Soil Testing Activity

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Forging new generations of engineers
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SOILS Civil Engineering ArchitectureTM
Unit 4 - Lesson 4.5 - Activity 4.5.1 Soil Testing
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Soil Testing
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Introduction

• Prior to developing a property for a commercial
  endeavor, a designer needs to investigate the
  soil conditions at the site.
• There is no construction material that has both
  the physical and engineering properties which are
  more variable than soil. Therefore it is highly
  desirable to have some information regarding both
  the surface and subsurface soil conditions.

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Soil What is it?

• Soils rarely exists as separate components
  such as sand or gravel.
• Soils contain various particle sizes of gravel,
  sand, silt and clay and each contributes to the
  characteristics of the soil.

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Why Test the Soil???

• The knowledge gained from soil testing allows
  the engineer to make estimates for
• Bearing Capacity of the soil
• Settlements of Foundation ( amount and rate)
• Earth Pressure both lateral and vertical
• Drainage
• These characteristics determine how certain
  soils behave as a construction material.

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What is Needed to Determine Soil Properties

• Site Plan
• Site Profile (Contour Map)
• Geological Information (USGS Maps)
• Soils Sample Data(obtained through soils
  analysis/testing)

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• Factors to be taken into consideration when
  determining the type of the building foundations
• Function of the structure
• Loads from the structure
• Bearing capacity of foundation material
• Total and differential settlement of foundation
• Uplift forces acting on the foundation
• Costs

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• The Soil Bearing Capacity needs to be determined
  before a foundation system can be designed. This
  can be determined by
• Local or State Building Codes
• Uniform Building Code (UBC)
• Soil testing/analysis
• Site inspection and simple soil testing methods
  ( surface soils- top 1 foot)
• Soil borings taken at proposed foundation
  locations (subsurface soils)
• Presumptive Bearing Capacity

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Sample Soils

• Soil testing must be done on soil samples that
  truly represent the the soil at the site.
• Soil sample about 1-2 below surface
• Boring samples are taken at various locations and
  depths below the surface (subsurface) for deep
  foundations

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Soils Testing

• Unified Soils Classification System is a method
  for for identifying and grouping soils. It was
  first developed by Casagrande for military
  construction of airfields.
• Many soils can be grouped visually with the USGS
  with additional tests for grain size and
  plasticity required to accurately classify the
  soil.

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Unified Soil Classification System

• The Unified Soil Classification System is a
  rapid method used to determine Simple Grain Size
  Analysis and categorizes the soil as either
• -Coarse-Grained Soils
• -Fine Grained Soils
• -Highly Organic Soils
• Only particles sizes smaller than 3 are
  considered in the USC System

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Coarse vs. Fine Grained Soils

• Many soils can be grouped visually with the USGS
  and additional tests for grain size and
  plasticity are required to accurately classify
  the soil
• Coarse-Grained soils described by grain size
• Fine-Grained Soils described on the basis of
  their plasticity

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Sieve Sizes

• Gravels range from 3 down to the size of peas

• Silt and clay can pass through the 200 sieve

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Sieves
40 sieve ( similar to window screen)
4 sieve ( ¼ squares, similar to hardware cloth)
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Grain Size(Gradation)

• Gravel Sand
• Boulder Cobbles Silt
• Coarse Fine Coarse Medium
  Fine
• Comparable Size
• gt12 312 ¾3 4 - ¾ 10 - 4
  40-10 200-40 lt200

Clay
NOTE Particles finer than fine sand ( 200
sieve) can not be seen by the naked eye at a
distance of 8 inches
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Gravel Identification
Coarse Gravel from 3 to ¾, a comparable size
Plum or Lemon
Fine Gravel from 4 to ¾, a comparable size
Grape or Pea
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Gravel Size

• Coarse gravel

Fine gravel
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Sand Identification
Coarse Sand from 4 to 10, a comparable size -
Rocksalt
Medium Sand from 10 to 40, a comparable size -
Sugar
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Sand Size

