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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:

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soil compaction

Soil Compaction

COSC 323: Soils in Construction

question
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
  • 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
compaction4
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
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 test7
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
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?
example10
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
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
facts about compaction
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
field compaction
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 compaction17
Field Compaction
  • Smooth wheel roller
    • Provide a smooth finished grade
    • Used for paving
field compaction18
Field Compaction
  • Sheepsfoot roller
    • Greater compaction pressure
    • Effective for compacting fine-grained soil
field compaction19
Field Compaction
  • Pneumatic roller
    • Effective for compacting clayey soil and silty soils
field compaction20
Field Compaction
  • Vibratory roller
    • Effective for compacting granular materials: clean sands and gravels
dynamic compaction
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 compaction23
Dynamic Compaction
  • How deep soil will be affected?
    • Approximate depth of influence of dynamic compaction (D)
dynamic compaction24
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
in place soil unit weight test
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
example27
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
In-Place Test: Nuclear Apparatus

Nuclear moisture-density apparatus

field control of compaction
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
example32
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
example33
Example
  • Solution
example34
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.
example35
Example
  • Solution
example36
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
example37
Example
  • Solution
example38
Example
  • Solution