Assessment of blasting operations effects during highway tunnel construction

Blasting operations are one of the fundamental parts of daily civil engineering. Drilling and blasting still remain the only possible ways of tunnelling in very adverse geological conditions. However, this method is a source of various disadvantages, the main one being tremors propagating through the geological environment which not only affect buildings, but also disturb the comfort of living in the vicinity of the source. Designing this procedure is mostly done using standardized empirical relations. This article shows the possibility of using a FEM technique in predicting blast effects. This approach is demonstrated in a simple case study on the impact of blasting operations on steel pipes

NUMERIČKA STUDIJA MEHANIKE LOMA OKO MINSKIH BUŠOTINA TE ISTRAŽIVANJE POJAVE DISKONTINUITETA NA UZORKU TAKVIH LOMOVA

The mechanism of rock fragmentation around blastholes is of prior importance in the evaluation of drilling and blasting performance in open pit and underground mines. This paper aims to numerically investigate the crack propagation mechanism around a single blasthole using the distinct element method (DEM). In this study, two specimens with different borehole diameters were considered and the effects of the stress waves on their cracking mechanism were simulated. To validate the numerical model, the length of the radial cracks around each blasthole was measured and compared against an analytical fracture mechanics model. The fractured zones around the blasthole were also compared against previous experimental tests and good agreement was observed. The effect of a single discontinuity on the crack propagation mechanism was also studied and it was found that the discontinuity normal stiffness plays a significant role in the fractured zones around the blasthole. For low values of normal stiffness, the discontinuity surface acted as a free surface, and the shock wave was significantly reflected, while at high values of normal stiffness, cracks propagate across the discontinuity surface.Mehanika loma stijena oko minskih bušotina važan je čimbenik u ocjeni varijabli bušenja i miniranja, bilo na površini ili pod zemljom. U radu je numerički ispitana mehanika širenja lomova u blizini jedne takve bušotine uporabom metode diskretnih elemenata. Simulirana su dva uzorka različitih promjera bušotina te način širenja tlačnih valova i nastanak pukotina. Numerički model provjeren je mjerenjem dužine radijalnih pukotina oko bušotine te usporedbom dobivenih vrijednosti s analitičkim modelom mehanike loma. Zone pucanja oko bušotine uspoređene su s prethodnim eksperimentalnim testovima te je opaženo dobro podudaranje. Također je istražen i utjecaj pojedinačnoga diskontinuiteta na širenje pukotina te je utvrđeno kako čvrstoća diskontinuiteta ima veliku ulogu u opisanim zonama lomova oko bušotina. Kod nižih vrijednosti čvrstoće zone diskontinuiteta djeluju kao slobodne zone gibanja s kojih se tlačni valovi uglavnom reflektiraju. Zone veće čvrstoće ne sprječavaju pukotine da prolaze kroz njih

ASSESSMENT OF AIR OVERPRESSURE FROM BLASTING USING COMPUTATIONAL FLUID DYNAMICS

Air overpressure is a shock wave that occurs when explosives detonate and travel through the air. This can cause damage and annoyance in mining blasts, making it a significant concern for the surroundings of the operation. Currently, the cube root scale distance is used to predict air overpressure, but this method has limitations. To accurately determine air overpressure behavior, a new method is needed. Computational fluid dynamics (CFD) is a reliable and advanced technique that can simulate and solve complex physical problems, including the behavior of air overpressure. In this thesis, two techniques, the bursting balloon, and total pressure boundary, have been used to create numerical models for air overpressure. In the bursting balloon technique, a compressed closed volume is released, creating a pressure wave that is analyzed while it travels from the source. In the total pressure boundary technique, a time vs pressure curve is used as input against a surface and then released. Both techniques have been used to model a signature hole, while the total pressure boundary technique has also been used to model a blasting pattern composed of 21 blasting holes. These models only consider the physical interaction among the elements of fluid motion without including any chemical reactions from the explosives. To reduce computational time, a simplified simulation is key, as the simulation can run from minutes to days, weeks, or months

An investigation of stress wave propagation through rock joints and rock masses

Tese de doutoramento. Engenharia Civil. Faculdade de Engenharia. Universidade do Porto, Laboratório Nacional de Engenharia Civil. 201

