Soils Final exam Flashcards
What is Overconsolidated soil?
A soil that has felt a pressure greater than a the pressure it feels today
What is a Nonconsolidated soil
The pressure today is greater than the max felt ever
Degree of saturation for soil under the water table
S = 100%
What is a typlical lift thickness for a soil being placed in the field
8 to 9 inches than compressed
Two natural processes that could make a soil overconsolidated
Glaciers, GWT lowering
Will raising the GWT cause settlement
No, raising the GWT will lower the pressure felt
What is meant by the term piping?
The progressive erosion of soil which often leads to failure
What soil property do you get from an unconfined compression test?
C = cohesion
When would a zoned earth dam be needed rather than a homogeneous earth dam?
When the local soil does not have the properties to be the only soil for the dam. For example, if the local soil has a low friction angle it would need support from a high friction angle soil.
The best method to determine in-situ permeability?
Falling head permeability test
Roller compacted concrete dam vs Concrete gravity dam?
Roller compacted conc is on a slope and uses less concrete and much stiffer concrete. A gravity dam is a massive wall of concrete that resists water with its weight
What does a direct shear test give you?
Cohesion and friction angle
C’ and phi’
C’ should be 0 for sand
Acceptable F.S of bearing capacity
3
Sieve analysis
gives soilclassification
Proctor compaction test
gamma d max and optimum moisture content
1-D consolidation test
sigma’c - max pressure ever felt
Cc
Cr
Atterburg limit test
LL-liquid limit
Pl - Plastic limit
Constant head permability test
k - Permability of soil
What is I sigma for large fills
1
For NC soils delta P +sigma/ sigma is what when water table is lowered
What is settlement before GWT change
Stress after/ stress before
0 in
Types of GEO distasters
Earthquakes -
Expansive soils
Sinkholes
What do Earthquakes causes and how to treat
Horizontal ground motion creates shear forces
causes lqiuidifcation(soil strength to 0) of cohesionless, loose and soil under GWT
Treatment - density soil with vibration, dropping big metal on it, and injecting cement into ground
What do expansive soils cause and how to treat?
Expand when water is added and shrink when its gone (fat clay or (silit and clay))
Prevent by remove and replace soil, control water, lime stabilizer, lower foundation
What are sinkholes and how to prevent
Soil collapses into rock cavities (caves)
generally limestone, dolomite and gypsum
caves from when water reacts with CO2 to form carbonic acid
Detect by
1. soil borings
2. geology maps
3. photos
4. geophysical tests
Solution
1. avoid the voids
2. fill the voids
3. penitate foundation through the void
Cantiliver wall
wall with large footing
MSE walls - mechanical stabilized earth
Reinfoceed rods into soil
crib wall
Precasts pieces that fit like jenga
Foundations types
What factors determine?
Shallow, Deep, intermediate
- soil strength and compressibility
- weight of structure
- money
- water table
Shallow foundations
column footing- square
wall footing - continuous
raft foundation - giant concrete slab
Deep foundations
Drivin piles
Drilled shaft
Caissons
Intermediate foundations
Helical piers
Geopiers
Relative compaction
95%
