Foundation Fundamentals GSD 6204 Building Technology Harvard Graduate School of Design.

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Foundation Fundamentals GSD 6204 Building Technology Harvard Graduate School of Design

Foundation : portion of a building that transfers structural loads to soil

Types of foundations 1. Shallow foundations: slab on grade footings (continuous or point) foundation walls mat slab 2. Deep foundations: piles and caissons

Shallow foundations: transfer loads to soil directly below structure

Depth of shallow foundations determined by : 1. Calculation of structural loads and distribution to soil 2. Depth of winter frost in local area (particularly for residential and light construction)

For maximum stability, the weight of soil excavated should be equal to the weight of the building

Soil compaction

Types of soils (listed from most to least stable) bedrock gravels sands silts and clays organic soils

Soil fails/deforms in shearing

Uniform vs. differential soil settlement

Angle of repose: f = natural slope of soil (depends on soil type)

Slope stability

Crushed stone under the footing distributes load evenly

Vertical loads on a single footing

Foundation beams give rigidity to bearing; point loads are distributed evenly across an area of soil

Deep foundations: transfer loads to bedrock or other highly stable soil layers well below structure, through bearing and/or friction

Deep foundations: point-resisting bell caisson group

Deep foundations: floating pile group

Examples of Caisson Construction

Boring Unit Service Crane Rebar Cage Dry Condition Boring hole using the boring unit and augur. Step 1 Step 2 Installing the reinforcement cage into the bored hole. Clays ( including no water) Gravels Unstable Soil Stable Soil

Dry Condition Casting concrete by direct discharge from the concrete mixer Step 3 Step 4 After excavation, remove the impure concrete of pile Clays ( including no water) Gravels Concrete Hopper Concrete Mixer Pipe Rebar Cage Pile cut Excavation Unstable Soil Stable Soil

Boring Unit Wet Condition Boring hole using the boring unit and augur. Step 1 Step 2 Installing the reinforcement cage into the bored hole. Silt or sand ( including water) Rebar Cage Stable Soil ( Gravels ) Unstable Soil Filled with stabilising fluids such as water or bentonite, (or all casing, depend on the situation) in order to prevent soil collapse

Wet Condition Inserting tremie pipe down to the bottom of the borehole Step 3 Step 4 After removing slime at the bottom, discharge concrete through the pipe. The plug prevents a turbulent contact between the concrete and the water. Silt or sand ( including water) Stable Soil ( Gravels ) Unstable Soil Concrete Hopper Service Crane Tremie Pipe Concrete Tremie Pipe Detail Filled with stabilising fluids such as water or bentonite, (or all casing, depend on the situation) in order to prevent soil collapse The concrete displaces the water from beneath