Post on 17-Apr-2019
transcript
Alternative Rock Mass Classification for Tunnel
Design in Sydney
Robert Bertuzzi and Andrew de Ambrosis
Pells Sullivan Meynink
16th Australasian Tunnelling Conference
30 October - 1 November 2017, Sydney
Pells Sullivan Meyninkfrom Pells et al (1998) and Bertuzzi & Pells (2002)
Sydney Classification System
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Mapped as
Class I
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Mapped as
Class II
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Mapped as
Class III
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Scale
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Class I
Class II
Class III
Class IV
Class V
0.001 0.01 0.1 1 10 100 1000
Q
Ash
fiel
d S
hal
e
Class I
Class II
Class III
Class IV
Class V
0.001 0.01 0.1 1 10 100 1000
Q
Haw
kesb
ury
San
dst
on
e
Q values from Bertuzzi (2014)
𝑄 =𝑅𝑄𝐷
𝐽𝑛×𝐽𝑎𝐽𝑟×𝑆𝑅𝐹
𝐽𝑤
Insensitive to defect spacing category
Relatively insensitive to Class
Overlap
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Failure mechanisms
Shallow stress induced failure in combination with discontinuity and gravity controlled failure
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Discontinuity controlled, gravity induced falling and sliding of blocks, occasional local shear failure on discontinuities
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Stress-induced spalling
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Target
Factors important to tunnel design in Sydney
• The magnitude of insitu stress, which to the most part is
dictated by tunnel depth
• Intact strength
• Fracturing of the rock mass
• The position of bedding plane partings relative to the
excavated boundary of the tunnel
• The size of the tunnel.
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Intact strength
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Fracturing
In underground excavation, 25 MPa Hawkesbury Sandstone with joints at an
average spacing of 0.5 m behaves differently to massive 10 MPa Hawkesbury
Sandstone.
Yet both are Class III.
The presence of bedding plane partings or clay seams or fragmented zones close
to the excavated crown has a marked impact on tunnel support.
Dependent on the tunnel span. A bedding plane parting 1 m above the crown has
less of an impact on a 5 m wide tunnel than it does on a 20 m wide cavern.
It is suggested that critical height above the tunnel crown is 10% of the tunnel span
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Proposed Matrix
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Comparison
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