Quantifying costs and lengths of urban drainage systems with a simple static sewer infrastructure model

A generic model is introduced that is capable of quantitatively representing the combined sewer infrastructure of a settlement. It consists of a catchment area module, which calculates the length and size distribution of the needed sewer pipes on the basis of rain, housing densities and area size. These results are fed into the sewer construction costs module in order to estimate the combined sewer costs of the entire catchment area.

The model could be successfully fitted to existing Swiss sewer systems, indicating that it can emulate their principal characteristics. It could also identify fundamental differences in sewer designs in cities with historic roots. The results confirm that there are economies of scale for combined sewer systems in Switzerland. The modelling approach proved to be an effective tool for understanding the factors underlying the cost structure for water network infrastructures.     

Optimisation of site layout planning for multiple construction stages with safety considerations and requirements

This paper develops a mathematical formulation to model and optimise site facility locations inside a construction site for a construction project's different stages. The existence and dimensions of a construction project's available locations and site facilities can be varied across the construction stages. Without proper planning, unnecessary facility relocations may be required in each construction stage, resulting in a higher construction cost and longer construction time due to the need to dismantle and set up site facilities. Site layout plans should be optimised using a multiple-stage model to avoid unnecessary changes to facility settings across construction stages, improving efficiency. The proposed site layout problem with multiple construction stages is formulated as a binary-mixed-integer-linear programme, which can be solved by a standard branch-and-bound algorithm using the commercial software package LINGO. The mathematical objective function established in the solution process aims to minimise the total cost, which consists of the material transportation cost between the relevant site facilities and the dismantling, setup and relocation costs for all of the involved site facilities in each construction stage. Numerical examples using the proposed mathematical model to optimise different site layout settings for a construction site are given, including (1) a reference site layout plan using the conventional static single-stage approach, (2) a multiple-stage construction site layout plan and (3) a multiple-stage site layout plan with additional safety design considerations.     

无锡市芦村污水处理厂进厂第四干管设计优化

介绍了无锡市芦村污水处理厂长为20.02 km的进厂第四干管的工程设计优化情况。在设计中充分考虑了系统布局的优化、与现状干管系统的匹配、管材的合理选用、管道与河道相交的做法并运用多种施工技术。在国内首次大规模将物联网技术应用于管网系统中,对同类型污水收集系统工程建设具有一定的借鉴作用。     

Measuring surplus capacity for multiobjective optimal design of foul sewer systems

ABSTRACT

This paper proposes a new performance index of foul sewer systems, i.e. sewer conveyance capacity (SCC) index, to quantify the surplus capacity for multi-objective optimization design problems. The use of the new SCC index is demonstrated using a hypothetical network and a real-world foul sewer network. Results obtained show clear trade-offs between SCC and the other two objectives considered, i.e., capital and operational costs and greenhouse gas emissions. The results show that the upstream sewers in the system often have a relatively large surplus capacity, while the sewer mains operate close to the design capacity. Moreover, SCC is compared with three common indicators at both individual sewer and system-wide levels. Strong correlations between SCC and other indicators are revealed, implying that SCC is a good representation of system performance and can provide a more comprehensive picture of the foul sewer system performance.     

污水管网的优化设计

对于污水管网的优化设计,采用了图论中树形结构的理论来描述污水管网,提出用三叉树的形式来处理污水管网的网络结构,把管段当作树的节点作为研究对象;利用树的遍历中的后序法(即节点递归算法)进行水力计算,在优化计算时采取了枚举标准管径法来选取管径,可以提高运算速度;在优化程序中寻求造价最低、最优的同时考虑了管道费用和泵站费用.采用Delphi语言编制了污水管网优化程序,并且用天津某一小区的污水管网对此程序进行了实例考核.其优化设计思路可推广到雨水管道.     

Optimization of material hoisting operations and storage locations in multi-storey building construction by mixed-integer programming

Material storage locations incurring minimum transportation costs in construction are a common construction management problem. Storage locations influence the delivery path and overall project efficiency. Lower floors of buildings after completion and developing sufficient structural strength will be utilized as storages and layout plans should be designed to achieve maximum construction efficiency in terms of total transportation and distribution costs. A mixed-integer programming is formulated to optimize the vertical hoisting and storage layout solvable by a branch-and-bound technique. Total transportation cost is derived as an objective for optimization. Material storage locations are defined as binary variables. Linear constraints are developed to satisfy design requirements. A numerical example storing 10 material types and delivering materials in a 30-storey building is given for illustration. Numerical results optimized by the MIP approach will be compared with those optimized by the genetic algorithms. The MIP solution shows better solution quality taking less computing time.     

