Getting the Low Down on Dirt in Wormtown: Hands On Soil - - PowerPoint PPT Presentation

Getting the Low Down on Dirt in Wormtown: Hands‐On Soil Classification Workshop

Zachary D. Baum, PE, Project Engineer November 19, 2019

Getting the Low Down on Dirt in Wormtown: Hands‐On Soil Classification Workshop

Construction Specifications Institute, Worcester Chapter is an approved AIA CES provider. This program is eligible for one Continuing Education Unit, qualifying for Health, Safety, Welfare.

Getting the Low Down on Dirt in Wormtown: Hands‐On Soil Classification Workshop

Program Description: This program will be a hands‐on educational experience and Q&A on the how‐tos of soil classification using the Modified Burmister Soil Classification System. Following this presentation, you can try your hand at soil classification at the Yankee Engineering & Testing lab. Attendees will also have the opportunity to view soil laboratory testing equipment, including soil sieves, hydrometer, and liquid limit test equipment.

Getting the Low Down on Dirt in Wormtown: Hands‐On Soil Classification Workshop

Learning Objectives: 1. Distinguish between the different major soil types in accordance with the Modified Burmister Soil Classification System 2. Visually classify soils and understand soil descriptions frequently presented in subsurface exploration logs 3. Understand how soil laboratory test results are used to confirm visual classifications 4. Compare soils encountered during construction to conditions described in geotechnical reports

Agenda

• Soil types
• Major/minor constituents
• Density/consistency
• Color
• Assembling the description
• Hands‐on classification exercise

Why is this Important?

• Accurate classification of soils serves as basis for geotechnical evaluation
• Architects and contractors should be aware of impacts of subsurface

conditions on design and performance of structure

• Structural/foundation design should be consistent with geotechnical

evaluation

• Understanding soils on logs is needed when observing excavation and

backfilling of foundations

Why is this Important?

• Exploration logs should present a clear, concise, and accurate

representation of subsurface conditions

• Good information can:
• Significantly reduce the risk of unanticipated conditions and

contractor claims

• Result in cost effective solutions

Pepco Waterfront Substation 223 / Washington, DC

Adventist HealthCare White Oak Medical Center / Silver Spring, MD

Cobbs Creek Reservoir Project / Columbia, VA

Why is this Important?

Modified Burmister Soil Classification System

• Commonly used by consulting engineers and

environmental scientists

• Visual/manual classification system
• Provides a clear, concise description of the soil

materials

• Can be confirmed with lab test results

Donald M. Burmister 1895‐1981

Soil Types

• Three main soil types
• Granular (non‐plastic)
• Fine grained (plastic or non‐plastic)
• Organic
• Each main soil type can be broken down to more specific groups
• Soil types are defined by ranges of sieve sizes

Soil Types – Granular Soils (Non‐Plastic)

The larger the sieve number, the smaller the particle size

Sieve Size = The number of openings per one linear inch

Gravel

• 3/4” to 3” ‐ Coarse Gravel
• No. 4 to 3/4” ‐ Fine Gravel

Sand

• No. 10 to No. 4 ‐ Coarse Sand
• No. 40 to No. 10 ‐Medium Sand
• No. 200 to No. 40 ‐ Fine Sand

Soil Types – Granular Soils (Non‐Plastic)

Identify grain size range for sand

Identify by weight (sand or gravel)

Sand Gradation Designation Proportion of Component Fine <10% coarse and medium Medium <10% coarse and fine Fine to Medium <10% coarse Medium to Coarse <10% fine Fine to Coarse All greater than 10%

>10% ‐ include it <10% ‐ exclude it

Soil Types – Granular Soils (Non‐Plastic)

Gravel Gradation Designation Proportion of Component Fine <10% coarse Coarse <10% fine Fine to Coarse All greater than 10% Test Pit: Identify the grain size for gravel Boring: Can’t define size of gravel from split spoon sample since

• pening is <2 inches

Soil Types – Fine Grained (Silt and Clay)

• Can be plastic or non‐plastic
• Fraction passing the No. 200

sieve

• Leaves the fingers dirty. Fills

in fingerprints. Cannot be seen with the naked eye.

