Blasting Excavation Research Articles

Effects of In-Situ Stress on Damage and Fractal during Cutting Blasting Excavation

Blasting excavation of rock masses under high in-situ stress often encounters difficulties in rock fragmentation and a high boulder rate. To gain a deeper understanding of this issue, the stress distribution of rock masses under dynamic and static loads was first studied through theoretical analysis. Then, the ANSYS/LS-DYNA software was employed to simulate the blasting crack propagation in rock masses under various in-situ stress conditions. The fractal dimension was introduced to quantitatively analyze the influence of in-situ stress on the distribution of blasting cracks. The results indicate that in-situ stress primarily affects crack propagation in the later stages of the explosion, while crack initiation and propagation in the early stages are mainly driven by the explosion load. In-situ stress significantly influences the damage area and fractal dimension of cut blasting. Under hydrostatic in-situ stress, as the in-situ stress increases, the damage area and fractal dimension of blasting cracks gradually decrease. Under non-hydrostatic in-situ stress, when the principal stress difference is small, in-situ stress promotes the damage area and fractal dimension of the surrounding rock, enhancing rock fragmentation. However, when the principal stress difference is large, in-situ stress inhibits the damage area and fractal dimension of the surrounding rock, hindering effective rock breaking.

Failure Mechanisms of Corrugated Hdpe Pipeline with a Gasketed Bell and Spigot Joint Subjected to Underground Blasting Excavation Load

Failure Mechanisms of Corrugated Hdpe Pipeline with a Gasketed Bell and Spigot Joint Subjected to Underground Blasting Excavation Load

Physical model test and numerical simulation study of cumulative damage to deep tunnel surrounding rock under cyclic blasting load

Cyclic blasting excavation of a deep tunnel frequently disturbs the surrounding rock, and cumulative damage effect will occur in cases multiple blasts are applied. To study the damage evolution trend of tunnel surrounding rock under multiple cyclic blasting load, a self-made physical model test system was used to test cyclic blasting excavation of a tunnel under high in-situ stress. Meanwhile, according to the characteristic that the damage of rock under frequent disturbance will appear cumulative superposition, an improved Bingham creep damage constitutive model was established. The constitutive model was applied to the numerical simulation of tunnel cyclic blasting excavation, and the numerical simulation reproduced the physical model test to study the rock damage evolution laws. The results from the physical model test and the numerical simulation revealed that the process of damage evolution of rock in in-situ stress state under the impact of multiple blasting disturbances had a non-linear cumulative characteristic. In addition, the results also shed light on the relationship between the damage zone expansion and the number of cyclic blast. This paper can provide a reference for studies of the damage evolution in deep rock under blasting impact.

Numerical modelling of the response of cemented paste backfill under the blasting of an adjacent ore stope

An in-depth understanding of the response of backfilled stopes during the blast excavation of adjacent ore stopes is crucial for the effective backfill design to improve workplace safety and ore recovery. In this study, numerical simulations are performed to explore the effects of blasting schemes and ratios of cement to tailings (c/t) on the responses of cemented paste backfilled stopes under blasting in adjacent ore stopes. Three-dimensional models comprised of ore stope, backfilled stope, explosive charge, and air were numerically established. The ore stope and backfilled stope were discretised by finite elements, while explosive charge and air were explicitly modelled using a particle-based approach. Three blasting schemes, including detonating the blastholes simultaneously, detonating the blastholes row-by-row, and detonating the blastholes column-by-column, were carried out in the ore stope, and four c/t ratios, i.e., 1:4, 1:6, 1:8, and 1:10, were used in the backfilled stope. The versatile Karagozian and Case concrete (KCC) constitutive model was used to describe the mechanical behaviour of ore and backfill materials. Its input parameters for cemented paste backfill samples with different c/t ratios were calibrated based on the uniaxial compression and Brazilian tensile testing results. The numerical results show that the row-by-row, column-by-column, and simultaneous blasting scenarios produce a similar breaking performance in the ore stope, but the latter induces the minimum damage volume in the backfilled stope. The damage generated in the backfilled stope induced by the blasting excavation in the ore stope decreases as the c/t ratio decreases. It is also found that the layered backfill structure lowers the cement cost and improves the blast resistance, and its damage tends to concentrate in the layers with higher c/t ratios. The results obtained here highlight the importance of the ductile behaviour of cemented paste backfill in the blasting resistance performance of backfilled stopes.

