HOW TO CLASSIFY ROCKS BASED ON DEGREE OF WEATHERING?

CLASSIFICATION BASED ON DEGREE OF WEATHERING OF ROCK MASS:-

Rocks can be classified on the basis of its degree of wreathing. These type of rock classification gives the engineer qualitative idea of rock mass. This type of classification is generally done on site and only by a through visual inspection rocks can be classified. While making classification as per degree of weathering rocks are classified as grade I, II, III etc.

The table given below shows the classification of rock based on degree of weathering of the rock mass as suggested by Geological Society of London.

Term	Description	Grade
Fresh	No visible sign of material weathering	IA
Faintly weathered	Discoloration on major discontinuity surfaces	IB
Slightly weathered	Discoloration indicates weathering of rock material and discontinuity of surfaces. All the rock material may be discolored by weathering and may be somewhat weaker than its fresh condition.	II
Moderately weathered	Less than half the rock material is decomposed and/or disintegrates to soil. Fresh or discolored rock is present either as a continuous frame work of as core stones.	III
Highly weathered	More than half the rock material is decomposed and/or disintegrated to soil. Fresh or discolored rock is present either as a discontinuous frame work or as core stones.	IV
Completely weathered	All rock material is decomposed and/or disintegrated to soil. The original mass structure is largely intact.	V
Residual soil	All rock material is converted to soil. The mass structure and material fabric are destroyed. There is a large change in volume, but the soil has not been significantly transported.	VI