basic soils presentation

BASIC SOIL

LEARNING OBJECTIVES•Why we test soils.•Understand the role of project personnel.•Awareness of applicable safety requirements:

•Radiation safety•Excavation safety•Working around earthmoving equipment

•Basic concepts.•Obtain samples for laboratory testing.

LEARNING OBJECTIVES (CONT’D)

•Basic familiarity with some laboratory tests.•Introduction to soil classification (USCS).•Interpret earthwork specifications and site plans.

•Familiarity with compaction equipment and proper use.

•Knows how to perform field density and moisture tests:

• Sand cone• Nuclear gauge

BEFORE WE START…

•Safety is non-negotiable!•Approved construction drawings and specifications must be used!

WHY DO WE TEST SOILS?•Foundation for most structures, and we want to build on “Good Stuff.”

•Reduce potential failures.

•Quality control.

SAFETY• Hard hat is required at ALL TIMES.• Safety glasses are required at ALL TIMES.• Proper clothing is required at ALL TIMES.

• No shorts• Shirts with sleeves on at ALL TIMES

• Avoid overexposure to the sun or cold.

SAFETY (CONT’D)• Watch for moving

equipment:• Announce your

presence• Be visible• Trench Safety

TRENCH SAFETY SUMMARY

• No protective system needed if:• Entirely in stable rock, or• Excavation less than 5 feet (4

feet in some jurisdictions), and

• No indicators of potential cave-in (“Competent person”).

• Otherwise, don’t go in.

TRENCH SAFETY SUMMARY (CONT’D)

• Reasonable exits within 25 feet if 4 foot deep or more:

• Stairs, ramps or ladders• No soil or rock steps

• Hazardous atmosphere check before entry if problems could be reasonably expected and if more than 4 feet deep.

TRENCH SAFETYSUMMARY (CONT’D)

• Material and equipment at least 2 feet back from edge.

• Competent person must inspect daily.

• > 20 feet: designed by an engineer.

• Trench boxes must extend 18 inches above edge.

TRENCH SAFETYSUMMARY (CONT’D)

•Notify the site superintendent if you suspect unsafe conditions.

•Document your observations in detail.

•Do not enter an unsafe trench!

•Never stay in a trench box when it’s moved.

RADIATION SAFETY• Radiation safety:

• Wear dosimeter properly• Gauge must be within your control at all

times (within 10’ when using).• Do not expose the source.• Wear reflective vest!

RADIATION SAFETY (CONT’D)

•If an accident:• Stop all activity near

incident• Tape off area 15 feet

around the gauge• Call the RSO

immediately• Do not leave the area

LEARNING OBJECTIVES•Why we test soils.•Understand the role of project personnel.•Awareness of applicable safety requirements:

• Radiation safety• Excavation safety• Working around earthmoving equipment

•Basic concepts.•Obtain samples for laboratory testing.

ORGANIZATIONS AND STANDARDS

• AASHTO: American Association of State Highway and Transportation Officials.

• ASTM: American Society for Testing and Materials.

• State Transportation Agencies:

• VDOT• MHD• TxDOT• etc.

• USACE: U.S. Army Corps of Engineers.

BASIC SOIL CONCEPTS •Soils/Rock form the foundation for virtually all buildings, roads, and structures.

•Understanding of soil characteristics and how they respond to structural loads is important in design & construction.

•Soils formed naturally from weathering of rock.

SOIL MECHANICS

• Soils are defined or categorized by particle size and plasticity.• Each category of soil or rock has different engineering characteristics.• Moisture content significantly effects how soils behave.• Compaction influences engineering characteristics.

PARTICLE SIZE• Soil/rock categories based on particle sizes:

• Boulder• Cobble• Gravel• Sand• Silt/Clay

PARTICLE SIZE AND DENSITY OF SOIL

• Rocks are more dense than soil.• The larger the particles are in a given volume, the greater the

density.

