Directional fracture blasting is widely used in rock control blasting, precise demolition, and resource extraction. To explore the effect of the slit in the borehole on the directional fracture blasting effect and optimize the directional fracture blasting technique, dynamic caustic line systems combined with numerical simulation are employed for this study, with PMMA used as the test specimen material. The result show that: slit blasting of the borehole has a significant directional fracture effect when compared with ordinary blasting, the length of cracks in the slit direction is significantly larger than that of ordinary blasting, and the length and number of cracks in the non-slit direction are significantly smaller than that of ordinary blasting. The slit in the borehole wall causes the blast energy to be released mainly in the slit direction and suppressed in the non-slit direction. Crack inhibition zone exists at the root of slit in the borehole wall. Once blasting produced the direction cracks in the slit direction, the surroundings of the blast hole wall will not produce cracks. Slit blasting can inhibit cracks near the slits, so as to achieve the purpose of controlling the direction of rock fracture. As the slit length increased, the major crack propagation length of the slits decreased before increasing. When the slit length increased to 5 mm (diameter-to-length ratio of 1.2), the crack propagation length was the largest, then the slit length continued to increase, the crack extension length did not change much. With the increase of the slit length, the peak value of the slit main crack propagation stress intensity factor and the peak value of the velocity show the trend of decreasing and then increasing, and the two peak values are the lowest when the slit length is 3 mm. The horizontal incident tensile wave reflected by rock mass defects and blast hole unloading waves increase the stress intensity factor and crack propagation rate, promoting crack propagation. Considering the blasting effect, the cost and time of drilling slits, it is more appropriate to choose a slit length of 0.5 mm (diameter-to-length ratio lambda is 12). The research results provide a certain significance of guidance for the slit blasting of the borehole wall in practical engineering.

Directional fracture blasting technology of the slit charge has broad application prospects in the drilling and blasting construction of the layered rock mass. In this paper, the method of model experiment and numerical simulation is used to preliminarily explore the fracture damage characteristics of slit charge blasting in the layered rock mass. The results show that the blasting effect of the slit charge in the layered rock mass is significantly different from that of the unlayered rock mass, and the pressure relief of the blasting gas at the layer is the main factor affecting the blasting effect. The length of directional cracks in the slit direction is significantly larger than that in other directions, and the directional fracture effect of the slit charge in the layered rock mass can still be played well. However, both the directional crack length and the damage range of rock mass in the slit direction gradually decrease along the detonation direction. In addition, the damage value of a single-layer rock mass also decreases gradually along the detonation direction. In engineering practice, the directional fracture effect of the layered rock mass can be improved by detonating at both ends of the slit charge at the same time.

Interconnected cracks are prefabricated on plexiglass plates (polymethyl methacrylate, PMMA) to study the effect of crack length on the initiation and propagation of interconnected cracks under impact loads. A new dynamic caustics test system was constructed to analyze the specimen's initiation process; the fractal method was used to quantify crack propagation; and the numerical simulation was used to monitor the specimen's full-field stress change. The results show that, with the direction of the impact loads as the axis of symmetry, interconnected cracks with different lengths and symmetrical angles, only the longer cracks initiate under the action of impact loads. With the increase in the length of one side of the interconnected crack, the crack initiation time is delayed, the trajectory of crack propagation becomes more irregular, and the peak propagation velocity of the crack increases first and then decreases. After the analysis, it was concluded that there is a certain competitive relationship in the crack tip propagation law between interconnected cracks with different lengths. In the energy storage stage, the tip of the longer crack is more likely to accumulate energy than that of the shorter crack, and it also has a suppressive effect on the energy storage of the latter. In the initiation and propagation stages, the energy at the tip of the uninitiated shorter crack will transfer to the tip of the longer crack, promoting its propagation. The research provides a basis for analyzing the initiation and propagation laws of interconnected cracks in practical engineering applications.

