RELOCATION OF SHATIN SEWAGE TREATMENT WORKS TO CAVERNS: Caverns and - PowerPoint PPT Presentation

Agreement No. CE 30/2014 (DS) RELOCATION OF SHATIN SEWAGE TREATMENT WORKS TO CAVERNS: Caverns and Sewage Treatment Works – Investigation, Design and Construction Rock Reinforcement Approach for Tunnelling 30 May 2019 (Thursday) Guy Bridges

Innotech Forum on Geotechnology 1. History of Cavern Development in HK 2. Recent Cavern Studies in HK 3. Overseas Examples of Treatment Plants in Caverns 4. Relocation of Sha Tin Sewage Treatment Works to Caverns 5. Cavern Design 6. Rock Reinforcement Approach 2

History of Cavern Development in HK 1985: MTR Station (Tai Koo) 1997: Explosives Depot (Kau Shat Wan) 2009: Western Service Reservoir (HKU) 1980 2000 2010 2020 1990 1985 1995 2005 2015 1997: Island West Transfer Station 2014: MTR Station (HKU) 1984: Western District Aqueduct 1985: MTR Station (Sai Wan Ho) 1995: Stanley Sewage Treatment Works 2010: Explosives Depot (MTR WIL) 2015: MTR Station (Sai Ying Pun) 2016: MTR Station (Admiralty) MTR Station (Lei Tung) MTR Station (Ho Man Tin) 3

History of Cavern Development in HK Relocation of Sha Tin Sewage MTR Station (Sai Ying Pun) Treatment Works Completion Year: 2015 • Category: Water Category: Transportation • • Max. Span: 32m Span: 22.8m • • Rock Type: Granite Rock Type: Granite • • Western Service Reservoir Completion Year: 2009 MTR Station (HKU) • Category: Water Completion Year: 2014 • • Span: 17.6m Category: Transportation • • MTR Station (Ho Man Tin) Rock Type: Tuff with Span: 22.4m • • Completion Year: 2016 • sedimentary bed Rock Type: Granite • Category: Transportation • Span: 22m • Island West Transfer Station Explosives Depot (MTR WIL) Rock Type: Granite • Completion Year: 2010 Completion Year: 1997 • • Category: Dangerous Goods Category: Waste MTR Station (Admiralty) • • Span: 5.5m Span: 27m Completion Year: 2016 • • • Rock Type: Tuff/granite Rock Type: Tuff Category: Transportation • • • interface Span: 24.3m • Rock Type: Granite • Explosives Depot (Kau Shat Wan) MTR Station (Tai Koo) Completion Year: 1997 • Completion Year: 1985 • Category: Dangerous Goods • Category: Transportation • Span: 13m • Span: 24.2m • Rock Type: Granite intruded by • Rock Type: Granite • feldsparphyric rhyolite Stanley Sewage Treatment Works MTR Station (Sai Wan Ho) Completion Year: 1995 • Completion Year: 1985 • Category: Water • Category: Transportation • Span: 15m • Span: 24.2m • MTR Station (Lei Tung) Rock Type: Granite • Rock Type: Granite Legend: • Completion Year: 2016 • ● Caverns developed in 1980s Category: Transportation • ● Caverns developed in 1990s Span: 19m • 4 ● Caverns developed after 2000 Rock Type: Tuff •

Recent Cavern Studies in HK 1990s • A Study of the Potential Use of Underground Space (1990)  Cavern Project Studies (1991)  Cavern Area Studies (1994)  2010s • Enhanced Use of Underground Space in Hong Kong (2011)  Enhancing Land Supply Strategy - Reclamation outside Victoria Harbour and Rock Cavern Development (2011)  Long Term Strategy for Cavern Development (2012)  Relocation of Sha Tin Sewage Treatment Works to Caverns – Feasibility Study (2013)  5 Cavern Master Plan for Hong Kong

Overseas Examples of Treatment Plants in Caverns Viikinmäki Wastewater Treatment Plant Käppala Wastewater Treatment Plant Location: Helsinki, Finland • Completion Year: 1994 (Expanded in 2003) Location: Stockholm, Sweden • • Span: 17-19m (height: 10-15m) Completion Year: 1969 (Expanded in 1990s) • • Rock: mostly over 10m cover of migmatite Rock: approx. 150m cover of igneous rock • • Support: grouted rebar bolts & shotcrete • 6

Overseas Examples of Treatment Plants in Caverns Blominmäki Wastewater Treatment Plant Location: Helsinki, Finland Under Construction 7 No. 20m span caverns 10m wide rock pillars 17 permanent shafts 4 No. 20m Dia. Digesters Depth to caverns 50 to 60m 870,000m 3 cavern excavation 800,000m 3 tunnel excavation Outfall tunnel ‘many km long’ Sewage inlet 30m below, is pumped up into the caverns 7

