Soil Mechanics and Road Construction

• These notes cover granular materials, soils, and their reuse in road construction, focusing on soil properties, testing, and classification.

Introduction to Soils

• Soils introduction covers general definitions, lab tests, soil classification
• Soils support structures through shallow and deep foundations.
• Soils can support structures via retaining walls and sheet pile walls.
• Soils can act as backfill for structures like embankments, dams, and dikes.
• Soils can act as the base for earthworks, roads, pavements, tunnels, and underground works.

Soil Composition and Phases

• Soils consist of mineral grains mixed with water (free, capillary, or adsorbed) and gas (air and water vapor).
• Soil has three phases: solid, liquid, gas
• Solid phase includes soil particles
• Liquid phase includes water
• Gas phase includes air, vapor
• Volumetric and weight relationships are important for defining soil properties.

Granular vs. Fine Soils

• Grain size determines whether a soil is granular/non-cohesive or fine/cohesive.
• Granular soils have particle sizes ranging from gravel to coarse sands.
• Fine soils have particle sizes ranging from silt to clay.

Properties of Granular Soils

• Frictional forces between grains depend on shape, angularity, and compaction.
• Granular soils do not resist tension and are permeable.

Properties of Fine Soils

• Cohesion ensures attraction between grains, influenced by shape, angularity, compaction, surface effects, and water content.
• These soils are sensitive to water content changes (swelling and shrinking).
• Fine soils resist shear stresses.
• Fine soils are prone to being impermeable

Key Soil Characteristics Parameters

• Parameters involves dimensional and dimensionless properties that define soil behavior.
• Dimensional Parameters include Volume Weight
• Volume weight refers to total soil
• Grain Volume Weight
• Water volume weight
• Dry Volume Weight
• Saturated Volume Weight
• Dimensionless parameters include porosity, void ratio, and degree of saturation
• Soil characterization requires knowing at least three independent parameters.
• Measure soil characterization in the lab

Laboratory Tests

• Water content is tested in the lab
• Determines weight before and after drying
• Key data includes total weight, solid weight, water weight, and volumes.

Particle Size Analysis

• Grains in soil vary in size significantly.
• Granulometric curve shows the mass distribution of grain sizes in a soil.
• Sieve analysis sorts particles through different mesh sizes.

Sieve Analysis Terms

• d = sieve opening size
• Tamisat = material passing through the tamis
• Granulometric class = elements between sieve openings (e.g., 0/50 mm)
• D = sieve diameter with x% cumulative passing.

Uniformity and Curvature Coefficients

• Uniformity coefficient (Cu) indicates if a soil is well-graded or poorly-graded/uniform.
• The Curvature coefficient (Cc) supplements uniformity

Sand Equivalent Test

• Determines relative proportions of clay-like materials in granular soils.
• Compares height of sand to clay after washing.

Atterberg Limits

• Atterberg limits (Liquid Limit WL and Plastic Limit WP) indicate consistency of fine soils when water content increases
• Solid state involves minimal volume change with water loss up to the shrinkage limit (Ws)
• Plastic state involves consistency between Wp and Wl

Plasticity Index

• The plasticity index (Ip) is the range of water content for which soil displays plastic properties (Ip = WL - WP).
• Casagrande chart uses the Plasticity Index (Ip) and Liquid Limit (WL) for classifying soils.

Methylene Blue Value

• It is an indirect measure of clay content, measuring absorption of methylene blue to saturation.
• VBS indicates soil type ranging from sand, silt, to clay

Proctor Compaction Test

• Proctor test determines optimum moisture content (WOPN) for max dry density (YdOPN).

Los Angeles Abrasion Test

• It measures resistance to fragmentation of a rock's matrix.

Micro-Deval Test

• It measures wear resistance of soil grains when abraded with water.

Sand Friability Test

• It evaluates the resistance of sand to fragmentation

Granular Soil Classification

• Classification applies a group of the soils to link similar qualities

Soil Types Based on the French GTR Standard

• Class A: fine soils, Class B: sandy and gravelly with fines, Class C: coarse elements with fines, and Class D: water-insensitive soils.
• Nature, mechanical behavior, and water behavior helps identify the soil types