IKT-LinerReport 2006: Glass Clearly Ahead?

IKT-LinerReport 2006 PDF Download (0,6 MB)

Is the material the only important factor in cured-in-place pipe rehabilitation? What quality standards do installers (contractors) achieve, and with what types of liner? The independent and neutral IKT Test Center for Pipe Liners now submits, for the third time, its IKT-LinerReport. This paints for 2006 a differentiated picture based on test results obtained from more than one thousand on-site samples.

Industry experts are increasingly questioning which are the best liner types and the best pipe lining methods. Two „families“ of technologies compete in the marketplace: Tube liners employing glass-fiber, and those employing needle-felt, as the support material.

It is no surprise that the various manufacturers emphasize only the benefits of their own systems. But what are the facts? What results are actually achieved on the building site?

The IKT-LinerReport 2006 provides answers to these questions on the basis of laboratory results obtained by the independent and neutral IKT Test Center for Pipe Liners.

Material and Man

The IKT laboratory: Tightness test in accordance with the APS test and inspection code

Pipe liners are, in principle, new pipes produced from ultra-modern composite materials. They are manufactured and cured at the construction site, however. Unlike pipes produced in a factory, these onsite cured pipeliners are subject to adverse conditions which frequently prevail on such sites. These conditions will differ significantly from location to location but the correct installation and cure must, nonetheless, be mastered at each location to achieve expected results and success.

This necessitates the highest qualities in the raw support materials and resins used. Only a highly experienced and well coordinated team, fully in control of the complex installation and curing processes, can produce from the raw materials, a tight fitting, structural and leakproof liner which will stand up to several decades of pipeliner service.

Data-base

The data for all installation companies for whom the IKT has performed at least twenty-five liner tests from five different sites in the course of the year (January to December, 2006) has been incorporated into the 2006 LinerReport. In case of repeat tests, the most recently obtained result is used, provided the repeat tests were also performed at IKT. This report is based on a total of 1084 site samples taken at construction sites throughout Germany and thoroughly tested at the IKT laboratory.

The 2006 IKT-LinerReport submitted herewith provides an overall view of tube liner qualities, classified by installation companies and liner systems. It follows the 2003/2004 and 2004/2005 LinerReports, and is therefore the Institute‘s third report of this type (see IKT-LinerReport 2003/2004 and IKT-LinerReport 2004/2005 on www.ikt.de).

Significance and Limits of Information

The laboratory results, obtained from site samples, cannot be used as the sole criteria for assessment of specific lining projects, since site specimens are only, at best, random samples. They are normally taken in the manhole or, in exceptional cases, directly from the pipe.

The overall condition of a renewed pipe can be evaluated only if further acceptance inspection procedures, such as camera inspection or internal manual inspection, are also included. Only these other methods detect wrinkles, incorrectly re-opened service connections and physical defects in the pipeliner.

The IKT-LinerReport can therefore not constitute the only standard for comparative assessment of installation companies and their liner systems. It provides results based on only one – but extremely important – aspect of quality assurance: laboratory testing.

Specified/Actual Analysis

At least four different parameters are generally used for the assessment of building site samples:

• Modulus of elasticity (short-term flexural modulus)
• Flexural strength (short-term σ_fb)
• Wall thickness
• Impermeability to water (water tightness)

In the case of the first three (mechanical) parameters, the specified results are compared against those actually achieved (Specified/Actual analysis). The fourth criterion, water-tightness or porosity, is determined in accordance with the APS test and inspection code. The result is either „Porous“ or „Non-Porous“.

Costumers Must Test

The clients for tests in 2006 included both municipalities and installers. IKT has, however, always emphatically recommended that municipal clients (or their consultant engineers), rather than the installers, should select and commission the testing institute directly. The testing function must not be left to those who’s products are being tested. In this way, potential attempts at influence, by such companies, can be eliminated from the beginning. The majority of tests performed at IKT, a total of 82 %, were conducted on behalf of the municipal client (see Table 1).

Modulus of Elasticity

Liner sample undergoing three-point bending test

Pipe liners are required to withstand locally differing loads (groundwater, traffic loads, soil pressure etc.). They therefore need to be designed specifically for these loads in each case, and to possess adequate load-bearing capability. A central mechanical characteristic parameter in this context is modulus of elasticity. The test method applied in the case of site samples is the threepoint bending test, which IKT performs in the form of a short-time test with reference to DIN EN ISO 178 and DIN EN 13566, Part 4 (see Table 2).

Flexural Strength

Flexural strength indicates the point at which the liner fails as a result of excessively high stress. If this point is too low, the liner does not possess adequate load-bearing capability and may fail before the permissible load is reached. Test method: The load in the three-point bending test is raised at a constant rate of deformation up to the first fall in loading. This indicates the inception of liner failure (short-time test, see Table 3).

Wall Thickness

Measurement of liner wall thickness

The third criteria relevant for assessment of the load-bearing capability of liners is wall thickness (Mean Combined Thickness em as per DIN EN 13566, Part 4). A specified figure (for the stressanalysis calculation, for example), is made for this and must be achieved during production of the liner on site. Test method: The statically loadbearing wall thickness is measured at six points using a precision slide gauge. Inner and outer films and non-structured layers consisting purely of resin (surplus resin layers) are not taken into account in this measurement (see Table 4).

Water-Tightness as per APS

Water (stained red) permeates through: Liner is not water-tight

Test method: Any outer film is firstly removed from the sample and a specified pattern is cut into the inner film. Water containing a red dyestuff is then applied to the inner side and an „underpressure“ (partial vacuum) of 0.5 bar is applied to the exterior side. The liner is „Porous“ (not water-tight) if droplets, foam or moisture form on the outer side (see Table 5).

