According to the surrounding rock and surrounding environmental conditions, what development methods can be used for shallow buried tunnels?

According to the surrounding rock and environmental conditions, the development methods of shallow tunnel include single-side heading method, double-side heading method and multi-step method.

1, unilateral heading method

Unilateral heading method is suitable for tunnels with long span, low flatness and poor surrounding rock, and it is necessary to control ground settlement. The single-side heading method is suitable for soft surrounding rock with large cross-section span and difficult surface subsidence control. The key points of its construction are as follows: this section is divided into side wall pilot pit, upper step and lower step; The width of the side wall pilot hole should not exceed 0.5 times the width of the hole.

2. Double-side wall pit finding method

Double-side heading method is a way of tunnel excavation. Also known as double-sided guide hole method or glasses construction method. It belongs to a branch of NATM and is based on the basic principles of NATM. The double-side heading method is suitable for tunneling under the condition of V-class surrounding rock with poor surrounding rock. In the construction of shallow-buried long-span tunnel, the double-side heading method can control the surface settlement.

3. Multi-step method

Step method refers to the construction method that the upper section of the tunnel is excavated first (the upper step), and then the lower section (the lower step) is excavated after the upper step is advanced for a certain distance, and the upper and lower steps go hand in hand. According to the length of step, it can be divided into short step, long step and ultra-short step (micro-step) method.

Construction sequence of single-side heading method:

1, excavate the pilot tunnel first.

Micro-positive bench method is adopted, the upper half section is 2.5 ~ 3m ahead of schedule, five air-leg rock drills are used for drilling, smooth blasting, and the footage per cycle is 2.0 ~ 2.5~3m, with front shovel loader for ballasting and dump truck for transportation.

2, the first pilot tunnel support

According to the surrounding rock conditions and design requirements, anchor rod, shotcrete and screen mesh are used for support. Anchor holes can be drilled by car platform, with the spacing of 1.0× 1.0 and the length of 3.5m/ root. The initial sprayed concrete is 125px, and then the grid is erected with the longitudinal spacing of 1/m ... In order to ensure the construction safety, the middle wall needs temporary support, the anchor rod spacing is 1.5× 1.5, and the sprayed concrete is10 ~ 375px. ..

3. Right side excavation and support

It should be carried out after the left pilot tunnel is 50m ahead of schedule, so as not to affect the pilot tunnel construction. The excavation and support methods are similar to those on the left except that the temporary support of the intermediate wall is no longer used.

4. Inverted arch construction

After the lower part is excavated to the design elevation, the foundation can be cleaned and inverted arch construction can be carried out on one side, and the inverted arch on the other side should be carried out after the middle wall is removed.

5. Full surface lining

After the inverted arch and backfilling are completed, the side wall construction will be started, and the waterproof layer and other drainage facilities will be constructed according to the design requirements. At the same time, install and check all kinds of embedded pipe fittings and reserved holes to prevent wrong burial and missing burial.