## Doctoral Dissertations

Spring 1991

Dissertation

Engineering

#### Degree Name

Doctor of Philosophy

Jean Benoit

#### Abstract

Self-boring pressuremeter (SBPM) tests were conducted at Interstate I-95 in Portsmouth, New Hampshire and Hamilton Air Force Base in Novato, California, in clays of low and high plasticity, respectively. Both sites were subjects of significant previous research.

Field testing, conducted at and away from the toe of an existing highway embankment, indicated that the SBPM is capable of measuring horizontal stress changes and stress anisotropy when stress differences are more significant than the measurement error of the test equipment and error due to insertion disturbance effects. Finite element modeling was used to assess the embankment stress effects as a basis for comparison to the SBPM measured horizontal stresses. The SBPM was used to evaluate shear strength, shear modulus, the horizontal coefficient of consolidation, and other stress-strain parameters in both K$\sb{\rm o}$ and non-K$\sb{\rm o}$ stress conditions. SBPM shear strength was found to be significantly greater than field vane results at Pease AFB, however, SBPM and vane results were similar at Hamilton AFB. These results seem to indicate that clays which mobilize peak strength at high strain are better suited to SBPM shear strength measurement than clays that peak at low strain.

A 9-arm Cambridge SBPM was used for the field testing which allowed improved definition of cavity deformation compared to conventional 3-arm versions. The 9-strain arms of the probe were found to be useful in predicting the trend of shear strength with depth. The results from the extra arms also suggest that the effect of deviation from plane strain conditions due to the limited length of the probe may not affect shear strength results to the extent previously reported.

Laboratory testing was conducted to assess mechanical characteristics and environmental effects on the SBPM. Findings from these tests facilitated development of a method of assessing excess pore pressures due to SBPM deployment and improvements to conventional membrane stiffness correction necessary for accurate horizontal stress determination.

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