Zonal Disintegration Research Articles

Study on Shear Failure Process and Zonal Disintegration Mechanism of Roadway under High Ground Stress: A Numerical Simulation via a Strain-Softening Plastic Model and the Discrete Element Method

Fracture expansion in rock masses can be observed by monitoring the break of contacts between the bounding particles via the discrete element method. The latter’s realization in this study via the PFC2D program tracked the evolution process of the zonal disintegration in an exemplary roadway-surrounding rock affected by mining. Besides, the damage evolution pattern in a high-stress soft rock roadway was simulated by the FLAC2D program using a strain-softening plastic model, revealing the effects of rock mass strength, stress state, and anchor support on the zonal disintegration of the roadway. Numerical simulation results show that in a roadway with high-level stress, the obvious fractures spread from the roadway surface to the depth of the surrounding rock along a series of geometric planes and cut the surrounding rock into rock mass blocks. Under high crustal stress, conjugate shear fractures occur near the roadway surfaces and form a closed-loop fractured zone after intersecting the conjugate fracture faces. The closed fractured zone becomes a free face, from which conjugate shear fractures develop, forming new closed fractured zones in the deep surrounding rock. By repeatedly generating the closed fracture zones, a fracture network appears in the roadway-surrounding rock. The development of zonal disintegration of roadway-surrounding rock mainly depends on the rock mass strength and its stress state. Zonal disintegration only occurs when the crustal stress of the roadway-surrounding rock exceeds its strength. When the horizontal stress is low and the vertical stress exceeds the rock mass strength, zonal disintegration only occurs on two sides of the roadway. When the vertical stress is low and the horizontal stress exceeds the rock’s mass strength, it only appears on the roof and floor. When the values of cohesion, internal friction angle, and tensile strength are reduced in the same proportion, cohesion has the greatest impact on the expansion of the zonal disintegration zone, followed by the internal friction angle, while the tensile strength effect is the least. In anchor-supported roadways undergoing zonal disintegration processes, the intact zone blocks slide relatively along the fracture surface during the process of loosening and deformation of the surrounding rock, making the anchor rods susceptible to tensile, shear, and bending actions.

Regularities of rocks zonal disintegration and methane emissions periodicity in mine roadways

The article presents the results of studies on the establishment of stable relationships between methane emissions into degassing wells and their spatial location, stress-strain state of rock massif and mining operations process. Vibroacoustic and electrometric of mine control methods have been used to establish zoning and alternation of fractured zones in the rock massif during mining operations. Using the finite element method, zones of different permeability in the roof above the longwall face were determined, and a qualitative transition from compressive deformations to tensile deformations was revealed. Based on data from mine experiments at 157 degassing wells, patterns of repeatability of rocks zonal disintegration and periodicity of gas emissions into mine roadways depending on the distance to the moving longwall face have been determined for the first time. It has been established that the concentration of methane gas in a wells with distance from the longwall face changes according to a damped quasi-periodic dependence with recombinant changes in stress-strain states. For wells aimed at the goafs, the period of the quasi-periodic function increases by 40%, the amplitude decreases to 30%. The obtained dependencies make it possible to increase the efficiency of degassing.

Numerical Study on the Zonal Disintegration of a Deeply Buried High-Temperature Roadway during Cooling

Zonal disintegration of surrounding rock is characterized by the intermittent distribution of failure zones, which can be observed in deep underground roadways and tunnels under high-geo-stress confinement. These deep underground roadways can be quite hot and thus require extensive cooling throughout their construction and operation. However, the way in which cooling affects the zonal disintegration of deeply buried high-temperature roadways has rarely been reported. We therefore studied the formation mechanism of zonal disintegration at room temperature using the strength reduction method as part of a self-developed numerical code: RFPA. Subsequently, the effects of cooling and geo-stress on the development of zonal disintegration were disclosed by examining the spatial and temporal distributions of the temperature and stress of the surrounding rock. Numerical results indicated without the thermal stress effect, zonal disintegration is caused by macroscopic shear failure, and cooling transforms the zonal disintegration into a hybrid tensile-shear failure. Although the acoustic emissions quantified revealed that high geo-stress is the primary factor affects roadway instability, the failure area caused by cooling cannot be ignored when it comes to roadway support and stabilization because the time and mechanism that damage the surrounding rock are different from those that caused by geo-stress.

