香港城市垃圾填埋场的发展历程及景观改造策略研究

封场垃圾填埋场的景观改造是中国香港地区对已开发土地进行综合再利用的重要举措。有别于将封场垃圾填埋场作为城郊绿化种植区的常规方式,香港地区已关闭的垃圾填埋场不仅多分布于城区内,而且景观改造的目标多样。首先,回溯了香港垃圾填埋场的独特发展历程,揭示不同时期推动填埋场发展的多元动因。其次,从城市发展的视角分析填埋场外部环境的变化对填埋场景观产生的整体性影响。通过梳理填埋场改造三阶段的总体技术路线,以及各阶段的工程策略和前后阶段之间存在的紧密联系,总结香港垃圾填埋场景观改造的基本策略与方法,以期为国内其他高密度城市地区垃圾填埋场的景观改造提供思路与方法层面的借鉴。     

Stiffness parameters of municipal solid waste

This paper presents results of the deformability parameters of municipal solid waste (MSW) determined through laboratory (oedometer and triaxial tests) and in situ tests [standard penetration tests (SPT) and cone penetration tests (CPT)], as well as by a monitoring system including topographic control marks, open-tube piezometers, earth and pore pressure cells and inclinometer tubes with magnetic settlement plates and spiders. The studied landfill is located in a textile industry area, and was landfilled with some direct waste (10 %) and mostly pre-treated waste (90 %, from composting and triage). The influence of: the waste age, construction phase of the landfill and confining stress on the results of stiffness modulus, lateral waste pressure coefficient at-rest (K ₀) and Poisson’s ratio (ν) are presented, as well as an attempt to establish correlations to estimate MSW stiffness modulus from SPT and CPT tests. The results indicate the increases of K ₀ and ν with the average effective confining stresses during the first 2 years of the post-construction phase, reaching maximum values of 0.7 for K ₀ and 0.4 for ν, and then decreasing gradually until stabilizing at values of around 0.23–0.48 for K ₀ and around 0.19–0.32 for ν. The stiffness modulus values determined by different methods are consistent with each other and corroborate the fact that typical values for MSW are low. These values are between 0.4 and 2 MPa for a mean confinement stress of about 50 kPa, and tend to increase linearly with the increase of the confinement stress. The correlations established with SPT and CPT tests are of the same type as usually proposed for granular soils; however, the constant values are significantly lower than the lowest values reported for normally consolidated sandy soils.     

城市生活垃圾填埋场固液气耦合一维固结模型

建立了一维固、液、气三相耦合的大孔隙垃圾固结数学模型。把垃圾视为大孔隙介质,假定基质吸力等于0,即孔隙气压等于孔隙液压,把填埋场简化为非稳定单向渗流场。模型中采用了Gibson和Lo一维压缩流变模型及Landgem产气方程,结合了达西定律、气体状态方程、有效应力原理和多孔介质流体动力学理论。填埋场的沉降按封场前和封场后两个阶段分别计算,封场前填埋场接受垃圾,导致堆载压力增加,而封场后的填埋场堆载压力保持不变。垃圾堆填时产生的超孔隙压力按Hilf分析法计算。运用差分法对固、气耦合问题进行了数值求解。计算结果表明:气压随深度增加而增大,透气率大的填埋场其气压消散速率快。在堆填期,气压随时间增加而增大;封场后,气压逐渐消散。气压增加,导致填埋场沉降速率和容量减小。     

垃圾土沉降的Logistic模型应用研究

垃圾土的沉降是卫生填埋场沉降机理设计时需考虑的一个重要因素。通过对垃圾土沉降的分析,指出垃圾土的沉降机理相当复杂,与土的沉降机理不尽相同。分析了现有垃圾土沉降模型计算存在的问题。采用使观测值和预测值残差平方和达到最小的方法对Logistic模型求取参数,并应用于香港Sai Tso Wan垃圾填埋场及巴西Bandeirantes填埋场封场期后的沉降预测研究。结果表明,只要选取合适的参数,可以克服现有沉降计算模型的缺陷,大幅度提高垃圾土封场期后沉降值的预测精度。     

