Exam 1 Flashcards
Who cares about dirt (soil)?
- Geologists
- Contractors
- Hydrologists
- Farmers
- Agronomists
- Soil chemists
Why does soil matter to a construction manager?
Most structures of all types rest either directly or indirectly upon soil. Proper analysis of the soil and design of the structure’s foundation are necessary to ensure a safe structure free of undue settling and/or collapse.
Soil is composed of particles, ___ and
___.
large, small
Soil includes :
solid matter, air, and water
Particles are the result of
of weathering (disintegration and
decomposition) of rocks and decay of
vegetation.
Cycles of rock disintegrating to form
soil, soil becoming consolidated under great pressure and heat to form rock, and so on.
Difference Between Soil and Rock:
If material can be removed without blasting, it is usually considered to be “soil,” whereas if blasting is required, it might be regarded as “rock.
Rock classification based on their origin and/or method of formation:
- Igneous 2. Sedimentary 3. Metamorphic
form when magma (molten matter) such as that produced by erupting volcanoes cools sufficiently to solidify
Igneous rocks
Being generally hard, dense, and durable, ______ often make good construction materials. Also, they typically have high bearing capacities and therefore make good foundation material.
igneous rock
can be coarse-grained or fine-grained, depending on whether cooling occurred slowly or rapidly.
Igneous rocks
Cool quickly and as a result these rocks are fine grained or has a lack of crystal growth.
Extrusive igneous rocks
Are formed from magma that cools slowly and as a result these rocks are course grained.
Intrusive igneous rocks
The most common coarse-grained igneous rock:
granite
A hard rock rich in quartz, widely used as a construction material and for monuments
granite
The most common fine-grained igneous rock. A hard, dark-colored rock rich in ferromagnesian minerals and often used in road construction.
basalt
what type of rock is granite?
Igneous
What type of rock is basalt?
Igneous
compose the great majority of rocks found on the earth’s surface.
Sedimentary rocks
They are formed when mineral particles, fragmented rock particles, and remains of certain organisms are transported by wind, water, and ice (with water being the predominant transporting agent) and deposited, typically in layers, to form sediments.
sedimentary rocks
Over a period of time as layers accumulate at a site, pressure on lower layers resulting from the weight of overlying strata hardens the deposits, forming _________.
sedimentary rocks
Can be identified easily when their layered appearance is observable.
Sedimentary rocks
The most common sedimentary rocks are
shale, sandstone, limestone, and dolomite.
The most abundant of the sedimentary rocks, is formed by consolidation of clays or silts.
Shale:
- Organic matter or lime may also be present.
- Have a laminated structure and often exhibit a tendency to split along laminations.
- They can become soft and revert to clayey or silty material if soaked in water for a period of time.
Shales
vary in strength from soft (may be scratched with a fingernail and easily excavated) to hard (requiring explosives to excavate).
Shales
Relatively hard shale makes a good _______.
foundation material
consisting primarily of quartz, is formed by pressure and the cementing action of silica (SiO2), calcite (calcium carbonate, CaCO3), iron oxide, or clay.
Sandstone:
Strength and durability of sandstones vary widely depending on
the kind of cementing material and degree of cementation as well as the amount of pressure involved.
generally good Construction materials.
Sandstones
is sedimentary rock composed primarily of calcium carbonate hardened underwater by cementing action (rather than pressure); it may contain some clays or organic materials within fissures or cavities.
Limestone
Its strength varies considerably from soft to hard (and therefore durable), with actual strength depending largely on the rock’s texture and degree of cementation.
Limestone
Limestone with what type of texture is low strength?
(A porous texture means lower strength.)
If strong, can be good foundation and construction materials
Limestone
are similar in grain structure and color to limestones and are, in fact, limestones in which the calcite (CaCO3) interbonded with magnesium. If strong, can be good foundation and construction materials
Dolomites
_______ are much less common at the earth’s surface than are sedimentary rocks
Metamorphic rocks
They are produced when sedimentary or igneous rocks literally change their texture and structure as well as mineral and chemical composition, as a result of heat, pressure, and shear.
