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Applications and Advantages of Using Internally Restrained PVC
Pipes for Installation by Horizontal Directional Drilling
Mustafa Kanchwala1, Trupti Kulkarni2, Mohammad Najafi3, Craig
Fisher4 and
Vijay Kumar Shivaji Rao5
1Research Assistant, Center for Underground Infrastructure
Research and Education (CUIRE), Email: [email protected]
2Research Assistant, Center for Underground Infrastructure
Research and Education (CUIRE), Email: [email protected]
3Director of the Center for Underground Infrastructure Research and
Education (CUIRE), Department of Civil Engineering, The University
of Texas at Arlington, Box 19308, Arlington, TX 76019, U.S.A.,
Phone: 817-272-0507, Email: [email protected] 4Former Vice President -
Technical and Municipal Services, S&B Technical Products, 1300
East Berry Street, Fort Worth, TX 76119, U.S.A., Phone:
817-921-8227, Email: [email protected] 5Former Graduate
Research Assistant, Center for Underground Infrastructure Research
and Education (CUIRE), Email: [email protected] Abstract
Horizontal Directional Drilling (HDD) has evolved steadily over
the last 20 years and currently is the preferred method for
municipal water installations due to its low impact on the
surrounding areas. The Bulldog Restraint System (BRS) has added
bell-and-spigot to PVC-U and PVC-M piping options for installation
by HDD. In North America, BRS is designed for integration into
diameters ranging from 3-in. (75-mm) to 16-in. (400-mm). This paper
presents the methodology for testing the BRS joints under axial
tension, and the corresponding results, for PVC pipes equipped with
BRS. In order to compare the BRS capabilities to expected loads for
an HDD installation, an Excel spreadsheet was developed to
calculate the anticipated pull forces, using ASTM F1962-05 design
procedures. In addition, to show the cost effectiveness of the HDD
method as applied to the internally restrained PVC pipe, a cost
comparison with the traditional open-cut installation is provided.
Product Description
An internal restraint system within the bell of a PVC pressure
pipe has been developed by S&B Technical Products, and
designated as the Bulldog Restraint SystemTM (BRS). In North
America, the current version of the BRS is designed for integration
into the following types of PVC pressure pipes: AWWA C900 PVC-U
pipe and fabricated fittings in diameters 4-in. (100-mm) through
12-
in. (300-mm),
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AWWA C905 PVC-U pipe and fabricated fittings in diameters 14-in.
(350-mm) through 16-in. (400-mm), and
ASTM D2241 PVC-U pipe and fabricated fittings in diameters of
3-in. (75-mm) through 8-in. (200-mm). The BRS mechanism consists of
a metal casing that sits adjacent to the Rieber gasket in the
bell; the casing is molded into the raceway of the bell during
the pipe belling process. A C-shaped grip-ring with several rows of
uni-directional serrations is manually inserted into the casing at
the manufacturing facility. Both the casing and the grip-ring are
made of ductile iron that has been coated using an electrophoretic
coating (e-coat) that achieves a uniform thickness and provides
superior corrosion resistance. Since the bell already contains the
casing with the grip-ring when the pipe arrives at the jobsite, no
additional hardware is needed to provide a restrained joint. Figure
1 illustrates a cross-sectional view of the BRS joint components.
In the field, the joint is assembled typical push-on joint, with
the spigot pushed into the bell to the insertion mark.
Figure 1: Integral PVC Joint Restraint Components (Source:
S&B Technical Products)
Joint Tensile Strength
BRS was originally designed to eliminate the need for concrete
thrust blocks by providing an internally restrained piping system,
capable of accommodating changes in pipe diameter or load
direction. The system has been used in the market place since its
product launch in 2006. The investigation of the suitability of
PVC-U pipe equipped with BRS for installation by HDD began in 2008.
In 2009, S&B Technical Products contracted with the University
of Texas of Arlington (UTA) to conduct tensile strength tests on
the BRS joint, verifying its usage with HDD. At UTA, this research
was coordinated by the Center for Underground Infrastructure
Research and Education (CUIRE) under the guidance of its Director,
Dr. Mohammad Najafi. The research facility used was UTAs Civil
Engineering Laboratory Building (Figure 2). Table 1 summarizes
Grip Ring
Rieber Gasket
Casing
PVC Pipe Spigot Gas PVC Pipe Bell Gas
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the joint tensile strengths of DR18, AWWA C900 product. DR18 has
a pressure rating of 235 psi (1620.3 kN/m2), which is comparable to
PN 161.
