Study of the Impact of Single-and Double-tube Tunnel Systems on Rockburst in Deep-buried Extra-long Tunnelling北大核心CSCD

Rockburst is one of the main disasters for tunnelling under high ground stress. Taking the rockburst section of Ping'an Tunnel with high ground stress, which is located on Chengdu-Lanzhou Railway, as the study object, this paper adopts combined methods of filed measurement, numerical analysis, and laboratory test, and with respect to rockburst development mechanism, energy density change and rockburst strength it comprehensively analyzes the impact of two construction schemes (single-tube double-track tunnel system and double-tube single-track tunnel system) on the rockburst in deep-buried extra-long tunnels with high ground stress. The study results show that the order relation of maximum energy density at various locations of the tunnel is Uside wall >Uhance >Utunnel face >Uvault, and rockburst easily occurs at the working face of the tunnel section to be excavated and both side walls of excavated and supported section; compared with vault, hance, side wall and other locations, more energy would be released at the tunnel face, and the stress release holes shall be reasonably installed in the process of excavation; the doubletube single-track tunnel system scheme can effectively reduce the rockburst intensity and the rockburst hazards, so as to better avoid the occurrence of rockburst. © 2022, Editorial Office of Modern Tunnelling Technology. All right reserved.     

某富水断层隧道涌水治理方案优化分析及工程应用北大核心CSCD

以武九高速高楼山公路隧道为例,针对以断层破碎带为主控因素的隧道突水治理问题展开数值分析研究。基于FLAC 3D有限差分法及流固耦合分析原理,研究了导水洞排水、注浆堵水和排堵结合等不同治理方式对隧道涌水量及围岩稳定性的影响。结果表明:对于富水断层隧道发生A、B级别的大量涌水时,建议同时采取导水洞排水、注浆堵水的排堵结合措施,导水洞设置在近断层处,且与隧道相对距离为0.75(D+l),注浆圈厚度控制在7 m以内,注浆圈相对渗透系数比不超过10,既能降低涌水量,又能保证围岩的稳定性;对于C级涌水隧道,可采取注浆措施,注浆厚度不低于3 m,相对渗透系数不低于20;对于D级及以下涌水隧道,采取常规抽排水措施即可。     

Facing the realities of non-motorized transportation in developing countries

The objective of this paper is to assess issues concerning non-motorized transportation in developing countries. This assessment is done through an examination of three topics: a brief overview of the transportation picture in developing countries; a study of city size and city form vis-a-vis pedestrian movement; and, a look at the characteristics of non-motorized modes, including their capacities. An analysis and discussion attempt to sort out the crucial issues connected with pedestrian planning in particular, and non-motorized transport in general. It is concluded (1) that special attention be paid to space/time capacity/cost issues connected with non-motorized modes (2)that some of the low-cost intermediate technology modes be examined for possible inclusion in traffic streams (3)that land-use patterns need to be rearranged keeping in mind the limitations of non-motorized modes, and (4)that the extent to which physical trip-making can be substituted by telecommunication needs to be examined very critically. An agenda for action reflects these concerns.     

A Methodology for estimating traffic safety improvements at intersections

Intersection accidents represent a significant proportion of overall motor vehicle accidents. More accurate estimates of the actual effectiveness of intersection safety improvements are required. This study develops an improved methodology for post-implementation evaluation of safety countermeasures at intersections. Accidents are random, rarely occurring events. For a given time period, this leads to random fluctuations in accident frequencies, which suggests that statistical analysis employing confidence intervals, rather than point estimates, is required. Two technical problems complicate this treatment of accident occurrence as a random variable. The first problem is that identifying of hazardous locations is generally based on above-average accident frequency during the most recent period(s) for which data is available. The second problem arises from changes in external factors such as traffic volume, motor vehicle safety standards, etc., during the period of analysis, which may also affect traffic safety. A “combined” approach which addresses these technical issues is developed. Empirical Bayesian methodology is combined with regression techniques to derive a more accurate measure of the effect of safety treatments. An important consideration is the derivation of the variance of this measure, so that appropriate confidence intervals may be constructed. The approach is then applied to a sample of locations that underwent treatment by the Massachusetts Department of Public Works (MDPW). We compare our results to those which might be obtained using alternative methodologies that correct for neither or only one of the technical problems. We also illustrate how preliminary conclusions may be drawn regarding the effectiveness of broad categories of treatments, and how individual sites requiring further investigation may be identified.     

Freight Transport Deceleration: Its Possible Contribution to the Decarbonisation of Logistics

The paper challenges the conventional view that the movement of goods through supply chains must continue to accelerate. The compression of freight transit times has been one of the most enduring logistics trends but may not be compatible with governmental climate change policies to cut greenhouse gas emissions by 60–80% by 2050. Opportunities for cutting CO₂ emissions by ‘despeeding' are explored within a freight decarbonisation framework and split into three categories: direct, indirect and consequential. Discussion of the direct carbon savings focuses on the trucking and deep-sea container sectors, where there is clear evidence that slower operation cuts cost, energy and emissions and can be accommodated within current supply chain requirements. Indirect emission reductions could accrue from more localised sourcing and a relaxation of just-in-time (JIT) replenishment. Acceleration of logistical activities other than transport could offset increases in freight transit times, allowing the overall carbon intensity of supply chains to reduce with minimal loss of performance. Consequential deceleration results from other decarbonisation initiatives such as freight modal split and a shift to lower carbon fuels. Having reviewed evidence drawn from a broad range of sources, the paper concludes that freight deceleration is a promising decarbonisation option, but raises a number of important issues that will require new empirical research.     

