Concept explainers
A 5 m wide braced excavation is made in a saturated clay, as shown in Figure P19.1, with the following properties: c = 20 kN/m2, ϕ = 0, and γ = 18.5 kN/m3. The struts are spaced at 5 m center to center in plan.
- a. Determine the strut forces.
- b. Determine the section modulus of the sheet pile required, assuming σall = 170 MN/m2.
- c. Determine the maximum moment for the wales at levels B and C.
a.
Find the strut force.
Answer to Problem 19.1P
The strut load at A, B, C is
Explanation of Solution
Given information:
The width of excavation is 5 m.
The height of excavation cut H is 7 m.
The unit weight of saturated clay
The coefficient of internal friction
The cohesion (c) is
The center to center spacing of strut s is 5 m.
Calculation:
Check the condition for soft to medium clay as follows:
Hence, the clay is considered as soft to medium clay.
Find the maximum lateral pressure using the formula.
The maximum lateral pressure is
Step-1:
Indicate the struts are labeled as A, B, and C and its carrying load as
Draw the pressure diagram as shown in Figure.
The strut sheet pile connection at B is assumed to be hinge.
Find the strut load per meter width of excavation as follows:
At the top block,
For the bottom block,
Find the strut force at A
Find the strut load at B
Find the strut load at C
Therefore, The strut load at A, B, C is
b.
Find the required section modulus for sheet pile section.
Answer to Problem 19.1P
The section modulus is
Explanation of Solution
Given information:
The allowable pressure
Calculation:
For top block,
Consider the maximum moment occurs at distance
Find the maximum moment as follows:
The maximum moment occurs at C in the lower block
Find the maximum moment at lower block as follows:
Consider that the higher value of maximum moment is
Find the required section modulus using the formula:
Refer Table 18.1, “Properties of some commercially available sheet-pile section” in the textbook.
Take the section designation as PZ-22 according to the values.
Therefore, the section modulus is
c.
Find the maximum moment for the two wales.
Answer to Problem 19.1P
The maximum moment for the wall at B is
The maximum moment for the wall at C is
Explanation of Solution
Find the maximum moment for the wall at B,
Find the maximum moment for the wall at C,
The maximum moment for the wall at B is
The maximum moment for the wall at C is
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Chapter 19 Solutions
Principles of Foundation Engineering (MindTap Course List)
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