TM
5-818-6/AFM
88-32
of clay minerals present. Common clay minerals encountered are kaolinite,
m o n t m o r i l l o n i t e , and illite. Kaolinite and montmorillonite are the most
common and are found in various combinations in most fine-grained soils.
Because of its ability to adsorb large quantities of water, a high percentage
of montmorillonite is desirable for clay grouts. The clay minerals will gen-
erally make tip most of the material finer than 2 microns.
c. P r o c e s s e d Clay. T h e most commonly used commercially processed
clay--is bentonite, a predominantly montmorillonitic clay formed from the
alteration of volcanic ash. The bentonite ore is crushed, dried, and finely
ground to form the commercial products. Most bentonites exhibit a liquid
limit of 350 to 500 and possess the ability to undergo thixotropic gelation.
The gelling property is desirable to produce sufficient strengths in the in-
jected grout to resist removal by groundwater under a pressure head. How-
ever, gelling can also create problems in pumping if not properly controlled.
d . Testing Clays for Grouts. In determining the suitability of a soil as
a grout$ sufficient information for most projects can be obtained from a few
c o m m o n mechanical tests. Samples of the grout material should be handled
and processed in conducting these tests in the same manner as that in which
the material will be processed in the field when making the grout. For ex-
ample, if the field procedure calls for air drying the raw material, the labo-
ratory specimen should also be air dried.
( 1 ) Gradation. One important property of a clay grout is the grain- size
distribution of its solid particles; this can be determined by a hydrometer
a n a l y s i s (see EM 1410-2-1906). The largest clay particles must be small
enough to readily penetrate the voids in the medium to be grouted.
( 2 ) Atterberg limits. Atterberg limits are indicative of the plasticity
characteristics of the soil. A high liquid limit (LL) and plasticity index (PI)
generally indicate a high clay mineral content, high ion exchange capacity, or
a combination thereof. Normally, a clay with a liquid limit less than 60 is
not suitable for grout where a high clay mineral content and/or high ion ex-
change capacity is required (see ref 36).
( 3 ) Specific g r a v i t y . Refer to EM 1110-2-1906. The specific gravity (Gs)
of the solid constituents of a soil mass is indicative, to some degree, of
their mineral composition. In addition, the value is needed in computations
involving densities and void ratios.
e . A d m i x t u r e s . For the purpose of modifying the basic properties of a
clay--grout to achieve a required result, certain additives can be used.
( 1 ) Portland cement. Portland cements can be used in clay grouts to
produce a set or to increase the strength. The amount of cement required
must be determined in the laboratory so that required strength will be
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