How Does Self-drilling Hollow Bolt Replace Leading Small Conduit in Conglomerate Layer

The underground excavation section between East Diaoyutai Station and Baishiqiao South Station of Beijing Metro Line 9 is mainly located in the Quaternary pebble layer and the Tertiary strongly weathered conglomerate layer. When the excavation reaches the full conglomerate section, the tunnel outline is all in the conglomerate layer, and the groundwater is abundant. The grouting support method with advanced small conduit was originally designed, but due to the high hardness of the conglomerate layer, the small conduit could not be driven in, resulting in an unsatisfactory grouting effect and continuous water leakage in many places in the tunnel. In order to ensure the normal construction, after many tests, the self-drilling hollow grouting bolt support method was finally selected.

Combined with the previous self-drilling hollow grouting bolt pipe diameter and wall thickness test, a φ30x5.0 mm bolt with a pipe length of 2.5 m and a cross alloy drill bit were used for construction. The grouting grout is made of cement and water glass double grout: after the bolt is grouted, a dense hard shell with a thickness of 1.5 m is formed within 140° of the section vault, so as to achieve the purpose of strengthening the stratum and stopping water.

It has been verified that the construction effect of self-drilling hollow grouting bolt construction and the original small conduit construction is as follows:

1. Improve soil reinforcement effect

In the original design, the grouting slurry diffusion radius of the small ducts in the vault is 0.5 m, and the maximum thickness of the grout reinforcement is 1.0 m. The grout reinforcement thickness of self-drilling hollow grouting bolt is 1.5 m, which is significantly improved compared with the original scheme.

2. Improve grouting water leakage phenomenon

There are many water seepage points in the vault before using bolt grouting, while the section vault of self-drilling hollow grouting bolt grouting is relatively dry, and the water leakage phenomenon has been well improved.

3. Reduce the amount of settlement

According to the monitoring data, the daily settlement of the vault with the standard section of the advanced small duct can reach a maximum of 2mm, the cumulative settlement of the vault reaches 8-9 mm when the settlement tends to be stable, and the maximum cumulative settlement is 12mm; self-drilling hollow grouting bolts The daily settlement of the vault is controlled within 1 mm, the cumulative settlement is 6-7 mm when the vault settlement tends to be stable, and the maximum cumulative settlement is 9 mm.

In summary, through the analysis and comparison of the construction of the test section, for the strata that are not easy to form holes with small pipes such as pebbles and conglomerates, the self-drilling hollow grouting bolt construction can improve the soil reinforcement effect, improve the water seepage phenomenon, and can improve the efficiency of soil reinforcement. The advantages of reducing sedimentation and so on.

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Created on Mar 26th 2022 21:36. Viewed 211 times.

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