WEATHERING INFLUENCE ON ENGINEERING … · weathering influence on engineering structures robert hack faculty of geo-information science and earth observation (itc), university of

WEATHERING INFLUENCE ON ENGINEERING STRUCTURES

ROBERT HACK FACULTY OF GEO-INFORMATION SCIENCE AND EARTH OBSERVATION (ITC), UNIVERSITY OF TWENTE, THE NETHERLANDS. PHONE:+31 (0)6 24505442; EMAIL: [email protected]

ITC, The Netherlands; 30 October 2012

WEATHERING INFLUENCE ON ENGINEERING STRUCTURES Robert Hack Faculty of Geo-Information Science and Earth Observation (ITC), University of Twente, Enschede, The Netherlands, [email protected] ABSTRACT An overview is given of the influence of weathering on engineering structures in and on natural materials. Some recently developed new ideas to incorporate weathering in design are discussed. All natural materials near and sometimes also deeper below surface of the Earth are subject to weathering. Notoriously difficult to forecast is the geotechnical behaviour due to future deterioration of the ground mass under influence of weathering. Weathering is a strongly local feature influenced by local circumstances such as local climate and weather, groundwater, and humans. Calculation methods and parameters used in design of engineering structures often do not properly anticipate the degradation of natural materials due to weathering. Preliminary failure, i.e. failure of the engineering structure before the end of the planned lifetime, may be the consequence. Slopes and tunnels start to raffle or may fail completely, and even buried foundations may be affected.

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what is weathering in engineering implications for engineering forecasting weathering weathering rate

30/10/2012 Weathering influence on engineering structures - Hack 2

WEATHERING

Physical, chemical, and biological alteration of rock and soil over time;

Influenced by the atmosphere and the hydrosphere, and

Cause rock or soil material to fall apart into smaller pieces or to dissolve in water.


STRESS RELIEF

Due to change in stress field (orientation or magnitude) discontinuities may form or existing discontinuities may open (discontinuities are bedding planes, joints, fractures, etc.)


WEATHERING & STRESS RELIEF

Difference between effects of weathering and stress relief difficult to distinguish:

Therefore in engineering taken together as being “weathering”


EFFECTS OF WEATHERING

• weakening of intact rock blocks and soil grains • integral become mechanical discontinuities (i.e. bedding planes

not being yet a mechanical plane of weakness become a mechanical plane of weakness)

• material between rock blocks becomes weaker (remains of weathered material)


WHAT GIVES ROCK AND SOIL MASSES STRENGTH

Rock and soil masses consist of: • intact blocks (rock) with discontinuities in-between (e.g. bedding

planes, joints, fractures, etc) • grains (in soil) with grain contacts in-between

Strength of a mass is given by:

• strength (shear & tensile) of intact rock blocks or soil grains • shear strength between blocks (rock) or grains (soil)


ENGINEERING EFFECTS

weaker rock blocks and soil grains smaller rock blocks and grains shear strength between blocks and grains less




reduction intact rock strength due to solution of cement (2)

blocks falling from disintegrating wall

Children playground made around 1995 Vandellos, Spain (photos: Hack, 2002)

REDUCTION BLOCK SIZE


SAME MATERIAL THE MORE EXPOSED THE SMALLER THE BLOCK SIZE

30/10/2012 Weathering influence on engineering structures - Hack 12 Slope Stability by Classification - Hack 12

CINDARTO SLOPE: VARIATION IN CLAY CONTENT IN INTACT ROCK CAUSES DIFFERENTIAL WEATHERING

bedding planes

Slightly higher clay content on bedding plane

April 1990

shear strength reduction between blocks and grains (1)

30/10/2012 Weathering influence on engineering structures - Hack 13 Slope Stability by Classification - Hack 13

CINDARTO SLOPE VARIATION IN CLAY CONTENT IN INTACT ROCK CAUSES DIFFERENTIAL WEATHERING

April 1992

mass slid


carbonate is dissolved at bedding plane – clay remains



DEGREES OF WEATHERING


Degrees of weathering

IMPACT OF WEATHERING


From: De Mulder, E.J.F., Hack, H.R.G.K., Van Ree, C.C.D.F., 2012. Sustainable Development and Management of the Shallow Subsurface. The Geological Society, London. ISBN: 978-1-86239-343-1. p. 192.