Geomechanical Model Test on the Zonal Disintegration of Deep Tunnel in Jinping II Hydropower Station

Zonal disintegration is commonly encountered during the construction of tunnels at large depth. To study the formation and evolution mechanism of zonal disintegration in deep tunnels, a geo-mechanical model test is conducted under three-dimensional condition. The results reveal that: 1) with the proceeding of tunnel excavation, the displacements and the stresses around the tunnel present oscillating variation with alternating peak and trough. 2) Four annular rupture zones can be found around the tunnel, where the distance between the outermost rupture zone and the tunnel periphery is approximately 9.6 m. 3) The rupture zone first forms on the sidewalls of the tunnel, and then gradually develops to the interior of the rock mass until a complete ring-shaped rupture zone is formed. 4) The evolution of zonal disintegration is affected by the shape of cross section. The reproduction of zonal disintegration in laboratory can effectively reveal the formation mechanism and develop the control measures. The results obtained will provide important scientific basis for the safety construction of deep underground engineering.

Zonal disintegration phenomenon based on triaxial dynamic load test of hollow cylindrical sandstone specimens

Zonal disintegration phenomenon based on triaxial dynamic load test of hollow cylindrical sandstone specimens

In-situ observations of damage-fracture evolution in surrounding rock upon unloading in 2400-m-deep tunnels

The damage-fracture evolution of deep rock mass has obvious particularity, which is revealed in 2400-m-deep tunnels by field tests. The evolution of the excavation damaged zone depth is consistent with that of the fractured zone depth. The ratio of the excavation damaged zone depth to the excavation fractured zone depth is greater than 2.0 in a rock mass with both high strength and good integrity, but less than 1.5 in a rock mass with lower strength or poor integrity. Zonal disintegration in a rock mass with high strength and fair integrity is more likely to occur when it contains more than two groups of primary fractures in damaged zones. Fractures develop outward in zonal disintegration but are totally different from the single-zone fracture, in which the fractures develop inward, and it is the starting position of the fractured zone when the excavation surface of the middle pilot is 7–9 m close to the pre-set borehole and it stops after the excavation surface of the baseplate is 11–14 m away. The most intense evolution occurs around 2–4 m from the pre-set borehole in the sidewall expansion stage. The research results provide a reference for the monitoring scheme and support design of CJPL-III in its future construction.

Crack Initiation and Propagation of Embedded Three-Dimensional Parallel Cracks in Transparent Rock-Like Material

Abstract In order to understand the initiation and propagation of three-dimensional (3D) embedded parallel cracks in brittle rock under uniaxial and biaxial compression, a preparation method of a transparent rock-like material was proposed in order to observe the propagation process of cracks in brittle rock. Uniaxial and biaxial compression tests were carried out on the transparent rock-like samples containing two embedded 3D parallel cracks. Four types of crack propagation modes were observed: wing crack, petaloid crack, flat-wing crack, and ring-like crack. It is also found that the direction of lateral pressure relative to the strike of the embedded crack has a significant effect on the propagation direction of new generated cracks: a lateral pressure parallel to the strike of the embedded cracks promotes crack propagation in the direction of the maximum principal stress; on the other hand, a lateral pressure normal to the strike of the embedded cracks promotes cracks propagation around the embedded crack at an angle of 30°–60°, forming ring-like cracks, which is similar to the zonal disintegration phenomenon monitored around deep underground excavations.

Multi-dimensional non-uniform deformation and failure of siltstone determined using acoustic, 3D-digital image correlation, and computed tomography

Uniaxial compression tests monitored using linear variable differential transformers (LVDTs), digital image correlation (DIC), computed tomography (CT), acoustic emission (AE), and ultrasonic velocity were utilized to study the multi-dimensional non-uniform deformation and failure characteristics of siltstone. Under one-dimensional (1D) conditions, the characteristic stress of the siltstone was determined by the AE counts, ultrasonic velocity, and volumetric strain measured by the extensometer. Under two-dimensional (2D) conditions, zonal disintegration was observed on the apparent fracture of the siltstone specimen. The crack nucleation process, stress release characteristics, and crack type were analyzed in the “broken area,” “penetrating crack area,” and “non-penetrating crack area” under different characteristic stress states. Subsequently, the evolution of the non-uniformity coefficient of the 2D strain field with the 1D characteristic stress was established. Under three-dimensional (3D) conditions, the fracture size of the siltstone was divided according to the equivalent length of fracture volume, and the spatial distributions of macro-, meso-, and microfractures were analyzed. The siltstone 3D zonal disintegration phenomenon was further quantitatively described by calculating the fractal dimensions of fractures in different radius ranges. Finally, the AE source localization method was improved by modifying the wave velocity. The transformation of the primary and secondary bearing areas in different stress stages was revealed based on the spatio-temporal evolution of the AE sources with different energy levels.

