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3. Underground Cavern and 6. Case Studies-20210907/.DS_Store __MACOSX/3. Underground Cavern and 6. Case Studies-20210907/._.DS_Store 3. Underground Cavern and 6. Case Studies-20210907/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 2.0 (5 Marks) 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-turbines. 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 Herrenknecht 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 turbines 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 Herrenknecht 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-turbines, 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 carried 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 Poor 24 0.5 25 Questions: As the geotechnical engineer, you are asked to validate the design and provide the corresponding supporting systems for the underground powerstation and the main access tunnel (the overburden 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 Parameter Unit GSI=65 GSI=25 Hoek-Brown parameters mb 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 corresponding 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 (Carranza-Torres 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 Carranza-Torres 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 briefly summarise the potential failure types of the main access tunnel and underground powerstations, respectively, and provide the corresponding 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 Rubrics 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-20210907/._RSE3010 Assignment 3+6 Final-updated.docx 3. Underground Cavern and 6. Case Studies-20210907/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 2.0 (5 Marks) 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-turbines. 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 Herrenknecht and one