Table 1 Design parameter of system bolts for XBS tunnels.

From: Mechanisms and optimization of system bolts in shallow four-track HSR tunnels based on deformation pressure theory

Rock grade

Type

Length

Array pitch

Installation position

III

\(\phi\) 32 mm Hollow grouting anchor

L = 5 m

2.0 × 1.2 m

Arch and sidewall

IV

\(\phi\) 32 mm Hollow grouting anchor

L = 6 m

1.5 × 1.0 m

Arch and sidewall

V

\(\phi\) 32 mm Hollow grouting anchor

L = 6 m

1.5 × 0.8 m

Arch and sidewall

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