Financial Outlay Modeling for a Local Sewer Rehabilitation Strategy

Modern infrastructure systems are highly developed, with considerable capital funding invested in them. While capital is spent on new infrastructure initiatives, the maintenance of the present infrastructure must not be neglected. Increasingly, public agencies are being urged to develop improved systematic methodology for allotting their period budgets more appropriately so that the capacity of the installed infrastructure is more fully utilized and sustained. When planning the allocation of investment funds, multiple objectives may exist that are dependent on the constraints, resources available for construction, and the interrelationships and dependencies among all of the alternatives. This makes the task of planning, prioritizing, and allocating funds a complex exercise. This paper presents a financial outlay model called PRISM, Proactive Rehabilitative Sewer Infrastructure Management, which uses linear programming to optimize allocation of funding for the local sewer network maintained by the City of Edmonton, Canada. By grouping sewer pipes into categories based on parameters of age, diameter, material type, waste types, and average depth of cover, the model provides a mechanism for determining the most appropriate allocation or appropriation of funding given a planning horizon and budgetary constraints.     

Unique Requirements of Building Information Modeling for Cast-in-Place Reinforced Concrete

The building information modeling (BIM) tools that have matured for structural steel and precast concrete construction are not suitable for production modeling of cast-in-place (CIP) reinforced concrete structures. The main reason is that CIP structures are monolithic in nature, as opposed to the discrete objects that are typical of steel and precast. A consortium of 12 major contractors and design firms collaborated over a one-year period to formulate the functional requirements for development of a BIM tool for cast-in-place reinforced concrete. The functional requirements were derived from a process model used to scope and understand the processes surrounding reinforced concrete design and production. The functional requirements were finally expressed as a set of object schemas, defining relations, methods, and attributes needed. These are essential for software companies to incorporate in their BIM tools to provide for the unique needs of modeling CIP structures.     

Technical Performance Assessment of Urban Sewer Systems

Performance assessment in urban water infrastructures is an increasingly important field of knowledge. Performance has traditionally been expressed in a variety of ways relating mostly to local design practice, with hardly any consensus on how it should be measured or compared. The efficient technical management of these systems deserves a specific approach, suited to the methodologies regularly employed while planning, designing, constructing, operating, and maintaining the systems. At the engineering level, decisions are based on operational, physical, and resources data and on analyses deploying simulation models, geographic information systems, or other information systems. However, such tools tend to produce vast amounts of insufficiently aggregated or performance-oriented information. This paper presents a performance assessment system that is based on the decisional concept of utility functions and designed as a technical analysis tool with the purpose of shifting the focus of technical management of urban drainage systems to a performance-oriented view.     

Durability of Wet Bond of Hybrid Laminates to Cast-in-Place Concrete

Wet bond is a chemical bond developed to connect fiber-reinforced polymer (FRP) stay-in-place formwork to cast-in-place concrete for a composite action. Curing of chemical adhesive and fresh concrete occurs simultaneously in wet bond. Since FRP-concrete composite structure so designed is strongly dependent on the bond between FRP and concrete, a durable bond is of paramount importance. This paper presents a study on durability performance of wet bond exposed to sustained low temperature, freeze-thaw cycles, and wet-dry cycles. Single lap pull-off tests were conducted to evaluate the effect of exposure on bond. It was found that both first crack load and ultimate load of wet bond were reduced in comparison to dry bond. This reduction was more severe in first crack load than in ultimate capacity and was associated with voids, thickness, and surface of adhesive layer. The epoxy in wet bond had reached comparable degree of cure to dry bond and even gained a higher Tg. Environmental exposures did not show more impact on wet bond than on dry bond.     

Hydraulic Performance Index of a Sewer Network

An objective methodology is proposed for evaluating the hydraulic performance for possible rehabilitation of sewer systems. It involves assigning a hydraulic performance index to each pipe section. This hydraulic index reflects both the local surcharge in a pipe and the surcharge induced at upstream sections of the same branch in a sewer network. The hydraulic index also takes into account the vulnerability and the retention capacity of each pipe section. This index may be used directly to establish the rehabilitation priority of different sections to maximize hydraulic performance for the entire network. This methodology was successfully applied to the sewer system of the city of Laval in Canada. The results show how pipe dimensions and locations have the effect of surcharging or relieving a pipe network and how the hydraulic performance index adequately rates the contributions of sewer network components.     

