Research Of Construction Parameter Optimization On Large-Cross Section Tunnel Based On Accumulative Damage Effect Of Surrounding Rock

Zhang Guohua (Engineering Mechanics) Directed by Prof. Liu MingguiBlasting, as an economical efficient shortcut method in rock mass engeneering excavation, has been widely used more and more. Yet blasting construction of Small clear distance tunnel not only causes rock mass crashed and peeled in blasting area, but also inevitably causes damage to nearby rock mass and vibration in moderate or remote areas as well. It is more outstanding to damage effect of rock mass in repeated frequently blasting operations. For example, accumulative damage of surrounding rock is significant in tunnel with large section excavating with two side-wall pilot tunnel method. damaged rock mass will threaten the security and stability of the rock mass due to inferior mechanics function, weaker rock strength and worse integrality. Character of rock mass accumulative damage in repeated blasting dynamic load and the control damage have always been one of the key techniques during construction, and is also a great concernin blasting and rock mechanics at home and abroad.Damaoshan tunnel with large section and small clear-distance is relied on in this paper, the on-site supervision measure of internal displacements of surrounding rock, blasting vibration velocity, acoustic wave velocity of rock mass are carried out. It was shown that the surrounding rock of the tunnel constructed by double side-wall heading excavation method would unavoidably be damaged in a certain degree because of repeating blasting, especially the interlaid rock wall in tunnel groups with closely-spaced. The more near the explosion source, the more big the extent of the damage degree and the displacement amount of the surrounding rocks, the more far the explosion source, the more small in advancing to-and-fro blasting load operations for any one of section.In construction of large cross-section tunnel with double side-wall heading excavation method, it is contradictory to control both damage extent and damage scope. The most optimization of construction method should be researched in engeneering practice, based on the character of surrounding rock and engeneering. In construction of large cross-section tunnel with double side-wall heading excavation method, accumulative damage scope of surrounding rock in any one of section is made up of blasting damage and vibration damage that develops from blasting damage. The evolvement of accumulative damage scope of surrounding rock that blasting damage happed when the excavating face of pilot tunnel I gradually is close to section. The damage increment, that caused by sigle blasting is the most close to section, is bigger than the sum of damage increments before blasting operations. The accumulative damage scope of surrounding rock is mainly determined by the blasting of excavating face of pilot tunnel I which is parallel to it. Vibration damage consist of distortion damage and fatigue damage of surrouding rock. Vibration damage is dominant for near excavating outline rock.The blasting dynamic load and anisotropic damage model of rock realized by software DYNA and UDEC can better simulate the accumulative damage range of surrounding rock in advancing to-and-fro blasting load operations. Based on the exciting tunnel save condition, construction of new tunnel, support parameters and cost et al factor, the result of numerical method is that the optimized sigle repeated excavating length is 1.2m.When sigle repeated excavating length of Damaoshan tunnel is 1.2m, the supervision results of internal displacements of surrounding rock and structure stress indicate the existing construction techonolog and support parameter is feasible, because of controllable surrounding rock distortion, stable surrounding rock, small operation force of support structure. Despite the construction technology is complexitical, the surrounding rock is stable.