Introduction to Soils by Jill-Ann Stolley, CTR, DMA
Jill-Ann Stolley
Introduction to Soils
Overview
- Terminal Learning Objectives
- Enabling Learning Objectives
- Lecture Method
- Power Point Presentation
- Video
- Demonstrations
- Practical Applications
- Vehicle Safety
- Sunburn
- Drink Water
- Bug Spray
- In the event of a casualty, all students will go back to the classroom and wait for further instruction.
Transition
- Are there any questions over:
- What will be taught?
- Methods used for teaching?
- Evaluation method?
Soil Basics
- Collecting the sample.
Definition of Soil
- Soil is defined as the entire unconsolidated material that overlies and is distinguishable from bedrock.
- Composed of loosely bound mineral grains of various sizes and shapes.
- Contains voids of varying sizes. These voids contain:
- Air
- Water
- Organics
Composition of Soil
Soil Formation
- Defined as the process by which rock is converted into soil.
- Two types of weathering:
- Mechanical
- Chemical
Mechanical Weathering
- Unloading – removal of overlying material
- Frost Action – up to 4000 psi
- Organism Growth – growth inside of joints causes wedging effect
- Abrasion - friction
- Wind
- Water
Wind and Water Abrasion
Chemical Weathering
- Decomposition of rock through chemical bonding
- Examples include:
- Hydration (combining with water)
- Oxidation
- Carbonation (saturation with carbon dioxide)
Engineering Properties of Soil
- Varies greatly depending on its physical properties, however, the behavior of a soils not exclusively dependant on physical properties.
- Also dependant on arrangement of particles (Compaction)
KSE K-2009 SOIL TEST SET
LABORATORY
SPEEDY MOISTURE TESTER
DYNAMIC CONE PENETROMETER
Laboratory Test Set
- #4, 40, 200 Sieves
- Mixing Bowls, mortar, & pestles, trowels
- Halogen water bottles
- Scale, spatula, towels, brush
- USACE Cone Penetrometer, water jug, printer
Speedy Moisture Kit
- Cleaning brush & scoop
- 200 gram Scale
- Steel balls
- Measuring cups
- Speedy Moisture Tester
Dynamic Cone Penetrometer
- Rod Assembly & Dual Mass Hammer
- Set Pins & Clips, Allen Wrench
- Magnetic ruler w/Digital Assembly
Grain Size
- Four major categories:
- Cobbles – greater than 3”
- Gravels – Passes a 3” sieve and retained on No.4 sieve (approx 0.25”)
- Sands – Passes No.4 sieve and retained on No. 200 sieve (0.072 mm)
- Fines – Passes No.200 sieve
Dry Sieve Analysis
Grain Size Groups
Gradation
- Distribution of particles within a soil.
- Soils are either:
- Well graded – good distribution of particle sizes
- Poorly graded – bad distribution of particles sizes
- Uniformly graded – only one soil size
- Gap graded – missing soil sizes
Soil Gradations
Grain Shape
- Influences a soils strength and stability
- Two general shapes:
- Bulky – three dimensional
- Angular – recently been broken
- Sub angular – sharper points and edges are worn
- Sub rounded – further weathered than sub angular
- Rounded – no projections and smooth in texture
- Platy – two dimensional
Soil Particle Shapes
Density
- Determined by the ratio of voids (air and water) to soil particles.
- A denser soil has greater strength and stability than a looser soil.
Moisture
- Most important factor affecting engineering characteristics.
- Moistures affect varies greatly depending on soil type:
- Course grained soils usually remains unchanged.
- Fine grained soils are susceptible to shrinking and swelling.
Plasticity and Cohesion
- Plasticity is the ability of a soil to deform without cracking.
- Fine grained soils, like clay, have a wide range of plasticity.
- Coarse grained soils, like clean sands and gravels, are non plastic
Concepts of Soils Engineering
- Settlement
- Shear Resistance
- Soil Failure
Settlement
- Soil settlement is dependent on:
- Density
- Grain size and shape
- Structure
- Past loading history of the soil deposit
- Magnitude and method of application of the load
- Degree of confinement of the soil mass
Shear Resistance
- Related to a soils ability to withstand loads.
- California Bearing Ratio (CBR) is a measure of shearing resistance
- CBR is a soil’s ability to support a load relative to that of soil with known strength (limestone).
- Determined by the Soils Test Kit (B2150)
Bearing Capacity
- The ability of a soil to support a load applied by an engineering structure.
- A soil with insufficient bearing capacity might fail, by shear, allowing the structure to sink and shift.
- Dense and well graded soil with angular particles generally has good bearing capacities.
Soil Failure
Soil Classification
Introduction
- The principle objective of any soil classification system is predicting the engineering properties and behavior of a soil.
- This is achieved with simple laboratory and field tests.
- These tests results place a soil into a group of similar soils.
Unified Soils Classification System
- Based on the characteristics of the soil which affect its engineering properties.
