Model Test on Grouting Law in Dynamic Water-Rich Sand Layers by the Electric Resistance Method北大核心CSCD

In order to study the diffusion law of grouting slurry in the water-rich sand layer under flowing water conditions, a grouting test model consisting of a main test system, a grouting system, and a measurement system was developed. And for detecting the diffusion scope of the grouts, a new resistivity method was proposed. It is found that the relationship between grouting pressure and grouting rate during the test is strong. Under hydrodynamic conditions, the grouting slurry diffuses elliptically. Due to gravity and the effect of the upper water flow, the center of gravity of the ellipsoid is below the grouting outlet, and the grouting effectively improves the physical and mechanical properties of water-rich sand bodies. At the same time, the resistivity method has a good application effect on the detection of grouting diffusion range. The range of slurry diffusion obtained by the resistivity method is basically consistent with the boundary of the stone body after excavation, indicating that the resistivity method is reliable for detection of grouting range in dynamic water-rich sand layer. © 2018, Editorial Office of "Modern Tunnelling Technology". All right reserved.     

Experimental Study on Mechanical Behaviors of Prefabricated Column-Base Joint with Grouted Sleeves Connecting Longitudinal Reinforcements in Tunnels北大核心CSCD

In recent years, large shield tunnels with internal double-decked lanes have been developing rapidly in the field of highway tunnels, and prefabricated elements are increasingly adopted in internal structure. Based on the columns-base joint in Zhuguanglu tunnel, which is under construction, 2 full-scale specimens are designed for the quasi-static test, one specimen is connected with grout sleeve splicing and the other is cast in place. The test results show that: the bearing capacity of specimen with grout sleeve splicing is equal to that of cast-in-situ specimen, but its ductility and energy dissipation capacity are worse than that of the cast-in-situ specimen. And for the specimen with grout sleeve splicing, there exists crack concentration on the area above the sleeve. The crack width is too larger in this area. © 2018, Editorial Office of "Modern Tunnelling Technology". All right reserved.     

Estimation of origin-destination matrices from link counts and sporadic routing data

Estimation of origin-destination (OD) matrices from link count data is a challenging problem because of the highly indeterminate relationship between the observations and the latent route flows. Conversely, estimation is straightforward if we observe the path taken by each vehicle. We consider an intermediate problem of increasing practical importance, in which link count data is supplemented by routing information for a fraction of vehicles on the network. We develop a statistical model for these combined data sources and derive some tractable normal approximations thereof. We examine likelihood-based inference for these normal models under the assumption that the probability of vehicle tracking is known. We show that the likelihood theory can be non-standard because of boundary effects, and provide conditions under which such irregular behaviour will be observed in practice. For regular cases we outline connections with existing generalised least squares methods. We then consider estimation of OD matrices under estimated and/or misspecified models for the probability of vehicle tracking. Theoretical developments are complemented by simulation experiments and an illustrative example using a section of road network from the English city of Leicester.     

Developing an enhanced weight-based topological map-matching algorithm for intelligent transport systems

Map-matching (MM) algorithms integrate positioning data from a Global Positioning System (or a number of other positioning sensors) with a spatial road map with the aim of identifying the road segment on which a user (or a vehicle) is travelling and the location on that segment. Amongst the family of MM algorithms consisting of geometric, topological, probabilistic and advanced, topological MM (tMM) algorithms are relatively simple, easy and quick, enabling them to be implemented in real-time. Therefore, a tMM algorithm is used in many navigation devices manufactured by industry. However, existing tMM algorithms have a number of limitations which affect their performance relative to advanced MM algorithms. This paper demonstrates that it is possible by addressing these issues to significantly improve the performance of a tMM algorithm. This paper describes the development of an enhanced weight-based tMM algorithm in which the weights are determined from real-world field data using an optimisation technique. Two new weights for turn-restriction at junctions and link connectivity are introduced to improve the performance of matching, especially at junctions. A new procedure is developed for the initial map-matching process. Two consistency checks are introduced to minimise mismatches. The enhanced map-matching algorithm was tested using field data from dense urban areas and suburban areas. The algorithm identified 96.8% and 95.93% of the links correctly for positioning data collected in urban areas of central London and Washington, DC, respectively. In case of suburban area, in the west of London, the algorithm succeeded with 96.71% correct link identification with a horizontal accuracy of 9.81 m (2σ). This is superior to most existing topological MM algorithms and has the potential to support the navigation modules of many Intelligent Transport System (ITS) services.     