Metamorphic rocks
can be hard and strong if unweathered.
Metamorphic rocks
sometimes contain weak layers between very hard layers
Metamorphic rocks
what type of rock is marble?
Metamorphic
What are soil particles the result of?
Soil particles are the result of weathering of rocks and organic decomposition.
Weathering is achieved by
mechanical (physical) and chemical means.
disintegrates rocks into small particles by temperature changes, frost action, rainfall, running water, wind, ice, abrasion, and other physical phenomena.
Mechanical weathering
causes of rock disintegration
breaking, grinding, crushing
causes chemical decomposition of rock, which can drastically change its physical and chemical characteristics.
Chemical weathering
This type of weathering results from reactions of rock minerals with oxygen, water, acids, salts, and so on. It may include such processes as oxidation, solution (strictly speaking, solution is a physical process), carbonation, leaching, and hydrolysis.
Chemical weathering
What are the three things chemical weathering can do?
Chemical weathering can
(1) increase the volume of material, thereby causing subsequent material breakdown;
(2) dissolve parts of rock matter, yielding voids that make remaining matter more susceptible to breaking; and
(3) react with the cementing material, thereby loosening particles.
The type of soil produced by rock weathering is largely dependent on _____.
rock type.
Soils can be categorized according to where they are ultimately deposited relative to the location of the _____.
parent rock
They remain where they were formed, simply overlying the rock from which they came.
Residual soils
They are formed when rock weathers at one site and the particles are moved to another location.
Transported soils
What are the four common transporting agents for particles?
(1) gravity, (2) running water, (3) glaciers, and (4) wind.
Geological Foundations of the Greater Cincinnati, including SW Ohio, N Kentucky, and SE Indiana are made up of what?
The Ordovician bedrock
It has layers of hard gray limestone alternating with soft gray shale. One thick rock unit, the Kope Formation, is mostly shale and therefore is particularly prone to failure.
The Ordovician bedrock, glacial deposits, and riverbank deposits.
They are more variable and their distribution is harder to predict.
The glacial deposits
Till, outwash sands and gravels, which are mined for construction aggregate in many stream valleys, and lake bed clays, the culprit in many damaging landslides. These are all classified as what?
Glacial deposits
They are lower in clay, consisting mostly of sandy silts. They make very attractive land for farming and for real estate development, but are prone to flooding.
The riverbank deposits
What are the three soil types?
Cohesive, Cohesionless, Organic
sticks together and acts in a plastic manner
Cohesive
like sand, will not hold a unified shape
Cohesionless
spongy, crumbly and highly compressible which is undesirable in construction
Organic
Three common types of cohesionlesssoils are ________.
gravel, sand, and silt
• Large Bearing capacities • Small settlements (movements) • Good foundation materials for roadway • Excellent retaining wall backfill material Easily compacted Well draining •High shear strength for embankments • Loose sand is poor for construction
Construction properties of Granular soils
high permeability make them bad for earthen dikes or dams
Granular materials
The common type of cohesive soil is ____, which has particle sizes less than about 0.005 mm.
clay
- Lower shear strength, properties change with water content
- Plastic, expansive and compressible
- Creep (deform) under long‐term loading
- Prone to landslides (related to Shales; limestone, sandstone)
- They expand when wetted and shrink when dried
- Low permeability causing high lateral pressures (bad for retaining walls)
- Impervious ‐excellent material for earthen dams and dikes
Cohesive soils construction properties
- On the border between clayey and sandy soils.
- Fine‐grained like clays but cohesionless like sands.
- Undesirable engineering properties.
- exhibit high capillarity and susceptibility to frost action, yet they have low permeabilities and low densities.
silty and organic soilds
What are three properties of silts?
- Undesirable for construction
- Susceptible to frost
- Low permeability
Five properties of organic soil
- Undesirable for construction
- Contains organic matter
- Highly compressible
- Strong odor
- Low shear strength
What are the two classifications of the soil types by particle size?
