T182 Environmental and Engineering Geology Division (Posters)

Tuesday, 24 September 2019
9:00 AM - 6:30 PM
Hall AB, North Building

A STUDY ON THE SLAKE DURABILITY INDEX OF DIFFERENT WEATHERED ROCKS IN SRI LANKA

Paper number: T182-22
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Studies on the engineering properties of different rock types provide a prior knowledge on the quality of such rock types as well as potential locations of suitable sources for the industry. Slake Durability Index (SDI) quantifies the resistance of a rock to wetting and drying cycles, and is seen as a measure of the durability of the rock. The SDI varies according to the type of minerals in a rock, its’ origin and the degree of weathering. If rocks are using for embankments or other construction related applications the estimation of their deterioration over a period of time when subjected to water immersion is necessary. With the aim of that, fresh and differently weathered samples of different major metamorphic rock types were collected from different localities in Sri Lanka to study the variation of Slake Durability Index with the degree of weathering. Samples were tested in the geotechnical engineering laboratory according to the Standard Method ASTM D4644. Using the results, classification of SDI values by Gamble (1971)* was used to classify the durability of the weathered rocks in Sri Lanka. The results are given in the following Table.

Accordingly, all fresh rocks (FR) show very high durability. Except hornblende biotite gneiss slightly weathered (SW) rocks show high durability. Moderately weathered rocks (MW) show medium durability category and all highly weathered rocks (HW) fall to low durability. This indicates that the recognition of weathering grade of a rock is enough to use the Gamble’s durability classification table temporarily in the field.

Table. Results of slake durability index tests for some rock types in Sri Lanka.

Rock type (Metamorphic Rocks only)

Weathering Grade

SDI Range %

SDI Mean %

Durability (according to*)

Charnockite/ charnockitic gneiss

FR

100

100

Very High

SW

98-97

97.5

High

MW

94-89

91.5

Medium High

HW

60-40

50

Low

Garnet sillimanite gneiss

FR

100

100

Very High

SW

98-97

97.5

High

MW

94-87

90.5

Medium High

HW

60-50

55

Low

Hornblende biotite gneiss

FR

100

100

Very High

SW

92-91

91.5

Medium High

MW

82-87

84.5

Medium

HW

50-55

52.5

Low

Granulite

FR

100

100

Very High

SW

96-98

97

High

MW

90-92

91

Medium High

HW

35-40

37.5

Low

Reference* https://www.slideshare.net/Shoaibafridi/6-40835695

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-330997

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