Study on the vibration effect on operation subway induced by blasting of an adjacent cross tunnel and the reducing vibration techniques

The Hongshan road tunnels in Nanjing cross up the metro Line 1 tunnel, the closest distance between Hongshan road tunnels and subway tunnels is only 4.14 m. In order to ensure the safety of the subway structure during the Hongshan road tunnels group excavation blasting, the vibration of the subway tunnel was monitored real time. The monitoring results showed that the main frequency distributions of the radial, tangential and vertical vibration of subway tunnel were significantly different. The main frequency and energy of tunnel vibration is mainly concentrated in the high frequency band. This characteristic is very beneficial for the protection of the subway tunnel and catenary. A series of techniques to reduce the vibration were taken during tunnel excavation blasting, which reduced the impact of the blasting vibration to subway tunnel and catenary, and ensured the operation subway safety. The vibration of subway tunnel can be controlled within a certain safety standard with proposed of reducing vibration techniques. It is shown that real-time monitoring and the comprehensive application of the reducing vibration technique are able to guarantee the security of adjacent cross operation subway, which provides references for similar tunnel projects

NUMERICAL APPROXIMATION OF THE GROUND REACTION AND SUPPORT REACTION CURVES FOR UNDERGROUND LIMESTONE MINES

Pillar stability has been a matter of study for the last 70 years. The determination of pillar strength had taken different solutions and approaches over that time. This research has led to numerous empirical formulations that have reduced the number of pillar failures worldwide. However, new numerical approaches are being studied. In the last 20 years, the Ground Reaction Curve concept has been examined as a way of understanding the convergence of the rock-mass. Although the Ground Reaction Curve was first introduced in the civil tunneling industry, several authors have introduced the Ground Reaction Curve concept as an approach for an integrated pillar design methodology. Furthermore, the intersection of the Ground Reaction Curve and Support Reaction Curves can be used to determine the appropriate support systems for underground excavations. The man-made support structures (i.e., pumpable cribs, concrete cribs, and wood cribs) in a mine will have a unique Support Reaction Curve. Literature suggests that the pillar structures in underground mines can also be regarded as support structures and their reaction to tributary and or abutment stress can be viewed with respect to the ground reaction curve at the pillar location. In this study, an underground limestone mine was instrumented with borehole pressure cells and roof extensometers. This thesis presents a series of two-dimensional and three-dimensional finite element numerical models that were used to estimate the Ground Reaction Curve and the Support Reaction Curve for a pillar. The numerical models consider the stages of development and benching around the pillar. Numerical results are compared with field measurements of the study case located in northern Kentucky

Rock-burst occurrence prediction based on optimized naïve bayes models

Rock-burst is a common failure in hard rock related projects in civil and mining construction and therefore, proper classification and prediction of this phenomenon is of interest. This research presents the development of optimized naïve Bayes models, in predicting rock-burst failures in underground projects. The naïve Bayes models were optimized using four weight optimization techniques including forward, backward, particle swarm optimization, and evolutionary. An evolutionary random forest model was developed to identify the most significant input parameters. The maximum tangential stress, elastic energy index, and uniaxial tensile stress were then selected by the feature selection technique (i.e., evolutionary random forest) to develop the optimized naïve Bayes models. The performance of the models was assessed using various criteria as well as a simple ranking system. The results of this research showed that particle swarm optimization was the most effective technique in improving the accuracy of the naïve Bayes model for rock-burst prediction (cumulative ranking = 21), while the backward technique was the worst weight optimization technique (cumulative ranking = 11). All the optimized naïve Bayes models identified the maximum tangential stress as the most significant parameter in predicting rock-burst failures. The results of this research demonstrate that particle swarm optimization technique may improve the accuracy of naïve Bayes algorithms in predicting rock-burst occurrence. © 2013 IEEE

ESTIMATING THE EFFECTS OF BLASTING VIBRATIONS ON THE HIGH-WALL STABILITY

The stability of the high-walls is one of the major concerns for open pit mines. Among the various factors affecting the stability of high-walls, blast vibrations can be an important one. In general, worldwide the established respective government regulations and industry standards are used as guidance to determine the maximum recommended levels of the peak particle velocity and frequency from the blast to avoid any effects on the structures around the mining project. However, most of the regulations are meant for buildings or houses and do not concern high-walls. This thesis investigates the response of high-walls under the effects of vibrations from mine blasting. In this research, the relationship between the high-wall response, the geometry of the slope, the frequency and the amplitude, of the ground vibration produced by blasting, is explored using numerical models in 3DEC. The numerical models were calibrated initially with data collected using seismographs installed in a surface mine operation and recording vibrations produced by an underground mine drill and blast operation. Once the calibration was accomplished, a parametric study was developed to explore the relationships between various parameters under study and its impact on the stability of high-walls

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

Proceedings of the 8th International Conference on Civil Engineering

This open access book is a collection of accepted papers from the 8th International Conference on Civil Engineering (ICCE2021). Researchers and engineers have discussed and presented around three major topics, i.e., construction and structural mechanics, building materials, and transportation and traffic. The content provide new ideas and practical experiences for both scientists and professionals