MICRO TO MACRO ARE UK LINEAR INFRASTRUCTURE GI S SUITABLE FOR INVESTIGATING MASS SOIL PROPERTY CHARACTERISTICS? Ben Gilson - Arup 1
OUTLINE 1. Context why linear infrastructure? 2. Geotechnical challenges 3. Soil heave 4. Characterising soil permeability 5. Successes 6. Access to investigate 2
1. UK LINEAR INFRASTRUCTURE Why linear infrastructure? National Infrastructure Plan 2014 ICE State of the Nation Infrastructure 2014 HM Treasury Budget 2016 Infrastructure pipeline - 2020 Linear transport infrastructure TRANSPORT Source: https://www.gov.uk/government/publications/national-infrastructure-pipeline-2016 3
1. UK LINEAR TRANSPORT INFRASTRUCTURE * London Underground, trams * Not an official logo 4
2. KEY GEOTECHNICAL CHALLENGES 1. 2. 3. 4. Acknowledgments: 3. www.openbuildings.com, 4. www.railengineer.uk 5
3. HEAVE IN CUTTINGS HS2 Phase 1: hybrid Bill submitted, GI ongoing HS2 Phase 2: 39% in cutting, of which 41% potential for heave = 14% of the alignment = 54km HS3: 80km? 11.2km heave? Network Rail stations UK Road network HS2 Phase 1 HS2 Phase 2 Acknowledgments: BGS 50k solid and drift geology. Contains British Geological Survey materials NERC 2016 6
3. IMPORTANCE OF GEOTECHNICAL ISSUES 7
3. DESIGN FOR HEAVE HS2 track displacement criteria (Sartain & Trinder, 2016): 30mm post construction (ballast) 15mm post construction (slab track) 5mm / yr Mitigation options: 2. Over excavation / reduce width 1. Piled slab 3. Vertical wells to accelerate heave 8
4. SOIL PERMEABILITY Degree of saturation Discontinuities Swelling / stress level Permeability Hydraulic gradient Cementation Void ratio/ cavitation Grain size 9
4. MEASURING SOIL PERMEABILITY Intrusive GI - Develop ground model Laboratory tests In-situ tests EN 1997-1:2004 3.3.9.1 Whenever possible, in-situ tests, which measure average properties of a large ground volume should therefore be preferred. 10
4. MEASURING SOIL PERMEABILITY Intrusive GI - Develop ground model Laboratory tests Triaxial testing Oedometer Rowe cell Hydraulic cell In-situ tests Micro structure Stress variation Saturation Piezocone and void (CPT) ratio Cavitation? Standpipe/piezometer/ Anisotropy packer Falling head Macro characteristics Rising head Variations in influencing Constant head factors Discontinuities Self boring (e.g. pressuremeter fissures) Sample disturbance Pulse testing Rowe (1986) 11
4. MEASURING SOIL PERMEABILITY Intrusive GI - Develop ground model Laboratory Macro testscharacteristics??? In-situ stress / saturation Triaxial Discontinuities testing Oedometer Anisotropy (SBP) Rowe cell Hydraulic cell Future changes: stress, void ratio, saturation Logistics, time Installation effects In-situ tests Piezocone (CPT) Standpipe/piezometer/ packer Falling head Rising head Constant head Self boring pressuremeter Pulse testing Tracer tests Geophysical methods Flowmeter/impeller 12
4. MEASURING SOIL PERMEABILITY Intrusive GI - Develop ground model Laboratory tests In-situ tests Field trials Fehmarnbelt (Morrison et al, 2015) - excavation Queensborough bypass (Nicholson & Jardine, 1981) - settlement 13
4. UNDERSTANDING PERMEABILITY Soil mass Sand / silt layering Groundwater CPT Cable percussion Rotary coring Acknowledgments: Left Lankelma (http://www.lankelma.co.uk/cone-penetration-testing/cpt-rigs/rail-truck/). Right: HS2 Ground Investigations, a non-technical guide (https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/412948/hs2_ground_investigations_-_a_non-technical_guide.pdf) 14
