160 research outputs found
Comprehensive research on the deformation mechanics, support design and health assessment of mountain tunnel in soft rock
No full textNagasaki University (長崎大学)博士(工学)長崎大学学位論文 学位記番号:博(工)甲第44号 学位授与年月日:平成29年9月20日Nagasaki University (長崎大学), 博士(工学) (2017-09-20)doctoral thesi
Comprehensive research on the deformation mechanics, support design and health assessment of mountain tunnel in soft rock
No full textResearch progress and prospect of interaction between rock engineering and geo-environments
No full textSimulation for non-point source pollution based on QUAL2E in the Jinghe River, Shaanxi Province, China
No full textWang, J., Huo, A., Hu, A., Zhang, X., & Wu, Y. (March-April, 2017). Simulation for non-point source pollution based on QUAL2E in the Jinghe River, Shaanxi Province, China. Water Technology and Sciences (in Spanish), 8(2), 117-126.
Water pollution in river basins is significantly influenced by point-source and non-point-source pollutants. Compared with point-source pollutants, the identification and quantification of non-point-source pollutants are critical but difficult issues in water environmental pollution studies. The Jinghe River is one of the main tributaries of the Weihe River. However, the non-point-source pollution of this river is not well understood. In order to analyze the sources of pointand non-point loads to river water, the river water quality model QUAL2E and Principal Component Analysis (PCA) & Factor Analysis (FA) were applied simultaneously to calculate the point- and non-point-source loads of ammonia nitrogen and nitrate nitrogen, respectively, in dry and wet seasons from 2002 to 2007. The results show that NO3 - -N can be associated with point-source pollution, such as domestic sewage in dry seasons, but non-point-source pollution generated by precipitation in wet seasons. NH4 +-N can be associated with point-source pollution throughout the year. The methods applied in this research provide reliable results on non-point-source pollution caused by storm runoff
Estimating the support effect of energy-absorbing rock bolts based on the mechanical work transfer ability
No full textAn interaction model is proposed to describe the interaction between the energy-absorbing rock bolt and the rock mass. Based on the plane-strain axial symmetry assumption and the incremental theory of plasticity, the equilibrium equations and compatibility equations of rock mass, as well as the response of the energy-absorbing rock bolt are deduced theoretically. The proposed method was programmed in a Visual Basic environment, and a semi-analytical solution for the coupling model was achieved. The reinforcement mechanism of the energy-absorbing rock bolt in conventional tunneling is clearly demonstrated through an illustrative case study. The reinforcement effect of the energy-absorbing rock bolt under different conditions was estimated quantitatively, and its mechanical work transfer ability is presented. In addition, the validity of the proposed method was verified through numerical simulations. Finally, a number of derivative cases were investigated to reveal the influence of the bolt and rock properties on the reinforcement effect and the bolt work transferred on the rock mass. In the case of higher in-situ stress or low-strength rock mass, the support effect of the energy-absorbing rock bolt is significantly improved, and the bolt absorbs more energy. Increasing the bolt installation density could always be helpful for the stabilization of the surrounding rock mass. However, additional rock-bolt length could hardly affect ground reinforcement because the bolt section embedded in the elastic region of the rock mass could barely help to constrain the elastic displacement release. The bolt should be installed no later than the stage of critical inner pressure, namely when the plastic region occurs
Numerical Simulation of Natural Gas Hydrate Exploitation in Complex Structure Wells: Productivity Improvement Analysis
No full textAbout 90% of the world’s natural gas hydrates (NGH) exist in deep-sea formations, a new energy source with great potential for exploitation. There is distance from the threshold of commercial exploitation based on the single well currently used. The complex structure well is an efficient and advanced drilling technology. The improvement of NGH productivity through various complex structure wells is unclear, and there is no more complete combing. Thus, in order to evaluate their gas production characteristics, we establish a mathematical model for exploitation of NGH, and then 13 sets of numerical models based on the geological parameters of the Nankai Trough in Japan are developed and designed, including a single vertical well, a single horizontal well, 1~4 branch vertical wells, 1~4 branch horizontal wells, and 2~4 branch cluster horizontal wells. The research results indicate that wells with complex structures represented by directional wells and multilateral wells can significantly increase the area of water and gas discharge, especially cluster wells, whose productivity can be increased by up to 2.2 times compared with single wells. Complex structural wells will play an irreplaceable role in the future industrialization of NGH
The nature frequency identification of tunnel lining based on the microtremor method
No full textMany tunnels all over the world have been in service for several decades, which require effective inspection methods to assess their health conditions. Microtremor, as a type of ambient vibration originating from natural or artificial oscillations without specific sources, has attracted more and more attentions in the recent study of the microtremor dynamic properties of concrete structures. In this study, the microtremors of the tunnel lining were simulated numerically based on the Distinct Element Method (DEM). The Power Spectra Density (PSD) of signals obtained from numerical simulations were calculated and the nature frequencies were identified using the peak-picking method. The influences of the rock-concrete joint, the rock type and the concrete type on the nature frequencies were also evaluated. The results of a comprehensive numerical analysis show that the nature frequencies lower than 100 Hz can be identified. As the bonding condition becomes worse, the nature frequencies decrease. The nature frequencies change proportionally with the normal stiffness of the rock-concrete joint. As the concrete grade decreases, the third mode of frequency also decreases gradually while the variation of the first two modes of frequencies can hardly be identified. Additionally, the field microtremor measurements of tunnel lining were also carried out to verify the numerical results
A modified strain-softening model with multi-post-peak behaviours and its application in circular tunnel
No full textA large number of laboratory experiments have shown that the rocks in post-peak state present strain-softening behaviour under low confining pressure, and gradually evolved into elastic-perfectly plastic with the increasing of confining pressure. Neither the elastic-perfectly plastic model nor the strain-softening model can accurately describe the behaviour of rock mass surrounding the deep buried excavations. In this paper, a modified strain-softening model was proposed to describe the non-linear evolution of residual strength under the influence of confining pressure. The new model can realize the gradually transition from strain-softening behaviour to elastic-perfectly plastic behaviour with the increasing of confining pressure. The equivalent residual strength was defined to quantify the strength of rocks in post-peak stage. The parameters involved in the model were estimated via non-linear regression analysis upon a series of stress-strain curves. Based on the plane strain axial symmetry assumption and the incremental theory of plasticity, equilibrium equations and compatibility equations of rock mass around a circular tunnel were deduced. The equations were implemented in the Visual Basic development environment, and a semi-analytical solution was obtained. The influence of post-failure behaviour of rock mass was demonstrated through an illustrative case. The distributions of stress, displacement and transitional strength around the tunnel were presented. The differences between the elastic-perfectly plastic model, the strain-softening model and the new model were estimated quantitatively. In addition, the validity of semi-analytical solution was verified by numerical simulations. Parameters analysis showed that the tunnel convergence was influenced by the post-peak behaviour of rock mass dramatically
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