1
University of California, Davis
Department of Civil and Environmental Engineering
ECI-173 Foundation Design
MEMORANDUM
TO:
ECI-173 Students
Date: January 24, 2011
FR:
Jason T. DeJong
SUBJECT:
Assignment No. 3 (Due by 4 pm Monday, January 31)
Question 1:
A 100-ft by 300-ft rectangular building will be supported on a mat foundation. The mat will be 6 feet thick, and its top surface
will be 20 ft below the ground surface.
The mat will carry a gross uniform bearing pressure of 6,000 psf (not counting its own
weight); for analysis, we can assume the gross bearing pressure spreads from the top surface of the mat, and that the net weight
of the mat itself is zero.
The site is underlain by a deep, relatively homogenous, deposit of over-consolidated clays that have an
average recompression ratio (C
ε
r
) of 0.025, an average coefficient of consolidation (c
v
) of 0.1 ft
2
/day, an average total unit
weight of 128 pcf, and an average Skempton's A parameter of 0.40. The clay is expected to remain overconsolidated under the
loading imposed by the mat.
The clay deposit extends to a depth of 400 ft. The water table is at a depth of 26 ft.
(a)
Compute the ultimate consolidation heave that is expected at the center of the mat due to the 20 ft of excavated soil.
Plot the initial and final vertical effective stresses versus depth beneath the center of the building, and the
corresponding vertical strain versus depth. Include the Skempton-Bjerrum 3D correction factor in your estimate of the
ultimate consolidation heave.
(b)
Compute the ultimate net consolidation settlement that is expected at the center of the mat. Include the same plots and
methods as for part (a).
(c)
Estimate the consolidation settlement at the center of the mat that the building will experience if 50% of the ultimate
consolidation heave occurs before the building loads are imposed.
(d)
Repeat part (c) for the corner of the mat.
You may assume that the Skempton-Bjerrum correction for 3D effects is
applicable to the corner as well as to the center point.
What is the ratio of the expected consolidation settlements at
the corner to those at the center of the mat?
(e)
Plot the consolidation heave versus time at the center of the mat for the following idealized conditions. Suppose that
there are thin, continuous, horizontal layers of clean gravelly sands at depths of 26 ft, 50 ft, and 100 ft, and that the
bedrock is highly fractured and pervious relative to the clay, and that these all represent freely draining boundary
conditions.
Assume that the 20 ft excavation occurs instantaneously, and that no other loads are applied. Indicate how
long it would take for 90% of the ultimate consolidation heave to occur, and what percent of the ultimate consolidation
heave would have occurred after 6 months?
Question 2:
Visit the website for the California Board for Professional Engineers and Land Surveyors, and read the 2011 Professional Engineers
Act.
Summarize the things that are required for a person to be able to use the title "Geotechnical Engineer." What qualifications
must they have and what steps must they go through?

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