Compacting and Finishing

Optimum Moisture content

Moisture content (% dry weight) which provides the highest density with a given level of compaction effort; standard proctor test/ modified proctor test, repeatedly drop hammer on samples with various MC's and measure density

Compaction v Consolidation

Compaction- forcing air particles out which increases density Consolidation- forces water out of voids in cohesive soils

Zero air voids curve

Density of which all air voids have been eliminated

Purpose of Compaction

Improve bearing strength Reduce Compressibility Improve volume-change characteristics Reduce permeability

Four methods used for soil stabilization

Mechanical (compaction) Hydraulic (subcharging, electroosmosis) Reinforcement (piles, soil railing) Physiochemical (lime, admixtures)

Compactive effort increases

OMC decreases

Degree of compaction depend upon

Physical and chemical properties of soil Moisture content Compaction method Compaction effort Thickness of soil layer

Trimming purpose

Process of bringing each roadway layer to its final grade

Grading purpose

Process of bringing earthwork to desired shape and elevation

Equipment for field compaction

Ramping foot (cohesive soil) Grid and mesh rollers (gravel + sand) Vibratory (non-cohesive) Steel wheeled roller (granular + pavements) Pneumatic roller (gravel + sand)

3 methods for measuring soil density in field

Sand Cone Test (ASTM D1556) Nuclear Density (ASTM D2292) Soil Modulus (soil stiffness)

Finishing purpose

Smoothing slopes, shaping ditches and brining earthwork to elevation as designed by plans + specs

Four basic compaction forces

Static Weight - All Manipulational Kneading - cohesive soils Impact - low frequency, plastic soils Vibration - high frequency, cohesion less sand + gravel