In order to study the influence of interconnected defects on the rock breaking effect under blast load, the relevant explosion experiment was carried out by prefabricating interconnected cracks on plexiglass plates (PMMA), and the propagation mechanism of interconnected cracks under blast load was studied from the length level. The dynamic caustic line system and finite element analysis software were combined to analyze the stress intensity factor, propagation velocity of the interconnected crack tip, and full-field stress of the specimen; the results show that with the radial stress wave propagation direction as the axis of symmetry, the two interconnected cracks with symmetrical angles but different lengths are under the action of blast load; there is a certain competition between the two cracks; the longer cracks are more likely to initiate and propagate, and the shorter cracks almost do not propagate. In addition, in terms of energy accumulation at the tips of the two cracks, the longer crack has a certain inhibitory effect on the shorter crack, and when the length of the longer crack remains unchanged, the inhibition effect weakens with the increase of the length of the shorter crack, and when the length of the shorter crack remains unchanged, the inhibitory effect increases with the increase of the length of the longer crack. After the crack initiation of the longer crack, the relationship curve between the stress intensity factor and the crack propagation velocity and time of the longer crack tip decreases first, and then the relationship curve rises to the peak as the energy of the tip of the shorter crack is transferred to the longer crack, and then the oscillation decreases, while the stress intensity factor and crack propagation rate of the shorter side crack tip show an overall downward trend. The numerical simulation is used to supplement the analysis of the stress propagation in the full-field of the specimen, which corroborates with the experiment results. The experimental study provides a theoretical basis for the analysis of the propagation mechanism of interpenetrating cracks under blast load in practical engineering.

The combination of the dynamic action of explosion stress wave and the static action of explosion gas expansion is what primarily drives rock-breaking blasting, and their different intensities lead to different blasting effects. Therefore, experiments were conducted to explore the damage behaviour of the surrounding medium caused by different blast-induced dynamic and static loadings using digital laser Schlieren and digital laser dynamic caustic systems. The results were as follows: In the air medium, when the explosives detonated, TATP (triacetone triperoxide) had the strongest quasi-static effect, and the highest velocity explosion shock wave and products compared with those of NHN (nickel hydrazine nitrate) and DDNP (diazodinitrophenol). Part of the TATP explosion product was ahead of the shock wave front, whereas for NHN and DDNP, their explosion products were behind the propagation of the shock wave front. The highest pressure peak of TATP was the result of the combined action of the shock wave and explosion product impacting the sensor. In the solid medium, NHN, the explosive with the strongest dynamic load, had the strongest stress wave and highest stress intensity factor peak of the main crack. The velocity reached the peak value at the early stage of propagation, and the dynamic action had a dominant effect on the cracking of the crack; the stronger the dynamic action, the higher the crack initiation energy. The stress intensity factor and propagation rate of the main crack of TATP with the strongest quasi-static effect decreased slower than those of the other explosives; therefore, the main crack propagation time and length were the longest. After cracking, the quasi-static effect dominated the process of crack propagation, where the stronger the quasi-static effect, the longer duration of the driving force of crack propagation. The research results provide a basis for customising explosives for different functions in practical engineering and realising the fine and efficient utilisation of explosion energy.

Imidazoline ionic liquids (IMILs) because of its unique performance in the synthesis, liquid phase extraction environment, energy and other fields have broad application prospects, for the safety of the unknown material, study the thermal decomposition characteristics and potential hazards is very necessary. The purpose of this study was to evaluate the risk of three IMILs during production, transportation, storage, and application using thermogravimetry (TG) and accelerating rate calorimeter (ARC). The influence of different lengths of alkyl substituents on ILs stability was systematically analyzed. The apparent activation energy (Ea) and pre–exponential factor (A) of IMILs were calculated by Flynn–Wall–Ozawa (F–W–O) and Coats–Redfern (C–R) methods. Then, the mechanical function of their decomposition reaction was obtained by using the C–R method. The kinetic compensation effect is discussed. Finally, according to the experimental data under adiabatic condition by accelerating rate calorimeter (ARC), it is proved that the runaway reaction of the three IMILs is slow. This study confirms the low potential harmfulness of the above three microorganisms, gives their safe temperature range, and provides a reference for their safe use.