BOREAID_ New HDD Design Tool

UCT 2008 January 29-31, 2008, Atlanta GA - 1 -

BoreAidTM

: a New HDD Design Tool

A. Bayat1, K.P. Lawrence1 and M. Knight2

1 PhD candidates, Department of Civil and Environmental Engineering, University of Waterloo, Ontario,

Canada, N2L 3G1

2 Associate Professor, Department of Civil and Environmental Engineering, University of Waterloo, Ontario, Canada N2L 3G1

Abstract

Horizontal directional drilling (HDD) has emerged as a cost effective and environmentally friendly construction alterative to continuous open cut procedures for the installation of new buried pipeline. BoreAidTM, a new HDD design tool, was developed at the University of Waterloo. The software consists of five modular components: 1) bore planning; 2) calculating loads/deflections; 3) designing the drill sequence; 4) considering consequences of drill; and 5) equipment/tooling selection. This paper discusses the framework for the design of each of the five modules and their interaction. The power of this tool, user friendly inputs, and three dimensional visualizations are demonstrated using two case study examples. The paper shows how the use of design tools such as BoreAidTM can reduce the risk of failed bores, ensure good HDD practices are used, and lower overall project costs.

1. Introduction Since its conception in the early 1970s, horizontal directional drilling (HDD) has evolved into a well established and accepted alternative to continuous open cut construction, especially in developed areas due to its lower economic, social, and environmental impacts. The rapid development of HDD equipment and the use of this construction method for large and complex pipeline installations have resulted in the development of best practice manuals and training such as the North American Society of Trenchless Technology (NASTT) HDD Good Practice Manual and training courses. HDD equipment manufacturers and suppliers, along with a few specialty consultants, have developed basic software tools that will aid HDD contractors or designers in a particular aspect of the HDD process. These software tools, however, are limited in scope and do not consider the inter-complexities of the design process. BoreaidTM is the first commercially available software package that can be used by contractors, pipeline owners, and engineers to design, evaluate, and construct HDD projects using state-of-the-art industry best practices.

BoreAidTM: a New HDD Design Tool Bayat, Lawrence, & Knight


The purpose of this paper is to introduce a new HDD design tool called BoreAidTM (BoreAid is a trademark of Terein, Inc.) which was developed in collaboration with the Center for Advancement of Trenchless Technologies (CATT) at the University of Waterloo. The chosen name reflects the intention of the tool to aid the contractor, engineer, or project manager in the completion of simple and complex HDD projects using ASTM F1962, pipeline design good practice guidelines, and proper design criteria (see ASTM F1962 guidelines, Pipeline Research Council International Inc (PRCI), NASTT and other industry best practice guidelines). In this paper, we introduce the framework upon which BoreAid was developed, highlight key areas where implementation of an inter-connected system is necessary for an efficient HDD design, and present two case studies that exhibit the capabilities of this new HDD software tool.

2. BoreAidTM Framework BoreaidTM consists of five distinct modules that allow for the exchange of information from one module to another. The five modules are:

1. Bore Tool (bore planning), 2. Pipe Load Verifier (loads and deflections), 3. Drill Planner (drill sequence, drill time, and drill fluid calculator), 4. Limiting Pressure (hydro-fracture component of drill consequences), and 5. Equipment/Supplies (equipment and tooling selection).

To complete an efficient design for a HDD project, it is necessary to consider each module starting with module one advancing to module five as listed above.

3. BoreAidTM Development BoreaidTM, developed for the Microsoft Windows platform (2000, XP and Vista), was designed to be extremely user-friendly via input prompted fields, automated warnings/comments/recommendations, and advanced graphical interfaces that allow users to navigate through the virtual site conditions and view all calculated outputs. It allows users to export all relevant data to be printed as part of a contract/design proposal or imported to a spreadsheet programs such as MS Excel. In each module there are a series of tabs representing elements which are successively accessed by the user in creating the design. Implementation of each module along with tools to aid the designer in the completion of the project is discussed below.

3.1 Bore Tool The end goal of the Bore Tool module is to determine a path for the pipe while taking all site constraints and other factors into consideration. The Bore Tool collects vital project information, such as drill lengths, pipe type, pipe measurements, and drill rod parameters as shown in Figure 1.



Figure 1. Screenshot of general information inputs in Bore Tool module.

Topographical aspects such as sudden rises in elevation or valleys/mountains can also be input as shown in Figure 2.

