Field monitoring and numerical analysis of ground deformation induced by tunnelling beneath an existing tunnel

Figures & data

Figure 1. Location and cross-section of the metro line 3 and sewer tunnel

Figure 2. Crossing layout of metro line 3 tunnel and the existing Sewer tunnel

Table 1. Sewer tunnel description at the crossing location

Diameter (outer/inner diameter) for segments	5020/4570 mm
Type of segments	Reinforced concrete
Internal diameter of secondary lining (blue bricks)	4000 mm
Type of secondary lining (blue bricks)	Acid-resistant bricks
Location	from Km 21.70 to Km 21.71
Ring location	from ring 2514 to 2538
TBM axis and sewer axis crossing	Ring 2525
The vertical distance between extrados	3.3 to 3.70 m
Ground layers in the area	Sand/sand & gravel

Table 2. Slurry parameters for the used shield machine

Property	Normal	Alert threshold	Stoppage point
Yield value	9–12 Pa	8 Pa	6 Pa
Filtrate	18–20 ml	30 ml	40 ml
Density	1.10	1.15	1.25
Cake	1 mm flexible	2 mm flexible	2 mm brittle
Bontonite losses	25–30 m3	35 m3	50 m3
Difference supply vs return	200 m3/h	300 m3/h	400 m3/h
Average flow rate is 1280 m3/h
Air bubble level in the mucking chamber
Air bubble level	0.4 m (± 20 cm)	0.4 m (± 0.5 cm)	1.4 m (± 7 cm)

Table 3. TBM working parameters

Property	Normal	Alert threshold	Stoppage
Confinement pressure variation	0.2 bar	0.4 bar	0.5 bar
Volume of mortar injected per stroke	5.5–6.5 m^3	7.0 m^3	8.0 m^3

Table 4. Soil design parameters at tunnel crossing

Layer	Soil unit weight (kN/m^3)	Case of during construction		Case of Final Condition
		Shear strength parameters	Deformation parameters	Shear strength parameters	Deformation parameters
Made ground	17.0	c=0.0 ϕ = 27	E = 4 MPa ν = 0.3	Made ground	E = 4 MPa ν = 0.3
Silty clay	19.5	Cu = 90 kPa ϕu = 0.0	E u = 13 MPa ν = 0.49	Silty clay	Ed = 11 MPa ν = 0.35
Upper sand	19.5	c = 0.0 ϕ = 36°	E = 40 MPa ν = 0.3	Upper sand	E = 40 MPa ν = 0.3
Middle sand	19.5	c = 0.0 ϕ = 38°	E = 70 MPa ν = 0.3	Middle sand	E = 70 MPa ν = 0.3
Sand & gravel	20.0	c = 0.0 ϕ = 41°	E = 100 MPa ν = 0.3	Sand & gravel	E = 100 MPa ν = 0.3
Soil treated by Jet grouting	19.5	c = 50 kPa ϕ = 38°	E = 260 MPa ν = 0.3	c = 50 kPa ϕ = 38°	E = 260 MPa ν = 0.3
Lower sand	19.5	c = 0.0 ϕ = 38°	E = 120 MPa v = 0.3	c = 0.0 ϕ = 38°	E = 120 MPa ν = 0.3

Figure 3. Soil treatment underneath the sewer tunnel area at the intersection location

Figure 4. 3D Model dimension of soil and the two crossing tunnels

Table 5. Material properties of concrete, shield & grout

Material	Modulus of elasticity (E) [kN/m2]	Poisson’s ratio (ν)	Unit weight (γ) [kN/m3]
Concrete	30x10E06	0.2	25
Shield	25x10E07	0.3	75

Figure 5. Simulation of analytical stages of tunnelling by mixed shield machine

Figure 6. Simulation of shield excavation stages for the numerical model

Figure 7. Comparison between model results and measured data for vertical deformation

Figure 8. Comparison between model results and measured data for transversal deformation

Figure 9. Settlements at the crossing points of two crossing tunnels at different angles

Figure 10. The relation between the crossing angle and maximum settlement at the crossing point

Table 6. The maximum settlement at the crossing point for various crossing angles, φ

Condition around Existing tunnel		Clearance distance (Cr)	Max. Settlement, mm
Without ground treatment,	φ = 22o	0.7D	10.9
	φ = 90o	0.7D	8.9
With ground treatment,	φ = 22o	0.7D	7.3
	φ = 90o	0.7D	6.7

Figure 11. The vertical clearance, C between the two crossed tunnels (C is related to the existing tunnel; 1.5D = 7.5 m)

Figure 12. The maximum settlements at the crossing point of the two crossing tunnels at different clearance distances

Figure 13. Variation of principal stresses (σ₁, σ₂, σ₂) in the existing tunnel lining

Figure 14. Von-Mises stresses in the existing tunnel lining

Figure 15. Settlements at the crossing points with different characteristics of treated soil

Figure 16. Settlements at the crossing point at different face pressures with and without soil treatment