Compaction

1
Compaction

• I.  Definitions
• The process of forcing air out of the soil,
  resulting an increase in density.
• The effect of compaction on pore space
• II. Types of compaction
• Rolling or kneading most effective for clayey
  soils
• Vibrating most effective for non-clayey soils
• Dropping a heavy weight effective for both types
  of soils
• III. Control of Compaction
• Determining the dry density of the soil as
  compacted and comparing it to the maximum dry
  density of the same soil as determined by a
  laboratory test.
• 1 Wednesday, October 14, 2015

2
Compaction

• III. Control of Compaction
• 2. The Proctor Tests (Standard Modified
  Proctor Tests)
• Purposes To determine the maximum dry density
  and the corresponding optimum moisture content of
  a field sample of soil
• Procedure
• Placing soils in layers (lifts) into a standard
  mold
• Compacting them by dropping a standardized hammer
  a specified number of times.
• Weighing and determining the density when the
  mold is full
• Oven-drying a portion of the soil to determine
  the moisture content by weight
• 2 Wednesday, October 14, 2015

3
Compaction

• III. Control of Compaction
• Difference between standard modified tests
• The amount of energy (the weight of hammer and
  the height from which it is dropped)
• The number of lifts
• Typical compaction curves
• The amount of compaction depends on compaction
  effort and water content of the soil
• Compaction effort
• Function of water in compaction
• (2) A specific relative compaction can be
  achieved for the soil over a range of moisture
  contents
• 3 Wednesday, October 14, 2015

4
Compaction

• Misconceptions about compaction
• The first is that 100 relative compaction
  implies that all of the air has left the soil
  (zero air voids). However, the compaction curve
  never reaches the zero air voids curve and it is
  impossible to remove all of the air voids with
  conventional techniques.
• The second is that the Modified Proctor test has
  been standardized to approximate typical compact
  efforts achieved in the field with modern
  conventional equipment. However, it is not
  practical to attempt to achieve relative
  compactions at or above 100.
• 4 Wednesday, October 14, 2015

5
Compaction

• Misconceptions about compaction
• The third is that a given soil has a specific
  optimum moisture content. The optimum moisture
  content depends on the amount of compact energy
  and the method of compaction, and the increase in
  the compact energy decreases the optimum moisture
  content.
• Soil Compaction Equipment (Rammer, plate
  compactor, rollers)
• Homework (Ex. II on page 224 in the textbook)
• 5 Wednesday, October 14, 2015