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OCR for page 397
APPENDIX G
SPECIMEN PREPARATION OF COHESIVE SOIL
G-1
OCR for page 398
APPENDIX G
SPECIMEN PREPARATION OF COHESIVE SOIL
Impact Compaction. In the impact procedure, the soil was compacted in a 4 in. diameter by
8.5 in. high cylindrical split mold. The lower 0.5 in. of the mold was used to create either
flat or sloped specimen ends for Phase ~ testing by placing a 0.5 in. thick steel plate at the
bottom of the mold. The flat steel plate made the extrusion of the soil sample much easier.
Impact compaction was achieved using 5 layers and 22 blows per layer of a 5.5 lb hammer
dropping 12 in. which was found by trial and error to produce a similar moisture density
curve to the conventional T-99 procedure. Each soil specimen was prepared according to
the following procedure:
~ . Weigh out 8.0 lbs of air dried soil.
2. Add the calculated mass of water to achieve the target water content.
3. Thoroughly mix the soil sample and water and then cover the container
with aluminum foil for 24 hours.
4.
Spray the mold with a lubricant to prevent the compacted specimen from
sticking to the mold walls, and then compact the wet soil in five layers using
the 5.5 lb. hammer applying 22 blows to each layer.
5. Extrude the wet soil sample using a hydraulic extruder and determine the
wet weight of the sample, WT
6.
Determine the water content from the remaining portion of wet soil.
Kneading Compaction. The spring loaded kneading compactor, which uses a pie shaped
foot, was used to compact the silty sand and clayey sand soils into a 4.0 in. diameter mold.
Specimens were compacted in 10 layers with 24 tamps per layer using a 70 lb. spring.
Ibis preparation procedure was determined by trial and error to give a dry density that
matches the T-99 density at optimum water content. Using this compaction energy the
following procedure was used:
~ . Weigh out 8.0 lbs of air dried soil.
2.
Add the calculated mass of water to achieve the target water content.
3. Thoroughly mix the soil sample and water and then cover the container
with aluminum foil for 24 hours.
4.
5.
Spray the mold with a lubricant to prevent the compacted specimen from
sticking to the mold walls, and then compact the wet soil in ten layers using
the 70 lb. spring loaded hammer to apply 24 tamps to each layer. Level
every layer before tamping, and generate 70 lbs. by just compressing the
spring. Relevel after 12 tamps.
After tamping the last layer, level the top and measure the total specimen
weight. Measure the water content from the trimmings and calculate the dry
density.
G-2
OCR for page 399
Compaction of CohesionIess Soil
All A-3 sand specimens were prepared by tamping the sand at a water content of
9.0% in eight equal layers by the following procedure using the apparatus shown In Figure
G-1:
Weigh out 7.0~Ibs. of air dried cohesionTess soil and mix with 286 ml of
water to obtain a water content of 9.0 %.
2. Determine the weight of each layer from the relative density and the needed
dry densities as follows:
WT=7dxVT
We, = WT / HT
3. Place a filter paper on top of the pedestal of the tnaxial cell.
4. Place each layer of sand In the split mold and tamp it as shown in Figure G
1.
5. After tamping the last layer, level Me top layer and weigh the extra soil to
determine the total compacted soil weight (WT)- Take a sample from the
remaining soil to find the water content.
6.
Apply a vacuum of about 2 to 3 psi to the specimen base to hold the soil
sample together while removing the split mold.
7. Add another membrane around the sample to prevent air leaks.
8.
9.
After mounting the tnaxial cell chamber and applying the confining
pressure, release the vacuum applied to the inside of the sample.
Leave the base drainage valve open throughout the test.
Soaking Cohesive Specimens
Cohesive soil specimens were soaked by applying a back pressure of lLO psi to the
specimen for about 15 days. The clayey sand (A-6) specimens were very difficult to soak
because of the presence of clay. While the A-5 specimens were easier to soak, they still
took about two weeks to reach a degree of saturation of more than 90%. Bow the
compacted A-6 and A-5 soil specimens were soaked in the cell shown in Figure G-2 by the
following procedure:
I. Compact the soil specimen following the procedure for cohesive soil given
earlier using a 4.0 in. diameter PVC mold.
2.
After removing the base, measure the total weight of the soil specimen and
the mold. Use this weight and We water content evaluated from the
remaining portion of the soil to calculate We initial degree of saturation.
OCR for page 400
Cover both ends with Alter paper.
4. Saturate the drainage line going into the bottom of the base before screwing
it into the base . Also saturate the porous stones.
5. Fix the bottom base to the mold which contains the soil specimen after
positioning the O-ring to prevent leakage.
