Chapter 3: Foundation Systems

Question 0

Settlement

Answer 0

is a gradual subsiding of a structure as the soil beneath its foundation consolidates under loading.
On coarse sand and gravel soils, consolidation is usually slight and occurs rather quickly.
On moist, cohesive clay soils with relatively large percentage of voids, consolidation can be quite large and occur slowly over a long period of time.

Question 1

Principal loads on a foundation and forces acting on it:

Answer 1

• dead and live loads acting vertically on the superstructure.

Foundation systems must anchor superstructure against wind-induced sliding, overturning, and uplift, withstand the sudden ground movements of an earthquake, and resist the pressure imposed by surrounding soil mass and groundwater on basement walls.

Question 2

Differential settlement

Answer 2

is the relative movement of different parts of a structure caused by uneven consolidation of the foundation soil.

Question 3

Foundation systems can be classified into two broad categories:

Answer 3

• shallow foundations: employed when stable soil of adequate bearing capacity occurs relatively near to the ground surface.
• deep foundations: employed when the soil underlying a foundation is unstable or of inadequate bearing capacity.

Question 4

Underpinning

Answer 4

refers to the process of rebuilding or strengthening the foundation of an existing building, or extending it when a new excavation in adjoining property is deeper than the existing foundation.

Question 5

Slurry wall

Answer 5

is a concrete wall cast in a trench to serve as sheeting and often as a permanent foundation.

Question 6

Dewatering

Answer 6

refers to the process of lowering a water table or preventing an excavation from filling with groundwater.

Question 7

Most common forms of spread footings

Answer 7

• strip footings: continuous spread footings of foundations walls.
• isolated footings: are the individual spread footings supporting freestanding columns and piers.

Question 8

Other types of spread footings include:

Answer 8

• stepped footings
• cantilever or strap footings
• combined footing

Question 9

Foundation walls

Answer 9

provide support for the superstructure above and enclose a basement or crawl space partly or wholly below grade.

Question 10

Footings should be placed…

Answer 10

on undisturbed soil below frostline.

Question 11

Concrete foundation walls are…

Answer 11

cast-in-place and require formwork and access to place the concrete.

Question 12

Masonry foundation walls do not require…

Answer 12

formwork and utilize easily-handled small units.

Question 13

Wood joists on top of foundation walls include:

Answer 13

• sill plate
• anchor bolts
• sill plate anchors or holddowns
• header or rim joist
• wood joist framing

Question 14

Wood beams on top of foundation walls

Answer 14

need a minimum 13mm air space on tops, sides and ends entering concrete or masonry wall unless pressure-treated wood is used. The minimum bearing for wood beams on concrete or masonry is 75mm, if area is not enough, then wall should be thickened with pilaster.

Question 15

Open-web steel joists

Answer 15

Minimum bearing for regular joists is 100 to 150mm. On concrete wall, they are anchored to steel base plates. On masonry walls, they are anchored to a continuous bond beam.

Question 16

A subsoil drainage system is required to…

Answer 16

collect and divert water away from a foundation to a storm sewer, dry well or natural outfall at a lower elevation on the site.

Question 17

Drainage mat or a gravel backfill allows…

Answer 17

water to flow down to the footing drains. Aprox 20mm thick.

Question 18

Cant strip

Answer 18

Chamber piece.

Question 19

Hydrostatic pressure

Answer 19

Pressure exerted by water.

Question 20

Dampproofing and waterproofing

Answer 20

Dampproofing is applied to a foundation wall when hydrostatic pressure from the groundwater table will not occur.

When subject to hydrostatic pressure, foundation walls should be waterproofed.

Question 21

Composite footing consists of…

Answer 21

a footing plate and a layer of gravel, sand or crushed stone.

Question 22

Types of Column Footings:

Answer 22

• reinforced concrete column
• wood post
• steel column

Question 23

Concrete slabs on grade require…

Answer 23

the support of a level, stable, uniformly dense or properly compacted soil base containing no organic matter. Minimum slab thickness is 100mm.

Question 24

Three types of joints used on concrete slabs on grade:

Answer 24

1. ISOLATION JOINTS (or expansion joints): allow movement to occur between concrete slab and adjoining columns and walls.
2. CONSTRUCTION JOINTS: prevent vertical differential movement of adjoining slab sections.
3. CONTROL JOINTS: create lines of weaknesses so the cracking that may result from tensile stresses occurs along predetermined spaces.

Question 25

Minimum depth of a footing is

Answer 25

305mm

Question 26

Pole foundations

Answer 26

elevate timber structures above ground plane, require minimal excavation and preserve the natural features and existing patterns of a site. They are particularly useful when building on steep slopes and in areas subject to periodic flooding.

Question 27

Two main types of deep foundations are:

Answer 27

1. pile foundations

2. caisson foundations

Question 28

A pile foundation

Answer 28

is a system of end-bearing or friction piles, pile caps, and tie beams for transferring building loads down to a suitable bearing stratum.

Question 29

Types of pile foundations:

Answer 29

• timber piles
• composite piles
• H-piles
• pipe piles
• precast concrete piles
• cast-in-place piles (cased or uncased)
• pedestal pile
• micropiles

Question 30

Caissons are…

Answer 30

cast-in-place, plain or reinforced concrete piers formed by boring with a large auger or excavating by hand a shaft in the earth to a suitable bearing stratum and filling the shaft with concrete. They are also referred to as drilled piles or piers.