Liner Types and Liner Systems

Test engineer explaining test procedure: Dipl.-Ing. Jens Fuchs in the IKT laboratory

Analysis of the liner types and systems evaluated and tested indicates the following (see Table 6):

• GRP liners systematically achieve better test results than needle-felt liners for the criteria of water-tightness and modulus of elasticity. This correlation is slightly less pronounced in the case of bending tension. No systematic correlation between liner-type and test results is discernible in the case of the wall-thickness criteria.
• Quality differences, of considerable significance in some cases, become apparent within the two materials groups, i.e., GRP and needle-felt; the results obtained with needle felt for the criteria of water-tightness and flexural strength, for example, fluctuate greatly. They are tightly grouped only for wall thickness. The results for GRP products scatter much less, the sole exception being wall thickness, where a significant bandwidth exists.

Results Classified by Liner Types

Installation Contractors

The quality of execution by the installers is however, also a critical factor in the achievement of success. This is apparent, in particular, in the case of liner systems which are used by more than one company, i.e., Berolina Liners, Brandenburger Tube Liners, City-Liners and Saertex-Liners. The scatter bandwidth of rates of success (percentage of tests passed) per liner system is significant for a number of test criteria (see Table 7).

Conclusion

Pipe lining continues to provide project customers with a suitable and reliable renewal method. The majority of installation contractors performed work which can be classified as good to extremely good in the twelve months of 2006. This is documented by high rates of testing success, ranging up to 100%.

Comparison with the 2004/2005 LinerReport indicates that many companies have actually succeeded in improving their performance, or at least keeping it at a constant high standard.

This constant high standard is extremely positive with a view to achievement of technically sound, cost-efficient and environmentally safe renewal of drain and sewer pipelines. It does, however, become exceedingly clear that a number of installation contractors still have adequate margin for improvement of their liner quality and work. This applies particularly to those companies using needle-felt liners. This group of technologies needs to improve their quality to catch up with the GRP liners in the fields of water-tightness, modulus of elasticity and flexural strength.

In the case of the „GRP liner companies“ however, the picture is also not totally perfect; here, too, the scatter bandwidths demonstrate that on-site quality is not always at a consistently high level.

Intensified efforts in the fields of product improvement, development and quality assurance are now at the very top of the agenda, if the tube lining „family“ is not to fall behind competing methods as the pipe rehabilitation market continues to grow.

Dipl.-Ök. Roland W. Waniek
Dipl.-Ing. Dieter Homann
IKT – Institute for Underground Infrastructure
Exterbruch 1
45886 Gelsenkirchen
Germany
Tel.: +49 (0) 209 17806-0
Fax: +49 (0) 209 17806-88
E-Mail: info@ikt.de
Internet: www.ikt.de

TAUP 2007

International Symposium

Trees and Underground Pipes

- Busting the myths -

in cooperation with

DBU - Deutsche Bundesstiftung Umwelt (German Environmental Foundation)		DWA Deutsche Vereinigung für Wasserwirtschaft, Abwasser und Abfall e.V. (German Association for Water, Wastewater and Waste)
Ministry of the Environment and Conservation, Agriculture and Consumer Protection of the State of North Rhine-Westphalia

Download proceedings

Download proceedings

23./24. May 2007
Gelsenkirchen, Germany

30 min. from Düsseldorf
- International Airport -

In urban areas trees grow in the vicintity of sewers, drains and service pipes. Their roots grow into cracks and pipe connections. This leads to a couple of conflicts between trees and underground pipes.
At IKT-Institute for Underground Infrastructure, Germany, researchers, aborists and network operators will meet to discuss problems and solutions.

Symposium

Excavation for gathering root growth under conditions of a sewer trench

In 1998 IKT started to work on projects dealing with root penetration into sewers. Actually IKT is working on four „root“-projects with various objectives, all to reduce the conflict between trees and underground infrastructure.

At the same time the EU-project COST C15 was working on strategies improving the relation between technical infrastructure and vegetation and preventing conflicts by an international, interdisciplinary approach.

The International Symposium „Trees and Underground Pipes“ will serve as a perfect venue to exchange recent results of interdisciplinary research, to discuss technical and organisational solutions and to create cooperation for further research.

Accompanying Exhibition

The conference is accompanied by an technical exhibition. Suppliers of pipes, root-protection-systems, substrates etc. are invited to present and demonstrate their products.

About IKT

IKT-Institute for Underground Infrastructure

The IKT is a neutral, independent, non-profit research, testing and consulting institute. It works on questions of the construction of underground pipes and networks for gas, water and waste-water. As an independent and reliable partner for utilities, sewer system operators, water associations and industry the IKT offers highly specialized and cutting edge research and testing technologies in a practical, application-orientated manner.

The cooperation of water management and research is practiced by the IKT – Institute for Underground Infrastructure since its establishment in 1994. Well-known companies for water supply/distribution and sewerage are working on transfer between science, research and economy within the IKT supporting bodies.

Further information:
IKT:           www.ikt.de
COST C15:  www-pot.lt.slu.se/costc15/

Programme in details (PDF, 1,5MB)

Symposium Venue:

IKT – Institute for Underground Infrastructure Exterbruch 1 D - 45886 Gelsenkirchen Tel.: +49 (0)209 17806-0 Fax: +49 (0)209 17806-88 Homepage: www.ikt.de E-Mail: taup2007@ikt.de

Contact:

Dipl.-Ing. Christoph Bennerscheidt
Tel.: +49 (0)209 17806-25
E-Mail: bennerscheidt@ikt.de

Programme Committee

• Bosseler, Bert (IKT, D)
• Bennerscheidt, Christoph (IKT, D)
• Naismith, Iain (WRc, UK)
• Ridgers, Don (Thames Water, UK)
• Schröder, Klaus (City of Osnabrück, D)
• Stål, Örjan (University Ålnarp, S)
• Streckenbach, Markus (Ruhr-University Bochum, D)
• Stützel, Thomas (Ruhr-University Bochum, D)

Root Penetration:
Causes, Tests and Prevention

Why do tree roots penetrate pipes - and not only where the pipe is damaged? Root damage to the pipe connections of duly laid, intact pipes causes millions of damages per year. Engineers and biologists prospected the reasons together. Their results are already turning past theories topsy-turvy and have consequences for laying pipes.

