Question 1

Which of the following definitions best describes the term &#34;serviceability limit state&#34; (SLS) used in foundation design?&#10;A)Maximum load-carrying capacity of the foundation&#10;B)Relates to the loss of functionality that occurs prior to foundation failure&#10;C)State reached through structural or geotechnical failure&#10;D)A. and C.

Accepted Answer

The serviceability limit state (SLS) is related to the loss of functionality that occurs prior to foundation failure. The SLS is reached through excessive foundation settlement, lateral displacement, or structural deterioration. The ultimate limit state (ULS) is related to a foundation's maximum load-carrying capacity.

Question 2

Which of the following characteristics is not commonly associated with isolated spread footings?&#10;A)Designed to distribute concentrated loads to prevent shear failure of underlying soil&#10;B)Structural design of the column includes consideration for moment resistance, shear and punching&#10;C)Address plane strain conditions assumed to exist parallel to long axis of the footing.&#10;D)Size of the footing is based on the loaded distributed by the support column and soil characteristics of the underlying soil

Accepted Answer

Plane strain conditions are not assumed to exist parallel to the long axis of an isolated spread footing. Plane strain conditions are taken into account with continuous (strip) footings and affect the depth of significant influence (DOSI) - the depth at which applied stresses are experienced in the underlying soil. For isolated spread footings, the DOSI ranges between 2 and 4 times the width of the footing. For continuous footings, the DOSI will always be greater than 4 times the footing width.

Question 3

A bridge abutment is required to perform all but which of the following functions?&#10;A)Serve as a transition to a bridge deck&#10;B)Retain the backfill or soils behind the abutment&#10;C)Support the bridge superstructure&#10;D)Support the bridge loads

Accepted Answer

A bridge abutment is not designed to support the bridge loads. An abutment is designed to distribute loads to the bearing materials below the foundation system, which is most typically a spread footing. A common bridge abutment configuration involves a spread footing and cantilevered stemwall.

Question 4

Which of the following elements is not considered when determining the minimum factor of safety against bearing capacity failure of a shallow foundation?&#10;A)Consequence of failure&#10;B)Structure life span&#10;C)Structure importance&#10;D)Confidence in design parameters

Accepted Answer

A structure's life span is not a consideration when determining the minimum factor of safety against bearing capacity failure of a shallow foundation. A factor of safety is applied to a calculated ultimate bearing capacity to account for the uncertainty of load magnitudes and available soil bearing strength. The required minimum factor of safety for shallow foundations typically ranges from 2.5 to 3.5.

Question 5

What is the allowed bearing capacity (in kips per square foot (ksf)) of a shallow bridge foundation with an ultimate bearing capacity of 2,000 ksf and an applied safety factor of 3.0?&#10;A)667 ksf&#10;B)2,000 ksf&#10;C)6,000 ksf&#10;D)Not enough information provided

Accepted Answer

The allowed bearing capacity of a shallow bridge foundation with an ultimate bearing capacity of 2,000 ksf and an applied safety factor of 3.0 is 667 ksf.
Solution: Use the allowable bearing capacity equation
qall = qult / FS
Given, qult = 2,000 ksf
FS = 3.0
qall = 2,000 ksf/ 3.0= 667 ksf

Question 6

Which of the following are the three common components of shallow foundation settlement?
1. Uniform
2. Tilt/rotation
3. Horizontal
4. Differential

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

Accepted Answer

The three common components of shallow foundation settlement are uniform, tilt/rotation, and differential. With uniform settlement, all elements of the shallow foundation settle equally. Tilt or rotation settlement can result in drainage issues, surface cracks, and damage to underlying systems such as foundation drains or buried infrastructure. Differential settlement, resulting in angular distortion, may occur because of a deformation in the structure that the foundation is supporting.

Question 7

Which of the following conditions is not required for shallow foundations?&#10;A)Soil must not settle excessively&#10;B)Loads must not cause failure of the supporting soil&#10;C)Available skilled labor needed for construction&#10;D)Depth is sufficient to prevent environmental damage (frost, erosion, swelling and shrinkage)

Accepted Answer

The condition that is not required for a shallow foundation is the availability of a skilled labor force. When the soil conditions are suitable, a shallow foundation may be an affordable alternative that can be constructed using mostly concrete and unskilled labor. A shallow foundation is typically not a feasible alternative for soils with excessive settlement, areas with irregular ground surfaces, or foundations that may be subjected to pullout, torsion, or motion forces.

Question 8

What are the four basic modes of geotechnical instability of an earth retaining structure?
1. Sliding
2. Expanding
3. Overturning
2. Bearing capacity
3. Global stability

A)1, 2, 3, 4
B)1, 3, 4, 5
C)2, 3, 4, 5
D)1, 2, 4, 5

Accepted Answer

The four basic modes of geotechnical instability of an earth retaining structure are: sliding, overturning, bearing capacity and global stability. These modes may not be applicable to all wall types. Depending on the wall type and the load support mechanism used, there may be additional internal instability modes encountered: pullout, tension breakage, bending, or shear.

Deck 5: Foundations