A COMPARISON OF PRINCIPAL STRESS EVOLUTION IN CYLINDRICAL AND PERICLINAL BUCKLE FOLDS USING 3D FINITE ELEMENT ANALYSIS

This study investigates whether the assumption of cylindrical folding is appropriate when considering the effective stress evolution during buckle fold initiation and growth. A 3-D finite element modeling approach is used to simulate buckling of a Maxwell viscoelastic layer while including the influence of pore pressure. Two model geometries (cylindrical and periclinal) are considered, and their influence on the stress evolution are analyzed while keeping all other material parameters fixed. The results from the simulation show that the fold geometry has a significant influence on the magnitudes and orientations of the principal stresses.

In the inner arc of the pericline, the magnitudes of σ₃, σ_2, and σ₁ are much more compressive compared to the inner arc of the cylindrical fold. For higher amplitude folds the pericline is more likely to develop tensile stresses in the outer arc than the cylindrical fold. σ₁ and σ₃ are parallel to the fold profile in the cylindrical fold and σ₂ is oriented parallel to hinge line of the fold. The principal stress orientations in the pericline vary along the entire length of the fold, and a complete 90 degree rotation of all three principal stresses can be observed at certain points along the hinge. The differences in magnitudes and orientations of the principal stresses highlight the importance of choosing the correct fold geometry when evaluating implications the principal stresses have on fracture initiation. An oversimplified geometry can lead to an incorrect estimation of the timing of fracture initiation as well as fracture orientation. It is concluded that while the stress distribution in the cylindrical folds and periclinal folds are similar, the magnitudes and orientations of the stresses are very different, and thus the assumption of cylindrical folding is not appropriate when conducting a mechanical analysis of the stress evolution.