Pore pressure coefficient in frozen soils

Chuangxin Lyu,Satoshi Nishimura,Gustav Grimstad

doi:10.1680/jgeot.21.00097

Chuangxin Lyu, Satoshi Nishimura + Show 1 more

Open Access

https://doi.org/10.1680/jgeot.21.00097

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Abstract

The Skempton pore pressure coefficient, B, is defined as the variation in pore pressure with the unit change in confining pressure under undrained conditions. The B parameter is an essential parameter to consider the coupled effects of solid–fluid compressibility and skeleton compressibility in a porous system. It is a key factor in exploring a possible definition of effective stress in frozen soil. However, limited experimental and theoretical research is available in the literature to give insight to the problem. Therefore, a series of B tests on frozen clay was conducted in this study. Results from these tests, along with tests on Ottawa sand, as available in the literature, are analysed considering the effect of the ice crystallisation mode on the skeleton stiffness. The measured B values were lower than expected compared with B values using models that consider single grain bulk stiffness. However, when the difference in bulk stiffness of ice and that of soil grains is considered, even an increase in pore volume, for an increase in fluid pressure, at constant Terzaghi effective stress is possible. The ‘pore stiffness’, which is different from the solid phase stiffness, can take a negative value and can be used to explain the low measured B values.

Highlights

INTRODUCTIONP-wave velocity for frozen Onsøy clay was measured using the experimental method suggested by Yun et al (2007) in order to estimate the unfrozen water saturation (UWS) defined as Sw = Vw/(Vw + Vi) in Fig. 1(b) and the skeleton stiffness
Frozen saturated soils generally consist of solid minerals, ice and water
The clay stiffness shows some influence on the B value of frozen soil, and a maximum variation of % 0·15 in the B value is suggested with the wide variation of clay stiffness

Summary

INTRODUCTION

P-wave velocity for frozen Onsøy clay was measured using the experimental method suggested by Yun et al (2007) in order to estimate the unfrozen water saturation (UWS) defined as Sw = Vw/(Vw + Vi) in Fig. 1(b) and the skeleton stiffness. This indicates that the grain coating model essentially deviates from reality, especially when it is applied to Onsøy clay. To the KT model, both equations (8) and (9) were used again to first update Ks with the variation of Sw. A set of equations (14)–(17) and (19)–(22) (in the Appendix) was adopted to calculate skeleton bulk modulus K at a given ice crystallisation mode (pore filling or grain coating).

DISCUSSION

Findings

CONCLUSIONS

À νg ð1 À νiÞ ð1 À 2νiÞ