WEATHERING IN TIME

weathering rate depends on: local climate & weather (e.g. wind direction) groundwater land-use (fertilizer) does it stay exposed or is it covered by weathered material

(erosion) method of excavation


WEATHERING & TIME Weathering based on rock & soil dissolution back analyses:

Intro Weathering - Hack 28/09/2012 18

rate [mm/y]

average world 0.006

(Olvmo, 2010) cold climate < 0.001

warmer climate > 0.1

tropics metamorphic rock mass 0.04 Brazil (Moreira-Nordemann, 1980)

tropics silica rock mass 0.058 Puerto Rico (White et al., 1998)

mountainous areas with high erosion rates mm's

WEATHERING & TIME

Dissolution in 50 years thus around ½ to 5 mm Dissolution in particular around discontinuities Dissolution in the order of fraction of mm Fraction of mm enough to reduce (shear) strength

Hence, even in relative short time spans of 50 to 100 years, weathering may have

a substantial negative influence on properties of soil and rock masses


Cleopatra’s needle Central Park, New York


1881

2011 copyright: michael martine, 2011

http://famousankles.files.wordpress.com/2007/09/20070923-central-park-14-cleopatras-needle-two-sides.jpg

http://www.examiner.com/slideshow/cleopatra-s-needle-under-fire

http://www.michaelmartine.com/




INFLUENCE WEATHERING ON DESIGN



Poor blasting of slope caused increased permeability and consequently allowed for loss of structure and rapid weathering of thin clay inter-bedded softer layers

POORLY BLASTED SLOPE

1990: new cut: slope height 13.8 m high, dip 70°

2002: slope dip about 55°

2005: slope dip about 52°

SSPC forecast final stability: slope dip about 45° (SSPC after Hack et al, 2003)



BLASTING DAMAGE CAUSES RAPID RAVELLING AND LOSS OF STRUCTURE AND CONSEQUENTLY WEATHERING

Diabase (subvolcanic rock equivalent to volcanic basalt) made in: 1995 photos: 2011

Silver Creek Cliff Tunnel, Route 61, Duluth, MN, USA

(photos: Hack, 2011)

Road protection wall built in 2010 to prevent stones on the road


debris

Fine grained calcareous mudstone falling apart within a couple of years after excavation South Korea

(photos Hack, 2008)

debris

FUTURE DEGRADATION


FUTURE DEGRADATION

Reduction in slope angle due to weathering, erosion and ravelling (after Huisman et al, 2006)


1.0

1.5

2.0

2.5

3.0

3.5

7.0 7.5 8.0 8.5 9.0 9.5

y [m]

z [m

]

Excavated 1999 May 2001 May 2002

FUTURE DEGRADATION

Main processes involved in degradation: Loss of structure due to stress release Weathering (In-situ change by inside or outside influences) Erosion (Material transport with no chemical or structural

changes)


WEATHERING RATE

The susceptibility to weathering is a concept that is frequently addressed by “the” weathering rate of a rock material or mass.

Weathering rates may be expected to decrease with time, as the state of the rock mass becomes more and more in equilibrium with its surroundings.



( ) ( )log 1appinit WEWE t WE R t= − +

WE(t) = degree of weathering at time t WEinit = (initial) degree of weathering at time t = 0 Rapp

WE = weathering intensity rate WE as function of time, initial weathering and the weathering intensity rate

GYPSUM CLAYSTONE SLOPE IN VANDELLOS

SSPC system with applying weathering intensity rate: - original slope cut about 50º (1998) - in 15 years decrease to 35º


KOTA KINABALU, MALAYSIA

30/10/2012 Weathering influence on engineering structures - Hack 32 32

10 years old

(after Tating, Hack, & Jetten, 2011)

