C8 Soil Classification - Universiti Sains Malaysia Soil Classification.pdf · Classification...
Transcript of C8 Soil Classification - Universiti Sains Malaysia Soil Classification.pdf · Classification...
Soil Classification
ENGINEERING DESIGN AND CONSTRUCTION
The Purpose
• To distinguish between the main soil types
• To assess the strength and structure of the soil
sand
clay
silt
Classification systems
• Unified Soil Classification Systems (USCS)
• BS Classification Systems (in BS 5930)• AASHTO/ASTM Classification Systems
Further reading:
1) Carter,M. Geotechnical Engineering Handbook. London: Pentech Press.
2) Other geotechnical references.
Soil Classification Tests
• Particle Size Analysis
• Atterberglimits
• Specific gravity
Particle size distribution
The size of particles within a soil mass can vary from less than 0.001 to over 100mm. The BS size ranges is shown below:
Sieve test (coarse grain)
• Oven dried sample of soil is weighted and passed through a series of sieves.
Particle size distribution form
Well graded
0
20
40
60
80
100
0.01 0.1 1 10 100
Grain size (mm)
Fine grain analysis
• Pipette method• Hydrometer method
Particle size distribution curve• Soil can be described according to the shape of
the curve and where it fits on to the chart.• Uniform soil – all particle are approximately the
same size, will have almost vertical curve.• Well graded soil – containing wide range of
particle size, will have a curve spread evenly across the chart.
• Poorly graded (or gap graded) – stretch across but shown deficiency of some intermediate sizes. Grading curve exhibit flat section or plateau.
Particle size distribution curve
• Effective size – the maximum particle size of the smallest 10% and called
D10
• Uniformity coefficient, CU – the ratio of the maximum particle size of the smallest 60% to effective size:
10
60
DD
CU =
Cu < 4.0 – uniformly graded
Cu > 4.0 – well graded or gap graded.
PSD curve
• Uniform soil will have Uniformity Coefficient approaching down to 1
• Well graded soil will have a high Uniformity Coefficient.
Example 1:PSD
7.40.06325.40.1845.30.35530.50.51.11.43.5212.92.85.75.68.46.32.3101.712.5020
Weight retained (g)Retained on sieve size (mm)
Total wt of sample = 147.2 g
2.03144.27.40.0637.110.4136.825.40.18
24.335.8111.445.30.35555.181.166.130.50.575.8111.635.61.11.476.6112.734.53.5278.9116.23112.92.887.7129.118.15.75.691.6134.812.48.46.397.3143.242.31098.8145.51.71.712.5100147.20020
% PassingWt. passing
Cumulative wt retained
Wt retainedSieve Sizes
Example 1: curve
0102030405060708090
100
0.01 0.1 1 10 100
Size (mm)
Perc
enta
ge p
assi
ng
D10 = 0.23
D60 = 0.7
U = D60/D10
= 0.7/0.23
=3.04
Atterberg limits (plasticity)• Quantitatively
describe the effect of varying water content on the consistency of fine-grained soil.
• The increasing water content cause the changes of the soil from solid to semi-solid to plastic and to liquid states.
Volume of Sample
Moisture content
SL PL
LLsolid
Semisolid
Plastic
liquid
Graphical representation….
solid Semi-solid plastic liquid
Increasing water content
SL LLPL
P.I.
The range of soil over which a soil is plastic.
Plasticity Index (PI)
The maximum moisture content at which further loss of moisture does not cause a decrease in the volume of the soil.
Shrinkage Limit (SL)
The minimum moisture content at which the soil can be rolled into a thread 3mm dia. w/out breaking up.
Plastic Limit (PL)
The minimum moisture content at which the soil will flow under its own weight.
Liquid Limit (LL)
PI
• Represent the relative amount of clay particles in soil
• Higher PI = greater amount of clay particles present = more plastic a soil.
• The more plastic soil will:– Be more compressible– Higher shrink swell potential– Less permeable
Liquid limit test
Casagrande Apparatus Cone penetrometer
Exercise
Sieve Sizes
Wt retained
50 037.5 15.5
20 1714 1010 116.3 33
3.35 114.51.18 63.30.6 18.2
0.15 170.063 10.5
The total mass of the sample was 311 g, plot the particle size distribution curve and from the curve, determine the effective size and uniformity coefficient. Classify the soil.
Answer: D10 = 0.7mm
D60 = 5.2 mm
Cu = 7.4
70 % gravel, 30 percent sand
Well graded Sandy Gravel.