Fig. 1: Excavating a pipe penetrated by roots calls an archaeological approach to mind

Sewers are a rather inconspicuous property of cities and municipalities. But there are few things so important for the community. This becomes particularly obvious, when sewers do not work properly. A frequent cause are roots growing into pipes. While one can resort to bottled mineral water instead of drinking water, help out with aggregates in the case of electrical current and simply do without television occasionally, a defective sewage system is always an acute problem, that has to be solved quickly. The IKT has investigated why roots represent a problem for piping systems at all in a co-operation project of the Chair for Systematic Botany and the Botanical Garden of the Ruhr-University. Concepts to avoid this damage are to be developed, based on the accurate knowledge of what happens when roots penetrate. Sound precautions are particularly important, since it usually takes more than 10 years from pipe laying to the occurrence of damage and pipes should last for a long time (service life: 50 to 100 years).

Fig. 2A: CCTV-inspection camera

Biologists and underground engineers seem to be „natural enemies“ in this respect, because one group argues, that nothing can happen, if the pipes are „decently“ laid, while the other considers wood as an aggressive destroyer of the marvel of their engineering art. A biology student, who jobbed in underground engineering and returned to his academic roots with this problem, made the contact between both worlds.

Fig. 2B: Root damage from close up.

Biologists and engineers both initially assumed, that the roots find the pipe, because small amounts of water escape through leaks: The roots grow along moisture gradients (soil area with increasing water saturation) towards the pipe, since the primary function of the roots is water absorption; they then penetrate into the pipe through the leaking locations - because there is even more water there. Robot cameras, driven through the pipes, show us nowadays from close up, what really is happening in the pipe. How the root grows towards the pipe connection before penetrating can however only be recognised, if a defective pipe area is carefully excavated (s. Fig. 1).

The driving videos already show amazing things: The roots usually hang into the pipe from above and end just over the water level. (s. Fig.2A and B)

They do not reach their assumed goal - the water. Thef IKT-researchers therefore examined, what happens during root penetration into the pipe in a project promoted by the Department of the Environment of the province North-Rhine/Westphalia. The IKT-researchers then experimentally examined the hypotheses gained from the excavations as a next step. The excavations also resulted in surprising results: Waste water and rain water conduits differ from each other in root growth (s. Fig. 3 and Fig. 4). The roots always penetrate the pipe above the medium water level in waste water conduits, where they immediately branch out strongly. The roots parts immersed in the waste water were strongly damaged or had died. They erode in the water and form a plug, which then does not dip or only slightly dips into the water.

Fig. 3: The roots penetrate the pipe above the medium water level in waste water conduits and immediately branch out strongly.

Fig. 4: The roots develop meter-long root trails on the base of rain water conduits.

The colour of the immersed roots already indicates that they had died, which was then confirmed by the histological analysis. (s. Fig. 5 A and B)

Fig. 5: A section of a root immersed in waste water makes the damage visible under the microscope (A). Comparison: Cross-section of a healthy root (B)

Fresh, well growing roots also died within days to weeks in different waste water samples in control experiments with rooted cuttings. The water from sewers will probably not be the goal of root growth, if it kills the roots so quickly. The penetration of the roots into the pipe above the water level also contrasts the idea that leaking water is the primary cause of damage. The moisture of the few water drops leaving leaking pipes is not sufficient for building up an adequate moisture gradient, since birches or populars need up to 300 litres water per day. Likewise because the root hardly branches out outside the pipe, which is normally the case in moisture gradients. The root also penetrates the side of the pipe connection in rain water conduits but meter-long root system develop every now and then on the conduit base (s. Fig. 4). The roots are in a much better condition than in waste water conduit, although there are many dead roots there as well. However these show no decomposition characteristics, but have probably just simply dried. Pure rain water conduits dry out faster than soil in summer during long fair weather periods. Sufficient water is also present outside the pipe during rain. The first excavations suggested that the roots do not grow towards leaking pipes and then into them due to loss of water. But then what is the reason for the root growth? Two approaches in the project were choosen: IKT researchers measured, which forces roots can actively muster. Pavements and tar coatings lifted by roots are not very informative in this respect, since thermal movements probably create the space, with in-grown roots only maintain.

Measuring the Root Force

Fig. 6: Test assembly for the determination of the root force: How far and with which force can the roots penetrate into an ever closer pressure sensitive film?

The physiological characteristics suggest, that some roots can apply pressures of approximately 6 bar. This was approved by a special test assembly at IKT. Root forces of 5.9 bar were be measured by a pressure sensitive film (s. Fig. 6).

Thereby the engineers measured in a first step the pressure of roots growing in a continuously decreasing growth space made of plaster (s. Fig. 7). In a second step they looked at the pipes. Using similar pressure sensitive films they messured the surface pressure of different joints while increasing the shear load up to a limit required by standards (s. Fig. 8 as an example). The comparision of both results leads to the statement whether the pressure applied by roots can push the seal aside.

Fig. 7: Plate made of plaster with decreasing growth space

At the Ruhr University it was examined how a root in the soil „decides“, where to grow. It is well-known that root tips perceive gravity by starch grains, because they sink downwards in the cell. Moisture, temperature and nutrient gradients are probably also important for directional growth. But how does a root find its way around an obstacle, e.g. a stone? There must still be other reasons for this growth, since roots grow into cellars through foundations or through green roofs into rooms, where it is neither damper nor richer in nutrients. Little is known about the behaviour of the roots in soil, since physiological investigations are usually carried out on radicles and in nutritive liquids for practical reasons.

Fig. 8: Measuring the changing of pressure and pressure area under shear-load using pressure sensitive films [1] (Tyton connection with a diameter of 150 mm). A Without load: Relevant surface pressure of 6.6 bar. B 1. Step: shear-load of 971 N: Relevant surface pressure of 5.5 bar. C 2. Step: shear-load of 1942 N. Relevant surface pressure of 3.1 bar. D 3. Step: Shear-load of 2914 N. Relevant surface pressure of 3.1 bar. E 4. Step: Shear-load of 4500 N. Relevant surface pressure of 2.6 bar. F After 1,5 hours, under a shear-load of 4500 N: No significant change in comparison to E.

