Implementation and evaluation of a recently developed rate-dependent effective stress soil model 'MIT-SR'

Reliable modeling of rate-dependency in soil properties remains a major challenge for accurate solutions of many geotechnical problems. Although there are many sources of experimental data concerning rate dependent properties of clays, most pre-existing soil models have been found to have severe predictive limitations. Yuan (2016) developed a new elasto-viscoplastic model, MIT-SR, for rate-dependent behavior of clays. The model unifies the existing elasto-plastic framework from prior MIT soil models (3-D surface system and generalized hysteretic formulation) with a physically-based evolution law that attributes the macroscopic viscoplastic strain to an internal strain rate related to the prior strain rate history. MIT-SR has the capability of describing a wide range of observed time-effects within a unified framework and resolves the long-stranding dilemma regarding creep effects at field scale (i.e., Hypothesis A vs B). This thesis implements MIT-SR model to evaluate strain rate effects on two longstanding geotechnical problems: insitu soil characterization from pressuremeter tests and long-term performance of embankments on soft clays. The first part of this research presents a review of the constitutive model framework and discuss the implementation and validation in non-linear finite element analyses using a User Defined Material (UMAT) in the ABAQUSTM program. Part two consists of the investigation of how disturbances (modeled using Strain Path framework; Baligh, 1985) and strain rate effects (modeled by MIT-SR) affect the results of the Full Displacement or cone-pressuremeter (FDPM) and self-boring pressuremeters (SBPM) for Resedimented Boston Blue Clay (RBBC). The results show that that disturbances of the stress field play a vital role in the interpretation undrained shear strength. For the FDPM case, using the same expansion rate, the disturbed NC RBBC can have as low as 40% of the undrained shear strength of the undisturbed NC RBBC. In contrast, for the SBPM case, the disturbed NC RBBC tend to have a slightly higher undrained shear strength (approximately 10%) than the undisturbed NC RBBC. The third part consists of a re-analysis of a well-instrumented test embankment built on a 40m deep layer of Boston Blue Clay. Finite element analyses of embankment performance are conducted using coupled consolidation with the MIT-SR effective stress model. The results were compared with previous numerical results using MIT-E3 presented by Ladd et al. (1994). Overall, MIT-SR contributes a significant improvement in predictions of settlements, but does not significantly improve predictions of lateral spreading. The overall results suggest that the dependent creep properties play only a secondary role in the performance of this particular test embankment.

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Civil and Environmental Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2016

Author dc:creator

• Sottile, Mauro Giuliano

Advisor dc:contributor.advisor

• Andrew J. Whittle.

• Civil and Environmental Engineering.

Statement dc:rights

• MIT theses are protected by copyright. They may be viewed, downloaded, or printed from this source but further reproduction or distribution in any format is prohibited without written permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/107071

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/107071