Geo-mechanical model test on the water inrush induced by zonal disintegration of deep tunnel under hydro-mechanical coupling

With the increase of burial depth, complex geological environments such as high in-situ stress and high seepage pressure will inevitably affect the generation of zonal disintegration and may induce water inrush disasters during the excavation of the deep tunnel. A true three-dimensional geo-mechanical model test is conducted to study the mechanism of water inrush induced by zonal disintegration under hydro-mechanical coupling. The distribution and variation of different physical information during excavation, including displacement, stress and seepage pressure, are comprehensively analyzed. Test results reveal that zonal disintegration may induce water inrush when the tunnel is excavated under the coupling action of high stress and high seepage pressure. The excavation disturbance causes the stress in the rock mass to be oscillating. As a result, rupture and non-rupture zones appear alternately around the tunnel. With the increase of seepage pressure, the rock mass in non-rupture zone, which acts as the water barrier, is damaged and connects with rupture zone to form a water inrush channel. Eventually, high-pressure water pours into the tunnel to form a water inrush disaster. The reproduction of this special phenomenon will provide an important test basis for further theoretical and numerical studies.

Numerical simulation of zonal disintegration of surrounding rock in the deep‐buried chamber

AbstractZonal disintegration is the phenomenon of cyclical rupture zone and nonrupture zone in the surrounding rock of a deep‐buried chamber, which is different from that of a shallow chamber. Based on the finite difference software FLAC3D, the numerical simulation of surrounding rock with different mechanical parameters was conducted by using the SU model (Bilinear Strain‐Softening Ubiquitous‐Joint). The influences of buried depth, cohesion, and internal friction angle of surrounding rock on zonal disintegration were analyzed to reveal the influence law. The results show that: (1) after the chamber excavation, multiple rupture zones gradually extend from the chamber surface or adjacent periphery to the deep surrounding rock. In the extension process, a single rupture zone may be forked into two or even multiple rupture zones, which cross each other and form the zonal disintegration zone. (2) Zonal disintegration is affected by both σ (in situ stress) and Ucs (uniaxial compression strength). Smaller Ucs and larger σ will lead to zonal disintegration. (3) The zoning fracture is not obvious in the case of . In the reverse case, zoning fracture appears remarkably in the surrounding rock around the chamber. These results reveal the influence law of zonal disintegration and provide theoretical support for the design of deep‐buried chambers.

Pressure Relief and Permeability Enhancement Mechanism of Short-Distance Floor Roadway in Deep Coal Roadway Strip

A pressure relief and permeability enhancement method through short-distance floor roadway was proposed to solve the difficult outburst prevention during the gas extraction at the coal roadway strips in deep outburst coal seams with high ground stress and low gas permeability. On the basis of an equivalent model of the surrounding rock in a deep roadway, the analytical solutions of deep roadway excavation to the stress and deformation of pressure relief at overlying short-distance coal roadway strips were obtained using the unified strength theory and nonassociated flow rules. Next, the criteria for determining the reasonable position of floor roadway were established, and a mechanical model of short-distance floor roadway for the pressure relief and permeability enhancement zone at the overlying coal seam was constructed. Finally, the scope of the zonal disintegration at the coal roadway strips in the elastic and elastic–plastic zones of the surrounding rock in the roadway, as well as the expression of gas permeability change, was given. The engineering trial calculation and practice showed that the stress and strain of the surrounding rock in the roadway were evidently influenced by the intermediate principal stress coefficient. Moreover, the vertical stress and vertical displacement of overlying coal seam were gradually reduced with the increase in the intermediate principal stress coefficient and vertical distance of the floor roadway. The minimum reasonable distance arranged for the 213 floor roadway in Qujiang Coal Mine was 6.21 m, and the effective pressure relief should be conducted within 10.6 m from the coal seam floor. When the pressure relief was located at 9.0 m from the coal seam floor, the investigation results were basically consistent with the theoretical analysis results, exerting obvious pressure relief and permeability enhancement effects on the overlying short-distance coal roadway strips.