Figure 2. Screenshot of topography inputs of Bore Tool module. Simple or complex topographical site conditions can be developed using BoreAidTM, as shown in Figure 3.



Figure 3. Different topographical condition. Site geological layering may then be input using a built-in existing database of sample soils based upon USCS, AASHTO, and typical soil classifications (Figure 4).

Figure 4. Screenshot of soil description inputs of Bore Tool module.

Above and below ground obstacles may then be input. Each type of obstacle has a corresponding “acceptable clearance zone” that may be input based upon existing standards (Figure 5).



Figure 5. Above and below ground obstacles. Surface obstacles inhibiting setup zones and no drill zones are automatically identified and warnings are generated should a utility conflict exist (Figure 6).

Figure 6. Set up and no drill zones. Once an acceptable bore path is created the program automatically checks that the radius of curvature, minimum depth of cover and entrance/exit angles are all within acceptable design limits. If they are not, a warning is automatically generated as shown in (Figure 7).



Figure 7. Screenshot of bore path calculation inputs of Bore Tool module.

3.2 Load Verifier In the Load Verifier module, the user is requested to input information on the pipe material to be installed and key installation parameters such as friction coefficients and bore slurry unit weight. It also contains easy to use check boxes to consider the effects of rollers and/or ballasts in load/deflection calculations. Once all information is input, the program automatically determines expected pipeline operational and installation loads. Both types of load calculations have design limitations/restrictions associated with them which are built directly into the software. Warnings are generated should the loads result in an inadequate factor of safety. Operational loads (earth pressure, water pressure, live load, net pressure) and deflections (earth load deflection, buoyant deflection, Reissner effect) are calculated based upon the bore path determined in the first module using Terzaghi, Stein or collapsed assumptions with respect to the bore condition (Figure 8).



Figure 8. Screenshot of operational load calculation in Load Verifier module

Various operational loads/pressures/deflections are calculated and available to the user either in spreadsheet or graphical format as shown in Figure 9.

Figure 9. Screenshot of soil pressure graph Estimated pipe pullback loads and stresses (bending stress, pullback stress, axial tensile stress) can be also be calculated using several user selected methods (following from



ASTM F1962, PPI, and other drag based models). Figure 10 shows a typical screenshot of calculated installation loads while Figure 11 shows the results in graphical form.

Figure 10. Screenshot of installation load calculation in Load Verifier module

Figure 11. Screenshot of pullback load graph All pipe loads are checked to make sure they fall within acceptable design limits for the proposed project. Figure 12 shows a typical screen shot of the evaluation tab.



Figure 12. Screenshot of load evaluation in Load Verifier module

3.3 Drill Planner The purpose of this module is to design a pilot bore/reaming sequence and estimate construction parameters such as total drill time, volume of drill fluid, etc. Additional parameters input first (over cut ratio, drill fluid to soil cut ratio, drill pump information). Then, the user can either graphically or manually enter the proposed reaming sequence.

Figure 13. Screenshot of utility to enter pilot bore and reaming sequence.



For each ream the soil volume cut, drill fluid volume, pump rate, total number of tanks of drill fluid required, and total time to complete the ream are determined (Figure 14). Warnings are generated if calculated parameters are outside good practice requirements or the drill pump capacity is exceeded.

Figure 14. Drill fluid/time requirements calculated by BoreAid

3.4 Limiting Pressure Hydro-fracture can occur when the pressure exerted inside the bore exceeds a limiting pressure. This limiting pressure is calculated using Delft Geotechnics method. Figure 15 shows this limiting pressure module input and calculation screen.

Figure 15. Limiting pressure calculated by BoreAid



3.5: Equipment/ Supplies The final module is Equipment/Supplies. Information from each of the previous modules is used to make recommendations and/or give general comments on factors of safety for proposed drill rigs, suitability of soils for completing the HDD project, and applicability/suitability of down hole tools and drill fluid additives (Figure 16 and 17).

Figure 16. Drill rig selection by BoreAid



Figure 17. Drill fluid selection by BoreAid

4. Application to Simple Drill Design In this section BoreAidTM is used to construct site conditions and perform load calculations/equipment recommendations for a typical simple HDD project. The client wishes to install an 8in nominal diameter HDPE DR 9 pipe that has a surface length of 2200 feet.

4.1 Geotechnical Considerations

Site conditions consist of a layer of well graded sand from the ground surface to a depth of 16 meters and the water table is at the surface. Typical sand properties are provided in Table 1.

