design redundancy on the premise of meeting the support requirements of the main beam. Our research provides a novel method and corresponding equipment for the temporary support of a mining face. Applications of the proposed approach in the 7900 mining area of a mine proves the effectiveness of the method and equipment.

Simulation analysis on bolting and grouting reinforcement of fractured rock using GPU parallel FDEM

Simulation analysis on bolting and grouting reinforcement of fractured rock using GPU parallel FDEM

The effect of fermentation of organic solid waste with C:N ratios with phosphate rock reinforcement on its biorecycling

A solid waste of organic materials was collected from the residential neighborhoods of Ramadi during 2017. To convert these wastes into valuable organic fertilizers resources that reduces their negative impacts. The study included two mixtures of collected solid waste of organic materials. The first mixture, involved preparing sample has Carbone over nitrogen ration of 40:1 prepared from the collected organic materials. While the second mixture had C/N of 30:1 by supporting the mixture with urea. The prepared mixtures were inoculated as percentage of its weight w/w with 5%( (organic waste: soil) using agricultural soil taken from 60 cm depth and the fermentation was completed aerobically for 40 days. The second stage of fermentation included application of 0,10 and 20 % of phosphate rock to the products of the first stage of fermentation. The results show reducing the concentration of carbon and increasing the concentration of nitrogen in the components of the mixtures. Regarding the interaction treatment of 30:1(C/N) with 20% RP recorded the lowest carbon concentration and the highest amount of fulvic acid 342 and 13.3 g. kg-1 respectively, the same mixture with no phosphate application gave the highest rate of N and humic acid reached 29.9 and 24.2 g. kg-1, respectively. The interaction treatment of 30:1 with 20% gave the highest average density of phosphate-dissolving bacteria reached 6.25 Logcfu.g-1, while 40: 1 with 10% RP gave the highest number of BFN bacteria reached 6.75 Logcfu.g-1. However, 40: 1 with no phosphate application gave the highest rate of formation of phenolic acids reached 8.8 g.kg-1, while the highest average amount of dissolved phosphorous was 9.69 g. kg-1 obtained from the treatment of 30:1 treated with 20% RP.

Soft Rock Reinforcement by Bicomponent Organomineral Resin Injection

Soft Rock Reinforcement by Bicomponent Organomineral Resin Injection