2. Site and Environment

Question 1

4 types of soils

Answer 1

sand - granular; low plasticity; good bases for building foundations

gravel - granular; low plasticity; good bases for building foundations

Silts - smaller than sands and grave; bigger than clay; granular but slightly plastic

clays - smaller particles than silts; has cohesion or tensile strength; swells when absorbs water; shrinks when it dries

Question 2

hardpan

Answer 2

unbroken mixture of clay, sand, and gravel

Question 3

standard penetration test (SPT)

Answer 3

measure of the density of granular soils and the consistency of some clays

• a 2 in samplers is driven into the bottom of the borehole by a 140 lbm hammer falling 30 in.
• the number of blowsrequried to drive the cylinder 12 in is recorded
• minimum of 4 borings are taken

Question 4

test pits

Answer 4

• trenches dug on site to inspect soil
• limited to 10 ft.

Question 5

auger borings

Answer 5

auger bit drilled into site

usually used for sand or clay

cannot penetrate hardpan or bedrock

Question 6

wash borings

Answer 6

2 in to 4 in diameter pipe is used though which a water jet is maintained to force up soil

analysis is difficult because material mixes together

useful for soils too hard for auger tests

good up to 100 ft.

Question 7

soils are classified according to

Answer 7

Unified Soil Classification System

Question 8

TO increase bearing capacity, decrease settlement, or do both, the following soil treatments are used:

Answer 8

• drainage: reduces moisture content of soil, thus increasing load carrying capacity; reduces hydrostatic pressure
• fill: is existing soil is unsuitable for building, it is removed and engineered soil is brough in; compacted before construction begins; proctor test used to determine a standard for compatction (there is an optimum relationship with a fill’s density and moisture content)
• compaction: existing soil can simply be compacted to provide adequate base; tool used to compact is a sheepsfoot roller
  densification: may involve vibration, dropping of heavy weights; pounding piles into ground and filling voids with sand; technique used depends on the grain size of soil
• surcharging: surchargins is the preloading of the ground with fill materials to cause consolidation and settlements before building; after settlement, fill is removed and construction begins
• mixing: instead of replacement of soil a layer of gravel or sand may be placed and mixed in

Question 9

earthwork

Answer 9

excavating soil for construction of a building foundation, water and sewer lines, and other buried items; includes modifying sites countours

Question 10

unshored sides of soil shold be no steeper than…

Answer 10

their natural angle of repose or not greater than a slope of 1.5 horizontal to the vertial

Question 11

grading

Answer 11

the modification of the contours of the site according to the grading plan

-finish grading is the final removal of soil prior to landscaping to paving

Question 12

common method used for shoring and bracing during excavation

Answer 12

• soldier beams and lagging
• braced excavation

Question 13

underpinning

Answer 13

method used to temporarily support existing foundations while they are being repaired or strengthened or when they are being extended to a lower level

-needle bemas supported by the adjacent grade and hydraulic jacks are used to temporarily support building while new foundation is constructed

Question 14

subsurface drainage

Answer 14

minimum slope of 1/4 in per foot is recommended

-perforated drain tile should be laid around the footings at least 6 in below the floor slab to collect water and carry it away to storm drain

Question 15

Surcharging

Question 16

battered wall

Answer 16

simply a type of retaining wall using a material, such as stones or brick slightly angled to support the adjacent earth.

Question 17

bentonite

Answer 17

an expansive type of clay than can push foundations and floor slabs upward when it gets wet.

Question 18

when buildings are build on benotnite what foundation would they have?

Answer 18

drilled piers with grade beams

to prevent the upward movement cause by bentonite when it gets wet, drillled piers are used to support the building weight on bedrock or stable soil below the bentonite, grade beams span continuously between the piers and transmit buildin loads from the superstructure to the piers

Question 19

raft foundation

Answer 19

Floating raft is type of land-based foundation that protects against settlement and the liquefaction of soft soil due to seismic activity

used to distribute a building load over a large area of low bearing capacity soil

Question 20

coarse grain soils

and fine grain soils

Answer 20

coarse: san and gravel
fine: sands and silts and clays

Question 21

sheet piling or sheeting

Answer 21

consists of vertical planks of wood, steel, or precast concrete that are placed tightly against one another and driven into the earth to form a solid wallbefore excavation begins

Question 22

slurry wall

Answer 22

complicated and expensive form of excavation support that is usually economical only if it becomes the permanent foundation of the building

see page 42 in FBC

Question 23

precast slurry walls

Answer 23

wall is prestressed and is produced in section on a plant

• slurry for precast walls is a mixture of water, bentonite clay, and portalnd cement
• before a wall section is lowered into slurry, its face is coated with a compund that prevents the clay-cement slurry from adhering to it

Question 24

advantages of a precast slurry wall over site cast slurry wall

Answer 24

• better surface quality
• more accurate wall alignment
• better water tightness
• thinner wall
• better structural efficiency

Question 25

soil mixing

Answer 25

a technique of adding a modifying substance to soil and blending it in place by means of augers or paddles rotating on the end of a vertical shaft

-used to remediate soil

Question 26

bracing types

Answer 26

crosslot bracing

rakers

tie backs

Question 27

proctor test determines ….

