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Assign_3_2011_Solution

Assign_3_2011_Solution - University of California Davis...

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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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