To investigate the rock mass crack propagation pattern in deep-buried tunnels during drilling and blasting excavation, two combined model tests (labeled as Model 1 and Model 2) consisting of multiple cement mortar blocks were carried out. The dimensions of the models were both 180 cm×80 cm×25 cm (length width height). Among them, the matrix size was 60 cm×80 cm×25 cm, and two sides had single and multiple joints. Furthermore, a thorough analysis was conducted to determine the influence of dynamic loads stemming from nine cumulative explosions on the crack propagation in a matrix by applying various static stresses, particularly on the direction of the applied static loading. The experimental results reveal that cracks emerge on both Model 1 and Model 2 surfaces along the direction of static stress loading when the static stress increases from 0.5 MPa to 5 MPa. The crack propagation direction forms an angle on the loading direction, and the main crack is longer than 60 cm. A blasting funnel contour with about 30 cm diameter is formed on the bottom of Model 1, which does not fall off. In comparison, a funnel with about 52 cm diameter and a 10 cm depth is formed on the bottom of Model 2, which has fallen off. Numerical analysis verified that the static stress has a guiding effect on the propagation direction of blasting cracks, which is consistent with the model test results. The difference was that the length of the main crack calculated by numerical calculation was smaller than that of the model test. Finally, the reason for this deviation was analyzed.

Abstract: A patented technology for bus current acquisition of electronic detonators is introduced, which uses a low-cost hardware solution to achieve high-precision and wide-range current acquisition. This technology is designed to monitor and acquire data related to the working current, communication current, charging current, and detonator bus current load for electronic detonators, thus enabling these devices' status monitoring, data communication, and bus protection. This system focuses on the innovative, low-cost circuit design concept and the methods employed to ensure high-precision, high-resolution, and wide-range current acquisition. The typical working current of the electronic detonator control module ranges between 10~30 uA, and data is transmitted to the detonation controller via a current carrier. The communication current typically falls within the 0.5~2 mA range, and the ignition energy storage capacitor is charged through the bus with a peak charging current of 1~2 mA. The detonation controller determines the working status of the electronic control module by acquiring bus current data, which includes communication and charging status, to determine the module's working condition. In the current acquisition method discussed, low-side resistors are used to sample the current, replacing a differential comparator with three low-cost operational amplifiers. Furthermore, a 12 bit AD converter integrated into the MCU replaces an external 16-bit AD converter, which reduces hardware costs by over 80%. By segmenting the current collection, the system maintains the required accuracy for small current sampling and expands the current sampling range by 30 times, covering the rated current of the bus. The absence of an external AD conversion module significantly improves the sampling efficiency.

This study presents a comprehensive approach to solve the problem of low ore recovery caused by the difficulty in separating small-particle size ore from soil after blasting in a limestone building stone mine. Firstly, a correlation model between blasting fragmentation and dynamic damage of rock mass was established based on field measurement data and numerical simulation results, which can determine dynamic damage thresholds corresponding to various rock particle sizes. Secondly, the numerical simulation test of bench blasting in a three-dimensional fractured rock mass was carried out by using different air-decked charging stages and borehole distribution parameters, which can improve the particle size yield of 0.3~0.9 m and control the bulk ratio to obtain the best blasting parameters. Finally, the field blasting tests were conducted to optimize the charge structure and borehole distribution parameters based on numerical simulation results. The results show a negative exponential function relationship between the blasting block size and the dynamic damage value of the limestone. Specifically, the dynamic damage thresholds corresponding to the blasting size of 0.3 m and 0.9 m are 0.793 and 0.286, respectively. Using only an air-decked charging structure alone can increase the particle size ratio of 0.3~0.9 m and significantly raise the bulk rate. Conversely, combining an air-decked charging structure with a reduced hole spacing markedly enhances the particle size ratio of 0.3~0.9 m while maintaining a stable bulk rate. Optimal blasting results are achieved using a two-stage air interval charging structure and a strategic reduction in hole distribution parameters. The field application results show a 20.09 percentage point increase in the 0.3~0.9 m particle size ratio, with the bulk rate remaining virtually unchanged. Additionally, the unit consumption of explosives decreased by 10.29%.

