1. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence C-Change in GEES Ground Subsidence and Slope Stability Session One Session One: Introduction to Ground Subsidence

2. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence How to use the teaching slides  These slides are not intended to form a complete lecture on the session topic.  These resources are designed to suggest a framework to help tutors develop their own lecture material  The resource slides comprise where appropriate; key points, case studies, images, references and further resources.  These resources may be used for educational purposes only, for other uses please contact the author  These slides were last updated in November 2009

3. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Disclaimer  Links within this presentation may lead to other sites. These are provided for convenience only. We do not sponsor, endorse or otherwise approve of any information or statements appearing in those sites. The author is not responsible for the availability of, or the content located on or through, any such external site.  While every effort and care has been taken in preparing the content of this presentation, the author disclaims all warranties, expressed or implied, as to the accuracy of the information in any of the content. It also (to the extent permitted by law) shall not be liable for any losses or damages arising from the use of, or reliance on, the information. It is also not liable for any losses or damages arising from the use of, or reliance on sites linked to this site, or the internet generally.  Pictures, photographs and diagrams within this presentation have been produced by the author unless otherwise stipulated  No content within this resource is knowingly an infringement of copyright. Any infringement can be immediately rectified on notification of the author of the resource

4. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Session Outline Introduce the main types of subsidence Explain why clays are susceptible to subsidence Assess differential settlement issues Discuss regional subsidence & man-made problems Case studies: Venice Leaning Tower of Pisa Mexico City Subsidence causing structural problems for this building in Gothenberg – notice the bottom left window Stuart Chalmers (flickr)

5. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Three main induced subsidence types: Ground-water withdrawal Karst & Evaporites (soluble rocks dissolved by carbonic acid & collapsed) Mining (past or present removal of subsurface material) Other types include: isostatic rebound, sediment loading & natural coal ignition Types of Subsidence Roger g1 (flickr)

6. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Groundwater withdrawal Exacerbated due to water over-extracting Groundwater pumped from pore spaces between sand/gravel grains Then slow drainage from clay/silt beds if present Reduced water pressure = loss of support for clay/silt beds Clay/silt beds compact & lowers ground surface Permanent! The regolith has 20 to 50 times the water storage capacity of the bedrock (USGS, 1983) USGS

7. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Subsidence in Clays Clays have high porosity with deformable grains of minerals, so high potential of compaction Compaction = volume decrease = consolidation Causes surface subsidence and structure settlement with imposed load or drained water loss –Greatest on thick clay, high smectite %, low silt %, no over-consolidation Bearing Capacity of clays = 50- 750 kPa, related to water content Older clays (shales & mudstones) stronger/less compressible –Self boring pressure (SBP) 2000kPa Exposed clay at Rio de Janeiro, Brazil (Alex Rio Brazil: wikimedia)

8. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Subsidence in Clays (2): Settlement Clays consolidated by imposed structural load All clays cause some degree of settlement Water squeezed out by applied stress Degree depends on water % and stress applied –Lab assessment by consolidation test Remedy to avoid clay loading or wait for settlement to stop Modest settlement beneath buildings may fracture drains, leakage from drains removes soil & secondary settlement ensues Differential settlement more serious –Due to: uneven load, lateral change in silt content or uncontrolled drainage –Accelerated by tall structures –Eg. Transcona grain elevator, Canada, tilted 27º in 1 day in 1912 Clays under raft base unevenly compacted over rockhead, sheared & laterally displaced structure which contained 875,000 bushels of wheat Note uneven ground movement –Some areas raised by 5 feet

9. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Subsidence in Clays (3): Monitoring Source: USGS

10. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Causes of Regional Subsidence Groundwater abstraction exceeds natural recharge Leads to water table lowering Pumping from sand Small but recoverable sand compaction (unlike clay!) –Usually recovery leaves ~10% compacted Clay compaction Occurs as groundwater pressures equal between sand & clay Time delay due to low clay permeability Subsidence:head loss varies with clay type –1:6 on young, unconsolidated Mexico City Montmorillonite –1:250 on old, consolidated, London Clay Illite –Subsidence stops if water tables recover due to pore water pressure support

11. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence US southwest problem Map sub-divides US subsidence problems Note most States have more than one type of subsidence problem Southwest region has a particularly high incidence of subsidence problems: mining, sinkholes, underground fluid withdrawal, hydrocompaction and drainage of organic soils Associated with high damage costs Source: USGS

12. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Karst and Evaporites Dissolution of limestone/carbonate rocks Similar process happens to Evaporites –e.g. rock salt & gypsum Water & CO 2 combine to form carbonic acid Acid water dissolves rock, leading to cave "basement“ removal, so "roof" tumbles down A cave formation mechanism –Takes 10,000 years to create continuous passage, 1,000,000 years for fully developed system Cavities typically water-filled, which supports surface load –Collapse when water is removed (above) Karst landscape – Combe laval, France (Berrucomons wikimedia) (below) Sinkhole in North Yorkshire (unknown source)

13. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Karst Topography Source: USGS

14. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence If water table goes down (pumping or drought), cavity collapses & forms sinkholes Sinkholes often water-filled, terrain characterised by string of circular lakes "Karst" topography (after Kars area in Montenegro/Albania) where common Sinkholes range from meters to 100s of meters in diameter & a few 10s of meters deep (some in China are > 200 m deep). Natural Karstic Environments: Topography & Sinkholes Source: Jamie Pringle Sequence showing cavity creation (from loss of water from the water table) and collapse of overlying soil

15. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Identification of Evaporite Karstic Environments Most common are gypsum (or anhydrite) & salt Readily dissolved forming typical karst features Where outcrops (or gypsum <30 m & salt <250 m) may partly or wholly be dissolved by unsaturated water Outcrops typically contain sinkholes, caves, disappearing streams & springs Other evidence: surface collapse features, saline springs, & saline plumes Many deeper evaporites show paleokarst features –dissolution breccias, breccia pipes, slumped beds & collapse structures

16. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Gypsum Karst Evaporitic Subsidence example – Ripon, UK Town subsidence caused by natural dissolution of Gypsum bedrock Upwardly migrating crown holes causing significant structural damage & even total collapse Image (left): Ripon Cathedral (j-pundt: flickr.com) (right): Ripon, North Yorkshire

17. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Groundwater extraction fissures M.C. Carpenter/ USGS S.R. Anderson/ USGS Fissuring often associated with over-extraction of groundwater 3.5 km longest documented in USA, 100’s m typical Often enlarged by erosion Sign warning motorists of subsidence hazard caused by earth fissure damage (S.R. Anderson/ USGS) Earth fissures near Picacho, Arizona

18. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Case Study: Venice, Italy Floods on around 100 high tides/year –Alla Rampa bar regulars wear wellies! Has over 1 km thick sediments underlying the city Top 350 m has six sand aquifers interbedded with clays (illite/chlorite) Historically wood piling used to penetrate to harder clay layers –Modern (including stone) buildings all based on these Clay soils have low plasticity & moisture content below plastic limit (water content at which soil starts to exhibit plastic behaviour) (Dimitry B: flickr)

19. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Venice, Italy Case Study (2) Subsidence experienced due to: –Natural (weight) (0.4 mm/yr), groundwater lowering by pumping & eustatic changes (~1.27 mm/yr) Subsidence mostly due to groundwater pumping (now controlled) –In 1900, artesian head 6m above sea level –By 1930 20 m below sea level –Controlled in 1970s & has recovered –Problem of Non-recoverable clay compaction (~1 m) Rising sea levels now demand new barriers & raised perimeter frontage Waltham, T., (2009) Foundations of Engineering Geology. 3rd edition, Spon: London. Acqua alta: exceptional tide peaks that occur periodically in the northern Adriatic Sea

20. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Venice, Italy (3) Spring High Tides 90 years ago not an issue, they are today –St. Mark’s Square flooded 79 times in 1997 In 1984, Italian Govt. started £2Bn scheme –Installation of mobile barriers –Reinforced coastal defences –Improved lagoonal ecosystem –3 lagoonal inlets, mobile flap gates allow shipping passage, only 2m difference between lagoon & sea Scheme now faces axe due to funding shortfall St Mark’s Square, Venice Source: radiowood2000 (flickr.com)

21. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Case Study: Mexico City Lies within a basin, 2250 m above sea level surrounded by volcanic rocks Divided into 3 geotechnical zones: 1.10-100m soft lacustrine clays 10% organic content 2.Transition zone with sand/silt alluvium 3.Hill zone with volcanic ash flows/tuffs Reproduced with the permission of Canada's International Development Research Centre (www.idrc.ca)www.idrc.ca

22. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Mexico City (2) Soils moisture content 650%, Liquid limit (LL) = 500%, Plasticity Index (PI) of 350% –Normally consolidated but thixotropic (with time, stiffness & strength increases) –Very high angle of repose (Φ 35-45º), probably due to presence of angular diatoms within soils Groundwater extraction problem –pumping started ~1850 By 1974, 3,000 shallow & 200 deep wells Estimated groundwater extraction 12m 3 /sec Between 1891-1973, estimated subsidence on Montmorillonite clays inter-bedded with over-pumped sands ~8.7m –Max. 460mm in 1950 –Estimated may be 20m due to clay compaction

23. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Mexico City (3) Ground settlement consequences –Well casings now protrude in the streets –Surface infrastructure disruption –Water supply loss from dislocated pumps –Piled buildings now raised from surrounds –In 1951, had to obtain water from outside sources, implement sewerage system plan & control groundwater abstraction –Rafted foundation buildings (e.g. Palace of Fine Arts) settlement Aerial view of Mexico City (Merrick Brown: flickr)

24. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Mexico City (4) Palace of Fine Arts had to be built on a massive concrete raft –Imposed 110 kPa load that caused 3 m of settlement –Heavy rafts cause their own subsidence bowls & damage to adjacent buildings Stable foundations should be piled to more stable material –In this area, these are the sand layers –Latino Americana Tower buoyant foundations (+basement) to reduce imposed load –Also piles driven to uppermost sand units –Settlement by compaction of lower clay = ground subsidence as less upper clay –Note subsidence:head loss is 1:6 –London Clay is 1:250 Old, consolidated & illite London Clay Diagram: copied from Waltham (2002) Photos: (left) mdanys; (right) Kevin Hutchinson (flickr.com)

25. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Other clay soil subsidence areas Bangkok –Fastest subsiding city at > 10 cm/year Santa Clara Valley, California –4 m ground subsidence since water table lowering –Now stopped as reduced extraction Photos: (above) Bangkok ( Swami Stream: flickr) (below) Santa Clara Valley (the tahoe guy: flickr)

26. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Case Study: Leaning Tower of Pisa Building started in 1173 Started to lean to north in 1178 when only 4 stories high (~0.6 º ) 1270s increased to seven stories using tapered masonry on southern side – made matters worse. Bell tower added in 1370 at angle to visually correct for the tilt, now (~1.6º) 58m high & weighs 14,000 Tn 1817 – first true tilt recording gave 4.6º Current tilt 5.5º or 5.5 m out of plumb with estimated movement of 1.2 mm per year Tower not settling now but rotating about an axis point near the first floor Photos: Argenberg (flickr.com)

27. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Pisa underlying geology Horizontally layered sands & clays Water table at about 1-2m Vertical settling occurred because of underling Pancone Clay plasticity & compressibility. Land surface difference now ~2m between N & S Main settlement due to compaction & deformation of soft clay at 11-22m Pisa tower imposes 500 kPa on clay with ABP ~50 kPa Differential movement probably started due to clay variation within silt layer; now accentuated by eccentric loading Waltham, T., (2009) Foundations of Engineering Geology. 3rd edition, Spon: London.

28. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Rotational weakness due to rotational creep in upper sands NOT the clay due to a weaker shear strength. Get a ‘racking’ effect as the tower expands & contracts during the heat/cool of the day. Made worse by saturation of the ground by shallow water table. Fluctuations in water table during storms cause northern side of the tower to slightly rise & fall more than southern side. The overturning forces of the tower are greater than resisting capacity of the sands. The tower is TOO TALL The different periods of building have actually helped as it compressed the sands & clays over time making them stronger. This is why the tower hasn't fall down (yet) Leaning Tower of Pisa (3)

29. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Other Settings (1): Isostatic rebound ‘See-saw’ affect Ice Age end (11,000 years bp) Scotland had 3 km thick ice sheet Glaciers retreated (melted): removal of weight leads to uplift –Documented varying uplift rates, initially ‘rapid’ (7.5 cm/yr) then slowed to today (1 cm/yr) –Will continue for 10,000 years A model of present-day surface elevation change due to post-glacial rebound. Red areas are rising due to the removal of the ice sheets. Blue areas are falling due to the re-filling of the ocean basins when the ice sheets melted and because of the collapse of the glacial forebulge. Source: NASA

30. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Other settings (2): Sediment Loading Mississippi-Missouri River system collects eroded debris from central half of US (3.3 km 2 ) Reaches Gulf of Mexico, slows & deposits (~2.4b kg/yr) Modern delta prograding 100-150 m/yr) Delta subsiding 2.5 cm/yr –Some debate on causes: sediment compaction, ground- water withdrawal & sea-level rise alternative theories (above) Map of Mississippi Basin (US EPA); (below) Aerial photograph of Mississippi Delta (NASA/USGS)

31. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Other Settings (3): Natural Coal Ignition Burning Mountain, NSW, Australia: –takes its name from a naturally combusting coal seam running underground through the sandstone –Documented since 1828 (white man’s arrival) –Part of Permian (235Ma) Greta Series coalfields –Sites moves 1m South each yr. –Whole area subsiding –All attempts to put out have failed (trenching/drilling/watering etc) Photograph at the summit of Burning Mountain, NSW (unknown author)

32. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Session Summary Clay compaction = volume decrease = consolidation Causes surface subsidence & structure settlement with imposed load or drained water loss –Greatest on thick clay, high smectite %, low silt %, young with no over-consolidation Clays consolidated by imposed structural load Differential settlement –Due to uneven load, lateral change in silt content or uncontrolled drainage –Accelerated by tall structures Regional subsidence caused by groundwater abstraction, pumping from sand, and clay consolidation

33. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Venice Case Study –Thick sediment pile –Over-extraction of water caused clay consolidation, now stabilised Mexico City –High water content of Montmorillonite Clay –Over-extraction by pumping consolidated clays –Lots of settlement problems –Latino Americana Tower overcame this by buoyant foundations & piles Leaning Tower of Pisa –Uneven settlement due to loading of clay layers –Eventually tilt reduced to stable (5º) angle by latest engineering phase Session Summary (2)

34. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence Baracos, A. (1957) ‘The Foundation Failure of the Transcona Grain Elevator.’ Engineering Journal 40(7): 1-6 Barnes G. E. (2000) ‘Soil Mechanics: Principles & Practice’ (2nd Edition), Palgrave MacMillan. pages 155- 158 Bell, F.G. (1998) ‘Environmental geology’, Blackwell Science Publications, pages 415-441. Hatheway, A.W. and Reeves, G.M. (1997) ‘Status of engineering geology in North America and Europe’ Engineering Geology 47(3): 191-215 Hatheway, A.W. and Reeves, G.M. (1999) ‘A second review of the international status of engineering geology: encompassing hydrogeology, environmental geology and applied geosciences’ Engineering Geology 53(3): 259-296 Jongmans D., Demanet D., C. Horrent, Campillo M., Sanchez-Sesma F.J. (1996) ‘Dynamic soil parameters determination by geophysical prospecting in Mexico City : implication for site effect modeling’, Soil Dynamics and Earthquake Engineering, 15(8): 549-559. Pringle, J.K., Stimpson, I.G., Toon, S.M., Caunt, S., Lane, V.S., Husband, C.R., Jones, G.M., Cassidy, N.J. and Styles, P. (2008). Geophysical characterisation of derelict coalmine workings and mineshaft detection: a case study from Shrewsbury, UK. Near Surface Geophysics, 6(3), 185-194. Waltham, T. (2009) ‘Foundations of Engineering Geology’ (3rd Edition), Spon Press. pages 56-7 Waltham, T. (2009) ‘Sinkhole Geohazards’. Geology Today, 25(3): 112-116 References

35. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence This resource was created by the University of Keele and released as an open educational resource through the 'C-change in GEES' project exploring the open licensing of climate change and sustainability resources in the Geography, Earth and Environmental Sciences. The C-change in GEES project was funded by HEFCE as part of the JISC/HE Academy UKOER programme and coordinated by the GEES Subject Centre. This resource is licensed under the terms of the Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales license (http://creativecommons.org/licenses/by-nc-sa/2.0/uk/).http://creativecommons.org/licenses/by-nc-sa/2.0/uk/ However the resource, where specified below, contains other 3rd party materials under their own licenses. The licenses and attributions are outlined below: 1.The name of the University of Keele and its logos are registered trade marks of the University. The University reserves all rights to these items beyond their inclusion in these CC resources. 2.The JISC logo, the C-change logo and the logo of the Higher Education Academy Subject Centre for the Geography, Earth and Environmental Sciences are licensed under the terms of the Creative Commons Attribution -non-commercial-No Derivative Works 2.0 UK England & Wales license. All reproductions must comply with the terms of that license

36. Dr Jamie Pringle, Keele University, j.k.pringle@esci.keele.ac.uk C-Change in GEES: Ground Subsidence and Slope Stability – Introduction to Ground Subsidence AuthorDr Jamie Pringle Stephen Whitfield Institute – OwnerKeele University, School of Physical and Geographical Sciences TitleGround Subsidence and Slope Stability 1 Date CreatedNovember 2009 DescriptionIntroduction to Ground Subsidence Powerpoint Educational Level3 Keywords (Primary keywords – UKOER & GEESOER) UKOER, GEESOER Creative Commons LicenseAttribution-Non-Commercial-Share Alike 2.0 UK: England & Wales Item Metadata