Characteristics on Rock Fractures Induced by Different Excavation Methods of Deep tunnels

Transcription

1 International Meeting of CSRME 14th Biennial National Congress, December 2016, Hong Kong, China Characteristics on Rock Fractures Induced by Different Excavation Methods of Deep tunnels Shaojun Li State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil Mechanics, Chinese Academy of Sciences

2 Outline Motivations Method of rock fracture measurement Deep tunnels excavated by different methods Characteristics of rock fractures and hazards Conclusions

3 Wave 声波速度 velocity (km s (km/s) -1 ) Motivations Fracture of hard rock induced serious instability of deep opennings : Example of Jinping I underground caverns Large deformation Big fractures 68.8m borehole Fall of sprayed concrete No excavation Distance 岩体距边墙深度 to the side (m) (s) Fractured marble Excavation halted for more than 6 months

4 Rockbursts in deep openings are also related to fracture evolution Sidewall rockburst Notch left. depth : 2.0m Steel mesh destroyed Tunnel floor Fractured Width: 10 cm, depth: 1.0m Tunnels of Jinping II hydroelectric project

5 Novel Potential EDZ Fracture distribution abundant boreholes around surrounding rock mass Sit investigations were conducted to understand the correlation between fracture and tunnel stability and hazards

6 Method of rock fracture measurement Comprehensive measurement by acoustic wave velocity and digital borehole televiewer Recorder 声波检测器 水 Water 接收 Receiver 2 1# 接收 Receiver 1 2# 发射 Launcher 声波检测器 Recorder Acoustic wave apparatus (single or cross-hole method) Water 水 Launcher 发射 Receiver 接收

7 Digital borehole televiewer system Image of borehole wall and fractures

8 P-wave velocity (m/s) Comprehensive recognition of excavation damaged zone (EDZ) new fractures observed by digital borehole camera and P wave velocity, >0.2mm Tunnel sidewall Borehole bottom EDZ Test tunnel Monitoring Borehole Critical boundary of EDZ Borehole depth (m) Lower than 30% of average velocity of original rockmass

9 Deep tunnels excavated by different method CJPL-1: China Jinping underground laboratory Excavated in marble by TBM and D&B, full face m 2370m m 1800m 1 Tunnel D, 3 3.2m Auxiliary tunnel A 2-1 Headrace tunnel no.2, D=13.0m TBM Tunnel B and F, m Headrace tunnel no.3, D=12.4m Tunnel C, 3 3.2m

10 2400m Expande d area Expand ed area CJPL-II: China Jinping underground laboratory Pilot tunnel Middel part Bench Excavated in marble by D&B Excavation scheme: Three layers, top heading (8.5m) with pilot tunnel, middle of 4.5m, bench with 1.0 m

11 4.5 m 10.0 m 9.7 m Baihetan hydropower station Excavated at different layers in basalt Drillng and blasting method The current biggest one, main power house,dimision:434 34(31) 86.7 m (L W H) Axises of columns Dip angle Top heading Middle σ1 σ1 Bench 5 diversion tunnels 19.7 m

12 Characteristics of rock fractures and hazards Change of Excavation damaged zone Test tunnel C m 2.35m Borehole Test tunnel F m 4.25 m Borehole EDZ test tunnel C EDZ Test tunnel F Test tunnel B m 5.2 m. Borehole. No.3 headrace tunnel B orehole SZ1-1 EDZ test tunnel B φ12.4 m EDZ 2.7m Headrace tunnel More than 80 boreholes were pre-drilled before excavation

13 Statistics of EDZ under different tunnel sizes of CJPL-1 Tunnel No. Width of EDZ/EdZ (m) EDZ (ew) EdZ (dw) Tunnel section (m) Width (w) Height (h) Relationship with tunnel geometry R ew R eh Excavation method Test tunnel B Test tunnel C Test tunnel F No.3 headrace tunnel D & B ) (Full-face) D & B (Full-face) D & B (two benches) TBM (Full-face) R ew ew/ w R eh ew / h R ew and R eh are times of tunnel width and height (For D&B and fullface excavation method) R ew and R eh are 0.55 times of tunnel width and height (For D&B excavation with two benches) R ew and R eh are 0.22 times of tunnel diameter (For TBM excavation)

14 Borehole depth (m) Property of rock fracture induced by excavation In situ observation on tunnel sidewalls Rock spalling occurred but fractures can also be found in deep rock mass Broken rocks Borehole depth (m) 5 Fractures Flattered image of borehole wall No.3 headrace tunnel

15 Tunnel face Tunnel advancing direction New cracks ED12 Intersection angle between crack strike and tunnel axis: 1-5 Test tunnel C Tunnel advancing direction New cracks ED04 Tunnel face Intersection angle between crack strike and tunnel axis: Test tunnel B