Understanding these processes requires the knowledge of the root tip structure (s. Fig. 9 and Fig. 10): The root tip is a short multifunction organ. Its root cap (Calyptra) protects the growth zone and consists of desintegrating cells. The initial zone is located below the cap.

Fig. 9: Build-up of the root tip

The longitudinal growth starts from here and new calyptra cells are also formed. The root hair zone follows the growth and elongation zone. Root hairs are usually short lived, their function is seen as surface enlargement for waterabsorbtion. The so called endodermis is an important root layer. Water is pumped into the conducting tissue of the root in the endodermis cells using energy. Energy is required, because the water absorption must take place against the concentration gradient of ions such as sodium or chloride; otherwise salt crusts would rapidly develop on the leaves, where large amounts of water evaporate. Oxygen must be present or transported to the root, where no photosynthesis takes place, since energy expenditure always means oxygen consumption.

The gradient is actively built up by the endodermis in the root. Surface enlargements take place above all, where the gradient is built up, where ever physiological processes play a role. The root hair surface enlargement is relatively insignificant in this respect. Surface enlargement seems to be irrelevant in respect to roothairs as the gradient is not performed there. An leek plant forms e.g. over 50 cm long roots, which however do not branch and only exhibit root hairs at the tip. If root hairs would primarily serve for water absorption, then the overall root length increase of the leek plant would be in vain, since the absorbing surface - the root hair zone - only shifts, but does not increase. It seems obvious, that roothairs are predominantly formed for anchoring purposes. They function quasi as counter bearings, when the root tip is pressed into the substrate.

Fig. 10: The root hair zone follows the growth and elongation zone

Soil Density determines Direction of Root Growth

The root cap has not only a passive protective function during this process. The cells are pressed forwards away from the initials and form a channel, into which the root grows. The root cap is therefore the drilling head of the root. But the root cap consists of dying, isolated cells, particularly within the foremost area. How does this drill find its direction? The calyptra cells are passively pressed forward by cells located farther back. The soil density (substrate) determines the direction of root growth, just as further groups move to where there is room in a football stadium crowd: The roots always grow into the less dense substrate at a density border.

Fig. 11: (above): The pipe connection seal is a „Density trap“ for the root.

The drilling head can work against this growth trend, although extremely limited, by unilateral growth behind the initial zone. The growth direction is thereby the result of at least two factors - the force of gravity and the substrate density. A dominating factor can sometimes define the growth direction. This happens e.g. if the root reaches a pipe connection. A cavity, which cannot be filled out and compressed, always results prior to the seal due to its construction (s. Fig. 11). The root grows into this cavity once it has found it and can only get out again, when this pipe connection area is filled with root mass as densely as or more dense than the surroundings. Whether it then grows into the surrounding substrate or into the pipe, is probably just by chance. But if the root grows around the pipe within the joint and enlarges afterwards due to secondary thickening growth, it blocks its way back to the substrate. It then pushes the rubber seal aside and penetrates inside of the pipe (s. Fig. 12).

To achieve better understanding of the relevant cavities between the spigot and the socket of a joint the engineers sliced several connection.

They messured the size of the cavities (no substrate density) that could give roots a place to grow (s. Fig. 13).

When Roots „block“ Their Own Way Back.

Fig. 12: (below): The root has „blocked“ its way back into the soil itself – the only way out is to push forwards. The root tip pushes the seal aside and grows into the pipe (s. arrow).

The pipe connections excavated so far show, that a root can grow in the pipe connection for more than two years, before it grows through the seal into the pipe. Researchers of IKT and RUB have proven this using the annual rings, which are also formed in roots. These findings confirm the hypothesis, that „Density traps“ - like the pipe connection cavity – lead the roots to the pipe connections. These results have been confirmed in model experiments. Growth areas in the substrate, e.g. pore spaces between the bedding and/or filling material seem to be primarily relevant for forming „Density traps“ and not primarily the degree of mechanical compression, as it is achieved with vibrating rollers or plates. The question of the pipe root fastness must therefore also be regarded in connection with bedding and backfilling. A further important starting point results from the root physiology. Since active transportation processes are carried out in the endodermis, oxygen is used there. Underground plant parts, which exhibit such transportation processes and live under oxygen deficiency, often form complicated aerification tissues. This is however not the case for european wood compared to Mangrove plants. The root penetration of the substrate ends, where the oxygen supply falls below a critical limit.

During the project it was examined, whether roots perhaps also find pipe connections exclusively along oxygen gradients, since it is known from other investigations, that seals - even if no liquid leaks are present – become permeable for gases over time. The oxygen supply could play an important role by means of pipe systems, particularly in cities, where the gas exchange through the soil surface is strongly reduced by sealing (e.g. road surfaces). IKT-researchers have however so far found no appropriate clues during the excavations.

„Oxygen Hypothesis“ investigated

Fig. 13: Example for a sliced joint. Socket and seal of a pipe (A). Compressed seal between socket and spigot (B).

This hypothesis could also not be experimentally confirmed yet: The IKT-researchers allowed cuttings rooted in clean water, to carry on growing in different waste water concentrations and provided them with oxygen over dialysis tubes. The damaging effect of the waste water could not be compensated and any root growth towards the oxygen source were not observed. The experiments do not allow to exclude the „oxygen hypothesis” fully, in case the gas supply of the root should play a role in further experiments, it is a minor one in comparison to the „Density trap model“. The „Leak hypothesis“ favoured so far could however not be confirmed in the investigations. Not only does the rooting process into the pipes oppose this, the quantities of leaking water also probably do not stimulate the roots sufficiently. Apart from that waste water pipe leaks usually close quickly again. The necessary pressures for noteworthy seeping losses are not achieved at water levels of usually less than 20 cm in the pipe. Penetrating ground water is more of a problem, because the groundwater pressure can considerably exceed the waste water pressure of deeply buried pipes. The IKT is now looking for experimental alternatives to the natural processes, because the growth of roots into conduits takes ten and more years and results - as in all research projects - have to be presented within approximately two years. The IKT-researchers want to shorten the investigation period, using suitable model organisms plentifully available in the RUB Botanical Garden, and by model tests. This is absolutely necessary, because mistakes made in pipe construction during the next ten years will cause immense costs in the coming 50 years.

