Soil Compaction and Field Density Flashcards
A simple ground improvement technique, where the soil
is densified through external compactive effort.
compaction
The process of bringing the soil particles closer to a dense
state by mechanical means
compaction
The ______ are reduced by
expulsion of air and the soil particles are packed together,
thereby increasing its unit weight.
voids
There is no substantial change in the volume of water in soil
during compaction. T or F
T
_________ is done to improve the Engineering properties of
soil such as increase of shear, increase the bearing strength,
reduce the compressibility of soil, change the soil properties
like shrinkage, frost susceptibility and permeability of soils.
Compaction
To compact a soil,
that is, to place it in a _________.
dense state
The __________ is achieved through the reduction of the air voids in the
soil, with little or no reduction in the water content. This process must
not be confused with _________, in which water is squeezed out under
the action of a continuous static load
dense state, consolidation
Objective of compaction
(1) Decrease future settlements
(2) Increase shear strength
(3) Decrease permeability
_________ in the early 1930’s was building dams for the old Bureau of
Waterworks and Supply in Los Angeles, and he developed the principles
of compaction in a series of articles in Engineering News-Record. In his
honor, the standard laboratory compaction test which he developed is
commonly called the ______
R.R. Proctor, proctor test
The purpose of a laboratory compaction test is to determine the _________________ to use when compacting the soil in the field and
the ___________ which can be expected from compaction
at this optimum water
proper
amount of mixing water, resulting degree of denseness
The proctor test is an ________. A hammer is dropped several
times on a soil sample in a mold. The mass of the hammer, height of drop,
number of drops, number of layers of soil, and the volume of the mold are
specified
impact compaction
Standard Proctor Test
_______ height of drop
_____hammer
______ blows/layer
_____ layers
Mold size: ______
Energy _________
12 in
5.5 lb
25
3
1/30 ft3
12,375 ft·lb/ft3
Modified Proctor Test
_____ height of drop
_____ hammer
_____ blows/layer
___ layers
Mold size: _______
Energy ______
18 in
10 lb
25
5
1/30 ft3
56,250 ft·lb/ft3
The ________ was developed during World War II by the U.S. Army Corps of Engineering
modified test
Several samples of the same soil, but at different water contents, are
compacted according to the ___________
compaction test specifications
The ______ of the compaction curve is the point with the maximum
dry density pd max.
peak point
Corresponding to the maximum dry density pd max is a
water content known as the ________
optimum water content
that the maximum dry density
is only a maximum for a specific compactive effort and method of
compaction. This reflects the maximum dry density
that can be obtained in the field. T or F
T, does not necessarily
The curve represents the fully saturated condition (S = 100 %). (It cannot
be reached by compaction)
Zero air voids curve
A line drawn through the peak points of several compaction curves at
different compactive efforts for the same soil will be almost parallel to a
100 % S curve, it is called the _________-
line of optimums
As the water content increases, the particles
develop larger and larger water films around
them, which tend to “_______-” the particles
and make them easier to be moved about and
reoriented into a denser configuration.
Below wopt (dry side of optimum):, lubricate
The density is at the maximum, and it does
not increase any further.
At wopt
Water starts to replace soil particles in the
mold, and since pw «_space;ps the dry density
starts to decrease
Above wopt (wet side of optimum):
Each data point on the curve represents a single
compaction test, and usually ___________
compaction tests are required to completely determine the
compaction curve.
four or five individual
At least two specimens wet and two specimens dry of
optimum, and water contents varying by about ____.
2%
Optimum water content is typically slightly less than the
plastic limit (___________)
ASTM suggestion
Typical values of maximum dry density are around _________ with the maximum range from about __________.
1.6 to
2.0 Mg/m3, 1.3 to 2.4
Mg/m3
Typical optimum water contents are between _________, with an outside maximum range of about ________
10%
and 20%, 5% to
40%
Five factors affecting compaction
- Physical & chemical properties
- Moisture content
- Method of compaction
- Amount of compactive effort
- Thickness of layer or “lift” being
compacted
The ______-that is, grain-size distribution, shape of the soil grains,
specific gravity of soil solids, and amount and type of clay minerals
present.
soil type
As the___________
increased, the max dry unit
weight of compaction is also
increased and the optimum
moisture content is decreased
to some extent.
compaction effort
The _________ is
not directly proportional to the
compaction effort.
degree of compaction
The_________
generally yield a somewhat
lower optimum water content
than the actual field optimum
laboratory curves
The majority of field
compaction is controlled by
the ______________
dynamic laboratory tests.
For a given compactive
effort and dry density, the
soil tends to be more
________ (random) for
compaction on the dry side
as compared on the wet side.
flocculated
For a given __________
content, increasing the
compactive effort tends to
disperse (parallel, oriented)
the soil, especially on the
dry side
molding water
Increasing the water content
results in a decrease in
permeability on the dry side of
the optimum moisture content
and a slight increase in
permeability on the wet side of
optimum. T or F
T
At low stresses the sample compacted on the wet side is
less compressible than the one compacted on the dry side. T or F
F, more
At the high applied stresses the sample compacted on the dry side
is more compressible than the sample compacted on the wet side. T or F
T
________ of compacted clays is greater for those compacted
dry of optimum. They have a relatively greater deficiency
of water and therefore have a greater tendency to adsorb
water and thus swell more
Swelling
the ratio between resistance required
to penetrate a 3-in^2 piston into the
compacted specimen and resistance
required to penetrate the same depth into a
standard sample of crushed stone.
