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EXAC EXAM 3 > 1. Final Project - Soil & Foundations > Flashcards

1. Final Project - Soil & Foundations Flashcards

1
Q

Place the following soil types in increasing order of their drainage capacity (from low to high).

  1. Clay
  2. Clean gravel
  3. Silty sand
  4. Peat

A) 1, 3, 2, 4
B) 1, 3, 4, 2
C) 1, 4, 3, 2
D) 4, 1, 3, 2
E) 4, 3, 2, 1

A

C) 1, 4, 3, 2

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2
Q

Soil testing is needed for what kinds of buildings?

A

All buildings except single family dwellings

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3
Q

Describe the function of and difference between test pits and boring.

A

The geotech Engineer generates a soil profile to show the strata (horizons) of varied soil types.

Test Pit (<3m)

Boring (>3m) - deeper, allow to insert piezometer to monitor water table level

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4
Q

Describe the 2 broad classes of soil.

A
  1. Coarse grain (particles visible to naked eye)
    • gravel
    • sand
  2. Fine grain
    • silt
    • clay
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5
Q

How does ASTME define soil types. (4)

A

1 - description (ex: silty gravel)

2 - bearing capacity (ex: 5000 psf)

3 - susceptibility (ex: slight) (Soil susceptibility to compaction is the probability that soil becomes compacted when exposed to compaction risk.)

4 - permeability + drainage (ex: poor)

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6
Q

Define ALLOWABLE BEARING CAPACITY.

A

Max unit pressure a foundation is permitted to impose VERTICALLY or LATERALLY on soil mass.

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7
Q

Define a standard penetration test.

A

Measures density of granular soils by recording the number of blows required to advance a standard soil sampler

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8
Q

Describe the shearing strength of cohesive and granular soils when unconfined.

A
  1. Cohesive - maintain strength when unconfined
  2. Granular - require a confining force for their shear resistance
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9
Q

Describe 6 potential soil problems.

A

1 - SETTLEMENT - dead load causes structure to compact soil and ‘settle’

2 - DIFFERENTIAL settlement causes cracks

3 - FROST action heaving during freeze thaw = stress on footing .: footing must be 12” below frost line

4 - EARTH MVMT prevalent w clay soils .: footings lower than 5’ subject to less mvmt

5 - soil DRAINAGE moisture content impacts bearing capacity .:must know water level & drain properly

6 - WATER TABLE foundation must be well above water table to avoid • hydrostatic pressure • capillary action

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10
Q

Describe 5 potential soil interventions.

A

1 - SOIL MODIFICATION - to improve consitancy/bearing etc.

2 - INCREASE BEARING CAPACITY - deepening of footing - increase bearing area of footing

3 - IMPROVE DRAINAGE - increase bearing capacity

4 - REMOVE/REPLACE UNSUITABLE SUBSOIL - typ. replaced w compacted granular engineered mix

5 - COMPACTION - w rollers

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11
Q

If soils are not adequately dense for a foundation to bear upon, what can be done?

A

The soil may need compaction in order to achieve optimum density or soaking to achieve optimum moisture content.

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12
Q

Silt and sandy soils are typically _____ and susceptible to _____.

A
  • impervious
  • frost
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13
Q

Ideal soil type for construction?

A

Clean (no silt or clay) sand or gravel

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14
Q

Which soil types have either very poor or unsuitable bearing capacity.

A

All organic soils:

  • Organic silt-clay
  • Organic clay and silt
  • Peat (highly organic = unsuitable)
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15
Q

What does the building structural integrity depend on in relation to soil (2)

A
  1. Soil Stability
  2. Soil Bearing Capacity
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16
Q

What does a geotechnical analysis (test pits) allow to determine about the soil? (5)

A
  1. Structure of soil
  2. Shear and compression resistance
  3. Water content
  4. Permeability
  5. Amount of settlement under loading
17
Q

What if the soil has a high bearing capacity?

What type of load-bearing pressure do these soils have?

A

Little issues.

Bedrock: 12,000 psf

Sedimentary rock: 6,000 psf

Gravel: 5,000 psf

18
Q

What if soil has a low bearing capacity?

What type of load-bearing pressure do these soils have?

A

Types of foundations and special attention to load repartition. Sometimes, it may decide the shape of the building.

