CONSOLIDATIONCONSOLIDATIONOF SOILSOF SOILS

andandHYDROCOMPACTIONHYDROCOMPACTION

J. David RogersJ. David Rogers

Part 1Part 1

COMPACTION COMPACTION andand

PRIMARY PRIMARY CONSOLIDATIONCONSOLIDATION

The The Proctor Compaction TestProctor Compaction Test employs a 5 lb weight employs a 5 lb weight being dropped 18 inches repeatedly on a soil sample being dropped 18 inches repeatedly on a soil sample of 1/30of 1/30thth of a cubic foot, in three lifts, or layers of soil. of a cubic foot, in three lifts, or layers of soil. The moisture content corresponding to the maximum The moisture content corresponding to the maximum achievable dry density is termed the achievable dry density is termed the optimum optimum moisture contentmoisture content

Soil moisture-density relationships are commonly Soil moisture-density relationships are commonly referred to as “referred to as “compaction testscompaction tests””

Note how Note how soil density is a function of the compactive soil density is a function of the compactive energyenergy; the more energy expended per unit volume ; the more energy expended per unit volume of soil, the greater the density and lower the water of soil, the greater the density and lower the water contentcontent

The The Standard ProctorStandard Proctor (ASTM D 698) test was (ASTM D 698) test was introduced in 1933 and employs 12,600 ft-lbs of input introduced in 1933 and employs 12,600 ft-lbs of input energy per ftenergy per ft33 of soil of soil

The The Modified ProctorModified Proctor (ASTM D 1557) test was (ASTM D 1557) test was introduced in 1957 and employs 56,200 ft-lbs of input introduced in 1957 and employs 56,200 ft-lbs of input energy per ftenergy per ft33 of soil of soil

Typical range of Typical range of dry densitydry density versus versus moisture moisture contentcontent for various soil mixtures, as for various soil mixtures, as determined by Standard Proctor compaction determined by Standard Proctor compaction teststests

WaterWater is added or deleted from soil mixtures to effect is added or deleted from soil mixtures to effect maximum achievable compactionmaximum achievable compaction

After placement, After placement, soil mixturessoil mixtures can be expected to can be expected to absorb additional moisture until equilibrium is absorb additional moisture until equilibrium is achieved, thereby lessened soil density achieved, thereby lessened soil density

Differential settlementDifferential settlement is a widespread and nagging is a widespread and nagging problem wherever fill has been placed to support problem wherever fill has been placed to support structures, such as highways. Improved compaction structures, such as highways. Improved compaction helps to reduce settlement.helps to reduce settlement.

Primary ConsolidationPrimary Consolidation

Primary consolidationPrimary consolidation occurs when occurs when interstitial interstitial pore waterpore water is squeezed out of is squeezed out of saturated claysaturated clay

One dimensional consolidation, or odometer test (upper)One dimensional consolidation, or odometer test (upper) Traditional representation of primary consolidation tests (lower)Traditional representation of primary consolidation tests (lower)

Primary consolidationPrimary consolidation exerts controlling influence on exerts controlling influence on soft soil sites. A number of options may be soft soil sites. A number of options may be employed to mitigate potential damage, listed above employed to mitigate potential damage, listed above