Effect of heterogeneity on occurrence of zonal disintegration around deep underground openings

By utilizing the two numerical codes RFPA3 D and FLAC3 D, the effect of heterogeneity on failure mode and failure mechanism of rock around deep underground excavations under tri-axial stress is analyzed. It is found that zonal disintegration is a large scale shear-slip failure developed in deep surrounding rock mass under tri-axial stress, which is accompanied by a large amount of tensile failure. The distance between fractures and the number of fractures have a close correlation with the rock mass heterogeneity. With an increase of the homogeneity index of the rock mass, the distances between fractures decrease and the number of fractures increases. For an intact hard rock mass with relative high homogeneity, only failure mode characterized as v-shaped notches can be formed due to the intersection of intensively developed shear bands. None of the zonal disintegration can be formed due to the fact that with increasing homogeneity, the failure mechanism of rock mass is gradually dominated by shear failure rather than tensile failure.

A tour-based analysis of travel mode choice accounting for regional transit service

The aim of this work is to explore the impact of regional transit service on tour-based commuter travel behavior by using the Bayesian hierarchical multinomial logit model, accounting for the spatial heterogeneity of the people living in the same area.With two indicators, accessibility and connectivity measured at the zone level, the regional transit service is captured and then related to the travel mode choice behavior. The sample data are selected from Washington-Baltimore Household Travel Survey in 2007,including all the trips from home to workplace in morning hours in Baltimore city. Traditional multinomial logit model using Bayesian approach is also estimated. A comparison of the two different models shows that ignoring the spatial context can lead to a misspecification of the effects of the regional transit service on travel behavior. The results reveal that improving transit service at regional level can be effective in reducing auto use for commuters after controlling for socio-demographics and travel-related factors.This work provides insights for interpreting tour-based commuter travel behavior by using recently developed methodological approaches. The results of this work will be helpful for engineers, urban planners, and transit operators to decide the needs to improve regional transit service and spatial location efficiently.

A bi-level optimization framework for charging station design problem considering heterogeneous charging modes

Purpose–The purpose of this paper is to optimize the design of charging station deployed at the terminal station for electric transit,with explicit consideration of heterogenous charging modes.Design/methodology/approach–The authors proposed a bi-level model to optimize the decision-making at both tactical and operational levels simultaneously.Specifically,at the operational level(i.e.lower level),the service schedule and recharging plan of electric buses are optimized under specific design of charging station.The objective of lower-level model is to minimize total daily operational cost.This model is solved by a tailored column generation-based heuristic algorithm.At the tactical level(i.e.upper level),the design of charging station is optimized based upon the results obtained at the lower level.A tabu search algorithm is proposed subsequently to solve the upper-level model.Findings–This study conducted numerical cases to validate the applicability of the proposed model.Some managerial insights stemmed from numerical case studies are revealed and discussed,which can help transit agencies design charging station scientifically.Originality/value–The joint consideration of heterogeneous charging modes in charging station would further lower the operational cost of electric transit and speed up the market penetration of battery electric buses.