Figure 2: Joint Tensile Testing of 12-in. DR18, AWWA C900
Table 1: DR18, AWWA C900 Joint Tensile Strengths (Sharma, et.al
2010) Nominal Diameter
(in.) Actual Outside Diameter
(in.) Dimension Ratio (DR)
Load at Failure (lbs)
4 4.800 18 19,479 4 4.800 18 21,237 6 6.900 18 38,163 6 6.900 18
35,722 8 9.050 18 54,249 8 9.050 18 54,181
10 11.100 18 72,700 12 13.200 18 110,100
Additional details on the testing equipment and procedures are
provided in Sharma, et.al,
2010. The testing was conducted in a straight alignment at a
constant displacement rate of 0.2-in./min (5.1 mm/min). The
displacement, load, and strain data were collected during each
test. Strains were measured on the bell and the spigot using strain
gauges.
1 PN 16 pipe can withstand 232 psi (1599.6 kN/m2) at 68oF
(20oC)
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In addition to obtaining the joint tensile strength of the
product, the research also validated two different pulling head
designs: the pinned external connection and the serrated internal
grip. The heads shown in Figure 3 (a and b) were able to achieve
the full joint tensile strength of the product equipped with BRS
and without causing failure at the pulling heads gripping location.
The external pulling heads were tested on all AWWA C900 sizes, and
the internal pulling heads were validated on sizes 4-in. (100-mm)
through 8-in. (200-mm).
Figure 3: Pulling Head Designs Validated Through Testing
Figure 4 plots the joint tensile strength as a function of the
actual outside diameter. A best
fitting polynomial trend line has been added to the figure, as
well as the corresponding formula.
Figure 4: Joint Tensile Strength vs. Pipe outside Diameter
(Sharma, et.al 2010)
The test results show that the tensile capability of BRS PVC
system is comparable to those of other thermoplastic piping
options, such as HDPE and fusible PVC, which are typically
installed by HDD. The safe pulling load, in straight alignment, is
usually obtained by dividing the joint tensile strength by a safety
factor of two. Although the test results demonstrate that the joint
tensile strength achieved with PVC pipe equipped with BRS is
suitable for installation by
Figure 3a: External Pulling Head, Pinned Connection
Figure 3b: Internal Pulling Head, Mechanical Connection via
Serrated Grips
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HDD in general, similar to other pipe products, the product may
not be sufficient for a particular HDD application. HDD Pull
Loads
To determine whether or not a particular pipe and jointing
system is feasible for a specific HDD installation, the safe
(allowable) pull loads are compared to the predicted pull loads for
the project. The pull loads on the pipe string are the greatest at
the leading end where it connects to the pulling head. The actual
pull load that the pipe string experiences; may be significantly
less than the load experienced by the drilling rig. In addition to
the load from the pipe string, the drilling rig will also bear the
load from the drill rods still in the borehole, as well as the
resistance from the reamer immediately in front of the pipe string.
Najafi (2010) provides more details on HDD and pipe load estimation
procedures for different HDD categories.
A conservative design procedure for estimating the pull forces
that the pipe string will experience during an HDD installation is
provided in ASTM F1962. To simplify the design process, CUIRE
developed a simple, user friendly, spreadsheet2 that calculates
these loads as per ASTM F1962 (Shivajirao, 2010). It is desirable
to calculate pulling loads at critical locations, while the product
pipe is being pulled towards the drill rig. To calculate these
pulling loads, the geometry of the bore paths profile is needed.
Figure 5 shows a bore path profile similar to that illustrated in
ASTM F1962. The design formulas in F1962 use the following terms
and units:
L1 = Additional length of pipe required for handling and thermal
contraction, ft L2 = Horizontal distance to achieve desired depth,
ft L3 = Additional distance traversed at desired depth, ft L4 =
Horizontal distance to rise to surface, ft H = Depth of bore hole
from ground surface, ft = Borehole angle at pipe entry, radians =
Borehole angle at pipe exit, radians
Figure 5 - Geometric Variables for Defining the Bore Path
2 This spreadsheet is available upon request to
[email protected]
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The pullback forces are calculated at four critical locations;
where the leading point of the pipe string reaches points A, B, C,
and D respectively. These four locations are illustrated in Figures
6 (a, b, c, and d). Although the pulling forces at the leading end
of the pipes is typically a maximum at the completion of the pull
back, this does not necessarily occur for all projects and site
conditions. The pullback force on the pipe string is a combination
of the frictional drag forces as the pipe string is pulled along
the ground on the pipe entry side, the drag forces as the pipe
slides against the surface of the borehole, and the force
amplification (capstan effects) as the pipe string is pulled around
curves. For simplicity, the relatively small contribution of the
hydrokinetic forces due to the pipe string being pulled against the
slurry flow, as calculated in the ASTM F1962 procedure, are not
addressed in this paper; however, the spreadsheet performs these
calculations.
