Microstructural Evolution alongside the Strength Degradation of Soft Marine Soil under Cyclic Loading
Publication: International Journal of Geomechanics
Volume 22, Issue 7
Abstract
This paper presents an investigation on the microstructural evolution alongside the strength degradation of the soft marine soil under T-bar cyclic penetration. The marine soil that was recovered from the seabed in deep-water areas in the South China Sea can be representative of the characteristics of typical soft marine clay in this water area. The microstructure of clayed soils is characterized by particle-constituted aggregates and interaggregate pores, which is commonly considered to predominate the strength of soils. To quantitatively capture the evolving microstructural characteristics of the soil during loading, a new indicator (i.e., probability entropy, H) is proposed based on statistics of the alteration in aggregate size and orientation of the soil. With the aid of the new indicator, the soil microstructural evolution is further evaluated and associated with strength degradation during the continuous T-bar cyclic loading course. In addition, through a comparison between the intact marine soil samples and reconstituted ones, the effect of microstructural cementation of marine soil is examined on the shearing strength during the cyclic loading. The two types of soil samples show a significantly different evolving trend of microstructure. The probability entropy of intact soil decreases, while that of reconstituted soil increases. Thus, the intact soil exhibits a higher probability degree of entropy change than does the reconstituted soil. This result may provide a plausible explanation for the difference in strength between the intact soils and reconstituted ones, even if they have been subjected to the same consolidation stress condition. The novel quantitative method to evaluate the soil microstructure can be further applied to understand the mechanism of strength degradation of soft marine soils. This will provide a deeper insight to the engineering properties of those marine soils, which will facilitate a precise design for practical offshore foundations in deep waters.
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Acknowledgments
The authors would like to acknowledge the financial support from the National Natural Science Foundation of China, Nos. 51890912 and 51879035.
Notation
The following symbols are used in this paper:
- A,B
- weight of Hd and Hθ in total probability entropy;
- a
- load cell area ratio;
- AR
- area ratio of T-bar penetrometer to probe shaft and T-bar penetrometer;
- d
- equivalent diameter of soil aggregate;
- e
- void radio;
- Gs
- specific gravity;
- Hd
- probability entropy of aggregate dimension;
- Htot
- total probability entropy of microstructure;
- Hθ
- probability entropy of aggregate orientation;
- IP
- liquid index (%);
- M
- total number of soil aggregates;
- m
- constant number in normalized cyclic strength;
- m
- total number of angle intervals;
- N
- cycle number;
- n
- total number of size intervals;
- pcyc,N
- penetration resistance at the Nth cycle (kPa);
- pini
- initial penetration resistance (kPa);
- pm
- measured penetration resistance (kPa);
- pT-bar
- T-bar penetration resistance (kPa);
- t
- cyclic strength degradation index;
- u
- measured pore water pressure (kPa);
- w
- moisture content (%);
- WL
- liquid limit (%);
- Wp
- plastic limit (%);
- σv
- vertical overburden stress (kPa); and
- θ
- angle of the major axis of the soil aggregate.
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Published In
International Journal of Geomechanics
Volume 22 • Issue 7 • July 2022
Copyright
© 2022 American Society of Civil Engineers.
History
Received: Jun 8, 2021
Accepted: Jan 11, 2022
Published online: May 4, 2022
Published in print: Jul 1, 2022
Discussion open until: Oct 4, 2022
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