weathering influence on engineering structures

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

what is weathering in engineering

implications for engineering

forecasting weathering

weathering rate

30/10/2012Weathering 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

30/10/2012Weathering influence on engineering structures - Hack 12Slope 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)

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

CINDARTO SLOPEVARIATION 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 mass0.04 Brazil (Moreira-Nordemann, 1980)

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

mountainous areas

with high erosion ratesmm'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://famousankles.files.wordpress.com/2007/09/20070923-central-park-14-cleopatras-needle-two-sides.jpg

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 1app

init WEWE t WE R t

WE(t) = degree of weathering at time t

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

RappWE = 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


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

[degre

es]

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.


weathering influence on engineering structures

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