| With the large-scale construction of Sichuan-Tibet,Yunnan-Tibet and other railways,a large number of ultra-deep buried tunnels have emerged.If the hole blocking effect of the cut hole is poor,the high ground stress environment will seriously affect the cutting effect,resulting in low utilization rate of the blast hole.In addition,for the tunnel with small section,the angle of the wedge cut hole is limited by the space.If the blocking effect of the cut hole is not improved,the footage can not achieve the desired effect.Therefore,it is necessary to explore the technology to improve the blocking effect of the cutting hole.In this paper,it is believed that the lack of friction between the gun mud and the hole wall is the main reason for the unsatisfactory blocking effect of the horizontal hole.Therefore,two composite hole blocking technologies,explosive hole blocking and wedge structure impact hole blocking,are proposed.(1)Explosive hole plugging technology utilizes the expansion characteristics of metal tubes under explosive loads to provide pre-pressure for the explosive hole plugging device to closely fit with the blasthole,thereby increasing the friction between the composite hole plugging device and the hole wall.In order to analyze the actual plugging effect of the explosion plugging device,the explosion experiment and mechanical experiment were used to study.Firstly,the maximum expansion size of the explosion plugging device is 6mm through the explosion expansion experiment.Secondly,the influence of two explosive loading methods of detonator and detonating cord on the friction between the plugging device and the hole wall is studied by uniaxial compression experiment.At the same time,the state of the plugging device after the experiment is analyzed and improved.The compressive strength of the improved explosive plugging device and the hole wall is 26.5～35MPa,and the shear strength is3.07～3.4MPa,which is much larger than the compressive strength and shear strength of the conventional gun mud.Then,the actual plugging effect of the explosive plugging device was studied by the cement pier blasting experiment.The results show that the combined use of the explosive plugging device and the gun mud can significantly improve the blasting effect.Finally,the application of straight-hole cutting in a tunnel is carried out to verify the effect of explosive plugging technology.(2)Wedge structure impact plugging technology utilizes the expansion characteristics of stemming under the impact of wedge structure to effectively enhance the friction between stemming and hole wall.In order to analyze the plugging effect of wedge structure impact plugging technology,static compression experiment and dynamic impact experiment were used to study.a.In order to analyze the effect of wedge structure on different positions of the hole wall,the static compression experiment is carried out first.In order to facilitate observation,the wedge structure is combined with the gun mud and filled into the organic glass tube.At the same time,the bottom of the gun mud is fixed,and then the wedge structure is axially loaded,and the strain curve of the outer surface of the organic glass tube is used to analyze the stress of different positions of the tube wall.The results show that the horizontal stress on the side of the wedge structure is twice that of the front,and the mortar under the wedge structure can exert uniform load on the pipe wall.In addition,increasing the angle of the wedge structure can reduce the horizontal pressure of the wedge.b.In order to simulate the plugging conditions in the field blast hole,the wedge structure is combined with different lengths of gun mud,and then loaded into the simulated blast hole for uniaxial compression experiment.The wedge structure is fixed on the hole wall by supporting member.The results show that the shear strength is 0.17 MPa when the 8cm mortar is filled in the simulated blast hole,and the shear strength of the wedge structure with the support member is about 0.39 MPa after the 8cm mortar is used,that is,the shear strength is increased by 1.3times,indicating that the wedge structure plugging method is obviously better than the mortar plugging method.In addition,under the influence of wedge structure,the shear strength of stemming increases with the increase of stemming length.c.In order to further analyze the dynamic process of wedge structure and gun mud in the hole,the wedge structure impact gun mud experiment and the gun mud impact wedge structure experiment will be carried out respectively.Among them,in the wedge-shaped structure impact mortar experiment,the PVDF pressure sensor is set at the end of the mortar to obtain the pressure peak under the impact of the wedge-shaped structure,and then the influence of the angle and speed of the wedge-shaped structure on the plugging effect is studied according to the change of the peak value,and the interaction process between the wedge-shaped structure and the mortar is analyzed according to the high-speed photography results.The results show that the impact of the wedge structure on the gun mud will go through three stages.When penetrating the gun mud,the pressure between the gun mud and the hole wall at the penetration site can be instantaneously increased,thereby increasing the friction between the gun mud and the hole.d.In the experiment of mud impact wedge structure,the interaction process between mud and wedge structure was recorded by high-speed photography system,and compared with the process of traditional plugging hole and wedge structure impacting mud.The results show that compared with the traditional plugging hole,the mud impact wedge structure can effectively suppress the movement of the mud;compared with the wedge structure impact mortar,the pressure rise speed between the wedge head and the hole wall is lower than that of the wedge structure impact mortar.Therefore,when the impact wedge structure of the stemming and the impact stemming of the wedge structure are used together,the blocking effect of the blast hole will be greatly improved.In summary,the two plugging technologies proposed in this paper can significantly improve the friction between the mud and the hole wall,thereby prolonging the action time of the explosive gas,thereby reducing the explosive unit consumption and improving the utilization rate of the hole,and achieving the purpose of improving the blasting effect.The relevant research results can provide a certain reference for increasing the footage of high-stress tunnels. |
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