Are millennials more multimodal? A latent-class cluster analysis with attitudes and preferences among millennial and Generation X commuters in California

Transportation - Millennials tend to use a variety of travel modes more often than older birth cohorts. Two potential explanations for this phenomenon prevail in the literature. According to the...     

The role of perceived environment,neighbourhood characteristics,and attitudes in walking behaviour: evidence from a rapidly developing city in China

Transportation - The associations between objective and subjective dimensions of the built environment and walking behaviour have been examined extensively in existing studies. However, the...     

Automation of paratransit reservation,routing, and scheduling

Santa Clara County, California experienced a sharp growth in demand‐responsive paratransit ridership for individuals with disabilities, as a result of the passage of the 1990 Americans With Disabilities Act (ADA). This paper describes an automated paratransit system for the ADA‐type paratransit operation implemented in Santa Clara County. It automated paratransit reservation, scheduling, and routing functions. The key components of this system were a digital geographic database (DGD) and an automated trip scheduling system (ATSS). Empirical evidence after one year of operation indicates numerous benefits of this automation. There were significant reductions in the paratransit operating costs and an increase in the percent shared rides. The savings in operating costs far exceeded the annualized capital cost of automation. A user survey indicates that these improvements were achieved without degradation to service quality such as vehicle on‐time performance, invehicle travel times, vehicle response to open return, and ride comfort.     

铁路隧道穿越岩溶群区施工控制技术研究

文章以渝(重庆)怀(怀化)铁路板桃隧道为工程背景,阐述了该隧道穿越DK215+650～DK216+105段岩溶群区的施工技术.为确保施工工期,施工中采取了"先绕行后处理"的原则,设置施工迂回导洞绕行岩溶区,并通过横通道与正线相连.针对岩溶区内不同的溶洞类型分别采取跨越、支顶、锚喷支护、浆砌片石回填等技术措施,同时根据暗河与溶洞内的水流大小及流向采取了诸如涵洞、小桥等设施或开凿泄水洞将水排出洞外,安全稳妥地通过了455 m岩溶群区.本工程取得的经验可供类似工程施工中借鉴.     

Back-Calculation of Ground Stress Field and Rockburst Analysis for Wunvfeng Tunnel北大核心CSCD

Studying the in-situ stress distribution at a tunnel site is very important to determine surrounding rock characteristics, the engineering design and the construction scheme. By using the multiple linear regression method based on the least square algorithm, the initial geostress field is analyzed and the corresponding regression coefficients are obtained. The ground stress obtained from the proposed back analysis is reasonable and can meet the demands of the engineering applications. From the rockburst risk level distribution diagram, it is speculated that the Wunvfeng tunnel is in the high filed stress area. Field monitoring should be strengthened and emergency plans should be made to cope with the rockburst risks during the construction process. © 2018, Editorial Office of "Modern Tunnelling Technology". All right reserved.     

Modification of the Highway Capacity Manual two‐lane highway analysis procedure for Spanish conditions

The US Highway Capacity Manual (HCM) methodology is used in Spain to evaluate traffic operation and quality of service. The effect of passing manoeuvre on two‐lane highway operational performance is considered through adjustment factors to average travel speeds and percent time spent following. The procedure is largely based on simulations in TWOPAS and passing behaviours observed during US calibrations in the 1970s. It is not clear whether US driving behaviour and vehicles' performance are comparable with Spanish conditions. The objective of this research is to adapt the HCM 2010 methodology to Spanish driver behaviour, for base conditions (i.e. no passing restrictions). To do so, TWOPAS was calibrated and validated based on current Spanish passing field data. The calibration used a genetic algorithm. The case study included an ideal two‐lane highway with varying directional traffic flow rate, directional split and percentage of trucks. The updated methodology for base conditions is simpler than the current HCM 2010 and does not rely on interpolation from tables. Copyright © 2016 John Wiley & Sons, Ltd.