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