Study Of Mechanism Of Smooth Blasting Combined With Water Jets Slotting In Soft-rock And Its Experiment

During the tunnel and roadway excavation process, the tunnel profile by blasting has the problems of poor flatness, serious excess under-excavation, great disturbance to the remaining rock, as well as easy collapse. Those problems are particularly prominent in the soft and broken rock excavation and tunneling process. Therefore, how to improve the shaping effect of soft surrounding rock in the tunnel under blasting and reduce the damage of blasting on the remaining rock is currently the urgent problem to be solved.To settle problem above, referring to Science Fund for Creative Research Groups of High-pressure Water Jets Rock Blasting Theory and Its Basic Application Research in Underground Engineering (50621403) and the National Natural Science Foundation of China of High-pressure Water Jet Assisting to Improve the Mechanism of Blasting the Soft Rock of the Tunnel to be the Joint Rate (No.50704039), combined with the characteristics of jet slotting and considering the characteristics of the soft rock engineering of tunnel, this paper introduces the directional jet slotting technology and put forwards the new method of slotting and blasting along the around eyes to achieve low-damage tunneling. This paper studies the cracking ,expansion and fracturing mechanism of soft rocks under the jet slotting from the perspectives of theory, similarity experiment and numerical calculation, preliminarily designs the experimental equipment which is suitable for low-damage tunneling of the soft surrounding rock and makes the on-site testing, achieving results.①Reveals the cracking and fracturing mechanism of rocks under the blasting after the jet slotting .In the soft rock blasting, the damage of rock is mainly the result of blast wave and explosive gas, Because of the jet slot, rock breaking efficiency of stress wave is weakened in the other direction. The wedging of the blasting gas results in high degree of stress concentration near the tip of the jet slot, force the rocks to fracture mainly along the jet direction.②Build the directed fracture model of the jet slot by the application of fracture mechanics and the blasting gas quasi-static theory, describe the pressure of the blasting gas is affected by several factors like the roughness on the fracture surface, crack width, crack length and other factors. Determine the fracture conditions of jet slotting hole and study the effect law of slotted geometry and the roughness(K) on the fracture surface for the blasting crack extension on the jet slotting holes. Point out an optimum the dynamic stress intensity factor of slot length to slot width: when the ratio factor is 4K, the dynamic stress intensity factor produced by the blasting gas in peak reaches a maximum.③Make blasting tests on the plexiglass plates after different size jetting and slotting with the dynamic caustics test system under blasting loading. The results show the law of distribution and extension: the cracks are more and distributed evenly after the blasting of the ordinary holes. However, the distribution is somewhat random. For the blasting effect of the test pieces after slotting, the main crack extension shows strong directional properties and is concentrated on the slot direction in a longest length. It has little short cracks and low damage on the wall of holes; compared with the ordinary hole, the slotted hole is easy to crack with long blasting loading effect and high degree of energy concentration.④Simulate the blasting after the jet slotted hole with ANSYS / LS-DYNA. The simulation analysis shows that under the effect of blasting and loading, the stress distribution near the slotted hole is different from that of the general holes. Due to the role of the jet slotting, the stress along the slot direction is strengthened, which is beneficial to the directed extension of cracks along the jet slot direction, realizing the purpose of directional cracking. At the same time, the directed extension of cracks along the jet slot direction is beneficial to the perforation of adjacent charge holes.⑤Through the field test of a highway tunnel through the coal seam, it shows that the application of water jet slotting in the smooth blasting of the soft surrounding rock in the tunnel can reduce the disturbance of the surrounding rocks and the damage on the remaining rocks by blasting, effectively increase the slotting rate of the eyes around by the smooth blasting and the flatness of the tunnel profile after blasting.The innovations of this paper:①It proposes a new method of assisting the soft surrounding rocks in the tunnel for the smooth blasting by water jet slotting, thus realizing the low-damage tunneling.②It reveals the mechanisms of rock fracture and cracks, extension of soft rock during blasting under jet slot. The directed fracture model of rock blasting under the jet slot is established.③Make a study on the distribution and extension principles of the blasting crack under the jet slotting with the caustics experimental system and obtain the proportional relationship between jet length and jet width when the dynamic stress intensity factor produced by the blasting gas reaches a maximum.