GRAVEL

• Particle sizes smaller than 3 inches in diameter and retained on No. 4 sieve.

• Pass No. 4 sieve, (4.75 mm) and retained on No. 200 (75 µm) sieve.

GRAVEL & SAND

• Good Structural fill material.

• Good for Drainage (pervious).

• Recommended for backfill of walls.

• Good roadway/slab subgrade material.

SILT AND CLAY

• Pass No. 200 (75 µm) sieve.

SILT & CLAY• Low permeability (less

pervious).• Excellent for dam and

pond construction.• Relatively weak for

road subgrades.• Very sensitive to

moisture.• Shrink/swell potential.

MOISTURE CONTENT (w)• Influences ability to compact soils.• Changes characteristics of silts and clays.

w = x 100

Weight of water = weight of wet soil – weight of dry soil

Weight of waterWeight of dry soil

COMPACTION

• Densification of soils by mechanical means.

• Higher densities (dry density) usually improve engineering properties.

OBTAINING SAMPLES• Determine where the sample should be taken:

• Sample the same that will be placed?• What type of tests will be run?

• Proctor: sample from the source of the fill.• CBR: sample from the subgrade.

OBTAINING SAMPLES (CONT’D)

• Must have enough to run required tests:

• 35 lbs for standard Proctor

• 65 lbs for CBR and Proctor

• Ask if you are not sure!

COMMON LABORATORY TESTS

• Atterberg Limits Tests:• Test the plasticity of the

soil.• The higher the plasticity,

the worse the soil is for structural backfill.

• Liquid Limit (LL) - Moisture content at boundary of plastic and semi-liquid states.

COMMON LABORATORY TESTS (CONT’D)

• Atterberg Limits Tests (cont’d):

• Plastic Limit (PL) - Moisture content at boundary of plastic and semi-solid states.

• Plastic Index (PI) - Moisture content range over which a soil acts plastic. PI = LL – PL.

ATTERBERG LIMITSAND SOIL STATES

Increasing W

Plastic StateSemi-Solid

SolidState

LiquidState

Plasticity Index

Plastic Limit Liquid Limit

Plastic State

Semi-SolidState

SolidState

LiquidState

Plasticity Index

• Grain-Size Analysis:•Determines the % of different sizes of the soil particles

in a sample.•Sample usually dried and sent through a series of

sieves.• #4 sieve has 4 openings per inch.• #10 sieve has 10 openings per inch.• 3/8-inch sieve has openings that are 3/8-inches wide.• #200 has 200 openings per inch.

• Grain-Size Analysis (cont’d):• % Retained.• % Passing. • Sample distribution

graphs at Tab II.

SAMPLE GRAIN SIZEDISTRIBUTION GRAPH

• Proctor Analysis / Moisture–Density Relationship:•Density is the mass per unit of volume (lb/ft3). •Soil is made up of, air, water and particles.•By adjusting the water content, we can obtain different densities.

•By adjusting the compactive effort, we can obtain different densities.

• Oversize material is removed.• Obtained by molding samples at different moisture contents

and a constant compactive effort. • The top of the curve is the uncorrected or “as tested”

Maximum Dry Density.• The corresponding moisture content is the uncorrected or

“as tested” Optimum Moisture Content.• Sample Report at Tab II.• What’s this zero air voids curve?

SAMPLE PROCTOR CURVE

PROCTOR METHODS

• Different procedures due to:• Maximum particle size• Desired compactive effort

• ASTM:• D 698• D 1557

• AASHTO:• T99• T180

• Others such as VTM-1.• Watch what the specifications

PROCTOR METHOD (CONT’D)

• ASTM D 698 (“standard”):

• 5.5 pound hammer• 3 equal layers• 12 inch drop height

Method Mold Diameter (inches)

Oversize Sieve

Blows Per

A 4 #4 25

B 4 3/8” 25

C 6 ¾” 56

• ASTM D 1557 (“modified”):

• 10 pound hammer

• 5 equal layers• 18 inch drop

height

Method Mold Diameter (inches)

Oversize Sieve

Blows Per

A 4 #4 25

B 4 3/8” 25

C 6 ¾” 56

• Does laboratory test agree with specifications?• ASTM D 698• ASTM D 1557• AASHTO T99• AASHTO T180• VTM-1

• Is oversize correction based on proper oversize fraction?

