Geotechnical Engineering Midterm 1

conceptual questions

illite vs montmorillonite

both clays

Montmorillonite has a high capacity for swelling due to weak bonds. Illite has potassium ions that bind sheets together, so water cannot penetrate as easily.

charge deficiencies in montmorillonite

Isomorphous substitution (switching in a cation of a similar size but with a different charge)

3 types of clay-water interactions

1. Hydrogen bond

2. Ion hydration

3. osmotic pressure

hydrogen bond

water molecule “locked” in absorbed layers. has different properties than bulk water due to the strong attraction from the surface.

increasing K (thickness of double layer)

repulsive forces increase

what is compaction

make soil denser by reducing air voids with little to no reduction in water content

goal of compaction

decrease future settlement, increase shear strength, and decrease permeability 

proctor test

determines the proper amount of mixing water to use when compacting soil in the field and the density to expect when compacting at optimum moisture content

when compaction happens dry of optimum

particles are more random (flocculated), soil is more permeable, higher strength, more likely to swell, and more compressible in high-pressure range

when compaction happens wet of optimum

particles are dispersed (more organized), les permeable, more inclined toward shrinkage, and more compressible in low-pressure ranges

lab compaction method - coarse soil

vibrating hammer

lab compaction method - fine soil

falling weight and hammer, kneading compactor, static loading and press

field compaction method - coarse soil

vibration plates, vibratory rollers, rubber-tired equipment, and free-falling weight

field compaction method - fine soil

hand-operated tampers, sheepsfoot roller, rubber-tired roller

rollers - general application

smooth-wheeled rollers (no rocky soil) and rubber-tired roller

rollers - clayey soils

sheepsfoot roller,

rollers - fine-grained soils (silt and clay)

tamping foot roller

rollers - rocky/granular soils

mesh (or grid-patterned), vibrating drum on smooth-wheeled roller,