Loose Rock Mass Research Articles

Flat problem to determine the forces of destruction of pieces n disintegrators while being grabbed in thick layer

Purpose. Research on analytical dependences of destructive stresses, acting on a piece of non-isometric shape at quasi-static deformation of a relatively thick layer of rock mass in disintegrators, on parameters of the piece shape, the pieces spatial orientation, also on the relative piece size in layer, taking into consideration the discrete nature of contact force application. Methodology. The flat scheme of a non-isometric shaped piece contacts in a thick layer of rock mass is obtained by composition of the central rectangular piece and the round pieces of average size for the given layer. The distribution of stress components in the layer of loose rock mass is accepted on the basis of the classical theory of elasticity and the theory of loose medium. The geomechanics criterion showing relationship of equivalent destructive stress and ultimate compressive strength of rock is used as a criterion of piece destruction in complex stress state. All force schemes of the piece loading are reduced to three-point bending schemes and two-point shear schemes, both across the long and the short sides of the piece. The most dangerous loading scheme is determined from the analysis of the mentioned schemes for each particular case. Dimensionless parameterization is applied both to specify the geometric parameters of pieces and to analyze the resulting destructive stresses. Findings. Analytical dependences of equivalent destructive stresses for an oblong piece are obtained depending on the piece relative length, the relative piece size in the rock layer, the angle of piece orientation relative to the direction of the maximum main stress and the side thrust coefficient in the layer. It has been set that lamellar pieces, especially those smaller than the average size for the layer, are destroyed mainly from the implementation of bending schemes across the long side, the shape of their fragments is improved by reducing the pieces relative length. Increasing the uniformity of the force field in the working zone of disintegrator also leads to improvement in the shape of fragments. On the other hand, as the shape of the piece approaches the isometric one, as well as when the piece relative size in layer raises, the probability of implementing shear schemes increases and the probability of implementing bending schemes decreases, including with a deterioration in the fragments shape compared to the original piece. At the same time, larger values of destructive stresses for the lamellar smaller pieces are proved analytically compared to the isometric bigger ones, all other things being equal. Originality. The versatility of application of the three-point bending scheme of a non-isometric shaped piece in combination with the two-point scheme of its shear for analysis of its destruction in the thick layer of rock mass is substantiated. For the first time, the dependences of equivalent destructive stresses for the non-isometric piece on its relative length, its relative size in layer, the angle of deviation of the pieces main axis from the main stress direction and on the side thrust coefficient in the layer have been obtained. Practical value. The results obtained allow making reasonable choice of parameters of disintegrators operational parts for destruction of materials in the thick layer, as well as predicting the change in lamellar pieces fraction during disintegration process. They give the possibility to determine key parameters of operational parts for new designs of disintegrators. This creates the basis for the development of calculation techniques for operational parts of modern samples of crushing and grinding equipment.

Structural Characteristics of Regenerated Roof and Distribution Law of Overburden Porosity in Downward Mining of a Bifurcated Coal Seam

During downward mining of a bifurcated coal seam, the roof of the lower coal seam is relatively broken and difficult to control due to the mining influence of the upper coal seam. Roof accidents occur frequently during mining of the lower coal seam, reducing mining efficiency. How to ensure safe and efficient mining of the lower coal seam is a significant issue. In this paper, overlying strata migration and fracture characteristics of the lower coal seam, the structure and stability of the regenerated roof, and porosity and permeability characteristics of the overlying strata under the mining influence of the upper coal seam are studied by using similar simulation tests. Results show that the overburden structure of the lower coal seam is altered due to the mining influence of the upper coal seam, and the regenerated roof of the lower coal seam is divided into three structural types from top to bottom, namely: intact rock mass+block fracture rock mass+loose rock mass (type I structure); intact rock mass+block fracture rock mass+loose rock mass+cataclastic rock mass (type II structure); and intact rock mass+block fracture rock mass+loose rock mass+cataclastic rock mass+slab-rent rock mass (type III structure). The stability of each type of rock mass structure is evaluated, and the stability of three types of rock mass structures is III > II > I. The overburden porosity and slurry permeability coefficient are relatively large at the cutting hole and stopping line. The porosity of the caving zone within 70 m of the cut hole and stopping line is greater than 5%, and the permeability coefficient is greater than 0.1 m/s. Based on differences in the surrounding rock porosity and permeability characteristics, the grouting difficulty of overburden is divided into three types of areas: extremely easy grouting areas, easy grouting areas, and difficult grouting areas. The results of this paper can provide reference for the stability evaluation of the regenerated roof and the selection of grouting treatment parameters for the broken roof under similar conditions.

