Research On Cumulative Damage Law Of Surrounding Rock In Circular Blasting Construction Of Tunnel Engineering

Drilling and blasting are used to build tunnels,and each construction cycle consists of one excavation footage.The surrounding rock is subjected to cyclic blasting.This paper uses the Jinjing single-track railway tunnel project in Sanming City,Fujian Province as a case study to explore the cumulative damage law of surrounding rock subjected to cyclic blasting by the application of various techniques including theoretical analysis,field measurement,numerical simulation,and orthogonal test.The results of this study can provide relevant theoretical direction for enhancing the construction safety and blasting dependability of tunnels that are constructed by drilling and blasting method.The primary results and conclusions are as follows:（1）Cyclic blasting in tunnel construction will cause periodic damage to the surrounding rock retained along the tunnel,and the damage area is funnel-shaped.The length of the periodic damage area is 1.5m.For the tunnel cross-section retained surrounding rock,in addition to the damage caused by the blasting action of the current excavation section,the blasting action of the latter excavation section will also create new damage based on existing blasting damage,forming cumulative damage.The length of the cumulative damage affected area was 40cm.The formation of cumulative damage affected area is affected by excavation footage length,Original damage distribution and blasting energy propagation.（2）Through dimensional analysis and fitting analysis,it can be known that:the periodic damage depth and width of the longitudinal retaining surrounding rock are positively correlated with the length of excavation footage;the length of the cumulative damage affected area of the retaining surrounding rock in the tunnel cross-section is negatively correlated with the length of the excavation footage.Under the condition that only the length of excavation footage is changed,the depth of the periodic damage is increases linearly related to the length of excavation footage;the length of the cumulative damage affected area is decreases linearly related to the length of excavation footage.（3）With excavation footage length,explosive density and explosive detonation wave velocity as test factors,through orthogonal test and weighted grey correlation analysis,the optimal combination is:the footage length is 1.3m,the explosive density is 1050kg?m^-3,the detonation wave velocity is 3900m?s^-1.It can be seen that,based on the original layout scheme of the hole on the tunnel face,reducing the length of excavation footage and selection explosives with relatively small density and relatively slow detonation wave velocity can reduce the damage of retaining surrounding rock and not affect the construction period too much.Timely initial support work can effectively reduce the cumulative effect of surrounding rock deformation under cyclic blasting.