Question 1

Which of the following equations is used for evaluating a structure's factor of safety with respect to bearing capacity (FSbc)?&#10;A)FSbc = ultimate bearing capacity of foundation soil / maximum pressure below the base&#10;B)FSbc = maximum pressure below the base / minimum pressure below the base&#10;C)FSbc = ultimate bearing capacity of foundation soil / minimum pressure below the base&#10;D)FSbc = maximum pressure below the base / ultimate bearing capacity of foundation soil

Accepted Answer

The equation FSbc = ultimate bearing capacity of the foundation soil / maximum pressure below the base is used for evaluating a structure's factor of safety with respect to bearing capacity. Typically, a minimum factor of safety of 3 is required. FSbc is expressed as follows:
FSbc = qu / qmax

Question 2

Which of the following practices will help to prevent moisture problems that negatively impact slab-on-grade foundations?&#10;A)Slope ground away from foundation at (0.5 ft per 10 ft)&#10;B)Install 10 mil vapor barrier beneath slab over a gravel drainage pad&#10;C)Install foundation drain assembly that includes filter fabric, gravel and perforated polyvinyl chloride (PVC) pipe&#10;D)All of the above

Accepted Answer

All of the above listed practices will help to prevent moisture problems that negatively impact slab-on-grade foundations. The basic concept behind these practices is to prevent water from coming into contact with the foundation walls by allowing for proper drainage away from the structure. Additionally, preventing the condensation and diffusion of moisture on concrete slab will minimize mold and moisture damage.

Question 3

Which of the following characteristics is generally not associated with slab-on-grade foundations?&#10;A)Edges of the slab are thicker than the interior of the slab&#10;B)Slab is poured in sections&#10;C)Slab normally rests on a bed of crushed gravel&#10;D)None of the above

Accepted Answer

The characteristic "slab is poured in sections" is generally not associated with slab-on-grade foundations. The slab is a composed of a single layer of monolithic concrete. Reinforcing rods typically strengthen the footings, and wire mesh is often used to reduce cracking. When necessary, design modifications are made to ensure adequate frost protection is provided.

Question 4

Although the design of a slab-on-grade foundation considers criteria related to soil properties, climate, and the structure it will support, unrelated post-construction activities such as drought conditions, floods, or extreme loading conditions may cause result in stability issues. Which of the following methods can be used to uniformly stabilize existing slab-on-grade foundations?

A)Underpinning
B)Excavation and replacement
C)Patching
D)All of the above

Accepted Answer

Underpinning can be used to uniformly stabilize existing slab-on-grade foundations. Underpinning generally involves building a foundation beneath an existing foundation, and can be accomplished using grout, concrete, mini-piles, piers, and/or beams. Although this method has been in use for over one hundred years, the process is proven to be successful in extending the life cycle of slab-on-grade foundations.

Question 5

What is the required minimum thickness of a concrete floor that will be constructed under water at a depth of 5 meters (m) below the soil surface? (Assume the water table is 1 meter below the soil surface and the weight of concrete is 25 kN/m³.)

A)1.57 m
B)2.58 m
C)4 m
D)Not enough information provided

Accepted Answer

The required minimum thickness of a concrete floor that will be constructed under water at a depth of 5 meters below the soil surface is 2.58 m. Solution: Use the equation (* assumed given in NCEES PE Reference Manual) D > (h-d) ?_w / (?_b - ?_w ) Where D = floor thickness, ?_b = weight of concrete, ?_w =unit weight of water, and h = depth below water h = 5 m d = 1 m ?_w = 9.81 kN/m³ ?_b = 25 kN/m³ Therefore, D > (4 m) (9.81 kN/m³) / (25 - 9.81 kN/m³) D > 2.58 m

Question 6

Which of the following practices should be followed when placing bedding material into a reinforced concrete pipeline trench during construction?&#10;A)The bedding should be placed on top of a firm and stable trench bottom&#10;B)When the water table is above the trench bottom, the water level should be lowered to at least the trench bottom&#10;C)The bed should be over-excavated at each joint location to ensure that the pipe has a continuous support and does not rest on the couplings&#10;D)All of the above

Accepted Answer

When placing bedding material into a reinforced concrete pipeline trench during construction, all of the practices listed above should be followed. Additionally, to ensure proper construction and employee safety, pipeline trenches and shoring should meet Occupational Safety and Health Administration (OSHA) standards. If unstable soil is encountered in an excavated trench, over-excavation and/or additional foundation measures may be required.

Question 7

Of the following situations, which is the most likely to present the most severe loading conditions on a concrete dam?&#10;A)Reservoir is full and soil is in a natural drained condition&#10;B)Reservoir is full and soil is in a natural undrained condition&#10;C)Reservoir is empty and soil is in a natural drained condition&#10;D)Reservoir is empty and soil is in a natural undrained condition

Accepted Answer

Of the given situations, the one that is most likely to present the most severe loading conditions on a concrete dam is when the reservoir is empty and the soil is in a natural drained condition. Concrete dams are designed to support the weight of soil and water, and the foundation pressures are assumed to act uniformly across the full width of the structure. When the groundwater table and surface water elevations are both extremely low, a significantly increased ratio of vertical to horizontal pressure may result.

Deck 2: Earth Structures