Weathering is the process of chemical and/or mechanical degradation of the rock mass over the course of time through exposure to the elements such as rain, wind, ground water, ice, changing temperature, etc. In general, the strength, stiffness, and general quality of intact rock tends to decrease with increase in the degree of weathering. As weathering advances significant changes occur in the physical properties and general quality of the intact rock, until ultimately the rock is decomposed to soil. Therefore, weathering is an important component of classification for engineering purposes.

Identify and record the weathering grades of the rock mass in accordance with the weathering grade shown in Table 4-6 below.

Table 4-6: Descriptive Terms for Weathering State of Rock

Term	Description	Grade
Fresh (F)	No visible sign of rock material weathering; slight discoloration on major discontinuity surfaces is possible.	I
Slightly weathered (WS)	Discoloration indicates weathering of rock material and discontinuity surfaces. All rock material may be discolored by weathering and the external surface may be somewhat weaker than in its fresh condition.	II
Moderately weathered (WM)	Less than half of the rock material is decomposed and/or disintegrated to a soil. Fresh or discolored rock is present either as a discontinuous framework or as corestones. A minimum 2 in. diameter sample cannot be broken readily by hand across the rock fabric.	III
Highly weathered (WH)	More than half of the rock is decomposed and/or disintegrated to soil. Fresh or discolored rock is present either as a discontinuous framework or as corestones. A minimum 2 in. diameter sample can be broken readily by hand across the rock fabric.	IV
Completely weathered (WC)	All rock material is decomposed and/or disintegrated to soil. The original mass structure is largely still intact. Material can by granulated by hand.	V
Residual soil (RS)	All rock material is converted to soil. Material can be easily broken apart by hand.	VI