Composition and Characteristics of Rock Vibration Generated in Blasting Excavation of Deep Tunnels

During blasting excavation in deep rock masses, the in situ stress initially exerted on blast-created free surfaces is rapidly released along with rock cracking by blasting. The rapid stress release can initiate seismic waves transmitting through the medium. In addition to explosion loading, the rapid stress release occurring on blast-created free surfaces is another excitation source of the rock vibration generated in blasting excavation of deep rock masses. In this paper, a theoretical model of seismic wave radiation from a circular blasting excavation in a deep rock mass is first developed to study the frequency differences between explosion seismic waves and stress release-induced seismic waves. Based on this, variational mode decomposition (VMD) is then introduced to separate explosion seismic waves and stress release-induced seismic waves from coupled vibration signals in the frequency domain. By utilizing the VMD separation, the composition and the amplitude and frequency characteristics of the rock vibration monitored in an actual deep tunnel blasting are investigated. The theoretical analysis and field investigation show that the vibration frequency of stress release-induced seismic waves is significantly lower than that of explosion seismic waves. Due to the existence of stress release-induced seismic waves with lower frequency, the coupled vibration amplitude is increased and vibration frequency is reduced. The monitored rock vibration in the near field is dominated by explosion seismic waves. However, in the far field, stress release-induced seismic waves become the major component due to their lower frequency and slower attenuation with distance. Extra care should be taken for the stress release-induced seismic waves in the far field. The stress release-induced seismic waves can be effectively reduced through shortening blast-created free surface sizes and increasing blasthole lengths moderately.

Dynamic response characteristics of adjacent tunnel lining under blasting impact in subway connecting passage

The connecting passage between two adjacent tunnels is conducive to the rescue and evacuation of subway tunnels when disasters occur. The blasting method is usually used in the construction of connecting passage. The vibration caused by blasting construction may endanger the safety of subway tunnel structure. As a result, the influence of blasting pressure on the stability of subway tunnel lining structure during the excavation of connecting passage is studied, and the safe blasting construction distance is proposed, which is crucial to the safety of adjacent subway tunnel lining. This study takes the connecting passage of Wuhan Metro Line 8 as an example. Using Finite element software ANSYS/LS-DYNA, an accurate numerical calculation model of construction site is established. The nonlinear elastoplastic mechanical characteristics of soil, rock, and tunnel lining are simulated by Drucker Prager, Plastic Kinematic, and Johnson Holmquist Concrete constitutive material models, respectively. The credibility of the three-dimensional numerical calculation model and material constitutive model was proved by contrasting the field measured data of the connecting passage with the numerical calculated results. Analysis of numerical results, the axial and radial PPV, frequency, and Von Mises stress of subway tunnel lining are obtained. The influence of subway tunnel lining under adjacent blasting can be obtained by analyzing the distribution law of PPV and Von Mises stress. Non-static tensile strength is needed considering the high pressure and high strain rate process of concrete during blasting. By fitting the relationship between PPV and dynamic tensile stress, and referring to DIF parameters, the safety range of PPV in subway tunnel lining blasting is determined. The critical safety distance between blasting construction and tunnel lining is obtained by Sadovsky vibration velocity attenuation formula, which is used to guide the subsequent blasting excavation of continuous tunnels.