Identity Smallest Diameter Plasticity Index SILT (non‐plastic) None Clayey SILT 1/4" 1‐5 SILT & CLAY 1/8” 5‐10 CLAY & SILT 1/16” 10‐20 Silty CLAY 1/32” 20‐40 CLAY 1/64” >40

Determine the identity

• Roll a thread of the fine‐grained soil in your hands
• May need to adjust the moisture content by

wetting or drying

• The smallest diameter rolled determines the identity

Peat

• Typically black or dark brown
• Fibrous ‐ Light weight, spongy, intact
• rganic matter, typically near top of

deposit

• Fine Grained ‐ Light weight, spongy, less

intact organic matter, more homogeneous, may contain roots, found below fibrous peat

Organic Silt

• Typically gray to dark gray
• Can have strong H2S odor
• Often found near coastal regions
• May contains sea shells or shell

fragments

Organic Soil Types – Peat and Organic Silt

Soil Classification – Assembling the Description

Density/Consistency

(if SPTs are performed)

Color Major Constituent Minor Constituents Other Comments Modified Burmister Soil Classification System

Soil Classification – Density/Consistency

• Based on “N” Value
• Only applies if Standard Penetration Tests (SPTs) are performed
• The sum of the middle foot of blow counts from the SPT
• Example: Blows per 6 inches are 6‐5‐4‐7. N‐value is 9.

N‐Value Consistency <2 Very Soft 2‐4 Soft 4‐8 Medium 8‐15 Stiff 15‐30 Very Stiff >30 Hard N‐Value Density 0‐4 Very Loose 4‐10 Loose 10‐30 Medium Dense 30‐50 Dense >50 Very Dense Granular Soils Plastic Soils (Fine Grained)

Soil Classification – Color (Keep it Simple!)

Use only one ordinary color

• “Black”
• “Brown”
• “Gray”
• “Orange”
• “Tan”

Max limit to 2‐word description

• “Light Brown”
• “Olive‐Brown”
• “Dark Gray”

Avoid lengthy combinations

• “Reddish dark brown/gray”
• “Light green/yellowish

brown”

Soil Classification – Major Constituent

• Example: medium to coarse SAND
• Example: SILTY CLAY
• Example: FIBROUS PEAT

Entirely CAPITALIZED

• Example: fine SAND
• Example: fine to medium SAND
• Example: fine to coarse GRAVEL

For granular soils grain sizes from smallest to largest

Follow the major constituent in the description Listed in order of decreasing percentage

• Example: some fine to medium Sand, little Silt
• Example: little fine to coarse Gravel, trace Silt
• Example: some Silt & Clay, trace Gravel

Only the first letter of the minor constituent is capitalized Always at least trace Silt!

Soil Classification – Minor Constituents

Percentage Label 0‐10 trace 10‐20 little 20‐35 some 35‐50 and

Soil Classification – Assembling Proper Order

Density / Consistency Color Major Constituent Minor Constituents

• Moisture (dry, moist, wet)
• % Cobbles/boulders
• Anthropogenic fill materials: brick, glass,

ash/cinders, wood, etc.

• Odors, contaminants (petroleum, solvents, etc.)

At end of description add any additional details:

• Could be natural material that is not native

Fill: Any material placed by humans

Medium dense, tan, fine to medium SAND, some Silt, trace fine Gravel, dry

Soil Classification – Assembling Proper Order

• Examples
• Stiff, gray, Clayey SILT, little Gravel, trace fine Sand, moist
• Medium, dark brown, FIBROUS PEAT, trace fine to medium Sand,

trace roots, wet

• Very dense, brown, fine to coarse SAND, some fine to coarse Gravel,

little Silt, trace brick, trace ash/cinders, petroleum odor, moist (FILL)

• Document and note everything you observe

QUESTIONS?

HANDS‐ON EXERCISE

Try your hand at classifying soil samples

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THANK YOU!