Earth Materials Flashcards
Describe the material properties of rock in construction. (3)
- continuous mass of solid mineral material
- generally, the strongest, most stable of earth materials
- strength varies with mineral content and physical structure
Describe the material properties of soil in construction. (2)
- particulate
- properties vary with particle size and shape, mineral content, and sensitivity to moisture content
How are boulders classified in ASTM D2487?
greater than 12 inches in diameter - takes two hands to lift
How are cobbles classified in ASTM D2487?
smaller than boulders but larger than 3 inches in diameter - can be lifted with one hand
How is gravel classified in ASTM D2487?
from 3 inches to .187 inches in diameter - individual particles can be lifted between two fingers
How is sand classified in ASTM D2487?
from .187 inches to .003 inches in diameter - can see but generally too small to be picked up singly
How is silt classified in ASTM D2487?
smaller than .0029 inches in diameter and spherical in shape - too small to see with the naked eye
How is clay classified in ASTM D2487?
smaller than .0029 inches in diameter - typically 10 times or more smaller - and flat or plate shaped
Describe the material properties of organic soils in construction. (3)
- peat, topsoil, and other soils with organic content
- generally weak, unstable, and not suited for supporting building foundations
- topsoil is often removed from the building site and stored for use later
What sort of earth materials are better suited for use as foundation material?
coarse-grained sands and gravels
What sort of earth materials are not a good choice for foundations?
fine-grained silts, clays, and organic soils
Describe the material properties of coarse-grained soils (sands/gravels) in construction. (2)
- properties little-affected by moisture content
- free-draining: good for draining water away from foundations and substructures or from under slabs on grade and pavements
Describe the material properties of fine-grained soils (silts/clays) in construction. (2)
- smaller particle size makes them less free-draining
- more sensitive to moisture: properties and strength vary with moisture content
Describe the material properties of clays in construction. (6)
- very small particles
- electrostatic forces cause particles to stick together: cohesive
- properties vary with moisture content and mineral composition
- some are highly expansive when wetted
- some are virtually impervious to water
- some clays are subject to consolidation, or gradual compression over time
How is expansive clay dealt with on construction sites? (4)
- change foundation type
- remove the clay and replace it with select/engineered fill
- employ the services of a professional engineer
- use void or “carton” forms
What is considered to be well-graded soil?
wide distribution of particle sizes
What is considered to be well-sorted soil? (2)
- limited range of particle sizes
- more void space; more free draining
What can be said of soils in terms of strength?
generally, the larger the particle size, the stronger the soil
What step typically precedes foundation design?
investigation of the soil conditions at the site
What is the purpose of subsurface investigations? (3)
- subsurface investigations can be accomplished by digging test pits or by test borings
- the information gained through subsurface exploration and laboratory testing is summarized in a written geotechnical report
- the geotech report is used by engineers to assist with foundation design
What sort of information do geotechnical reports provide? (3)
- location of the water table
- load-bearing capacity of the soil
- soil stratum
