1. Final Project - Soil & Foundations

Question 1

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

Answer 1

C) 1, 4, 3, 2

Question 2

Soil testing is needed for what kinds of buildings?

Answer 2

All buildings except single family dwellings

Question 3

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

Answer 3

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

Question 4

Describe the 2 broad classes of soil.

Answer 4

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

Question 5

How does ASTME define soil types. (4)

Answer 5

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)

Question 6

Define ALLOWABLE BEARING CAPACITY.

Answer 6

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

Question 7

Define a standard penetration test.

Answer 7

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

Question 8

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

Answer 8

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

Question 9

Describe 6 potential soil problems.

Answer 9

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

Question 10

Describe 5 potential soil interventions.

Answer 10

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

Question 11

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

Answer 11

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

Question 12

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

Answer 12

• impervious
• frost

Question 13

Ideal soil type for construction?

Answer 13

Clean (no silt or clay) sand or gravel

Question 14

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

Answer 14

All organic soils:

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

Question 15

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

Answer 15

1. Soil Stability
2. Soil Bearing Capacity

Question 16

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

Answer 16

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

Question 17

What if the soil has a high bearing capacity?

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

Answer 17

Little issues.

Bedrock: 12,000 psf

Sedimentary rock: 6,000 psf

Gravel: 5,000 psf

Question 18

What if soil has a low bearing capacity?

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

Answer 18

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

Clay, silty clay : 2,000 psf

Question 19

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

Answer 19

Better drainage

Less susceptible to frost

Question 20

Soils sloped above 25%

Answer 20

Prone to erosion

Difficult construction

Question 21

Soils sloped above 10%

Answer 21

Doesn’t suit exterior activities

Higher construction prices

Question 22

Soils sloped between 5% - 10%

Answer 22

Suits some exterior activities

Little construction issues

Question 23

Soils sloped below 5%

Answer 23

Suits most exterior activities

Easy construction

Question 24

Describe 5 main types of excavation support systems

Answer 24

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

Question 25

Describe 4 types of **earthwork** in order of execution.

Answer 25

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"

Question 26

Define **underpinning**.

Answer 26

rebuilding / strengthening foundation of existing buillding

Question 27

Describe the dimensions shown below:

Answer 27

width of foundation wall = **W** projection = **1/2 W** height of footing = **W** width of footing = **2 W**

Question 28

Describe the **cone of bearing**, how in impacts **footing spacing**, and what angle is shaped by _rock_ and _soil/sand_ respectively.

Answer 28

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)

Question 29

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?

Answer 29

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**

Question 30

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

Answer 30

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.

Question 31

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

Answer 31

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

Question 32

What should a **retaining wall** resist?

Answer 32

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

Question 33

4 types of **retaining wall** materials

Answer 33

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

Question 34

Name 4 types of **reinforced concrete** retaining walls

Answer 34

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

Question 35

When use a **gravity** concrete retaining wall?

Answer 35

1. Resists overturning and sliding by sheer weigth and volume of its mass 2. Used for **less than 10'** height.

Question 36

When use a **t-type cantilevered** concrete retaining wall?

Answer 36

1. Used for **up to 20'** height. Above that, use _counterfort walls_.

Question 37

When use a **L-type cantilevered** concrete retaining wall?

Answer 37

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.

Question 38

When use a **counterfort** concrete retaining wall?

Answer 38

1. Uses triangular-shaped cross walls spaced intervals one half the height 2. Used for **Above 20'** height.

Question 39

Should we **drain** retaining walls?

Answer 39

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