Soil Compaction

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# Soil Compaction - PowerPoint PPT Presentation

Soil Compaction. COSC 323: Soils in Construction. 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:

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### Soil Compaction

COSC 323: Soils in Construction

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?
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
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.
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
Compaction Test
• Dry out soil sample
• Add water to the soil sample
• Compact the soil sample in the compaction mold
• Measure wet unit weight (g)
• Measure moisture content (w)
• Calculate dry unit weight
• Repeat 4 times with different moisture contents
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?
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.
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
• 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
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
Field Compaction
• Smooth wheel roller
• Provide a smooth finished grade
• Used for paving
Field Compaction
• Sheepsfoot roller
• Greater compaction pressure
• Effective for compacting fine-grained soil
Field Compaction
• Pneumatic roller
• Effective for compacting clayey soil and silty soils
Field Compaction
• Vibratory roller
• Effective for compacting granular materials: clean sands and gravels
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.
Dynamic Compaction
• How deep soil will be affected?
• Approximate depth of influence of dynamic compaction (D)
Dynamic Compaction
• How many drops do we need?
• Typically 5~10 drops
• Additional drops beyond 10 drops improves little
• Need to be backfilled and compacted by other means
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
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%
In-Place Test: Nuclear Apparatus

Nuclear moisture-density apparatus

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
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
Example
• Solution
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.
Example
• Solution
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
Example
• Solution
Example
• Solution