3. Underground Cavern and 6. Case Studies XXXXXXXXXX/.DS_Store
__MACOSX/3. Underground Cavern and 6. Case Studies XXXXXXXXXX/._.DS_Store
3. Underground Cavern and 6. Case Studies XXXXXXXXXX/RSE3010 Assignment 3+6 Final-updated.docx
RSE3010 Mine Geotechnical Engineering
Second Semester 2021
RSE3010 Mine Geotechnical Engineering
Second Semester 2021
Assignment 3 – Empirical Design and Support of Caverns (10 Marks)
Assignment 6 – Case Studies: Design of Snowy XXXXXXXXXXMarks)
Project Information:
The Snowy 2.0 project involves the delivery of a 2000 Megawatt pumped storage scheme in Australia. The project aims to provide increased storage capacity and security for the national electricity network. The proposed scheme will augment the existing 4100 Megawatt Snowy Mountains Hydroelectric Scheme, which is the largest hydropower complex in Australia. Snowy 2.0 combines a high head differential, long and deep waterway tunnels and six 340 MW reversible pump-tu
ines. It will link two existing reservoirs, Tantangara and Talbingo, through 27 km of waterway tunnels and an underground power station. The conceptual design of Snowy 2.0 is shown in Figure 1. Three tunnel boring machines (TBMs) of 11m diameter, two supplied by He
enknecht and one by CREG, are prepared to be delivered to the site and start excavation with drill+blast of the powerhouse caverns once access is achieved, and the photos of 3 TBMs are shown in Figure 2. TBM 1 will excavate the Emergency, Ventilation and Cable Tunnel from the surface in Lobs Hole down to the power station complex. From there, it will tunnel the inclined pressure shaft, linking the headrace tunnel (the upper waterway tunnel) to the large tu
ines within the power station. TBM 2 will excavate the Main Access Tunnel from the surface in Lobs Hole down to the powerstation complex. From there, TBM 2 will be dismantled underground and reassembled at the Talbingo Portal. It will then be shifted on a concrete cradle along the 700m-long Talbingo construction adit before being relaunched underground to excavate the tailrace tunnel. TBM3 will excavate 17km of the headrace tunnel.
Figure 1 Conceptual design of Snowy 2.0 pumped storage project (From Snowyhydro)
Figure 2 Three tunnel boring machines (TBMs) of 11m diameter, two (TBM 1 on Left and TBM 3 on Right) supplied by He
enknecht and one (TBM 2 in the Middle) by CREG (From Snowyhydro)
The main components of the underground powerstation complex are the machine hall, transformer hall and tailrace surge tank. These components are connected via the waterway tunnels, shafts and main access tunnels. The underground powerstation complex is located approximately 750 m below ground. The machine hall will be 30 m wide, 55 m tall and 238 m long. It will house the six pump-tu
ines, motor-generators, main inlet valves and auxiliary balance of plant. The transformer hall will be 21 m wide, 28 m tall, 204 m long and be located downstream of the machine hall. TBM 2 (diameter 11m) will excavate the Main Access Tunnel (the tunnel internal diameter 10m) from the surface in Lobs Hole down to the powerstation complex.
Figure 3 A typical cross-section of the machine hall (Left, 30 m wide and 55 m tall) and transformer hall (right) of Snowy 2.0 (From Chapman et al. 2019)
Geological mapping and borehole investigations are ca
ied out at the project sites. There are two critical geological ground conditions with good quality and poor quality of rock masses, respectively. The estimated rock mass classifications based on RMR, Q-system and GSI are listed in Table 1. The major and intermediate in-situ stresses are 2.3 and 1.5 times the vertical stress, respectively. Mechanical properties of intact sandstone samples from the tests are: σci = 65 MPa, Ei =27 GPa, σt = 9.5 MPa, v= 0.2, γ = 27 kN/m3, c = 4.2 MPa and Φ =34.6°. Two joint sets are observed and can be considered as very unfavourable for the main access tunnel. With a scan line of 285 m, a total of 2569 joints are counted.
Table 1 Estimated rock mass classifications of Snowy 2.0 Projects
Rock mass quality
RMR
Q values
GSI
Good
62
15
65
Poo
24
0.5
25
Questions:
As the geotechnical engineer, you are asked to validate the design and provide the co
esponding supporting systems for the underground powerstation and the main access tunnel (the ove
urden depth can be considered as 750m).
(1) Please estimate the rock mass parameters at the site of the main access tunnel. The below table is recommended to be used to summarise your answer.
Table 1 Rock mass parameters and plastic zone of the main access tunnel
Paramete
Unit
GSI=65
GSI=25
Hoek-Brown parameters
m
s
a
Uniaxial compressive strength
Triaxial compressive strength
Tensile strength
Deformation modulus
Mohr-Coulomb parameters
c
Φ
Kirsch solutions
Crown and invert
Side walls
Any failure
Hoek 1998 Analytical solutions
(2) By using the ‘Decision tree’, Martin’s empirical equation and Kaiser et al’s design chart, identify the dominant modes of failure and potential stress-induced failure depth of the main access tunnel, and compare these results and provide your comments on the failure types. The below tables are recommended to be used to summarise your answer.