Figure 6a - Pipe String Entirely above Ground and about to Enter
the Insertion Pit
Figure 6c - Pipe String has Completed Horizontal Run at Desired
Depth
Figure 6b - Pipe String has Reached Desired Depth
Figure 6d - Pullback Complete
Figure 6: Four Scenarios Checked for Calculating Maximum
Pullback Force Design Example: Clay County, Florida
The following sample calculation demonstrates the use of the
ASTM F1962 design formula and the convenience of a spreadsheet that
facilitates the procedure. The given data is based on a recent pipe
replacement project in Clay County, Florida. Additional information
on this project is provided in the Cost Analysis Example Section of
this paper. Given Total Length = 540 ft Pipe Entry Angle, = 20 =
0.3491 radians Pipe Exit Angle, = 10 = 0.1745 radians Piping
Product: 4-in. DR-18, AWWA C900 Depth of Path, H = 5 ft Outside
Diameter, Do = 4.8-in. Distance from Pipe Entry to Point A, L1 = 0
ft
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Assumptions Coefficient of Friction at the surface before the
pipe enters borehole, va = 0.4 Coefficient of Friction within the
lubricated borehole, vb = 0.25 Specific Gravity of the slurry,
g(slurry) = 1.5 Specific Gravity of pipe material, g(PVC) = 1.4
Unit Weight of water = 62.4 lbs/ft3 Pipe Properties Wall Thickness,
t = Do/DR = 4.800-in./18 = 0.267-in. Inside Diameter, Di = Do 2t =
4.800-in. 2 (0.267-in.) = 4.267-in. Pipe Cross-sectional Area, Ax =
(/4) (Do2- Di2) = (/4) (4.8002- 4.2672) = 3.798-in.2 Ax = 0.026374
ft2 wa = (Ax) (g(PVC)) (Unit Weight of Water) = (0.026374 ft2)
(1.4) (62.4 lbs/ft3) wa = 2.305 lbs/ft Area of Slurry displaced
when pipe is submerged = (/4) (Do2) = (/4) (4.82) Adisp =
18.096-in2 = 0.1257 ft2 Buoyant Force acting on pipe, Fb = (Adisp)
(g(slurry)) (Unit Weight of Water) Fb = (0.1257 ft2) (1.5) (62.4
lbs/ft3) = 11.762 lbs/ft wb = Fb - wa = 11.762 lbs/ft 2.305 lbs/ft
= 9.458 lbs/ft Bore Path Distances L1 = 0 ft (known) L2 = 2H/ = 2(5
ft) /0.3491 rad = 28.6 ft L4 = 2H/ = 2(5 ft) /0.3491 rad = 57.3 ft
L3 = Total Length L1 L2 L4 = (540 0 28.6 57.3) ft = 454.1 ft
Natural Log Products e(va ) = e (0.4)(0.3491) = 1.1498 e(vb ) = e
(0.25)(0.3491) = 1.0912 e(vb ) = e(0.25)(0.1745) = 1.0446 Pullback
Force at Point A, TA (ASTM F1962, Eq. 8) TA = e(va ) (va) (wa) (L1
+ L2 + L3 + L4) = (1.1498) (0.4) (2.305 lbs/ft) (540 ft) TA = 572
lbs Pullback Force at Point B, TB (ASTM F1962, Eq. 9) TB = e (vb )
[ TA + (vb)(|wa|)(L2) + (wb) (H) - (va)(wa)(L2)( e (va ))] TB =
(1.0912) [572 lbs + (0.25) (9.458 lbs/ft) (28.6 ft) + (9.458
lbs/ft) (5 ft)
(0.4) (2.305 lbs/ft) (28.6 ft) (1.1498)] TB = (1.0912) (572 +
67.6 + 47.3 30.3) lbs = 716.5 lbs Pullback Force at Point C, TC
(ASTM F1962, Eq. 10) TC = TB + (vb) (|wb|) (L3) [( e(vb )) (va)
(wa) (L3) ( e(va ))] TC = (716.5 lbs) + (0.25) (9.458 lbs/ft) (57.3
ft) [(1.0912) (0.4) (2.305 lbs/ft) (454.1 ft) (1.1498)]
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TC = (716.5 + 1073.7 525.3) lbs = 1,264.9 lbs Pullback Force at
Point D, TD (ASTM F1962, Eq. 11) TD = ( e(va )) {TC + (vb) (|wb|)
(L4) (wb) (H) - [(e(vb )) (va) (wa) (L4) ( e(va ))]} TD = (1.0446)
{1,264.9 lbs + (0.25) (9.458 lbs/ft) (57.3 ft) (9.458 lbs/ft) (5
ft) - [(1.0912) (0.4) (2.305 lbs/ft) (57.3 ft) (1.1498)]} TD =
(1.0446) (1,264.9 + 135.5 47.3 66.3) lbs = 1,344.2 lbs
The above design example shows how the peak pullback forces
change during the HDD
operation. This information is necessary in the planning and
design of HDD projects. Figure 7 plots the pullback forces at the
four critical points. These calculations verify that the 4-in.