In order to study the gas diffusion-transport law and the influence of ventilation on the gas concentration of high gas tunnel after blasting, an optimization blasting scheme under gas conditions was carried out, and a gas diffusion-transport characteristic near the working face was investigated under both ventilated and unventilated conditions in a project. The study shows that the residual rate of the blast hole and the utilization rate of the blast hole are above 90%, and the over-excavation control effect is better with an expected blasting footage of 1.2 m and an uncoupling coefficient of 0.76. Under the condition of unventilated condition by numerical simulation, the gas accumulation near the arch top and the arch waist at the tunnel's working face is severe as the gas concentration is close to 30%. Meanwhile, the gas concentration is higher in the area 7 m away from the working surface, and the gas concentration gradient is smaller in the area beyond 7 m after the gas state is stabilized. The gas concentration can be reduced to the safe range around 30 days after ventilation. However, gas accumulation quickly occurs at the arch foot and the arch waist on the other side of the air duct, especially the gas accumulation at the arch foot is more prominent, and the gas concentration is close to 20%. There is a ventilation blind area at the arch foot of the same side of the air duct, and the gas accumulates in a small range as the concentration is about 5%. The monitoring and prevention of the above areas should be strengthened. The field measured gas concentration distribution and gas influence range are consistent with the simulation results, and the research results can provide a reference for similar gas tunnel blasting construction and ventilation optimization.

The construction of a blasting network is challenging, with high risks and costs associated with blasting equipment. Considering the geological structure, physical and mechanical properties of the excavation target, and the detonation characteristics of the detonating cable, a delayed detonation network was designed to combine a digital electronic detonator and a detonating cord. This design replaced the digital electronic detonator with the detonating cord in auxiliary and peripheral holes within the same section. In contrast, a single digital electronic detonator was used to initiate detonation to reduce the networking complexity and improve the overall reliability of the network. Field tests conducted at Guangshan iron mine and Gemstone phosphate mine verified the applicability of this method in different mineral environments. The results show that the fusion delay detonation network can significantly reduce detonation equipment costs, simplify initiation network construction, improve cutting effectiveness, and reduce safety risks during excavating small-section roadways in iron mines. However, during the underground phosphate rock test, the unique geological structure and the properties of phosphate rock prevented the designed network from achieving the expected results, indicating a need for further research.

Researching blasting similar simulation materials for ultra-deep shaft surrounding rock and conducting physical model tests are the basis for studying the dynamic response law of ultra-deep shaft surrounding rock under blasting. This paper used the monzonitic granite in Xiling subsidiary shaft of Sanshandao gold mine as the simulation object to prepare similar granite materials. The iron ore powder and barite powder were selected as fine aggregates, the quartz sand was selected as coarse aggregate, the rosin alcohol solution was selected as binding material, and the gypsum was selected as adjusting material. The orthogonal design method was used to prepare the simulation materials. The mechanical parameters of similar materials with different proportions were determined, and the sensitivity analysis of each influencing factor and the blasting test of the simulated materials were carried out. The results show that the selected proportion can meet the requirements of indoor blasting model tests based on the specimen's density, unaxial compressive strength and elastic modulus. The proportion of fine aggregate in the total aggregate significantly affects the density of the simulated materials. The binder concentration significantly affects the compressive strength, tensile strength, elastic modulus and cohesion of the simulated materials. The proportion of gypsum significantly affects the internal friction angle of the simulated materials. The peak strain value in the model test block under high confining pressure is more significant as a whole, and the attenuation rate of the peak strain gradually decreases with the distance increase.

For the blasting and demolition project of a 130 m multi-tube sleeve chimney, the LS-DYNA finite element software was used to simulate the blasting incision by unit failure using a separated common-node model. The collapse process of the multi-tube sleeve chimney was numerically simulated, analyzed and compared with the actual blasting effect. The results show that the effective stress is mainly concentrated on the edge of the remaining part of the support when the blasting notch is forming. However, the notch closure stage of the falling speed is different due to the length and slenderness ratio and the nature of the material of the outer chimney and the inner sleeve are different. The simulation shows that the external chimney and the steel inner tube would be collisional at the notch closure stage as the internal and external detonation simultaneously. Choosing the detonation method with a delay of two seconds between internal and external components will achieve the ideal collapse effect.