Relocation of STSTW to Caverns Nui Po Shan Proposed STSTW in Caverns Ma On Shan Existing STSTW 8 8

Relocation of STSTW to Caverns Geological Plan • 3 3 2 2 1 1 Cavern Orientation at 11 o to North 9

Relocation of STSTW to Caverns Isometric View and Cross Sections • Ventilation Shaft Ventilation Adit 32 m Main Cavern Complex Branch Driveway Secondary Access Tunnel Effluent 24 m Rock Pillar Tunnel 6 Main Access Tunnel 10

Relocation of STSTW to Caverns General Layout of Sewage Treatment Works • Effluent Influent Emergency Bypass Flowmeter Chamber 6mm Bar Screens/ Aerated Grit Channels Primary Sedimentation with Plate Settlers Bioreactors (MBBR) DAF and UV Sludge Treatment Electrical Sewage Flow Direction Bypass Flow Direction 11

Cavern Design Cast concrete lining has recently been • adopted for permanent support 12

Cavern Design Rock Reinforcement Approach Cast-in-situ Concrete Lining Hoop Stress Rock Arch General Arrangement Temporary Shotcrete + Rock Bolts Support Permanent Shotcrete + Rock Bolts Elements Permanent Plain/Reinforced Concrete Lining Design Rock as structural materials to self- Concrete and rebar as structural materials Approach support by rock bolt reinforcement to support all loads An array of load combinations (overburden, Design Load Field Stresses imposed, water, grout pressure, E&M etc.) Structural FEM and DEM Bedded-beam Structural Model Analysis Design Individual failure modes and Shear stress, M-N diagram etc. with partial Checking Numerical Modelling factors according to structural code 13

Rock Reinforcement Approach Conventionally, “Rock Support” is adopted and cast -in-situ • Lateral Vertical Design Pressure Lateral Earth concrete lining is used to sustain all possible loadings Earth Pressure Pressure In Hong Kong, strong igneous rock has a compressive • strength typically greater than concrete Rock is a structural material to self-support itself by utilizing • the “arching effect”. It is perfectly capable to support the ground above the excavation through a theoretical arch For STSTW, the concept is switched to “Rock Reinforcement”. Rock Support • (Rock is considered as loading) Permanent rock bolts are considered as reinforcement and permanent shotcrete supports rock wedges between bolts The inherent strength of rock mass is utilized by applying • confining pressure via rock bolts The thrust capacity is therefore increased • and the rock arch formed around the tunnel is capable of providing the required force to stabilise the opening Rock Reinforcement (Rock is a part of solution NOT problem) 14

Rock Reinforcement Approach Design Procedures • 1. Empirical Q-system 1 Derive initial support from the NGI Q-system  Rock Support Chart (i.e. shotcrete thickness, rock bolts spacing and length) Rock Mass 2 Establish Rock Mass Parameters for Generalized  Parameters Hoek-Brown Criterion 2. Analytical Rock 3 Check the adequacy of support using Rock Reinforcement  Approach Reinforcement Approach, and amend as necessary Numerical 3. Numerical 4 Modelling Verify the design by numerical analyses and  confirm the support requirement Checking of Support Capacity 15

Rock Reinforcement Approach Rock Bolts • Systematic bolting to reinforce the overall stability  Spot bolting to secure individual loosened blocks  Typical diameter: 20 to 32 mm  Typical length of 2 to 6 m  Common type: Fully grouted, (temporary) expansion shell at end  Design life 100 years  Double corrosion protection – Galvanized with epoxy coating  Bischoff and Smart (1977) Lang (1961) and later re-modelled by Hoek (2007) 16

Rock Reinforcement Approach Shotcrete/Sprayed Concrete • Thin layer (75 to 200 mm) along the uneven excavated profile  Does not act as an arch, and does not support loads via compression  or bending Failure modes of shotcrete in the RRA are very hypothetical  Compression or tension cannot develop within the shotcrete  Six Potential Failure Modes:  *Adhesive Failure Flexural Failure *Direct Shear Failure Punching Shear Failure Compressive Failure Tensile Failure 17 Figure 6.23 from GEOGUIDE 4 (2018)

Rock Reinforcement Approach Verification of Design by Numerical Analyses • Can model a continuum with material properties suitable for the • rockmass, or discontinuum with joints Discontinuum Model Continuum Model Need to model different excavation sequences as they can give • different results 18

Rock Reinforcement Approach Details of Waterproofing Elements • Cast-in-situ Lining – Sheet Waterproofing Membrane  Sprayed Concrete – Drainage Strips  Tunneltalk, Sep 2008 19