16 Tunnel advancing direction Tunnel face Test tunnel F New cracks Perpendicular to tunnel axis ED08 ED06 Intersection angle between crack strike and tunnel axis: 3-40 Northern sidewall Southern sidewall No.3 headrace tunnel Tunnel No.3 headrace advancing tunnel axis: direction 302 TBM face New cracks 新生裂隙 Borehole SZ1-1 Intersection 隧洞轴线与裂隙走 angle between 向夹角 : 1 ~ crack 20 strike and tunnel axis: 1-20 Different direction of fracture can be found in D&B tunnels Fractures in TBM tunnel are almost parallel to axis

17 River side Fracture evolution and spalling Observation and calculation during the excavation layer , the workers heard a big sound, spalling happened inside the rock mass Following detail check found that there were many cracks along at the crown. Main power house of Baihetan Two borehole preinstalled

18 Observation and calculation during the excavation layer 3 Observation in the boreholes at m 11.0m 13.0m Date: m 12.0m 10.5m 10.0m 8.5m 8.0m 7.5m 9.5m 11.5m 7.0m 9.0m 11.0m

19 Observation and calculation during the excavation layer 3 Observation in the boreholes at 0+72 Date: m 12.5m 11.0m 10.5m 9.0m 8.5m Crack 12.0m Breakout 10.0m 8.0m 11.5m 9.5m Breakout 7.5m 11.0m 9.0m 7.0m Crack

20 Observation and calculation during the excavation layer 3 Observation in the boreholes at PB2:

21 Fracture evolution and rockburst Horizontal distance originated from the entrance of tunnel F(m) southern side wall Joints Joints Vault Stress relaxed zone Joint Corrosion fissure with the width of 2 to 10mm Northern side wall Rock burst zone Zone of monitoring facilities J18 Joints Rockburst pit Unfolded geological sketching of tunnel F in CJPL-1 project Rockburst occurred on January 09, 2010,with the volume about 6.3 m 3

22 Borehole depth (m) Borehole depth (m) Borehole depth (m) Borehole depth (m) Crack initiation and evolution 0.8m to the tunnel sidewall Rockburst occurred on Jan Brightening of crack tip Color change of crack tip (a)oct. 13, 2009, before excavation (b)dec. 22, 2009, 19.3 m 22.0 (a) 22.0 (b) excavated at the top heading of test tunnel F (c)dec. 28, 2009, 33.1 m Brightening of crack tip Brightening of crack tip excavated at the top heading of test tunnel F (d)jan. 03, 2010, the excavation was finished at the top heading of test tunnel F 22.0 (c) 22.0 (d)

23 2.0m to the tunnel sidewall Evolution of cracks before rockburst Rockburst occurred on Jan 09 (a)oct. 13, 2009, Preexisted cracks before excavation 19m 19 20m 20 (b)jan. 03, 2010, New cracks appeared in red line, the upper layer excavation finished 19m 19 20m 20 Collapsed area (c) Jan. 04, 2010, Abundant of new cracks appeared, 10.0 m excavated at the bottom layer 19 19m 20m 20 Collapsed area (d) Jan. 07, 2010, cracks run through, 21.0 m excavated at the bottom layer 19 19m 20m 20

24 Maximum crack width (mm) Change of macro cracks width in borehole M2-DB01 at different borehole depth Oct Jan Jan Jan Jan Tunnel face This borehole segment collapsed due to excavation Borehole depth (m) New cracks occurred, crack propagation and closure

25 Collapsed segment Wave velocity (m/s) Change of elastic wave velocity The decrease magnitude of elastic wave is up to 4% Tunnel face Borehole depth (m) The change of elastic wave of rock mass between monitoring boreholes M2-EW01 and M2-EW02 measured by cross-hole method

26 Borehole depth /m Time depended evolution of fracture in hard rock I II I New crack: 6mm II Crack development: 5mm I II I New cracks: 5mm II New cracks run Through: 2mm I II Width: 2mm Width: 5mm Width: 6mm Width: 6mm Width: 9mm 23.9 Cracks almost closed (a)2009/10/20 (b)2009/11/22 (c)2009/11/27 (d)2010/03/28 (e)2010/08/19 During Figure 18 excavation EDZ formation and evolution observed by digital borehole camera in branch tunnel C After excavation 8 months after excavation New cracks occurred and existed joint propagation and closure

27 Conclusions Important role of fracture in situ measurement for Formation and evolution process of excavation damaged Rock spalling process Rockburst evolution and prewarning Mechanism of stability of underground openings under deep environment and high stress condition

28 Thanks for your attention!