• Type A• Type B• Type C

• Is as-tested oversize the same as field results?42

•Basic familiarity with some laboratory tests.•Introduction to soil classification (USCS).•Interpret earthwork specifications and site plans.

•Familiarity with compaction equipment and proper use.

USCS CLASSIFICATION

• USCS: Unified Soils Classification System (ASTM D 2487). (Summary at Tab III).

• Classifies soils based on Atterberg limits and grain-size analysis.• USCS system breaks soil into 2 categories (No. 200 sieve):

•Coarse-grained: Gravel and Sand•Fine-grained: Silt and Clay

USCS CLASSIFICATION (CONT’D)

• S = Sand• G = Gravel• M = Silt• C = Clay• O = Organic

– Pt = Peat – P = Poorly Graded– W = Well Graded– L = Lean Clay or Silt (low

compressibility)– H = Fat Clay or Elastic Silt

(high compressibility)

• Then use a combination of letters to classify soils:

USCS SUMMARY

PLASTICITY CHART

USCS CLASSIFICATION #1

• Given:• % passing #4 = 56.7%• % passing #200 = 16.3 %• Liquid limit = 48• Plastic limit = 15• Gravel is well graded

• Classification?• See Tab III

COARSE–GRAINED OR FINE–GRAINED?

SAND OR GRAVEL?

CLEAN GRAVEL OR GRAVEL WITH FINES?

ML/MH OR CL/CH?

GM OR GC?

USCS EXAMPLE CLASSIFICATION #1

• Given:• % passing #4 = 56.7%• % passing #200 = 16.3 %• Liquid limit = 48• Plastic limit = 15• Gravel is well graded

• Classification?

54• Answer: GC

• Given:• % passing #4: 100%• % passing #200: 75%• Liquid limit: 52• Plasticity Index: 12

• Classification?

• Given:• % passing 3/4”: 100%• % passing #4: 85%• % passing #200: 36%• Liquid limit: 29• Plasticity Index: 10

• Classification?

• Given:• % passing ¾”: 100%• % passing #4: 72%• % passing #200: 33%• Liquid limit: 35• Plasticity Index: 0 (not plastic)

• Classification?

USCS EXAMPLE CLASSIFICATION ANSWERS

• #1: GC

• #2: MH

• #3: SC

• #4: SM

VISUAL CLASSIFICATION

•Not as accurate as laboratory classification.

•Use ASTM D 2488 as guide.•Always identify when classification is by visual methods.

COMPACTION EQUIPMENT

• Size• Weight• Types:

• Smooth drum• Sheepsfoot• Vibratory• Rubber–tired

OPTIMUM COMPACTIONEQUIPMENT

GW or GP

GM or GC

SW or SP

SM or SC

Rubber-tire or steel-wheel

Rubber-tire or

sheeps foot

Rubber-tire

Rubber-tire or

sheeps foot

COMPACTION EQUIPMENT(CONT’D)

Note: Operator’s PPE

COMPACTION EQUIPMENT (CONT’D)

SAND CONE METHODOLOGY

• Wet weight of soil from hole.• Volume of hole.• Wet density of soil.• Moisture content of soil.• Dry density of soil.• Does it pass specifications?

SAND CONE

• Tools Needed:• Sand Cone• Calibrated Sand• Sand Cone Plate • Empty Jar with air tight

lid• Digging tools• Digital scale

SAND CONE (CONT’D)

• Step 1:• Determine weight of sand

to fill cone.• Step 2:

• Fill Sand Cone with Calibrated sand and weigh.

