TM 5-818-1 / AFM 88-3, Chap. 7
Table 2-6. Descriptive Criteria for Rock-Continued
3.
Discontinuities
a. Joints
(1)
Type: bedding, cleavage, foliation, schistosity, extension
(2)
Separations: open or closed, how far open
(3)
Character of surface: smooth or rough; if rough, how much relief, average asperity angle
(4)
Weathering of clay products between surfaces
b. Faults and shear zones
(1)
Single plane or zone: how thick
(2)
Character of sheared materials in zone
(3)
Direction of movement, slickensides
(4)
Clay fillings
c. Solution, cavities, and voids
(1) Size
(2) Shape: planar, irregular, etc.
(3) Orientation (if applicable): developed along joints, bedding planes, at intersections of joints and bedding
planes, etc.
(4) Filling: percentage of void volume and type of filling material (e.g. sand, silt, clay, etc.).
(Sheet 3 of 3)
U. S. Army Corps of Engineers
Referring to figure 2-4, with a core advance of 60 inches
and a sum of intact pieces, 4 inches or larger, of 34
ment of texture or structural features in any type of rock;
inches, the RQD is computed as:
e.g., cleavage in slate or schistosity in a metamorphic
34
rock. The term is most commonly applied to
RQD = 60
= 0.57
metamorphic rock.
b. Samples that are tested in the laboratory
Also shown in figure 2-4 is a qualitative rating of the rock
mass in terms of RQD. RQD depends on the drilling
(termed "intact" samples) represent the upper limit of
technique, which may induce fracture as well as rock
strength and stress-strain characteristics of the rock and
may not be representative of the mass behavior of the
identified by careful inspection of the recovered sample.
rock. Coring causes cracks, fissures, and weak planes
to open, often resulting in a recovery of many rock
2-7.
Shales.
fragments of varying length for any core barrel advance.
a. Depending on climatic, geologic, and
Only samples (intact pieces) surviving coring and having
exposure conditions, shale may behave as either a rock
a length/diameter ratio of 2 to 2.5 are tested. Rock
or soil but must always be handled and stored as though
Quality Designation (RQD) is an index or measure of the
it is soil. For these reasons, shale is considered
quality of the rock mass. RQD is defined as:
separately from either soil or rock. Shale is a fine-grained
∑ Lengths of intact
sedimentary rock composed essentially of compressed
RQD =
pieces > 4 in. long
Length of core advance
2-13
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