The Expansion Law Of The Surrounding Rock Loose Circle In The Roadway Under Multiple Blasting Loads

In the excavation project of coal mine roadway,the drilling and blasting method is an efficient and economical excavation technology,it also easily leads to a series of disasters such as roadway instability.At present,it is one of the effective means to solve the problem of roadway stability during blasting construction by studying the evolution law of surrounding rock loose circle under blasting load and supporting roadway according to loose ring support theory.Hence,based on the theory of loose circle support,this paper uses theoretical calculation,laboratory test,numerical simulation and engineering measurement to analyze the expansion law of surrounding rock loose circle under multiple blasting loads,and provide theoretical basis and engineering experience for blasting technology and roadway support.Based on the Hawke Brown's strength criterion and elastoplastic theory,this paper analyzes the two parameters of disturbance parameters and surrounding rock strength,and introduces the value and calculation of engineering parameters in the macroscopic view,and the “early” weakening effect of the surrounding rock strength is supplemented in the mesoscopic view.At the same time,based on the previous research on the plastic zone in front of the blasting work,the relationship between plastic deformation and mesoscopic damage factors of sandstone was obtained by using the indoor triaxial loading test and mesoscopic observation test.It is preliminarily believed that the plastic zone in front of the blasting work is the “early” weakening zone of the surrounding rock strength.Then,based on the blasting and excavation project of Qingyuan Tunnel,the surrounding rock in front of the tunnel was probed by geological radar,and the damage range of the surrounding rock in front of the hand was obtained.The paper determines the existence of the “early” weakening zone of the surrounding rock strength in front of the blasting work,and supplements the theoretical calculation formula and engineering application of the loose circle radius considering the mesoscopic damage.In order to obtain the expansion law of surrounding rock loose circle under multiple blasting conditions.Based on the blasting and tunneling project of Baoyuan Coal Mine Pipeline,the numerical simulation of roadway blasting and excavation is carried out by using 3DEC and LS-DYNA procedures,and the field measurement is carried out by using the transient electromagnetic instrument.Through the statistical analysis of numerical simulation and engineering measured data,the expansion law of loose ring under multiple blasting load conditions is obtained.The research shows that the expansion of the surrounding rock loose circle of the roadway under multiple blasting loads can be divided into two stages: forming stage and expanding stage.The loose ring is mainly formed in the forming stage;in the expansion stage,the surrounding rock of the roadway is affected by multiple blasting,and the range of the loose circle will increase(the growth rate is 2%-8%).The loose circle of surrounding rock in the roadway shows anisotropy under multiple blasting loads.In the forming stage,the range of loose circle in the roadway's sides is larger,and the range of the loose circle of the roof and bottom in the roadway is smaller.In the expanding stage,the range of loose circle in the roadway is small(2%-3%),the range affected by the blasting load is small(2-3 times footage),and the range of the loose circle of the roof and bottom in the roadway is greatly increased(4%-10%),the range affected by the blasting load is large(3 times footage).The transient electromagnetic oscilloscope was used to detect the pipe roadway of Baoyuan Coal Mine.The detection found that due to the blasting effect,the range of the loose circle in the roadway roof was gradually stabilized from 1.04 m to 1.11 m(increased by 6.7%),and the range of the loose circle of the roadway bottom was gradually stabilized from 1.07 m to 1.12 m(increased by 4.6%),and the range of the loose circle of the roadway left side was gradually stabilized from 1.15 m to 1.17 m(increased by 2.6%),and the range of the loose circle of the roadway right side was gradually stabilized from 1.10 m to 1.13 m(an increase by 2.7%).Based on the research conclusions and the loose circle support theory,the design parameters of the pipe roadway support of Baoyuan Coal Mine are optimized,and the stability of the surrounding rock of the roadway is better after optimizing the support scheme.