• Weigh empty sample jar.

• Step 3:• Place sand cone plate on area to

be tested.• Area must be level and smooth.• Dig hole apprx 4-6” deep.• Put all soil from hole in empty

jar and seal.• Step 4:

• Place sand cone over hole on plate.

• Step 4 (cont’d):• EQUIPMENT MUST STOP

WORK IN AREA.• Carefully open the sand cone

valve and allow sand to fill hole and cone.

• Once sand stops flowing, carefully close valve.

• Step 5:• Weigh Jar with soil.• Weigh Sand Cone.• Do not re-use sand

SAND CONE EXAMPLE

• Weight of Sand Cone Before Test = 13.52 lbs.• Weight of Empty Sample Jar = 2.52 lbs.• Density of Sand (provided) = 99.20 lb/ft3 • Weight of Sand Cone After Test = 9.42 lbs.• Weight of Full Sample Jar = 4.32 lbs.• Weight of Sand to Fill the Cone = 2.73 lbs• Weight of soil after drying = 1.57 lb

SAND CONE EXAMPLE (CONT’D)

• Wet weight of soil:(weight of full jar) – (weight of empty jar): 4.32 lb – 2.52 lb = 1.80 lb

• Volume of hole:

(weight of full apparatus) – (weight after test)– (weight of sand in cone)

density of sand

1 3.52 lb – 9.42 lb – 2.73 lb 1.37 lb 99.20 lb/ft3 99.20 lb/ft3

• Round volume to nearest 0.0001 ft3

= 0.0138 ft3=

•Wet density of the soil (w):wet weight of soil from hole

volume of holeTherefore:

1.8 lb 0.0138

WD or w = = 130.44 lb/ft3

•Compute moisture content of soil: weight of water weight of dry soil

weight of wet soil-weight of dry soil weight of dry soil

1.80 – 1.57 1.57= 14.7%

w = x 100

= x 100

•Moisture content of the soil:

•Methods:• Microwave oven• Laboratory

determination• Field stove

•Dry density ( d): Wet density ( w)

1 + (w/100)

130.44 130.44 1 + (14.3/100) 1.143

• Report 114.1 lb/ft3

= 114.12 lb/ft3

BACKFILLING UTILITY LINES

• Issues:• Safety!!• Nuclear Gauge Trench

Correction (more later)• Thinner lifts• Distorted gauge results

when close to pipes or culverts

• Good judgment is essential

GEOTECHNICAL REPORTS

STRIP CHECKS & PROOFROLLING• Type of Testing:

• Strip Check:

• After site has been cleared of trees, roots and grass.

• Visual check that roots, topsoil, organics, debris, etc. removed.

STRIP CHECKS & PROOFROLLING (CONT’D)

• Type of Testing (cont’d):• Proofroll:

• After strip check, proofroll area to receive fill.

STRIP CHECKS & PROOFROLLING (CONT’D)

• Proofroll (con’t):• Use a LOADED dump.• Look for signs of loose or soft soils…

PUMPING or RUTTING:

STRIP CHECK & PROOFROLLING (CONT’D)

• When an area is pumping or rutting you must inform the the Project Engineer:– Undercut?– Bridge lifts?– Geosynthetics?

• Only evaluates surface material (2-3 feet).

CALIBRATION OF FIELD EQUIPMENT

• Nuclear Gauge: • Must be calibrated every 12 months • Leak tested every 6 months (12 months in some instances).• Standard counts (“standardization”) required each day used.

• Sand Cone:• Must be calibrated every 12 months, not including the sand• Sand must be calibrated every new bag

CALIBRATION OF FIELD EQUIPMENT (CONT’D)

• Sand Cone (continued):• Recalibrate sand if significant humidity changes.• Recalibrate sand at intervals not exceeding 14 days

• One-Point Proctor Equipment:• Calibrate annually• Scale, mold, hammer, & sieve

QUESTIONS&REVIEW

SOILS DEFINITIONS

• Bridge Lift: a lift of soil to stabilize soft or unsuitable soil so additional lifts of soil may be placed and compacted.