Consequences for Laying Pipes

A whole set of consequences for pipe laying can already be deduced from the present results. The rooting problem is not only a question of the seal contact pressure. Geometry and size of the cavity prior to the pipe connection seal play a crucial role, if the „Density trap model“ can be further confirmed. The bedding and filling material for pipe trenches are however also of great importance according to this model. The whole pipe trench represents a „Density trap“, if the grain size of the filling material offers sufficient pore channels, which roots can easily penetrate: The roots can then more or less grow parallel to the pipe and reach as a consequence nearly all pipe connections. Seal design, bedding and backfilling are therefore under the criterion of the independent variables in pipe laying, but closely inter-dependent factors. It seems justified to hope, that the results of the study will show, how this pipe damages can be avoided in the future [2].

Literature

[1] Firmeninformationen der Fa. TEKSCAN: Druckfolien zum Erfassung des Druckes in räumlicher Auflösung; www.tekscan.com

[2] Stützel, Th.; Bosseler, B.; Bennerscheidt, C.; Schmiedener, H.:Wurzeleinwuchs in Abwasserleitungen und Kanäle. IKT – Institute for Underground Infrastructure, Juli 2004, download: www.ikt.de

IKT – Institut für Unterirdische Infrastruktur gGmbH
Exterbruch 1
45886 Gelsenkirchen
Tel.: 0209 17806-0
Fax: 0209 17806-88
E-Mail: info@ikt.de
Internet: www.ikt.de

First International Pipe Jacking Symposium

Pipe jacking is a hotly discussed topic not only in Germany. This was made clear not least of all by the first international symposium held at the IKT on February 14, 2007. Guests from Europe and India had the opportunity of admiring the IKT Pipe Jacking Simulator and of reporting on their own programs and projects.

Diverse Approaches Parallel Results

Dr.-Ing. Bert Bosseler, Scientific Director of the IKT

Dr. Bosseler, Scientific Director of the IKT, presented the IKT Pipe Jacking Simulator, which is unique in the world, to the international participants. This test facility, developed and constructed by the IKT in the context of an ongoing research project, permits 1:1 scale simulation of pipe jacking operations.

Nico Verburg, of the Technical University (TU) of Delft (Netherlands), reported on a project for computation of the frictional forces that occur during pipe jacking. He illustrated in his address the interactions which exist between the work of his university and the IKT: Differing approaches leading to parallel conclusions. The researchers in Delft calculate jacking operations and observe real projects in situ - unlike the IKT, where the simulator supplies the results. The frictional forces occurring generate reactions in the pipe bed and thus have an influence on the necessary jacking forces.

Prof. Dr.-Ing. Bernd Falter, University of Applied Sciences Münster

Prof. Dr. Ing. Bernd Falter, of the University of Münster, has verified the results obtained on the IKT Pipe Jacking Simulator by means of FEM simulation. Prof. Falter developed, on the basis of FEM simulation, a rod model, which can be used to compute any pipe jacking operation.
Andreas Redmann of the IKT presented the first results obtained from the IKT simulator: Contrary to the general assumption that, in an ideal case, uniformly distributed deflections occur between the pipes, an effect of joints expanding to differing extents actually takes place in practice. Measured and calculated bed reactions indicate that, when negotiating curves, the individual pipes group together to form "straights" (the "rod" or "straightening" effect). The irregular distribution of bed forces results in edge pressures and transverse forces.

International Platform

Niranjan Swarup, Director of IndSTT

The paper presented by Niranjan Swarup, Director of the Indian Society for Trenchless Technology (IndSTT) demonstrated that pipe jacking is a subject of global significance. In India`s densely populated conurbations, open trench pipe installation is a virtual logistical impossibility, which is why Indian system operators use pipe jacking in many cases for installation of new conduits.

The special circumstances of installing drains and sewers of the dimensions necessary for waste water management in New Delhi and the surrounding region (with a total of some 18.1 million inhabitants) will be examined by the "No Dig India" conference to be held in the city on March 28 and 29. Around sixty Indian system operators will be discussing with the responsible ministry the potentials for the use of trenchless methods. Niranjan Swarup kindly extended to IKT an invitation to attend this event, which the institute has been pleased to accept.

For more information on the IKT pipe jacking simulator, contact:

Dipl.-Ing. Martin Liebscher
Dipl.-Ing. Andreas Redmann
IKT – Institut für Unterirdische Infrastruktur gGmbH
Exterbruch 1
45886 Gelsenkirchen
Tel.: 0209 17806-0
Fax: 0209 17806-88
E-Mail: info@ikt.de
Internet: www.ikt.de

Large Profiled Plastic Pipes:
Practical Experience and Test Concepts

Besides the so-called classic materials concrete, reinforced concrete, vitrified clay and cast iron, plastic products are increasingly used for the construction, renewal and renovation of drains and sewers. Numerous surveys, research projects and product tests by the IKT have dealt with the behaviour of single products under practical and laboratory conditions. Here, the recently completed IKT research project "Large Profiled Plastic Pipes" has set in and offers detailed recommendations for the testing of large profiled pipes in its result.

Background

Besides the so-called classic materials concrete, reinforced concrete, vitrified clay and cast iron, plastic products are increasingly used for the construction, renewal and renovation of drains and sewers. Numerous surveys, research projects and product tests by the IKT – Institute for Underground Infrastructure (Gelsenkirchen, Germany) have dealt with the behaviour of single products under practical and laboratory conditions (cf. [1], [2], [3], [4]). Special emphasis was put on the rehabilitation of sewers, the investigation of special applications, the influence of quality as well as the determination of demands on the dimensioning and testing of pipes and construction methods.

