A construction method for excavation and support of cross openings with holes first and then walls

Abstract

The invention provides a tunnel-before-wall-type crossed tunnel portal excavation supporting construction method. A tunnel is excavated before cavern side walls, after system supporting is completed,the tunnel extends into a cavern, temporary supporting is conducted to ensure site construction safety, locked anchor bars and countersunk anchor bars are implemented to protect intersections, pre-splitting holes are formed in the circumferential direction along the cavern side walls for blasting, rock mass, nearby the intersections, inside and outside the cavern side walls is separated, during later excavation of the cavern, the rock mass within the pre-splitting range is mechanically excavated, secondary blasting damage is avoided, and system supporting follows till the intersections are excavated. A scheme for solving the problem of excavation supporting of the large underground cavern intersections is provided for a tunnel-before-wall-type excavation mode, excavation forming of the intersections can be ensured to a great extent, stability of surrounding rock of the tunnel intersections and the cavern high side walls is facilitated, overexcavation is reduced, later backfilling of alarge amount of concrete is avoided, the construction period is shortened, and the engineering cost is saved.

Description

technical field [0001] The invention relates to a construction method for excavating and supporting a cross opening with a hole first and a wall behind, which is suitable for underground engineering fields such as hydropower and water conservancy. Background technique [0002] In modern hydropower and water conservancy projects, the caverns in the underground powerhouse area are huge, and the height of the main powerhouse and tailwater surge chamber is often hundreds of meters. The diversion tunnel, busbar tunnel, and tailwater tunnel intersect with it, and the height generally exceeds 15-20m. And the number is very large, forming a large number of tunnel entrance and exit intersections. These large intersections are subjected to complex forces, coupled with unfavorable factors such as large differences in geological conditions and high ground stress. After excavation, problems such as relaxation and collapse of surrounding rocks are more serious. The excavation is serious a...

AI Technical Summary

Problems solved by technology

The first excavation method is more commonly used, and there is no systematic solution for the second excavation method to solve the problems of intersection excavation formation and surrounding rock stability

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