Answer 27

the optimal desnity of a s psecific sample of soil.

• level of moisture in the sample is a factor in determining the ideal denisty
• sol is then compacted to within a specific percentage of the proctor desnity as specified by the soils engineer so that the soil has the bearing capacity necesaary to support the building load

Question 28

percolation test

Answer 28

measure the ability of saturated soil to absorb a given quantity of water within a specified period of time

Question 29

soil testing is perfrmed on a project site an reveals a suitable bearing stratum at a depth of 100 ft. the composition of the soil is silt, clay, and sand. the water table is 10 ft below the surface. Which of the following foundation strategies is the best choice?

a friction piles

b. concrete footings and CMU foundation walls with waterproofing
c. end bearing piles
d. belled caisson

Answer 29

a friction piles

friction piles are a good choice in the situation described

• as the pile is driven into the soil, frictional forces willl develop between the soils and the pile, whoch allow the pile to develop load carrying capacity even though the end of the pile will not bear on soil capable of carrying the building load
• bearing stratum is too depp at 100 ft for end bearing piles or belled caissons to be a resonable or economical choice
• high water table at 10 ft below grade would make footings and concrete masonry unit foundationwalls very expensive when dewatering and waterproffing are added into the project costs

Question 30

WHen to use belled caissons

Answer 30

-In cohesive soils the shaft bottom can be enlarged by a process known as belling

The bell is constructed after the
straight shaft portion of the caisson has been drilled to the
required founding elevation. A mechanical belling tool is
attached to the base of the drill rig Kelly bar (figure 6). The
wings of the tool are forced open as the bar of the drill rig is
turned. This process forms the bell. When the belling tool is
extracted from the hole the wings retract which traps the
excavated soil inside (figure 5). Belling results in a
substantial increase in bearing capacity while minimizing the
quantity of concrete required for the caisson. The potential
concrete savings are more significant in caissons with long
shafts.

Question 31

difference between pile and caisson

Answer 31

a pile is distinguished froma caissson by being forcibly driven ino the earth rather than drilled and poured

-used where noncohesive soils, subsurface water conditions, or excessive depth of bearing strata make caisson impractical

Question 32

end bearing pile

Answer 32

if a pile is driven until its tip encounters firm resistance from a suitable bearing straturm such as rock, dense sand or gravel

Question 33

frictional pile

Answer 33

if the pile is driven only into softer material, without encountering a firm bearing layer, it may still develop a considerable load carrying capacity through frictional resistance between the sides of the pile and the soil through which it is driven

Question 34

Answer 34

A. Belled Caisson

B. Socketed Caisson

C. End Bearing Pile

D. Friction Pile

Question 35

the EPA has determined that no action is required of the level of radon detected is…

Answer 35

…less than 4 pCi/L (picocuries per liter)

-appropriate remedial action for concentrations over 4 pCI/L include sealing any cracks in the foundation walls or floor slab and ventilating or depressurizing the basement or crawlspace area

Question 36

the limits of an excavation and building footprint are located by a surveyor and marked using

Answer 36

batter boards

they are temporary supports erected to hols wires or strings that indicate the excavation line for a building site

Question 38

the corners of the building or limits of excavation are marked at the intersection of the lines using a …

Answer 38

plumb bob

Question 39

batter board are preferred to corner stakes or pins because…

Answer 39

…they are set back from the excavation lines and will not be disturbed during construction operations

Question 40

grade stakes

Answer 40

used to inicate how much cut or fill is required at a specific location to reach finish grade

-set by a survey crew and reset periodically as excavation is taking place to monitor progress

Question 41

transit

Question 42

Radon …

Answer 42

is a chemical element with symbol Rn and atomic number 86. It is a radioactive, colorless, odorless, tasteless[2] noble gas, occurring naturally as an indirect decay product of uranium or thorium.

Question 43

How Radon Enters Your Home

Answer 43

Radon is a naturally occurring radioactive gas produced by the breakdown of uranium in soil, rock, and water. Air pressure inside your home is usually lower than pressure in the soil around your home’s foundation. Because of this difference in pressure, your home acts like a vacuum, drawing radon in through foundation cracks and other openings.

Question 44

The U.S. Congress has set a long-term goal that indoor radon levels be no more than outdoor levels; about ___ pCi/L of radon is normally found in the outside air.

Answer 44

0.4

Question 45

Active Subslab suction — also called subslab depressurization — is ….

Answer 45

…the most common and usually the most reliable radon reduction method. One or more suction pipes are inserted through the floor slab into the crushed rock or soil underneath. They also may be inserted below the concrete slab from outside the home. The number and location of suction pipes that are needed depends on how easily air can move in the crushed rock or soil under the slab and on the strength of the radon source. Often, only a single suction point is needed.

Question 46

Passive subslab suction is …

Answer 46

…the same as active subslab suction except it relies on natural pressure differentials and air currents instead of a fan to draw radon up from below the home.

Question 47

submembrane suction

Answer 47

An effective method to reduce radon levels in crawlspace homes involves covering the earth floor with a high-density plastic sheet. A vent pipe and fan are used to draw the radon from under the sheet and vent it to the outdoors.