Here, the recently completed IKT research project "Large profiled plastic pipes" (cf. [5]) has set in and offers detailed recommendations for the testing of large profiled pipes in its result. Furthermore, interesting conclusions could be drawn from the practical experience of the network operators as well as from the project-related discussions with users and manufacturers. In the following the substantial findings are summarized.

Application of Large Profiled Plastic Pipes

For the new construction of drains and sewers, pipes of various materials are offered. Besides pipes made of concrete, reinforced concrete, vitrified clay and cast iron also plastic pipes are increasingly used. If the information by the DWA [6] is taken as a basis, between 2001 and 2004 the proportion of plastic pipes in the German sewer system has grown from around 3 % to around 6 %. In the range of nominal diameters ≥ ND 800 (large pipes) the proportion of plastic pipelines amounts to around 1 %.

Figure 1: Large profiled plastic pipe ND 2000 during the experiment: pipe deformation and water tightness testing of the connections

For the range of accessible nominal diameters, besides pipes with monolithic wall structure (solid wall pipes), predominantly pipes with an open wall structure (profiled pipes) are offered. In connection with the IKT-project [5] public sewer network operators predominantly put the comparatively low application rate of large profiled plastic pipes down to insecurities regarding the installation as well as the later behaviour during operation. Essential points in the discussion are the sustainable stability, deformation development as well as bedding requirements, possible difficulties in the installation and the behaviour under point loads. These insecurities are opposed by the intention to use the possible advantages of the offered plastic pipes such as low weight, weldability (PE, PP) and chemical resistance under corresponding structural tasks.

Figure 2: Wall sections (examples) of large profiled plastic pipes (ND 2000) a) Example 1 of a profile: profile height h = 123 mm, partial heights h1 = h2 = 58 mm, profile width b1 = 66 mm, profile distance b2 = 300 mm, main wall thickness e4 = 7 mm (dimensions according to [7])

Core-foamed multi-layer pipes as well as pipes with open wall cross sections belong to the product group of profiled plastic pipes. Due to the special construction of their wall structure profiled pipes have a smaller weight compared to solid wall pipes of the same nominal diameter and stiffness. As an example Figure 1 shows a large profiled pipe of the nominal diameter ND 2000 during deformation testing. Figure 2 gives examples of different wall structures of the same nominal diameter, which were also used as testing bodies in connection with the IKT-analysis.

Practical Experience

Figure 2: Wall sections (examples) of large profiled plastic pipes (ND 2000) b) Example 2 of a profile: profile height h = 76.0 mm, main wall thickness s1 = 15.0 mm, hose jacketing s4 = 10.0 mm (dimensions according to [8])

To determine the actual state of plastic pipelines, which have already been installed, with regards to possible precarious features sewer inspections were carried out and inspection videos of non-accessible sections were sifted. In connection with the inspection of passages with large profiled pipes, 24 sections with a total length of around 1.5 km were inspected and additionally, the cross sections were comprehensively measured. The videos viewed contained TV inspections of altogether 248 sections with a total length of around 10 km. Weak points, cases of damage (such as leaks, for example) or other peculiarities that were found were identified as well as pictured and described. In the following substantial precarious features in the area of pipes, pipe joints, side inlets, manholes and manhole constructions are compiled.

Figure 2: Wall sections (examples) of large profiled plastic pipes (ND 2000) c) Example 3 of a profile: profile height h = 103 mm, profile width b1 = 110 mm, profile distance b2 = 180 mm, profile wall thickness s = 8 mm, wall thickness of the inner layer e4 = 11,0 mm, wall thickness of the inner layer under a hollow profile e5 = 19 mm (dimensions according to [9])

In connection with the sewer inspections the internal diameter of accessible pipes was measured and analysed in the horizontal as well as the vertical direction by employing a telescopic measuring stick in regular intervals (beginning, middle and ending of the pipe). Only in one of the 24 sections the permissible limiting value of deformation (permitted δ_V = 6 %) according to [10] was exceeded. In comparison the analysis of the inspection videos for non-accessible sewers showed noticeable deformation figures such as arch profiles, three- or four wave figures, upward ovalisation. An extreme ovalisation of around 30 %, however, was only observed in one single, 5 m long section of the total inspected length of approximately 10 km. To some extent misalignments appeared in the non-accessible sewers. Presumably, they originate from the installation process, for instance, from insufficient positioning. Local deformations that can probably also be led back to deficient construction, such as square timber that remained in the ground, were hardly observed in the area of the pipe invert.

Leaks inside the pipe shaft were only observed in single cases in places with water dripping in. It could not be revealed in what sense these lacks can be put down to damages during installation or to point loads. In the accessible area no leaks whatsoever could be visually observed.

In large pipes as well as non-accessible pipes displaced joints (maximum heights: 3 cm) were determined in the area of pipe joints. They were probably caused by diameter tolerances that are linked with the manufacturing process (cf. Figure 3).

Figure 3: Pipe joint with a displacement of 3 cm (ND 2000, year of construction: 1999)

Welding seams of varying width showed at pipe joints that were created by extrusion. A deflection in the pipe joint could be the reason for this variation, for example. So as a consequence, the butt joint has a different width in the direction of the circumference. In connection with the sewer inspection as well the sifting of TV inspection videos, however, no leaks were detected. At some pipe joints, which were created with the helical-coil-welding-socket method, weld metal was visible. Presumably, this resulted from a deviation during the connection of the pipes. Leaks were not noticed in these areas.

Within the scope of sewer inspections as well as of the sifting of inspection videos precarious features at the side inlets were observed only in exceptional cases. So in large pipes only in one case an uneven cutting edge at the inlets could be noticed and in another case an extremely wide welding seam. In non-accessible pipes, on the other hand, leaking connection areas could be observed due to infiltration of groundwater.