Dynamic cumulative damage characteristics of deep-buried granite from Shuangjiangkou hydropower station under true triaxial constraint

Deformation and failure of rocks under loading is an energy- driven progressive process of damage evolution, and the abrupt energy release from rocks storing strain energy under high- geostress conditions is a determinant inducing catastrophic effects. Therefore, studying the progressive fracture mechanism of rocks from the perspectives of energy accumulation and dissipation is conducive to prediction and evaluation of catastrophic effects of surrounding rocks. In this study, granite was taken from an underground powerhouse of Shuangjiangkou Hydropower Station, Sichuan Province, China to study cumulative damage characteristics of the rock under dynamic triaxial loading by considering factors, such as in-situ stress, number of impacts and strain rate through use of a true-triaxial split Hopkinson pressure bar (SHPB) as a loading device and a three- dimensional (3-d) X-ray computed tomography (CT) system. Mechanisms inducing catastrophic effects in deep-buried granite were explored from the perspectives of energy evolution, progressive damage, and failure mode. The research results demonstrate that under a single impact, the dynamic compressive strength of granite increases exponentially with the impact load, while the rate of increase gradually decreases. Moreover, failure effects of the rock are strengthened with increasing impact load. Under multiple impacts, the energy absorbed by the rock shows cumulative effects and the amount of energy dissipated per unit volume increases. Furthermore, progressive damage is significant, and the damage evolution exhibits obvious anisotropy. Under dynamic triaxial loading, shear failure predominates in granite. The confining pressure inhibits damage to the rock during static loading and the rock is severely damaged in the direction of its free face, where it is more likely to induce catastrophic effects. The 3-d visualization of fracture networks reveals the progressive damage process of granite under dynamic triaxial loading and the cumulative absorbed energy and volume of microcracks in rock increase linearly with the number of impacts. Therefore, taking cumulative damage effects caused by frequent blasting excavation into consideration can better evaluate catastrophic effects, such as rock burst or rib spalling of surrounding rock of side wall of deep-buried caverns in Shuangjiangkou Hydropower Station.

Hollow Effect of Ground Vibration Induced by Electronic Detonator in Shallow Tunnel

Blasting excavation is extensively used in tunnel construction, and the adverse effect of ground vibration induced by blasting on surrounding structures and inhabitants is a critical problem. This study aims to investigate the tunnel hollow effect on triaxial peak particle velocities (PPV) and dominant frequencies induced by electronic detonator. Field experiments were conducted in a shallow tunnel construction site and the ground vibration waveforms were recorded. Variational mode decomposition (VMD) was applied to denoise and correct the zero-drift phenomenon, and the proposed method of selecting the optimal parameter was verified. A series of statistical analyses and tests were performed to evaluate the differences of peak particle velocity and dominant frequency among various monitoring points. The results showed that the hollow effect on Z-axis PPV is significant, and triaxial PPV is also affected when the horizontal distance exceeds 30 m. The hollow effect on dominant frequency could not be identified since the hollow of tunnel is a free face, and the dominant frequency of reflected wave remains unchanged. An augmented factor of 1.229 is determined carefully as the hollow effect factor on PPV. Therefore, blasting vibration induced by electronic detonator of the excavated zone should be attached with greater importance, and hollow effect on PPV should be considered in the blasting design of tunnel excavation.

Detection and numerical simulation of blasting-induced damage in shallow-buried twin tunnels with small spacing

In order to study the damage effect of blasting load on the surrounding rock of shallow-buried small spacing twin tunnels, the shallow-buried tunneling section of the south extension project of Shunhe Expressway is taken as the engineering background. Firstly, based on the dynamic damage evolution and Hoffman failure criterion, an anisotropic dynamic damage constitutive model for rock materials is established. Then, by using the secondary development function of the LSDYNA software, the constitutive model is applied to the numerical simulation of the tunnel blasting damage. Finally, based on the acoustic wave measurement theory, the wave velocities in the surrounding rock of the shallow-buried small spacing twin tunnels before and after blasting were measured by using non-metallic ultrasonic detectors, and the damage of the surrounding rock is evaluated from changes in wave velocity. The applicability of the anisotropic dynamic damage constitutive model and the accuracy of the numerical results are verified by comparing the numerical simulation results with the field test results. The numerical simulation results show that the maximum damage radius of single-hole blasting is 0.58 m, and the maximum damage depth is 1.88 m. According to the damage threshold of the rock mass, the horizontal failure range of the rock mass can reach 0.14 m, and the failure depth is 1.70m. According to the field test, the damage degree of the middle intercalated rock is higher than that of the other parts of the surrounding rock in the alternate blasting excavation of the double track tunnel. The damage depth of the surrounding rock caused by blasting excavation is about 0.5 m, which is close to the simulation results, and verifying the accuracy of the anisotropic dynamic damage constitutive model. The research results have a certain guiding role on the blasting excavation and damage control of shallow-buried twin tunnels with small spacing..

