High-stress Rock Mass Research Articles

Stability Index of Surrounding Rock during Deep Rock Excavation Considering Energy Release Speed

Rockburst is a kind of dynamic rock failure process that is easily induced by the excavation of a high-stress rock mass. However, from an energy perspective, the existing indexes for rockburst tendency have a limitation in that they do not consider the energy release speed. In this study, energy release effectiveness was proposed based on the local energy release rate while considering the influence of the energy release speed. The index can evaluate the stability of surrounding rock during the excavation of high-stress rock. The index can be obtained by recording the strain energy density of every element in the model during excavation and identifying the maximum strain energy density (Eimax), the minimum strain energy density (Eimin), the maximum time (timax), and the minimum time (timin) to calculate energy release speed and energy release effectiveness. A case study of the excavation of an experimental tunnel, namely, the URL of AECL, was adopted to validate the index. The results indicated that the proposed index can clearly identify the location and strength of the impact tendency area, and it can be effectively applied to the stability analysis during the excavation of deep tunnels.

Nature and mechanism of rock and gas outbursts

Experience of construction and operation of deep mines proves the necessity of making deep-level openings in the strongest rocks, mainly, in sandstone, limestone and dolomite. However, such rocks at a depth of 800 m and deeper are the most rockburst-hazardous. Rock outbursts impair safety of mining, and lead to deceleration and appreciation of production processes. The study into the failure-causing residual stresses in rockburst-hazardous rocks is performed. The direct tests of the residual stresses in rockburst-hazardous sandstone make it possible to state the absence of such stresses and, thus, the absence of the residual tectonic stresses in such rocks. The petrographic research proves the essential and crucial role of diagenesis when physicochemical transformations of rocks are assessed. These transformations reinforce the conclusion on the absence of the residual tectonic stresses in rockburst-hazardous sandstone in Donbass. The main cause of the anomalous stress zones is the high-pressure gas (methane) in rocks. The internal stresses to add the gravitational stresses are governed by the swelling property of sandstone when saturated with methane and by the degree of “constraint” of this swelling. The main cause of failure in a high-stress rock mass is the transition of a brittle material from the volumetric compression to the complex stress state when there are the conditions for the elastic recovery deformation, i.e. tensile deformation. Failure is possible when the latter reaches the ultimate values. The cause of the stress redistribution is the instantaneous separation of a part of the high-stress rock mass during blasting.

Rock Burst Intensity Classification Prediction Model Based on a Bayesian Hyperparameter Optimization Support Vector Machine

Rock burst disasters occurring in underground high-stress rock mass mining and excavation engineering seriously threaten the safety of workers and hinders the progress of engineering construction. Rock burst classification prediction is the basis of reducing and even eliminating rock burst hazards. Currently, most of mainstream discriminant models for rock burst grade prediction are based on small samples. Comprehensive selection according to many pieces of literature, the maximum tangential stress of surrounding rock and rock uniaxial compressive strength ratio coefficient (stress state parameter), rock uniaxial compressive strength and uniaxial tensile strength ratio (brittleness modulus), and the elastic energy index are used as a grading evaluation index of rock burst based on the collection of different construction engineering instances of rock burst in 114 groups of extensive sample data in different regions of the world, which are used to carry out the training study. The representativeness and accuracy of the index selection were verified by the indicator variance analysis and Spearman correlation coefficient hypothesis test. The Intelligent Rock burst Identification System (IRIS) based on an optimizable SVM model was established using data set samples. After extensive data cross-validation training, the accuracy of the SVM discriminant analysis model can reach 95.6%, which is significantly better than the prediction accuracy of the traditional SVM model of 71.9%. The model is used to classify and predict the rock burst intensity of 10 typical projects at home and abroad. The prediction results are consistent with the actual rock burst intensity, which is better than the discriminant model based on small sample data and other existing prediction models. The application of engineering examples shows that the results of the rock burst intensity classification prediction model based on extensive sample data processing analysis and the SVM discriminant method are in good agreement with the actual rock burst intensity, which can effectively provide a reference for the prediction of rock burst intensity grade in a construction area.

