Influence of rock mass properties on tunnel inflow using hydromechanical numerical study

One of the primary geotechnical problems encountered during tunnel construction involves the inflow of groundwater into the tunnel. Heavy inflows make tunnel construction difficult and result in higher costs and delays in construction period. Therefore, it is essential to estimate the volume and rate of water inflow that is likely to appear in the tunnel. In this research, water inflow to the tunnel was calculated using numerical hydromechanical analysis. Effect of rock mass properties including fracture characteristics (normal and shear stiffness, hydraulic aperture, dilation angle, and fracture nonlinear behavior) on inflow was studied using a two-dimensional distinct element method. Results show that fracture properties play important role in inflow to the tunnel and must be considered in prediction of inflow to the tunnel. Based on numerical analysis results, inflow of groundwater into the tunnel increases with the increasing of normal and shear stiffness, dilation angle, and hydraulic aperture of rock mass fractures. The measured inflow with considering nonlinear fracture behavior was more than the calculated inflow with linear constitutive behavior.     

Numerical evaluation of liquefaction-induced damages in composite breakwaters and its application for performance-based improvement design

Breakwaters provide a calm sea basin for ships and protect harbor facilities by reflecting wave energy toward the open sea area. Their performance under environmental loadings is the main concern for coastal engineers. Liquefaction susceptibility of loose sediments of seabed threatens performance of these structures. The article investigates soil liquefaction effects on the seismic performance of Iran liquefied natural gas (LNG) composite breakwater. Performance-based design method, considering both grade of the breakwater and acceptable level of damages, was selected as design philosophy. Liquefaction-induced damages to the breakwater were determined by numerical analysis. Since the obtained level of deformations did not meet allowable damages, soil improvement against liquefaction was considered. Different improvement patterns were proposed based on distribution of pore pressure ratio (r_u) beneath the breakwater to control its seismic performance. This investigation revealed that the most important area for soil improvement is located near the toes of breakwater to control the slope instability and performance of the breakwater.     

Tectonic architecture through Landsat-7 ETM+/SRTM DEM-derived lineaments and relationship to the hydrogeologic setting in Siwa region, NW Egypt

Fracture zones on the Earth’s surface are important elements in the understanding of plate motion forces, the dynamics of the subsurface fluid flow, and earthquake distributions. However, good exposures of these features are always lacking in arid regions, characterized by flat topography and where sand dunes extensively cover the terrain. During field surveys these conditions, in many cases, hinder the proper characterization of such features. Therefore, an approach that identifies the regional fractures as lineaments on remotely-sensed images or shaded digital terrain models, with its large scale synoptic coverage, could be promising.In the present work, a segment tracing algorithm (STA), for lineament detection from Landsat-7 Enhanced Thematic Mapper Plus (ETM+) imagery, and the data from the Shuttle Radar Topographic Mission (SRTM) 30 m digital elevation model (DEM), has been applied in the Siwa region, located in the northwest of the Western Desert of Egypt. The objectives are to analyze the spatial variation in orientation of the detected linear features and its relation to the hydrogeologic setting in the area and the underlying geology, and to evaluate the performance of the algorithm applied to the ETM+ and the DEM data.Detailed structural analysis and better understanding of the tectonic evolution of the area could provide useful tools for hydrologists for reliable groundwater management and development planning. The results obtained have been evaluated by the structural analysis of the area and field observations. Four major vertical fracture zones were detected corresponding to two conjugate sets of strike-slip faults that governed the surface, and subsurface environments of the lakes in the region, and these correlate well with the regional tectonics.     

EXPERIMENTAL STUDY ON BED SCOUR IN A 90° CHANNEL BEND

1 INTRODUCTION Scouring in the bend ways leads to deep sections at the toe of the outer bank of the bend. The presenceof secondary currents and the greater depths at the outer bank cause high velocity along the outer bank.The high velocity and shear stres…     

Reliability upgrading of lifeline networks for post-earthquake serviceability

Efficient procedures for reliability upgrading of existing lifeline networks for post-earthquake serviceability are presented. A simple method is developed to determine critical components of the network whose strengthening improves the network reliability for specified serviceability criteria. Measures of effectiveness of strengthening each component are also introduced. Based on critical components and measures of effectiveness, step-by-step upgrading procedures are proposed. Both connectivity and minimum-flow serviceability criteria may be specified. Two upgrading objectives considered are achieving a specified target reliability and reducing the total costs of upgrading plus expected losses due to failure of the lifeline. A hypothetical application to a water-distribution system in the San Francisco Bay Area illustrates the proposed method.     

