Nutrient and sediment removal by stormwater biofilters: a large-scale design optimisation study

A large-scale column study was conducted in Melbourne, Australia, to test the performance of stormwater biofilters for the removal of sediment, nitrogen and phosphorus. The aim of the study was to provide guidance on the optimal design for reliable treatment performance. A variety of factors were tested, using 125 large columns: plant species, filter media, filter depth, filter area and pollutant inflow concentration. The results demonstrate that vegetation selection is critical to performance for nitrogen removal (e.g. Carex appressa and Melaleuca ericifolia performed significantly better than other tested species). Whilst phosphorus removal was consistently very high (typically around 85%), biofilter soil media with added organic matter reduced the phosphorus treatment effectiveness. Biofilters built according to observed 'optimal specifications' can reliably remove both nutrients (up to 70% for nitrogen and 85% for phosphorus) and suspended solids (consistently over 95%). The optimally designed biofilter is at least 2% of its catchment area and possesses a sandy loam filter media, planted with C. appressa or M. ericifolia. Further trials will be required to test a wider range of vegetation, and to examine performance over the longer term. Future work will also examine biofilter effectiveness for treatment of heavy metals and pathogens.     

Influence of filter media depth and vegetation on Faecal Coliform removal by stormwater biofilters

Biofilters are promising technologies that widely applied in the treatment of urban stormwater. However, the microbial removal capacity performance depends greatly on the design of biofilters. Hence, this laboratory study attempts to investigate the influence of filter media depths (i.e. 150, 250, 350 and 450 mm) and the variation of native plants, that is, Cow Grass (Axonopus compressus) and Pearl Grass (Axonopus compressus, dwarf) in removing stormwater microorganism particularly Faecal Coliform (FC). Findings showed that a minimum media depth of 300 mm was required to achieve >1 log FC removal. The mean removal of FC at 450 mm depth filter exceeded 2 log for both Cow and Pearl grass biofilter columns. Results showed that there was no statistically significant difference in vegetation type on the performance of FC removal, however, Cow grass biofilter column revealed higher FC mean log removal compared to Pearl grass biofilter column.     

Influence of intermittent wetting and drying conditions on heavy metal removal by stormwater biofilters

Biofiltration is a technology to treat urban stormwater runoff, which conveys pollutants, including heavy metals. However, the variability of metals removal performance in biofiltration systems is as yet unknown. A laboratory study has been conducted with vegetated biofilter mesocosms, partly fitted with a submerged zone at the bottom of the filter combined with a carbon source. The biofilters were dosed with stormwater according to three different dry/wet schemes, to investigate the effect of intermittent wetting and drying conditions on metal removal.Provided that the biofilters received regular stormwater input, metal removal exceeded 95%. The highest metal accumulation occurs in the top layer of the filter media. However, after antecedent drying before a storm event exceeding 3–4 weeks the filters performed significantly worse, although metal removal still remained relatively high. Introducing a submerged zone into the filter improved the performance significantly after extended dry periods. In particular, copper removal in filters equipped with a submerged zone was increased by around 12% (α = 0.05) both during wet and dry periods and for lead the negative effect of drying could completely be eliminated, with consistently low outflow concentrations even after long drying periods.     

软弱地基浅埋隧洞对场地设计地震动的影响

针对南京地铁建设的实际背景和南京软弱地基的特点,以某典型软弱地基浅埋隧洞为研究对象,对该软弱场地土的动参数进行了室内外试验研究,给出了各类土的剪切模量比G/Gmax和阻尼比与剪应变幅值之间的关系曲线及各土层的剪切波速;λγ同时,采用等效线性化模型描述土的非线性性能,考虑地基土与地下浅埋隧洞动力相互作用的影响,采用二维有限元整体分析法对软弱地基浅埋隧洞开挖引起的场地地震效应的变化进行了数值模拟。计算结果表明与自由场的地震效应相比,浅埋隧洞对所处场地的地震效应有很大的影响,本文初步给出了这种影响的范围和影响的程度,以及开挖浅埋隧洞所引起的场地地震效应的一些变化规律,为确定地铁附近已建或新建建筑的设计地震动参数提供了参考依据;浅埋隧洞开挖对软弱场地设计地震动参数的影响应引起工程界足够的重视。     

楼板大开洞及穿层柱对结构抗震设计影响

建筑单体存在塔楼与裙房未设缝脱开,抗侧力构件收进宽度超限,楼板大开洞,穿层柱的抗震超限情况;通过楼板应力分析来查看楼板大开洞对结构影响;通过对穿层斜柱截面有限元分析对其进行抗震性能设计;通过Push-over静力弹塑性分析得出结构在大震下塑性铰发展顺序。     