- The American Association of State Highway and Transportation Officials (AASHTO) system
- The Unified Soil Classification System (USCS)
Coarse‐grained(granular): Gravel and sand, with soil grains coarser than ____ , or a ____ sieve size.
- 0.075 mm
2. No. 200
_____ will a natural soil be encountered in which all particles are exactly the same size and shape.
Never
The Atterberg Limits, Hydrometers tests are for what kind of soils?
for fine Grained Soils
Sieve Analysis is for what type of soils?
for Coarse Grained Soils
If soil is varied what should you do to test the soils?
Modifications to tests may occur
In the case of most cohesionless soils, distribution of grain size can be determined by _____.
sieve analysis
Is similar to a cook’s flour sifter: It is an apparatus containing a wire mesh with openings the same size and shape.
A sieve
When soil is passed through a sieve, soil particles smaller than the opening size of the sieve will pass through, whereas those larger than the opening size will be ______.
retained
Certain sieve‐size openings between _______ mm are designated by U.S. Standard Sieve Numbers
4.75 and 0.075
- Diameterofsoilparticlesatwhich50%passes(i.e.,50%ofthesoilby weightisfinerthanthissize)
- Mediansizegivesan“average”particlesizeforagivensoilsample
(D50)
Thediameteratwhich10%passes
(D10)
CU is the what?
Uniformity coefficient, it describes the steepness of the curve.
What is the equation for CU?
CU = D60 / D10
Indicatestheirregularityofthecurve. WhereD60andD30arethesoilparticlediameterscorrespondingto60% and30%,respectively,passingonthecumulativegrain‐sizedistribution curve.
Cc=CurvatureCoefficient
What is the equation used to find the curvature coefficient?
Cc = (D30)2 / (D10 x D60)
- Indicates the irregularity of the curve
- where D60 and D30 are the soil particle diameters corresponding to 60% and 30%, respectively, passing on the cumulative grain‐size distribution curve.
Curvature coefficient
Particle sizes varying over a wide range and have
higher Cu values (15 or higher).
Well‐graded soils:
Poorly graded soils:
- A deficiency or an excess of some particle sizes (gap‐graded or skip‐graded)
- Most soil particles approximately the same size and have low Cu (uniformly graded soils)
What is Good—Cu, Cc, when it comes to Gravel well grade?
Gravel Well Grade
• Cu≥4 and1
What is Good—Cu, Cc, when it comes to sand well graded?
- Sand Well Graded
• Cu≥6 and1
Distribution of grain size is not determined by sieve
analysis because the particles are too small.
Cohesive soils:
Cohesive Soils Analysis Techniques:
- Hydrometer method:
Process for indirectly observing the settling
velocities of the particles in a soil–water mixture. - Atterberg limits
- Calculates the drag force on a sphere as it travels through a fluid.
F=viscous drag force acting on the sphere.
r=radius of the sphere
n= viscous drag of the sphere
v = velocity of the sphere
F = 6 pie r Nv
Strokes law
• Relates the terminal velocity of a freely falling sphere to the diameter of the sphere
• ________ is applied to soil particles in the _______.
• The individual particles will fall at different rates
• Taking readings over time w
ill indicate the particle sizes
- Stoke’sLaw
2. hydrometer test
determines particle sizes
Hydrometer
The big difference between silt and clay is its behavior in the _________.
presence of water
In 1911 Atterberg defined the states of soils based on the ________.
Moisture Content
Plastic and Liquid Limit tests combined to form _________, which classifies the firmness of silts and clays. Evaluate soil for shrink/swell with changes in moisture
Atterberg Limits Test ASTM C4318
Consistency refers to clays or silts degree
of _______.
firmness
What are the four states of soil in Atterberg limits?
- Liquid state
- Plastic state
- Semi-solid state
- solid state
- The dividing line between the semi‐solid and solid states
- Quantified for a given soil as a specific water content, and from a physical standpoint it is the water content that is just sufficient to fill the voids.
