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Aiming at the cyclic impact deformation and failure of tunnel surrounding rock under shear stress, a self-developed rotation-impact simulation test platform was used to determine the number of failures, stress-strain curves, and energy in the process of cyclic impact failure. The failure process of rock under different impact velocities and shear stresses has been systematically studied. Results show that, under the same impact speed, the shear stress will increase with the increase in the rotation speed, but an upper limit will exist. When the rotation speed reaches this upper limit, the shear stress will no longer increase. The presence of shear stress will reduce the number of impacts required for rock failure. When the impact speed is 7.2 m/s, the number of impacts at the maximum rotation speed is 60% of the static state. When the impact velocity is 16.8 m/s, this value is only 33.3%. At the same impact velocity, the stress-strain curves under different rotation speeds do not change significantly, but with the increase in the rotation speed, the slope of the elastic stage of the stress-strain curve gradually decreases, and the corresponding stress of the rock sample decreases when the maximum strain is reached. With the increase in shear stress, the crushing specific energy required for rock failure gradually decreases. The greater the impact velocity, the more obvious the impact of shear stress on energy dissipation. In the tunnel process, when the surrounding rock is subjected to impact loads from different directions, only the axial strain analysis will have certain safety hazards, and timely support and reinforcement work are required.

Pre-conditioning by hydraulic fracturing is a vital work in block caving mining of hard-rock metal mine, and breakdown pressure is one of the important parameters in rock hydraulic fracturing process, which determines the equipment selection and job-parameter control. Based on numerical simulation method, a pre-holed cylindrical hard rock sample was built for simulation of hydraulic fracturing process to investigate the effect of stress condition, rock properties and water injection rate on breakdown pressure. The results show that the breakdown pressure is increased with the confining stress, and the breakdown pressure is 2.28 times confining stress based on rock tension strength. The variation of rock tension strength affects the breakdown pressure and a positive linear relation exists. Pre-formed notch could obviously reduce the breakdown pressure and control the orientation of hydraulic fracture. And the borehole diameter has a reverse influence on rock breakdown pressure.

The layout of single transportation level and multiple production levels in one panel made it possible to mine gently dipped orebody by block caving method. However, with the collapse of the orebody in the main sublevel, the ground pressure damage of the extraction structure in the vice sublevel presented some specific characteristics. In order to study the damage evolution mechanism of ground pressure in extraction structure during the process of mining gently dipped orebody, a numerical simulation model was established by using finite difference software FLAC3D, Mohr–Coulomb strength criterion was adopted in calculation. The stress state of the extraction structure in the vice sublevel after each step was monitored and analyzed separately. The research results show that: undercutting in the main sublevel can aggravate the ground pressure damage of the extraction structure in front of an advancing undercut front in the vice sublevel while undercutting in the main sublevel can reduce the probability of secondary occurrence of ground pressure damage in the vice sublevel. The results are beneficial to the guidance of mining gently dipped orebodies in block caving method.

Drilling a borehole and inserting high-pressure fluid to induce rock fracture is a rock-mass pre-conditioning method in block caving mining of hard rock metal mines, and the borehole surrounding rock is under the complex loading conditions with in-situ stress and borehole inner pressure. In order to further understand the failure mechanism of borehole rock during hydraulic fracturing, a numerical model of hollow cylindrical rock sample was built with FLAC3D and the deformation and strength characteristics of this sample was studied by conducting simulation tests. The results show that oblique shear failure was found during uniaxial compression test and the uniaxial compression strength and elastic modulus of hollow cylindrical rock sample were weakened with the increasing of inner hole diameter. The rock triaxial compression strength increased linearly with the confining pressure during triaxial compression tests. The confining and internal pressure were the major factors to induce rock failure during hydraulic fracturing tests and the breakdown pressure increased linearly with confining pressure. For the rock type in this paper, the breakdown pressure was 2.28 times confining pressure plus rock tension strength.

