Exam one Flashcards
3 things that make soil different
- Natural material
- Individual unconnected particles
- Has all three phases of matter, (air, water, soilds)
Void ratio
e
Porosity
n
Degree of saturation
S cannot go over 100%
moisture content
w, cannot go over 100%, = Ww/Wd, (Weight wet sample - Weight dry sample)/weight dry
Relative density
Dr
Specific Gravity
Gs
Saturated unit weight
γ(sat)
Moist unit weight
γ(m)
appartent unit weight
γ’
γ(w)
Specific weight of water
what does relative compaction need to be (RC)
95%
5 steps - Process of cut and fill
- Remove vegetation and topsoil
- Evaluate the subgrade
- Place soils in lifts (do in 8-9 in thick max)
- Compact soil
- Evaluate compaction, relative compaction needs to be 95%
Most common method to find dry specifc weight field
Nuclear method, it correlates gamma radiation to dry specific weight
What are the two options if a soil is too wet
- Scarify and let nature dry
- add lime stabilization good for wetlands (downside - it makes soil not as dense)
Lightweight fill
geofoam, weakness is gasoline
Shinkage factor
= ((Dry unit weight in fill/ dry unit weight in cut) - 1) *100%
what is the I value for large fills
1
5 causes of settlement
- applied loads
- Lower groundwater table
- Shrinkage from clay
- Vibration from machinery or earthquake (hurts sandy soil)
- thawing of frozen soil
3 types of settlement
- elastic (soil particles compress elastically
- consolidation (water squeezes out of the soil
- secondary compression (soil creeps over time)
Normally consolidated (NC)
A soil that has never felt an effective stress greater than today (never had glaciers)
Overconsolidated (OC)
Soil that has felt an effective stress greater than today (had glaciers on it)
OCR ratio
max pressure ever/ pressure today, if over 1 OC, if less than 1 NC
4 causes of overconsolidation (OC)
- Glaciers
- Lowering of GWT
- Erosion from upper layers
- Aging (older soil is more consolidated
Log(sigma’ + Delta P/sigma’) is the same as
log(stress after dewater/stress before dewater)
If the GWT goes down will the soil feel more stress
Yes when the water table lowers pressure felt goes up
What test gets you sigma’ c (Highest stress ever felt)
1-D consolidation test (undisturbed sample from field, trim into hockey puck, slowly add load over a weeks time
Steps to find sigma’ c from chart
- sharpest point of curvature
- draw horizontal at step 1
- Draw a tangent at step 1
- Bisect through step one between steps 2 and 3
- extend straightline from Cc slope
- intersection of 4 and 5 is sigma ‘ c
who is the father of soil mechanics
Karl Teraghi
Ʊ
Degree of consolidation
Hdr
the longest distance a particle of water has to travel to get out
Tv relates to Ʊ from table, time should be in days,
yes
