2.3.3. PERMANENT DEFORMATION TEST (REPETITIVE TRIAXIAL)
Overview
Repeated loading causes plastic (irrecoverable) deformations in soil
Same moduli soils can have different plastic deformations
Common form of models
Test Procedure
Test soil sample at constant deviator stress
Measure plastic and plastic deformations
Plot cumulative plastic deformations with repetitions
Perform regression analysis to determine constants
Results
2.3.4. CALIFORNIA BEARING RATIO (CBR; ASTM D-1883)
Overview
Developed by California Division of Highways in 1930
Measures the resistance of the soil to penetration (shear)
Compare to penetration of a standard, well-graded crushed stone: The CBR is a ratio of the
resistance to penetration in a selected soil to the resistance to penetration in a standard
high-quality crushed stone material
Not a fundamental soil property
Procedure
Samples soaked for 4 days to mimic the worst condition
10 lbs of surcharge weights to simulate the weight of pavement and to prevent heaving of
soil during testing
A standard piston with 3 in2 end area at the penetration rate of 0.05 inch/minute
CBR Value
Ratio (%) obtained by dividing the penetration stress required to cause 3 in2 area piston to
penetrate 0.1 in. into the soil by a standard penetration stress of 1,000 psi 1,000 psi is a
required stress to penetrate 0.1 in. into a mass of crushed rock
Factors Influencing CBR Results
Soil Type
Moisture content
Density
Limitations
Not a fundamental property: can’t use for modeling
Soaking is not representative of field conditions
Static test: No repeated loading
2.3.5. CALIFORNIA R-VALUE (ASTM D-2844)
Overview
Use Hveem Stabilometer
2.5 in. diameter and 4.5 in. height specimen
Vertical pressure of 160 psi and the resulting horizontal pressure measured
Not a fundamental soil property
Application
R = 0 is a liquid (no internal friction)
R < 10 for weak soil
R = 30 to 70 for granular material
R = 100 (rigid block)
Use R-value for thickness design: thickness of cover to prevent plastic deformation of the
subgrade under loading
2.3.6. PLATE BEARING TEST
Overview
Evaluates the supporting ability of the pavement system under the circular plate of which
area is close to actual tire imprint area
Plates of 30”, 24”, 18” and 12” diameters
30 in diameter – 6 to 8 inch thick PCC pavement under wheel loads typical of the 1940’s
Modulus of Subgrade Reaction ( k Value )
Limitations of PLT
Extremely expensive test
Tim-consuming
Static k-value vs. actual dynamic k-value
Depends on plate size/slab size
2.3.7. DYNAMIC CONE PENETROMETER
Overview
Developed by Corps of Engineers
Quick and inexpensive
Device for measuring in situ characteristics of soil
Locates different soil layers
Correlated to CBR value
DCP value: number of blows to achieve 150 mm (6 in) of penetration
DCP-CBR Correlation (after Harison, 1987)
2.3.8. CORRELATIONS
REFERENCES
도로공학, 천병식, 고용일, 새론, 1998
도로포장공학, 남영국, 구미서관, 2004
최신도로공학총론, 남영국, 최한중, 청문각, 1996
An Introduction to Geotechnical Engineering, Holtz and Kovacs, Prentice Hall, 1981.
Highway Pavement Design, Lecture by Prof. Kim, North Carolina State University
Pavement Analysis and Design, Huang, Prentice Hall, 2004
Pavement Engineering, Lecture by Prof. Choi, Korea University
Principles of Geotechnical Engineering, Das, Thomson, 2006.