Study on supporting time of tunnel lining in thin-layered rock mass

The thin-layered rock mass of Baokang tunnel has the characteristics of large deformation and failure of soft rock under the excavation unloading. More seriously, a serious question is that the lining cracking is prominent. The cause of the cracking can be traced to different failure modes of the surrounding rock mass. Specifically, the rock layer on left arch spandrel is prone to bending failure due to the action of tangential stress, while the right-side wall is prone to sliding failure due to the action of higher shear stress. Furthermore, the lining cracking may beyond the ultimate compressive capacity when the loosely collapsed rock mass acted on the lining. According to the transversely isotropic characteristics of layered rock mass, the failure approach index (FAI) was selected to evaluate the damage and failure of thin shale. Meanwhile, the result of the example shows that this index can effectively characterize the failure characteristics of the thin-layered rock mass. Hence, the FAI was used as an evaluation index of the loose failure of layered rock mass. In order to determine the lining support time, the stability of the lining under the action by the loose rock mass was analyzed by the numerical simulation. As a result, the distance between the lining and the face should not be bigger than 120m. According to the Feedback through onsite construction, the lining cracks didn’t appear under this supporting time, which ensured the stability of the lining structure. The research methods and ideas can provide reference for the similar tunnel lining construction in thin-layered rock mass.

PRINCIPLE AND APPLICATION OF CONTROLLABLE GROUTING OF CEMENT-SODIUM SILICATE SLURRY IN LARGE LOOSE ROCK MASS DUE TO MINING CAVING

Loose rock mass is a kind of common rock mass structure in mining,tunnel,underground space and other projects. It has the characteristics of low strength and poor stability. Grouting reconstruction is one of the important technologies to enhance its integrity and strength in site. To meet the special needs of the plugging project of the main ore pass with large-scale collapse under the condition of full rocks in Hebei provincial Xingshan Iron Mine,the concept of the controllable grouting of cement-sodium silicate slurry in the large loose rock mass is adopted. Based on the experimental study of cement-sodium silicate slurry grouting in the large volume loose rock mass,the grouting process was divided into the following five stages. They are vertical dominant seepage with macrovoid,circumjacent seepage with macrovoid,superior seepage stone,splitting and seepage of the first layer and splitting and seepage of the nth layer. According to the spatiotemporal propagation of slurry,the controllable grouting problem was divided into the one-dimensional vertical dominant seepage of cement-sodium silicate slurry and the circumferential spatiotemporal diffusion of single-stage grouting. and the mechanism of its occurrence was revealed that there is an exponential function with base e between the diffusion distance and the time of the one-dimensional vertical dominant seepage of cement-silicate slurry in the loose rock mass. On the basis of the above experimental results,the technology of the controllable grouting of cement-silicate slurry in the loose rock mass was applied to the plugging project of the main ore pass fully filled with large-scale collapsed rocks in the Xingshan Iron Mine,and good engineering performance were achieved.