Evaluation of High-Density Polyethylene Pipe Installed Using Horizontal Directional Drilling

This paper presents the results of field installations of high-density polyethylene (HDPE) using the horizontal directional drilling process. One each of 114 mm (4 in.) diameter standard dimension ratio (SDR) 17 HDPE pipe, 219 mm (8 in.) diameter SDR 17 HDPE pipe, and 324 mm (12 in.) diameter SDR 17 HDPE pipe were installed in a cohesionless soil medium. Various testing parameters were captured during the pullback phase of these three installations. These testing parameters consisted of utilizing pressure transducers to capture the pullback and rotational pressures on the drilling rig, installing linear potentiometers inside the HDPE pipe to measure the axial strain on the pipe, and applying an external load cell to quantify the loading on the pipe during the pullback phase. Comparisons of the pullback and rotational pressure on the drilling rig, loading on the HDPE pipe, and average and maximum strain experienced by the HDPE pipe are presented with respect to the installed pipe diameter.     

Dimensionless Approach for the Design of Flushing Gates in Sewer Channels

The various hydraulic and environmental problems related to the accumulation of solids have recently drawn increasingly attention to deposits in the management of sewer systems. Among the mechanical and hydraulic devices used for deposit removal, hydraulic flushing gates have proved to be a cost-effective solution and have been adopted in several sewer networks. This paper reports the results of an investigation on the scouring performance of flushing waves produced by hydraulic flushing gates. A numerical model based on the De Saint Venant–Exner equations in dimensionless form was validated by using data derived from laboratory experiments and was then utilized in this investigation. Simulations were carried out considering various values of the dimensionless parameters involved in the analysis, in order to obtain indications for the design and positioning of flushing devices in sewer channels. The problem of optimal flushing frequency was also investigated.     

Prediction of Sewer Condition Grade Using Support Vector Machines

Assessing the condition of sewer networks is an important asset management approach. However, because of high inspection costs and limited budget, only a small proportion of sewer systems may be inspected. Tools are therefore required to help target inspection efforts and to extract maximum value from the condition data collected. Owing to the difficulty in modeling the complexities of sewer condition deterioration, there has been interest in the application of artificial intelligence-based techniques such as artificial neural networks to develop models that can infer an unknown structural condition based on data from sewers that have been inspected. To this end, this study investigates the use of support vector machine (SVM) models to predict the condition of sewers. The results of model testing showed that the SVM achieves good predictive performance. With access to a representative set of training data, the SVM modeling approach can therefore be used to allocate a condition grade to sewer assets with reasonable confidence and thus identify high risk sewer assets for subsequent inspection.     

Effects of Iron on Chemical Sulfide Oxidation in Wastewater from Sewer Networks

Effects of iron on the kinetics and stoichiometry of aerobic chemical sulfide oxidation in wastewater from two different sites were studied at pH 8 and 20°C. Iron(III) chloride was added to the wastewater in concentrations of up to 20?g?Fe?m?3. The rate of aerobic chemical sulfide oxidation increased linearly with the iron(III) additions resulting in equal effects with wastewater from the two sites. Despite the significant effect of the iron(III) additions, the background concentrations of iron cannot explain the significant temporal and spatial variability of aerobic chemical sulfide oxidation kinetics reported in this study and in the literature. In this respect, other metals are probably also important. In addition to the impacts on the oxidation kinetics, the iron(III) additions resulted in a change of the oxidation stoichiometry. With increasing amounts of iron(III) added to the wastewater, less dissolved oxygen was required for the sulfide oxidation.     

Dynamics of Air Flow in Sewer Conduit Headspace

Pressurization in sanitary sewer conduit atmosphere is modeled using computational fluid dynamics techniques. The modeling approach considers both turbulent and laminar flow regimes. The turbulent model takes into consideration the turbulence-driven secondary currents associated with the sewer headspace and hence the Reynolds equations governing the air flow field are closed with an anisotropic closure model which comprises the use of the eddy viscosity concept for the turbulent shear stresses and semiempirical relations for the turbulent normal stresses. The resulting formulations are numerically integrated. The turbulent model outputs are verified with experimental data reported in the literature. Satisfactory agreement is obtained between numerical simulations and experimental data. Mathematical formulas and curves as functions of longitudinal pressure gradient, wastewater velocity, and sewer headspace geometry are developed for the cross-sectional average streamwise velocity.     

