Construction stability and reinforcement technology for the super-large rectangular pipe-jacking tunnel passing beneath the operational high-speed railway in composite stratum

Figures & data

Figure 1. Project geographic location.

Figure 2. The Hangzhou-Shenzhen High-Speed Railway; (a) high-speed railway train; (b) tracks.

Figure 3. The Tianfei pipe-jacking machine.

Table 1. Main parameters of the pipe jacking machine.

Excavation size(width × height)	12620 × 7670 mm	Drive motors [quantity (power)]	24(30kW)+21(55kW)
Cutter head working pressure	3 bars	Rated speed [speed (diameter)]	0-1.3 (Φ3500) 0-1.06 (Φ4800)
Excavation form of the cutter head	Combined excavation	Rated torque [torque (torque)]	1214 (Φ3500) 3410 (Φ4800)
Excavation rate	100%	Screw conveyor	3 sets
Number of cutterhead	7	Maximum jacking force	119082 kN
Cutter head specification [Diameter(quantity)]	Φ3500 mm (4) Φ4800 mm (3)	Maximum jacking speed	40 mm/min

Figure 4. Detailed dimensions of segments.

Figure 5. Geological conditions.

Figure 6. The composite stratum.

Figure 7. Refined numerical model.

Figure 8. CDP parameters; (a) Cracking strain-damage parameter in tension; (b) Inelastic strain-damage parameter in compression; (c) Yield stress-crack strain curve in tension and(d) Yield stress-crack strain curve in tension in compression.

Table 2. Calculation parameters.

Surrounding rock	Density (kg/m^3)	Elastic modulus (MPa)	Poisson’s ratio	Internal friction angle (°)	Cohesion (MPa)
Weak rock	1860	210	0.37	18	0.0005
Hard rock	2500	6000	0.25	45	1
Track	7800	2.06 × 105	0.23	–	–
Ballast	2500	130	0.35	–	–
Sleeper	2450	3.15 × 104	0.2	–	–
Foundation	2300	2.80 × 104	0.33

Figure 9. Arrangement of measuring points of displacement, stress, and safety factor.

Figure 10. Schematic diagram of the composite stratum.

Figure 11. Track settlement of the high-speed railway.

Figure 12. Segment convergence of the pipe jacking tunnel.

Figure 13. Minimum safety factor of the pipe-jacking tunnel.

Note: The circumferential and the radial number represent the measuring point (i.e., Figure 9) and the minimum safety factor, respectively

Figure 14. Risk factors of pipe-jacking construction under high-speed railway.

Table 3. Risk classification of super-large rectangular pipe jacking under high-speed railway.

Likelihood (P)		Loss grade (C)
		1	2	3	4	5
		Disastrous	Extremely severe	Serious	Worth considering	Negligible
1	Frequent	Level I	Level I	Level I	Lever II	Level III
2	Possible	Level I	Level I	Lever II	Level III	Level IV
3	Occasional	Level I	Lever II	Level III	Level IV	Level IV
4	Rare	Lever II	Level III	Level IV	Level IV	Level V
5	Impossible	Level III	Level III	Level IV	Level V	Level V

Table 4. Risk level of pipe jacking under high-speed railway construction.

Hard rock ratio (n)	Probability level (P)	Loess level (C)	Risk level (R)
0	1	1	Level I
0.25	2	2	Level I
0.5	3	3	Level III
0.75	3	3	Level IV
1	4	3	Level IV

Table 5. Reinforcement schemes.

Scheme	Contents
1	The advanced grouting
2	The hand-dug pile + D-shaped beam
3	The diaphragm wall + D-shaped beam

Figure 15. Numerical model of reinforcement schemes.

Figure 16. Stress nephogram of the reinforcement models; (a) Scheme 1; (b) Scheme 2; (c) Scheme 3.

Figure 17. Track settlement of the high-speed railway.

Table 6. Maximum of track settlement (Unit: mm).

Hard-rock ratio(n)	Tunnel without reinforcement	Advanced grouting	The hand-dug pile + D-shaped beam	The diaphragm wall + D-shaped beam
0	5.78	2.96	1.65	1.59
0.25	4.59	2.76	1.62	1.57
0.50	3.60	2.39	1.59	1.56
075	2.74	1.85	1.42	1.34
1.00	2.57	1.78	1.31	1.26

Figure 18. Minimum safety factor of pipe jacking tunnel.

Note: The circumferential and the radial number represent the measuring point (i.e., Figure 9) and the minimum safety factor, respectively

Table 7. Minimum of safety factor.

Hard-rock ratio(n)	Tunnel without reinforcement	Advanced grouting	The diaphragm wall + D-shaped beam	The hand-dug pile + D-shaped beam
0	0.10	1.98	10.26	9.95
0.25	0.14	3.25	13.65	12.12
0.50	3.19	5.46	18.96	15.96
075	7.32	9.85	27.89	23.49
1.00	9.95	15.56	35.59	30.95

Table 8. Construction risk grade after reinforcement measures.

Hard rock ratio (n)	Tunnel without reinforcement	Advanced grouting	The hand-dug pile + D-shaped beam	The diaphragm wall + D-shaped beam
0	Level I	Level III	Level IV	Level IV
0.25	Level I	Level III	Level V	Level V
0.5	Level III	Level III	Level V	Level V
0.75	Level IV	Level IV	Level V	Level V
1	Level IV	Level V	Level V	Level V

Figure 19. Reinforcement scheme of the Hangzhou-Shenzhen Railway.

Figure 20. Site construction.

Figure 21. Construction scheme of pipe jacking tunnel crossing high-speed railway.

Figure 22. Monitoring equipment.

Figure 23. Track geometry monitoring system.

Table 9. Monitoring frequency.

Construction stage	The monitoring frequency
Before the jacking construction	Observe continuously for 7 days, and take the average value as the initial value
During the jacking construction	4 times / 1 day at least
After the jacking construction	Once a day
After the completion of main works	Once every 7 days for a month

Table 10. The double control value system.

Monitoring items	Warning value		Control value
	Cumulative value /mm	Speed/(mm/d)	Cumulative value /mm	Cumulative value /mm
Track settlement	± 1.6	0.8	± 2	1.0
Settlement of the subgrade, the pile top and the expanded foundation	−6-3	More than 1 for 2 consecutive days	−8-4	More than 1 for 3 consecutive days
Settlement of the temporary beam	−6-3	More than 1 for 2 consecutive days	−8-4	More than 1 for3 consecutive days
Vertical convergence of the pipe segment	−6-14	More than 2 for 2 consecutive days	−8-16	More than 2 for3 consecutive days
Transverse convergence of pipe segment	±6	More than 2 for 2 consecutive days	±8	More than 2 for3 consecutive days
Inclination of buildings (structures)	0.3/%	/	0.4/%	/
Surface subsidence	−6-14	More than 2 for 2 consecutive days	−8-16	More than 2 for3 consecutive days

Figure 24. Track settlement of high-speed railway.

Table 11. Comparative analysis of the field investigation and numerical simulation.

Monitoring items	Control value /mm	Numerical simulation/mm	Field investigation/mm
Track settlement	±2	1.52	1.46
Vertical convergence of the pipe segment	−8 ∼ 16	10.52	8.8
Transverse convergence of pipe segment	±8	6.46	5.8
The settlement of the D-shape beam	−8 ∼ 4	3.51	3.20
Pile top settlement	−8 ∼ 4	3.62	3.20
Inclination of buildings (structures)	0.4/%	/	0.1/%
Other	/	/	/

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article.