Plugging and Its Stability Evaluation for the Ore Pass in the Nonempty Condition Based on Controllable Grouting of Cement-Sodium Silicate Grout

Aimed at the problem to plug the main ore pass with the large collapse at Xingshan Iron Mine, the viscosity-time test and the heap perfusion test of cement-silicate grout in a loose rock mass are carried out. The relationship between the vertical diffusion distance of cement-silicate grout and setting time of grout is studied, and research results are applied to the design of plugging engineering of the main ore pass in -330 m. Based on the numerical simulation of the plugging structure and the long-term stress monitoring of the cable sensors, the stability of the plugging structure itself and the control for the movement of shafts nearby are comprehensively evaluated. The test results show that for a specific loose rock mass, the vertical diffusion distance of cement-silicate grout in the loose rock mass is a power function of grout setting time. Based on the design concept to plug the main ore pass with the large collapse using artificially constructed “bite-bonded arch,” the plugging design and construction procedures are proposed. A numerical model and long-term monitoring of cable stress show that the plugging structure is stable and has an obvious effect on the control movement of abutment shafts.

Stability Analysis and Reliability Evaluation in Cataclastic Loose Rock Mass Blocks

Cataclastic rock masses with multiple failure modes and mechanisms are critical geological problems in the construction of rock slopes. Cataclastic rock masses are widely distributed in slopes of a hydropower project located on Lancang River, which is located in Tibet, China. In this study, the potentially unstable block of the slope is divided into key block and secondary key block based on the key block theory, and the system reliability evaluation theory is introduced. The method for quantitatively analyzing the rock mass stability of cataclastic slopes with sliding failure is established. Then, the spatial distribution of cataclastic rock masses and discontinuities in several rock slopes of a hydropower project are determined using traditional geological surveying and 3D laser scanning. At last, combining the BATE 2.0 software and the stereographic projection of the vector, the proposed method is applied to the study area. The results show that the main failure mode of the studied slope is wedge failure, and the system reliability is 1.69. With the increase in the instability probability of the key block, the increase in the instability probability of the system block is obvious, which reflects the controlling effect of the key block on the stability of the system block. The calculated system instability probability is slightly larger than the key block instability probability.

Landslide disaster and its prevention works in Shikoku region of Japan

This study introduces two examples of landslide countermeasures in Shikoku, Japan. The first case is a landslide that occurred in the Chichibu belt. This landslide was characterized by loose rock mass (past landslide mass) distributed at a maximum thickness of approximately 30m. As a result of comparing and examining the three types of construction methods as countermeasures against this landslide, it was judged that the countermeasure works combining the anchor works and the drainage boring works was the most appropriate. This landslide experienced the largest downpours since the completion of the countermeasures, but no landslide activity has been confirmed. The second case is a landslide that occurred in the Mikabu belt. This site was a place where fragile geology was distributed, but a cut at the lower end of the slope was implemented for road construction. After this cutting work, landslides occurred on the slope during heavy rain. Two landslides occurred step by step with the rainfall. As a result of a comparative study of the two countermeasures for this landslide, it was determined that the countermeasure that combined earth removal, anchoring and drainage boring was the most appropriate. The landslide activity was stopped after the countermeasure work was completed, and road construction was completed safely.

Seepage calculation method of loose rock mass under mining unloading

Seepage calculation method of loose rock mass under mining unloading

Experimental Studies of Effect of Shearer Auger Operating Device Effective Width on Effectiveness of Loading Process

Intensification of coal mining from mine seams of 0.55–1.20 m thick requires increasing efficiency of loose coal loading that may be achieved by selecting the optimal parameters of auger operating device of a shearer. The most reliable way to determine effect of the auger parameters on the energy parameters of the shearer operation is experimental research in actual operating conditions. As the subjects of the research, we selected up-to-date UKD400 and UKD200-500 shearers, operating in representative conditions of the Krasny Partizan mine of SE SVERDLOVANTRATSIT and Ternovskaya mine of DTEK PAVLOGRADUGOL PJSC. An adaptive method for specific mining operating conditions is proposed for determining the specific energy consumption of the shearers on material disruption and loading for thin seams in actual operating conditions based on fixing the values of currents of the cutting drive motors. Based on processing of the experimental data, an indicative dependence of the power for rock mass loading on the feed rate and the effective width of the operating device is determined. Increasing the auger effective width results in increasing the loading power and specific energy consumption. At the same time, the higher the shearer feed rate, the greater the growth of the loading power and specific energy consumption. This is due to the beginning of the process of loose rock mass circulation, and the larger the auger effective width, the more intensive the circulation process, and at the lower feed rate of the shearer the process starts. A method is proposed for selecting the auger optimum effective width based on the criteria of minimum specific energy consumption and maximum commercial productivity.