Shrinkage limit
Below the ________, any water content change
will not result in volume change; above the shrinkage limit, any water content change will result in an accompanying volume change.
shrinkage limit
Soil moisture content when a reduction of water causes the soil to act as a solid. From semi‐solid to plastic state.
Plastic Limit
What are the sets to the plastic limit test?
- Water is added to soil in small amounts.
- Soil is molded into balls and then rolled into a thread or snake.
- If the snake crumbles before it reaches 1/8” diameter, it is too dry and more water is added.
- When the snakes is rolled and reaches 1/8” diameter,
moisture is removed by remolding or evaporation. - Continue the process until the snake crumbles at 1/8”.
- Determine weight with moisture.
- Repeat process with additional samples.
- Dry all samples and compare dry weight to
wet weight. - Not all soils have a plastic limit
- A material with no plastic state is called non‐plastic “NP” (silts or organics)
- Soil moisture content when an increase in water causes the soil to act as a liquid.
- From liquid state to plastic state
- Casagrande device & grooving tool
Liquid limit
- Three samples are used.
- Water is added to the sample.
- The sample is placed in the Casagrandedevice and smoothed until flat and 1/3” deep.
- Groove placed in the sample
- Casagrandedevice is tapped in order to close the gap
- Moisture content is determined by oven drying the sample
liquid limit test
What is the equation for plastic index?
PI = LL - PL
The ___ gives an indication of how much a soil will expand and contract. The higher the ___ the more exp./cont.
PI
Typical PI’s range from ____.
2-30
- In the field, _______ are a guide for how much settlement or consolidation will occur under load.
- Find the field moisture content and compare it to the _________.
- Field Moisture is near the Liquid Limit,»_space; settlement is likely
Atterberg limits
Why is it important to use atterberg’s limit to figure out how much soil will expand?
- All loads transfer to the soil
2. If foundations move…there is a problem!
Three reasons for movement:
1.Settlement –downward movement of foundations due to consolidation of underlying materials.
2. Shrink / Swell –vertical movement, either downward or upward, caused by moisture changes.
3.Shear Failure –downward movement of the foundation by lateral
movement of underlying soils
What are the three types of settlement?
- Uniform settlement
- Tipping settlement (mostly without cracks)
- Differential settlement (with Cracks)
- Geological Classification System
- Agronomic Classification System
- Textural Classification System (USDA)
- American Association of State Highway Transportation Officials System (AASHTO)
- Unified Soil Classification System (USCS)
- Federal Aviation Agency System (FAA)
Various soil classification systems
Soil classification systems must be:
- Based on a Scientific Method
- Simple
- Permit Classification by Visual and Manual Tests
- Describe Certain Engineering Properties
- Should be Accepted to All Engineers
- Used by the US Department of Agriculture
- Limits are assigned for the soil fractions
- Mostly sand, some clay–So, sandy clay
- Deal with superficial soils
Textural classification
- Silty clay
- Clayey sand
- Sandy gravel
- Need size limits on soil fractions
- Establish percent compositions
- US Department of Agriculture
- Particularly where characteristics of only superficial soils are of principal concern, which for construction purposes they frequently are.
Textural classification USDA
When using Textural classification USDA, Gravel is not in chart. If soil contains ____ or more gravel, a gravelly prefix is added to classification.
20%
Grain Size Distribution
- Mechanical Sieve Analysis
2. Well, Poor, or Gap
When dealing with coarse grained soils, what affects the Shape of Particles/ Angularity?
- Manufactured Aggregate‐Angular
- Crushed Stone or Interlocking
- Natural Deposits
- Rounded or River Rock
When dealing with _______is the ( % passing #200).
silt of clay
Fines Content
- Do not retain the in‐situ properties
of the soil during the collection process. - Consider these samples to be representative of underground soils except for tests that do not rely on the structure of the soil itself.