- Basic classification considerations:
- % of gravels, sands, and fines
- Gradation of the soil
- Plasticity and compressibility of the soil
USCS Soil Categories
- Coarse grained soils – less than 50% fines
- Gravels and gravelly soils
- Sands and sandy soils
- Basic classification considerations:
- Fine grained soils – more than 50% fines
- Silts (0.05mm to 0.005mm)
- Clays (smaller than 0.005mm)
- Organics
- Highly organic soils (peat)
USCS Soil Groups
- A symbol is assigned to each soil category, and categories can be combined to create a two letter designator.
USCS Soil Symbols
Possible USCS Soil Types
- Loam – mix of clay, sand, and organics
- Most critical component in horizontal construction.
- Durability and stability of structures is related to proper compaction.
- Structural failure can often be traced to improper compaction.
Effects of Soil Compaction
- Settlement – Compaction brings a closer arrangement of soil particles which, in turn, reduces settlement.
- Shearing Resistance – Increasing soil density usually increases shearing resistance.
- Water Movement – Compaction decreases the size and number of voids leaving less room for water.
- Volume Change – Generally not of great concern except with clayey soils.
- The moisture content has a great impact on a soils ability to densify.
- Optimum Moisture Content (OMC) – the percentage of water, at which a soil will achieve maximum dry density (MDD) under a given compactive effort.
- When at MDD, most of the air voids have been expelled from the soil.
Effect Of H2O on Density
Typical H2O-Density Relationship
Compaction Characteristics of Various Soils
- The nature of a soil has an effect on its response to compaction.
- Light weight soils can have maximum densities under 60 pcf under a given compactive effort.
- The same compactive effort applied to clay could yield 90 to 100 pcf.
- Well graded soils can yield maximum densities up to 135 pcf under a given compactive effort.
Selection of Materials
- Use the indigenous material from cut sections of the road as much as possible.
- Tables 13, 14, and 15 provide a listing of soil types and the value as construction materials.
Soil Stabilization
Introduction
- Soil Stabilization is the alteration of one or more soil properties, by mechanical or chemical means, to create an improved soil material possessing the desired engineering properties.
- Typically, soil stabilization seeks to alter texture, gradation, or plasticity.
Stabilization Techniques
- Geotextiles
- Mechanical Stabilization
- Chemical Stabilization
Geotextiles
- Geotextiles serve three primary functions:
- Reinforcement – Good in low load bearing soils such as swamps and peat bogs.
- Separation – Separates weaker layers in a project.
- Drainage – Allows water to pass while preventing soil particle movement.
Geotextiles Separation
Mechanical Stabilization
- Mechanical Stabilization is the blending of one or more soil types with in place soil to obtain a material the will have engineering properties better than that of the other.
- Does not include compaction.
Chemical Stabilization
- Chemical Stabilization is adding granular or chemical admixtures to a soil.
- Used when an inadequate soil is too costly to remove and replace
- Common methods are:
- Portland Cement
- Lime
- Fly-Ash
- Mixtures
- Bituminous
- Portland Cement
- Transforms the soil into a cemented mass increasing strength and durability
- Good for a wide range of materials
Portland Cement
Chemical Stabilization
- Lime
- Reacts with medium to fine grained soils to decrease plasticity
- Not normally used with SW,SP, GW, or GP because of the low amount of fines
- The increased plasticity increases strength and reduces shrinkage and swell
- Fly-Ash
- By-product of coal fired electric power plants
- Reacts with lime and water to produce a strong, slow-hardening cement
- Capable of high compressive strengths
- Mixtures (if materials are available)
- Lime/Fly-ash
- Lime/Cement/Fly-ash
- Expedient mix:
- 1% Cement
- 4% Lime
- 16% Fly-ash
- 79% Soil
- Bituminous
- Not normally available to the Marine Corps
- Types include:
- Asphalt cement
- Cutback asphalt
- Asphalt emulsions
Dust Abatement
What is Dust?
- Dust is simply soil particles which have become airborne.
- Generally, dust are those particles which pass the #200 sieve.
- Causes of dust:
- Wind
- Physical Abrasion
- Vehicles
- Foot Traffic
- Dust is typically a problem with sandy soils of Greater than 10% fines
- Soils with 10% to 40% fines are the most difficult to deal with
- Soils with greater than 40% fines generally respond the best to dust abatement products
Factors Influencing Dust
- Soil texture and structure
- Soil moisture content
- Presence of salts and organic matter
- Smoothness of the ground cover
- Vegetation cover
- Wind velocity and direction
- Humidity
Dust Control Methods
- Agronomic
- Examples include:
- Mulch
- Sodding
- Planting vegetation
- Not normally used in traffic areas
-
Surface Penetrates
- Applied to the soil surface and allowed to “seep” in
- Examples include:
- Bitumen's
- Resins
- Salts
- Water
- Polymers
- Surface Blanket
- Covers the soil to prevent dust
- Examples include:
- Aggregates
- Geofabrics
- Bituminous surface treatments
Dust Abatement Products
- Gretch
- EK-35
- EnviroKleen
- Tar
- Mobi-matting
- Tri-PAM
- Soiltac
