Concept explainers
A 1.5 m square footing carries a column with a service load of 105 kN. It is founded at a depth of 2 m on a medium stiff clay with an undrained shear strength of 42 kPa, an overconsolidation ratio of 4, and a plasticity index of 35. The clay layer is 5 m thick and overlies a very stiff shale. Estimate the undrained settlement of the footing using the generalized elastic method with Christian and Carrier’s (1978) influence factors.
The undrained settlement of the footing using the generalized elastic method with Christian and Carriers (1978) influence factors.
Answer to Problem 8.1QPP
3.1 mm
Explanation of Solution
Given data:
Size of footing = 1.5m
Service load = 105kN
Depth = 2m
Undrained shear strength = 42kPa
Overconsolidation ratio = 4
Plasticity index = 35
Thickness of clay layer = 5m
Formula used:
The ratio of depth to width of footing is
The influence factor accounting for depth of footing from the following figure is
The aspect ratio of footing is
The relative thickness of compressible layer is
The influence factor accounting for shape of footing and compressible layer thickness from the above figure is
The average soil modulus over depth of compressible layer is
Substituting the values in the above equation,
The undrained settlement of the footing is
Conclusion:
The undrained settlement of the footing is 3.1 mm.
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Chapter 8 Solutions
Foundation Design: Principles and Practices (3rd Edition)
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