TM
5-818-6/AFM
88-32
S E C T I O N 2. SUBSURFACE INVESTIGATIONS
3.
GENERAL REQUIREMENTS. An investigation of subsurface conditions
such as that normally made for foundation design purposes is usually suffi-
cient to determine whether unfavorable conditions are present that can be
improved by grouting. The discovery of any of the following in the course of
these investigations warrants consideration of treatment by grouting if the
success of the project could be affected thereby: soluble rocks or evidences
of solution activity, prominent open joints, broken or intensely jointed rock,
faulting, losses of circulation or dropping of drill rods during drilling, or
unusual groundwater conditions.
4.
SPECIAL
REQUIREMENTS.
a. Exploratory Borings. Specific information on subsurface conditions
is needed to plan the grouting program. In order to determine the scope and
estimate the costs of the drilling and grouting operations in rock, informa-
tion on orientation, attitude and spacing of joints, joint openings including
type of filler if any, boundaries of rock types, location of faults, location of
broken zones, depth to sound rock, and position of water table should be
a v a i l a b l e . The borehole camera or television camera can be of particular
assistance in obtaining this information. If soil is to be grouted, information
on its stratification, density, grain size, and permeability will be required.
If these data, as pertinent to the project, cannot be obtained from the design
investigations or from rock exposed by the first excavation at the site, ad-
ditional explorations (borings, trenches, etc. ) should be made to supply the
missing data.
b.
Field
Tests.
( 1 ) Pressure tests. Pressure testing by pumping measured amounts of
water into exploratory boreholes under known pressures serves a useful
purpose if the injection of gel-forming grouts is contemplated. The results
of the pressure tests will show the permeability of the soil or rock mass to
water or other fluid of the same viscosity. The best way to determine the
permeability of uniform, porous , water-bearing soil layers is by a pumping
t e s t , as discussed in Civil Works Technical Letter 63-16. Pressure testing
of rock to learn whether it will accept a cement or clay grout is rarely worth-
w h i l e . If pressure testing is done for this purpose each tested increment of
borehole should be examined by television or borehole camera to obtain in-
formation on the size of the openings that are presumed to take water.
( 2 ) Test grouting. The most reliable means of obtaining realistic an-
swers to questions on the capability of rock to take a grout containing solids
in suspension is by test grouting. The test-grout program should be planned
not only to provide information on the groutability of the rock, but also on the
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