State of Technology Report for Force Main Rehabilitation, Final ...
State of Technology Report for Force Main Rehabilitation, Final ...
State of Technology Report for Force Main Rehabilitation, Final ...
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the jacking pipe needs to have high axial compressive strength and stiffness. “In wall” joints are used to<br />
avoid projections beyond the OD <strong>of</strong> the shield and to minimize friction between the pipe wall and the soil.<br />
Bentonite slurry is usually introduced between the pipe barrel and the soil to minimize friction, but<br />
smooth, non-porous pipe surfaces are also beneficial. The intermediate jacking stations (IJS) used on<br />
long drives are operated in sequence so that only sections <strong>of</strong> the jacking pipe are slid through the ground<br />
at any one time. This minimizes the jacking <strong>for</strong>ce needed to drive the tunneling machine and pipe column<br />
<strong>for</strong>ward.<br />
Typical pipes that have been used <strong>for</strong> jacking <strong>of</strong> pressure pipes are GRP, polymer concrete, rein<strong>for</strong>ced<br />
concrete, steel, and DI. PVC can also be jacked, but requires a large number <strong>of</strong> IJS, making it somewhat<br />
uneconomical.<br />
GRP<br />
Hobas pipe, which is a centrifugally cast glass-rein<strong>for</strong>ced plastic mortar pipe, has been used on a large<br />
number <strong>of</strong> intermediate diameter (24 to 84 inches [600 to 2,100 mm]) microtunneling projects. Hobas<br />
pipe, with its tight tolerances on OD and relatively high axial compressive strength, has dominated the<br />
gravity sewer microtunneling market in Houston, TX. Although the pipe itself might be capable <strong>of</strong><br />
carrying internal pressure, the joint used <strong>for</strong> microtunneling does not lend itself to pressure applications.<br />
A variation on ordinary GRP pressure pipe <strong>for</strong> microtunneling is produced in Germany by Hume Rohr.<br />
Hume Rohr is a manufacturer <strong>of</strong> precast concrete pipe. They purchase GRP pressure pipe from the<br />
Flowtite ® producer near Dresden and then use the GRP as an inner mold casting a concrete pipe outside.<br />
The end result is a composite <strong>of</strong> concrete and GRP with the concrete handling the axial jacking loads<br />
during installation and the GRP handling the internal pressure. With GRP’s inherent corrosion resistance,<br />
this composite provides a very suitable jacking pipe <strong>for</strong> a sewer <strong>for</strong>ce main replacement. Un<strong>for</strong>tunately,<br />
there are no producers <strong>of</strong> this composite pipe concept in North America at the moment.<br />
Polymer Concrete<br />
A variation to the composite made <strong>of</strong> GRP and concrete is the polymer concrete pipe. There is a standard<br />
specification (ASTM D6783) <strong>for</strong> polymer concrete pipe. Meyerh<strong>of</strong> in Germany was one <strong>of</strong> the pioneer<br />
developers <strong>of</strong> polymer concrete pipe. Meyer’s Polycrete ® is now produced by US Composite Pipe in<br />
Zachary, Louisiana. Polycrete is a composite consisting <strong>of</strong> polyester resin, sand, aggregate, and a mineral<br />
filler. Polymer concrete, which actually doesn’t use any cement, uses 9% to 10% by weight <strong>of</strong> polyester<br />
resin to bond the silicate aggregate, creating a dense, corrosion resistant matrix. The pipe is produced<br />
using a vertical casting process, similar to concrete pipe. The joint has a 316 stainless steel collar<br />
mounted integral to the pipe wall <strong>for</strong> microtunneling applications. With an average axial compressive<br />
strength <strong>of</strong> 15,000 psi (1,034 bar), the Meyer Polycrete pipe has ample strength <strong>for</strong> jacking <strong>for</strong>ces. The<br />
pressure limitation <strong>of</strong> the joint is only 35 psi (2.4 bar), so the pipe’s usefulness as a replacement pipe <strong>for</strong> a<br />
sewer <strong>for</strong>ce main is limited.<br />
Steel<br />
Permalok is an interlocking pipe joining system. Permalok is produced by Permalok Corporation in<br />
St. Louis, MO and is available in diameters from 30 to 120 inches (750 to 3,000 mm). The steel pipe is<br />
manufactured by the rolled and welded cylinder method utilizing the double submerged arc welded<br />
(DSAW) process. The joint is an integral, machined press-fit connection incorporating a double “o” ring<br />
gasket, which is intended to be used <strong>for</strong> low to medium pressures (up to 300 psi [21 bar]). The joint is<br />
assembled in the field by the jacking frame. The T7 pr<strong>of</strong>ile (Figure 3-26), which is the pressure joint, was<br />
introduced in 2002. Once assembled, the Permalok joint is flush with the exterior and interior surfaces <strong>of</strong><br />
the pipe rendering it suitable <strong>for</strong> both pipe jacking and HDD applications. Coatings and linings suitable<br />
<strong>for</strong> a variety <strong>of</strong> applications are available from Permalok. Permalok, with the right lining, would be a<br />
candidate <strong>for</strong> replacing a sewer <strong>for</strong>ce main using microtunneling/pipe jacking or HDD.<br />
Figure 3-26. Permalok T7 45 Pressure Joint