• Medium sand

• Coarse sand

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Graded Soils

• Soils can be defined by how the particle sizes
  are distributed within the soils sample.
• Well-Graded Soils-have a good representation of
  all particle sizes from the largest to smallest
• Poorly-Graded Soils- two types
• Uniformly-soil particles are nearly the same size
• Gap-Graded- contains both large and small
  particles but the graduation continuity is
  broken by the absence of some particle sizes

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Clean vs. Dirty Graded Soils for Gravel and Sand

• If a soil is identified as being Clean it
  contains little or no fines (lt5)
• If a soil is identified as being Dirty it
  contains an appreciable amount of fines (
  gt12)
• Silty fines
• Clayey

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Soil Designations

• The USCS divides soils that have been
  classified into the major soil categories by
  letter symbols, such as
•   S for sand
•   G for gravel
• M for silt
• C for clay
• O for organic
• Pt for peat

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Grain Shape
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Soil Color

• Color can aid in distinguishing soils types
• Can vary with moisture content
• May indicate the presence of certain chemical or
  impurities
• Dark brown /black may indicate organic material
• Gray, olive green indicate inorganic soils
• Red or yellow may indicate iron oxides
• Gray-blue or gray-yellow indicates poor drainage
• White to pink may indicate considerable silica,
  calcium carbonate, or aluminum compounds.

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Plasticity

• Plasticity of the soils refers to the varying
  water content on the consistency of the soil in
  fine-grained soils.
• This system is sometimes referred to as the
  ATTERBERG LIMITS, named after the Swedish
  scientist who developed this test.
• Plastic Limit-lowest moisture content at which
  soils can be rolled into 1/8 dia.thread with out
  breaking
• Liquid Limit- minimum moisture content at which
  soil will flow when a small shear or cutting
  force is applied

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Soils Groups
Soil Type Gradation Liquid Limit
Gravel- G Sand-S Silt-M Clay-C Organic O Peat- Pt Well Graded- W Poorly Graded - P LL over 50- H LL under 50 -L
These letters are then used in combination to
form the soils groups
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Determining the Silt or Clay Characteristics of
Fine Grained Soil

• In addition to the Sieve Analysis the following
  tests will be done to determine of the Fine
  Grained soils
• Dry Strength- crushing characteristics
• Dilatancy- reaction to shaking
• Toughness- consistency near plastic limit

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Unified Soil Classification System
Start here
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Equipment for Testing

• Sample of soil about the size of a coffee can and
  collected below the top soil horizon (about 1 to
  2 feet).  
• 2 mason jars with tops   
• 5 gallon pail 
• Water
• Mixing bowl
• A 2 x 2 metal pan and rubber mallet
• Sieve collection, ASTM No 4 and ASTM No. 40Bottom
  sieve pan and cover
• Triple-beam balance or Digital Scale

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Testing
USCS SYSTEM SEIVE ANALYSIS
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• Weigh each sieve separately

Weigh mason jars for later use
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Soils Sampling

• Take a representative soil sample from the
  property
• A shovelful or coffee can of soil should be enough

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• Soil sample should be dry
• Pulverize the soil with a rubber mallet

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• Continue to Pulverize the soil with your hands
• Be sure that all small and large clumps are
  completely broken apart.

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Stack sieves with Number 4 on top, then the
Number 40 sieve below that, and then finally the
bottom pan.
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Place soil in Number 4 sieve, place cover on top
and shake vigorously.
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• Shaking the Soil Sieves
• Shake with up and downward motion
• or / and
• Shake with side to and side motion
• Shake vigorously.

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Weighing of each Sieve with Sample Particles

• Weigh the sample material and the sieve.
• Subtract the weight of the sieve to obtain weight
  of soil. In this case , the weight of the
  particles is the Gravel fraction in the soil
  sample
• Do this for each sieve.

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4 Sieve with Gravel
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4O Sieve with Sand

• Record and subtract the weight of the No.40 sieve
  only (i.e., without the soil sample). The
  difference is the coarse and medium grained SAND
  fraction in the soil sample.

