LARE SECTION 3 2021 Flashcards
What is an important factor in how soil will behave under different conditions?
Grain size distribution
What are issues for engineers regarding soil?
The variations caused by grain size distribution, clay mineralogy, and organic content in the presence of water
What are the 12 soil classifications?
- 4 coarse-grained soils
- 4 fine grained soils (half the soil is silt or clay) and
- 4 combinations of fine and coarse grained soils
(Classification also includes 3 organic soils)
What type of soils are preferred for sub-grade and base materials?
Coarse grained soils (GW)
*Poorly graded gravels (GP) and silty gravels (GMd) may be used under some circumstances
Definition: Water > 50%, high plasticity (very cohesive or sticky clay)
High Liquid Limit
Definition: Water Content < 50%, low plasticity
Low Liquid Limit
Definition: Soils that include particles of all sizes
Well graded soils
Definition: The moisture content at which a soil deforms plastically
Plastic Limit (PL)
Moisture vs Plastic: If a soil can be rolled into finer threads without cracking then…
It contains MORE moisture than its plastic limits
Moisture vs Plastic: If a soil can be rolled into finer threads and cracks before 3mm is reached then…
It contains LESS moisture than its plastic limits
What is the numerical difference between the LL (Liquid Limit) and PL (Plastic Limit)?
Plasticity Index (PI)
A PI (Plasticity Index) provides what?
Gives the range of moisture in which a soil behaves as a plastic material
A PI (Plasticity Index) over 15 is a good indicator of what?
An expansive soil
Regarding soil, what does porosity refer to?
The amount of pore space in a soil.
Related to the grain size and distribution and consolidation
Regarding soil, what does permeability refer to?
The rate at which water will freely drain through a soil
What is Soil Strength?
A soil’s ability to resist deformation, which is a function of the friction and cohesion in the grain-to-grain contact in soil.
What is Soil Cohesion and what is high cohesion most often associated with?
The measure of the capacity of soil particles to stick together.
Clays
What is Shear Strength in soil?
The measure of the frictional resistance and cohesion of a soil. The shear strength of the soil is the THE FORCE APPLIED AT THE TIME OF FAILURE.
What is Bulk Density?
The weight per volume of any soil unit. The higher the bulk density, the greater the support it can provide for a foundation
Calculation for Walkways
W (Width) = V (Volume) (M) (Space Module) / S (Speed)
Stair Calculation
2R+t = 26 - 28 inches
Ramps with a slope of between 1:12 and 1:16 should be designed to not exceed…
A rise of 30 in (760 mm) or a run of 30 ft (9 m)
Flatter ramps of 1:16 to 1:20 slope may be designed to a run of…
40 ft (12m), but the maximum rise should not exceed 30 in (760 mm).
Minimum clear width of a ramp?
36 in (915 mm)