Modelling the response of chemically degraded carbonate sands

ABSTRACT

Carbonate sands are prone to chemomechanical degradation in the form of particle size reduction and change in particle morphology due to their biogenic formation. Such degradation consequently alters strength and stiffness of the sand. Therefore, it is essential to model the mechanical response of carbonate sand accounting for the particle size variation and its impact on the strength parameters. The present study explores a possible avenue based on experimental observations and phenomenological understanding to represent those parameters as the functions of index properties, which are affected by the grain size and shape variation. A set of chemically treated carbonate sand specimens having different grain size distributions was examined; the mechanical responses, especially the strength, stiffness and critical state, were determined via drained triaxial compression tests with different initial packing conditions. The experiments show that variation in the granular packing due to dissolution influences the shear strength. Based on the obtained results, a simple constitutive modelling framework is proposed to capture the shear strength of degraded carbonate sand in reference to the undegraded sand sample while accounting for the initial grain size distributions and packing. Finally, a discussion is presented to augment the model for predicting the coupled chemomechanical deformation response.

KEYWORDS:

• Relative density
• grains size distribution
• carbonate sand
• stress–dilatancy relation
• constitutive modelling

Acknowledgments

The second author wishes to thank DORD IIT Kanpur (grant no. IITK/CE/2014156) for the financial support for this research on carbonate sand.

Symbols and notations

$C$	=	Non-dimensional constant related to bulk modulus
$D^e$	=	Elastic stiffness matrix
$D_{ri}$	=	Initial relative density
$e$	=	Current void ratio
$e_i$	=	Initial void ratio
$e_{max}$	=	Maximum void ratio
$e_{min}$	=	Minimum void ratio
$e_{min0}$	=	Minimum void ratio of the reference material
${\epsilon }_v,{\epsilon }_s$	=	Volumetric and shear strain
${\eta }_y$	=	Hardening parameter
${\eta }_p$	=	Limiting stress ratio
$K$	=	Bulk modulus
$m$	=	Constant for contact between particles
$M$	=	Material constant for controlling dilatancy
$\mu$	=	Poisson’s ratio
$p$'	=	Mean stress
$p_r$	=	Reference pressure
$q$	=	Deviatoric stress
$\psi$	=	Helmholtz free energy function
$X_d$	=	Non-dimensional degree of dissolution

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by DORD IIT Kanpur [grant no. IITK/CE/2014156].