4. UNDERSTANDING PERMEABILITY Soil mass Sand / silt layering Groundwater Continuous profile soil layering PWP with CPTu Increased metreage Sampling limited Depth limited Dissipation tests need significant period to reach equilibrium Installations limited CPT Acknowledgments: Lankelma (http://www.lankelma.co.uk/cone-penetration-testing/cpt-rigs/rail-truck/). 15
4. UNDERSTANDING PERMEABILITY Soil mass Sand / silt layering Groundwater Groundwater strikes Risk of wash-out reduced Sampling quality limited Significant disturbance Water for lubrication Cable percussion 16
4. UNDERSTANDING PERMEABILITY Soil mass Sand / silt layering Groundwater High sample quality Complete stratigraphic inspection Groundwater strikes limited Core loss in important strata clay to sand interface! Drill fluid! Workmanship Rotary coring Acknowledgments: HS2 Ground Investigations, a non-technical guide (https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/412948/hs2_ground_investigations_-_a_non-technical_guide.pdf) 17
4. BETTER MEASUREMENT OF PERMEABILITY What do we need, and why? Better average or governing mass permeability values? Increase scale, reduce test time Vary sample volume and understand influencing factors Pore water pressures after 3 months PWP PWP K = 1x10-8 K = 1x10-10 18
5. SUCCESSFUL CHARACTERISATION OF MASS SOIL PROPERTIES - NON-INTRUSIVE Characterise soil stiffness Downhole logging stiffness and stratigraphic understanding Acknowledgments: left image: Hope et al. (1998) 19
5. SUCCESSFUL CHARACTERISATION OF MASS SOIL PROPERTIES - INTRUSIVE 1. Triple barrel rotary 2. SEM / XRD 3. Lubricated CPT 10µm 4. Westbay standpipe 5. Measurement whilst drilling (MWD) Acknowledgments: 3) www.lankelma.com; 4) Westbay system Schlumberger water services (2016), www.water.slb.com. 5) Emerson Moore Drilling Ltd. at http://www.geolsoc.org.uk/. 20
6. DEEP GI WITH RESTRICTED ACCESS Wide tracts of rail land >30m deep retaining walls 21
6. DEEP GI IN A RAIL ENVIRONMENT Constraints 1. Rig toppling 3. Overhead line equipment (OLE) 2. Restricted access Risks Casing limitations weight and torque Sampling Depth limitations 22
7. CONCLUSIONS Are UK linear infrastructure GI s suitable for investigating mass soil property characteristics? Innovations & improvements, but many challenges remain. Understanding ground conditions permeability fine-grained soil key. Robust and refined. Field trials to justify reduced conservatism. 23
REFERENCES Clayton, C. (2011) Stiffness at small strain: research and practice. Geotechnique 61, No. 1, 5 37 Deighton, M. & Rigby-Jones, J. (2016) Technical paper: Improved estimation of ground stiffness for railway projects using continuous surface wave testing. Ground Engineering May 2016. EN 1997-1:2004 +A1:2013 Geotechnical Design. General Rules. Hope, V., Clayton, C. & Sutton, J. (1998) The use of seismic geophysics in the characterization of a weak rock site. Proceedings of the symposium on geotechnical site characterization (eds P. K. Robertson and P. W. Mayne), pp. 479-484. Rotterdam: Balkema. Sartain, N., & Trinder, S. (2016) Geotechnical Challenges of HS2. Presentation at 1 Great George Street, 13 March 2016. HM Treasury & Infrastructure and Projects Authority (2016) National Infrastructure Pipeline Spring 2016, 15 April 2016, https://www.gov.uk/government/publications/national-infrastructure-pipeline- 2016. Morrison, P., Kammer, J., Hammami, R., Frederiksen, J., Hansen, G. & Humpheson, C. (2015) Fehmarnbelt Fixed Link trial excavation. Nicholson, D. & Jardine, R. (1981) Performance of vertical drains at Queenborough bypass. Geotechnique 31(1) p67-90. Rowe, P. (1968) The Influence of Geological Features of Clay Deposits on the Design and Performance of Sand Drains, Proceedings ICE. 24