Optimization of sewer networks using the mixed-integer linear programming

This paper introduces a method for optimizing sewer networks using the mixed-integer linear programming (MILP) for a given layout. The objective function is defined as the sum of the costs for pipe purchase, pipe-laying, and manhole construction expressed in linear terms and subject to minimum and maximum allowable slopes, velocities, and relative depths for both minimum and maximum sewage discharge rates in each pipe. Additionally, provisions are made as constraints or conditions to ensure that a minimum pipe cover is required, that pipe diameters do not decrease in the flow direction, and that pipes maintain a steady elevation at each manhole. All the non-linear constraints are transformed into the linear format. Pipe slope, binary variables accounting for commercial pipe diameters and average implemented depths have also been considered as decision variables. Finally, the performance of the proposed optimization method is evaluated in a benchmark sewer network from the literature.     

A decision-making system for construction site layout planning

A decision-making system, which consists of input, design, evaluation and selection, and output stages, is proposed to solve dynamic, multi-objective and unequal-area construction site layout planning (CSLP) problem. In the input stage, the multiple objectives, schedule planning and site condition are determined. In the design stage, two mathematical optimization models max-min ant system (MMAS) and modified Pareto-based ant colony optimization (ACO) algorithm are employed to solve single objective optimization (SOO) and multi-objective optimization (MOO) problem respectively. In the evaluation and selection stage, the intuitionistic fuzzy TOPSIS method is used to evaluate and select the best layout plan among the generated layout alternatives from the design stage. The performance of the proposed decision-making system, which was verified by a residential building project, shall assist the practitioners in the construction industry to deliver construction projects in a more efficient and effective manner, and thus construction costs could be reduced significantly.     

Constrained Ant Colony Optimisation Algorithm for the layout and size optimisation of sanitary sewer networks

The incremental solution building capability of Ant Colony Optimisation Algorithm (ACOA) is used in this paper for the efficient layout and pipe size optimisation of sanitary sewer network. Layout and pipe size optimisation of sanitary sewer networks requires optimal determination of pipe locations, pipe diameters and pipe slopes leading to a highly constrained mixed-integer nonlinear programming (MINLP) problem presenting a challenge even to the modern heuristic search methods. A constrained version of ACOA equipped with a Tree Growing Algorithm (TGA) is proposed in this paper for the simultaneous layout and pipe size determination of sewer networks. The method is based on the assumption that a base layout including all possible links of the network is available. The TGA algorithm is used in an incremental manner to construct feasible tree-like layouts out of the base layout, while the constrained ACOA is used to optimally determine the cover depths of the constructed layout. Proposed formulation is used to solve three hypothetical test examples of different scales and the results are presented and compared with those produced by a conventional application of ACOA in which an ad-hoc engineering concept is used for layout determination. The results indicate the effectiveness and efficiency of the proposed method to optimally solve the problem of layout and size determination of sewer networks.     

An economic loss model for failure of sewer pipelines

Estimating the costs of failure for sewer pipelines is usually accompanied with uncertainties because of the difficulty in capturing the relationship between the physical and economical characteristics of failed pipelines. To reduce such uncertainties economic loss models are usually used to evaluate the consequences of failure. This paper presents a methodology to estimate economic loss as a result of sewer pipelines’ failure using cost benefit analysis approach. Costs of sewer pipelines’ failure in addition to costs resulting from avoiding such failures are identified and analysed. To validate the proposed methodology, actual costs from a real failure incident were compared with the proposed model outputs. The model could estimate the direct and indirect costs with a deviation ranging between 10–12% and 22–30%, respectively. By implementing the proposed methodology on two case studies, it was found that the indirect costs as a result of sewer pipelines’ failure represent a significant portion ranging between 89 and 94% of the total costs of failure. Also, it was found that costs related to environment, delays to work and traffic disruptions contribute by 12–35% to the indirect costs.     

Long-term field test of an electrochemical method for sulfide removal from sewage

Corrosion caused by hydrogen sulfide leads to significant costs for the rehabilitation or replacement of corroded sewer pipes. Conventional methods to prevent sewer corrosion normally involve the dosing of significant amounts of chemicals with the associated transport and storage costs as well as considerable maintenance and control requirement. Recently, a novel chemical free method for sulfide abatement based on electrochemical sulfide oxidation was shown to be highly effective for the removal of sulfide from synthetic and real sewage. Here, we report on the electrochemical removal of sulfide using Ta/Ir and Pt/Ir coated titanium electrodes under simulated sewer conditions during field trials. The results showed that sulfide can successfully be removed to levels below the normal target value at the end of a simulated rising main (i.e. <1 mg/L). A coulombic efficiency for dissolved oxygen generation of ∼60% was obtained and was independent of the current density. Scaling of the electrode and the membrane was observed in the cathode compartment and as a result the cell potentials increased over time. The cathode potentials returned to their original potential after switching the polarity every two days, but a more frequent switching would be needed to reduce the energy requirements of the system. Accelerated lifetime experiments indicated that a lifetime of 6.0 ± 1.9 years can be expected under polarity switching conditions at a pH of 14 and significantly longer at lower pH values. As operating the system without switching simplifies construction as well as operation, the choice whether to switch or not will in practice depend on operational cost (higher/lower energy) versus capital cost (reactor and peripherals). Irrespective of the approach, our study demonstrates that electrochemical sulfide control in sewer systems may be an attractive new option.     

