(4) Drag and fishtail bits. The drag bit is a general service bit for ro-
tary drilling. Capable of drilling soft rock and most soils, it is used exten-
sively in foundation explorations and grout-hole drilling. The fishtail bit is
so named because of its resemblance to a fish tail. The divided ends of its
single blade are curved away from its direction of rotation. , Other drag bits
have three or four blades, which may or may not be replaceable. The cutters
or cutting edges of the blades are made of hardened steel or are covered
with hard alloys. Almost any desired size is available.
c . Summary. Drill bit types and the materials in which they are gen-
erally--used are as follows:
Drill Bit Type
P r i n c i p a l Use
Not Well Suited for
Diamond:
Core
Rock and concrete
Unconsolidated soils
`Plug
Rock
Extremely hard rock,
extremely soft rock,
unconsolidated soils,
and shattered or
fractured rock
Hard
metal
Soft rock, hard clay,
Hard rock and uncon-
and cemented soils
solidated soils
Rock
Rock
Unconsolidated soils
and very hard rock
Drag and fishtail
Soft rock and soil
Hard
rock
Percussion
Rock and concrete
Unconsolidated
soils
15.
GROUT
PLANT.
G r o u t M i x e r s . Many types of grout mixers have been used, including
a.
hand-turned d ough m i x e r s , concrete mixers of various sizes, and especially
designed grout mixers. Any machine is suitable that has the desired capac-
ity and that mixes the grout mechanically to a uniform consistency. Two
mixers can be arranged to discharge into the same sump to satisfy high ca-
pacity
requirements. Manual stirring of cement and clay grouts in a tub is
not satisfactory except in emergencies. Hand-powered dough mixers are not
recommended because of their limited capacity.
(1) Central Valley-type grout mixer, 8-cu-ft capacity. During the
grouting at several d ams of the Central Valley Project, a small, air-
operated, lightweight grout mixer was needed that could be set up and oper-
ated in a 5- by 7-ft gallery. The mixer shown in figure 9 was designed for
42
Previous Page
