Rock Weathering – Tropical climate LO2- Characterization and classification by weathering grade Determine the quality of rock mass

BS 5930

Clause 44 – pp 132, 1999 Clause 44,pp 112,1981

1 DEVELOPMENTOF ROCK MASS CLASSIFICATION BY WEATHERING GRADE FOR ENGINEERING WORK.(Zainab,2004)

soil mechanics

Weathered rock

rock mechanics

2 Weathering profile of Granite rock mass Quarry

Weathering profile of Granite rock mass Puchong Quarry

3 Weathering profile of Granite rock mass Lembah

Weathering profile of Granite rock mass Ipoh

4 Weathering profile of Granite rock mass Hulu Langat -

Weathering profile of Granite rock mass Hulu Langat - Semenyih

5 Weathering profile of Meta Sedimentary rock mass

Excavation of Hard material at ,

6 Failure of Sedimentary cut slope at Lebuhraya Pantai Timur

Schematic diagram of weathering profiles (Fookes,97)

Granite Metamorphic Carbonate

7 * Rock mass deterioration with time * Lost of strength * Weakening of discontinuities with time * Engineering mechanics

Soil Mechanics No Mechanics Rock Mechanics

Physical weathering

Chemical weathering

8 Figure 2: Rock slope failure at Bukit Lanjan, from left; a year after construction, during the collapse and after rehabilitation work.

A year after construction During the collapse After rehabilitation work

Construction of Pergau Dam

9 Steep cliff ALLUVIUM Pinnacle Floater

Cavity LIMESTONE

KARSTIC PROFILE

10 PROBLEM/RISKS OF BORED PILES SOCKETED IN LIMESTONE BEDROCK

11 (Mohamed, 2010)

GENETIC TROPICAL WEATHERING INFLUENCE IN SITU CHARACTER e.g. Mineralogy Geology Fabric Climate Structure Landform Strength Hydrology Moisture Time condition Vegetation

PROJECT PROJECT GEOTECHNICAL INFLUENCE PERFORMANCE Changes in: e.g.: Stress Actual swell Hydrology Actual settlement Fabric Working strength Working strain

12 Site investigation is a process of site exploration consisting of boring, sampling and testing so as to obtain geotechnical information for a safe, practical and economical geotechnical evaluation and design. Generally it is an exploration or discovery of the ground conditions especially on untouched site.

To study the general suitability of the site for an engineering project. To enable a safe, practical and economic design to be prepared. To determine the possible difficulties that may be encountered by a specific construction method for any particular civil project. To study the suitability of construction material (soil or rock).

13 Methods for study of rock masses : 1. Desk study of existing data and photo-interpretation 2. Surface investigation, geological and engineering geological mapping and sampling of outcrops 3. Subsurface investigation, using geophysical and mechanical techniques as well as methods for visual inspection and logging zones of the rock masses at depth 4. Laboratory test for the characterization of rocks and discontinuities 5. In-situ tests for the assessment of rock mass properties 6. Monitoring the behaviour of rock masses

SI of rock - si of small rock samples in the lab provides only approx info. Small specimens represent stronger rock material than the rock mass in situ

14 - Joints in a rock mass reduce its effective shear strength at least in a direction parallel with the discontinuities - Strength of jointed rocks is highly anisotropics - Joints offer no resistance to tension and high resistance to compression

- Nevertheless, they deform under compression if there are compressible filling or aperture along the joint or if the wall of the rock is weathered - Where discontinuities dip into a rock face, they only impose a direct mechanical instability on the face when they are of the same scale

15 - They allow the ingress of water into the rock mass and as a result facilitate an increase in pore water pressure, hence reduces the effective strength of rock mass - When discontinuities daylight into a rock face they adversely affect stability. In this case the slope of the face is to a greater or lesser extent controlled by the discontinuities

16 Failure modes in rock masses- depend on Type and structure of the rock Seepage water conditions and other characteristics Geometric conditions of the slope Possible external loads (including seismic forces)

Heterogeneity and anisotropic Structural features joints, bedding planes cleavage shear zones Voids rock pores cavities fissures cracks partially or fully filled with air, gas/water

17 Effect of water pressure Increasing water content effects on stability, namely seepage pressure lateral water pressure in tension crack shear strength deterioration of gouge

• How do you decide on the allowable risk to rock slope failure? Degree of calculated risk is influenced by the extent to which rock investigations are take , most rock slope-slope failures occur along discontinuities or zone of weakness • Amount of deformation that can be tolerated in the foundation of a dam

18 • Allowable loads in the reinforcing cables in an underground cavern or tunnel • Rock excavation techniques? – - drill and blast method? – - tunnel boring machine? – - especially….cost implication.

• Boulders within a decomposed rock mass lead to a stress concentration on the retaining wall • The pressure of water in cracks, pores, joints or bedding planes causes mechanical disintegration, splitting of rock and a local overstressing of retaining structures

19