Excavation and support construction methods for large-section tunnels crossing soil-rock boundary strata

Abstract

The invention discloses a large-section tunnel excavation and support construction method for crossing a soil-rock boundary stratum. The method comprises the following steps of first, upper middle step excavation and initial support construction, specifically, carrying out upper step excavation and initial support construction on a construction tunnel by a plurality of excavation sections from rear to front, and when any excavation section is subjected to upper step excavation and initial support construction, the process comprises the following steps of measuring pay-off, drilling and blasting construction, excavation and initial support of an upper cave, and excavation and initial support of a middle cave; second, lower step excavation and initial support construction; and third, carrying out secondary lining construction. The method is reasonable in design, simple and convenient to construct and good in use effect, the upper blasting area in the upper step and the middle blasting area on the middle step are separately subjected to blasting zone division, the arrangement position of each shot hole in each blasting zone is defined, the collapse of a tunnel face or the collapse ofa vault caused by large vibration generated by blasting when one-time loading of the large section is excessive can be effectively prevented, the safety and reliability of the tunnel excavation process are ensured, and the stability of the tunnel structure is ensured.

Description

technical field [0001] The invention belongs to the technical field of tunnel construction, and in particular relates to a method for excavating and supporting a large-section tunnel passing through an earth-rock boundary stratum. Background technique [0002] In the construction process of railway and highway tunnel projects, due to the limitation and influence of geological conditions, it will cause great influence and difficulties to the construction during the construction process. In the process of tunnel construction, various combinations of rock formations are often encountered, such as weak and uneven surrounding rock, shallow buried bias landform, soil-rock mixed geology and so on. For the excavation and support of tunnels that pass through soil-rock mixed strata (also known as soil-rock interface geology or soil-rock boundary strata), at present, the main methods in China are advanced pipe shed grouting support, advanced horizontal jet grouting pile reinforcement, ...

AI Technical Summary

Problems solved by technology

During the actual tunnel construction, the main problems of tunnel excavation in the soil-rock boundary stratum are as follows: first, the hardness of the rock and soil is not uniform, and the blasting of the weathered rock layer in the lower part will easily cause the upper soil layer to collapse, which is harmful to the construction personnel; second, the groundwater The enrichment area further softens the soil-rock boundary strata, causing serious deformation of the surrounding rock; third, the swelling of the expansive soil with water causes the primary support to deform and crack, and in severe cases, the deformed structure of the primary support arch will be damaged and the support capacity will be lost

Moreover, the loose load of the overlying soil basically acts on the initial support. When the inverted arch does not follow up in time and the initial support is not closed in time to form a ring, a closed stressed structure cannot be formed, resulting in insufficient bearing capacity, resulting in Subsidence of the floor and vaults, creating cracks

In addition, the insufficient bearing capacity of the loess tunnel foundation will also cause the tunnel arch foot to sink and cause cracks

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