Optimal design program for gravity sanitary sewers

The development and implementation of a Fortran computer program called OGSDP to design a least-cost gravity sanitary sewer system are presented. OGSDP is a model that finds the least-cost design for a non-looping, gravity sanitary sewerage system for a given set of design parameters, costs and lay-out. The final design is the least-cost combination of pipe sizes, upstream and downstream invert elevations (of each pipe) and the corresponding manhole sizes. OGSDP respects most Ten States Standards' (1978) design guidelines. OGSDP determines an initial sewer system design using a heuristic procedure, and then improves the design using discrete dynamic programming with successive approximations to obtain the final least-cost design. It is a practical and efficient tool in the design of sanitary sewer systems.     

Automated detection of sewer pipe defects in closed-circuit television images using deep learning techniques

Sanitary sewer systems are designed to collect and transport sanitary wastewater and stormwater. Pipe inspection is important in identifying both the type and location of pipe defects to maintain the normal sewer operations. Closed-circuit television (CCTV) has been commonly utilized for sewer pipe inspection. Currently, interpretation of the CCTV images is mostly conducted manually to identify the defect type and location, which is time-consuming, labor-intensive and inaccurate. Conventional computer vision techniques are explored for automated interpretation of CCTV images, but such process requires large amount of image pre-processing and the design of complex feature extractor for certain cases. In this study, an automated approach is developed for detecting sewer pipe defects based on a deep learning technique namely faster region-based convolutional neural network (faster R-CNN). The detection model is trained using 3000 images collected from CCTV inspection videos of sewer pipes. After training, the model is evaluated in terms of detection accuracy and computation cost using mean average precision (mAP), missing rate, detection speed and training time. The proposed approach is demonstrated to be applicable for detecting sewer pipe defects accurately with high accuracy and fast speed. In addition, a new model is constructed and several hyper-parameters are adjusted to study the influential factors of the proposed approach. The experiment results demonstrate that dataset size, initialization network type and training mode, and network hyper-parameters have influence on model performance. Specifically, the increase of dataset size and convolutional layers can improve the model accuracy. The adjustment of hyper-parameters such as filter dimensions or stride values contributes to higher detection accuracy, achieving an mAP of 83%. The study lays the foundation for applying deep learning techniques in sewer pipe defect detection as well as addressing similar issues for construction and facility management.     

Optimization of tower crane and material supply locations in a high-rise building site by mixed-integer linear programming

Facility layout design and planning within construction sites are a common construction management problem and regarded as a complex combinatorial problem. To transport heavy materials, tower cranes are needed and should be well located to reduce operating costs and improve overall efficiency. Quadratic assignment problem (QAP), non-linear in nature, has been developed to simulate the material transportation procedure. Applying linear constraint sets, the quadratic problem can be linearized and the problem could be formulated into a mixed-integer-linear programming (MILP) problem solvable by a standard branch-and-bound technique for true optimal results. Numerical findings show that MILP results outperform those optimized by Genetic Algorithms with almost 7% on improving the objective function values in which facilities and locations can be modeled using integer variables. To demonstrate the design flexibility of using MILP formulation, the problem is also extended to non-homogeneous storages where different materials can be stored at a single supply point.     

Experimental study of water hammer-induced forces and deformations in dry pipe fire protection systems

When designing a fire protection system, every effort should be taken to ensure its maximum operational safety. Therefore, correct identification of the dynamic load affecting the system during water hammer occurrence is essential to increase the operational reliability of such fire protection systems on their design stage. A test stand with a simple deluge system was designed for the experiments. The layout consisted of a distribution duct and one straight branch line (including three different diameter values) equipped with three fire nozzles. However, the main objective of this study is not to study the water hammer itself but, rather, to study the forces and displacements induced by the water hammer. The measurement results will be used to calibrate a mathematical model created using MATLAB software. The verified model will in turn enable numerical determination of the dynamic force values for larger systems. Furthermore, these force values will allow for pinpointing the critical sections, for which it is necessary to prevent displacements or transfer the acting forces to the building structure.     