The multi-objective network design problem using minimizing externalities as objectives: comparison of a genetic algorithm and simulated annealing framework

Incorporation of externalities in the Multi-Objective Network Design Problem (MO NDP) as objectives is an important step in designing sustainable networks. In this research the problem is defined as a bi-level optimization problem in which minimizing externalities are the objectives and link types which are associated with certain link characteristics are the discrete decision variables. Two distinct solution approaches for this multi-objective optimization problem are compared. The first heuristic is the non-dominated sorting genetic algorithm II (NSGA-II) and the second heuristic is the dominance based multi objective simulated annealing (DBMO-SA). Both heuristics have been applied on a small hypothetical test network as well as a realistic case of the city of Almelo in the Netherlands. The results show that both heuristics are capable of solving the MO NDP. However, the NSGA-II outperforms DBMO-SA, because it is more efficient in finding more non-dominated optimal solutions within the same computation time and maximum number of assessed solutions.     

Estimating salinity to complement observed temperature: 1. Gulf of Mexico

This paper and its companion [Thacker, W.C., Sindlinger, L., 2007-this issue. Estimating salinity to complement observed temperature: 2. Northwestern Atlantic. Journal of Marine Systems. doi:10.1016/j.jmarsys.2005.06.007.] document initial efforts in a project with the goal of developing capability for estimating salinity on a region-by-region basis for the world oceans. The primary motivation for this project is to provide information for correcting salinity, and thus density, when assimilating expendable-bathythermograph (XBT) data into numerical simulations of oceanic circulation, while a secondary motivation is to provide information for calibrating salinity from autonomous profiling floats. Empirical relationships between salinity and temperature, which can be identified from archived conductivity–temperature–depth (CTD) data, provide the basis for the salinity estimates.The Gulf of Mexico was chosen as the first region to explore for several reasons: (1) It's geographical separation from the Caribbean Sea and the North Atlantic Ocean makes it a “small ocean” characterised by a deep central basin surrounded by a substantial continental shelf. (2) The archives contain a relatively large number of CTD data that can be used to establish empirical relationships. (3) The sharp fronts associated with the Loop Current and its rings, which separate water with different thermal and haline characteristics, pose a challenge for estimating salinity. In spite of the shelf and the fronts, the relationship between salinity and temperature was found to be sufficiently regular that a single empirical model could be used to estimate salinity on each pressure surface for the entire Gulf for all seasons. In and below the thermocline, root-mean-square estimation errors are small — less than 0.02 psu for pressures greater than 400 dbar, corresponding to potential density errors of less than 0.015 kg/m³. Errors for estimates nearer to the surface can be an order of magnitude larger.     

Matching biological traits to environmental conditions in marine benthic ecosystems

The effects of variability in environmental conditions on species composition in benthic ecosystems are well established, but relatively little is known about how environmental variability relates to ecosystem functioning. Benthic invertebrate assemblages are heavily involved in the maintenance of ecological processes and investigation of the biological characteristics (traits) expressed in these assemblages can provide information about some aspects of functioning. The aim of this study was to establish and explore relationships between environmental variability and biological traits expressed in megafauna assemblages in two UK regions. Patterns of trait composition were matched to environmental conditions and subsets of variables best describing these patterns determined. The nature of the relationships were subsequently examined at two separate scales, both between and within the regions studied. Over the whole area, some traits related to size, longevity, reproduction, mobility, flexibility, feeding method, sociability and living habit were negatively correlated with salinity, sea surface temperature, annual temperature range and the level of fishing effort, and positively associated with fish taxon richness and shell content of the substratum. Between the two regions, reductions in temperature range and shell content were associated with infrequent relative occurrences of short-lived, moderately mobile, flexible, solitary, opportunistic, permanent-burrow dwelling fauna and those exhibiting reproductive strategies based on benthic development. Relationships between some traits and environmental conditions diverged within the two regions, with increases in fishing effort and shell content of the substratum being associated with low frequencies of occurrence of moderately mobile and moderately to highly flexible fauna within one region, but high frequencies in the other. These changes in trait composition have implications for ecosystem processes, with, for example, reductions in permanent-burrow dwellers within one of the regions potentially compromising the ability of the assemblages to process and store chemicals and waste products. However, the connections between environmental conditions and trait composition are complex and incorporate many factors. Experimental investigations will be necessary to determine the extent and consequences of these important relationships.     

Dynamic Stability of Vehicle Systems via Poincaré Maps

Computer simulations of a driven vehicle are performed to assess and quantify the automobile stability. The analytical methodology is based on PoincarS maps and Floquet theory, which are commonly used to investigate the stability of periodic systems. The approach accommodates the study of the complex dynamics of vehicle locomotion under various configurations of the system. The proposed method does not require any knowledge regarding the inner structure of the vehicle model. Kinematic data is simply collected at the specific instants to conduct the analysis. It is found that this method has the potential for real time warning and control of vehicle instabilities.