Interpretation of T-Bar Penetration Data in Two-Layer Clays
Publication: International Journal of Geomechanics
Volume 23, Issue 11
Abstract
This paper explores the interpretation of undrained shear strength and layer boundaries from T-bar penetration resistance profiles in layered soft–stiff and stiff–soft clay sediments. The proposed interpretation framework was based on extensive parametric large deformation finite-element analyses by varying the strength ratio between the two layers, and the relative thickness of the top layer. For soft–stiff clay deposits, the squeezing mechanism dominated the behavior when the T-bar approached the layer interface. No soil plug was trapped at the base of the T-bar. The interface can be identified as the kink point with a sharp increase in resistance profile sensing the stiff layer. For stiff–soft clay deposits, a stiff soil plug was trapped at the base of the T-bar and penetrated into the soft layer. Resistance profiles dropped before reaching the layer interface being influenced by the soft layer. A minimum thickness of 25D was needed to mobilize the ultimate resistance of the top layer. The layer boundary can be identified as 4.2D above the kink point on the resistance profile in the bottom layer. The stabilized resistance in the bottom layer increased with increasing the strength ratio owing to the thicker stiff soil plug at the base of the T-bar.
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Data Availability Statement
All data, models, and codes generated or used during the study appear in the published article.
Acknowledgments
The research presented here was undertaken with support from the Australian Research Council (ARC) through the Discovery Grant DP140103997. The first author was the recipient of a University of Western Australia SIRF scholarship. The second author is an ARC Future Fellow and is supported by the ARC Project FT190100735. This support is gratefully acknowledged.
Notation
The following symbols are used in this paper:
- D
- diameter of a T-bar;
- d
- penetration depth of a T-bar from the soil surface to the invert of a penetrometer;
- E
- Young’s Modulus;
- h
- thickness of soil layers (h1 for a first or top layer);
- Nt,b
- resistance factor of a T-bar for a bottom layer in stiff–soft soil;
- Nt,u
- resistance factor of a T-bar for uniform soil;
- q
- net penetration resistance of a T-bar;
- su
- undrained shear strength of soil (su1 for a first or top layer and su2 for a second or bottom layer);
- t
- distance from the invert of a penetrometer to a soil–layer interface underneath;
- α
- T-bar surface roughness factor; and
- γ′
- effective unit weight of soil.
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Published In
International Journal of Geomechanics
Volume 23 • Issue 11 • November 2023
Copyright
© 2023 American Society of Civil Engineers.
History
Received: Jun 4, 2022
Accepted: May 22, 2023
Published online: Aug 30, 2023
Published in print: Nov 1, 2023
Discussion open until: Jan 30, 2024
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