The Form of the Core

This article assesses the public water and sewer costs associated with alternative housing patterns. These patterns are defined in terms of lot size, tract dispersion, and distance from existing water and sewer service centers. The engineering cost model presented here gives empirical evidence of how sensitive local government service costs are to the spatial pattern of single-family residential development. The results show that more spread out housing patterns are more costly to supply with public water and sewer services, but that shifting a majority of these costs to the private sector may be a relatively simple matter.     

深埋硬岩隧洞开挖诱发破坏的防治对策研究

 针对深埋硬岩隧洞围岩脆性破坏分析时传统应力指标的局限性和相应防治措施理论研究不足的特点,在数值分析中应用反映高地应力下硬岩脆性破坏特点的RDM本构模型,结合局部能量释放率评价指标分析硬岩脆性破坏过程中能量释放的强弱,对深埋隧洞开挖过程中防治围岩脆性破坏的设计及施工措施进行综合性研究。首先,通过评价隧洞群洞间距、施工进度等设计方案对围岩能量释放的影响,提出预防岩爆发生的区域性对策。然后,针对能量释放的时空演化规律,本着减压卸能的原则,给出支护时机、支护类型和参数的设计建议。同时,在施工控制措施方面通过分析在掌子面上布置应力释放孔爆破卸压防治岩爆的效果,给出应力释放孔布置方案的优化建议。最后,应用上述方法对锦屏二级水电站辅助洞围岩的脆性破坏提出工程防治措施,实践结果表明,所提出的防治对策完全可行,可供类似工程借鉴。     

Fast network multi-objective design algorithm combined with an a posteriori procedure for reliability evaluation under various operational scenarios

This paper presents a methodology for the optimal design of water supply networks. It features a multi-objective optimisation (aimed at minimising costs and maximising resilience) and a subsequent ‘retrospective’ evaluation of network reliability under various operational scenarios. The multi-objective optimisation is based on an algorithm specifically developed for the design of real networks which feature a very high number of nodes and pipes. The ‘retrospective’ evaluation of network reliability is assessed considering resilience contrasted with several other indexes adopted to describe the operational performance of the network under critical scenarios such as segment isolation or hydrant activation, and different water demand conditions. In the applications two case studies, made up of a simple benchmark network and a real network respectively, are considered for the multi-objective optimisation; the ‘retrospective’ evaluation of reliability is performed only on the real network. The latter example clearly highlights that the procedure proposed allows reliability and performance to be offset against cost, consenting informed choice of the optimal network configuration.     

开口拱塔斜拉桥空间布置拉索优化设计

某跨高速公路斜拉桥主塔为空间弧形变截面结构,拉索采用带螺纹的套筒连接。为研究这种开口拱塔斜拉桥拉索的布置及设计,首先根据该桥的受力特点,选取索力、控制截面弯矩及塔顶横桥向位移为约束条件,以主梁、主塔的应变能最小为目标,建立二次规划模型;然后采用多约束条件下的最小能量法,在同样的目标下对不同布置形式的拉索进行成桥恒载索力优化;最后基于优化后的索力,对拉索的布置形式进行对比分析,选取优化后的布置形式进行了拉索的设计。分析结果表明:拉索不同布置形式下的塔顶横向位移相差不大;网状布置可以减小拉索的活载应力幅,节省材料用量;拉索设计需考虑螺纹连接处的应力集中现象。     

A database and model to support proactive management of sediment-related sewer blockages

Due to increasing customer and political pressures, and more stringent environmental regulations, sediment and other blockage issues are now a high priority when assessing sewer system operational performance. Blockages caused by sediment deposits reduce sewer system reliability and demand remedial action at considerable operational cost. Consequently, procedures are required for identifying which parts of the sewer system are in most need of proactive removal of sediments. This paper presents an exceptionally long (7.5 years) and spatially detailed (9658 grid squares - 0.03 km² each - covering a population of nearly 7.5 million) data set obtained from a customer complaints database in Bogotá (Colombia). The sediment-related blockage data are modelled using homogeneous and non-homogeneous Poisson process models. In most of the analysed areas the inter-arrival time between blockages can be represented by the homogeneous process, but there are a considerable number of areas (up to 34%) for which there is strong evidence of non-stationarity. In most of these cases, the mean blockage rate increases over time, signifying a continual deterioration of the system despite repairs, this being particularly marked for pipe and gully pot related blockages. The physical properties of the system (mean pipe slope, diameter and pipe length) have a clear but weak influence on observed blockage rates. The Bogotá case study illustrates the potential value of customer complaints databases and formal analysis frameworks for proactive sewerage maintenance scheduling in large cities.