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Factors controlling pore pressure generation during K0 consolidation of laboratory tests

IP.com Disclosure Number: IPCOM000128044D
Original Publication Date: 1998-Dec-31
Included in the Prior Art Database: 2005-Sep-14
Document File: 7 page(s) / 24K

Publishing Venue

Software Patent Institute

Related People

Force, Erin A: AUTHOR [+3]

Related Documents

http://theses.mit.edu:80/Dienst/UI/2.0/Describe/0018.mit.theses/1998-270: URL

Abstract

During triaxial testing of cohesive soils, the specimen is consolidated to the desired stress state prior to either drained or undrained shear. Advances in technology have allowed more realistic simulation of field conditions, including continuous Ka consolidation rather than incremental hydrostatic consolidation. However it is necessary to select a conservatively slow consolidation strain rate to ensure negligible excess pore pressure which results in exceedingly long test durations. This experimental study of the factors controlling excess pore pressure generation provides insight for selecting more acceptable rates. An extensive experimental program was conducted on Resedimented Boston Blue Clay to study the behavior during constant rate of strain consolidation. Strain rate sensitivity was measured using the Wissa constant rate of strain device with tests ranging from 0.07 %/hr to 12.7 %/hr. The influence of specimen height and boundary drainage conditions was measured using a modified version of the MIT automated stress path triaxial apparatus. A special base with a removable needle probe was used to measure excess pore pressure in the middle of the test specimen. The results from tests without radial drainage firmly establish the relationship between excess pore pressure, hydraulic conductivity of the soil, strain rate, and height. Further, they support the use of equations based on a linear soil model developed for the CRS test to predict excess pore pressure. A second method of analysis for continuous loading based on equations for drained shear was also examined since it considers the presence of filter drains and the effectiveness of the drains. The results do not support the use of this theory in constant rate of strain tests and indicate a need for a more general model to account for radial drains. The research also provides several practical recommendations for testing. Regarding the CRS test, the current findings strongly support the use of the 'linear theory over the nonlinear theory in test interpretation. The results at higher strain rates indicate that the current ASTM guidelines for limits on the pore pressure need to be reduced and redefined in terms of hydraulic gradient in order to obtain correct hydraulic conductivities. Finally, the current consolidation strain rate of 0.1 %/hr for RBBC in the triaxial apparatus results in negligible pore pressures and may be increased by almost an order of magnitude. Thesis Supervisor: Dr. John T. Germaine Title: Principal Research Associate in Civil and Environmental Engineering

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FACTORS CONTROLLING PORE PRESSURE GENERATION DURING K0 CONSOLIDATION OF LABORATORY TESTS

by

Erin A. Force
Bachelor of Science in Civil and Environmental Engineering Tufts University, Medford, Massachusetts (1996)

Submitted in partial fulfillment of the requirements for the degree of Master of Science in Civil and Environmental Engineering

at the Massachusetts Institute of Technology

August 1998 [September 1998]
SIGNATURE OF author: [[signature omitted]]

Department of Civil and Environmental Engineering,

August 31, 1998
CERTIFIED BY: [[SIGNATURE OMITTED]]

Dr. John T. Germaine

Thesis Supervisor

ACCEPTED BY: [[SIGNATURE OMITTED]]

Prof. Joseph M. Sussman

Chairman, Departmental Committee on Graduate Studies ARCHIVES MASSACHUSETTS INSTITUTE OF TECHNOLOGY LIBRARIES OCT 26 1998

Massachusetts Institute of Technology Page 1 Dec 31, 1998

Page 2 of 7

Factors controlling pore pressure generation during K0 consolidation of laboratory tests

FACTORS CONTROLLING PORE PRESSURE GENERATION DURING K0 CONSOLIDATION Or, LABORATORY TESTS

By

Erin A. Force

Submitted to the Department of Civil and Environmental Engineering on August 31, 1995 in partial fulfillment of the requirements for the degree of Master of Science in Civil and Environmental Engineering

ABSTRACT

During triaxial testing of cohesive soils, the specimen is consolidated to the desired stress state prior to either drained or undrained shear. Advances in technology have allowed more realistic simulation of field conditions, including continuous Ka consolidation rather than incremental hydrostatic consolidation. However it is necessary to select a conservatively slow consolidation strain rate to ensure negligible excess pore pressure which results in exceedingly long test durations. This experimental study of the factors controlling excess pore pressure generation provides insight for selecting more acceptable rates.

An extensive experimental program was conducted on Resedimented Boston Blue Clay to study the behavior during constant rate of strain consolidation. Strain rate sensitivity was measured using the Wissa constant rate of strain device with tests ranging from 0.07 %/hr to 12.7 %/hr. The influence of specimen height and boundary drainage conditions was measured using a modified version of the MIT automated stress path triaxial apparatus. A special base with a removable needle probe was used to measure excess pore pressure in the middle of the test specimen.

The results from tests without radial drainage firmly establish the relationship between excess pore pressure, hydraulic conductivity of the soil, strain rate, and height. Further, they support the use of equations based on a linear soil model developed for the CRS test to pr...