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Bottom pan with Fines

• Weigh the bottom pan and its contents. Record
  and subtract the weight of the empty pan. The
  difference is the fine SAND, SILT, and CLAY
  fraction of the soil sample.

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Relative Particle Sizes
40 sieve
4 sieve
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Sieve Analysis Results
USCS Classification for Coarse Grained Soils

• Coarse-grained soil, also called granular soil
  has more than half of the soil grains visible to
  the naked eye.
• If the percentage of GRAVEL and SAND is greater
  than 50, then the soil is a granular soil.
• If the soil is predominantly coarse-grained,
  identify the soil sample as being gravel or sand
  by estimating whether 50 or more, by weight, of
  the coarse grains (GRAVEL and SAND) are larger or
  smaller than the No 4 sieve size.

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USCS Classification for Fine Grained Soils

• Fine-grained soils, also called cohesive soils
  contain greater than 50 SILT and CLAY particles.
  
• It is classified further into either SILT or CLAY
  and them determined if it is high or low
  plasticity by estimating its dry strength
  (crushing characteristics), dilatancy (reaction
  to shaking), and toughness (consistency near the
  plastic limit)
• Individual fine- grains are not visible to the
  naked eye

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Determining the Fine Grained Sand Fraction of Soil

• Place the contents of the bottom pan from the
  sieve test in a Mason jar.
• Weigh and Record results
• Fill jar with water so that I
• it is ¾ full
• Shake jar with lid on and let the fine sand
  settle 5 to 10 seconds
• Drain off

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• Determining the Fine Grained -
• Sand, Silt and Clay fraction of the soil sample

• Pour off the dirty water, be careful not to spill
  any of the soils at the bottom of jar
• Repeat the shake, settle and drain off procedure
  several times
• Repeat until water is clear

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Determining the weight of Silt and Clay in Soil
Sample

• Place the Mason jar, without top, and the
  contents into the oven and dry.
• Weigh the jar and contents. Record the weight and
  subtract the weight of the empty jar. The
  difference is the fine grained SAND fraction in
  the soil sample.
• Determine the weight of SILT and CLAY in the soil
  sample
• Determine the percentage of Silt and Clay in the
  soil sample

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Dilatancy Test

• Dilatancy is the reaction to wet shaking
• Prepare a pat of moist soils approximately 3/4
  in3 in size
• Add water, if necessary, to make soil soft but
  not sticky, like soft putty
• Place pat in open palm of hand
• Shake horizontally, striking with other hand
  several times

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Dilatancy Test

• Observe rapidity of water rising to the surface
  when sample is shaken and when the sample is
  squeezed between fingers
• Speed of appearance during shaking and
  disappearance when squeezed assists in
  identifying the fines in the sample
• If sample become soft and glossy when shaking and
  then become hard, dull and forms crack when
  squeezed between the fingers , it has a reaction
  to shaking, or dilatancy

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Dilatancy Test Results

• Very clean sands give the quickest and most
  distinct reaction ( S)
• Rapid reaction, sample is silt ( M)
• No reaction indicates clay ( C)

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Toughness Test Effect of Water on Fine-Grained
Soils

• A method of testing the plasticity of the soil is
  referred to as the Toughness Test.
• Water is added to the fines portion of the
  soils sample ( those particles that passed the
  No. 40 sieve) and the sample is then rolled into
  a 3mm ( 1/8) diameter thread.

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Toughness Test

• Mixing about a 100 cm3 ( 1/3 cup of the
  soil that passed through the No. 40 sieve) with
  water. Mixture should be the consistency of putty

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Toughness (Thread Test)

• Roll out specimen on a smooth surface until it is
  approx. 1/8 in diameter.
• Fold and re-roll thread repeatedly
• Soil samples moisture content will gradually be
  reduced
• Thread breaks and sample becomes lumped
• Continue until lumps crumble

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Toughness Test Results

• The toughness of the thread that forms when
  the soil is rolled will identity the fines as
  either silt or clay.
• Inability to form thread or very weak thread
  indicates a plastic silt (ML)
• Weak spongy thread indicates silt (either organic
  or inorganic) with a high liquid limit and a low
  low-plasticity (MH)
• Firm thread indicates low-plasticity clay (CL)
• Tough thread indicates highly plastic clay ( CH)
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Dry Strength

• Form a moist pat of approximately 2-3 in
  diameter and ½ thick
• Allow to dry with low heat
• The crushing characteristic of the soil sample
  will be evaluated after this sample is completely
  dry.

