Large-span tunnel excavation method for upper soft and lower hard compound strata

Abstract

The present invention relates to a large-span tunnel excavation method for upper soft and lower hard compound strata. The present invention aims at providing a large-span tunnel excavation method for upper soft and lower hard compound strata so as to ensure large-span tunnel construction safety for the upper soft and lower hard compound strata, accelerate the construction progress and shorten the construction period. The technical scheme is that a tunnel is divided into upper and lower steps for excavation by the method, and the steps are as follows: a, determining a boundary of the upper soft and lower hard strata of an excavation surface according to geological prospecting data; b, constructing the upper step by using the center diaphragm method; c, constructing the lower step by using the method of reserving core soil; d, lagging the lower step with 2-3m headings at two sides; e, arranging earthwork cloth and an EVA waterproof board on a surface of a lower step inverted arch preliminary bracing, and pouring an inverted arch second lining; and f, dismounting a center diaphragm temporary bracing of the upper step and a temporary inverted arch of the upper step with segments, and pouring a pavement lining close to a preliminary bracing of the upper step and preliminary bracings of the headings at the two sides of the lower step. The large-span tunnel excavation method is applied to the technical field of tunnel construction.

Description

technical field [0001] The invention relates to a method for excavating a large-span tunnel in an upper-soft and lower-hard composite formation. It is suitable for the technical field of tunnel construction. Background technique [0002] In tunnel construction, the excavation method is one of the important factors affecting the stability of the tunnel, and it also restricts the construction progress and cost of the project. For large-span tunnels with Class III and IV surrounding rocks, the step method is often used for construction. There is a large working space in the tunnel, which is suitable for mechanized construction and the construction speed is fast, but the excavation surface is large and the relative stability of the surrounding rock is reduced; For the weak surrounding rocks of grades V and VI, the cross-middle partition method (CRD) is mostly used at present. It divides the large section into 4 or 6 small sections for construction, which can avoid excessive dam...

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Problems solved by technology

[0003] However, due to the heterogeneity of the stratum, the excavation section of the tunnel often appears in the composite stratum with soft top and hard bottom, that is, the upper part of the tunnel section is a soft soil layer, while the lower part is a harder soil layer or rock. It is usually level V, or even level VI; under this stratum condition, the applicability of the traditional step method or the cross middle partition method (CRD) is poor. With multiple excavations, the working space of the excavation surface is small, and mechanized construction cannot be realized, and the process is complicated and the construction progress is slow

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