Study on Stability of Support for Tunnel Damaged by Blasting

Blasting excavation will induce damage of surrounding rock of tunnel, and bolt-mesh-shotcrete support is often used for damaged tunnel. This paper learns force characteristics of bolt, location of fracture surface of tunnel and corresponding stability coefficient through analysis on stability of supported tunnel based on strength reduction method. The study indicates that: it’s easy to induce damage of local rock mass of surrounding rock when the bolt spacing is too big, while tunnel support has limited stability and poor economy when the bolt spacing is too small. The reasonable spacing and length of supporting bolts are 1.0m and 3.5m respectively. Results of the study have certain guiding significance for tunnel engineering construction.

Prediction of Bench Blasting Vibration on Slope and Safety Threshold of Blasting Vibration Velocity to Undercrossing Tunnel

The reconstruction and expansion project of oil reserve base often faces the excavation and blasting of the slope and undercrossing tunnel at the same time. Due to the flammable and explosive liquid storage nearby, the tight construction period, and the high requirements of collaborative construction, once the blasting accident occurs, the consequences are unimaginable. To facilitate safe and timely cooperative blasting construction of the slope and undercrossing tunnel, a vibration monitoring test of the slope and tunnel surrounding rock is conducted. The vibration response characteristics of the rock surrounding the slope and tunnel are analyzed, and a mathematical prediction model for the peak particle velocity (PPV) with consideration of the influence of the relative slope gradient (H/D) is established based on dimension analysis theory, which improves the prediction accuracy of PPV at the slope surface. ANSYS/LS‐DYNA is used to establish a 3D finite element model for the slope and tunnel, and the dynamic response of the tunnel surrounding rock under blasting load is verified through field monitoring data. A linear statistical relationship between PPV and effective tensile stress (ETS) of the tunnel surrounding rock is established. The PPV safety criterion of the tunnel surrounding rock under blasting load is proposed to be 10 cm/s according to the first strength theory, and hence, the minimum safety distance from the tunnel working face to the slope surface is calculated to be 36 m. Finally, the excavation timing arrangement of the slope and tunnel is proposed, which has been successfully applied to the expansion project, and the construction period has been effectively shortened by 45 days while ensuring construction safety. The research results have great guiding significance to similar cooperative blasting excavation engineering for high slope and adjacent tunnel with safety and efficiency.

建筑基坑微差爆破开挖施工技术

建筑基坑微差爆破开挖施工技术

Bench Blasting Excavation Test for Multifault Foundation Pit of DG Hydropower Station

A DG hydropower station is studied in a high-altitude area, where the air is thin and a fault fracture zone develops on the left and right banks of the dam foundation and riverbed dam section. To ensure the quality of the foundation pit blasting excavation and reduce the blasting disturbance to the surrounding unexcavated rock mass, a bench blasting excavation test is conducted on the dam foundation and the relaxation depth detection is adopted for the foundation rock blasting excavation. The average attenuation rate of acoustic wave velocity before and after blasting of all control points of rock mass meets the relevant standards and specifications, and the overall performance of excavation and cleaning is good. Test results show that reasonable blasting parameters are favorable for the formation of foundation excavation, and this technology can be used as a reference in similar projects.