A Semi-analytical Solution of Face Extrusion Deformation Considering Nonlivnear Changes of Rock Mass Mechanical Parameters

The stress state of rock mass is redistributed after the tunnel excavation, resulting in different confining stress at different radial distances. Relevant studies demonstrate that the mechanical characteristics of rock are related with the confining stress, causing various the mechanical parameters of rock mass at different radial distances. This paper aims to take these kinds of mechanical properties of rock mass into the analytical solutions of stress and deformation around the tunnel face. Firstly, the calculation formulas of the rock mass mechanical parameters changing with the confining stress is determined based on the existing rock triaxial test data. Then, a new model considering the influence of confining stress is proposed based on Mohr-Coulomb (M-C) failure critical. At the same time, an given radial length increment divides the plastic zone into a series of concentric annuli. The finite difference approach may be used to compute consecutive stress and strain increases for each annulus. A comparative analysis of the Pierpaolo Oreste's model and the proposed model is carried out through calculation examples, and the results show that: ignoring the effect of the confining stress on the mechanical parameters of rock mass, the plastic radius of the tunnel face will be smaller than the actual value, and the face extrusion deformation value will be larger. It is emphasized that the influence of confining stress on the mechanical parameters of rock mass should be considered in actual engineering calculations, especially the high initial stress rock mass. Finally, combined with the numerical calculation model, the rationality of the application of the circular tunnel elastoplastic model in the non-circular tunnel is verified.

Geomechanical foundation for mining in rockburst-hazardous conditions: Concept development

The article describes basic approaches and trends in advancement of rock mass stress–strain behavior prediction in rockburst-hazardous mining. The prediction systems based on the dedicated program package Sigma GT are introduced in some Russian mines which operate in very hard rock masses prone to brittle fracture and subjected to gravitational–tectonic stresses. The manmade impact is accompanied in this case by the induced dynamic pressure phenomena. The use of geomechanics prediction systems in mines for more than 10 years proves their high efficiency, first of all, owing to the stress–strain analysis and assessment in real time. The ‘do-it-yourself’ analysis of different mining scenarios with a view to reducing stress concentration, selecting proper mine support systems as well as distressing minimizes risks associated with mining in high-stress rock masses. While being used, the geomechanical prediction program Sigma GT undergoes continuous development, updating and adaptation to specific mining conditions. The urgent tasks of the present day are: complexing of the stress–strain modeling results and monitoring data, which means the seismic monitoring in the first place; construction of correlated different-scale 3D models; fullest inclusion of structural discontinuities of rock masses; elaboration of guidance package on safe mining with regard to the geomechanical prediction results; development of instruments for determining current and prognostic parameters of rockburst-hazardous zones based on a set of factors in geological information systems of operating mines.

Justification of stability strategy for underground mine openings under higher effective anisotropic stresses

Stability of underground openings is one of the critical challenges in the mining industry. A mine support system design and installation depends on the conditions of mining. This is especially pronounced in the regions of active tectonics with horizontal stresses higher than vertical stresses up to 2–5 times. The tectonic stress-induced activity accompanies even comparatively shallow mining operations. Dense fracturing, spalling and bursting are observed in mines in Gornaya Shoria, or in Apatit JSC mines, at the depths of 150 to 400 m in Russia, at the depth of 260–400 m in uranium mines in Canada, 250 m in Tirol in Austria, or 100–200 m in Norway. As a result of the accomplished studies, the mechanism of fracture zones in adjacent rock mass during heading and mining in high-stress rock mass is defined. The parameters of these zones are determined subject to the rock mass quality, structure and stress–strain behavior. This allows developing the heading technology and mine support system design for the conditions of higher tectonic stresses. The main transient factors capable to affect underground openings are identified, and it is shown that the technology of heading and mine support under dynamic events caused by rock pressure depends on such determinants as: the quality of fragmentation by blasting, blasting sequence, temporary and permanent support designs and lag of the mine support behind the face advance. The proposed approach to the underground mine stability under higher effective anisotropic stresses ensures safe mining at optimal rates of heading.