垃圾填埋场的沉降分析、计算及灰色模型预测

分析了垃圾场的沉降原理,并给出计算方法,应用灰色系统理论,对沉降实际数据进行处理,建立灰色动态GM模型,作出对填埋过程中和封顶后的沉降预测。这对解决城市垃圾填埋场的沉降问题提高垃圾场的潜在处理能力、增加填埋场的有效存贮容量有着十分重大的意义。     

Characterization and Treatment of Leachates from Hong Kong Landfill Sites

Development of a large landfill site in the North-Eastern New Territories of Hong Kong, which will receive 25 million m³ of wastes during a life of about 13 years, must include the provision of a scheme to manage leachates which will arise in the tropical climate of the region.
The paper presents detailed results from a study commissioned by the Environmental Protection Department of the Hong Kong Government, to characterize and treat leachates generated by landfills in Hong Kong, in order to design a suitable management scheme. Field and laboratory trials which were carried out during 1989 showed that, although leachates from Hong Kong landfills have some specific characteristics (e.g. concentrations of amm.N to 5000 mg/l), they can be treated to high standards by aerobic biological processes.
As a result of these studies, a scheme has been designed which will provide a high degree of environmental protection in respect of leachate, as the landfill is developed.     

Numerical study of strain development in high-density polyethylene geomembrane liner system in landfills using a new constitutive model for municipal solid waste

Tensile strain development in high-density polyethylene (HDPE) geomembrane (GMB) liner systems in landfills was numerically investigated. A new constitutive model for municipal solid waste (MSW) that incorporates both mechanical creep and biodegradation was employed in the analyses. The MSW constitutive model is a Cam-Clay type of plasticity model and was implemented in the finite difference computer program FLAC?. The influence of the friction angle of the liner system interfaces, the biodegradation of MSW, and the MSW filling rate on tensile strains were investigated. Several design alternatives to reduce the maximum tensile strain under both short- and long-term waste settlement were evaluated. Results of the analyses indicate that landfill geometry, interface friction angles, and short- and long-term waste settlement are key factors in the development of tensile strains. The results show that long-term waste settlement can induce additional tensile strains after waste placement is complete. Using a HDPE GMB with a friction angle on its upper interface that is lower than the friction angle on the underlying interface, increasing the number of benches, and reducing the slope inclination are shown to mitigate the maximum tensile strain caused by waste placement and waste settlement.     

Performance monitoring and numerical assessment of a test embankment with preloading and vertical drains on Texcoco lacustrine soft clays

This paper presents the performance monitoring results and long-term numerical analyses of a 2.8-m-high test embankment with vertical drains on soft highly compressible clays during a four years and two months observation period (1525 days). The peculiar study site is characterized by thick layers of lacustrine soft clay with water contents up to 300%, void ratios between 7 and 9 and ratios C_α/C_c range from 0.06 to 0.03. The loading applied by the test embankment was 43.4 kPa. The vertical drains installed were of two types: sand and prefabricated. The settlements that only take into account the effect of the preloading embankment at the end of the observation period were 2.62 m and 2.71 m, in the zones with sand and prefabricated vertical drains, respectively. The settlement measured by regional subsidence was 0.47 m. The ultimate primary settlement was approximately 2.0 m and was estimated by two observational methods based on field settlement records. The settlement developed by secondary consolidation in the embankment ranged from 0.62 m to 0.71 m at the end of the observation period. The test embankment behavior was simulated by 2D and 3D numerical analyses. The 2D analyses used a theory to convert the axisymmetric drainage into plane drainage. The long-term numerical results and the field measurements were compared and discussed.     

