gl shrestha tunnel design steps

8/17/2019 GL Shrestha Tunnel Design Steps

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TUNNEL DESIGN STEPS

DR. GYANENDRA LAL SHRESTHACEO, NYADI HYDROPOWER LTD.

19 DECEMBER 2014


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3 Main Effects of Underground Excavation X-Sections)

Rock block falls

locally

Water runs in to

tunnel

Stress c

after ex


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Preliminary Support Estimation By Empirical


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Final support chart for Headrace Tunnel.

0

100

200

300

400

500

600

700

0.01 0.1 1 10 100

D e p t h

Q*

Support type ISupport type IISupport type III

Support type IV

Squeezing zone


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Empirically Estimated Preliminary Supports

StructureSpan/

Height (m)ESR De

25 mm dia

Rock Bolt

Length (m)

Class I

15


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Assessment of stress condition

Depth (m) 100 200 300 400 500

Unit weight (kN/m3) 25 25 25 25 25

Major Principal Stress – σ1 (MPa)

2.5 5 7.5 10 12.5

Unconfined CompressiveStrength (UCS) - σci

22 22 22 22 22

Maximum Tangential

Stress (σφ)

5 10 15 20 25

σci/( σ1) 8.8 4.4 2.9 2.2 1.7

σφ /σci 0.2 0.4 0.7 0.9 1.1

SRF Category J/K K/L L/M M O/N


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Overburden and Q* values for support Class I, II, III

SupportClass

Cover (m)

100 200 300 400 500 600

SRF 1 1 2 3 4 5

Class I 15 15 30 45 60 75

Class II 4 4 8 12 16 20

Class III 0.4 0.4 0.8 1.2 1.6 2

Class IV 0.04 0.04 0.08 0.12 0.16 0.2


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Preliminary Support Class Boundaries WithQ* and Overburden

0

100

200

300

400

500

600

700

800

0.01 0.1 1 10Q* Value

O v e r b u r d e

n ( m )


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Class II, 600m, GSI 80 at 100% Relaxation

Shear

Tension

ShearTension

Both

Sigma 1

MPa

0.00

3.00

6.00

9.00

12.00

15.00

18.00

21.00

24.00

27.00

30.00

2 0

1 5

1 0

5

250 255 260 265 270 275 280


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Axial force in Bolt - Class II, 600m, GSI 80100% Relaxation


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Phase2 Output –Support Class Boundaries wQ* & Overburden depth

Support

Class

Cover (m)

0 100 200 300 400 500

Class I 15 15 20 30 45 70

Class II 4 4 4.2 8 15 25

Class III 0.4 0.4 0.6 0.8 1.2 2

Class IV 0.04 0.04 0.05 0.08 0.12 0.2


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Revised Support Requirements for DifferenRock Class

Structure

Span/

Height

(m)

ESR De

25 mm dia

Rock Bolt

Length (m)

Class I

15


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Boundaries for support class I to IV with Q*Verses Overburden

0

100

200

300

400

500

600

700

0.01 0.1 1 10 100Q* Value

O v e r b u r d e

n ( m )


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Support Class Boundary Before and After Ana

0

100

200

300

400

500

600

700

0.01 0.1 1 10 100

Tunnel supports

Q* Value

O v e r b u r d

e n ( m )


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Hoek & Marinos Method (2000)

σ cm = (0.0034 mi0.8) σci {1.029+0.025 e

(-0.1 mi) }GSI

Ε = δi/do = [0.002-0.0025 pi/po] (σcm /po)(24 pi/po -2)


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Squeezing Based on Strain - Hoek and Marino

Depth (m) 55 69 155 330 525

Q* 0.02 0.04 0.4 4 15

Major principle stress σ1 MPa 1.375 1.725 3.875 8.25 13.12

GSI 10 15 36 56 68

Percentage Strain in ε* 1 1 1 1 1


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Squeezing Demarcation Line

0

100

200

300

400

500

600

700

0.01 0.10 1.00 10.00Q* Value

O v e r b u r d e n ( m )


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Details of support for squeezing tunnel


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Capacity Check of RC Liner - SqueezingTunnel, 500m, GSI 56 at 100% Relaxation


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Final support chart for Headrace Tunnel.

0

100

200

300

400

500

600

700

0.01 0.1 1 10 100

D e p t h

Q*

Support type ISupport type IISupport type III

Support type IV

Squeezing zone


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Primary Supports for Headrace Tunnel

Structure

Span/

Height

(m)

ESR De

25 mm dia

Rock Bolt

Length (m)

Class I

15


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Unlined Tunnel


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Shotcrete and rockbolt support


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Tunnel With Steel Rib Supports


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Concrete Lined Tunnel


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Conclusion and recommendation

• The support chart considers two variables

namely, overburden depth and Q*-value, couldrealistic.

• It prescribes support needed for squeezing tun

• As it also includes outcomes of Numerical mod

helps to make construction period optimum aproject cost economic.

• It is recommended to develop similar chart latdetailed design.


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THANKS

gl shrestha tunnel design steps

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