Location

Chicago, Illinois

Session Start Date

4-29-2013

Session End Date

5-4-2013

Abstract

Estimation of static and seismic settlements is critical for the design of a structure to assess whether the structure can tolerate given levels of total and differential settlements and angular distortion. The design of a public school building required the estimation of both liquefaction-induced settlement due to the presence of a potentially liquefiable layer, and settlement from cyclic softening of soft clay layers. Tolerable levels of differential settlements for the proposed school building were not to exceed 2 inches across the building. The soft clay had a plasticity index of 12, a liquid limit of 32, and SPT blow counts of less than 4. Recent publications do not consider this clay potentially liquefiable, but consider it susceptible to cyclic softening. In addition to the borings, in-situ vane shear testing and CPT soundings were conducted at the site to supplement the data for our analysis. Using published methods we conducted an assessment of the soft clay and calculated factors of safety against cyclic softening as low as 0.0. In-situ vane shear testing resulted in soil sensitivities ranging from 1.6 to 3.4. Using CPT data we conducted a cyclic softening analysis of the entire soil column to a depth of about 50 feet. This paper describes the encountered site conditions, methodology for estimating both seismic and static settlements, criteria for acceptable foundation performance, importance of evaluation of cyclic softening of soft clay layers, and the challenges working with the regulatory agency. The results of our analyses indicate differential settlements of about 2 inches.

Department(s)

Civil, Architectural and Environmental Engineering

Appears In

International Conference on Case Histories in Geotechnical Engineering

Meeting Name

Seventh Conference

Publisher

Missouri University of Science and Technology

Publication Date

4-29-2013

Document Version

Final Version

Rights

© 2013 Missouri University of Science and Technology, All rights reserved.

Document Type

Article - Conference proceedings

File Type

text

Language

English

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Apr 29th, 12:00 AM May 4th, 12:00 AM

Estimating Seismic Settlements from Liquefaction and Cyclic Softening and Their Impact to Design of a School Building

Chicago, Illinois

Estimation of static and seismic settlements is critical for the design of a structure to assess whether the structure can tolerate given levels of total and differential settlements and angular distortion. The design of a public school building required the estimation of both liquefaction-induced settlement due to the presence of a potentially liquefiable layer, and settlement from cyclic softening of soft clay layers. Tolerable levels of differential settlements for the proposed school building were not to exceed 2 inches across the building. The soft clay had a plasticity index of 12, a liquid limit of 32, and SPT blow counts of less than 4. Recent publications do not consider this clay potentially liquefiable, but consider it susceptible to cyclic softening. In addition to the borings, in-situ vane shear testing and CPT soundings were conducted at the site to supplement the data for our analysis. Using published methods we conducted an assessment of the soft clay and calculated factors of safety against cyclic softening as low as 0.0. In-situ vane shear testing resulted in soil sensitivities ranging from 1.6 to 3.4. Using CPT data we conducted a cyclic softening analysis of the entire soil column to a depth of about 50 feet. This paper describes the encountered site conditions, methodology for estimating both seismic and static settlements, criteria for acceptable foundation performance, importance of evaluation of cyclic softening of soft clay layers, and the challenges working with the regulatory agency. The results of our analyses indicate differential settlements of about 2 inches.