Figure 4: Precarious features at manholes a) Crack in the area of the manhole (ND 1600, year of construction 1999)

Clear weak points showed on manholes with a change of material from PE pipes to shafts of concrete or brickwork. Here, precarious features in the form of cracks, cleavages, material removal and root ingress were observed in the transition area between the pipe and the shaft construction (cf. Figure 4).

Usually leaks within manhole constructions occurred in the area of the material transition between PE manhole base unit and the installed concrete shaft ring or brickwork. As a cause mostly the use of an deficient sealing medium or a deficient installation process, e.g. sealing with wrong direction of installation, could be assumed. In the vicinity of material transition from PE to brickwork no infiltration could be observed, but leaks must be expected, because of bad connection characteristics between those materials.

Figure 4: Precarious features at manholes b) Crack between pipe (ND 500, year of construction 1985) and brickwork manhole channel

In addition to sewer inspections and the sifting of TV inspection videos, also interviews with approximately 130 public sewer network operators (local authorities and water associations) were made in order to include further experience by the network operators in planning, construction and operation. Here it became clear that on the side of the sewer network operators there are special uncertainties with regards to pipe stability, feasibility of soil compaction requirements and necessary company know-how in the installation, especially in soil compaction and positioning. Furthermore, they pointed at possible difficulties during rehabilitation (method and costs). The low weight and the weldability as well as positive experience in sewer cleaning and water tightness were mentioned as advantages on the other hand. It has to be pointed out that numerous sewer network operators reported noticeable deformations of the cross section, but in connection with the approval or inspection the cross sections were only infrequently measured. In most cases no statements on the development of the deformation of plastic pipes with reference to the time were made.

Figure 4: Precarious features at manholes c) Material removal in the mortar joint between pipe (ND 700, year of construction: unknown) and brickwork manhole channel

In order to include the current practice of dimensioning of large profiled plastic pipes, some of the available static calculations were analysed with regards to the calculation assumptions and conditions as well as the calculative verification. Altogether, the analysis of the static calculations of twelve completed constructions shows that in the past the installation conditions, e.g. soil groups and degree of compaction, had been determined in a very optimistic way; the verification limits (especially deformation- and stability verification) had usually been exploited and the possibility of a profile collapse had by no means been taken into account.

Furthermore, it was found out that the selection of a cross section for large profiled plastic pipes usually derives from the limiting conditions of the project. That means that the profiling corresponds to the static requirements of the individual application. Reserves for unexpected incidents such as changes of soil groups, that are detected on the construction site later on, deviations in the selection of the lining type and the geometry of the trenches are usually not available. That means that special importance is attached to the static calculation of the strongly exploited construction [11].

Figure 4: Precarious features at manholes d) Root ingress in the crown area of the manhole of a collector (ND 500, year of construction: 1972)

The fact that the different material- or pipe characteristics of the plastic pipes are often unknown to the network operators is to be considered particularly critical. Furthermore, on the site an identification of the installed materials is basically left out. Usually the network operator summarizes the different materials under the term "plastic" so problems with a material or pipe type are often related to the entire material family.

The questions raised in connection with the in-situ investigations, interviews and construction site analyses were summarized in the following five main topics with reference to the research project:

• condition assessment in situ
• deformation of the cross section
• influence from operation loads
• (time-dependent) stability collapse
• local external loads (point loads).

The development of the test concepts and their realisation is presented in detail in [5]. As an example, the following deals with condition assessment in connection with construction approval or warranty check, and possible investigations concerning stability collapse of profiled pipes.

Measurement of Deformation and Approval

Figure 5a: Determination of the horizontal diameter

DWA standard A 127 (cf. [12]) classifies pipes as flexible if, due to their deformation, the surrounding soil is part of the bearing system. Correspondingly, to verify long-term deformations a vertical change of diameter of 6 % (or 9 % when looking at additional verification) is permitted. Also regarding the effects of extreme deformations on the functional safety and water tightness, special importance is attached to assessing pipe deformations. Starting from the current state of experience with deformation measuring data, a method for acquiring and analysing deformation measuring data has been developed, which can be summarized as follows:

Figure 5b: Determination of the vertical diameter

• Measuring is carried out by employing a telescopic measuring stick, by means of which the internal pipe diameter is measured in regular intervals or locations with precarious features in the horizontal and vertical direction (cf. Figure 5).
• The measuring data is processed and is recorded graphically (cf. Figure 6). Here, the horizontally and vertically measured diameter values are plotted on the y-axis; the stations are to be taken from the x-axis.
• A permissible deformation range (DR) is chosen, e.g. from the regulations in [12] or from the static calculation (DR = 2 x permissible δ_V), and is inserted into the diagram by means of two horizontal lines. Since the actual diameter of the undeformed pipe does not have to correspond to the target diameter according to the manufacturer, the deformation range is oriented at the mean value of all measuring values by especially taking into account extreme deformations (cf. [4]).
• Spots with extraordinary deformations or figures are identified as critical pipe cross sections for further observation and are correspondingly marked in the analysis of the measuring data. With regards to a possible long-term stability collapse in future inspections these cross sections should generally be assessed in detail and should be checked for possible changes or increase of deformation.

Figure 6: Horizontal and vertical diameter values compared to the permissible deformation range (long-term, DR = 2 x δV), example

Time-Dependent Stability Collapse

Basically, the stability behaviour of large pipes can also be determined by large-scale experiments of the scale 1:1. However these experiments, under hydrostatic external pressure at the IKT large-scale experimental rig, for example, hardly seem economically efficient. Usually a mathematical stability proof is advisable when verifying the calculation model by small-scale model experiments. A corresponding concept was developed by the IKT and the University of Applied Sciences in Münster (field of statics and constructional computing).

Global stability collapse is investigated by taking into account the special material behaviour by means of crown pressure experiments and buckling experiments with unbedded, profiled plastic pipes of the nominal diameter ND 300 on a scale of 1:1. On this basis calculation bases for the FEM model developed for the mathematical stability proof can be calibrated and the applicability of existing calculation concepts can be analysed. Figures 7 and 8 show the deformation of pipes at the end of one of the external water pressure experiments that have been carried out as an example. They also show the result of a corresponding FEM calculation.

