Mechanical Response Characteristics Of Mechanical Behaviour Of Bolt Under The Joint Action Of Pre-tension Load And Blast Dynamic Load

Blasting operation is the most common mining operation method for underground mining.The tunnel bolt supporting structure is not only subjected to static load due to mining ground pressure,but also often affected by dynamic loads such as blasting.However,the mechanical behaviour and failure modes of rock bolt under combined action of dynamic and static loads are not further studied,which cannot meet the needs of rock bolt support design and mining blasting control.Therefore,it is very important to study the mechanical behavio ur of rock bolt under combined action of dynamic and static loads.Firstly,based on the Kelvin’s problem,the maximum instantaneous stress generated by blasting is regarded as the concentrated stress,a new approach was propose to describe the mechanical behaviour of fully grouted rock bolt under combined action of dynamic and static loads.And based on the reflection and transmission process of stress wave between the rock mass and the grouted section and the free sectio n,a new approach was propose to describe the mechanical behaviour of end anchoring-grouting rock bolt under combined action of dynamic and static loads.Secondly,basis for a new approach was propose to describe the mechanical behaviour of end anchoring-grouting rock bolt and fully grouted rock bolt under combined action of dynamic and static loads,the approach was applied to analyze the axial and shear stresses distribution characteristics of rock bolt under blast dynamic load according to the supporting conditions and parameters of Jinshandian iron ore.The results show that with the increase of the Young’s modulus of rock,the axial stress of rock bolt is decreased and the shear stress of rock bolt is increased firstly and then decreased,the axial and shear stresses decreased quickly with the distance between the point of interest and the blasting source increased,and the influence of the quantity of explosives on rock bolt is significant.The axial and shear stresses of fully grouted rock bolt are mainly distributed in a small region near the bolt collar under combined action of dynamic and static loads.The axial stress of free section of rock bolt is the same value and the axial stress at the interface between the free section and the grouted section of rock bolt rapidly increases to the peak value,and then along the grouted length decreased quickly.The peak shear stress occurs at the interface between the free section and the grouted section of rock bolt,and then along the grouted length decreased.The end anchoring-grouting rock bolt are less affected by the blasting dynamic load than the fully grouted rock bolt,and the fully grouted rock bolt are more likely to be destroyed under the action of blasting dynamic load.Then,the FLAC3 D numerical calculation software was used to analyze the mechanical behaviour of end anchoring-grouting rock bolt and fully grouted rock bolt under combined action of dynamic and static loads.The results show that the peak axial stress of fully grouted rock bolt occurs at the interface between the free section and the grouted section of rock bolt under dynamic load.The axial stress of free section of rock bolt is the same value and the axial stress at the interface between the free section and the grouted section of rock bolt rapidly increases to the peak value,and then along the grouted length decreased quickly.When the installation angle of the rock bolt is different,the axial stress of the rock bolt is also different under the action of dynamic load.The smaller the included angle between the installation direction of the rock bolt and the conduction direction of the dynamic load,the greater the influence of the dynamic load on the axial force of the rock bolt.The numerical calculation results verify the theoretical analysis results,and show that a new approach was propose to describe the mechanical behaviour of rock bolt under combined action of dynamic and static loads can reflect the mechanical response the mechanical behaviour of rock bolt.Finally,the optimization measures of tunnel bolt support under blasting dynamic load are studied according to the above research results.It is proposed t hat the end anchoring-grouting support bolt has good adaptability to blasting dynamic load,the dynamic load of tunnel should adopt the end anchoring-grouting rock bolt support.The grouting reinforcement of the broken rock mass in the soft rock roadway and the optimization measures for increasing the density of rock bolts and reducing the spacing of supporting rock bolts.The results of the paper provide theoretical basis for rock bolt support design,mining blasting control and blasting dynamic failure evaluation of supporting rock bolts,and further improve the end anchoring-grouting rock bolt and fully grouted rock bolt supporting theory under combined action of dynamic and static loads.