The effect of Pb reduction in petrol on the Pb content of kerbside dust in Hong Kong

Before 1981, Pb in petrol in Hong Kong averaged about 0.84 g/l. Then the Pb level was stepwisely reduced and by early 1987, it was at 0.25 g/l. The effect of Pb reduction in petrol on the roadside environment was assessed by comparing the Pb content in kerbside dust samples (extracted by hot 3.5 M NO₃ and analysed by flame AAS) taken in Nov 77–Jan 78 and in Jan 1987 from 37 sites which covered a wide range of traffic density. The arithmetic mean Pb levels for the 1977–1978 and 1987 samples were 3280 and 1080 μg/g respectively and their difference was highly significant (P = 0.0005, paired t-test). Parallel studies on the levels of Cu, Zn and Mn in the two batches of samples showed no significant changes. Thus Pb reduction in petrol has drastically lowered the metal's contamination in the roadside environment in Hong Kong.     

考虑垃圾体沉降的生物反应器填埋场 渗滤液回灌运移规律

生物反应器填埋场在渗滤液的回灌过程中,垃圾体会产生较大的沉降变形,这主要是由于填埋体的自重和生物降解所致。由于沉降变形会导致生物反应器填埋场中垃圾体的孔隙比减小,孔隙比的减小会影响垃圾体的渗透系数和填埋场所能容纳的渗滤液量。为了研究考虑垃圾体沉降的生物反应器填埋场渗滤液回灌运移规律,根据质量守恒原理,以修正的Darcy定理为基础,结合Elagroudy等人提出的沉降模型,建立了考虑垃圾体沉降的生物反应器填埋场渗滤液回灌的计算模型,应用该模型研究了非饱和条件下渗滤液在生物反应器填埋场中的运移规律,分析了回灌强度、垃圾体初始孔隙比、初始含水率和组成成份等参数变化对垃圾体含水率和填埋场单位表面积回灌量的影响规律。     

Flooding of municipal solid waste landfills — An environmental hazard?

Municipal solid waste (MSW) landfills pose a long-lasting risk for humans and the environment. While landfill emissions under regular operating conditions are well investigated, landfill behaviour and associated emissions in case of flooding are widely unknown, although damages have been documented. This paper aims at developing a methodology for determining the proportion of MSW landfills endangered by flooding, and at evaluating the impact flooded landfills might have on the environment during a flood event.The risk of flooding of MSW landfills is assessed by using information about flood risk zones. Out of 1064 landfills investigated in Austria, 312 sites or about 30% are located in or next to areas flooded on average once in 200 years. Around 5% of these landfills are equipped with flood protection facilities. Material inventories of 147 landfill sites endangered by flooding are established, and potential emissions during a flood event are estimated by assuming the worst case of complete landfill leaching and erosion. The environmental relevance of emissions during flooding is discussed on the basis of a case study in the western part of Austria. Although environmental hazards need to be assessed on a site- and event-specific basis, the results indicate that flooded MSW landfills represent in general small environmental risks for the period of flooding. The longer term consequences of flooding are discussed in a next paper.     

城市生活垃圾填埋场沉降分析与计算

城市生活垃圾填埋场无论在填埋过程中还是封顶后都会产生显著的沉降.填埋场的沉降一方面可以增加场区的垃圾消纳量,另一方面将对填埋场的维护和场地再利用产生不利影响.垃圾填埋体的沉降受垃圾土的自重压缩和有机质降解的综合影响.本文从分析填埋场沉降机理人手,提出填埋体的沉降由主沉降、次沉降和有机物分解沉降三部分组成,并给出了沉降估算公式;结合工程实例分析了填埋体的沉降过程,计算表明,一座设计容量为472万m3,设计填埋高度73m的填埋场的扩容率可达97%;封顶后的最终沉降约为填埋高度的10%.文中提出了实行分区填埋、分层压实和加速有机物分解等控制填埋场沉降的建议.     

