2. Question
The contractor, during construction of the soil
embankment, conducted a sand-cone in-place density
test to determine whether the required compaction was
achieved. The following data were obtained during the
test:
Weight of sand used to fill test hole and funnel of sand-cone
device = 845 g.
Weight of sand to fill funnel = 323g.
Unit weigh of sand = 100 lb/ft3
Weigh of wet soil from test hole = 600g
Moisture content of soil from test hole = 17%.
Based on the contract, the contractor is supposed to
attain the 95% compaction. Will you approve the
contractor’s work?
3. Compaction
Compaction – expelling air from the void space
Consolidation – extrusion of water
Effects of compaction
Increase soil’s shear strength
Decrease in future settlement of the soil
Decrease in its permeability
How to quantify – use dry unit weight of soil
contentmoisture
tunit weighwet
1
=
=
+
=
w
w
d
γ
γ
γ
4. Compaction
What does water do for compaction?
Lubricant
Too much water lesser density
Optimum moisture content
(=maximum dry unit weight) best compaction
How to use maximum dry unit weight?
Target unit weight at the job site
Need to know how much the soil can be compacted.
5. Compaction Test
ASTM D 698
Standard Proctor Compaction Test
Hammer: 5.5 lb
Drop Height: 12in
ASTM D 1557
Modified Proctor Compaction Test
Hammer: 10 lb
Drop Height: 18in
For higher value of dry unit weight
6.
7. Compaction Test
Dry out soil sample
Add water to the soil sample
Compact the soil sample in the compaction mold
Measure wet unit weight (γ)
Measure moisture content (w)
Calculate dry unit weight
Repeat 4 times with different moisture contents
w
d
+
=
1
γ
γ
9. Example
Condition
The combined weight of a mold and the
specimen of compacted soil it contains is 9.0
lb.
The mold’s volume is 1/35ft3
The mold’s weight is 4.35 lb.
The specimen’s water content is 12%.
What is dry unit weight of the specimen?
10. Example
A set of laboratory compaction test data and
results is tabulated as follows. Determine the
soil’s maximum dry unit weight and optimum
moisture content.
Determination
Number 1 2 3 4 5
Dry unit weight
(lb/ft3
) 112 115 115 113 109
Moisture
content(%) 5 10 15 20 25
11. What affects Compaction?
Moisture content
Compaction effort
Compaction energy per unit volume (function of
number of blows per layer)
For the stand proctor test: 12,400 ft-lb/ft3
For the modified proctor test: 56,000 ft-lb/ft3
Type of soil
Grain size distribution
Specific gravity of solids
Type and amount of clay materials
13. Facts about Compaction
Maximum dry unit weight
Min: Organic soils (60lb/ft3
)
Max: Well-graded granular material (145 lb/ft3
)
Optimum moisture contents
Min: Granular material (5%)
Max: Elastic silts and clays (35%)
Higher optimum moisture contents = Lower dry
unit weight
14.
15.
16. Field Compaction
Compacted in layers
8 in. loose horizontal layer compacted to a
thickness of 6 in.
Sprinkling or drying to control moisture content
Scarifying to provide bonding between layers.
Equipments
Tempers – Limited in scope and compacting ability
Rollers
Smooth wheel roller, Sheepsfoot roller, Pneumatic roller,
Vibratory roller
21. Dynamic Compaction
When
Existing surface or near-surface soil is poor with
regard to foundation support
For which soil?
Both cohesive and cohesionless soils
How
Drop a very heavy (2~20 tons) weight onto the soil
from a relatively great height (20 ~ 100 ft)
Dropping weight randomly? a closely spaced grid
pattern is selected.
23. Dynamic Compaction
How deep soil will be affected?
Approximate depth of influence of dynamic
compaction (D)
(m)height:
tons)(metricWeight:
(m)compactiondynamicofinfluenceofDepth:
soilcohesive:
soilsscohesionle:5.0
h
W
D
WhD
WhD
=
=
24. Dynamic Compaction
How many drops do we need?
Typically 5~10 drops
Additional drops beyond 10 drops improves
little
What about craters?
Need to be backfilled and compacted by other
means
25. In-Place Soil Unit Weight Test
Destructive testing method
Sand-cone
Rubber-balloon methods
Nondestructive method
Nuclear moisture-density apparatus
Soil unit weight is inversely proportional to the
amount of radiation that reaches the detector.
Speedy Moisture Tester
27. Example
During construction of a soil embankment, a
sand-cone in-place unit weight test was
performed in the field.
Weight of sand used to fill test hole and funnel of
sand-cone device = 867g
Weigh of sand to fill funnel = 319g
Unit weigh of sand = 98.0 lb/ft3
Weigh of wet soil from the test hole = 747g
Moisture content of soil from test hole = 13.7%
31. Field Control of Compaction
Required percent of compaction
the required in-place dry unit weight
= ----------------------------------------------------- x 100%
the maximum laboratory dry unit weight
Minimum number of field unit weight tests
required.
Maximum thickness of loose lifts (layers)
Methods to obtain maximum dry unit weight
Methods to determine in-place unit weight
32. Example
Given
Soil from a borrow pit to be used for construction of
an embankment gave the following laboratory results
when subjected to the ASTM D 698 Standard Proctor
test
Maximum dry unit weight = 118.5 lb/ft3
Optimum moisture content = 12.5%
The contractor, during construction of the soil
embankment, achieved the following
Dry unit weight reached by field compaction = 117.8 lb/ft3
Actual water content = 13.7%
Required
Percent of compaction achieved by the contractor
34. Example
Given
A borrow pit’s soil is being used as earth fill at a construction
project.
The in situ dry unit weight of the borrow pit soil was determined
to be 17.18 kN/m3
The soil at the construction site is to be compacted to a dry unit
weight of 18.90 kN/m3
The construction project requires 15,000m3
of compacted soil fill.
Required
Volume of soil required to be excavated from the borrow pit to
provide the necessary volume of compacted fill.
36. Example
Given
The in situ void ratio of a borrow pit’s oil is 0.72.
The borrow pit soil is to be excavated and transported
to fill a construction site where it will be compacted to
a void ratio of 0.42.
The construction project requires 10,000 m3
of
compacted soil fill.
Required
Volume of soil that must be excavated from the
borrow pit to provide the required volume of fill