(100-mm) BRS pipe system has sufficient joint tensile strength for
the installation, since the joint pulling capacity was determined
through testing to be approximately 10,000 lbs (44.51 kN). As shown
above, ASTM F1962 conservatively estimates safe pulling force to be
in order of magnitude of 1,344 lbs (5.98 kN).
Figure 7: Pullback Forces at Point A, B, C and D Cost Analysis
Example: Clay County-Florida
Pipe installation cost depends on many parameters, such as the
pipe size, pipe length, pipe materials, project location, surface
and subsurface conditions, existing utilities, frequency of
connections, etc. Thus, while each project cost is unique, cost
comparisons can be made as reality checks when there is consistency
among major variables. For this paper, the cost for HDD
installation was obtained from the contractors bid, and the
estimated open-cut cost was obtained using R.S. Means Cost Data
(2010).
The Clay County project included replacement of existing 2-in.
(50-mm) cast iron water pipe with 4-in. (100-mm) DR 18 PVC pipe
(AWWA C900) using HDD. Figure 8 illustrates the site conditions and
alignment of the project. The project was bounded on the North by
Aquarius Concourse and on the south by Blairmore Blvd West, and the
new pipe was installed on the east side of Libra Lane. The new
alignment followed the eastern curve of Libra Lane. Table 2
presents Clay County installation project specifics for using PVC
pipe with the BRS joint.
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Figure 8: Site Conditions and Existing Utilities near Proposed
Alignment
Table 2: Specifics of HDD Project in Clay County, Florida
Project Description Date of Installation 02-24-2010 Owner Clay
County Utility Authority Contractor Bore Hawg, Inc, Contact: Jason
Riggs, President Project Contact Steve Rencarge, Operations
Coordinator, Length of Pipe Installation 540 ft (165 m) Nominal
Diameter of the Pipe 4-in. (100-mm) Dimension Ratio (DR) AWWA
C900-18 Depth from Ground to the Center of the Pipe 5 ft (1.52
m)
Crew Details 1 Superintendent 3 Workers 1 Backhoe Operator
1 HDD Rig 1 HDD Rig Operator 1 Truck Operator
Equipment HDD Machine Model: Ditch Witch JT 1720
Vacuum Excavator Slurry Truck, Backhoe
For HDD, the major cost items are attributed to the boring and
pullback operations using
the HDD drilling rig, vacuum truck and backhoe. For open-cut,
the major cost items are trench excavations using a backhoe, pipe
placement and proper embedment, including service laterals, fire
hydrant connections and installations, trench backfill and
compaction, traffic management, and surface reinstatement. The
lateral and fire hydrant connections also apply to the HDD
alternative. Pipe is the major material cost for both methods.
Table 3 presents a comparison and cost breakdown of the work
related items for the Clay County HDD and open-cut installation
methods. Kulkarni, et. al, (2011) provides detailed cost
information for HDD and open-cut operations. The calculations
indicate that the HDD alternative is estimated to be only half
the
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cost of the traditional open-cut method, illustrating the
cost-effectiveness of the BRS system. Although open-cut costs as
obtained from R.S. Means Cost Data (2010) are generally considered
to be conservative, the results nonetheless suggest a potentially
large major cost savings for the HDD procedure.
