Earthworks Flashcards
3 Layers of soil (horizons)
Topsoil - O: Organic/humus, A: Topsoil
Subsoil - B: Subsoil
Bedrock - C: Parent material, R: Bedrock
What is the layer of decayed matter in topsoil called
Humus
3 Different types of rocks
Igneous - Come from magma
Sedimentary - formed from loose sediment (rocks, plants, animals) over millions of years
Metamorphic - are igneous and sedimentary rocks that have been transformed by pressure/heat.
Soil is composed of what 3 materials?
Rocks of varying size
Water
Air
Particle size for boulders
Anything above 200mm
Particle size of Cobbles
60-200mm
Particle size of coarse, medium, and fine GRAVELS
(2-60mm)
Coarse: 20-60mm
Medium: 6-20mm
Fine: 2-6mm
Particle size of coarse, medium, and fine SANDS
(0.06-0.2mm)
Coarse: 0.6-2mm
Medium: 0.2-.6mm
Fine: 0.06-0.2mm
Particle size of coarse, medium, fine SILTS
(0.002-0.06mm)
Coarse: 0.02-0.06mm (compacts either soft or loose)
Medium: 0.006-0.02mm
Fine: 0.002-0.006mm
Particle size of CLAY and characteristics
smaller than 0.006mm
Dry lumps can be broken but not powdered between fingers.
Smooth to the touch
shrinks on drying which usually leaves cracks
compactness: soft
Characteristics of PEAT
Particle size varies
Mostly plant material which remains dark brown or black
distinctive smell and low-bulk density
compactness: spongy, plastic
What has an object reached when it stops sinking into the soil
Equilibrium
A GRAVEL is made of crushed rock and sand, ranging from ___” to 1/64”
1” to 1/64”
Typically a 4” layer
Commonly used under asphalt parking areas and concrete slabs
PROPERLY COMPACTED “A” GRAVEL CAN BE USED UNDER THE FOOTINGS OF BUILDINGS
Granular B GRAVEL is a blend of sand and stone ___” to 1/64”
6” TO 1/64”
Blend of sand and stone
Commonly used under Granular A under parking areas and concrete slabs
6”-8” layers
PROPERLY COMPACTED “B” GRAVEL CNA BE USED UNDER THE FOOTINGS OF BUILDINGS
What Effect does too much water in the soil have on compaction?
Particles press apart, soupy mix? Negatively affects shear strength?
What effect does too little water in the soil have on compaction?
Particles are too close together, thick mix?
What is pit run used for?
Unmanufactured gravel dug out of the ground at the gravel pit
Rocks typically 6” and less
COMMONLY USED FOR A BASE FOR ROADS AND DRIVEWAYS AND SHOULD BE PLACED IN LAYERS 12” THICK OR MORE
CAN BE USED FOR A HOUSE BUT NOT LARGE BUILDINGS
Does well graded soil composition compact better than an ungraded soil composition? Why?
Yes, because it is a mix of different sizes of particles, fills in all the spaces better
What is the primary processing done at a gravel pit?
Rock crushing
What does a standard proctor test determine?
The optimal soil moisture content for compaction for it’s bearing capacity
What is the primary reason for sink holes to form?
Internal erosion, either natural or human made infrastructure failure, etc
Why is clay not a desirable material to build on?
It can expand and contract with moisture
Is an “expansive soil”