Unit Weight (Dry), lbs/in3 0.000686

Unit Weight (Saturated), lbs/in3 0.000738

Friction Angle, degrees 30

Cohesion, kPa 0

Shear Modulus NA

Table 1. Soil parameters



4.2 Bore Path Design The bore is constructed automatically in BoreAid using the entrance/exit angles and the minimum depth of cover. In this project entrance and exit angles were chosen as 10 and 12 degrees, respectively, and the depth of cover was taken to be 35 feet. The resulting bore path is shown in the figure below. In determining this path, BoreAid calculates the required radius of curvature and checks to see if this value falls within acceptable limits.

Figure 18. Bore path calculated by BoreAid (exported from BoreAid).

BoreAid also allows the user to access the calculated bore path information. For instance, the user can print the bore path via drill rod locations along the path (see Figure 19)

Figure 19. Drill rod locations calculated by BoreAid (printed directly from BoreAid).

BoreAid allows the user to export these drill rod locations directly into an Excel (.xls) file. The user may then include them in their own analysis.



4.3 Load Calculations In this project, the operational loads calculated by BoreAid are given in Table 2 below.

Deformed (Terzahgi method)

Deformed (Stein method)

Collapsed

Earth Pressure 2.83 psi 1.89 psi 16.44 psi

Water Pressure 15.17 psi 15.17 psi 15.17 psi

Surcharge 0.0 psi 0.0 psi 0.0 psi

Internal Pressure 0.0 psi 0.0 psi 0.0 psi

Net Pressure 18.0 psi 17.06 psi 31.62 psi

Earth Deflection 0.77 % 0.51 % 4.48 %

Buoyant Deflection

0.071 % 0.071 % 0.071 %

Reissner Effect 5.8E-6 % 5.8E-6 % 5.8E-6 %

Net Deflection 0.84 % 0.58 % 4.55 %

Table 2 Calculated pressures and pipe deflections.

The values in this table represent pipe deflections at the location of maximum net pressure. The point-by-point values of each of these quantities as a function of drill rod location may be exported to an Excel file, if required. Alternatively, BoreAid contains an interface to plot and export all of the above parameters along the bore path as shown in Figure 20.

Figure 20. Earth pressure along the bore path (exported from BoreAid).

The built-in plotting environment allows you to label axis, change axis limits, and even convert the x-axis value automatically between inches, feet, and meters, regardless of the



units of the problem. In addition, BoreAid automatically labels key points of interest along the bore path which are crucial in the calculation of installation forces. Installation loads are also calculated and are summarized in Table 3. The four locations of interest are: the pipe entrance location (A), the location when the pipe reaches the depth of cover and is about to transverse horizontally (B), the location when the pipe is about to begin its rise to the surface (C), and the exit location (D).

A B C D

Pullback Stress 5.240E2 psi 6.651E2 psi 8.292E2 psi 8.734E2 psi

Pullback Strain 9.113E-3 1.157E-2 1.442E-2 1.519E-2

Pullback Force 1.209E4 lbs 1.535E4 lbs 1.914E4 lbs 2.016E4 lbs

Bending Strain 0 1.560E-4 2.244E-4 0

Bending Stress 0 psi 8.970 psi 12.90 psi 0 psi

Resultant Axial Tensile Stress 5.240E2 psi 6.741E2 psi 8.421E2 psi 8.734E2 psi

Resultant Axial Tensile Strain 9.113E-3 1.172E-2 1.465E-2 1.519E-2

Table 3 Summary of Installation loads

Table 4 shows installation loads if rollers are used under the pipe during installation. Rollers, ballasts, and additional bends are all options available to the user during the design procedure.

A B C D

Pullback Stress 9.773E1 psi 2.976E2 psi 7.613E2 psi 8.771E2 psi

Pullback Strain 1.700E-3 5.176E-3 1.324E-2 1.525E-2

Pullback Force 2.256E3 lbs 6.870E3 lbs 1.757E4 lbs 2.025E5lbs

Bending Strain 0 1.560E-4 2.244E-4 0

Bending Stress 0 psi 8.970 psi 12.90 psi 0 psi

Resultant Axial Tensile Stress

9.773E1 psi 3.066E2 psi 7.742E2 psi 8.771E2 psi

Resultant Axial Tensile Strain

1.700E-3 5.332E-3 1.346E-2 1.525E-2

Table 4. Installation Loads with Rollers

Note that the use of the rollers at pipe entrance significantly reduces the required pullback force at locations A and B (subsequently at C and D). The effect of adding these rollers can also be viewed graphically (Figure 21), exported to Excel or printed.