Table 2 Quantitative data of Martin’s empirical method
GSI=65
GSI=25
Failure level
Table 3 Quantitative data of the Kaiser et al’s design chart
GSI=65
GSI=25
Failure types
Table 4 Quantitative data of the ‘Decision tree’ method
GSI=65
GSI=25
Failure types
(3) By using RMR based design chart, estimate the maximum and minimum unsupported spans and their co
esponding stand-up times of these two rock masses. What will be the stand-up time for the main access tunnel without support? The below table is recommended to be used to summarise your answer. The use of relevant charts by following the Lecture materials should also be presented to support your results.
Table 5 Quantitative data of the RMR based design chart
RMR=62
RMR=24
The minimum unsupported span (m)
The maximum stand-up time
The maximum unsupported span (m)
The minimum stand-up time
The main access tunnel span = 11m
The maximum stand-up time of the tunnel without support
Adjusted RMR
Support categories
Rock bolt sapcing (m)
Rock bolt length (m)
(4) By using the Q-value and Rock Support Chart, design the support for the machine hall, transformer hall and the main access tunnel, respectively. The below table is recommended to be used to summarise your answer. The use of relevant charts by following the Lecture materials should also be presented to support your results.
Table 6 Quantitative data of the Q-value and Rock Support Chart
Machine hall
Transformer hall
Main access tunnel
Span
Wall
Span
Wall
Span
Wall
Q values
ESR
De (m)
Support category
Bolt spacing (m)
Bolt length (m)
(5) By using the convergence confinement method (CCM) and RocSupport software, calculate the radius of plastic zones and factors of safety of the main access tunnels by selecting these two different solutions (Ca
anza-To
es 2004, Vrakas and Anagnostou 2014) for the shapes of the ground reaction curve (GRC). Please use the (1) Shortcut (reinforcement concrete with σci = 40 MPa, Ei =30 GPa, v= 0.2) to represent the TBM segment, (2) Support installation at the distance from the tunnel face of 3 m, and (3) in terms of Longitudinal Deformation Profile (LDP), select Vlachopoulos and Diederichs, 2009. List a table for the values including the Tunnel Section View and Ground and Support Reaction Curves. The below table is recommended to be used to summarise your answer. The RocSupport charts by flowing the Lecture materials should also be presented to support your results. Apart from the regular word submission, you are required to also submit the saved application file in RocSupport original format (.rsp).
Table 7 Quantitative data of the CCM and RocSupport
GRC Shape
Ca
anza-To
es 2004
Vrakas and Anagnostou 2014
GSI
65
25
65
25
Radius of plastic zone (m)
Radius of plastic zone after support (m)
Tunnel convergence (%)
Tunnel convergence after support (%)
Factor of safety
(6) Based on the above empirical and analytical results, please
iefly summarise the potential failure types of the main access tunnel and underground powerstations, respectively, and provide the co
esponding comments on the support methods.
Marking criteria (15 Marks)
Criteria
Description
Marks allocated
Quantitative calculation and/or qualitative clarification
Rock mass parameters and plastic zone
15%
Empirical methods for the main access tunnel
15%
RMR based Design Chart for the main access tunnel
15%
Q-value and Rock Support Chart
15%
RocSupport for the main access tunnel
10%
Summarise potential failure types and comments
10%
Formality and readability
According to the Marking Ru
ics of Assessment Format outlined in the ‘Report Format Guideline’
20%
Assignment submission
Please submit the assessment on Moodle. There will be penalty for late submission at a rate of 10% each day that the submission is late. This assignment is due on 26th September, 2021
Page 1
Page 4
__MACOSX/3. Underground Cavern and 6. Case Studies XXXXXXXXXX/._RSE3010 Assignment 3+6 Final-updated.docx
3. Underground Cavern and 6. Case Studies XXXXXXXXXX/RSE3010 Assignment 3+6 Final-updated.pdf
RSE3010 MINE GEOTECHNICAL ENGINEERING
SECOND SEMESTER 2021
Page 1
Assignment 3 – Empirical Design and Support of Caverns (10 Marks)
Assignment 6 – Case Studies: Design of Snowy XXXXXXXXXXMarks)
Project Information:
The Snowy 2.0 project involves the delivery of a 2000 Megawatt pumped storage scheme in Australia. The project
aims to provide increased storage capacity and security for the national electricity network. The proposed scheme
will augment the existing 4100 Megawatt Snowy Mountains Hydroelectric Scheme, which is the largest hydropower
complex in Australia. Snowy 2.0 combines a high head differential, long and deep waterway tunnels and six 340
MW reversible pump-tu
ines. It will link two existing reservoirs, Tantangara and Talbingo, through 27 km of
waterway tunnels and an underground power station. The conceptual design of Snowy 2.0 is shown in Figure 1.
Three tunnel boring machines (TBMs) of 11m diameter, two supplied by He
enknecht and one