6. Attach the top end plate having a hole pattern and size similar to the one
used when soaking CBR specimens and screw it on tightly.
7. Apply a back pressure of 10 psi to the specimen base using a biaxial
pressure board. To reduce the tone required for saturation, a larger back
pressure could be used for production work.
8.
9.
Monitor the amount of water flowing to the soil specimens with the help of
the pressure board burettes.
Make sure that the lines and the burettes do not run out of water while
· ~
soa sing specimens.
10. After two weeks disassemble the setup and find the weight of the soaked
sample. The increased weight of the soil sample equals the weight of water
that flowed into the soil specimen.
Calculate the degree of saturation of the soaked sample.
Specimen End Preparation
To give better contact between the top and bottom plates and the specimen, the ends
of selected specimens were grouted with hydrostone I-. The clamps used to grout the
specimen ends are shown in Figure G-3. The grouting procedure is shown in Figure G-4
and described as follows:
. Mix 28 ml of water with 70 gm of hydrostone cement until it becomes a
liquid. The water-hydrostone cement (W/C) ratio is 0.4 by weight.
2. Let the mixture hydrate for about 15 min. as to become a paste.
3.
Pour the paste into the aluminum split clamps around the pedestal shown in
Figure G-4(a). Place the sample on top of the hydrostone grout.
4. Center the sample vertically by using an acrylic plate with a 5.0 in. diameter
hole in Me middle and supported horizontally on three steel rods Elxed to the
base of the biaxial cell as shown in Figure G-4(b).
5. Remove the clamps from around the bottom of the sample 10 min. after
pouring the grout into the mold.
6. Repeat steps ~ and 2.
Place the clamps around the top end of the sample using the acrylic plate as
a support as shown in Figure G-4(b).
G-4
OCR for page 401
8
9e
Repeat step 3.
Place the top cap on the top of the hydrostone paste and center it in the
direction to fit the EVDT clamps.
Place a rubber membrane around the specimen and form a seal using two
rubber O-rings. Leave it for about two hours to allow the hydrostone paste
to reach its required strength.
I. Fix the EVDT rod carriers to the bottom of the tr~ax~al cell and attach the
EVDT's to them.
The specimen is now ready for testing.
Attaching EVDT Clamps
Figure G-5 shows the Inside EVDT clamps (Figure G-5a) used in Phase ~ and He
alignment supports (Figure G-5b) developed to install these clamps. Four steel arms carry
the four clamps and each clamp is fixed by a screw to the end of the arm. Me arms are
connected to two horizontally fixed bars which are cattier on a veridical steel rod and kept a
fixer} distance apart. The vertical steel bar is supported by a steel base to give stability.
The alignment support device maintains the four clamps on He middle of the sample at a
fixed separation distance equal to half of the total specimen height. The clamps are fixed to
the sample by rubber bands.
References
Gut. Pezo, R.F., CIaros, G., Hudson, W.R., and Stoke, K.H., (1992), "Development
of a Reliable Resilient Modulus Test for Subgrade and Non-Granular Subbase
Materials For Use in A Routine Pavement Design", Research Report ~ 177-4F.
(prepared for Texas DOT), University of Texas-Austin, January.
G-S
OCR for page 402
1 ' ~ 1'
o
- -
~ ~ Ple glass Coil
, ~ __ , ~
~ ~ Plexiglas Split Sold
Hem; ~9 `` ~ ~
C oh 4t
~ ~ _
o
Collar
Figure G- 1. Setup for preparing cohesionless soil specimen
G-6
Vacuum
Tribal Cell Base
OCR for page 403
Holes Similar to Those of CBR Soaking Plate
_ :/
I Tl 11 11 1~lL
/
.
Back Pressure
\
Soil Specimen
D = 4.0 in.
H = 8.0 in.
11
~ '\ 11 ~
c- ~
~N ' O-Ring
Screws
. ~
Figure G-2. Setup used to soak cohesive soil specimens
G-7
Filter Paper
PVC Mold
Filter Paper
OCR for page 404
~ D.4.0~.
Hi_ A//
=
0.1 ~
Spat ~
Hy~tone Grout
~ Space
1 '' - _
~ ~C~8~
. ~
Figure G-3. Clamps used in grouting the ends of the test specimen
G-8
OCR for page 405
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OCR for page 406
Al
sat // //
LOOT Hole
3\~\ Lt~ R"1 Hole
R ~ 2 0 loch
~ JO
(a) One pair of internal LVDT clamps
1 1
1 - ~ ' _ 1
,
~ , ,, , i,
1
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(b) Side view of alignment support device
Figure G-5. Eternal L~VDT clamps and alignment support device
C-10
Representative terms from entire chapter:
soil specimen