Optimal Layout of Sewer Systems: A Deterministic versus a Stochastic Model

The optimization of a new or partially existing urban drainage system may be modeled as a subproblems sequence of layout and optimal design within the discrete search space. The design optimization, incorporating the optimal selection of the pumping stations, intermediate manholes, pipe sections, and installation depths, for a general system fixed layout in plan, is a high level sequential decision problem which may be efficiently solved deterministically through a multilevel dynamic programming model. The optimal general layout may be selected in a deterministic way by means of a simple economical comparison of all plan solutions having optimized designs, for small to medium sized systems (if the specific restrictions of the applications are appropriately exploited) in practicable computer time. For larger dimension networks, where it is clearly impossible to achieve plan optimization with full enumeration (which is a NP complete), stochastic search models can be used. For the subproblem layout, an effective enumeration model is presented; the results of a stochastic model proposed previously, using simulated annealing for an application example, are compared and discussed in detail.     

Estimation of Uncertainty in Long-Term Sewer Sediment Predictions Using a Response Database

Regulations require U.K. water companies to reduce the number of properties at risk of sewer flooding. One of the potential causes of sewer flooding is the presence of persistent sediment deposits in sewers, such deposits are a common problem in many combined sewers. Although the regulations are risk based, there is a gap in the current knowledge on how the risk assessment is affected by the uncertainty in sewer sediment transport prediction. This paper describes the development of a methodology for estimating uncertainty in sewer sediment deposit depth predictions using existing empirically calibrated sediment load equations and Monte Carlo simulations combined with a response database. This methodology has been used to estimate the range of uncertainty of in-pipe deposit build-up predictions for a U.K. combined sewer system that suffered persistent deposition problems.     

Integrated Decision Support System for Optimal Renewal Planning of Sewer Networks

Municipalities are under increasing pressure to adopt proactive and optimized renewal strategies to reduce the risks, life-cycle costs, and resources needed to maintain acceptable performance and service levels of their infrastructure assets. A new integrated approach for optimal renewal planning of municipal infrastructure systems has been developed. This paper discusses the application of the proposed approach to implement a GIS-based decision support system (DSS) to support the renewal planning of sewer networks. Condition rating, risk assessment, and prioritization techniques are described. A procedure for identifying and selecting the most suitable renewal technologies is also presented. A genetic algorithm-based multiobjective optimization technique is used to find a Pareto front of feasible solutions, each comprising a set of sewers to be renewed each year, along with the associated costs and expected benefits in terms of condition improvement and risk reduction. The paper also presents an example application of the prototype DSS on the sewer network in Regina, Canada.     

Improved Simulation of Flow Regime Transition in Sewers: Two-Component Pressure Approach

Operational problems and system damage have been linked to the flow regime transition between free surface and pressurized flow in rapidly filling stormwater and combined sewer systems. In response, emphasis has been placed on the development of numerical models to describe hydraulic bores and other flow phenomena that may occur in these systems. Current numerical models are based on rigid column analyses, shock-fitting techniques, or shock-capturing procedures employing the Preissmann slot concept. The latter approach is appealing due to the comparative simplicity, but suffers from the inability to realistically describe subatmospheric full-pipe flows. A new modeling framework is proposed for describing the flow regime transition utilizing a shock-capturing technique that decouples the hydrostatic pressure from surcharged pressures occurring only in pressurized conditions, effectively overcoming the cited Preissmann slot limitation. This new approach exploits the identity between the unsteady incompressible flow equations for elastic pipe walls and the unsteady open-channel flow equations, and the resulting numerical implementation is straightforward with only minor modifications to standard free surface flow models required. A comparison is made between the model predictions and experimental data; good agreement is achieved.     