Mechanism and application of new prestressed yield bolt for controlling deep high-stress rock mass

The elastic elongation of the bolt itself is insufficient to meet the surrounding rock deformation in deep high-stress roadway, resulting in a large number of breakage of the bolt and the instability of the surrounding rock. Aiming at this problem, this paper proposed a new prestressed yield bolt with the engineering background of Shangping roadway in Huafeng Coal Mine. Based on the analysis of instability of Shangping roadway surrounding rock, the structure, characteristics and mechanical properties of the prestressed yield bolt was investigated. The yielding properties and deformation process of different yielding members were researched in detail. According to the engineering background, the yielding support scheme were designed and applied. The results showed that the yielding effect of yielding pipe was more obvious than that of the wooden pallet. The yielding load, the maximum yielding deformation, the yield stability coefficient of the designed yielding pipe were 190 kN, 25 mm, 1.6 kN/mm, respectively. The stability forces of the bolts in the roof, the top corner of the right side and the bottom corner of the left side of the roadway were almost the same. The overall deformation of the roadway controlled by the yielding support scheme was not large. So, the yielding pipe protected the bolt-rod from being damaged due to excessive deformation, thereby realizing the yield bolt to control the stability of the roadway surrounding rock for a long time.

Justification of process flows and designs for mining blind ore bodies in the vicinity of mined-out voids

The trending deep-level mining governs substantial alteration of geomechanical situation in mines. The key approach to the stress–strain behavior assessment in rock mass when predicting and preventing geodynamic events is the geomechanical analysis of the rock mass behavior in the course of mining. The rockburst-hazardous mining research can use such methods as microseismic investigation, acoustic micromeasurements, electrometry, deformation monitoring, etc. The authors have accomplished the stress–strain behavior assessment in rock mass during mining at rockburst-hazardous deposits of Tashtagol and Sheregesh. The process solutions on underground mining in high-stress rock mass are analyzed. The process flow charts are developed. Alternative stoping technologies are identified, and the design data of mining systems for blind ore bodies are justified. It is shown that safe and efficient mining of blind iron ore bodies in the vicinity of mined-out voids in rockburst-hazardous conditions is achievable using: room-and-pillar mining, with rooms arranged across the strike of an ore body, and with subsequent transition to sublevel caving with levels 70 m high and sublevels 25–30 m high; shrinkage stoping and bulk caving; cut-and-fill method with cemented backfill. It is found that in top-downward mining of blind ore bodies, the transition from the room-andpillar system to sublevel caving and cut-and-fill method ensures reduction in ore loss and dilution by 1.1–1.5 and 7.5–10 %, respectively.

Research on the Reasonable Strengthening Time and Stability of Excavation Unloading Surrounding Rock of High-Stress Rock Mass

This study is aimed at better understanding the deformation and failure mechanism of surrounding rock during excavation unloading of a high-stress rock mass and determining the reasonable reinforcement time for the surrounding rock. To fulfill this aim, true triaxial tests were carried out on different loading and unloading paths during the unilateral unloading of a high-stress rock mass. The variational condition for minimization of plastic complementary energy is obtained, the optimal reinforcement time is determined, and the range of the plastic zone in the surrounding rock reinforced by anchor mesh-cable-grouting is compared and analyzed. The results are as follows: (1) Based on the Mohr-Coulomb yield criterion and the deformation reinforcement theory of surrounding rock, the stable state with the minimum reinforcement force is obtained. (2) After the true triaxial tests on the unilateral unloading of the third principal stress were carried out under different confining pressures, loading continued to be performed. Compared with rock failure without confining pressure, in the conventional uniaxial compression test, the failure of samples is dominated by composite splitting-shear failure; the unilateral unloading stress-concentration failure is a progressive failure process of splitting into plates followed by cutting into blocks and then the ejection of blocks and pieces. (3) The relationship between the time steps of the surrounding rock stability and the excavation distance is obtained. The supporting time can be divided into four stages: presupport stage, bolt reinforcement stage, anchor cable reinforcement stage, and grouting reinforcement stage. (4) In the range of within 5 m behind the tunneling face, the plastic zone of the surrounding rock with support is reduced by 7 m as compared with that with no support. In the range of over 5 m behind the tunneling face, the plastic zone of the roadway floor with support is reduced by 2.6 m as compared with that without support, and the deformation is reduced by 90%. These results can serve as a reference for controlling the behavior of surrounding rock during excavation unloading of high-stress rock masses.

