Geology Reference
In-Depth Information
relative density. Compact the soil in the permeability cylinder by
these procedures in thin layers to a height about 2.0 cm (0.80 in.)
above the upper manometer outlet.
Note 2 —In order to bracket, systematically and representa-
tively, the relative density conditions that may operate in
natural deposits or in compacted embankments, a series of
permeability tests should be made to bracket the range of field
relative densities.
(6) Preparation of Specimen for Permeability Test:
(6.1) Level the upper surface of the soil by placing the upper porous
plate or screen in position and by rotating it gently back and forth.
(6.2) Measure and record: the final height of specimen, H 1 - H 2 ,by
measuring the depth, H 2 , from the upper surface of the perforated
top plate employed to measure H 1 to the top of the upper porous
plate or screen at four symmetrically spaced points after com-
pressing the spring lightly to seat the porous plate or screen dur-
ing the measurements; the final mass of air-dried soil used in the
test ( M 1 - M 2 ) by weighing the remainder of soil, M 2 , left in the
pan. Compute and record the unit weights, void ratio, and relative
density of the test specimen.
(6.3) With its gasket in place, press down the top plate against the
spring and attach it securely to the top of the permeameter cylinder,
making an air-tight seal.
(6.4) Using a vacuum pump or suitable aspirator, evacuate the
specimen under 50 cm (20 in.) Hg minimum for 15 min to remove air
adhering to soil particles and from the voids. Follow the evacua-
tion by a slow saturation of the specimen from the bottom upward
(Figure 18-2) under full vacuum in order to free any remaining air
in the specimen. Continued saturation of the specimen can be main-
tained more adequately by the use of (1) de-aired water, or (2) water
maintained at an in-flow temperature sufficiently high to cause a
decreasing temperature gradient in the specimen during the test.
Native water or water of low mineral content (Note 3) should be used
for the test, but in any case the fluid should be described on the
report form.
Note 3 —Native water is the water occurring in the rock or soil
in situ . It should be used if possible, but it (as well as de-aired
water) may be a refinement not ordinarily feasible for large-
scale production testing.
(6.5) After the specimen has been saturated and the permeameter is
full of water, close the bottom valve on the outlet tube (Figure 18-2)
and disconnect the vacuum. Care should be taken to ensure that
the permeability flow system and the manometer system are free
of air and are working satisfactorily. Fill the inlet tube with water
 
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