- For soil type and texture, moisture content, and nutrient and contaminant analysis, among other evaluations.
- The majority of soil samples engineers and geologists collect are disturbed samples because they are easier to collect and the precision necessary for collecting an undisturbed sample is not required for many soil tests.
Disturbed soil samples
- soil samples retain the structural integrity
of the in‐situ soil. - Collecting a perfectly undisturbed sample is difficult and the samplers may contain a small portion of
undisturbed soil at the top and bottom of the sample length. - Undisturbed samples allow an engineer to determine the geotechnical properties of strength, permeability, compressibility and fracture patterns among others.
- Results of these analyses are instrumental in the design of a new building.
Undisturbed soil samples
- Shelby Tube (Thin Walled)/SPT (Standard Penetration Test):
- Retrieve a sample with an auger and tube leaves soil as intact as can be (almost in situ…):
- Truck mounted, like drilling rig
Undisturbed (kind of)
- Taken by shovel, post hole digger, handheld auger
- Sealed to retain moisture
- All granular soils are taken this way
Disturbed soil sample
Types of soil samples:
- Disturbed
2. Undisturbed kind of
When doing Visual Soil Classification identify soil by using what three easy methods?
- Color (e.g. brown, gray, brownish gray)
- Odor (if any)
- Texture (coarse or fine‐grained)
When doing Visual Soil Classification Identify the major soil constituent ________.
(>50% by weight)
When using Visual Soil Classification Identify the major soil constituent (>50% by weight) for what types of soils?
- Coarse gravel
- Fine gravel
- Coarse sand
- Medium sand
- Fine sand
- Fines (clay and silt)
Visual Soil Classification:
Estimate percentages of all other soil constituents by weight:
- Trace ‐0 to 10%
- Little ‐10 to 20%
- Some ‐20 to 30%
- More ‐30 to 50%
Little
10 to 20%
Trace
0 to 10%
When doing a visual soil classification test, if major soil constituent is Sand or Gravel:
Identify particle distribution. Describe as well graded or poorly graded
soil consists of particle sizes over a wide range.
Well‐graded
Consists of particles which are all about the same size or gap graded
Poorly graded soil
Visual Soil Classification: Identify particle shape (granular soils)
- Angular
- Sub‐angular
- Rounded
- Sub rounded
Visual Soil Classification: If major soil constituents are
Fine particles, perform the following tests:
- Dry strength test
- Dilatancy Test
- Plasticity or Toughness (Snake) Test
Field / Visual Classification:
- Rely on eyes to determine coarse vs. fine
- Well graded vs. poorly graded
- If soil is coarse but has fines:
Must run field tests to determine the classification of the fines.
- Passing #40 material, moist soil
- Shake, squeeze
- The rapidity appearance of water during shaking, and disappearance when squeezing
- Is the soils reaction to shaking.
Dilatancy
1.Fine clean sands reaction to dilatancy:
quick reaction
- Plastic clay reaction to dilatancy:
no reaction
- Inorganic silts reaction to dilatancy:
Moderate reaction
Visual classification of fine grained soils:
- crushing characteristics of soil
- Passing #40 material, dry it
- Test its strength by breaking with fingers
- Fat clays –high strength
- Silt –slight strength
Dry strength
Visual Classification of Fine Grained Soils:
- ________ –consistency near plastic limit
- Passing #40 material, moist
- Roll out like the Plasticity Index test
- Lean Clays –weak thread near plastic limit
Toughness
Why Do We Classify Soils?
- Engineering applications based on the soil characteristics
- Safety Regulations on Trenching
- Max allowable slope for a Clayey Soil vs. Sandy Soil
- Suitable Fill
- Low Volume Change (LVC)
Soil is made up of solids, liquids and gas.
Soil Components
Are the soil that are visible.
Solids
Are typically water, although petroleum and other _____ may be present.
Liquids
Gas is also called _____ and has many constituents.
air
The volume of the liquid and gas is known as the ____.
void
Soil components
Air, Water, Solids
Relative Density:
- For cohesionless soils
- Relative density can be defined in terms of ______.