In constructing hard rock mine deep shafts, the failure caused by high stress is a significant problem. A construction section extending from the -930 m to -1271 m level of a 1527 m deep shaft was selected as a case study. Q, RMR, and GSI rock mass quality classifications of the surrounding rock were obtained to determine the shaft’s maximum unsupported sinking cycle height in different construction sections. The potential failure mode, failure zone shape, and failure depth of the surrounding rock shaft under high stress were then analyzed theoretically, empirically, and by numerical simulation, sequential stress control and delayed support technology was proposed according to the results. The temporary and permanent support timing parameters were calculated and verified by the empirical chart, numerical simulation, convergence-confinement theory, and theoretical formula. Results show that the surrounding rock in all the construction sections from -930 m to -1271 m belongs to the mild or severely pressure squeezed strata. The potential failure mode is stress-controlled, and the failure zone of the surrounding rock is “ear” shaped. Temporary support strengthens the rock mass, improves the shear capacity of surrounding rock, and prevents the broken rock from falling but does not release stress. Permanent support, conversely, cannot bear the stress of surrounding rock. The stress and elastic strain energy in rock mass should be released to the greatest extent possible before installing permanent support; it is not advisable to install it too early. The time and cycle height of delayed permanent shaft support were comprehensively determined to be four days and 16 m, respectively. The numerical simulation and safety factor proof show that the sequential stress control process effectively minimizes stress in surrounding rock and ensures long-term shaft stability.

Aiming at the problems of multi-attribute and uncertainty in the selection of stope structural parameter scheme, we proposed a new multi-attribute decision-making model of stope parameters based on set pair analysis and grey relational theory. Based on the SPA-GRA theory, we used the dialectical viewpoint of opposition and unity to combine the determinacy and uncertainty factors, and establish the set pairs between evaluation set and index set respectively. In addition, we quantitatively analyzed the correlation degree of the set pair’s identity, diversity and opposites. Through comprehensively evaluating 6 characteristics of 5 stope schemes, we determined the grade of stope structural parameters and chose the best scheme. The research shows that the evaluation method is used to fully consider the identity, diversity and opposites of the comparison set, which avoids the inevitable one-sidedness in the past evaluation process. It is more objective, comprehensive and reasonable and it can be applied and popularized in the engineering field.

The traditional geotechnical engineering deformation repair method takes a long time, has low precision and poor effect. In order to solve this problem, a method of geotechnical engineering deformation damage repair based on elastic–plastic mechanics is proposed. Firstly, the balance equation, constitutive equation and evolution equation of deformation and damage in geotechnical engineering are established; then the deformation and failure process of geotechnical engineering is deduced, and the failure value of rock mass is calculated; finally, the deformation and damage repair in geotechnical engineering is completed by using elastic–plastic mechanics method. The experimental results show that, compared with other methods, the damage value of this method is consistent with the actual damage value, and the repair accuracy is high. The calculation time is in the range of 2–4 s, and the repair efficiency is high. Moreover, this method can achieve the ideal effect of geotechnical engineering deformation repair.

Under the condition of bad undercutting, ore pillars are easily left in undercut level in block caving method. In order to reveal the evolution mechanism of ground pressure damage induced by bad undercutting, according to the actual engineering and physical parameters of the mine, a numerical simulation model was established by finite difference software FLAC3D. In the simulation process, the extraction level excavations were excavated first according to the post-undercutting method, and the process of the undercutting were divided into three steps. In the first step, a pillar of 15 m × 5 m was formed. The stress state of extraction level excavations and overlying ore body after each step was monitored and analyzed separately, and it was compared with the actual situation of ground pressure disaster on site. The results show that: Under the influence of high horizontal in situ stress, with the development of undercutting, the special stress state in the extraction level excavations are gradually formed, which is that the compressive stress concentrates on the upper part and the tensile stress concentrates on the lower part. With the development of undercutting, the remaining ore pillar form a certain range of tension stress release area above the undercut level, which makes it difficult for overlying ore and rock to cave in, thus causing the phenomenon of “less ore and no ore” in the draw bells.

In deep hard-rock mines, the failure of subsurface structures (e.g., tunnels, stopes, and shafts) has been a significant problem affecting mining safety due to the high-stress environment. In this paper, the mechanism of structural failure and instability is discussed, and optimized excavation methods are proposed for stress control in deep gold mines. Based on the field observation and investigation of the joints distribution and rock failure modes at 800–1200 m depth of several large gold mines and a typical ultradeep borehole (2017 m depth) in northwest Jiaodong Peninsula, three engineering methods for reducing stress, including the stress transferring by mining optimizations, pressure relief by boreholes, and energy release in advance by optimizations of excavation and support, are analyzed by numerical simulation and field monitoring. Results show that stress reduction by excavation alone is limited and the backfill mining method is more conducive to stress transfer than the opening stope method. Roof contacted backfill can produce an unloading zone around the stope and reduce the stress of the surrounding stope. Relief boreholes can reduce the stress concentration of stopes, but the effect of cutting seams generated by presplitting blasting on pressure relief is not significant. The technology “short excavation and short support” releases less energy. By increasing the bench height and the reasonable timing of support by calculating, the elastic strain energy of rock in the shaft is prereleased, which benefits the long-term stability of the shaft.

