Study on influence of key blasthole parameters on tunnel overbreak

Abstract

To determine the influence of key blasthole parameters on tunnel overbreak during blasting construction, an intelligent detection system for tunnel blasting construction is independently developed. And the key blasthole parameters and overbreak of a typical section of a single line tunnel under the condition of Class V surrounding rock are analyzed and detected. The actual data obtained is compared with the results of numerical simulations and theoretical calculations. The results are as follows: (1) Quantitative analysis is performed based on the blasthole angle, opening position, and charge mass by the self-developed intelligent detection equipment for blasthole parameters, which can be used to guide the drilling construction. Intelligent scanning equipment for outline excavation can be used to image the actual excavation section in real-time and has the advantages of high precision and fast speed; (2) Tunnel overbreak can be regarded as consisting of two parts: the surrounding rock damage caused by the blasting load, and the collapse of the surrounding rock caused by the blasthole opening position. Every parameter of the peripheral hole will affect the tunnel overbreak; however, the key parameter is the blasthole opening position; (3) The distributions of the tunnel overbreak volume obtained with the theoretical analysis, finite element simulation, and measurements are basically consistent. Under the condition of Class V surrounding rock, the overbreak of this single line tunnel can reach 14.1–78.2 cm. To meet the specification requirements, the opening position and construction accuracy of the peripheral hole should be strictly controlled.