Effect of clogging of stone column on drainage capacity during soil liquefaction

Stone columns act as vertical drains, and due to their high permeability, allow for the quick dissipation of earthquake induced excess pore water pressure. When water flows through a loose sandy soil, it washes away fine soil particles. The fine sand particles get detached when the hydrodynamic force applied on the soil particles breaks the inter particle bonds between soil grains. These detached soil particles are then migrated by the seepage water. Based on the concentration of the soil particles in the seepage water, these may be captured at the pore constriction of gravels during the flow of water through the stone column. Thus, the clogging of stone column initiates which reduces of the permeability of column. The rate of dissipation of pore water pressure during earthquake is affected due to the clogging of column. In this paper, a mathematical model is proposed to determine the rate of dissipation of pore water pressure of stone column-reinforced ground by considering the clogging effect of column. The result obtained from the proposed model is verified with the available in-situ experimental data. A parametric study is also performed to investigate the effect of different parameters of the proposed model on the clogging of stone column. It is observed that when the permeability ratio, compressibility ratio and area ratio decrease, the possibility of clogging increases. The peak value of the excess pore water pressure ratio can increase up to around 50% due to clogging.     

Model test of clogging effects on composite foundation of geosynthetic-encased steel slag column

Experiments were conducted to study the performance of geosynthetic encased steel slag column with a diameter of 150 mm and a length of 900 mm in a soft clay foundation. The effect of clogging was simulated by mixing the slag with 10% and 20% fines. The measured bearing capacity of the column treated foundation is notably increased to about 10 times than that of the untreated foundation, and is seldom affected by the intrusion of fines. The vertical stress within the soil at column tip attenuates to 85% and 60% of the stress close to the ground surface for the column with no fines and 20% fines, respectively. For the cases with fines content of 10% and 20%, the maximum excess pore pressure is in average 5% and 10% greater than the case without fines, respectively, and the dissipation rate of excess pore pressure is in average 18% and 24% slower than the case without fines. The column treated foundation prevents the water ponding on the surface as that occurs for the untreated foundation. The undrained shear strength of the soil close to the column increases by 18% at the depth of 100 mm, and 6% at the depth of half column, regardless of the fines.     

A study on biological clogging of nonwoven geotextiles under leachate flow

This paper presents results of long-term permittivity tests using leachate to evaluate biological clogging of nonwoven geotextiles. Three types of geotextiles with varying masses per unit area were used in the tests. The identification and quantification of microorganisms in the geotextile were carried out as well as microscopic investigations. The accuracies of semi-empirical models to evaluate the kinetics of bacteria growth and to correlate hydraulic properties and microbiological parameters were examined. Permittivity tests under increasing water heads were also performed on the geotextile samples already subjected to long-term leachate flow in order to evaluate the values of water heads required to wash the biofilms out of the geotextile pores. The results of the tests showed the marked reduction of geotextile permeability due to biological clogging and that the results of the predictions by semi-empirical methods were consistent with the biological mechanisms observed.     

大型换流站阀厅结构参数优化设计

针对阀厅结构在纵向地震作用下存在较明显的扭转效应,对阀厅结构进行结构优化设计,并对比分析在多遇地震作用下原结构模型与优化结构模型的地震响应。分析表明,采用轻质混凝土砌块砖减小结构自重,适当地加大剪力墙、构造柱和圈梁截面尺寸均可以改善阀厅结构纵向扭转效应,其中采用轻质混凝土砌块砖的方式控制结构纵向扭转效应最明显;适当增大构造柱和圈梁截面能有效地控制结构横向地震响应;结构抗侧力构件的参数变化对悬吊设备地震响应的影响不显著。     

金刚石钻头钻削石材参数对其表面温度影响研究

本文采用热压烧结金刚石钻头钻削花岗岩、大理石和砂岩.采用红外线测温仪在线测量金刚石钻头表面温度.实验结果表明金刚石钻头表面温度随主轴转速和进给速度增加而加大,同时表面温度随钻削时间增加而加大.钻削花岗岩时表面温度最高,钻削砂岩时表面温度最低.     