Organic indicators of groundwater pollution by a sanitary landfill

The organic composition of leachate from the Barcelona sanitary landfill is described. According to the low degree of stabilization of the disposed garbage the acid fraction accounts for 80–90% of the total organic extract. More than 50 individual organic components have been identified, indicating catabolic degradation of lipids (e.g. C₄–C₁₁ carboxylic acids), proteins (e.g. indole derivatives) and lignins (e.g. p-hydroxyphenyl derivatives) or simply compounds originally present in the refuse that have been washed out by percolating waters (nicotine, caffeine, phthalates).To obtain a monitoring system for the groundwater pollution originated by this landfill leachate, an analytical method is proposed based on the GC-ECD fingerprinting of groundwater acidic extracts after derivatization with PFB bromide. The chromatogram contains carboxylic and phenolic components and the profiles exhibited by waters from several test wells in the downstream edge of the landfill were indicative of the suspected leachate pollution.     

Technical report on the compression,structure, and creep behaviors of lacustrine soil deposits in Bogotá, Colombia

This technical report on the compression behavior of soft soils in the Colombian capital, Bogotá, was conducted because the city’s recent construction history has led to excessive settlement of soils in the city over the last forty years. Several studies have shown the city’s soil to contain unusually high concentrations of diatoms. The stationary piston method was used to obtain samples from depths of between five and 100 m. Samples were subsequently examined in the laboratory, being subjected to triaxial and oedometer compression tests, and tested also for Atterberg limits and grain size distributions. Test results for undisturbed soil returned very high liquid limit values, compressibility indices C_C, secondary compression coefficients C_α, and soil structure effects. Some samples showed particle mixtures of different sizes, mineralogy, and diatom concentrations. Although high C_C and C_α indices explain the excessive settling of the city’s buildings, most construction projects do not currently take settlement caused by secondary compression into account. This report shows that secondary compression is an important parameter in the total settlement of buildings in Bogotá and that, furthermore, settlement is also affected by geological history. Finally, useful correlations such as the relationship between the liquid limit, C_α and geological history are presented.     

Calibration of Methods for Designing Large-Diameter Bored Piles: Serviceability limit state

Limit-state design methodologies for serviceability of foundations are an important area under development. Due to various sources of uncertainty, settlement analysis models and the soil or rock properties required for settlement analysis may be in error; hence any settlement estimate is a random variable. To develop limit-state design codes for large-diameter bored piles, analysis methods for estimating the settlement of large-diameter bored piles need to be carefully calibrated. This paper aims at calibrating four analysis methods for bored piles in soils (Vesic's elastic method, Mayne and Harris's analytical solution, O'Neill and Reese's load-transfer method, and a method based on load-transfer curves established in this paper based on Hong Kong data) and three methods for bored piles socketed in rocks (Vesic's method, Kulhawy and Carter's method, and a load-transfer method using the correlations established in this paper based on Hong Kong data). For rock-socketed piles, two methods for estimating the rock deformation modulus are further studied: One based on a correlation with rock quality designation and the other based on a correlation with rock mass rating. These analysis models have been calibrated at the working load level using 36 cases of static loading tests on large-diameter bored piles in Hong Kong with complete soil and rock information. The effects of construction on pile settlement have also been included.     

考虑降解率下的垃圾土降解压缩量计算模型

从无机物质量不变出发,在考虑降解率与密度变化的情况下,围绕垃圾土的密度、质量与体积三者关系,结合由自配试样进行降解试验获得的降解率规律,推导了垃圾土一维降解压缩模型。研究结果表明,降解压缩量与初始时刻有机物的体积百分含量、降解率及初始高度有关,且成正比关系。利用该模型对重庆市某垃圾填埋场的有机物降解沉降量进行了计算,可以看出降解沉降量与时间呈指数函数关系,在填埋初期降解沉降速率较大,随着时间推移,降解沉降量趋于稳定。     

Assessing economic,social and environmental impacts on housing prices in Hong Kong: a time-series study of 2006, 2011 and 2016

