Answered: Two alternative solutions are proposed…

Structural Analysis

6th Edition

ISBN:9781337630931

Author:KASSIMALI, Aslam.

Publisher:KASSIMALI, Aslam.

Chapter2: Loads On Structures

Section: Chapter Questions

Problem 1P

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Please solve part 5 only

Transcribed Image Text:The figure below shows a soil profile located at a site for a bridge construction. The profile consists of a layer of normally consolidated clay with thickness of 5.0 m laying over the bedrock and overlain by layer of sand with thickness of 5 m. The water table is observed to be at 2.0 m below the ground surface. A shallow foundation is designed to support the bridge pier at this site. The vertical load imposed on the foundation is Q = 850 kN. A 2.5 cm maximum settlement criterion was set for the foundation. A square footing with B=L=1.0 m was proposed to be constructed at the ground surface to support the pier. 1. Assuming that consolidation settlement is the only settlement contributing to the total settlement of the foundation, does the foundation meet the design specification. 2. To ensure that the foundation meet design specification a layer of soil fill is will placed to pre- consolidate the clay layer. The thickness of the soil fill is 1.0 m and the dry unit weight of the soil is 17 kN/m?. a. How much does the soil settle under the fill. b. Update the soil profile after the fill is removed at the end of consolidation. What is the over-consolidation ratio of the clay layer in the new soil profile. с. 3. How much is the foundation expected to settle in the current soil profile. 4. After the soil has been pre-consolidated, new piezometric reading indicated that the ground water table has the potential to drop to the top of the clay layer. How much would the bridge pier settlement change at this point. 5. Two alternative solution drop, a. Increasing the dimensions of the footing supporting the pier, to reduce the increase in stress are proposed to mitigate the settlement that may occur due to the GWT due to the impose load from the pier. b. Replace a portion of the sand layer with geofoam' (p=11kg/m³) to reduce the overburden stress on the clay layer. As an engineer you need to decide on which is the most suitable approach to use and provide the supporting calculations. GL Gs=2.65 e=0.55 2.0 m Sand 3.0 m Gs=2.78 w=25% 5.0 m Cc=0.28 Clay Cs=0.056 Bedrock Note: using a spreadsheet to perform you calculations will help in editing and revising. Make sure the formulas used in your calculations are included in your solution.

Foundation B X L
B
2 vertical to
2 vertical to
I horizontal
I horizontal
Ao
B+z
FIGURE 8.9 2:1 method of finding stress increase under a foundation
9, × B × L
Ao =
(8.15)
(В + 2) (L+ 2)

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