S E C T I O N 4. GROUTING METHODS
a. General. Regardless of the number of exploratory borings or other
investigations, information on the size and continuity of
groutable natural openings in rock below the surface will be relatively mea-
ger at the start of grouting operations and only slightly better after the
grouting is completed. The presence of groutable voids can be ascertained
before grouting and verified by grouting, but their sizes, shapes, and ramifi-
cations will be largely conjectural. In large measure, the "art" of grouting
consists of being able to satisfactorily treat these relatively unknown sub-
surface conditions without direct observation. The discussions of grouting
practices in this manual are intended to guide the apprentice, but not to re-
p l a c e experience. All the procedures and methods presented for grouting
rock apply to portland-cement grouting; some of them apply equally well to
grouting with other materials.
b. Curtain Grouting. Curtain grouting is the construction of a curtain
or barrier of grout by drilling and grouting a linear sequence of holes. Its
purpose is to reduce permeability. The curtain may have any shape or atti-
tude. It may cross a valley as a vertical or an inclined seepage cutoff under
a dam; it may be circular around a shaft or other deep excavation; or it may
be nearly horizontal to form an umbrella of grout over an underground in-
A grout curtain may be made up of a single row of holes, or it
may be composed of two or more parallel rows.
c. Blanket or Area Grouting. In blanket grouting the grout is injected
into s--hallow holes drilled on a grid pattern to improve the bearing capacity
and/or to reduce the permeability of broken or leached rock. Such grouting
is sometimes called consolidation grouting. Blanket grouting may be used to
form a grout cap prior to curtain grouting lower zones at higher pressures,
or it may be used to consolidate broken or fractured rock around a tunnel or
other structure underground.
d. Contact Grouting. Contact grouting is the grouting of voids between
the walls of an underground excavation and its constructed lining. These
voids may result from excavation over break, concrete shrinkage, or a mis-
fit of lining to the wall of the excavation. The crown of a tunnel is a common
locale for contact grouting.
e. Mine and Cavity Filling. Grout may be used to fill abandoned mines
or large natural cavities underlying engineering structures to prevent or
stop roof collapse and subsidence. The size of these openings permits use of
a grout containing sand or sand and small gravel, If seepage control is in.
volved, a second or a third phase of grouting may be required with the