• Coarse Fraction: the portion of the sample that is larger than (retained on) a #200 sieve, includes both soil and gravel.

SOILS DEFINITIONS (CONT’D)

• Cohesive soils: soil that tends to adhere or stick to themselves (clay and most silts). Can usually be rolled and shaped in your hand.

• Cohesionless soil: soil that falls apart or cannot be shaped in your hand (sands, gravels, and some silts).

• Compaction: the mechanical densification of soil.

• Density: the weight of a material per unit volume.

• Engineered fill: fill that has been placed and monitored to ensure it meets the minimum requirements for a specific project.

• Fill: man placed deposits of soil or material.

• Fines: All material smaller than a #200 sieve. Includes silt and clay.

• Foundation: the portion of a structure that transmits the load to the soil. Footing, caisson, pile, drilled pier, etc.

• Gravel: All material Larger than a #4 sieve and less than 3 inches.

• Liquid Limit (LL): The w that defines the boundary between liquid/semi-liquid and plastic states.

• Maximum Dry Density: the highest dry density obtained from the Proctor analysis.

•Moisture content (w): the ratio, expressed as a percentage, of the weight of the water in a given sample to the weight of the dry soil.

•w = X 100soildry the of weight waterof weight

•Optimum Moisture Content: moisture content at which the maximum dry density is reached for a specified compactive effort.

• Percent Compaction: the ratio expressed as a percentage of the dry density of the field tested soil vs. the (corrected) maximum dry density of that soil as determined in the laboratory by the Proctor test.

• Plastic Limit (PL): The w that defines the boundary between plastic and semi-solid states.

• Plasticity Index (PI): The numeric difference between the liquid limit and the plastic limit.

• Proctor Analysis: Laboratory test to determine the Maximum Dry Density of a soil sample. Also known as the Moisture – Density Relationship, (ASTM D 698,D 1557; AASHTO T-99,T-180).

• Proofroll: Field test of natural soil that indicates soft or wet soils. A ten – ton single axle weight truck is driven across area to be tested.

• Pumping: The soils will appear to be moving under the loading of the truck. A wave like motion of the soil is often seen. Indicates wet or soft soil below the surface.

• Rutting: Proofrolling leaves indentations from the truck tires. Indicates soft or wet soils at the surface.

• Sand: Material smaller than a #4 but larger than a #200 sieve.

• Sand Cone: a apparatus used in the field to determine the in–place density of the soil.

• Sheepsfoot Roller: equipment used for compacting cohesive soils, has "feet" on the drum to knead the soil in place. (Silt and Clay).

• Smooth Drum Vibratory Roller: equipment that uses weight and vibration to compact the soil, used for cohesionless soils. (Sand and Gravel).

• Specific Gravity (SG): The ratio of the weight of the unit volume of a solid to the same volume of water.

• Subgrade: the prepared or compacted soil that will support a structure or pavement section. Soil under footing, slab, pavement.

• USCS: Unified Soil Classification System, used to classify soil based on laboratory tests (uses Atterberg Limits and Grain Size Analysis).

• Zero Air Voids Curve”: A curve showing the zero air voids unit weight as a function of water content.

BASIC RELATIONSHIPS

•1 gallon = 8.33 pounds of water•1 ft3 = 7.49 gallons•Unit wgt of Material/ Unit wgt of water = Specific Gravity

•1 oz = 28.35 g•1 lb = 454 g•1 ft3 of water = 62.4 lb•1 meter = 3.281 feet

BASIC RELATIONSHIPS (CONT’D)

•3 ft = 1 yard•1 yard = 0.9144 m•1 ft3 = .02832 cubic meters•1 in = 2.54 cm• 1 yd3 = 27 ft3

• 1 cubic meter = 1.31 yd3

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