Rock damage control for large-diameter-hole lateral blasting excavation based on charge structure optimization

Controlling rock damage induced by lateral blasting excavation is a source of concern. In underground mines, large-diameter-hole lateral blasting excavation often causes engineering disasters such as large blocks falling and overall collapse of the remaining rock mass. Because of their high cost and cumbersome operation, conventional contour blasting techniques, such as smooth and presplit blasting, are unsuitable for production boreholes. In this paper, based on the large-diameter-hole lateral blasting excavation of the Shaxi underground mine in China, a field lateral blast test with a single row was initially conducted, and the sonic wave speeds and goaf boundaries were measured to evaluate the damage degree to the remaining rock mass. A numerical model with three rows of boreholes was developed and calibrated against the lateral blast test with a single row. The calibrated numerical model was used to simulate the blasting process. The blast-induced damage characteristics with different charge structures in different rows were investigated, and the optimal charge structure for each row was obtained. The results indicate that the rock damage control effect can be achieved by a reasonable combination of charge structures and number of blasted rows, and it is more satisfactory with an increasing number of blasted rows and a reasonable decrease in the charge coefficient row by row. The rock breaking pattern at Cut X2 shows that most of the boulders are caused by the collapse of the remaining rock mass under the impact of blasting excavation. The ratio of broken rock in Part 4 indicates that the blast impact of the last row plays a dominant role in the damage to the remaining rock mass. Two optimized schemes were applied to the field of large-diameter-borehole lateral blasting, and satisfactory effects were achieved in the blast-induced damage control of the remaining rock mass.

Ground Vibration Test and Dynamic Response of Horseshoe-shaped Pipeline During Tunnel Blasting Excavation in Pebbly Sandy Soil

In order to ensure the safety of horseshoe-shaped pipeline during tunnel blasting excavation, the vibration test and dynamic response of horseshoe-shaped pipeline were investigated. The velocity and frequency of tunnel blasting vibration were analyzed. Sodev's empirical formula was used for regression analysis of the velocity of blasting vibration. 3D numerical model of a horseshoe-shaped pipelines was established with ALE algorithm using ANSYS/LS-DYNA. The propagation law of a blasting seismic wave was analyzed, and the transverse and longitudinal vibration response characteristics of pipelines under tunnel blasting vibration were studied. The velocity of the pipeline increases gradually and the frequency tends to decrease with the decrease of the distance away from the explosion source center under the same charge. The principal frequency of vibration in the Z direction is mainly distributed from 50 to 80 Hz, which is difficult to generate resonance with the pipelines. The maximum relative error between the simulated and measured velocity of X, Y and Z directions was 8.2%. It was reliable to study the dynamic response of pipelines under blasting vibration based on this numerical model. The blasting seismic wave first reached the bottom of the pipeline right above the explosive. Subsequently, seismic waves propagated along the transverse and the longitudinal axes of the pipeline, and the pressure on the pipeline increased gradually. And when it attenuated completely in the soil, the pipeline stopped its response. The peak value of tensile stress of each element of the vault is the largest. However, the velocity of the bottom plate and the arch roof of pipeline are the largest. The peak values of velocity and tensile stress exist in 0 to 4 m away from the explosion source, and gradually decrease as the distance away from the explosion source increases.

Elastic-slip interface effect on dynamic stress around twin tunnels in soil medium subjected to blast waves

Blasting excavation of deep-buried structures is a complex dynamic process which can cause blast loading and insitu stress redistribution. An elastic-slip interface model is introduced to analyze the dynamic response of twin tunnels subjected to blast waves. The blast waves is expressed by Fourier-Bessel expansion method of wave function, and the wave field is superimposed by Graf coordinate transformation method. To analyze the interface effect, the elastic and slip coefficients of interface are introduced to describe the interface properties. Through numerical examples, it is found that the dynamic stress at the upper points of tunnels is larger than that at the sides of tunnels. However, the interface effect on the dynamic stress at the sides of tunnels is larger than that at the upper points, especially a small distance between twin tunnels is selected. Due to the interface effect, not only compressive but also tensile deformations can be seen, and the large oscillation of dynamic stress at the sides of tunnels can be observed. Excellent agreement with existing numerical results validates this dynamic model.

