CEG4011 Test 2 Study Guide

D_r

relative density

e_max

maximum void ratio

e_min

minimum void ratio

G_s

specific gravity of solids

e

insitu void ratio

ρ_w

density of water

𝛾 = 𝛾_m

moist unit weight

𝛾_sat

saturated unit weight

𝛾_d

dry unit weight

𝛾_s

unit weight of solids

𝛾’

effective unit weight

C_R

relative compaction

K

coefficient of lateral earth pressure at rest

σ_H′

horizontal effective stress

σ_V′

vertical effective stress

σ_V

vertical stress

u

pore water pressure = (unit weight of water 𝛾w)(depth below ground water table H)

z

depth below soil

densification of soils

Removal of air voids

Application of mechanical energy

Consolidation removes water slowly

purpose of densification of soils

Reduce settlement potential

Increase strength

Decrease permeability

water added to soil

Act as lubricant

Reduces surface tension

Obtain higher dry unit weight (If too much water is added, dry unit weight goes down)

most suitable soils for smooth wheel/drum roller

well-graded sand gravel, crushed rock, asphalt

most suitable soils for pneumatic or rubber-tired rollers

coarse grained soils with some fines

most suitable soils for grid rollers

weathered rock, well-graded coarse soils

most suitable soils for sheepsfoot rollers, static

fine grained soils with >20% fines

most suitable soils for sheepsfoot rollers, vibratory

fine grained soils with >20% fines and sand-gravel mixes

most suitable soils for vibrating plates

coarse soil, 4-8% fines 

tampers/rollers

all types

standard proctor test

3 layers (lifts)

25 blows

5.5 lb hammer

12” height

modified proctor test

5 layers

25 blows

10 lb hammer

18” height

Requires more energy

why was the modified proctor test made?

Soils needed higher unit weights to support heavier vehicles and aircraft in and after WW2

method specification

follow a procedure designed by the engineer

Type of roller, weight of roller, # of passes, lift thickness, acceptable moisture content range

end product specification

defines final required properties (given by engineer). Contractor can achieve in any way they desire

factors affecting field compaction

1) Weight of Roller (heavier roller = greater density. NOT TRUE IF BEARING CAPACITY OF SOIL IS EXCEEDED

2) Number of Coverages (minimum 4-8 passes required for efficient use of rollers. less passes = more cost efficient)

3) Contact Pressure (higher contact pressures = compact deeper lifts due to deeper stress penetration)

4) Lift Thickness (higher pressures allow for thicker lifts to be compacted)

5) Water Content (very important for compaction efforts and equipment operation)

field compaction steps

Select borrow soil

Haul to site to dump

Spread into layers

Alter moisture content (dry or wet the soil)

Mix soil to make uniform and break lumps

Compact the soil by rolling (Method Specification or End-Product Specification)

methods to measure water content and density

Sand Cone - Direct

Oven Drying - Direct

Nuclear Probes – Indirect

Assumptions

homogeneous (same properties throughout), isotropic (same properties in all directions at a point), elastic, half-space (semi-infinite).