Figure 8: Buckling shape of an orthotropic shell (Ultra Rib 2, ND 300), from [13] a) Front view

Figure 8: Buckling shape of an orthotropic shell (Ultra Rib 2, ND 300), from [13] b) Isometric view

The only aspect that remains unclear in the external water pressure experiment, however, is the influence occurring with complex profile geometries and high axial force loading that can develop with bedded pipes. Thus, also a profile collapse before or together with global collapse cannot be excluded as well as the likeliness that material behaviour is only insufficiently considered. Also the large pipes that were investigated partially showed clear deviations from the target geometry (measurement of wall structure and nominal diameter) due to production. So a weakening of the profile cross section and – without further safety considerations and analyses of weak points – corresponding risks with mathematical use of the theoretical profile shape can be expected.

For this reason, a test concept was developed, by means of which a distinct deformation of profile samples (pressure cartridge) is provoked under high axial force loading. Based on this, the significance of the FEM model can be checked. To minimise the bending moment, which is a consequence of the curvature of the testing body, small-sized wall sections are used for the experiments. The result of experiments that were carried out as an example showed good correspondence between the deformation types in the experiment and the deformation states simulated by means of FEM calculations (cf. Figure 9). Imperfections of the profile geometry created by local load introduction are developed by lateral pressure experiments (cf. [5]) on similar testing bodies and are aligned with the FEM model.

Figure 9: Deformation of the profile sample under vertical load at the cross sections a) Deformation in the experiment

Figure 9: Deformation of the profile sample under vertical load at the cross sections b) Result of an FEM calculation, from [14]

Conclusion and Outlook

Against the background of the practical experience, laboratory tests and mathematical analyses the following conclusion can be drawn for practice:

The installation quality is decisive for the safety of the entire system of pipeline, bedding and shaft constructions. Besides deformations of the cross section, in situ also misalignments were often observed and in few cases local deformations. In connection with the actual construction, special care should be taken of an adequate positional safety of the pipes without disturbing bodies (e.g. squared timber), with a consistent soil compaction and the minimisation of pre-deformation (e.g. due to solar irradiation). Point loads are a special case that is difficult to describe within the scope of testing. For example, this applies to the information about the size of the catchment area of the of possible disturbing bodies and the number of their contact spots to the pipe.

The analysis of the static calculation of twelve completed construction measures showed that in the past the installation conditions, such as soil groups and level of compaction, were determined very optimistically, the verification limits – especially deformation- and stability proof – were exploited. The possibility of a profile collapse was not taken into consideration at all.

Leaks within the pipe shaft were hardly observed. Only in two single cases dripping water could be seen in the crown area of non-accessible sections. Material transitions from PE to concrete or brickwork cannot be regarded as special weak points for the water tightness of the entire system. Here, the solutions for water tight material transitions, which are offered on the market in connection with system tests, should be analysed with regards to their basic suitability. Concerning the construction approval, the question for manageable methods for water tightness testing raises in these transition areas. Manholes and changes of material in shaft superstructures should already be scrutinised more during planning, the construction period and the product development.

A more detailled inspection of large plastic pipes is hardly taking place. Deformations on large profiled plastic pipes are scarcely measured in connection with the approval of the construction and during the operation stage. Due to the operational situation, e.g. partial filling as well as the slippery surface (slip hazard), sewers are only inspected in single cases. Critical deformation states, large vertical deformations, for instance, can only be assessed reliably if also information about the delivered quality, the installation and the temporal development of the deformation is available. Thus, special importance is attached to the approval of the delivered goods, the approval of the construction as well as the regular inspection and measuring of the cross section – for noticeably great deformations. In order to achieve significant inspection results in situ with arguably effort a combination of visual inspection and deformation measuring is recommended. Then, on this basis, critical areas for further detailed observations can be identified.

The network operators seem to have particular uncertainties regarding the demands on material quality (e.g. PE-HD and PE 80/100), the connection technique (e.g. welding method or sockets) and on the special qualification of the construction companies. Interested network operators now intent to follow up these questions together with the IKT in a collaborative project. The start of the project is planned for 2007, a participation of other operators is possible (for further information sokoll@ikt.de; +49 (0)209-17806-26).

Authors:

Dr.-Ing. Bert Bosseler, Research Director, IKT – Institute for Underground Infrastructure

Dipl.-Ing. Oliver Sokoll, Project Manager, IKT – Institute for Underground Infrastructure

Prof. Dr.-Ing. Bernhard Falter, Münster University of Applied Sciences

Dipl.-Ing. Frank Holthoff, Münster University of Applied Sciences

Bibliography

[1] Bosseler, B.; Kaltenhäuser, G.: IKT-Warentest – Hausanschluss-Liner; final report of the IKT - Institute for Undergorund Infrastructure (November 2005), download on www.ikt.de.

[2] Bosseler, B.; Liebscher, M.: Erneuerung mit dem Berstverfahren: Bemessung, Prüfung und Qualitätssicherung von Abwasserrohren; final report of the IKT - Institute for Underground Infrastructure by order of the Ministry for Environment and Nature Protection, Agriculture and Consumer Protection of NRW (November 2003).

[3] Bosseler, B.; Schlüter, M.: Qualitätseinflüsse Schlauchliner; Stichproben-Untersuchung an sanierten Abwasserkanälen; final report of the IKT - Institute for Underground Infrastructure by order of the Ministry for Environment and Nature Protection, Agriculture and Consumer Protection of NRW (December 2003), download on www.ikt.de.

[4] Bosseler, B.: Beitrag zur Darstellung, Analyse und Interpretation von Verformungsmessdaten aus der Inneninspektion biegeweicher Abwasserleitungen. Technisch-wissenschaftliche Berichte, IKT-Bericht 97/4 (June 1997).

[5] Bosseler, B.; