Foundations

1
Foundations
2

• Foundation supports weight of structure
• Includes soil and rock under foundation
• Building construction described by foundation
  type
• Slab on grade
• Crawl space
• Basement provides useful space if dry

3
Spread footings

• Most common type of foundation
• Square or rectangular pad which spreads building
  load over an area
• Load is less than bearing capacity of soil
• F10-2
• Isolated footing support single column
• Wall footing supports wall
• Combined footing support multiple columns or
  walls
• Mat supports entire building, uses a heavily
  reinforces slab

4
Spread footings

• Mat supports entire building,
• uses a heavily reinforces slab
• Floating slab mat foundation where weight of
  soil removed weight of building (building
  floats on soil)

5
Piles

• Column driven into soil
• Common types
• Timber inexpensive, easy to cut splice, no
  special handling
• Max length 100, load carrying limited, pile
  ends may splinter, subject to insects and decay
• Can use pressure treated
• Good underwater
• Precast concrete piles
• Come in almost any size and shape round, square
  , octagonal

6
Piles

• Precast concrete piles
• Come in almost any size and shape round, square
  , octagonal
• High strength, no decay
• Heaviest type of pile, brittle, no tensile
  strength
• Need careful handling, hard to cut splice
• Cast in Place Piles
• Shell piles steel shell driven into ground and
  then concrete poured in
• Steel serves as additional reinforcement
• Types uniform taper, step taper and straight
• Light, easy to handle, easy to cut splice

7
Piles

• Steel Piles
• Capable of heavy loads
• Driven to great depths, easy to cut splice,
• Common types H-piles, pipe piles
• High cost
• Composite piles
• Made from 2 materials
• Timber bottom, steel top
• Wont decay
• Bulb piles

8

• Bulb Piles
• Franki Piles or pressure injected footings
• Special form of cast in place pile with an
  enlarged base for increased load bearing
• F 10-4
• Minipiles, micro piles
• Small diameter piles (2-8 inches)
• High capacity (to 60 ton)
• Used where there is restricted access or headroom
  to underpin or temp support a building
• Usually placed as a steel casing with reinforcing
  then whole thing is grouted to soil

9
Pile driving

• Drop hammer ancient pile driver F10-5
• Pile driver is usually crane driven
• Pile driver consists of a
• Drop weight
• Leads guide for weight
• Pile driving consists of placing a pile in the
  lead
• Dropping the weight
• Lifting weight
• Repeat
• Must have a stop block to keep weight on leads

10

• Power Hammer Pile Drivers
• Use a working fluid to drive hammer
• Steam or compressed air was first type used
• Hydraulic is newer version
• Single acting hammer
• Fluid lifts weight which then falls down
• Double acting hammer
• Fluid lifts weight and drive weight down
• Hammer Lighter than single acting

11

• Diesel hammer
• F10-6 explain steps

12

• Pile Driving Procedures
• F10-8
• Impact type pile driver
• F 10-7
• Power hammers work on piles not driven straight
  down

13
Piers Caissons

• Pier reinforced concrete column constructed
  below ground surface
• Drilled piers holes drilled in cohesive soils
  are filled with a slurry until concrete is poured
• Holes drilled in non-cohesive soil has a liner
  which can be pulled as concrete is placed
• Caisson structure used to provide all around
  lateral support to an excavation
• Pneumatic caisson air or watertight structures
  open at bottom to permit excavation
• Air pressure keeps water soil out
• Must take safety into account bends
• Brooklyn Bridge

14
Stability of Excavation

• Slope stability
• Cohesive and non cohesive soils
• F 10-10, 10-11
• Embankment failure
• Based on soil type and angle of internal friction
• Safe depth range 5 -18 ft
• OSHA anything over 4 must be guarded
• Failure modes F 10-12
• Stability effected by weather, ground water,
  loads on banks

15
Stability of Excavation

• Stability of Cut Bottom
• Bottom can heave due to weight of soil on sides
• Usually seen when in a cut
• Boiling or piping
• Occurs when water pressure moves soil up from
  bottom of cut
• F 10-16

16
Preventing Bank Failure

• Need to strengthen soil or hold it back
• To hold back use columns or piles across slip
  plane
• Soil reinforcement F 10-17
• Dewatering

17
Protecting Excavations and Workers

• OSHA has regulations
• Protection can be sloping or benching side walls
• Supporting sidewalls with shoring
• Trench boxes
• Exception is when in stable rock

18
Shoring and Benching

• Slope or bench walls away from cut
• Takes up more room
• Requires more excavation and backfill

19
Shoring and Shielding

• Laterally support side walls of cut
• Timber shoring F 10-18
• Aluminum Hydraulic shoring F 10-19
• Lagging horizontal sheet piles
• Sheet piling
• Trench shields F10-20
• Slurry trench F 10-21

20
Dewatering

• Remove water from excavation
• Well point F 10-22
• Vacuum well F 10-23
• Pressure grouting
• F 10-24
• Grout is pumped into soil and fills voids
  creating a stronger soil bond