Environmental Engineering Reference
In-Depth Information
FIGURE 2.77
Removal of HX diameter limestone core from the inner barrel of a double-tube swivel-type core barrel.
Reaming shells , slightly larger than the core barrel diameter and set with diamonds or
carbide insert strips, ream the hole, maintaining its gage and reducing bit wear.
Bit Types
Sawtooth bits are the lowest in cost and have a series of teeth cut in the bit which are faced
with tungsten carbide. They are used primarily to core overburden and very soft rock.
Carbide insert bits ( Figure 2.53) have tungsten carbide teeth set in a metal matrix and are
used in soft to medium-hard rocks.
Diamond bits (Figure 2.53) are the most common type, producing high-quality cores in
all rock types from soft to hard. Coring is more rapid, and smaller and longer cores are
retrieved than with other bit types. The diamonds are either surface-set in a metal matrix,
or the metal matrix is impregnated throughout with diamond chips. There are various
designs for cutting various rock types, differing in quality, size, and spacing of the dia-
monds, matrix composition, face contours, and the number and locations of the water-
ways.
Core Recovery and RQD
Reporting Methods
Percent core recovery is the standard reporting method wherein core recovery is given as a
percentage of total length cored. Rock Quality Designation (RQD) was proposed by Deere
(1963) as a method for classifying core recovery to reflect the fracturing and alteration of
rock masses. For RQD determination, the core should be at least 50 mm in diameter (NX)
 
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