Stability of a Rock Tunnel Passing through Talus-Like Formations: A Case Study in Southwestern China

Table 3

Configuration of dynamically adaptive support system in talus-like formations in Tayi tunnel.

Supporting system		Vd-1	Vd-2	Vd-3
Presupport		φ76 × 6 pipe shed, 9 m length, 6 m × 30 cm spacing, splicing length ≥3 m
Primary support	Mortal anchor	φ25, 60 cm × 120 cm spacing
		3.5 m length	4 m length	4 m length
	Steel mesh	φ8, 20 cm × 20 cm spacing
	Steel arch	60 cm spacing
		I 22b	I 25b	Double layer
	Shotcrete	C25
		28 cm	31 cm	Double layer
	Foot reinforcement bolt (each side)	Upper bench: φ42 × 2, 4.5 m length	Upper bench: φ42 × 2, 5 m length	Matched to steel arch
		Middle bench: φ89 × 2, 6 m length
		Lower bench: φ89 × 1, 6 m length
Reversed deformation		30∼35 cm	35∼40 cm	35∼40 cm
Secondary support	Reinforced concrete	C30
		50 cm	60 cm	60 cm
	Reinforcement	N1: φ22@20	N1: φ[email protected]	N1: φ[email protected]
		N2: φ22@20	N2: φ22@20	N2: φ22@20
		N3: φ14@30	N3: φ14@30	N3: φ14@30
		N4: φ8@30	N4: φ8@30	N4: φ8@30

Note: the primary support for Vd-3 is in the form of double-layer as shown in Figure 15. The unit for diameter of pipes, anchors, and steel bars is mm. The steel bars in N1, N2 and N3 are HRB 400 while the ones in N4 are HPB 300.