国内某60 万千瓦压水堆核电站反应堆内部结构±0.00 m 以下土建施工方案研究

通过对反应堆内部结构±0.00 m 以下主体结构土建施工方案的研究,从钢筋、模板、预埋件、混凝土等多方面对土建施工过程进行技术指导,以确保工程质量及安全。     

Laboratory measurement of hydraulic conductivity functions of two unsaturated sandy soils during drying and wetting processes

The importance of applying unsaturated soil mechanics to geotechnical engineering design has been well understood. However, the consumption of time and the necessity for a specific laboratory testing apparatus when measuring unsaturated soil properties have limited the application of unsaturated soil mechanics theories in practice. Although methods for predicting unsaturated soil properties have been developed, the verification of these methods for a wide range of soil types is required in order to increase the confidence of practicing engineers in using these methods. In this study, a new permeameter was developed to measure the hydraulic conductivity of unsaturated soils using the steady-state method and directly measured suction (negative pore-water pressure) values. The apparatus is instrumented with two tensiometers for the direct measurement of suction during the tests. The apparatus can be used to obtain the hydraulic conductivity function of sandy soil over a low suction range (0–10 kPa). Firstly, the repeatability of the unsaturated hydraulic conductivity measurement, using the new permeameter, was verified by conducting tests on two identical sandy soil specimens and obtaining similar results. The hydraulic conductivity functions of the two sandy soils were then measured during the drying and wetting processes of the soils. A significant hysteresis was observed when the hydraulic conductivity was plotted against the suction. However, the hysteresis effects were not apparent when the conductivity was plotted against the volumetric water content. Furthermore, the measured unsaturated hydraulic conductivity functions were compared with predictions using three different predictive methods that are widely incorporated into numerical software. The results suggest that these predictive methods are capable of capturing the measured behavior with reasonable agreement.     

Multidimensional modeling of biofilm development and fluid dynamics in a hydrogen-based,membrane biofilm reactor (MBfR)

A two-dimensional, particle-based biofilm model coupled with mass transport and computational fluid dynamics was developed to simulate autotrophic denitrification in a spiral-wound membrane biofilm reactor (MBfR), where hydrogen is supplied via hollow-fiber membrane fabric. The spiral-wound configuration consists of alternating layers of plastic spacer net and membrane fabric that create rows of flow channels, with the top and bottom walls comprised of membranes. The transversal filaments of the spacer partially obstruct the channel flow, producing complex mixing and shear patterns that require multidimensional representation. This study investigated the effect of hydrogen and nitrate concentrations, as well as spacer configuration, on biofilm development and denitrification fluxes. The model results indicate that the cavity spacer filaments, which rest on the bottom membranes, cause uneven biofilm growth. Most biofilm resided on the bottom membranes, only in the wake of the filaments where low shear zones formed. In this way, filament configuration may help achieve a desired biofilm thickness. For the conditions tested in this study, the highest nitrate fluxes were attained by minimizing the filament diameter and maximizing the filament spacing. This lowered the shear stress at the top membranes, allowing for more biofilm growth. For the scenarios studied, biomass limitation at the top membranes hindered performance more significantly than diffusion limitation in the thick biofilms at the bottom membranes. The results also highlighted the importance of two-dimensional modeling to capture uneven biofilm growth on a substratum with geometrical complexity.     

Time–cost optimization: using GA and fuzzy sets theory for uncertainties in cost

Uncertainties should be considered in any time–cost trade‐off problems when minimizing project cost and duration, which leads to the so‐called stochastic time–cost trade‐off problem. A new approach to investigate stochastic time–cost trade‐off problems employing fuzzy logic theory is presented. The proposed approach fully embeds the fuzzy structure of the uncertainties in total direct cost into the model. An appropriate GA is used to develop a solution to the multi‐objective fuzzy time cost model. The accepted risk level of the project manager is defined through α cut approach for which a separate Pareto front with set of non‐dominated solutions has been developed. To compare the alternative set of options for any assumed project duration, associated fuzzy costs for different values of α cut are ranked employing two appropriate approaches for fuzzy costs comparison. The proposed models are applied to solve two benchmark test problems. It is shown that the models facilitate the decision‐making process by selecting specified risk levels and employing the associated Pareto front.     

