ENGINEERING ASPECTS AND TIME EFFECTS OF RAPID DETERIORATION OF SANDSTONE IN THE

TROPICAL ENVIRONMENT OF SABAH, MALAYSIA

Frederick F Tating, Robert Hack, Victor Jetten

Symposium Ingeokring 2012 “Engineering in Exotic Environments” Date: 28 September 2012 Time: 13.45 – 18.00 Location: TUDelft

Area: Kota Kinabalu, Sabah, Malaysia Tropical Humid Climate Temperature (22 – 33o C) Rainfall (1900 – 3200 mm)

Sedimentary Rock Formation

Recent Sediment (Riverine and Coastal Alluvium)

Research Area

7 years after excavation 16 years after excavation

To established the relationship between rock weathering and (exposure) time for thick bedded sandstone in tropical areas

Weathering is defined as: “breakdown and alteration processes of rock at or near the Earth’s surface by physical, chemical and biotic processes” (Selby, 1993; Anon 1995; Ollier,1969)

In application geotechnology: “irreversible response of soil and rock materials and masses to their natural or artificial exposure to the near surface geomorphological or engineering environment” (Price, 1995a)

DISCOLORATION

DISINTEGRATION

DECOMPOSITION

Excavation : • Stress and Strain

Redistribution

• Exposing Fresh and Weathered Rock to External Processes (Weathering Agents)

• Erosion

“decay and change in state from an original condition to a new condition as a result of external processes" (Price, 1995b)”

Modified from Chigara (1990)

Weathering Grade Based on BS5390 (1981), ISO 14689-1(2003)

OXIDATION ZONE

DISSOLVED ZONE

Brownish Color Iron Precipitation

Greyish Color No Iron Precipitation

INTACT ROCK :Blocks of rock that do not contain discontinuities

ROCK MASS: Assemblage of rock blocks which include discontinuities

Sandstone Shale

Intact Rock

DDifferences ◦ Strength ◦ Weathering Effect

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Weathering along Discontinuity

Residual Layer

Weathering Intensity “degree of decomposition or amount of alteration from the original state shown by rock at a certain point of time” (Bland and Rolls, 1998) Weathering Grade for masses( BS 5930, 1981, ISO 14689-1 2003)

Weathering Intensity Rate

◦ “amount of change in the weathering intensity per unit of time” (Bland and Rolls, 1998)

The general empirical relationship function of weathering (property value change as an effect of weathering) and time (Colman, 1981; Huisman, 2006)

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P(t) = Property value at time of observation, t P(init) = Initial value of material R(app) = Apparent rate of property changes t = Exposure time

WWeathering apparent intensity rate ◦ “changes in property value from the initial state divided by a function

of total exposure time”Weathering dynamic intensity rate ◦ “property values assessed during successive time series divided by the

elapsed time of each assessment at that particular time and location”

Modified from Huisman, 2006

P(t) = P(init) + R(app) log (1 + t)

Data collection : ◦ Road cuts, Hill cuts and Quarry sites

Duration of Excavation/Exposure Time : ◦ Obtained from Government Agencies, Quarry Operators or Residents

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Hill Cut Quarry

Hill Core Road Cut

Three main geotechnical units : Shale (SH), Thick – very Thick Bedded Sandstone (SST) and Shale, Siltstone and Sandstone Interbed (IB)

Engineering geological mapping Rock discontinuity characterization and description based on SSPC (Slope Stability Probability Classification System, Hack et al., 2003) Determination of Intact Rock Strength (IRS) using Geological Hammer (BS 5930:1999), verify by using Point Load Test and Schmidt Hammer

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Weathering and Time relationship ◦ IIntact Rock Strength (IRS)

Rock mass friction angle and cohesion can also be estimated from an empirical formula e.g. SSPC (Hack et al. 2003 ) or Hoek and Brown (1997)

thh ii dd TTi l ttii hhithh ii dd TTi l ttii hhi

IRS(t) = IRS(init) + R(app) log (1 + t)

IRS(t) = IRS value at time of observation, t IRS(init) = Initial value of IRS (Fresh) R(app) = Apparent rate of IRS changes t = Exposure time

IRS(t) = 105 - 34 log (1 + t)

CUT SLOPE CONSIST OF VARIOUS WEATHERING GRADE

EXPOSURE TIME ADJUSTED

IRS(t) = 105 - 34 log (1 + t)

Thick Weathering Profile

Full Range of Weathering Grade

Cohesion(t) = 27004 - 6850.27Log (1 + t) Friction(t) = 56.1 – 15log (1 + t)

Wedge

Plane

Plane with Reinforcement

Circular

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REDUCTION RATE OF ROCK PROPERTIES HIGH IN FIRST 100 YEARS

(Wyllie and Mah, 2004)

IRS

Cohesion

Friction

Weathering intensity rate (weathering effect on rock properties) decreases non-linearly with time Decreases logarithmic Weathering effects are (very) significant in the first 100 years after excavation in a tropical environment Reduction of design parameters (IRS, Cohesion, Friction) due to future weathering to be used for a sustainable design of engineering structures in and on rock masses over the full lifetime of a structure

Anon, 1995. The description and classification of weathered rocks for engineering purposes. Geological Society Engineering Group Working Party Report. Quarterly Journal of Engineering Geology 28, 207 – 242. Bland, W., Rolls, D.,1998. Weathering: An Introduction to the Scientific Principles. Arnold Publishers, London, 288pp. BS 5930, 1999. The Code of Practice for Site Investigations. British Standards Institution, London, 192pp. Chigara, M., 1990. A mechanism of chemical weathering of mudstones in a mountainous area. Engineering Geology 29, 119 – 138. Colman, S.M., 1981. Rock-weathering rates as functions of time. Quaternary Research 15(3), 250 – 264. Hachinohe,S., Hiraki, N., Suzuki, T., 1999. Rates of weathering and temporal changes in strength of bedrock of marine terraces in Boso Peninsula, Japan. Engineering Geology 70, 231 – 237. 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), 167-184. DOI: 10.1007/s10064-002-0155-4 Huisman, M., 2006. Assessment of rock mass decay in artificial slopes. PhD Thesis, ITC, Enschede. ISO 14689-1:2003, 2003. Geotechnical investigation and testing. Identification and classification of rock. Part 1: Identification and description. 1st edition. International Organization for Standardization, Geneva, Switzerland, 16pp. Ollier, C.D., 1969. Weathering. Oliver and Boyd, 304 pp. Price, D.G., 1995a. Weathering and weathering processes. Quarterly Journal of Engineering Geology 28, 243-252. Price, D.G., 1995b. A suggested method for the classification of rock mass weathering by a ratings system. Quarterly Journal of Engineering Geology and Hydrogeology 26 (1), 69-76. Selby, M.J., 1993. Hillslope Materials and Processes, 2nd ed. Oxford University Press, Oxford, UK, 415pp. Wyllie , D.C., Mah, C.W., 2004. Rock Slope Engineering. 4th Ed. Taylor and Francis Group, 431 pp.

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