Influence of Wastewater Constituents on Hydrogen Sulfide Emission in Sewer Networks

Transport of wastewater in sewer networks causes potential problems associated with hydrogen sulfide in regard to odor nuisance, health risk, and microbially induced corrosion. To what extent these problems occur depends not only on the rate of sulfide formation but also on the rate of hydrogen sulfide emission into the sewer atmosphere. To gain understanding of the influence of wastewater constituents on the emission process, a number of batch experiments were conducted on domestic wastewater collected from sewer networks. The emission rate of hydrogen sulfide in the wastewater investigated was found to be approximately 60% of that in de-ionized water in terms of the overall mass-transfer coefficient, resulting in a correction factor (alpha) of 0.6. The alpha factor did not change significantly within the turbulence range studied (Froude numbers of 0.04–0.23). The Henry’s law constant for hydrogen sulfide in wastewater was observed to be close to that in de-ionized water, reflecting a correction factor (beta) of 1.0. By taking these results into account, modeling aspects of hydrogen sulfide emission in sewer networks are presented in this paper.     

Upgrading Torsional Resistance of Reinforced Concrete Beams Using Fiber-Reinforced Polymer

An experimental investigation is conducted on the improvement of the torsional resistance of reinforced concrete beams using fiber-reinforced polymer (FRP) fabric. A total of 11 beams were tested. Three beams were designated as control specimens and eight beams were strengthened by FRP wrapping of different configuration and then tested. Both glass and carbon fibers were used in the torsional resistance upgrade. Different wrapping designs were evaluated. The reinforced concrete beams were subjected to pure torsional moments. The load, twist angle of the beam, and strains were recorded. Improving the torsional resistance of reinforced concrete beams using FRP was demonstrated to be viable. The effectiveness of various wrapping configurations indicated that the fully wrapped beams performed better than using strips. The 45° orientation of the fibers ensures that the material is efficiently utilized.     

Liquefaction Induced by Auger-Cast Piles: How Common?

Clear water was observed percolating from the tops of fresh auger-cast piles and from the surrounding ground. This transient event, typically lasting less than an hour, occurred in approximately 40% of nearly 700 piles. The percolating water was apparently due to liquefaction of saturated loose to very loose sand, induced by the auger during installation of the piles. The liquefaction water was observed during this project because of a locally high water table; however, temporary flow of excess pore water through fresh grout must be a regular occurrence in loose sands, but is usually unnoticed because the groundwater table is normally well below the ground surface.     

Decision-Support System for the Rehabilitation of Deteriorating Sewers

This paper describes an automated and integrated detection, structural assessment, and rehabilitation method selection system for sewers based on the processing of video footage obtained by closed circuit television surveys. The system is based on a neural network classifier (NNC) trained to identify longitudinal cracks in sewers. Results obtained from experimentation with the NNC indicate that crack detection based on single-frame processing is not sufficient, and frame sequence processing substantially improves crack recognition rates. Based on the location of the cracks, local and global structural damage is assessed and a rehabilitation method is selected. Based on the significance of damaged sewers, the rehabilitation projects are being prioritized. An expert system coordinates the various modules in the system and connects them to a geographic information system.     

Structural Condition Assessment of Sewer Pipelines

The need of immediate supportive measures for sustainability of municipal infrastructures calls for better understanding of the behavior of various infrastructure network systems and their components. This paper presents a study which uses artificial neural networks to investigate the importance and influence of certain characteristics of sewer pipes upon their structural performance, expressed in terms of condition rating. In this study, back propagation and probabilistic neural network (NN) models were developed and validated. The data used in the development of these models were provided by the municipality of Pierrefonds, Quebec. It comprised of parameters related to sewer pipelines, pipe diameter, buried depth/cover, bedding material, pipe material, pipeline length, age, and closed circuit television (CCTV) based structural condition rating. The first six parameters are the independent variables of the models whereas CCTV based condition rating for these pipes is the dependent variable (i.e., the output of the models). The developed NN models were used to rank the parameters, in order of their importance/influence on pipe condition. It was found that, among the studied parameters, material attributes have highest influence on pipe structural condition, respectively, followed by the geometric and physical attribute group. Sensitivity analysis was then performed to simulate the structural condition of a pipe at a range of values of each input parameters. Results of sensitivity analysis describe the nature and degree of the influence of each parameter on pipe structural condition. The developed models are expected to benefit academics and practitioners (municipal engineers, consultants, and contractors) to prioritize inspection and rehabilitation plans for existing sewer mains.     

钻孔灌注桩加固柱基础在二轧成品库栈桥柱纠偏大修中的可行性探讨

结合工程实际情况认为采用钻孔灌柱桩的施工方法,可以解决在软弱地基土层上加固柱基础的难题,以及施工与正常生产的矛盾。