Abstract
In blasting excavation of neighborhood tunnels, damage accumulation process in surrounding rock is inevitable. To explore the influence of damage accumulation of rock mass under multiple blasting loads, we analyzed the vibration damage accumulation process of ultrasonic wave velocity of rock mass in shared rock of Liuyuetian neighborhood tunnel through ultrasonic test. Moreover, the effects of cyclic blasting loads on damage to the shared rock in the neighborhood tunnel were discussed and reported. The results demonstrate that the damage accumulation to the shared rock in the neighborhood tunnel is generated after multicycle progressive blasting operations. Influenced by cyclic blasting loads during the posterior excavating tunnel, the damage range of shared rock at the anterior excavating tunnel is 1.2 to 1.4 m, and the damage range of shared rock at the posterior excavating tunnel is 2.2 to 2.4 m. The damage range of shared rock in the posterior excavating tunnel is about 1.71 to 1.83 times that in the anterior excavating tunnel. Under blasting load, the stress concentration zone of shared rock is close to the blasting excavating face and is mainly within 2 m along the longitudinal axis of the tunnel. With continuous advancement of the blasting excavating face, the stress concentration zone moves forward continuously, and a striped stress concentration zone, which is approximately 2 m deep, is formed gradually. Thus, a method was proposed to determine the damage range of shared rock in the neighborhood tunnel during blasting excavation, as well as the variation law of damage. The experiences and conclusions presented can be used as references in the design and construction of similar engineering projects in the future.
Highlights
Drilling and blasting method has been widely used in mining, hydropower, transportation, and other industries due to its advantages such as low cost, simple construction technology, and possibility to deal with various shapes and sizes of openings [1,2,3,4,5]
Few studies have been conducted on the damage shape and size of shared rock in the neighborhood tunnel under cyclic blasting loads, and it lacks a principle to determine the sphere of influence of blasting
Rock mass is considered as a continuous material with original defects in the damage mechanics theory; that is, rock mass is a continuum with many cracks [50,51,52]. e damage can be regarded as the opening and expansion of the original cracks due to the propagation, reflection, and interaction of the explosion stress wave, resulting in the deterioration of the rock mechanical properties such as elasticity modulus, wave velocity, damping, and frequency [53,54,55]
Summary
Drilling and blasting method has been widely used in mining, hydropower, transportation, and other industries due to its advantages such as low cost, simple construction technology, and possibility to deal with various shapes and sizes of openings [1,2,3,4,5]. When the drilling and blasting method is used to excavate the rock mass in the neighborhood tunnel, the blasting vibration may influence the surrounding rock, support system, and lining structure of the tunnel significantly [6,7,8,9,10]. Few studies have been conducted on the damage shape and size of shared rock in the neighborhood tunnel under cyclic blasting loads, and it lacks a principle to determine the sphere of influence of blasting. The influences of surrounding rock at different levels and thickness of the shared rock on the lining structure of anterior excavating tunnel under blasting load of posterior excavating tunnel were analyzed by ultrasonic test.
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