Figure 21. Calculated pullback force.

Finally, there is an interface within BoreAid to check that all loads/deflections fall within acceptable limits for design (see Figure 22).

Figure 22. Screenshot of BoreAid tab that shows that loads/deflections fall with

acceptable limits of design.

Should one of the values result in a factor of safety less than one, a warning is issued.



4.4 Drill Fluid and Reaming Sequence Design Table 5 shows the proposed drilling/reaming sequence for the project.

Pilot Bore 3 inch

Reamer Pass 1 5.5 inch

Reamer Pass 2 8 inch

Reamer Pass 3 10 inch

Reamer Pass 4 12.9 inch

Table 5. Proposed pilot bore and ream diameters.

For this project a reamer to pipe overcut ratio of 1.5, drill fluid to soil volume ratio of 2.5, total drill fluid tank volume of 600 gallons, maximum pump rate of 60 gallons/min, and pump efficiency 80% was selected. The user must also input the expected drilling time per rod.

Figure 23. Drill fluid/time requirements calculated by BoreAid.

BoreAid calculates total (and per rod) soil and fluid volumes required for each reamer pass as well as the total drill time. Key calculations are summarized in Figure 23. Note that BoreAid issues warnings if the pump capacity is exceeded during any stage of the drilling/reaming. For example, if we change the drill time per rod to 1 minute for the final reamer pass, as shown in Figure 24, BoreAid issues a warning that the pump rate required exceeds the pump capacity.



Figure 24. Drill fluid/time requirements calculated by BoreAid.

Drilling results may be viewed via bar charts. A sample bar chart representing the drill time required per reamer pass is shown in Figure 25.

Figure 25. Drill time requirements per reamer pass calculated by BoreAid.

4.5 Hydrofracture Considerations Based upon the reaming sequence designed in Section 5 above, BoreAid calculates estimates bounds on the maximum limiting pressure inside the bore to prevent hydro-fracture or frac-out. Figures 26 and 27 shows estimated limiting bore pressures when the radius of plasticity is set at 120 and then 20 inches.



Figure 26. Limiting pressure along the bore path with radius of plasticity 120 inches (exported from BoreAid).

Figure 27. Limiting pressure along the bore path with radius of plasticity 20 inches (exported from BoreAid) -

different colors represent each reamer pass as noted by text color inside BoreAid.

4.6 Equipment and supplies Using the equipment and supplies module (the drill rig portion is shown in Figure 28), BoreAid lets the user see that a large mini-HDD or small size midi-HDD drill rig is required to achieve a pullback factor of safety of 2. The factor of safety for the pump rate is also given. BoreAid also allows the addition of custom drill rigs if the user has a drill rig pump/pullback properties not given in the pull down list.



Figure 28. Screenshot of drill rig section of equipment supplies module.

In addition, in other sections of the equipment and supplies module, BoreAid also indicates that well-graded sand is generally suitable for drilling using a spade drill bit.

5. Conclusion In this paper we have introduced a structured framework for HDD design and its implementation in a new software package called BoreAid. We have addressed the capabilities of the BoreAid in detail and displayed how complicated designs, site conditions, topographies, etc may be described with ease using BoreAid. BoreAid provides a clear method in which to consider the parameters and makes connections between inter-connected elements of the design. A simple example is described which exhibits only the very basic capabilities of the software.

Acknowledgements The authors wish to thank the Center for Advancement of Trenchless Technologies and Department of Civil and Environmental Engineering at the University of Waterloo for their support during the completion of this project.

References [1] ASCE, 2005. Pipeline Design for Installation by Horizontal Directional Drilling. American Society of

Civil Engineers, aSCE Manuals and Reports on Engineering Practice No. 108.

[2] ASTM-F1962, 2007. Standard guide for use of maxi-horizontal directional drilling for placement of polyethylene pipe or conduit under obstacles, including river crossings.

[3] Bennett, D., Ariaratnum, S., Como, C., 2001. Horizontal Directional Drilling: Good Practices Guidelines. HDD Consortium.



[4] Plexco/Spirolite, 1998. Engineering manual (CD-ROM), 2nd Ed. Chevron Chemical, Bensenville, Illinois.

[5] PPI, 2006, Handbook of PE Pipe. Plastic Pipe Institute (PPI).

BOREAID_ New HDD Design Tool

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