A layer of sand, 4m thick, overlies a layer of low permeability clay, 5m thick. The bulk unit weight of the sand is 16.5 kN/m3 and its saturated unit weight is 18 kN/m3 . The saturated unit weight of the clay is 21 kN/m3 . The water table exists initially at 1.0m below ground level but pumping will permanently and rapidly lower the water table to 3.0m below ground level. Determine the variation of total stress and porewater pressure at depth h in the clay and the long-term variation in effective stress. Calculate the initial (before pumping) and the long-term (after pumping) effective stress at the middle of the clay layer.

A layer of sand, 4m thick, overlies a layer of low permeability clay, 5m thick. The bulk unit weight of the sand is 16.5 kN/m3 and its saturated unit weight is 18 kN/m3 . The saturated unit weight of the clay is 21 kN/m3 . The water table exists initially at 1.0m below ground level but pumping will permanently and rapidly lower the water table to 3.0m below ground level. Determine the variation of total stress and porewater pressure at depth h in the clay and the long-term variation in effective stress. Calculate the initial (before pumping) and the long-term (after pumping) effective stress at the middle of the clay layer.

Fundamentals of Geotechnical Engineering (MindTap Course List)

5th Edition

ISBN:9781305635180

Author:Braja M. Das, Nagaratnam Sivakugan

Publisher:Braja M. Das, Nagaratnam Sivakugan

Chapter9: Consolidation

Section: Chapter Questions

Problem 9.8P

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Concept explainers

Calculation of Settlement

The vertical displacement of the structural foundation due to the loading from the superstructure is known as settlement. It is due to the reduction of air voids present in the soil. The amount of vertical displacement depends on the bearing capacity of the soil on which the foundation is laid. The effect of the settlement depends on the magnitude of settlement, uniformity, and the structural design of the structure. The maximum allowable settlement for residential and office buildings should be less than 18 mm, for industrial buildings, it is 38 mm and for commercial buildings, it is 25 mm.

Question

A layer of sand, 4m thick, overlies a layer of low permeability clay, 5m
thick. The bulk unit weight of the sand is 16.5 kN/m3 and its saturated
unit weight is 18 kN/m3 . The saturated unit weight of the clay is 21
kN/m3 . The water table exists initially at 1.0m below ground level but
pumping will permanently and rapidly lower the water table to 3.0m
below ground level.
Determine the variation of total stress and porewater pressure at depth
h in the clay and the long-term variation in effective stress.
Calculate the initial (before pumping) and the long-term (after
pumping) effective stress at the middle of the clay layer.

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