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USS Steel Sheet Piling Design Manual


Quiz Questions

1. Earth pressure is the force per unit area exerted by the soil on the sheet pile structure. The magnitude of the earth pressure depends upon the physical properties of the soil, the interaction at the soil-structure interface and the magnitude and character of the deformations in the soil-structure system.
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False
2. Earth pressure is also influenced by the time-dependent nature of soil strength, which varies due to creep effects and chemical changes in the soil.
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False
3. Two stages of stress in the soil are of particular interest in the design of sheet pile structures, namely the active and-passive states.
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False
4.When a vertical plane, such as a flexible retaining wall, deflects under the action of lateral earth pressure, each element of soil adjacent to the wall expands laterally, mobilizing shear resistance in the soil and causing a corresponding reduction in the lateral earth pressure. One might say that the soil tends to hold itself up by its boot straps; that is, by its inherent shear strength.
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5.The lowest state of lateral stress, which is produced when the full strength of the soil is activated (a state of shear failure exists), is called the active state. The active state accompanies outward movement of the wall. On the other hand, if the vertical plane moves toward the soil, such as the lower embedded portion of a sheet pile wall, lateral pressure will increase as the shearing resistance of the soil is mobilized. When the full strength of the soil is mobilized, the passive state of stress exists. Passive stress tends to resist wall movements and failure.
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False
6.There are two well-known classical earth pressure theories; the Rankine Theory and the Coulomb Theory. Each furnishes expressions for active and passive pressures for a soil mass at the state of failure.
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7.The Rankine Theory is based on the assumption that the wall introduces no changes in the shearing stresses at the surface of contact between the wall and the soil. It is also assumed that the ground surface is a straight line (horizontal or sloping surface) and that a plane failure surface develops. When the Rankine state of failure has been reached, active and passive failure zones will develop as shown in Figure 1. (page 7)
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8.An inherent assumption of the Rankine Theory is that the presence of the wall does not affect the shearing stresses at the surface of wall contact. However, since the friction between the retaining wall and the soil has a significant effect on the vertical shear stresses in the soil, the lateral stresses on the wall are actually different than those assumed by the Rankine Theory. Most of this error can be avoided by using the Coulomb Theory, which considers the changes in tangential stress along the contact surface due to wall friction.
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9.The function of a sheet pile structure is often to retain various surface loadings as well as the soil behind it.
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10.These surface loads, or surcharge, also exert lateral pressures on the wall which contribute to the active pressure tending to move the wall outward. Typical surcharge loadings are railroads, highways, buildings, ore piles, cranes, etc.
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False
11. When a uniformly distributed surcharge is applied at the surface, the vertical pressures at all depths in the soil are increased equally.
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False
12. Sheet pile structures built today in connection with waterfront facilities are subjected to maximum earth pressure when the tide or river level is at its lowest stage.
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False
13.The design example No 1. in Page: 88 is the design of cantilevered sheet piling wall in:
Cohesive soil
Granular soil
14.The design example in page No. 97 is the design of anchored sheet pile wall in:
Sandy soft soil
Granular soil
15.The design example in page No. 116 is the design of Cofferdam in:
Cohesive soil
Granular soil
16.In the design of sheet pile retaining walls which one of the following operations is required?
Evaluation of the forces and lateral pressures that act on the wall,
Determination of the required depth of piling penetration,
Computation of the maximum bending moments in the piling,
Computation of the stresses in the wall and selection of the appropriate piling section
The design of the waling and anchorage system.
All of the above
17.Before the design of sheet piling wall which one of the preliminary information must be obtained.
The elevation of the top of the wall,
The elevation of the ground surface in front of the wall (commonly called the dredge line),
The maximum water level,
The mean tide level or normal pool elevation
The low water level.
A topographical survey of the area is also helpful.
All of the above
18.Tie rods are frequently subjected to tensions much greater than the calculated values.
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False
19.The horizontal reaction from an anchored sheet pile wall is transferred to the tie rods by a flexural member known as a wale. It normally consists of two spaced structural steel channels placed with their webs back to back in the horizontal position. Figure 39 shows common arrangements of wales and tie rods located on both the inside and outside of a sheet pile wall.
True
False
20.A cofferdam is a retaining structure, usually temporary in nature, which is used to support the sides of deep excavations. Such structures generally consist of vertical steel sheet piling braced by a system of (a) wales and struts, (b) circular wales, and (c) prestressed tiebacks.
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False
21. Cofferdams are used primarily for the excavation of multi-level basements and trenches in construction situations where adjacent ground must be supported against settlement or slides. Usually in urban areas the need to prevent settlement of the adjacent ground is a matter of prime importance, as such settlements can have disastrous effects on the structural integrity of adjacent buildings. Sheet pile cofferdams can also be used with economy in the construction of bridge piers and abutments in relatively shallow water.
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False
22. After the subsurface data has been obtained, the first step is to determine the loads acting on the cofferdam. The loads to which the cofferdam may be subjected include earth pressures, surcharge loads, hydrostatic pressures, wave pressures, and earthquake loads.
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False
23.A cellular cofferdam is a gravity retaining structure formed from the series of interconnected straight web steel sheet pile cells filled with soil, usually sand,, or sand and gravel. The interconnection provides water-tightness and self-stability against the lateral pressures of water and earth.
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False
24.For purposes of stability analysis cellular cofferdams are classified according to the type of foundation (i.e., cofferdams on rock and cofferdams on deep soil deposits). Cellular cofferdams founded on rock must be analyzed for several types of failure.
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False
25.Problem No. 1 (pages 129-132) illustrates the design of a circular cofferdam founded on rock.
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False