Prediction of Landslide Position of Loose Rock Mass at Mountain Tunnel Exit

Landslide of loose rock mass at mountain tunnel exit occurs easily, and prediction of landslide position is one of the engineering problems to be solved urgently. Currently, existing and used prediction methods, such as field monitoring measurement, numerical analysis, nonlinear theories, and the geometric method, play a very important role and have their limitations. For example, there is a bigger difference between calculation mode by Wang et al.’s method and actual engineering situation; besides, there exists a relatively big discrepancy between the predicted and true position. Aiming to solve this problem, this article combined theoretical analysis and actual engineering situation to establish an optimal calculation mode. At the same time, this article re‐deduced instability criteria based on the stress‐transferring theory and examined the factors that influence solutions. The improved method can predict landslide position more accurately because the parameters (β, s, H, α, γ, c, φ, and T) related to the occurrence of landslide are taken into consideration. It is pointed out that landslide possibly occurs in the case of Δ ≥ 0 and Y ≤ 0. In addition, the equations s1 < s < s2 and 0 ≤ s ≤ H/sin α can determine landslide position accurately. The method is applied to two engineering examples, and the calculation results show that the deviations of predictive position from the actual landslide position are only 0.10% and 0.07%, respectively, indicating that prediction results are accurate and reliable. It is suggested that the proposed method is a useful tool in the design of tunnel engineering.

A New Plugging Technology and Its Application for the Extensively Collapsed Ore Pass in the Non-Empty Condition

Aiming at some long ore passes with severe damages and extensive collapses, we describe an optimal measure to plug a local area of ore pass in order to maintain the capacity of continued use. This paper, taking a new plug for the extensively collapsed long ore pass in the non-empty condition as a breakthrough, builds a structure-plugging system for ore pass based on plug effect, suspension effect, arch effect, and span-reducing effect. Meanwhile, a key plugging technology has been integrated which includes a stability evaluation method of plugging structure, controlled technology of drilling with casing in the composite rock mass, and controllable grouting for inhomogeneous loose rock mass. According to this structure-plugging system and technology, a case has been successful for the main ore pass in the Xingshan Iron Mine in China, which has created a precedent in the world. The practice results show that using this technology to plug the extensively collapsed long ore pass has a series of advantages including of scientific design, strong safety, high efficiency, and low cost.

Acoustic Method Based on Integrity Coefficient for Testing the Loose Circle of Surrounding Rock

The thickness of the loose circle of surrounding rock is an important index in tunnel support parameter design and rock mass stability evaluation. Accurate and rapid determination of thickness is critical to ensure the safety of underground chamber construction. Field test is the most intuitive and accurate method for thickness determination. Acoustic method is also widely used because of its high precision, low cost, and simple operation. However, existing discriminative standards for analysis of test results are ambiguous and subjective; as such, a uniform standard that defines a loose circle has not been established yet. In this study, the complete degree of rock and loose rock mass is quantitatively analyzed by introducing the concept of and the calculation formula for the integrity coefficient of broken rock (Rv) and the integrity coefficient of loose circle (Lv). According to the formation principle of loose circle, the criteria and test method for surrounding rock loose circle are proposed on the basis of the integrity coefficient. The integrity coefficient of the loose circle (Rv) is assumed to be approximately equal to that of the broken rock (Lv) in chamber excavation. In the test of the surrounding rock loose circle in the Shimen tunnel at Baohan highway, the integrity coefficient (Rv) of the rock of the grade Ⅲ gneiss was 0.53 according to the combined indoor and field tests. The thickness of the type Ⅲ surrounding rock loose circle was 0.55-1.35 m, and the distribution along the circumference was not uniform. The arch shoulder was thick, and the wall was thin, consistent with the initial stress state of the surrounding rock. Comparison with the results of the original acoustic wave loosening test showed that the new discriminant method based on the integrity coefficient is more accurate and reliable. The proposed method could be used for the design and construction of tunnels.

