WSPC03161

• File Number: 8040.950
• Description: Section D General Studies-General Water Studies
• Date: 1/1/1962
• Author: RD Dirmeyer Jr
• Title: Bentonite Program-Corres Reports-Dirmeyer-1960-1961-Progress Report of Clay Sealing Investigations During 1961
• Water Supply Pro - Doc Type: Report/Study

CLAY TESTING

The results of laboratory testing of the clay
samples collected thus far in the Colorado State
University program are summarized in Tables I(a),
(b), (c), and II at the end of this report. As men-
tioned previously, the clay deposits or sample loca-
tions are shown on Figure I. As of January 1, 1962.,
237 samples from 99 deposits or sample locations
have been tested. Of the total, 112 samples were
tested during 1961.

While the test results in the tables are
grouped as to favorable and unfavorable, this division
is extremely arbitrary and tentative. Actually, only
a very few of the samples are of satisfactory relia-
bility. The cross-section samples from stockpiles
of mined bentonite usually are considered reliable,
but mast of the samples are exploration samples
from outcrop areas. The test results of the latter
type of sample can be expected to vary widely from
one sample location to another.

Even with reliable and representative samples,
the results of the laboratory testing should be tem-
pered with the knowledge of where and how the clay
is to be used. For example, in very coarse rocky
materials a gritty clay will often hold better than a
pure grit-free clay--to use such a gritty clay for
sealing a sandy soil could be wasteful.

For a brief description of the test procedures,
see the bottom of Tables 1(c) and II. While not infal-
lible nor final, the following test limits are offered
for general guidance concerning clays to be used for
sealing of canals and reservoirs:

1. Layer permeability-- A permeability of
.009 ftl day or less is desirable. As may be seen in
the tabulation at the bottom of Table II, the recom-
mended thickness of clay layer increases as the
permeability increases.

Z. Filter permeability -- A value of
10 mi. / min. or less is desirable.

As a note of caution and explanation, the
laboratory layer permeability test is run on a
loosely-placed layer--compaction of the clay layer
or salt treatment, if properly utilized, will lower the
permeability of the clay layer. In addition, the filter
permeability test is pointed at the float-in applica-
tions of clay in canals. Here again proper use of a
dispersing agent. such as Calgon> can result in a
lower permeability rate.

Although exceptions to the following have been
noted, the best sealing clays (as indicated in field
trials) usually exhibit the following characteristics:

1. A colloidal yield (clay content) of
30~0 or more.
Z. A grit or sand content (.074 mm or more)
of 15'0 or less.
3. A swell index (ratio of wet to dry volume
of clay) of 100010 or more.
4. A cation-exchange-capacity of
40 meq/l 00 gms or more.
5. An exchangeable-sodium-percentage of
10'0 or more.
6. Montmorillonite as the dominant clay mineraL
7. A mixability index (ease of mixing) of 50<yo or
more, if the clay is to be useful in float-
in (sedimenting) applications.

As to future laboratory work on Colorado
clays, all of the testing procedures are still in a pro-
cess of development and refinement. This work will
be intensified and essentially completed during 1962.
Samples from new clay deposits and fOllow-up
samples from deposits under development also will
be tested. The objective of this work is develop-
ment of simple reliable test procedures for use by
commercial, state and federal laboratories in future
evaluations of clays for canal and reservoir sealing
purposes.

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