Since the early 90es Trolining GmbH, Germany is an internationally recognized expert in the field of trenchless pipe rehabilitation. Its patented GIPP (Grouted-in-place pipe) method has been successfully installed in about 20 countries around the globe. The continuously growing demand for reliable methods for the reinstatement of large sewers was a clear sign for Trolining to further increase the effectiveness of its system in that market segment. Pipes sizes between diameter 800mm (32”) and 2000mm (80”) I.D. today represent Trolining’s main field of application, regardless of whether the cross-sectional pipe profile to be rehabbed is circular or a special geometry.
In the second half of 2006 TROLINING completed a typical project in the city of Bielefeld. Bielefeld is a medium-sized German town with about 330.000 inhabitants and an urban area of 258 sqkm. The total length of public sewers herein is approx. 1840km. Regular inspections revealed leaking and a variety of other damages at one of the main collectors located along the Mühlen Str., nearby the city center. Especially the joints of the brick work sewer, constructed around 1898, were found severely eroded. In some areas the mortar between the bricks was missing down to a depth of 40mm (1.5”).
After assessment of the inspection reports the municipality decided that 520m (1705ft) of the sewer needed urgent repair. Whereas 310m (1015ft) showed the standard egg-shape 1200x1800 mm (48x72”) I.D., further 210m (690ft) measured 1400x2100 mm (56x84“). A few months later, Bielefeld’s environmental authority released a relating call for tender not only containing the trenchless rehabilitation of the mentioned sewer lines, but also a number of other preparatory and adjacent works. Installation of a bypass line, preliminary sealing of major groundwater infiltrations, rehabilitation of the adjacent manhole chambers and re-connection of the lateral pipes were just some of the performances requested from the bidders.
The TROLINING trenchless pipe rehabilitation system is based on various HDPE (
High
Density
Poly
Ethylene) liner components which can be combined in a wide range of alternative configurations. The heart of the system is the Troliner with its V-shaped embedment studs. The annular void created by the studs is filled with TROLINING Injektor, a specially engineered injection grout. This high-strength grout fixes the Troliner permanently in place and provides the load-bearing shell of the system.
TROLINING liners are available for pipes ranging from 250mm to 2000mm (10” to 80”) I.D.. Segmental lining sheets are offered for rehabilitation of lines greater than 2000mm (80”) I.D. and for elbows and corners in man-sized lines. The rehab system improves the host pipe’s flow characteristics and provides exceeding mechanical and chemical resistance.
Every liner is tailor made according to the exact measurements taken on the job site. That procedure guarantees the systems „Close-fit“ characteristics, thus limiting the cross sectional reduction to an absolutely minimum. Prior to the liner insertion, the pipe section to be rehabilitated is plugged-off at both ends, cleaned and visually inspected. A cable winch is then used to unroll each HDPE liner from its transport drum and draw it through the line into position. After insertion, all HDPE liners are welded together at their both ends. The resulting liner –“sandwich” is then inflated with a defined pressure through passages in the temporary plugs closing the ends of the liner section.
When the required inflation pressure is attained, the annular void is filled with TROLINING injection grout fed from the down stream end. The grout’s extremely low viscosity ensures 100% grouting of the annular void, even for long distances. Additional grout characteristics are a defined material expansion and an exceeding short term strength. The latter is decisive to keep the interruption time at an acceptable low level.
Arguments for TROLINING’s GIPP method Despite of the GIPP method’s economic advantages, TROLINING’s tender for project “Bielefeld” also succeeded due to the certified quality assurance and the high experience level in the field of large pipe rehabilitation, especially egg-shapes. The TROLINING Double System with a wall thickness of 43mm (1.75”) was quoted in that case;
“Double” due to comprising 2 layers of studded HDPE liners. Additional reasons for choosing the GIPP method were the environmental friendliness and drinking water approval of HDPE as well as the material’s compatibility with other lining components. State-of-the-art PE extrusion welding allows absolutely tight connections between the actual pipe liner and manhole rehabilitation sheets or the inverted HDPE saddles used for lateral connection.
A real exceptional difference to other lining systems was the special system configuration TROLINING was able to provide for dealing with Bielefeld’s specific project needs. While the “common” TROLINING Double System involves an outer Preliner, i.e. a smooth HDPE liner that gets inserted prior to the studded ones, the Preliner was omitted in that case. Leaving the Preliner means that the outer annular void of the Double System was limited at the outside by the host pipe itself, while the 1
st studded liner represented the inside boundary. In that way it was possible to properly re-fill all defective joints between the brick work and embed the whole interior host pipe wall into a highly protective alkaline milieu by direct adhesion of the cementitious grout.
One year before, in August 2005, Trolining had successfully rehabbed a comparable host pipe, a pear-shaped brick work sewer sized 1800x2250 mm (72x90“) I.D., by application of the same method. Drilling cores taken at this project proved the deep and reliable penetration of the TROLINING grout into deteriorated brick wall joints.
Before the actual system installation could start, a number of essential preparations had to be done. Major item with these preparations was the erection of a bypass line to divert the arising sewage around the construction area for the period of works. A steel pipe measuring 800mm (32”) in diameter was laid over ground to provide sufficient capacity for keeping the rehab sections dry. After dewatering the whole 520m, technicians could access the host pipe and evaluate the further steps. Intensive cleaning and the provisional stopping of strong water infiltrations were required. At the same time subcontractors enlarged those manholes that were designated for the HDPE liners’ insertion, to chambers of 2 by 2 m.
About 3 weeks after starting the preparations the first liners could be installed. The common manhole distances for the 1200x1800 mm (48x72”) were 60m (200ft) in average which is a standard pipe length to rehab in municipal areas. More challenging were the manhole distances of the 1400x2100 mm (56x84“) host pipe. 103m and 107m were the lengths that had to be lined in one step. While liner production above dia. 1200mm (48”) was limited to 85m (280ft) in the past, the mentioned distances required additional efforts from both TROLINING’s liner manufacture and the installation crew. TROLINING engineers and site experts tackled the situation and presented the solution after a number of technical meetings and process improvements.
Insertion of the 2.5 tons weighting liners occurred from the intermediate manhole which separated the 210m of egg-shaped pipe into 103m & 107m, both into up-stream and down-stream direction. Large triangle stands were placed next to the insertion pit to hang-up the liner coils. For drawing the liners into the pipe, diversion rollers had to be placed right above manhole chamber. After insertion of both studded liners, the resulting annulus was sealed by manual extrusion welding. Inflatable egg-shape packers were then used to plug-off the liner-package at both ends and water was fed-in to build-up a defined hydrostatic pressure. Special attention had to be given to the plug bracing: with a water column of 8m (= 11.6 psi back pressure) and a cross sectional area of 2.45 sqm, an equivalent horizontal force of approximate 20 tons had to be taken by the construction that held the plugs in place.
The 103m and the 107m long pipe sections were rehabbed separately. Grouting of both occurred with the TROLINING-specific mixing technology. 3 standard mixing units were employed to prepare the injection grout. The Double System’s outer annular void space was filled first, needing approx. 1.5h for completion. The inner annulus could then be grouted within just 1h. After further 16h of curing the high-strength grout attained the necessary short-term strength necessary for releasing the inside pressure from the lining system. Right afterwards the incoming house connections could be re-opened and connected.
The GIPP method finds worldwide application. Projects like the above are valuable references and strengthen TROLINING’s market position continuously. Not only TROLINING itself profits from such developments, but also its international cooperation partners which have unrestricted access to these improvements.