Research on Zonal Disintegration Characteristics and Failure Mechanisms of Deep Tunnel in Jointed Rock Mass with Strength Reduction Method

To understand the fracture features of zonal disintegration and reveal the failure mechanisms of circle tunnels excavated in deep jointed rock masses, a series of three-dimensional heterogeneous models considering varying joint dip angles are established. The strength reduction method is embedded in the RFPA method to achieve the gradual fracture process, macro failure mode and safety factor, and to reproduce the characteristic fracture phenomenon of deep rock masses, i.e., zonal disintegration. The mechanical mechanisms and acoustic emission energy of surrounding rocks during the different stages of the whole formation process of zonal disintegration affected by different-dip-angle joints and randomly distributed joints are further discussed. The results demonstrate that the zonal disintegration process is induced by the stress redistribution, which is significantly different from the formation mechanism of traditional surrounding rock loose zone; the dip angle of joint set has a great influence on the stress buildup, stress shadow and stress transfer as well as the failure mode of surrounding rock mass; the existence of parallel and random joints lead the newly formed cracks near the tunnel surface to developing along their strikes; the random joints make the zonal disintegration pattern much more complex and affected by the regional joint composition. These will greatly improve our understanding of the zonal disintegration in deep engineering.

The evolution regularity and influence factor analysis of zonal disintegration around deep jointed rock mass: a numerical study based on DEM

The evolution regularity and influence factor analysis of zonal disintegration around deep jointed rock mass: a numerical study based on DEM

Zonal Disintegration Characteristics of Roadway Roof Under Strong Mining Conditions and Mechanism of Thick Anchored and Trans-boundary Supporting

Zonal Disintegration Characteristics of Roadway Roof Under Strong Mining Conditions and Mechanism of Thick Anchored and Trans-boundary Supporting

Mechanical problems for the long-term stability of rocks surrounding deep level underground tunnels

Based on the research of Academician Tan Tjong-Kie on the long-term stability mechanics of underground tunnel and considering Academician Sadovsky’s structural hierarchy theories on complex geological rock masses, the inherent statistical mechanical properties of inhomogeneous structure and closed stress in deep rock masses were investigated. Two mechanical problems were mainly studied, i.e. characteristics of inherent non-uniform deformation and closed stress of rock masses, and long-term stability of deep tunnels. The quantitative mathematical characterization of inherent non-uniform deformation and closed stress of rock masses were given using the method of statistical mechanics. Based on the law of mass conservation, a general calculation method of long-term stability and deformation of rock masses surrounding deep level tunnels was proposed. The Maxwell model was used to calculate the threshold of splitting. A post-peak failure model of rock was established to estimate the in-situ stress at which rock undergoes post-peak failure. With the help of the theory of the hirerachical structure of rock masses, the maximum value of rock displacement due to splitting dilatation was obtained. A dimensionless energy factor was introduced to define the extent of zonal disintegration of surrounding rock masses. It was concluded that the splitting and dilatancy deformation is the main part of the deformation of surrounding rocks. The reasons why unloading splitting failure is more likely to take place in rock masses surrounding deep level tunnels were explained. The split evolution pattern of rock masses surrounding deep level tunnels and the calculation method of dilatancy displacement were obtained. The calculation results of the range of loosening zone, the location of the rupture zone in rock masses surrounding deep level tunnels, and the displacement of the sidewall were compared with the existing monitoring data in the underground powerhouse of the Jinping Ⅰ Hydropower Station, and the agreement is good.

Simulating the Formation of Blasting-Excavation-Induced Zonal Integration in Deep Tunnels with an Elastoplastic Damage Model

More deep tunneling projects will be constructed due to the increasing demand of underground energy and resource. The zonal disintegration phenomena are frequently encountered with the surrounding rock of deep tunnels. To explain the mechanisms underlying the formation of zonal disintegration, an elastoplastic damage model and failure criterion are proposed in this study based on the strain gradient theory and the damage property of rock mass. A coupling calculation subroutine is thereafter developed by the ABAQUS code. The dynamic formation and development regularity of zonal disintegration in the deep tunnel are simulated by this subroutine. The radial displacement, radial stress, and tangential stress show the oscillated variation of peaks and troughs alternately. The coupling effect of the blasting load and the initial geostress transient unloading leads to the variation of alternation oscillation in the surrounding rock stress field, which is an important reason for the zonal disintegration of the surrounding rock. The morphological characteristics of fractured zones and nonfractured zones obtained from numerical simulations are in good agreement with the results from the in situ observations, which confirm the correctness and feasibility of the damage and numerical approach. The method proposed in the current study can be utilized to provide a basis for the prediction and supporting design of fractured modes.

Consideration of block structure in mathematical models of rock mass

For the media with periodic changes in Young’s modulus and yield strength, the problems of stress, strain and displacement distribution around single excavations of spherical and cylindrical shape are solved. Block structure of the medium is determined by the difference between the elastic modules and the yield strength in the blocks and interblock space. In each case analytical solutions are obtained. The influence of blocks quantity, difference in block properties and interlayers on the nature of changes in stresses, strains and displacements was studied. It is noted that block structure is one of the factors for forming zonal disintegration around excavations.

