1 introduction to soil mechanics. 2 laboratory tests and equivallent field experiments soil index (...
TRANSCRIPT
1
Introduction to Soil Mechanics
2
LABORATORY TESTS AND EQUIVALLENT FIELD EXPERIMENTS
Soil Index (, , e, GS etc.)· Measurement of soil volume and mass· Sieve analysis test· Atterberg test
Compaction : proctor, field compaction
Shear Strength (c, )· Triaxial Test (UU, CU, CD)· Direct Shear· Unconfined Compression Test · CPT, SPT,Vane Shear test,….
Compresibility (Cc, Cv)Consolidation test
Permeability (k)· Constant Head· Falling Head
3
Three Phases in SoilsS : Solid Soil particle
W: Liquid Water (electrolytes) A: Air Air
4
Three Volumetric Ratios
(1) Void ratio e (given in decimal, 0.65)
(2) Porosity n (given in percent 100%, 65%)
(3) Degree of Saturation S (given in percent 100%, 65%)
)V(solidsofVolume
)V(voidsofVolumee
s
v
)V(samplesoilofvolumeTotal
)V(voidsofVolumen
t
v
%100)V(voidsofvolumeTotal
)V(watercontainsvoidsofvolumeTotalS
v
w
e1
e
)e1(V
eVn
s
s
5
Engineering Applications (e)
Typical values Engineering applications:
·Volume change tendency·Strength
(Lambe and Whitman, 1979)
Simple cubic (SC), e = 0.91, Contract
Cubic-tetrahedral (CT), e = 0.65, Dilate
Link: the strength of rock joint
)itan(strengthShear n
i
6
Engineering Implications (e)(Cont.)
· Hydraulic conductivity–Which packing (SC or CT)
has higher hydraulic conductivity?
SC
e = 0.91
CT
e = 0.65
The fluid (water) can flow more easily through the soil with higher hydraulic conductivity
7
Engineering Applications (e)(Cont.)
SC
e = 0.91
CT
e = 0.65
The finer particle cannot pass through the void
• Clogging
· Critical state soil mechanics
Filter
8
Engineering Applications (S)Completely dry soil S = 0 %
Completely saturated soil S = 100%
Unsaturated soil (partially saturated soil) 0% < S < 100%
Demonstration:
Effects of capillary forces
Engineering implications:·Slope stability·Underground excavation
%100)V(voidsofvolumeTotal
)V(watercontainsvoidsofvolumeTotalS
v
w
9
Engineering Applications (S) (Cont.)
• 80 % of landslides are due to erosion and “loss in suction” in Hong Kong.
• The slope stability is significantly affected by the surface water.
(Au, 2001)
10
Density and Unit Weight
• Mass is a measure of a body's inertia, or its "quantity of matter". Mass is not changed at different places.
• Weight is force, the force of gravity acting on a body. The value is different at various places (Newton's second law F = ma) (Giancoli, 1998)
• The unit weight is frequently used than the density is (e.g. in calculating the overburden pressure).
w
s
w
s
w
ss
3
2
g
gG
mkN8.9,Water
secm8.9g
gravitytodueonaccelerati:g
Volume
gMass
Volume
Weight,weightUnit
Volume
Mass,Density
11
Weight Relationships
(1)Water Content w (100%)
For some organic soils w>100%, up to 500 %
For quick clays, w>100%
(2)Density of water (slightly varied
with temperatures)
(3) Density of soila. Dry density
b. Total, Wet, or Moist density (0%<S<100%, Unsaturated)
c. Saturated density (S=100%, Va =0)
d. Submerged density (Buoyant density)
%100)(
)(
s
w
MsolidssoilofMass
MwaterofMassw )V(samplesoilofvolumeTotal
)M(solidssoilofMass
t
sd
)V(samplesoilofvolumeTotal
)MM(samplesoilofMass
t
ws
)V(samplesoilofvolumeTotal
)MM(watersolidssoilofMass
t
wssat
wsat'
333w m/Mg1m/kg1000cm/g1
12
Weight Relationships (Cont.)
Submerged unit weight:
Consider the buoyant force acting on the soil solids:
wsat'
wsat
t
wtws
t
wwts
t
wwts
t
wss
V
VWW
V
WVW
%)100S(V
)VV(W
V
VW
13
Engineering Applications (w)• For fine-grained soils, water plays
a critical role to their engineering properties (discussed in the next topic).
• For example,
The quick clay usually has a water content w greater than 100 % and a sensitive structure. It will behave like a viscous fluid after it is fully disturbed.
Clay particle
Water
(Mitchell, 1993)
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Other Relationships
(1) Specific gravity
(2)
Proof:
w
s
w
ssG
s
sw
GweS
weS
s
w
w
w
s
s
s
w
w
s
s
ws
s
w
s
v
v
w
s
V
V
VM
VM
M
M
M
MGw
V
V
V
V
V
VeS
GweS
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Typical Values of Specific Gravity
(Lambe and Whitman, 1979)
(Goodman, 1989)
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Determination of Atterberg limits
17
CASAGRANDE METHOD (LL)
18
CASAGRANDE METHOD
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CASAGRANDE METHOD
SINGLE-POINT
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Plastic behaviour
The test is done by rolling up the soil sample to 3.2mm diameter
Defined as the water content, in percent, at which the soil crumbles, when rolled into threads of 1/8 in (3.2mm) in diameter.