Precipitation of salts during capillary hoist in solutions in subsurface aeration zone

Series of experiments on seepage of water solutions of nickel and cobalt through an evaporation barrier in a porous loose rock mass is described. Evaporation intensity shows tendency toward linear decrease with time due to change of the rock mass porosity as a consequence of salt precipitation in the subsurface aeration zone. It is possible to control evaporation intensity by redistributing vertical zonality of precipitate in the subsurface zone. The authors find mechanism of precipitated salt distribution in subsoil.

Design of High Speed Railway Tunnel and its Construction Method in Abrupt Slope with Loose Rockmass

This paper mainly deals with the structural design of high speed railway tunnel and its driving method in abrupt slope with loose rockmass, meanwhile summarizes the connection between tunnel portal and bridge abutment in loose rockmass according to complicated landform and geology. The anti-slide piles are adopted to retain the stability of abrupt slope near the tunnel portal. In order to eliminate the risk and cost in tunnel construction, four bench cut method is invented to satisfy the safe excavation of loose rockmass in the tunnel. Composite fiber rockbolt is also employed to keep the stability of working face while driving the tunnel. The innovative tunneling method presented in the paper can be applied to guide the rational design and economical construction of high speed railway tunnels in loose surrounding rock under harsh geological conditions.

Rockfall risk assessment for pilgrims along the circumambulatory pathway, Saptashrungi Gad Temple, Vani, Nashik Maharashtra, India

This paper mainly describes the assessment of rockfall risk for the large number of pilgrims along the parikrama path (circumbultory or pathway around the shrine) at the Saptashrungi Gad Temple, Vani, Nashik, Maharashtra, India. The temple is constructed on moderately weathered and fractured basaltic terrain along the steep high hill slope. The loose rockmass from the top of the hill occasionally fall, bounce, roll and slide down along the slope of the temple with some rockmass blocks landing on or passing the parikrama path. This leads to risk while taking parikrama along the hill. A quantitative risk assessment (QRA) was undertaken to determine the risk for the pilgrims performing parikrama along the parikrama paths struck by rockfalls and the risk reduction capabilities of various remedial work. The obtained QRA results indicate that, the societal risk cannot be acceptable.

Study of the Three-Dimensional Global Limit Equilibrium Method Applied to the Stability of Rock Slope

Amending the normal stress over the slip surface based on the stress field by numerical analysis, applying the three-dimensional global limit equilibrium method to the stability analysis of tension-slackened rock mass in the right bank of Yagen hydropower station. Stability analysis shows that if do not take any measures, the loose rock mass stability can cater to the Specification demand, but some small sliders is in the limit state under the water and earthquake condition, if use the cutting slope and unloading scheme, the whole loose rock mass and the all small sliders can meet the Specification standard stability requirements.

Experimental Study on Highway Tunnel Surrounding Rock Reinforced by Small Pipe Pre-Grouting

Small pipe of staggered by length leading-drilling and grouting support technology was adopted for per-reinforcement of Lion-shaped Tunnel typeII rock, cement paste filled into loose rock mass rock fracture for adglutinate broken rock into a integrality, thus enhance the coherence and solidity of rock. Thesis introduced process flow of small pipe drilling grouting, grouting equipment, grouting parameters selection and practical applications. Through tunnel deformation monitoring and analysis, grouting reinforcement has achieved very good effect.