Abstract: Vibration is a primary detrimental effect generated by blasting operations, and accurately evaluating its impact remains crucial and challenging. Based on the blasting excavation of a tunnel under the Central Yunnan Water Diversion Project, this study combines numerical simulation and field investigation to assess the damage characteristics of buildings affected by various factors. The results show that blasting vibration causes “X-shaped” cracks at the four corners of windows and doorways, while uneven settlement leads to 45° diagonal cracks. Subsequently, time-frequency analysis was performed on vibration data from buildings at varying distances from the blast source. The findings indicate that forced vibration predominates in building foundations, with minimal free vibration and quickly attenuating after the blasting load ends. As horizontal distance increases, the main frequency and blasting vibration energy exhibit a downward trend based on Fast Fourier Transform (FFT) analysis. However, the main frequency is less sensitive to distance changes than energy. Additionally, the sensitivity of energy to distance varies across different frequency bands. Generally, energy in each frequency band rapidly attenuates close to the blast source, with slower attenuation as distance increases. Furthermore, as the distance from the last source increases, there is a shift in energy from higher to lower frequency bands towards lower frequency bands, and the effect of low-pass and high-filter results in distinct variations in energy attenuation within different frequency bands. Finally, the study highlights a significant disparity between human perception of blasting vibrations and building safety standards. Based on this observation, a comprehensive evaluation method is proposed to combine structural damage assessment with considerations of the human settlement environment.

The rock mass joints can affect the propagation of explosive stress waves. The angle between their direction and the surrounding holes and the relative position changes have different effects on the blasting effect. Based on the attenuation law of stress waves at different jointed angles, a method was proposed for zoning the surrounding holes of tunnel blasting in jointed rock masses. The parameters of the surrounding holes are optimized when the angle between the joint and the surrounding hole is 30°, 60°, 90°, and 0° (parallel). The zoning layout method was validated by combining LS-PREPOST numerical simulation and on-site tests regarding rock damage depth and blasting vibration speed. The results show that the rock mass's damage depth and blasting vibration speed under the zoning arrangement of surrounding holes are significantly better than that of the original layout plan of surrounding holes. Based on the geological conditions of the research section of the Bayueshan Tunnel of the Tongliang Anyue Expressway, the angles between the joints and the surrounding holes are set to 30°, 60°, and 90°, respectively. The spacings between the surrounding holes are set to 43 cm, 50 cm, 58 cm, and 60 cm when the joints parallel the surrounding holes. The average over-excavation value can be controlled at 18cm after blasting, and the over-consumption of concrete is controlled within 100% per linear meter.

To carry out deep coal mining safely and efficiently, the dynamic mechanical characteristics and fracture mechanism of coal rock in deep earth were investigated under the ‘three high and one disturbance’ environment. A dynamic impact test of coal rock was carried out using the self-improved ϕ 50 mm high temperature synchronous split Hopkinson pressure bar (SHPB) test equipment at temperatures between 25~200℃. A ZWT viscoelastic constitutive model was also improved to establish a dynamic constitutive equation considering the temperature effect. The influence of high temperature on crack development law and the dynamic strength of coal rock was investigated based on the coupling of the finite difference and discrete element methods. The results show four stages to the dynamic stress-strain curve of coal rock under high-temperature impact: compaction, elastic, crack propagation, and softening failure. The dynamic compressive strength and dynamic elastic modulus of coal rock significantly decrease as temperature increases. In contrast, the failure strain increases, and the absorbed energy varies in a W-shaped pattern. The fractal dimension increases linearly as the particle size decreases. The degree and complexity of the fragmentation mechanism increase as the compressive strength decreases. Although the improved dynamic constitutive model based on ZWT could adequately express the stress-strain relationship following a high-temperature impact, it does not apply to the compaction stage. According to the simulation and test results, water and adsorbed gas actively escape in the coal rock at 150℃. The coal matrix is also heated and expanded, which induces cracks. There are apparent mesoscopic cracks initially and gradually developed through cracks, mainly shear ones. The crack development of coal rock under dynamic compression at 100℃ develops through the impact surface, and the high temperature deteriorates the strength of coal rock.