Issue 47

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S.C. Li et alii, Frattura ed Integrità Strutturale, 47 (2019) 1-16; DOI: 10.3221/IGF-ESIS.47.01

In the similar model test, overload test is carried out after tunnel excavation. Keeping the coefficient of lateral pressure unchanged, increase the buried depth of tunnel step by step with the gradient of 50 m buried depth. That is to say, vertical loads at a specific buried depth are applied on the top of the tunnel and horizontal loads at corresponding horizontal in situ stress are applied on both sides of the tunnel to study the progressive failure characteristics of the tunnel. In the simulation calculation, the tunnel model is loaded in the same way. During the numerical simulation, the damage and failure of surrounding rock around the tunnel are as follows: (1) When loaded to 250 m buried depth, the damage and failure of surrounding rock is shown in Fig. 17. It can be seen that at this time, the surrounding rock has not been destroyed, and the surrounding rock in the tunnel top and bottom within about 1 times the diameter of the tunnel begins to damage, and a small part of the elements at the distance of about 1 times the diameter of the tunnel on both sides of the side wall also occurs damage. The maximum damage value of the element is 2, and it occurs at the vault and the inverted arch.

FLAC3D3.00

Step7230 ModelPerspective 10:50:26SatApr 302011

Step7230 ModelPerspective 10:51:44SatApr 302011

Center: X:0.000e+000 Y: -7.500e+000 Z:5.000e-001 Rotation: X: 90.000 Y: 0.000 Z: 0.000 Dist:3.918e+002 Mag.: 3.05 Ang.: 22.500

BlockContourofZoneExtra2

BlockGroup 4

0.0000e+000 to 1.0000e+000 1.0000e+000 to 2.0000e+000 2.0000e+000 to 2.0000e+000

Interval= 1.0e+000

ItascaConsultingGroup, Inc. Minneapolis,MN USA

Figure 17 : Damage and failure contour of surrounding rock.

(2) When loaded at 350 m burial depth, the elements closest to the free surface of the vault and inverted arch begin to fail, and the damage value of the element is the largest, reaching 16. The damage scope of surrounding rock at the top and bottom of the tunnel has expanded by two times, and the damage of the elements in the range of about 0.8 times of the tunnel diameter on both sides has also occurred. Fig. 18 shows the damage and failure of surrounding rock.

FLAC3D3.00

Step19893 ModelPerspective 21:05:41WedMar 302011

Step19893 ModelPerspective 21:03:44WedMar 302011

Center: X:0.000e+000 Y: -7.500e+000 Z:5.000e-001 Rotation: X: 90.000 Y: 0.000 Z: 0.000 Dist:3.918e+002 Mag.: 3.05 Ang.: 22.500

BlockContourofZoneExtra2

BlockGroup 4 fail

0.0000e+000 to 1.0000e+000 2.0000e+000 to 3.0000e+000 4.0000e+000 to 5.0000e+000 6.0000e+000 to 7.0000e+000 8.0000e+000 to 9.0000e+000 1.0000e+001 to 1.1000e+001 1.2000e+001 to 1.3000e+001 1.4000e+001 to 1.5000e+001 1.6000e+001 to 1.6000e+001

Interval= 1.0e+000

ItascaConsultingGroup, Inc. Minneapolis,MN USA

Figure 18 : Damage and failure contour of surrounding rock.

(3) When loaded to the 600 m burial depth, the failure area of the vault and inverted arch continues to expand, extending to the tunnel spandrels, and some elements at the waist of the arch begin to fail. The damage value of the elements at the vault and inverted arch within about 1 times the diameter of the tunnel reaches the maximum value of 20, which indicates that they have completely broken and lost their bearing capacity, as shown in Fig. 19.

FLAC3D3.00

Step30381 ModelPerspective 21:27:26WedMar 302011

Step30381 ModelPerspective 21:26:27WedMar 302011

Center: X:0.000e+000 Y: -7.500e+000 Z:5.000e-001 Rotation: X: 90.000 Y: 0.000 Z: 0.000 Dist:3.918e+002 Mag.: 3.05 Ang.: 22.500

BlockContourofZoneExtra2

BlockGroup 4 fail

Interval= 1.0e+000

ItascaConsultingGroup, Inc. Minneapolis,MN USA

Figure 19 : Damage and failure contour of surrounding rock.

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