Void Ratio; e
Highest void ratio possible for a given soil (void ratio of the soil in it’s loosest condition)
e max
Void ratio of the soil in place
e0
lowest void ratio possible for the soil (void ratio of the soil in its densest condition.
e min
- Developed by Arthur Casagrade
- To classify soils for use in roads or airfields
- Permits Field or Lab Classification
- ASTM D2487
Unified Soil Classification System
Unified soil classification system classifies soils into six major soil types based on?
- Particle size
- Liquid limit
- Plasticity index
Unified soils classification system uses a _______.
Two-symbol designation
The first symbol in Unified soils classification system classifies what?
soil type
G
gravel
S
sand
M
silt
C
clay
O
organic
Pt
Peat
is an accumulation of partially decayed vegetation or organic matter.
Peat
What does the second symbol in the Unified Soils Classification system designate?
Condition of soil with respect to Gradation or plasticity
W
Well Graded
P
Poorly Graded
L
Low liquid limit: LL less than 50
H
High liquid limit: LL greater than 50
NP
Non-plastic
M
silty
C
clayey
If less than 5% passes the No. 200 Sieve Gravels and Sands are classified as?
GW, GP, SW, or SP
When dealing with Gravels and Sands, the well verses poorly graded depends upon the ______.
particle size distribution
When dealing with Gravels and sands, if more than 12% passes the No. 200 Sieve
GM, GC, SM, or SC
When dealing with gravels and sands, iff between 5% and 12% of the material passes the No. 200 Sieve
GW‐GC Well‐graded gravel with clay
SW‐SC
Well‐graded sand with clay
GP‐GC
Poorly‐graded gravel with clay
SP‐SC
Poorly‐graded sand with clay
When dealing with gravels and sands, if between 5% and 12% of the material passes the No. 200 Sieve.
- GW‐GM Well‐graded gravel with silt
- SW‐SM Well‐graded gravel with silt
- GP‐GM Poorly‐graded gravel with silt
- SP‐SM Poorly‐graded sand with silt
Fine grained soils:
ML, OL, CL, MH, OH, CH
- If more than 50% passes the No. 200 sieve
2. If the Liquid Limits are less than 50
ML, OL, or CL
- If more than 50% passes the No. 200 sieve
2. If the Liquid Limits are greater than 50
MH, OH, CH
This determines whether sample is Coarse or Fine Grained.
% Passing the No. 200 Sieve
This separates gravel from sand
% Passing No. 4 Sieve
(Difference between liquid limit and plastic limit; ___ )
LL‐PL
Coarse
(More than 50% on #200)
less than 5% fines, greater than 12% fines (#200)
clean or dirty
- Determine Cu, Cc
2. Determine Well or Poor
Clean
Determine LL, PI –Plot on Plasticity Chart
Determine Silty or Clayey
Dirty
To determine is a soil is fine grained, ___ or more passes #200.
50%
Determine if organic:
must be told it is organic or has odor
Plot on Plasticity chart to determine if ____.
Silt or Clay
If soils have less than 5% fines_________.
Atterberg’s limits are irrelevant
_____ should be determined by their dark color and smell.
Organic soils
- Can determine by running LL on sample after air drying and oven drying.
- If LL is <3/4 the standard value due to drying it is ____.
organic
- Describe soils with seven basic soil groups
- A-1(best) through A-7(worst)
- A-8 is for organic soils
- A-1 through A-3 are sands and gravels
- A-4 through A-7 are silts and clays
AASHTO classification system
Best soil in AASHTO
A-1
Worst soil in AASHTO system
A-7
Organic soils in AASHTO system
A-8
Sands and soils in AASHTO are classified as what?
A-1 through A-3 are sands and gravels
Silts and clays are classified as what in AASHTO?
A-4 through A-7 are silts and clays
What is the difference between ASSHTO and USCS?
