What do surface & subsurface features determine? - What can be built on site
- Foundation req
What factors are necessary for planning construction techniques? - Surface/subsurface
features
- Site access
- Equip type
- Ground water (or if surface water develops)
What info needs to be collecte...
CMP 305 Final
Questions and Answers
What do surface & subsurface features determine? - What can be built on site
- Foundation req
What factors are necessary for planning construction techniques? - Surface/subsurface
features
- Site access
- Equip type
- Ground water (or if surface water develops)
What info needs to be collected for surface evaluation? - Soil maps
- Topographic maps
- Aerial photos
- USGS topographic quadrangle maps
- USDA soil conservation maps
What features can be observed from bird's eye view of maps? - Land patterns
- Sink holes
- Drainage patterns (low areas)
What things should you check when visiting a site? - Water level
- Existing wells
- Water marks
- Underground utilities
- Talk to residents
Subsurface evaluation To define vertical & horizontal boundaries of soils/rock under the
site
- Obtain lab samples @ various depths
- Locate ground water table
- Aid in equip selection
- Safety equip (hazard analysis)
2 Types of soil exploration 1. Direct exploration
2. Semi-direct exploration
Devices used in direct soil exploration? - Test pit
- Shelby tube
- Split barrel
- Pocket penetrometer (TSF)
,- Torvane
- Thumb penetration
Devices/techniques used in semi-direct soil exploration? - Auger drilling
- Rotary drill
- Wash-boring
- Drilling rock
- Cone penetrometer
Test pit Direct observation of subsurface material, limited to shallow exploration
- Pit or trench: visual inspection (15'-20')
- Back hoe: excavator
Adv:
- view soil profile (type, color)
- obtain undisturbed sample
Disadv:
- limited depth
- ground water may limit depth
- safety
Auger drilling Hand, truck-mounted
Types:
- solid: dry regions (no ground water), removed for sample, collapse hole
- hollow: faster (split barrel, shelby tube), stem acts as casing
Disadv:
- disturbed sample from the auger
Rotary drill Auger w/ clay slurry
- slurry moves soil up
- slurry stabilizes sides of drill hole
Wash-boring Drill/jet water, casing required
Adv:
- small unit
Disadv:
- disturbed sample, don't know original location/water content
Drilling rock Drill - sample
- soft rock: drill
- hard rock: diamond (carbide tip)
Rock quality designation (RQD): rock sample tested to determine strength
Cone penetrometer Pushed into ground
- records readings for different sections
Adv:
, - provides continuous record of test results
- provides eng. prop. for entire soil profile
Disadv:
- no sample
Geophysical tests & two types *usually w/ road work
- fast results, but more subjective
- less expensive
- borings: still required to determine soil prop.
Types:
- seismic refraction
- electrical resistivity
Seismic refraction Velocities of seismic wave transmitted thru soil
- increasing density = faster wave speed
- sensors pick up waves from explosion
- disadv: boundaries poorly defined
Electrical resistivity Measures electrical resistance thru soil
- varies w/ different soil types
- effected by water content & ion concentration
Which soils have low and high resistance? - Clay soils have ions: low resistance
- Coarse materials (sand/gravel/rock): high resistance
Types of soil sampling - Disturbed sample
- Undisturbed sample
Disturbed sample Used for grain size analysis (LL, PL, PI)
- drilled sample
Split barrel (standard penetration test - SPT) Tube used to collect sample at bottom of test
hole
- pass thru hollow tube auger
- sample may be compressed, suitable for soil classification
- measurement of resistance to penetration
- SPT valves
SPT values Sampler driven for 3 consecutive 6" increments
- # of blows per 6" increment
- blow count summation (total 2 last sets of #s)
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