Mathematical Problems in Rock Mechanics and Rock Engineering

With increasing requirements for energy, resources and space, rock engineering projects are being constructed more often and are operated in large-scale environments with complex geology. Meanwhile, rock failures and rock instabilities occur more frequently, and severely threaten the safety and stability of rock engineering projects. It is well-recognized that rock has multi-scale structures and involves multi-scale fracture processes. Meanwhile, rocks are commonly subjected simultaneously to complex static stress and strong dynamic disturbance, providing a hotbed for the occurrence of rock failures. In addition, there are many multi-physics coupling processes in a rock mass. It is still difficult to understand these rock mechanics and characterize rock behavior during complex stress conditions, multi-physics processes, and multi-scale changes. Therefore, our understanding of rock mechanics and the prevention and control of failure and instability in rock engineering needs to be furthered. The primary aim of this Special Issue “Mathematical Problems in Rock Mechanics and Rock Engineering” is to bring together original research discussing innovative efforts regarding in situ observations, laboratory experiments and theoretical, numerical, and big-data-based methods to overcome the mathematical problems related to rock mechanics and rock engineering. It includes 12 manuscripts that illustrate the valuable efforts for addressing mathematical problems in rock mechanics and rock engineering

Master of Science

thesisAn ever-present challenge at most active mining operations is controlling blastinduced damage beyond design limits. Implementing more effective wall control during blasting activities requires (1) understanding the damage mechanisms involved and (2) reasonably predicting the extent of blast-induced damage. While a common consensus on blast damage mechanisms in rock exists within the scientific community, there is much work to be done in the area of predicting overbreak. A new method was developed for observing near-field fracturing with a borescope. A field test was conducted in which a confined explosive charge was detonated in a body of competent rhyolite rock. Three instrumented monitoring holes filled with quick-setting cement were positioned in close proximity to the blasthole. Vibration transducers were secured downhole and on the surface to measure near-field vibrations. Clear acrylic tubing was positioned downhole and a borescope was lowered through it to view fractures in the grout. Thin, two-conductor, twisted wires were placed downhole and analyzed using a time-domain reflectometer (TDR) to assess rock displacement. Fracturing in the grout was easily observed with the borescope up to 3.78 m (12.4 ft) from the blasthole, with moderate fracturing visible up to 2.10 m (6.9 ft). Measured peak particle velocities (PPV) at these distances were 310 mm/s (12.2 in./s) and 1,490 mm/s (58.5 in./s), respectively, although no fracturing was observed near the depth of the vibration transducers located 3.78 m (12.4 ft) from the blasthole. TDR readings were difficult to interpret but indicated rock displacement in two of the monitoring holes. Three methods were used to predict the radial extent of tensile damage around the blasthole: a modified Holmberg-Persson (HP) model, a shockwave transfer (SWT) model, and a dynamic finite element simulation using ANSYS AutodynTM. The extent of damage predicted by the HP and SWT models is similar to field measurements when using static material properties of the rock, but is underestimated using dynamic material properties. The Autodyn™ model significantly overpredicted the region of damage but realistically simulated the zones of crushing and radial cracking. Calibration of material parameters for the AutodynTM model would be needed to yield more accurate results

High fidelity fluid-structure turbulence modeling using an immersed-body method

There is an increasing need for turbulence models with fluid-structure interaction (FSI) in many industrial and environmental high Reynolds number flows. Since the complicated structure boundaries move in turbulent flows, it is quite challenging to numerically apply boundary conditions on these moving fluid-structure interfaces. To achieve accurate and reliable results from numerical FSI simulations in turbulent flows, a high fidelity fluid-structure turbulence model is developed using an immersed-body method in this thesis. It does this by coupling a finite element multiphase fluid model and a combined finite-discrete element solid model via a novel thin shell mesh surrounding solid surfaces. The FSI turbulence model presented has four novelties. Firstly, an unsteady Reynolds-averaged Navier-Stokes (URANS) k−ε turbulence model is coupled with an immersed-body method to model FSI by using this thin shell mesh. Secondly, to reduce the computational cost, a log-law wall function is used within this thin shell to resolve the flow near the boundary layer. Thirdly, in order to improve the accuracy of the wall function, a novel shell mesh external-surface intersection approach is introduced to identify sharp solid-fluid interfaces. Fourthly, the model has been extended to simulate highly compressible gas coupled with fracturing solids. This model has been validated by various test cases and results are in good agreement with both experimental and numerical data in published literature. This model is capable to simulate the aerodynamic and hydrodynamic details of fluids and the stress, vibration, deformation and motion of structures simultaneously. Finally, this model has been applied to several industrial applications including a floating structure being moved around by complex hydrodynamic flows involving wave breaking; a blasting engineering simulation with shock waves, fracture propagation, gas-solid interaction and flying fragments; fluid dynamics, flow-induced vibrations, flow-induced fractures of a full-scale vertical axis turbine. Some useful conclusions, e.g. how to model them, how to make them stable and how to predict when they will break, are obtained by this FSI model when applying it to the above applications.Open Acces