Alternative work schedule interventions in the Australian construction industry: a comparative case study analysis

Project‐based construction workers in the Australian construction industry work long and irregular hours and experience higher levels of work‐to‐family conflict and burnout than office‐based workers, giving rise to an interest in alternative work schedules as a means of supporting work–life balance. Alternative work schedules were implemented in four case study construction projects in Australia. Interventions differed between projects, with two implementing a compressed work week, and the others introducing reduced hours schedules (one of which was optional). Data were collected from each case study project, using various combinations of focus groups, surveys, interviews and daily diary collection methods. The results were mixed. The compressed work week appears to have been favourably received where it was introduced. However, waged workers still expressed concerns about the impact on their weekly ‘take‐home’ pay. Attempts to reduce work hours by changing from a six‐ to a five‐day schedule (without extending the length of the working day between Monday and Friday) were less favourably received. Waged workers, in particular, did not favour reduced hours schedules. The results confirm the existence of two distinct labour markets operating in the Australian construction industry and markedly different responses to alternative work schedules, based upon whether workers are waged or salaried. The results clearly show that attempts to improve work–life balance must take the structural characteristics of the industry's labour markets into consideration in the design of interventions. The impact of alternative work schedules is likely to be moderated by institutional working time regimes within the construction industry.     

Multifaceted public outreach and cost–benefit analysis for its effectiveness validation

A heavily trafficked 4.5km highway stretch on Interstate 15 east of Los Angeles was rebuilt using two extended closures, each spanning nine days with 24/7 operations. Before and during the closures, a multifaceted, extensive, dynamic public outreach programme was implemented to gain public support for the project and to minimize inconvenience to the public. That outreach programme is described, its overall effectiveness in terms of total net benefit and traffic inconvenience during lane closures is assessed, and changes in public perception of the accelerated construction strategy resulting from the outreach programme is examined. Pre‐ and post‐construction surveys performed using the project website mirrored the findings of the traffic measurement study, indicating that the outreach programme effectively reduced traffic demand. The results of two web‐based surveys with a combined total of approximately 400 respondents indicated a dramatic change in public perception of the accelerated construction strategy. The survey results showed that strong initial objection to the accelerated project eventually became supportive of future, accelerated projects. The cost–benefit analysis showed that the additional cost of the outreach programme was outweighed by the savings achieved from reduced road user delay costs.     

Public reaction to wind development in California

Substantial controversy has been produced from the location of over 4000 wind turbines in San Gorgonio Pass, California. The principal point of controversy is the conflicting land use which results from developing wind power in a populated area. A public opinion survey was conducted which demonstrated that the vocal opposition to the wind turbines so commonly expressed is not borne out in fact. While there is indeed some opposition to the development of wind power at this site, particularly in terms of aesthetic degradation, the majority of respondents favoured the development. This level of approval will be of interest to those developing large wind projects elsewhere.     

Wind characteristics and energy potential assessment in Akure,South West Nigeria: econometrics and policy implications

This paper analysed 11 years of daily mean wind-speed data, measured at Akure, Ondo State, Nigeria, using Weibull and Rayleigh distribution functions. While both distributions showed good agreements in extreme-value estimation patterns, investigation of their wind-speed characteristics modelling criteria, using goodness-of-fit statistics, revealed that the wind data followed the Weibull more than Rayleigh. Monthly wind-speed of Akure city ranged from 1.41 to 4.24 m/s by the Weibull fittings and from 1.40 to 4.16 m/s by the Rayleigh fittings. Overall results, of 2.71 m/s (Weibull) or 2.70 m/s (Rayleigh) mean wind-speed and 18.51 W/m² (Weibull) or 22.26 W/m² (Rayleigh) mean power density, indicated Akure a low wind-speed site, requiring low wind-speed turbine for generating wind energy. Econometric analyses of power output simulations using such turbine system resulted in affordable wind energy cost. These bear policy implications for sustainable wind energy usage in this and similar regions of the world.     

A Wildland–Urban Interface Typology for Forest Fire Risk Management in Mediterranean Areas

The transitional areas that lie between wildlands and urbanized spaces, generally defined as wildland–urban interfaces (WUI), represent an increasing risk factor in Mediterranean areas; these define a new scenario in forest fire fighting and prevention. We have developed a methodological approach in order to assess the hazard and vulnerability of WUI which is based on landscape analysis, on the use of Geographic Information Systems (GIS) techniques and remote sensing. Unlike traditional approaches which are based on local scale characterization of WUI, we propose a progressive multi-scale approach. In order to reach an operative classification of the WUI the methodology was developed in three stages: a regional urban development model, a landscape character assessment and finally, a WUI typology. The last WUI typology has been based on the identification of different urban morphologies and their context within the type of landscape in which they occur.