Abstract
During the construction of newly built tunnel (NBT) adjacent to the existing service tunnel (EST), stability of the EST with small interval is affected by vibration waves which are caused by blasting load. The support structures of the EST will be cracked and damaged, while the unreasonable blast-excavation methods are adopted. Presently, the studies on behavior of support structure in the EST under blasting load are not totally clear, especially for the bolts system. Besides, the responses of support structure on blasting load are lacking comprehensive research. In this paper, New Zuofang tunnel is taken as a study case to study the influence of step blast-excavation in NBT on support structures of the EST through field experiment and numerical simulation. Some data, such as blasting vibration velocity (BVV) and frequency of support structures, are obtained through field measurement. Based on these data, the formula of BVVs is obtained. Research on stability of tunnel support structures affected by step blast-excavation is conducted using numerical simulation method. The dynamic-plastic constitutive model is adopted in the software ABAQUS to assess safety of support structures. The range and degree of damage for the support structures are obtained. In addition, change laws of axial force and stress with time for the bolts are analyzed.
Highlights
The structural types of tunnel with small interval exist widely in the tunnelling projects
It is necessary to carry out both experiments and numerical analysis to research the impact of blasting vibration velocity (BVV) on the support structures of the Existing service tunnel (EST)
Hisatake et al [1] have researched a dynamic method with respect to effects of adjacent blast operation on vibration behavior of the EST
Summary
The structural types of tunnel with small interval (less than 1.5 times of tunnel width) exist widely in the tunnelling projects. Zhang et al [17] have researched the vibration properties and change laws of middle wall and tunnel face in tunnel with small interval by vibration effect experiment of surrounding rock under blasting load. Yang et al [20] have researched the degree and range of rock masses damage in the EST under blast-excavation by using of twoside-wall pilot tunnel method. There are many successful cases in which the adverse influences of blast-induced vibrations on EST lining have been avoided or minimized, the studies on response of support structures of the EST under the blast-excavation are mostly only to analyze the damage cracking of concrete lining, while ignoring the influences on other support structures, such as bolts system and shotcrete. The responses of blasting load on bolts and shotcrete support are analyzed based on stress wave theories and vibration mechanics theories
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