Surface modification study of borate materials from B K-edge X-ray absorption spectroscopy

The B K-edge X-ray absorption near-edge structure (XANES) spectra of two borates with tetrahedrally-coordinated B [^[4]B; natural danburite (CaB₂Si₂O₈) and synthetic boron phosphate (BPO₄)] have been recorded in total electron yield (TEY) and fluorescence yield (FY) modes to investigate the surface and bulk structure of these materials. The TEY XANES measurement shows that danburite is susceptible to surface damage involving conversion of ^[4]B sites to ^[3]B sites by reaction with moisture and/or mechanical abrasion (grinding, polishing, etc.). The bulk of the mineral is essentially unaffected. Commercial boron phosphate powder exhibits more extensive surface and bulk damage, which increases with air exposure but is recovered on heating at 650°C. In contrast to ELNES, the XANES technique is not affected by beam damage and when collected in the FY mode is capable of yielding meaningful information on the coordination and intermediate-range structure of B in borate and borosilicate materials. Received: 7 April 1997 / Accepted: 30 July 1997     

Prediction of Dust Emission Due to Open Pit Mine Blasting Using a Hybrid Artificial Neural Network

Natural Resources Research - This study developed a new perspective of artificial neural networks using dimensional analysis to be applicable to certain prediction problems. To this end,...     

Seismic response of multi-frame bridges

Long cast-in-place concrete bridges are often constructed in multiple frames separated by in-span hinges. The multi-frame system offers lower construction and maintenance costs, fewer adverse effects due to creep, post-tensioning, and thermal deformations as a few of its advantages. However, the seismic response of multi-frame bridges has been uncertain owing to the complexities of their discrete system. This study intends to improve the understanding of the seismic response of multi-frame bridge systems and evaluate the applicability of current design assumptions. Responses of multi-frame bridges and comparable single-frame bridges of the same length are compared. Seismic demands on multi-frame bridge columns, abutments, and in-span hinges were investigated through high-fidelity analytical simulations. Approximately 3400 nonlinear time history analyses of prototype bridges with realistic designs were performed using the OpenSees platform. Analysis of variance was implemented along with a factorial design to study the effect of several independent factors, including the number of frames, substructure system, unequal column heights, soil type, ground motion intensity, and capacity-to-demand ratio. It was observed for elastic dynamic analysis that a 90 % modal mass participation ratio is not adequate to accurately estimate dynamic responses. Seismic demands on columns in multi-frame bridges are typically smaller than those in comparable single-frame bridges. The multi-frame system is seismically more robust than the single-frame system, specifically for bridges spanning non-uniform valleys that include unequal column heights. To prevent longitudinal unseating at in-span hinges, it is critical to consider the interaction of transverse and longitudinal responses. The seismic damage to abutment backwalls and backfills in multi-frame bridges is expected to be extensive owing to small expansion joints.     

Development and application of a stochastic optimization model for groundwater management: crop pattern and conjunctive use consideration

The need for irrigation water in arid and semi-arid regions is mostly supplied by groundwater. Furthermore, the agricultural development in these areas is not generally based on a comprehensive plan, which can cause aquifers depletion. On the other hand, to properly manage an aquifer and to have an optimal crop plan, the stochastic nature of the different parameters of a groundwater system such as groundwater recharge and water demands should be taken into consideration. In this paper, we develop an explicit stochastic optimization model for Firouzabad aquifer in Iran. This formulation is based on the first and second moment analysis for groundwater head which has been initially proposed for surface water resources management by Fletcher and Ponnambalam. We extend the model to create a new random withdrawal policy for conjunctive use setting in which the randomness in available precipitation is taken into account. The interesting point is that the model provides the respective probabilities of shortage and surplus without imposing the extra decision variables into the optimization model. A genetic-based algorithm is used to solve the stochastic nonlinear and non-convex formulation. The outcome results indicate that the current crop pattern should be changed, that is, the allocated areas of some crops have to be meaningfully reduced. Finally, to validate our model efficiency, we demonstrate that how much close the statistical characteristics obtained from the optimization model are to those estimated from the Monte Carlo simulation. Furthermore, the optimal benefits obtained using the proposed optimization model are as suitable as the benefits achieved using the corresponding Monte Carlo-based optimization model.