Study on the Key Technology of Controlling the Instability of Deep High-Stress Coal and Rock Mass and Relieving the Danger

In order to solve the problem of stress concentration and gas overrun in the process of uncovering high gas and thick coal seam, combined with the occurrence characteristics of coal seams in Wuyang Coal Mine, the measures of “hydraulic and mechanical cavity making + steel screen pipe + surrounding rock grouting” are adopted to establish a method for mutual verification of multiple effect test indexes of residual stress, residual gas content, coal seam moisture content, and microseismic signal characteristics, and the three-dimensional accurate analysis of the influence range of hydraulic cavitation is effectively realized. By comparing and analyzing the gas extraction amount, the surrounding borehole stress change and the microseismic monitoring signals before and after the application of hydraulic cavitation technology are studied. The results show the following. (1) The pressure relief effect of the hydraulic cavity on surrounding coal decreases with the increase of distance, and the pressure relief effect is most obvious at 1.0∼2.5 m, in the range of 2.5–3.5 m around the hydraulic drilling hole, the duration, rate, and amplitude of pressure relief are reduced compared with those in the range of less than 2.5 m, while in the range of more than 3.5 m, the effect of pressure relief is very weak. (2) During the period of hydraulic cavitation release hole, the radius of water supply to coal seam is within 1.5 m, which accounts for 79% of coal wall area. (3) It is also a process where the stress distribution in the coal and rock body needs to be rebalanced before and after hydraulic caverning, which is often accompanied by microfracture of coal and rock mass. The analysis shows that, before hydraulic caverning, the waveform of coal and rock fracture signal has a short duration, large amplitude, and obvious signal mutation, and the dominant frequency of the signal is about 250 Hz, with large total energy. After hydraulic caverning, the intensity of coal and rock fracture events is greatly reduced. The research results can effectively identify the influence range of hydraulic cavitation, improve the detection accuracy and efficiency of hydraulic cavitation range, effectively predict and warn the hidden danger of mine safety, and provide a reference for the work of similar mines.

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.

Of forming loads on the mounting of shaft shafts in the hierarchic block environment under the influence of modern geodynamic movements

The subject of the research is the lining of mine shafts and surrounding rock mass. The subject matter is the features of the stress-strain behavior of lining and adjacent rock mass in shafts and near-shaft underground openings in the Tenth Anniversary of Independence of Kazakhstan mine located in the tectonically high-stress and low-strength rock mass. The loading of the lining in the shafts and near-shaft openings in the Tenth Anniversary of Independence of Kazakhstan mine during construction is investigated, and the damages of the lining in the course of drivage in the nonuniform stress field are analyzed. The long-term periodic in-situ instrumental monitoring of stress variation in the lining of the mine shafts and near-shaft openings revealed the main influences on the process of load formation on the lining in the conditions of post-limiting deformation of surrounding rock mass. It is validated that the surrounding rock mass of the mine has a complex hierarchical block structure and is subjected to modern geodynamic movements. As the depth of mining is increased, surrounding rock mass of the mine shafts transfers to the condition of postlimiting stresses and strains. As a consequence, the lining of the shafts and near-shaft openings at different stages of construction experiences nonuniform concentrated loads, which violates integrity of the lining.

