Prediction of Shallow Footing Settlements on Cohesionless Materials from Seismic Testing
Abstract
The practice of predicting settlements of shallow foundations has evolved in the past 50 years, but the basic principles and obstacles in making such predictions remain the same. First, the engineer must accurately characterize the soil beneath the proposed foundation. Second, the engineer must choose an analytical technique to model the behavior of that soil under the load. Since settlement, rather than bearing capacity, is most often the controlling design factor (Schmertmann, 1970), the accuracy with which an engineer estimates the settlement directly bear on the design and cost of the foundation. The practice of estimating settlements of shallow footings on cohesionless soils has historically been over-conservative. The goal of this study is to investigate how well measured soil stiffnesses determined by field and laboratory dynamic tests predict the settlement of a shallow footing on a granular soil. The stiffness, or modulus, of the soil was estimated based on SPT tests, field seismic tests (SASW and crosshole tests), and dynamic laboratory tests (torsional resonant column tests). The moduli from these tests were then used in two different settlement analysis techniques, Schmertmann's method and a finite element analysis, to predict the settlement of the footing and the soil mass beneath it. A series of field load tests were performed and settlements were measured at the top of the footing and at several depths beneath it. These field measurements are compared to the predicted values. The results indicate that seismic field and dynamic laboratory tests can be effectively used to conduct a site investigation for the purposes of predicting the settlement potential of this shallow footing on the nonplastic sandy silt. Very importantly for working load levels, the seismic-based settlement predictions were more accurate than the SPT-based predictions.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 2005
- Accession Number
- ADA442251
Entities
People
- Andrew J. Sheehan
Organizations
- University of Texas at Austin