Foundations

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

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

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)

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

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

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 –Won’t decay Bulb piles

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

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

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

Diesel hammer –F10-6 explain steps

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

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

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

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

Preventing Bank Failure Need to strengthen soil or hold it back –To hold back use columns or piles across slip plane –Soil reinforcement F –Dewatering

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

Shoring and Benching Slope or bench walls away from cut –Takes up more room –Requires more excavation and backfill

Shoring and Shielding Laterally support side walls of cut –Timber shoring F –Aluminum Hydraulic shoring F –Lagging – horizontal sheet piles –Sheet piling –Trench shields F10-20 –Slurry trench – F 10-21

Dewatering Remove water from excavation –Well point F –Vacuum well F Pressure grouting –F –Grout is pumped into soil and fills voids creating a stronger soil bond