KOTA KINABALU

Side road (dip 45°, 5 years old) sandstone: slightly weathered SSPC stability: Sandstone: stable (92%) Shale: unstable (< 5%) (after Tating et al., 2012)


KOTA KINABALU

Main road (dip 30°, 10 years old): sandstone: moderately weathered SSPC stability: Sandstone: stable (95%) Shale: ravelling (<5%) (after Tating et al., 2012)


10 years old

KOTA KINABALU

time [years]

dip [degrees]

SSPC visual

unit RM friction RM cohesion

[degrees] [kPa]

shale

slightly 5 45 4 2.4 instable

moderately 10 30 2 1.1 instable

sandstone

slightly 5 45 20 10.0 stable

moderately 10 30 11 6.3 stable


SSPC system in combination with degradation forecasts gives: reasonable design for slope stability with minimum of work and in a short time (likely a reasonable tool to forecast susceptibility to weathering)


REFERENCES De Mulder, E.J.F., Hack, H.R.G.K., Van Ree, C.C.D.F., 2012. Sustainable Development and Management of the Shallow Subsurface. The Geological Society,

London. ISBN: 978-1-86239-343-1. p. 192. Hack, H.R.G.K., 2002. An evaluation of slope stability classification; Keynote lecture. In: Dinis Da Gama, C., Ribeira E Sousa, L. (Eds) ISRM EUROCK 2002, Funchal,

Madeira, Portugal. Sociedade Portuguesa de Geotecnia, Av. do Brasil, 101, 1700-066 Lisboa, Portugal, pp. 3–32. Hack, H.R.G.K., Price, D.G., Rengers, N., 2003. A new approach to rock slope stability : a probability classification SSPC. Bulletin of Engineering Geology and the

Environment. 62 (2). DOI: 10.1007/s10064-002-0155-4. pp. 167-184. Hack, H.R.G.K., Price, D., Rengers, N., 2005. Una nueva aproximación a la clasificación probabilística de estabilidad de taludes (SSPC). In: Proyectos, U.D., Minas,

E.T.S.I. (Eds), Ingeniería del terreno : ingeoter 5 : capítulo 6. Universidad Politécnica de Madrid, Madrid. ISBN: 84-96140-14-8. p. 418. (in Spanish) Huisman, M., Hack, H.R.G.K., Nieuwenhuis, J.D., 2006. Predicting Rock Mass Decay in Engineering Lifetimes: The Influence of Slope Aspect and Climate.

Environmental & Engineering Geoscience. 12 (1). DOI: 10.2113/12.1.39. pp. 39-51. Moreira-Nordemann, L.M., 1980. Use of 234U/238U disequilibrium in measuring chemical weathering rate of rocks. Geochimica et Cosmochimica Acta. 44 (1). DOI:

10.1016/0016-7037(80)90180-5. pp. 103-108. Olvmo, M., 2010. Review of denudation processes and quantification of weathering and erosion rates at a 0.1 to 1 Ma time scale; Technical Report TR-09-18. Svensk

Kärnbränslehantering AB; Swedish Nuclear Fuel and Waste Management Co, Stockholm, Sweden. p. 56. Price, D.G., De Freitas, M.H., Hack, H.R.G.K., Higginbottom, I.E., Knill, J.L., Maurenbrecher, M., 2009. Engineering geology : principles and practice. De Freitas, M.H.

(Ed.). Springer-Verlag, Berlin, Heidelberg. ISBN: 978-3-540-29249-4. p. 450. White, A.F., Blum, A.E., Schulz, M.S., Vivit, D.V., Stonestrom, D.A., Larsen, M., Murphy, S.F., Eberl, D., 1998. Chemical Weathering in a Tropical Watershed, Luquillo

Mountains, Puerto Rico: I. Long-Term Versus Short-Term Weathering Fluxes. Geochimica et Cosmochimica Acta. 62 (2). DOI: 10.1016/s0016-7037(97)00335-9. pp. 209-226.


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WEATHERING INFLUENCE ON ENGINEERING … · weathering influence on engineering structures robert hack faculty of geo-information science and earth observation (itc), university of