Table 3: Costs Breakdown for Open-cut and HDD Methods using PVC
Restraint Joint Pipe
Clay County, Florida, 4-in. PVC Installation Length 540 ft 540
ft
Installation Method Open-cut (Estimated) HDD (Bid) Cost, $/ft %
Cost, $/ft % Labor Cost 10,708 17 4,923 15 Material Cost (Pipe,
Consumable Materials, etc.) 21,766 35 15,794 49
Equipment Cost 3,830 6 1,138 5 Labor Burden 6,773 11 3,102 10
General Expenses 5,446 9 2,767 7 Project Markup 4,555 7 2,277 7
Misc. Cost (Bond, Taxes, Mobilization) 9,554 15 2,193 7
Total Cost ($) 62,632 100 32,194 100 Unit Cost ($/ft) $116/ft
$60/ft
Conclusions and Limitations The results obtained from the
tensile tests and subsequent calculations show the BRS
joint can safely withstand HDD pulling loads as per ASTM F1962.
The tensile strength of the BRS is well within the capability of
other thermoplastic products typically used in HDD applications.
Future research efforts will include tests on PVC pipes equipped
with BRS joints under combined loading of tension and bending.
Based on the cost comparison case study for the recent water
pipe replacement project in Clay County, Florida, the conventional
open-cut method would have potentially been twice as expensive as
the HDD method actually used for the installation of 4-in. (100-mm)
diameter PVC pipe equipped with the BRS joint. The unit costs
obtained in this study are specific to Clay County project and
cannot be generalized to other projects; however, the methodology
could be used to obtain similar cost comparisons.
Acknowledgements
The authors would like to thank S&B Technical Products, Fort
Worth, Texas, for providing the opportunity and financial supports
to work on this project. S&B Technical Products owns Bulldog
Restraint System (BRS) technology, enabling bell-and-spigot PVC
technology to be used in HDD applications. The authors would also
like to thank Dr. Lawrence Slavin of Outside Plant Consulting
Services, Inc., Rockaway, New Jersey, for reviewing and providing
valuable feedback on this paper. This study would not have been
possible without cooperation and help of Clay County Utility
Authority, Florida.
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List of Abbreviations ASTM AWWA BRS CUIRE DR HDD PN PVC-M PVC-U
UTA
American Society for Testing and Materials American Water Works
Association Bulldog Restraint System Center for Underground
Infrastructure Research & Education Dimension Ratio Horizontal
Directional Drilling Pressure Rating of a Pipe Polyvinyl
Chloride-Modified Polyvinyl Chloride-Unplasticized The University
of Texas at Arlington
References ASTM F1962 (2005). Standard Guide for Use of
Maxi-Horizontal Directional Drilling for
Placement of Polyethylene Pipe or Conduit under Obstacles,
Including River Crossings. American Society for Testing and
Materials, West Conshohocken, Pa.
AWWA C900 (2007), Standard for Polyvinyl Chloride (PVC) Pressure
Pipe and Fabricated Fittings, 4-in Through 12-in (100 mm Through
300 mm), for Water Transmission and Distribution. American Water
Works Association, Denver
AWWA C905 (2008), Standard for Polyvinyl Chloride (PVC) Pressure
Pipe and Fabricated Fittings, 14-in Through 48-in. (350 mm Through
1,200 mm), for Water Transmission and Distribution. American Water
Works Association, Denver.
ASTM D2241 (2009), Standard Specification for Poly (Vinyl
Chloride) (PVC) Pressure-Rated Pipe (SDR Series). American Society
for Testing and Materials, W. Conshohocken, Pa.
Kulkarni, A., Kanchwala, M., Najafi, M., and Fisher, C. (2011).
Cost Comparison of Small Diameter Horizontal Directional Drilling
(HDD) and Open-cut for PVC and HDPE Pipe Options. Proceedings of
Underground Construction Technology (UCT), January 2011, Houston,
TX.
Kulkarni, A., Kanchwala, M., Najafi, M., and Fisher, C. (2011).
Cost Comparison of Different Pipe Options for Horizontal Direction
Drilling (HDD) & Open-Cut Projects. Proceedings of North
American Society of Trenchless Technology (NASTT), March 2011,
Washington, DC.
Najafi, M. (2010). Trenchless Technology Piping Installation
& Inspection, McGraw-Hill, NY. R.S. Means Cost Data (2010).
Building Construction Cost Data. Construction Publishers &
Consultants, Kingston, MA. Shivajirao, V., (2010). Applicability
of Restrained Joint Polyvinyl Chloride (PVC) Pipe in
Horizontal Directional Drilling. Unpublished Masters Project,
Department of Civil Engineering, The University of Texas at
Arlington.
Sharma, J. R., Najafi, M., Fisher, C., Jain, A., Huli, A., and
Shivaji, V.R. (2010). Applicability of Restrained Joint PVC Pipe in
Horizontal Directional Drilling. Proceedings of ASCE Pipelines
Conference August 2010, Colorado, Keystone.
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