The instability of extraction structure under the undercut space in the block caving stope presents specific characteristics: rib spalling and floor heave in ore-loading roadway and collapse of major apexes. In order to study the stress and displacement evolution law of extraction structure under undercut space and reveal the instability mechanism of extraction structure, the numerical simulation model of block caving stope was established using the finite difference software FLAC3D. According to the postundercutting strategy in Tongkuangyu Mine in China, extraction structure was formed first in the simulation process, and then the undercut level was divided into eight units for excavation step by step. The stress and displacement of extraction structure after each step of undercutting were monitored and analyzed. Based on the thin plate theory, the mechanism of stress change and deflection deformation of extraction structure was revealed. The research results show that, under the action of high horizontal tectonic stress and vertical stress, the extraction structure under undercut space produces vertical upward bending deformation after undercutting during the block caving. The tension stress concentration gradually appears in the side wall of the ore-loading roadway and the tip of the major apexes; with the increase of the undercutting area, the degree of tensile stress concentration gradually becomes strong; when the tensile strength of the rock mass in extraction structure is exceeded, extraction structure presents instability. It is necessary to make the overlying ore collapse on extraction structure as soon as possible after undercutting, which is beneficial to release the tension stress in the extraction structure under undercutting space.

In geotechnical engineering and geological survey, the stratum structure and its corresponding physical and mechanical properties are the most concerned. The stratum structure not only affects the safety of the project but also plays a decisive role in the construction method and construction sequence. In this paper, a new type of stratum geological interface recognition system is adopted, and an R-20 rotary drilling rig is used to conduct on-site drilling experiments for a granite site with no ventilation. The research results show that the system can monitor and record the main parameters (axial pressure, drilling rate, rotation speed, flushing fluid pressure, and torque) of the drilling rig during the drilling process. The comparative analysis of monitoring data and on-site survey results shows that different drilling parameters have different sensitivities to changes in the formation structure. According to the prediction accuracy, the ranking from high to low is drilling rate, axial pressure, torque, rotation speed, and flushing fluid pressure. In drilling engineering, by observing the change law of drilling rig parameters, not only can the position of the special rock mass interlayer be predicted, but also the stratum structure and strength can be identified, and the prediction formula is also given. Based on the established drilling specific energy formula, the energy analysis method is used to predict the formation structure and compressive strength, and the corresponding prediction formula is given. The research results show that, compared with the single drilling parameter prediction method, the rock-soil structure and strength identification method based on energy theory has higher prediction accuracy and can meet engineering needs.

This paper made a research about the change rule of elastic wave velocity with stress applied on rock from theoretical and experimental aspect. Firstly, a mathematical model of P-wave velocity and confining pressure of rock was set up from the point of acoustoelastic character. Effect of axial stress on P-wave velocity in granite and sandstone during uniaxial compression process was studied experimentally by using GAW-2000 rock mechanical testing system and RSM-SY5 ultrasonic wave testing system, and the relation curves of axial stress with P-wave velocity were obtained. Based on test data, acoustoelastic theoretical formulas of granite and sandstone were established and the best empirical formulas were fitted by using regression method. Meanwhile, a comparative analysis of the empirical and theoretical calculated values was carried out. Finally, the reliability of applying acoustoelastic theoretical formula in hard rock range was further verified based on the experimental data of granitic gneiss. The results show that the P-wave velocity experiences a rapid increase, gentle increase and then a sharp fall during the uniaxial compression process. The B-value in acoustoelastic theoretical formula (proportion coefficient determined by elastic modulus and third-order elastic constant) decreases exponentially with axial stress. The acoustoelastic theoretical formula can effectively reflect the relationship between rock acoustic velocity and stress within the allowable error, which can be the theoretical foundation of acoustoelastic geo-stress measurement of subsurface rock mass.

In order to estimate the strength parameters of rock, as the direct method by conducting rock mechanical tests is time-consuming and expensive, an indirect method based on soft computing technique is proposed. Least squares support vector machine (LS-SVM) is utilized to develop rock uniaxial compressive strength (UCS) and shear strength (SS) prediction models by considering indirect parameters such as rock density, point load strength, P-wave velocity and slake durability index. The results show that according to the rock physical and mechanical parameters of four rock types, empirical relationships based on statistical regression method are rock type specific, only linear relations existed between point load strength and rock strengths are acceptable with high determination coefficients for whole rock types. The LS-SVM models built for rock UCS and SS prediction have greater determination coefficients than the regression models. The prediction values based on LS-SVM prediction models for rock UCS and SS are both extremely close to the measured values, which indicates the applicability of LS-SVM is supported for estimation of strength parameters of rock.

Rotary-percussive drilling is a common form of drilling in geotechnical engineering. in order to study the effect of rotational speed and impact speed on rock-breaking efficiency, a drilling simulation platform developed by ourselves and a drill pipe equipped with diamond bit were used to conduct simulated drilling experiments. By monitoring the stress wave during drilling, the strain, stress and energy changes at different rotational speeds and impact velocities can be obtained, and the optimal drilling parameters can be determined. The results show that both speed and impact velocity have direct influence on the drilling process. When the rotational speed is kept constant, the drilling efficiency increases first and then decreases with the increase of the impact velocity. When the impact velocity remains constant, the drilling efficiency decreases with the increase of rotating speed. With the increase of rotational speed, the optimal impact velocity also increases. It is helpful to improve the drilling efficiency by reasonable choice of speed and impact speed.

Based on the complex stratigraphic characteristics of the Chengmenshan copper mine slope, the stability should be analyzed and additional reinforcement measures need to be implemented to ensure safety in production. In this paper, the stability of the slope was analyzed with numerical simulation model under nature and dynamic loading state. According to the analysis results, the design of orthogonal experiment was discussed for the key factors which influence the reinforcement effect of anchors with SPSS software, and the master-subordinate relationship of the factors and optimal combination were obtained by using range analysis method. Finally, the slope stability with optimal reinforcement measure was tested. The results show that the safety factor of slope under nature state is low and it is in the critical instability condition. Under dynamic loading state, the failure probability of slope increases from 0 to 18% as the seismic magnitude varies from 6 to 8. Primary and secondary sequence of factors that influence the anchor reinforcement effect is the bonding length, anchor installing angle, anchor length at 3rd bench, anchor length at 2nd bench and anchor length at 1st bench. The safety factor of slope reinforced with anchors is larger than 1.1, which could ensure the safety and stability of the slope.

Accurate characterizations of rock strengths under higher loading rates are crucial in many rock engineering applications. The split Hopkinson pressure bar (SHPB) system has been used to quantify the dynamic compressive strength of rocks using the short cylindrical specimen and the dynamic tensile strength of rocks using the Brazilian disc (BD) specimen. However, SHPB is a standard tool that is suitable for metal testing; there are some fundamental issues that need to be carefully visited in applying SHPB to rock dynamic tests. This paper addresses several such critical issues, including the choice of slenderness ratio of the compressive specimen, the effect of friction between the sample and bars on the measured results of compressive strength, the necessity of dynamic force balance on the dynamic BD test, and the validity of using the standard BD equation in the data reduction. We show that with proper experimental designs that address these issues, the dynamic compressive strength and dynamic tensile strength of rocks measured using SHPB are valid and reliable.

The successful application in drilling for HK simple weathered granite foundation has revealed its further use in instrumented drilling system as a ground investigation tool in the detection of other lithology formations, geohazards, underground water, and boundary of orebody. To expand the further use and test the accuracy in identification of formation, an R-20 rotary-hydraulic drill rig was instrumented with a digital drilling process monitoring system (DPM) for drilling in an intricate decomposed granite site. In this test ground, the boreholes revealed that the weathered granite alternately changes between moderate and strong. The qualitative and quantitative analysis of the penetrating parameters, indicates the effective thrust force, rotary speed, flushing pressure, penetrating rate, and displacement of the bit fluctuate at ground interfaces. It shows that the parameters get a good response with the change of rock strength at the interfaces, which can reveal the change of the intricate granite formation. Besides, a variable-slope method has been established, for identification of dominative and subsidiary interfaces in the granite site. The result from a t -test shows that the confidence of the instrumented drilling system in identification of the geotechnical interfaces is up to 99%.