The CBR (California bearing ratio)
Because of the differences between lab and field compaction
methods, the maximum dry density in the field may reach ________
90% to
95%.
- 100% coverage under the wheel
- Contact pressure up to 380 kPa
- Can be used on all soil types
except for rocky soils. - Compactive effort: static weight
- The most common use of large
smooth wheel rollers is for proof
rolling subgrades and compacting
asphalt pavement.
Smooth-wheel roller (drum)
- 80% coverage under the wheel
- Contact pressure up to 700 kPa
- Can be used for both granular and
fine-grained soils. - Compactive effort: static weight
and kneading. - Can be used for highway fills or
earth dam construction.
Pneumatic (or rubber-tired) roller
- Has many round or rectangular
shaped protrusions or “feet”
attached to a steel drum - 8% ~ 12 % coverage
- Contact pressure is from 1400 to
7000 kPa - It is best suited for clayed soils.
- Compactive effort: static weight
and kneading.
Sheepsfoot rollers
- About 40% coverage
- Contact pressure is from 1400 to
8400 kPa - It is best for compacting fine
grained soils (silt and clay). - Compactive effort: static weight
and kneading.
Tamping foot roller
- 50% coverage
- Contact pressure is from 1400 to
6200 kPa - It is ideally suited for compacting
rocky soils, gravels, and sands.
With high towing speed, the
material is vibrated, crushed, and
impacted. - Compactive effort: static weight
and vibration.
Mesh (or grid pattern) roller
Vertical vibrator attached to
smooth wheel rollers.
* The best explanation of why roller
vibration causes densification of
granular soils is that particle
rearrangement occurs due to cyclic
deformation of the soil produced
by the ________ of the roller.
* Compactive effort: static weight
and vibration.
* Suitable for granular soils
Vibrating drum on smooth-wheel
roller, oscillations
________ and ______ correlate well with the
engineering properties, and thus they are convenient
construction control parameters.
Dry density, water content
Since the objective of compaction is to stabilize soils and
improve their engineering behavior, it is important to keep
in mind the desired engineering properties of the ______, not
just its dry density and water content. This point is often
lost in the earthwork construction control.
fill
_______ are conducted on samples of the proposed
borrow materials to define the properties required for
design.
Laboratory tests
After the earth structure is designed, the compaction
specifications are written. Field compaction ________
are specified, and the results of these become the standard
for controlling the project
control tests
This specification is used for most highways and building
foundation, as long as the contractor is able to obtain the
specified relative compaction , how he obtains it doesn’t
matter, nor does the equipment he uses
End-product specifications
The type and weight of roller, the number of passes of that
roller, as well as the lift thickness are specified. A maximum
allowable size of material may also be specified.
It is typically used for large compaction project.
From
Method specifications
Field Compaction depends on:
· Weight of roller
· No of passes of roller
_________ is given in specification for
field compaction, which is the ratio of field dry
density to the maximum lab density, whereas the
________ is determined by Standard or
Modified AASHTO tests.
Relative compaction, Lab dry density
Typical required R.C.
90% ~ 95%
Typical specifications call for a new
field test for every _________ or so, or when the borrow material
changes significantly.
1000 to 3000 m2
Field control tests, measuring the dry density and water content in the
field can either be ________
destructive or nondestructive
Destructive
Methods
(a) Sand cone
(b) Balloon
(c) Oil (or water) method
compaction test is usually done on materials finer than
________
corrected maximum dry density, 4.75 mm
· sample contains coarse grained sized particles– gravel in a soil composed mainly of fine grains can
be compacted to ________ of their theoretical maximum
density– assuming gravel RD=____
90%, 2.65
Sometimes, the laboratory maximum density may not be
known exactly. It is not uncommon, especially in__________, for a series of laboratory compaction tests to be
conducted on “representative” samples of the borrow
materials for the highway. If the soils at the site are highly
varied, there will be no laboratory results to be compared
with. It is time consuming and expensive to conduct a new
compaction curve. The alternative is to implement a ___________, or _______
highway
construction, field
check point, 1 point Proctor test.
The measuring error is mainly from the determination of
the volume of the ___________.
excavated material
Nondestructive
Methods
Nuclear density meter
(a) Direct transmission
(b) Backscatter
(c) Air gap
The _________ is scattered by the soil
particles and the amount of scatter is
proportional to the total density of the material.
The ___________ is typically provided by
the radium or a radioactive isotope of cesium.
Gamma radiation
The ____________ can be determined based on
the neutron scatter by hydrogen atoms. Typical
neutron sources are __________
water content, americium-beryllium
isotopes
____________ against compacted materials of known density is
necessary, and for instruments operating on the surface the
presence of an uncontrolled air gap can significantly affect
the measurements.
Calibration