Fine and course soils:
AASHTO defines fines as greater than 35% passing
USCS defines it as 50% passing .
GI = (F - 35) (0.2 + 0.005(LL-40)) + 0.01(F-15) (PI - 10)
GI = group index
For A-2-7 and A-2-6 use what?
Partial Group index
PGI = 0.01 (F-15) (PI - 10)
Partial Group Index
F = fines _______.
(#200 or 0.075 mm passing)
If you have a negative GI what should you do?
report it as zero
Refers to a volume of earthen material that is placed and compacted for the purpose of raising the grade of a roadway (or railway) above the level of the existing surrounding ground surface.
Embankment
- Grain size distribution
- Particle shape
- Specific gravity of solids
- Clay
- Maximum dry unit weight (density)
- Optimum moisture content
The factors that affect Compaction of soils.
- Typically 8” loose compacted to 6” at finish
- Typically accomplished in 6-10 coverages
- Scarifying between layers: to provide bonding between layers
Field Compaction
- Tampers deliver a succession of light blows
- Held in place
- Operated by hand
- Used in areas not accessible by larger equipment
Ramming or tamping foot compactors (Wacker Packer)
- Uses 1 or more rollers
- Self-propelled or pulled by tractors
- Compacting base courses, and provides a smooth finished grade
Smooth Drum
- Vibration frequencies of 1,500-2,000 cycles/min
2. Effective for clean sands & gravels
Vibratory rollers
- rotating drum with metal “feet”
- Creates greater pressures
- Provides kneading action for fines-grained soils (clays & silts)
Sheepsfoot roller
–are the index values for fine particles
- Not always enough information to draw conclusions about soils.
- Need info on
- Soil Unit Weight
- Water Content
- Other correlations between air-water-soil
LL, PL, and PI
- This number indicates how much heavier/lighter a material is than
water. - In soils, SG refers to the mass of solid matter of a given soil sample as
compared to an equal volume of water.
Specific Gravity
When dealing with specific gravities soil solids = what?
W= 187.2 lbs
When dealing with specific gravities of water, it equals what?
W = 62.4 lbs
If the W of the soil solids w=187.2 lbs and the w of the water w=62.4 lbs what is the specific gravity.
SG = 187.2 / 62.4 = 3.0
Specific gravity of Sand is:
2.65-2.67
Specific gravity of silty sands is:
2.67-2.70
Specific gravity of Inorganic Clay is:
2.70-2.80
Specific gravity of soils with mica/iron:
2.75 - 3.00
Specific gravity of organic soils:
less than 2.00
Soil Consists of the following:
- Solids
- Water
- Air
What is the equation for the volume of soil.
Volume = volume of soil + volume of water + volume of air
What is the equation for weight of soil?
water = water weight + water weight
Vt=
Total soil volume
Va =
Air volume
Vw =
Water volume
Vs =
solids volume
Vv
voids volume
What is the equation for void volume?
Vv = Va + Vw
Wt =
total weight
WW=
Water Weight
WS=
Solids Weight
What is the equation for void ratio?
e = Vv / Vs
What is the Porosity (N) ratio?
n = Vv/V x 100%
What is the degree of saturation (S) Stopped on page 8 of 2.6. A little confused.
S = Vw/Vv x 100%
1. Natural decrease in soil volume w hen subjected to an increased effective stress 2. Foundations (surface loads) 3. Embankments (fill)
Compressibility
- Results in surface settlement
2. Which in turn can cause damage to structures
compressibility
Total settlement as a two‐phase process:
- Immediate settlement : occurs very rapidly—within days or even hours after a structure is loaded.
- Consolidation settlement: occurs over an extended period of time (months or years) and is characteristic of cohesive soils.
- ________ involves expelling water from soil voids.
2. Due to permeability and void ratio (e)
consolidation
High permeability = ______ soils (sandy)
2. Consolidation happens quickly; i.e. during construction
coarse grained
- Low permeability = ________
- Consolidation happens slowly: Because of lower permeabilities, cohesive soils compress much more slowly because the expulsion of water from the small soil pores is so slow.
fine grained soils (clays)
- Change in height can be predicted based on the loaded void ratio.