To solve the technical cruxes of the conventional system in deep rock mass, an automatic testing system for hydraulic fracturing that includes a single tube for hydraulic loop, a pressure-relief valve, central-tubeless packers, and a multichannel real-time data acquisition system was used for in-situ stresses measurement at great depths (over 1000 m) in a coalfield in Juye of Northern China. The values and orientations of horizontal principal stresses were determined by the new system. The virgin stress field and its distributing law were decided by the linear regression from the logged 37 points in seven boreholes. Besides, the typical boreholes arranged in both the adjacent zone and far away zone of the faults were analyzed, respectively. The results show that a stress concentration phenomenon and a deflection in the orientation of the maximal horizontal stress exist in the adjacent zone of the faults, which further provides theoretical basis for design and optimization of mining.

In view of the complex structural characters of Chengmenshan copper mine slope, the slope stability should be analyzed and additional reinforcement measures need to be considered to ensure mining safety. In this paper, the slope model was built and its stability was analyzed by numerical simulation method under nature and dynamic loading state. After that the design of orthogonal experiment was discussed for the key factors which influence the reinforcement effect of anchors with SPSS software, and the primary and secondary relation of factors and the optimal combination were obtained using the range analysis method. Finally, the slope stability with optimal reinforcement measure was tested. The results show that the safety factor of slope under nature state is low and it is in the critical instability condition. Under dynamic loading state, the failure probability of slope increases from 0 to 18% as the seismic magnitude varies from 6 to 8. Primary and secondary sequence of factors that influence the anchor reinforcement effect is the bonding length, anchor installing angle, anchor length at 3rd bench, anchor length at 2nd bench and anchor length at 1st bench .The safety factor of slope reinforced with anchors is larger than 1.1, which could ensure the safety and stability of the slope.

Rainfall infiltration exerts great effect on the stability of soil slopes. Based on the actual rainfall data, saturated-unsaturated seepage theory and the mechanical theory of unsaturated porous media, numerical simulations were conducted to examine the seepage field of saturated-unsaturated slope during rainfall infiltration in this paper. The influence of the coefficient with rainfall duration, rainfall patterns, rainfall intensity and soil saturated permeability on seepage field are studied, and the relationship between the factor of safety and the position of sliding surface is obtained. The simulated results show that the saturated hydraulic conductivity has a great effect on slope stability. If the permeability of soil is relatively large, the changing range and the velocity of the factor of safety increase with the rainfall intensity; and if it is relatively in a low degree, the influence of the rainfall intensity on the slope stability is also low

This study aims to conduct research about the microstructure and basic properties of recycled aggregate concrete under seawater corrosion. Concrete specimens were fabricated and tested with different replacement percentages of 0%, 30%, and 60% after immersing in seawater for 4, 8, 12, and 16 months, respectively. The basic properties of recycled aggregate concrete (RAC) including the compressive strength, the elastic modulus, and chloride penetration depth were explicitly investigated. And the microstructure of recycled concrete aggregate (RCA) was revealed to find the seawater corrosion by using scanning electron microscope (SEM). The results showed that higher amount of the RCA means more porosity and less strength, which could lower both the compressive strength and resistance to chloride penetration. This research could be a guide in theoretical and numerical analysis for the design of RAC structures.

The engineering characteristics of recycled material made of waste concrete debris after crushing, washing and grading selection, is different from natural bone materials and presents a huge difference in endurance. The migration of dissociative ion in recycled concrete has been initially conducted by few scholars with method of chloride ion electric migration fast test (IIEMFT)[1–7]. However, it is seldom reported that the penetrability of binding chloride ion is experimented with natural diffusion method of ion in recycled concrete. In practice, the ion transfer is mainly motivated by diffusion and capillary effect, so, it will lead to different results from general cases when IIEMFT is carried out in studying ion penetrability in concrete. It is obvious that the quantity of dissociating chloride ion play a major effect on steel corrosion. There is less dissociating ion left if more ions are combined when the total quantity of ion immigration in the concrete is kept constant. As a result, the rust damage to steel will be minimized. Therefore, it is of paramount significance to study the law of ion distribution in concrete. In this paper, the natural diffusion method is applied in order to systematically study the effect of recycled bone material, dry-wet circulation, fly ash quantity on ion content, which will provide comprehensive basis for the application of recycled concrete in engineering.

In the mining converted from underground to open-pit, the existence of various complex goaf in the open-pit mining realm poses a grave threat to the safety of operation. This paper summarizes the composition of these various complex goaf, and introduces the principles and techniques from which the GPR (ground penetrating radar) was used to detect shallow complex goaf in the open-pit mining realm including data acquisition, processing and explanations. Utilizing GPR had obviously been effective for this specific project to detect shallow complex goaf in the mining converted from underground to open-pit. Thus the GPR can be equally useful and worthy to be applied and popularized in related fields.