Microseismic and precursor analysis of high-stress hazards in tunnels: A case comparison of rockburst and fall of ground

In rock engineering, microseismic monitoring technology has been extensively applied for the interpretation and forecast of rockburst hazards. However, highly stressed hard rocks could suffer dynamic geological hazards (rockburst) and gravity-driven geological hazards (fall of ground), both of which have distinct developmental processes and precursory features that await comprehensive exploration. Hence, in this study, we adopted microseismic monitoring and an advanced method based on the source parameters of seismic energy, seismic moment, and apparent stress (the EMS method). The source parameter space was constructed to ascertain microseismic events as stress-adjusting, deformation-driven, or energy-releasing type. The evolution of the event type and the microseismic path precisely revealed the characteristics of the hazard development. In a case study of a deeply buried tunnel, we analyzed the process by which high-stress hazards occur using the proposed method and distinguished between the respective microseismic characteristics of the rockburst and fall of ground in the development and occurrence stages. Finally, we proposed the key precursory of rockburst and fall of ground in high-stress rock masses. While deformation-driven events increase notably in rockburst, stress-adjusting events are dominant in fall of ground. Overall, this study could facilitate precise interpretation and warning about different high-stress hazards and provide effective measures to curb the development of hazards.

Evaluation of the propensity of strain burst in brittle granite based on post-peak energy analysis

The increasing demand for resources and depletion of near ground mineral resources caused deeper mining operations under high-stress rock mass conditions. As a result of this, strain burst, which is the sudden release of stored strain energy in the surrounding rock mass, has become more prevalent and created a considerable threat to workers and construction equipment. It is, therefore, imperative to understand how strain burst mechanism and stored excess strain energy are affected due to the high confinement in deep underground conditions. For this purpose, post-peak energy distributions for brittle rocks were investigated using a newly developed energy calculation method associated with acoustic emission (AE). A series of quasi-static uniaxial and triaxial compression tests controlled by the circumferential expansion were conducted. Snap-back behaviour known as Class-II behaviour associated with energy evolution and the material response under self-sustaining failure were analysed on granites under a wide range of confining pressures (0–60 MPa). The experimental results underline that the energy evolution characteristics are strongly linked to confinement. Stored elastic strain energy (dUE), energy consumed by dominating cohesion weakening (dΦCW) and energy dissipated during mobilisation of frictional failure (dΦFM) showed a rising trend as the confining pressure was increased. An intrinsic ejection velocity was proposed to express the propensity of strain burst that was purely determined by the excess strain energy released from Class II rock.

Experimental Investigation of Energy Evolution in Sandstone Failure during Triaxial Unloading Confining Pressure Tests

The deformation and failure of sandstone samples are closely related to energy changes in the material. To explore the energy evolution during the process of sandstone sample damage, loading and unloading tests with different test paths were conducted. The results show that more energy is stored and consumed before the stress reaches its peak, while after the peak stress, more energy is released and consumed. Energy dissipation increases internal cracking, leads to sample damage and lithologic deterioration, and reduces the bearing capacity of the sample. During triaxial unloading of the confining pressure, the higher the initial unloading confining pressure, the more the elastic energy stored, and the more the energy released when the sandstone sample fails, resulting in more severe damage. Therefore, during the excavation of high‐stress rock masses, large amounts of elastic energy stored in sandstone can be rapidly released, leading to rock burst disasters. Additionally, during triaxial unloading confining pressure tests, the damage in sandstone when the sample is close to failure increases more rapidly than that during conventional triaxial compression tests because of the unloading effect of the confining pressure. This phenomenon also illustrates that the failure of sandstone induced by unloading is more sudden than that induced by loading.

Analytical Description of Surface of Blasting-Formed Underground Cavities by Laser Scanning Data

In terms of Tashtagol Mine, the authors address the issues connected with the configuration and surface of cavities formed by blasts of explosive charges in high-stress rock mass structured as a hierarchy of blocks. Laser scanning of a cavity offers the data on linear and angular characteristics of the cavity surface. The analysis of the surface structure provides details of the rock mass block hierarchy, which essentially influences formation of the roof and sidewalls of the cavity. Individual areas of the cavity surface are described with the help of approximation of measured coordinates of the cavity boundary in the cross sections using the second order curves, including circumferences and ellipses the radius of which are canonically connected with the phenomenon of zonal disintegration of rock mass.