BOOTSTRAP METHODS FOR INVESTIGATING THE ROCK MASS ZONAL FRACTURE AROUND UNDERGROUND WORKINGS

Objective. Investigation of the problems of zonal disintegration of rocks around deep underground workings in extremely small sampling, arising in geomechanical phenomena and processes in rock mass during mining. Methods . The primary tool used is numerical resampling methods, namely randomization, bootstrap, and Monte Carlo methods, which allow increasing the sample size, according to the available field data, to the required size for conducting a statistically sound analysis. Results. The problem of zonal fracture of rocks around deep underground workings is solved, for which the analytical dependence of the periodicity parameter of the defect function on the rock strength limit is estimated. The primary indicator of the statistical significance of the constructed model in work is the determination factor, based on which the type of analytical dependence under study is selected. Its deviation in the final model does not exceed 0.5% for any bootstrap sample volume, while in the other models considered in this paper, this value is achieved at n>200. Conclusion . The obtained interval estimates using bootstrap methods have a significant advantage over traditional approaches, increasing the reliability of the result in extremely small data samples without losing the level of significance.

Development prospects of creating armo-bearing shells theory

Abstract. In the article, the prospects for the use of load-bearing armored shells are discussed, which create the possibility of their application in the arising zones of stress concentrators, increased fracturing or zonal disintegration (ZDI) for the formation of objects of special-purpose or with special characteristics. This increases the resistance of the rock mass due to the use of special materials with certain properties (hydrophobic additives, etc.), which in total makes it possible to create formations for various purposes and with specified parameters. Technical problems in the construction of underground structures are mainly caused by the need for the creation and subsequent operation of the internal space. For example, in relation to solving the problems of underground construction of special structures, construction of underground gas storage facilities (UGS), underground construction of protective structures (bomb shelters), construction of earthquake-resisting structures and buildings. The main problems of underground construction, its technical capabilities and solutions are considered. The possibility of using the worked-out underground space of mines is shown in connection with the problems of construction of underground protective structures (bomb shelters), underground gas storages. The possibility of using the phenomenon of zonal disintegration (ZDI) as the main economic prerequisite for the construction of earthquake-resisting buildings and structures in regions with earthquake-resisting mining and geological conditions is proposed, and schematic diagrams of technological solutions are given. The tasks are considered, the solution of which is of paramount importance for the problems listed above. The prospects for the application of technologies for the formation of load-bearing armored shells (LBAS) in conditions of zonal disintegration (ZDI) are shown, namely: control and forecasting of the occurrence of the phenomenon of the rocks ZDI in the course of various underground construction works; control of the state of the massif in which the LBAS are constructed to ensure the specified operating parameters; the use of the fracture zone between the rings of disintegration for filling with materials with certain properties (hydrophobic impurities, etc.), which ultimately makes it possible to create formations for various purposes and with specified parameters.

Space‐Time Evolution Laws of Zonal Disintegration in Deep Underground Caves Based on Coordination Deformation between the Bolt Body and Surrounding Rock

Zonal disintegration refers to the special phenomenon whereby fractured zones and intact zones appear alternately in deep‐buried surrounding rocks under high stress conditions, which are different from that of the shallow rock mass. Because the divisional rupture law in engineering practice is closely related to the force characteristics of the bolt body, this paper analyzed stress distribution rules of the same bolt body at different times and that of different bolt bodies at the same time in the case of zonal disintegration based on coordination deformation between the bolt body and surrounding rock. The nonlinear rheological mechanics model of rock mass on the elastic‐plastic interface under the maximum support pressure was established. It puts forward the theoretical calculation formula about the mechanics criterion and breakdown moment of the zonal disintegration. Using the mechanics model of interaction between a bolt and the surrounding rock, the distribution locations along the bolt body of the anchor neutral points and its maximum axial forces were discussed with the multiple theoretical neutral points. Furthermore, the location and width of each fracture zone were back analyzed. The results show that the rock mass on the elastic‐plastic interface of the surrounding rock has a significant creep effect after the excavation of the deep underground cave. While maximum deviator stress of the rock mass is more than its long‐term strength, the rock mass will fracture along a radial direction and come into the fractured zone. The multiple redistribution of the surrounding rock stress will generate alternate distribution phenomena of the fractured zone and intact zone. Meanwhile, the distribution regularity of the peaks and troughs interval of the displacement of surrounding rock leads to multiple neutral points along the anchor length direction. The computed results of zonal disintegration through the back analysis can reflect the actual space‐time evolution laws of zonal disintegration in deep underground caves.