Earth Materials

Question 1

Describe the material properties of rock in construction. (3)

Answer 1

• continuous mass of solid mineral material
• generally, the strongest, most stable of earth materials
• strength varies with mineral content and physical structure

Question 2

Describe the material properties of soil in construction. (2)

Answer 2

• particulate

- properties vary with particle size and shape, mineral content, and sensitivity to moisture content

Question 3

How are boulders classified in ASTM D2487?

Answer 3

greater than 12 inches in diameter - takes two hands to lift

Question 4

How are cobbles classified in ASTM D2487?

Answer 4

smaller than boulders but larger than 3 inches in diameter - can be lifted with one hand

Question 5

How is gravel classified in ASTM D2487?

Answer 5

from 3 inches to .187 inches in diameter - individual particles can be lifted between two fingers

Question 6

How is sand classified in ASTM D2487?

Answer 6

from .187 inches to .003 inches in diameter - can see but generally too small to be picked up singly

Question 7

How is silt classified in ASTM D2487?

Answer 7

smaller than .0029 inches in diameter and spherical in shape - too small to see with the naked eye

Question 8

How is clay classified in ASTM D2487?

Answer 8

smaller than .0029 inches in diameter - typically 10 times or more smaller - and flat or plate shaped

Question 9

Describe the material properties of organic soils in construction. (3)

Answer 9

• 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

Question 10

What sort of earth materials are better suited for use as foundation material?

Answer 10

coarse-grained sands and gravels

Question 11

What sort of earth materials are not a good choice for foundations?

Answer 11

fine-grained silts, clays, and organic soils

Question 12

Describe the material properties of coarse-grained soils (sands/gravels) in construction. (2)

Answer 12

• 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

Question 13

Describe the material properties of fine-grained soils (silts/clays) in construction. (2)

Answer 13

• smaller particle size makes them less free-draining

- more sensitive to moisture: properties and strength vary with moisture content

Question 14

Describe the material properties of clays in construction. (6)

Answer 14

• 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

Question 15

How is expansive clay dealt with on construction sites? (4)

Answer 15

• 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

Question 16

What is considered to be well-graded soil?

Answer 16

wide distribution of particle sizes

Question 17

What is considered to be well-sorted soil? (2)

Answer 17

• limited range of particle sizes

- more void space; more free draining

Question 18

What can be said of soils in terms of strength?

Answer 18

generally, the larger the particle size, the stronger the soil

Question 19

What step typically precedes foundation design?

Answer 19

investigation of the soil conditions at the site

Question 20

What is the purpose of subsurface investigations? (3)

Answer 20

• 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

Question 21

What sort of information do geotechnical reports provide? (3)

Answer 21

• location of the water table
• load-bearing capacity of the soil
• soil stratum