- Consolidation tests predict Δh
- Consolidation removes water without replacing
the water with air.
loaded compressible stratum
- Moist sand has _________.
apparent cohesion
- Surface tension holds the _____.
sand together
- Loose sand when shaken will ___.
densify
- For water filled voids, water must be expelled before _______.
densification
- When water is expelled, pressure
between soil grains is reduced - When the pressure reduction is sufficient, the soil has no strength (like unconfined sand) or has liquefied
- Liquefaction can occur after earthquakes causing mudslides
Soil liquefaction
- Cohesive strength based on
- Water content
- Plastic limit
- Liquid limit
- Stiff to hard _____ pose problems in construction
- Must be excavated or remediated
- Unsatisfactory for foundations of shoring
Clays
- Soils are loaded in compression
- NATURAL so strength and properties vary as the RULE
- Designs and methods must change to match the soil property encountered.
Soil strength
Load carrying capacity of soil is dependent on its _____.
shear strength
The ability of soil to support an _____ is determined by its shear strength
imposed load
- Made in advance of construction
- Assist in design of structures
- Subsurface exploration
- Made available to the contractor during estimating
period
Soil exploration
- Locate and define vertical and horizontal boundaries of:
a. Various soils and rock strata
b. Underlying the site of proposed construction - Locate the groundwater table
- Determine engineering properties of subsurface material
Field exploration
a. Preliminary examination or survey of a job site.
b. Some useful information on the area (e.g., maps or aerial photographs) will already be available
c. Astute person can learn much about surface conditions and get a general idea of subsurface conditi
ons by simply visiting the site.
d. The geotechnical engineer should then visit the site in person.
e. Observe thoroughly and carefully, and interpret what is seen.
1-Reconnaissance
What are the steps of soil exploration?
- Boring
a. Direct exploration
b. Semi‐direct exploration - Sampling
a. Disturbed
b. Undisturbed - Testing
Direct Exploration is Performed by visual inspection through:
- Test pits
- Test trenches
- Test holes
Preferred when groundwater is 20’or more below the surface: Because most saturated soils will not cling sufficiently to the auger for lifting.
Direct Exploration
- excavations into the earth t
hat permit a direct, visual
inspection of the soil along the sides of the pit. - They may be large enough to allow a person to enter : make inspections by viewing the expos
ed walls, taking color photographs of the soil in its natural condition, testing in situ, and taking undisturbed samples.
Test pits:
- Press the thumb firmly into the soil in question
- If the thumb makes an indentation in the soil only with great difficulty, the soil is probably Type A
- If the thumb penetrates no further than the length of the thumbnail, it is probably Type B soil
- If the thumb penetrates the full length of the thumb, it is Type C soil.
Thumb penetration test
- The _______ is subjective and is therefore the least accurate method.
- Used for determining shoring requirements: For deeper pits, the excavation may need to be shored to protect persons entering the pits.
thumb test
Support system to hold soil back during excavation for
underground construction or exploration
Shoring:
- Determines unconfined compressive strength of soil (qu) through penetration of soil.
- Direct exploration method
- Based on allowable pressure(psf), not density (pcf)
- Have error rates in the range of ±20‐40%
Pocket Penetrometer
Direct exploration advantages:
- Permits observation in natural state
2. Can obtain undisturbed samples
Direct exploration disadvantages:
- Usually depth is restricted
2. By equipment or groundwater
- Auger drilling rig
- Drills and samples
- Solid Stem
- Hollow Stem
- Rotary Drilling
- Uses Slurry or Drilling Mud
Semi-direct exploration
- Thin walled tube sampling
- Shove sample tube into bottom of boring
- 2‐5 in in diameter
- Up to 4’ in length
- Obtain an undisturbed sample
Shelby Tubes