Given Hong Kong’s unique high-density urban environment and limited land resources, more and more general public has been concerned about the living quality. Based on three waves of census data (2006, 2011 and 2016), combined with our spatial–temporal urban environmental database consisting of three local datasets of urban climate and air quality, this paper assesses the impacts of social, economic and environmental factors on the logarithm of housing prices in Hong Kong through linear regression analysis. Specifically, both supply- and demand-side economic factors have significant impacts on housing prices. Demographic factors are not as significant as expected in affecting housing prices. Transportation factors have more significant effects in the short run than in the long run. Environmental factors, including the number of hot night hours, Annual Air Quality Index (AAQI) of nitrogen dioxide (NO₂) and particulates with particle sizes less than 10 microns (PM₁₀), significantly affect housing prices over time. The results have important implications: current policy instruments to prevent housing price escalation are focused on increasing property tax or land supply (economic factors), while little attention is paid to social or environmental factors, which are geographically heterogeneous. Our findings suggest that housing provision in the New Territories may be a feasible solution to alleviate the housing crisis as its demographic pattern, transportation connectivity and air quality are significantly different from Hong Kong Island or Kowloon Peninsula. In regard to urban environmental problems brought by the high-density development in Hong Kong despite land-use saving, intensified urban infrastructure and promotion of public transportation, our study contributes to the understanding of its housing price dynamics from a more holistic perspective by comparing the impacts of economic, social and environmental factors.

     

Construction site safety in Hong Kong

The structural characteristics of the Hong Kong construction industry, most notably its elaborate system of subcontracting and the casual basis on which labour is employed, pose serious problems for safety managers. By international standards, Hong Kong's construction industry performs very badly in the area of safety. Recent work in the UK and Finland highlights the effectiveness of behavioural techniques to improve safety performance on construction sites. Work is currently under way to test these techniques in the Hong Kong construction setting. The structural properties of the Hong Kong construction industry have been taken into consideration and labour commitments to the group and to the organization have been identified for additional consideration in research. It is expected that these variables will intervene in the application of behavioural techniques to determine their effectiveness. This paper investigates the theoretical background to commitment at the group and organizational level and presents a site level research model which is illustrative of the possible effects that group and organization level commitment may be found to have on the use of behavioural techniques.     

Paving blocks made with recycled concrete aggregate and crushed clay brick

Clay brick generated from construction sites is usually delivered to landfills for disposal. With the limited landfill space in Hong Kong, there is an immediate need to explore the possible use of crushed clay brick as a new civil engineering material. In Hong Kong, government specifications promote the use of paving blocks made with 70–100% recycled concrete aggregate in order to facilitate the recycling of construction and demolition (C&D) waste. This paper presents a recent study at the Hong Kong Polytechnic University on the investigation of blending recycled concrete aggregate and crushed clay brick as aggregates in the production of paving blocks.The results indicated that the incorporation of crushed clay brick reduced the density, compressive strength and tensile strength of the paving blocks. Due to the high water absorption of crushed clay brick particles, the water absorption of the resulting paving blocks were higher than that of the paving blocks that did not incorporate crushed clay brick. Although it was found that crushed clay brick impaired the quality of the resulting paving blocks to a certain extent, the paving blocks using 50% crushed clay brick met the minimum requirements specified by AS/NZS 4455 and ETWB of Hong Kong (Grade B) for pedestrian areas. Furthermore, it was feasible to produce paving blocks prepared with 25% crushed clay brick that satisfied the compressive strength requirement for paving blocks (Grade B) prescribed by ETWB of Hong Kong for trafficked area.     

Carbon capture and storage for Hong Kong's fuel mix

Policy-makers in Hong Kong are considering the fuel mix of electricity generation for the coming decades, but to a large extent have neglected carbon (CO₂) capture and storage (CCS). Our analysis finds that a largely depleted natural gas field, having supplied Hong Kong since 1995, should be sufficient for CO₂ storage and the connected natural gas pipeline should be capable for CO₂ transport. We examine an alternative fuel-mix plan, burning coal with CCS, to demonstrate that CCS could broaden the fuel choices for achieving the same policy goals. Hong Kong could seriously consider CCS before closing the current policy debate.