A Review of Research on Catastrophic Formation and Evolutionary Mechanism of Deep High Stress Rock Mass under Impact Loading

With the exploitation of resources expanded to deep, the geological environment which is “three tenors one disturbance” of rock mass in great depth has been more complex, resulting in some new engineering geological disasters, such as rock burst, pressure bumping, large deformation of surrounding rock, brittle-ductile transition of rock and zonal disintegration of rock mass, which occur frequently in deep underground engineering rock mass. The impact load caused by collision, explosion, extrusion and outburst is the root cause of the dynamic instability of the deep rock mass. What should be emphasized is that high in-situ stress and blasting excavation disturbance complicate disaster developing mechanism of deep underground engineering rock mass and sharply increase the difficulty of controlling disaster. This paper is aimed at the research status and development trend, of which dynamic characteristics of deep high stress rock mass and its damage and failure effect each other under impact, and conduct analysis, in the later stage where I would discuss how to carry out the response law of the deep high-stress rock mass under the impact load and the mechanism of catastrophe developing, which is of great significance to build a model of instability and fracture evolution about deep rock mass under shock disturbance and to maintain its safety and stability.

A New Yielding Bolt for Rock Support in High Stress Rock Masses

High stress in the surrounding rock mass causes serious stability problems. The applied support system used in this conduction should be able to carry high loads and also accommodate large deformations without experiencing serious damage. In this paper, a brief overview of the history of yielding/energy-absorbing rock bolts is provided. And then, a new yielding bolt invented by the author is introduced in detail, including its layout and principle. Theoretical analysis shows that the bolt has large load-bearing and deformation capacities, thereby absorbing a large amount of energy to maintain the stability of surrounding rock.

Microseism Induced by Transient Release of In Situ Stress During Deep Rock Mass Excavation by Blasting

During deep rock mass excavation with the method of drill and blast, accompanying the secession of rock fragments and the formation of a new free surface, in situ stress on this boundary is suddenly released within several milliseconds, which is termed the transient release of in situ stress. In this process, enormous strain energy around the excavation face is instantly released in the form of kinetic energy and it inevitably induces microseismic events in surrounding rock masses. Thus, blasting excavation-induced microseismic vibrations in high-stress rock masses are attributed to the combined action of explosion and the transient release of in situ stress. The intensity of stress release-induced microseisms, which depends mainly on the magnitude of the in situ stress and the dimension of the excavation face, is comparable to that of explosion-induced vibrations. With the methods of time–energy density analysis, amplitude spectrum analysis, and finite impulse response (FIR) digital filter, microseismic vibrations induced by the transient release of in situ stress were identified and separated from recorded microseismic signals during a blast of deep rock masses in the Pubugou Hydropower Station. The results show that the low-frequency component in the microseismic records results mainly from the transient release of in situ stress, while the high-frequency component originates primarily from explosion. In addition, a numerical simulation was conducted to demonstrate the occurrence of microseismic events by the transient release of in situ stress, and the results seem to have confirmed fairly well the separated vibrations from microseismic records.

A new energy-absorbing bolt for rock support in high stress rock masses

An energy-absorbing rock support device, called a D bolt, has been recently developed to counteract both burst-prone and squeezing rock conditions that occur during underground excavation. The bolt is a smooth steel bar with a number of anchors along its length. The anchors are firmly fixed within a borehole using either cement grout or resin, while the smooth sections of the bolt between the anchors may freely deform in response to rock dilation. Failure of one section does not affect the reinforcement performance of the other sections. The bolt is designed to fully use both the strength and the deformation capacity of the bolt material along the entire length. The bolt has large load-bearing and deformation capacities. Static pull tests and dynamic drop tests show that the bolt length elongates by 14–20% at a load level equal to the strength of the bolt material, thereby absorbing a large amount of energy. The impact average load of a 20 mm D bolt is 200–230 kN, with only a small portion of the load transferred to the bolt plate. The cumulative dynamic energy absorption of the bolt is measured to be 47 kJ/m. D bolts were tested in three deep mines. Filed measurements show that D bolts are loaded less than rebar bolts. This paper presents the layout and principle of the D bolt, and corresponding results from static, dynamic, and field tests.