CONSOLIDATION OF SOILS and HYDROCOMPACTION J. David Rogers

COMPACTION and PRIMARY CONSOLIDATION Part 1 COMPACTION and PRIMARY CONSOLIDATION

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

Soil moisture-density relationships are commonly referred to as “compaction tests” Note how soil density is a function of the compactive energy; the more energy expended per unit volume of soil, the greater the density and lower the water content

The Standard Proctor (ASTM D 698) test was introduced in 1933 and employs 12,600 ft-lbs of input energy per ft3 of soil The Modified Proctor (ASTM D 1557) test was introduced in 1957 and employs 56,200 ft-lbs of input energy per ft3 of soil

Typical range of dry density versus moisture content for various soil mixtures, as determined by Standard Proctor compaction tests

Water is added or deleted from soil mixtures to effect maximum achievable compaction After placement, soil mixtures can be expected to absorb additional moisture until equilibrium is achieved, thereby lessened soil density

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

Primary Consolidation Primary consolidation occurs when interstitial pore water is squeezed out of saturated clay

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

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