Interactive Software for Selection of Technologies for Installation and Replacement of Utilities

Dec 06, 2005

The decision of how to accomplish the installation or repair of a buried pipe in an urban environment involves tangible and intangible parameters. This paper outlines the development of comprehensive, yet straightforward and easy to use interactive software for the evaluation of alternative construction methods that can be employed in the installation, rehabilitation, or replacement of buried pipes and conduits. The software emphasizes simplicity and practicality, and limits input data to those readily available to utility engineers at the design stage of the project. Based on the specific characteristics of the problem(s) facing the decision-maker, the software performs a preliminary screening, eliminating technologies unlikely to meet the project’s requirements. A technical evaluation is then undertaken during which the technical capabilities of the various technologies identified in the first step are compared with the project’s attributes. Next, a risk analysis is performed based on the characteristics of the project's environment and the anticipated soil conditions. The model offers an interactive graphical user interface, and it is compiled as a standalone application compatible with common Microsoft operating systems platforms.

Background

This project was commissioned by the National Utility Contractors Association (NUCA) Trenchless Technology Sub-Committee and is intended to be a companion to NUCA's Trenchless Construction and Rehabilitation Methods Manual (4th Edition). The program, titled U-COMET (Utility Construction Methods Evaluation Tool), was designed as stand-alone software to assist municipal and utility engineers in evaluating the technical feasibility of various traditional open cut, trenchless construction, and inline replacement methods for a specific project. U-COMET is compatible with IBM operating platforms such as Windows XP and Windows 2000. The program takes into account extensive performance data for 26 construction methods commonly used in utility type projects.
The objective of this project was to develop and codify an algorithm to accomplish the following tasks. First, the program needed to perform a sound technical evaluation as a screening measure to eliminate incompatible construction methods. Next, U-COMET would need to evaluate the overall perceived risk associated with the competing alternatives. Finally, the program needed to raise awareness and provide guidance to the utilization of trenchless technology methods.
Method Database

The relational method databases contain a plethora of information about each method. The databases contain general information about each method, which includes a detailed method description, a color picture and the methods expected environmental impact and extent of excavation. The databases also contain information about the method's technical capabilities, which includes the maximum and minimum pipe diameters, the maximum and minimum drive lengths, and the maximum and minimum allowable depths of cover. The databases also contain pipe compatibility information for ten commonly used pipes as well as soil compatibility information for ten types of soil as well as ground water table limitations. A schema showing the relationships among the relational tables in the databases are shown in Figure 1.
The relational method database contains information about twenty-six construction methods, eighteen of which are trenchless technology methods, six of which are inline replacement methods, and two open cut methods. Table 1 lists the twenty six methods which U-COMET contains in its construction method relational database.
The construction method database is updatable, customizable and expandable. The user can easily add new methods or pipe materials, and update the capabilities of existing methods as technology develops and new innovations are introduced into the trenchless market. Changes can be made directly from the construction method database forms by inputting new values and pressing Update. The database can also be expanded from the Microsoft Access file entitled U-COMET Database. Thus the software is expected to remain a 'living application', remaining a useful and relevant decision support tool for a prolonged period of time. Figure 2 shows a sample method database form for Pipe Ramming from U-COMET.
Technical Evaluation

The technical evaluation begins by defining the type of problem the user is facing. It is believed that all buried pipe problems can be reduced to either a structural problem or a capacity problem. U-COMET incorporates a built in wizard, which is based on a series of interactive questions presented to the user. Based on the user's answers, certain categories of construction methods might be eliminated. Figure 3 shows the built in wizard which contains a set of interactive questions for a structural problem.
The next step in the technical evaluation is the input of the project specific data. Four categories of information are input during this stage. The first category includes project specific parameters such as drive length, the pipe diameter, the depth of cover, and elevation of the ground water table, shown in Figure 4. Also included in the input are the anticipated degree of accuracy of alignment and profile, (defined in the U-COMET user's manual).
The second category of information is the new pipe material(s) and the user is asked to select from a list of commonly used pipe materials, as shown in Figure 5.
The third category of user input is the soil compatibility parameters, in which the input consists of the dominant soil(s) conditions (at least one, but no more than three) in terms of percentages along the proposed alignment. Figure 6 shows the soil parameters input data form for a typical project.
The final category of user specified information is related to the viability of inline replacement options, as shown in Figure 7.
Risk Analysis