短柱的设计

介绍了短柱的概念,对短柱的破坏形态进行了分析,提出了易形成短柱的部位,深入地探讨了短柱的设计要点,以帮助设计人员搞好短柱设计,从而提高短柱的延性,改善短柱的变形能力,避免脆性破坏的发生。     

单井回灌中回灌堵塞与回灌压力波动对渗流场影响的理论研究

为分析承压含水层单井回灌过程中回灌堵塞与回灌压力波动对渗流场的影响,通过引入渗透系数衰减模型和设置正弦变化的水头边界,建立了考虑回灌堵塞效应的单井变压力回灌模型,并利用Weber变换得到了模型的解析解,进而据此分析了渗透衰减与回灌压力波动对渗流场的影响。研究结果表明:①渗透系数衰减对回灌流量与承压水头抬升具有抑制作用,且该抑制作用随着衰减指数的增大及回灌时间的推移而愈加显著;②回灌压力波动对渗流场分布存在影响,且当波动幅值越大而频率越小时影响越显著;③回灌总量受波动幅值和频率的影响相对较小。提出的回灌模型可为回灌压力与回扬周期设计提供依据。     

中国城市雨洪管理教育能力提升研究

探讨了雨洪管理新理念,提出提升中国雨洪管理教育能力的相关措施。通过分析中国雨洪管理教育的必要性和雨洪管理教育的现状,剖析当前雨洪教育管理存在的问题,挖掘提升教育管理的新举措。结合中国发展的实际情况,熟练掌握并运用发达国家城市雨洪管理的经验知识,以自主创新的精神探索适合中国城市雨洪管理的教育模式;构建以人为本的核心理念,牢固的专业知识,"天人合一"的设计理念,并搭建与教育质量保障措施并轨运行的新模式。研究显示,采用良好的教学模式,中国雨洪管理教育能力在新的管理理念引导下必然能稳步提升。     

钢筋保护层设计对结构裂缝的影响研究

探讨了混凝土保护层的作用机理及保护层开裂的原因,并通过计算,分析了影响保护层最大裂缝宽度的因素,指出采用相对合理的保护层厚度能够在一定程度上控制和减小混凝土裂缝宽度。     

原路面当量模量对沥青路面大修设计的影响

应用GAMES程序分析了原路面当量模量取值不同时对沥青路面大修路面结构的影响,并研究了铣刨前路面弯沉值与铣刨后原路面当量模量之间的相关关系,以提高铣刨后原路面当量模量取值的合理性。     

Case study: the performance and design outline of a buffering stormwater drainage system for a low-lying area

Performance evaluation and safety assessment of a buffering stormwater drainage system (BSDS) for a low-lying area are discussed in this paper. Unlike a conventional pump drainage system, the BSDS, which drains stormwater runoff of a low-lying area to a nearby channel system through underground conduits with gravity, and then buffering peak flows with the storage capacity of a channel system, will discharge stormwater to rivers outside the low-lying area with pumps or flood gates if necessary. This kind of drainage system is considered to be environment friendly and economic both in terms of capital cost and operating & maintenance expenses. To investigate the design parameters and evaluate the performance and safety of BSDS, a hydraulic model coupling the conduit systems and a channel system was developed in this paper, and a case-study approach based on field investigation and simulation test was used. Moreover, the design requirements for safety of BSDS were drawn through a simulation test.     

溶洞因素对上部结构柱应力的影响

在岩溶地质条件下,考虑上部结构与地基基础的相互作用,通过三维整体建模考虑变形协调。利用ANSYS有限元软件计算分析某一算例,通过改变溶洞半径、埋深、形状及改变溶洞围岩的弹性模量、泊松比及厚度,得出溶洞因素对上部结构应力的影响变化规律。     

国外绿色屋顶对雨水径流水量水质影响的研究

介绍了绿色屋顶的起源及发展现状,分析了绿色屋顶对雨水径流中水量与水质的影响,指出在水量方面,绿色屋顶可有效减少雨水径流,但在水质方面,需加强对污染物的控制。     

混凝土墩柱塑性铰区箍筋设计用量试验研究

建立塑性铰区箍筋用量与墩柱抗震性能目标的定量关系,通过延性指标计算箍筋设计用量,是当前延性抗震构造设计的重要研究内容。大批学者给出众多箍筋用量的计算公式,但其中大部分无法给出任意延性系数对应的设计配箍率,少量可定量公式的适用性和准确性有待提高。为此,基于课题组21个桥墩试验结果、PEER数据库中135个墩柱试件及相关学者的18个墩柱试件,在大量试验数据的基础上,分析实心及空心墩延性性能的主要影响因素,以轴压比、剪跨比、纵筋及混凝土强度、配筋率及位移延性系数等为参数,回归得到不同类墩柱塑性铰区约束箍筋用量的简化算式。关于试验墩柱的计算结果表明,回归公式比既有公式更适用于估算各类墩柱约束箍筋的设计用量。     

基于粗糙集的大型公用建筑设计项目技术风险评价

根据建筑业设计规范和标准,构造大型公用建筑设计项目的技术风险指标体系,运用基于粗糙集和模糊数学理论,建立了大型公用建筑设计项目的技术风险模糊综合评价模型,通过算例说明,该模型是可行的,且评价结果符合实际情况。