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Dry Strength Test and Results

• Dry strength is a measure of the character and
  quality of colloidal fraction of soil.
• Break dry pat sample between thumb
  and index finger

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Dry Strength Test Results

• Breakage Easy Silt
• Breakage Difficult - Inorganic Clays of low to
  medium plasticity
• Breakage Impossible- Inorganic Clays of high
  plasticity

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Soils Test Results for Fine Grained Soils
Soils Type
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Soils Types for Foundations

• Sand and Gravel Best
• Medium to hard Clays- Good
• Soft Clay and Silt- Poor
• Organic Silts and Clays- Undesirable
• Peat- No Good - Avoid

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Soil Bearing Capacities
Soil Type Allowable Bearing(lb/ft 2) Drainage
BEDROCK 4,000 to 12,000 Poor
GRAVELS 3,000 Good
GRAVELS w/ FINES 3,000 Good
SAND 2,000 Good
SAND W/ FINES 2,000 Good
SILT 1,500 Medium
CLAYS 1,500 Medium
ORGANICS 0 to 400 Poor
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Soil Preparation

• What is the site has poor soils, is there
  anything that can be done?
• If the soils at the site are not suitable to
  carry the foundation loads, the site may have to
  be prepared using some of the following methods

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Soils Preparations for foundations if soil is
undesirable

• Compaction of the soil- increase the density of
  the soils and therefore increases the bearing
  capacity of the soil. Compaction of the soils is
  down by rolling the soils
• Bring in Engineered Fill, must remove old soils
  first
• Blasting to remove rock or soil

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Soil Types and Properties
Source U.S. Army Corps of Engineers. (1953). The
unified soil classification system. U.S. Army
Technical Memorandum, No.3-357.
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Soil Description

• Color Dark Brown to White
• Grain size, including estimated maximum grain
  size is an estimated percent by weight of fines
  (material passing the No. 200 sieve)
• Coarse-grained soils, maximum particle size 2,
  estimating 60 percent gravel, 36 percent sand,
  and 4 percent passing the 200 seive,
• Gradation Poorly-graded, insufficient fine
  gravel
• Grain shape  Gravel particles well rounded

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Soils Description (continued)

• Plasticity Nonplastic
• Predominant type Predominantly gravel
• Secondary components Considerable sand and trace
  amounts of nonplastic fines(silt)
• Classification symbol GP ( Poorly Graded Gravel
  and sandy gravel mixture with little or no fines)
• Other remarks, such as organic, chemical, or
  metallic content compactness consistency
  cohesiveness near PL dry strength and source
• No dry strength, dense in undisturbed states

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References
Sowers, G.F. (1979). Introductory Soil Mechanics
and Foundations Geotechnical Engineering,New
York, NY Macmillan Publishing Lindeburg, M. R.
(1994). Civil Engineering_Reference Manual (9th
ed.). Belmont, CA Professional Publications,
Inc. GGuthrie, P. (2003). Architects portable
handbook First step rules of thumb for building
design. NY McGraw-Hill. Unified Soil
Classification http//www.hydro.unr.edu/homepages/
benson/classes/hydro/uscs.html August 2004
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References (continued)
U.S. Army Corps of Engineers. (1953). The Unified
Soil Classification System. U.S. Army Technical
Memorandum, No.3-357. US Army Unified Soil
Classification System. On-line. Available
http//www.adtdl.army.mil/cgi-bin/atdl.dll/fm/5-47
2/apb.pdf (August 5, 2004)
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Narration PLTW Editor Production Video
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