After the technical evaluation stage, the methods that were deemed technically suitable for the project are then reevaluated for the relative level of risk associated with four different categories of risk. The first category is the installation parameters: drive length, pipe diameter, and depth of cover. In this category the project specific values are compared to the limits of each of the remaining construction methods. This comparison results in a percentage which is then assigned a risk level based on the percentage ranges shown in Table 2.
An example of how the program would assign a risk classification is shown in the following sample project. If the project has a drive length of 280 feet, a pipe diameter of 12 inches, and a depth of cover of 21 feet and one of the technically viable methods is Pipe Bursting (Static), then the risk classification will be assigned according to Table 3.
The second category of risk is the assessment of the compatibility of a given construction method with anticipated geological conditions. Geological conditions were divided into ten categories, with soil types been further quantified in terms of the number of blows per foot (as per ASTM 1452). The geological conditions considered by U-COMET are: soft cohesive soils (N ≤ 5), firm cohesive soils (5 ‹ N ≤ 15), stiff-hard cohesive soils (N › 15), loose cohesionless soils (N ≤ 10), medium cohesionless soils (10 ‹ N ≤ 30), dense cohesionless soils (N › 30), gravel, cobble and/or boulders, sandstone and bedrock. The compatibility of each construction method with the ten soil classes is designated in the database as either: fully compatible (Y), possibly compatible (P), or incompatible (N). The rules of acceptance or rejection are given below:
  1. If one or more of the dominant soil types is considered incompatible (N) with a given method, the method is deemed not permissible and is eliminated from further consideration.
  2. If all geological conditions were found to be compatible (Y) with the construction method in question, then the method is considered to be permissible and the associated level of risk is considered to be very low.
  3. If all geological conditions were found to be possibly compatible (P) with the construction method in question, then the method is considered to be permissible and the associated level of risk is considered to be very high.
  4. If geological conditions were found to be a combination of compatible (Y) and possibly compatible (P) with the construction method in question, then the method is considered to be permissible and the associated level of risk will ranged from very low to very high depending on the percentage of length of the alignment of the possibly-compatible soils which is shown in Table 4.
The third category of risk is the SET Index, which takes into consideration the availability of specifications, owner’s experience with a given method and the method’s track record. Each of these parameters has three possible "values" which are summarized in Table 5.
The risk classification of the SET Index is based on the sum of the score for the three parameters, which is calculated based on the user selected value and can range from a minimum value of 3 to a maximum value of 9. The associated risk levels are defined in Table 6.
The final category of risk contains two distinct factors, site accessibility and environmental impact. Each method has an assigned risk value in the database for environmental impact based on the potential for ground settlement and heave (potential damage to paved surfaces, nearby utilities and foundations), erosion, removal of trees and flora, creation of temporary hazards (i.e. open trenches) and migration of drilling fluids to the surface. Environmental impact is one of the six primary risk factors which are used in the calculation of the Initial Risk Analysis Index Number (RAIN). The other five factors are: (A) the length ratio factor; (B) the diameter ratio factor; (C) the depth ratio factor; (D) the soil compatibility factor; and (E) the SET index factor. All of which were previously discussed. Before the calculation of the Initial RAIN a weight is assigned by the user to each of the six factors as shown in Figure 8 by adjusting the position of the sliding scale.
After the weights have been assigned for each of the six primary risk factors, an Initial RAIN calculation is performed. The Initial RAIN calculation is shown in Equation (1).

IRAIN Initial Risk Analysis Index Number
LR Risk Classification for Length Ratio
DR Risk Classification for Diameter Ratio
HR Risk Classification for Depth Ratio
SETI Risk Classification for SET Index
SCI Risk Classification for Soil Compatibility Index
EI Risk Classification for Environmental Impact
wLR Weight for the Length Ratio
wDR Weight for the Diameter Ratio
wHR Weight for the Depth Ratio
wSETI Weight for the SET Index
wSCI Weight for the Soil Compatibility Index
wEI Weight for the Environmental Impact


After computing the IRAIN a site accessibility adjustment is made, via the selection of the appropriate gamma value based on the description shown in Figure 9.
The gamma value and the IRAIN are then substituted into Equation (2) to complete the risk analysis.

RAIN = IRAIN x (1 + eγY) ⁄ (1 + eγ) (2)

RAIN Risk Analysis Index Number
IRAIN Initial Risk Analysis Index Number
(γ) Value from Figure 9
(Y) Value from Equation (3)


Y = (IRAIN-1) ⁄ 4 (3)

The Risk Analysis Index Number (RAIN) is the final risk value given by the program for each technically viable method. The final step consists of a form which displays each technically viable method and its RAIN score. The user is then able to make an educated decision about which method is best for their particular project.
Conclusion

U-COMET is a fully computerized algorithm for the evaluation of competing construction methods capable of installing, repairing, or replacing buried pipes and utilities. This approach emphasizes simplicity and practicality, while limiting the input data to that which is readily available to municipal and utility engineers via the utilization of an extensive built-in database. A built-in wizard as well as an extensive database is used to assist users who have limited experience with trenchless construction methods.

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