Quantification of Hidden Whole-Field Stress Inside Porous Geomaterials Via Three-Dimensional Printing and Photoelastic Testing Methods

Quantification and visualization of the three-dimensional (3-D) whole-field stress distribution in porous geomaterials are significant for solving various subsurface engineering problems in which stress governs the deformation, fracture propagation, and fluid transport inside the materials. However, quantitatively characterizing the whole-field stress distribution inside 3-D porous geomaterials is challenging because of the complications involved in identifying and extracting the hidden structures and stress distribution. This paper presents a method for extracting and characterizing whole-field distributions of principal stress difference and shear stress inside a cubic model containing irregular pores, which are replicated using three-dimensional printing techniques to model the real complex porous structures of natural geomaterials. We combine frozen-stress, phase-shifting, and unwrapping methods to identify and characterize the whole-field distributions of principal stress difference and shear stress inside the pore structure. The unwrapped-algorithm-incorporated traditional phase-shifting approach is proposed to determine the stress fringe deviation around irregular pores. A comparison of numerical simulation and photoelastic tests shows that this method can visually and quantitatively characterize the whole-field stress of a 3-D porous model. The stress distribution characterization and potential failure bands in the 3-D porous structure model subjected to uniaxial compression load are discussed, and findings indicate that potential shear fractures with high-concentration stress are formed before porous model failure, and 3-D annular zones with high stress appear around individual pores. The proposed method and results will support future work on uncovering the mechanism of crack propagation and shear fracture formation in reservoir geomaterials.