PLASTIC LIMIT (PL)
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Ü Test Standard : ASTM D 427
Ü After drying the soil sample in an oven, and determining the mass and volume of sample before(i) and after (f) drying:
SHRINKAGE LIMIT (SL)
[ ( ) ] 100mi mf vi vf
SL wmf mf
22
23
Sieve Analysis
Test Standard
ASTM D422, AASHTO T88
The testing should be only carried out once for one sample
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Curve of Particle Size Distribution
10
60
D
DCU
6010
230
.DD
DCC
25
SOIL COMPACTION
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INTRODUCTION
Soil compaction is defined as the method of mechanically increasing the density of soil. In construction, this is a significant part of the building process. If performed improperly, settlement of the soil could occur and result in unnecessary maintenance costs or structure failure
27
SOIL COMPACTION
PURPOSE· Improving the soil quality by:
– Increasing the shear strength of soil
– Improving the bearing capacity of soil
· Reduces the settling of soil· Reduces the soil permeability· To control the relative volume
change
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TYPES OF COMPACTION
4 types of compaction effort on soil : · Vibration · Impact · Pressure
29
BASIC THEORY
Developed by R.R. Proctor at 1920-an with 4 variables :· Compaction efforts (Compaction Energy)· Soil types· Water content· Dry Unit Weight
LABORATORY COMPACTION TEST· Standard Proctor Test· Modification Proctor Test· Dietert Compaction· Harvard Miniatur Compaction
SOIL COMPACTION
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STANDARD PROCTOR TEST
The soil is compacted at cylindrical tube
Specification of test and equipments· Hammer weight = 2,5 kg (5,5 lb)· Falling height = 1 ft· Amount of layers = 3 · No. of blows/layer = 25· Compaction effort = 595 kJ/m3
· Soil type = pass sieve no. 4The test is carried out several time
with different water contentAfter compacted, the weight, moisture
content and unit weight of samples are measured
Test Standard :· AASHTO T 99· ASTM D698
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MODIFIED PROCTOR TEST
• The soil is compacted at cylindrical tube
• Specification of test and equipments– Hammer weight = 4.5 kg (10
lb)– Falling height = 1.5 ft– Amount of layers = 5 – No. of blows/layer =
25, 56– Compaction effort = 2693
kJ/m3
– Soil type = pass sieve no. 4• The test is carried out several
time with different water content
• After compacted, the weight, moisture content and unit weight of samples are measured
• Test Standard :– AASHTO T 180– ASTM D1557
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TEST RESULT
.
..
GSS
SGSwd
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FIELD COMPACTION
Type of Compaction Equipment :· Smooth Wheel Roller :
compaction equipment which supplies 100% coverage under the wheel, with ground contact pressures up to 400 kPa and may be used on all soil types except rocky soils. Mostly use for subgrades and compacting asphalt pavements.
34
FIELD COMPACTION
Type of Compaction Equipment :· Rubber Tire Roller :
A heavily loaded wagon with several rows of three to six closely spaced tires with tire pressure may be up to about 700 kPa and has about 80% coverage (80% of the total area is covered by tires).
This equipment may be used for both granular and cohesive highway fills.
35
FIELD COMPACTION
Type of Compaction Equipment :· Sheepsfoot Roller :
This roller has many round or rectangular shaped protrusions or “feet” attached to a steel drum.The area of these protusions ranges from 30 to 80 cm2.Area coverage is about 8 – 12% with very high contact pressures ranging from 1400 to 7000 kPa depending on the drum size and whether the drum is filled with water.The sheepsfoot roller is best suited for cohesive soils.
36
FIELD COMPACTION
Type of Compaction Equipment :· Grid Roller :
This roller has about 50% coverage and pressures from 1400 to 6200 kPa, ideally suited for compacting rocky soils, gravels and sand. With high towing speed, the material is vibrated, crushed, and impacted.
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FIELD COMPACTION
Type of Compaction Equipment :· Baby Roller :
Small type of smooth wheel roller yang, which has pressure ranges from 10 to 30 kPa. The performance base on static weight and vibration effect.
38
FIELD COMPACTION
Type of Compaction Equipment:· Vibrating Plate :
Compaction equipment, which has plate shape. In Indonesia this equipment sometimes called as “stamper”. Usually used for narrow area and high risk when use large compaction equipment like smooth wheel roller etc.
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CONDITIONER FACTORS
Characteristic of compaction equipment· Weight and size· Operation frequency and frequency range
Soil Characteristic· Initial density· Soil type· Size and shape of soil particle· Moisture Content
Compaction Procedure· No. of passes of the roller· Layer thickness· Frequency of operation of vibrator· Towing speed
40
FIELD COMPACTION CONTROL
Excavate a hole with certain diameter and depth. Determine the mass of excavated material.
Determine the moisture contentMeasure the volume of excavated
material by:· Ottawa Sand Sand cone· The balloon method· Pouring water or oil
Compute the total density, and d,field
Compare d, field with d,max and calculate the relative compaction
41
SPECIFICATION OF COMPACTION
End Product Specification
Method of Specification· Minimum soil sample 100 kg· Need special experience to find out the optimum moisture
content in order to get optimum compaction performance
%100(max)
)( xRCd
fieldd