Clay, silty clay : 2,000 psf

19
Q

Advantages of coarse soils as opposed to fine soils (2)

A

Better drainage

Less susceptible to frost

20
Q

Soils sloped above 25%

A

Prone to erosion

Difficult construction

21
Q

Soils sloped above 10%

A

Doesn’t suit exterior activities

Higher construction prices

22
Q

Soils sloped between 5% - 10%

A

Suits some exterior activities

Little construction issues

23
Q

Soils sloped below 5%

A

Suits most exterior activities

Easy construction

24
Q

Describe 5 main types of excavation support systems

A

1 - SHEET PILING steel (corrugated), timber or precast planks driven vertically into ground

2 - SOLDIER PILES steel h-sections driven down vertically to support horizontal lagging

3 - TIE BACKS used if rakers would interfere with const. steel cables anchored into predrilled soil or rock

4 - CROSS BRACING sheet piling and soldier beams are supported by horizontal steel cross bracing or by steel rakers bearing on heal blocks

5 - SLURRY WALL poured into a trench and often becomes permanent wall

25
Q

Describe 4 types of earthwork in order of execution.

A

1 - ROUGH GRADING - permanently filled slopes stable @<2:1

2 - EXCAVATION - removal of existing - permanently cut slopes are stable @ <1.5:1

3 - BACKFILL - earth replaced around foundations + footings - deposit in 6-12” layers - tamp to avoid settlement

4 - FINISH GRADING - final distribution of earth @ conclusion of construction - accurate win 1”

26
Q

Define underpinning.

A

rebuilding / strengthening foundation of existing buillding

27
Q

Describe the dimensions shown below:

A

width of foundation wall = W

projection = 1/2 W

height of footing = W

width of footing = 2 W

28
Q

Describe the cone of bearing, how in impacts footing spacing, and what angle is shaped by rock and soil/sand respectively.

A
  1. Cone of bearing is the compacted soil below the footing
  2. each footing must be separated by the width of two footings @ min.
  3. rock results in an angle of 60deg
  4. soil and sand results in an angle of 30deg

(see below)

29
Q

When siting a building near the top or base of a slope what sort of setback can be used as a rule of thumb for stability of the foundation?

A
  1. at the base = H/2 (height of the slope/2) or 5m max - protection from site drainage & erosion
  2. at peak = H/3 or 12m max - vertical & lateral support for the footing and prevent settlement
30
Q

What building/soil type are floating foundations used for, and why are they successful?

A
  1. They use a mat (or raft) foundation that is deep enough in the ground that the weight of the excavated soil is roughly equal to the construction supported. It causes nearly no settlement because of the equilibrium in weight (balancing raft foundation)
  2. Soils that have good sheer strength but have large settlements OR soils that have poor sheer strength with no hard layer of soil at reasonable depth.
31
Q

Why should ground water be kept away from foundations? (2)

A
  1. Keep the load bearing capacity of the soil intact.
  2. Reduce risks of water infiltration inside the building.
32
Q

What should a retaining wall resist?

A

Retaining wall should resist lateral pressure of the soil being retained.

33
Q

4 types of retaining wall materials

A
  1. Reinforced concrete walls
  2. Horizontal timber walls
  3. Brick veneer walls
  4. Dry stone walls
34
Q

Name 4 types of reinforced concrete retaining walls

A
  1. Gravity wall
  2. T type cantilevered wall
  3. Counterfort wall
  4. L type cantilevered wall
35
Q

When use a gravity concrete retaining wall?

A
  1. Resists overturning and sliding by sheer weigth and volume of its mass
  2. Used for less than 10’ height.
36
Q

When use a t-type cantilevered concrete retaining wall?

A
  1. Used for up to 20’ height. Above that, use counterfort walls.
37
Q

When use a L-type cantilevered concrete retaining wall?

A
  1. Used when abutting a property line or obstruction.
  2. Bottom of L = 0.6H if on empty side or 0.7H if on soil side.
38
Q

When use a counterfort concrete retaining wall?

A
  1. Uses triangular-shaped cross walls spaced intervals one half the height
  2. Used for Above 20’ height.
39
Q

Should we drain retaining walls?

A

Use drainage system to relieve the buildup of water pressure behind the wall:

  • drainage mat with filter fabric or porous gravel backfill
  • 2” weepholes @ 4’-6’ or perforated drainpipe

EXAC EXAM 3 (14 decks)

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