State of Technology Report for Force Main Rehabilitation, Final ...

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