Numerical Simulation of Dynamic Damage and Stability of a Bedding Rock Slope under Blasting Load

Blasting excavation of a bedding rock slope is a common problem in highway construction in mountainous areas. Accurate simulation of damage area caused by blasting excavation is of great significance for the subsequent maintenance of slopes. Based on a highway construction project in Guangdong province of China, a tensile and compressive damage model was used to simulate the whole process of blasting excavation of a typical bedding rock slope. The analysis results show that damage first appears just around the blasting hole and then develops to the both sides and the bottom of the blasting hole, and finally a large range of damage appears in the lower part of the blasting hole, and the damage depth on the right‐side slope is around 2 m, which is in consistent with the scene. Besides, damage also occurs in the middle of the bedding rock mass of the slope. At the same time, the history analysis of vibration velocity also indicates that tensile failure appears on the right‐side slope under the blasting hole. Therefore, the stability of the slope can be assessed by analyzing the distribution of damage factors and the vibration velocity characteristics synthetically. In addition, parameter analysis was also carried out to optimize the blasting design by controlling the blasting load so as to obtain the ideal blasting excavation effect and ensure the stability of the slope under blasting load.

Development of Double-arm Rock Drilling Car for Full Face Tunnelling

Blasting excavation is widely used in coal mine roadway excavation, its construction method is flexible, convenient, low cost and adaptable. It can excavate mine tunnels of any shape and length under any environmental conditions. However, the main rock drilling equipment used in the mine is pneumatic rock drilling equipment generally. Although these equipment are simple and reliable, their drilling efficiency is low, the degree of automation is poor, and the working conditions are bad, especially the ability to drill deep holes and large holes is poor, which can not meet the needs of large structural parameters mining method. The newly developed double-arm rock drilling rig for full-face roadway excavation is suitable for the current common construction method of roadway blasting driving. It can replace the traditional pneumatic rock drilling equipment, and drill large holes and small holes simultaneously. It fully meets the requirements of blasting technology. It can not only drill and excavate holes, but also drill roof, side wall and floor bolts holes, to achieve high and low position of drilling operations, for improving the efficiency of roadway excavation, promoting the level of coal mine machinery and equipment in China, these have important practical significance.

Safety Threshold Determination for Blasting Vibration of the Lining in Existing Tunnels under Adjacent Tunnel Blasting

The effects of tunnel blast excavation on the lining structures of adjacent tunnels are comprehensively studied for the Xinling highway tunnel project. First, the LS‐DYNA software is applied to obtain the characteristics of vibration velocities and dynamic stresses at different positions of the tunnel liner. The results indicate that the maximum peak particle velocity (PPV) is located on the haunch of the lining facing the blasting source and that the PPV and peak tensile stress decrease with the increase in the surrounding rock grade. Second, a site test on blasting vibration is conducted to verify the simulation results. By using regression analysis of the measured vibration data, the calculation method of maximum charge per delay for optimizing blasting excavation under different surrounding rock grades is obtained. Finally, based on the statistical relationship between crack alteration and PPV on the lining before and after blasting, the safety thresholds of PPV for different portions of the tunnel are determined. The recommended safety threshold of PPV is 10 cm/s for intact lining and for B‐grade and V‐grade linings of the surrounding rock tunnel. However, if the lining crack grade falls between 1A and B, then the recommended safety thresholds of PPV for the III‐grade and IV‐grade surrounding rock tunnel are 5 cm/s and 6 cm/s, respectively. The threshold PPV proposed in this study has been successfully applied to restrict blast‐induced damage during new tunnel excavation of the Xinling tunnel project.

Study on the Influence of Quarry Blasting on Adjacent Tunnel

The blasting in the adjacent quarry would cause the existing tunnel structure damage and strength weakening. But the degree of damage to the tunnel structure and the stress redistribution state caused by adjacent blasting need to be accurately quantified and evaluated. In order to find out the actual situation of the disease and judge the current stability of the tunnel, and comprehensively evaluate the influence of the mining activities on the safety of the tunnel structure, the influence of adjacent quarry blasting excavation on the stress and displacement of tunnel structure was analyzed through static and dynamic numerical analysis.