An Improved Form of 2D SPH Method for Modeling the Excavation Damage of Tunnels Containing Random Fissures

The excavation damage of deep tunnels is one of the most important factors contributing to the failure of tunnel structures. In order to investigate the influence of tunnel shapes and fissure geometries, the kernel function in the traditional SPH method has been improved, which can realize the brittle fracture characteristics of particles and can be called the Improved Kernel of Smoothed Particle Hydrodynamics (IKSPH-2D). Meanwhile, the random fissure generation method in IKSPH has been put forward. Different tunnel shapes, fissure geometries, and locations are considered during the simulation of tunnel excavation, and results show that (1) the typical “V”-shaped shear damage zones appear after the tunnel excavation, which is consistent with engineering practice. Meanwhile, tunnel excavation also has an “activating” effect on the preexisting fissures. (2) The stability of circular-shaped tunnel is the best, while horseshoe shaped tunnel is worse, and the “U”-shaped tunnel is the worst. (3) Fissures with small and large dip angles have the greatest influence on the stability of tunnel excavation. With the increase of fissure numbers and lengths, the tunnel tends to be instable. (4) The IKSPH method gets free from traditional grids in FEM, which can dynamically reflect the fracture processes of tunnel excavation. Meanwhile, developing 3D IKSPH parallel program will be the future directions.

Insights into Unloading Relaxation Mechanism of Columnar Jointed Basalt at the Baihetan Left Dam Foundation

Columnar jointed basalt (CJB), characterized by unique geometric and geological properties, poses a great challenge for geotechnical designs due to its unloading relaxation and damage during excavation. In this paper, the geometrical structure and field failures of the CJB exposed on Baihetan left dam foundation were briefly presented. A systematic field test was conducted to study the excavation damage zone of the CJB on the dam foundation using ultrasonic P wave measurements. The excavation damage zone of the CJB not only showed time-dependent damage in depth but also showed spatially inhomogeneous distribution in depth. Corresponding three-dimensional numerical analysis was also carried out to analyze the unloading relaxation mechanism of CJB. The unloading relaxation of CJB on dam foundation was mainly caused by the joint opening under tension stress during excavation. The difference of excavation damage zone of the CJB located in different test zones was also discussed in this article.

Comparison of DFN Modelled Microfracture Systems with Petrophysical Data in Excavation Damaged Zone

Physical and petrographic properties of drill core specimens were determined as a part of investigations into excavation damage in the dedicated study area in the ONKALO® research facility in Olkiluoto, Western Finland. Microfractures in 16 specimens from two drillholes were analysed and used as a basis for fractal geometry-based discrete fracture network (DFN) modelling. It was concluded that the difference in resistivity between pegmatoid granite (PGR) and veined gneiss (VGN) specimens of similar porosity was likely due to differences in the types of microfractures. This hypothesis was confirmed from microfracture analysis and simulation: fractures in gneiss were short and mostly in one preferred orientation, whereas the fractures in granite were longer and had two preferred orientations. This may be due to microstructure differences of the rock types or could suggests that gneiss and granite may suffer different types of excavation damage. No dependencies on depth from the excavated surface were observed in the geometric parameters of the microfractures. This suggests that the excavation damaged zone cannot be identified based on the changes in the parameters of the microfracture networks, and that the disturbed layer observed by geophysical methods may be caused by macro-scale fractures.

Distribution Reliability Using Machine Learning

This paper describes the reliability assessment of a distribution pipeline network in the city of Regina, Saskatchewan. The results of the assessment help prioritize integrity program activities by complementing existing programs based on leak surveys, ground movement events, and excavation damage.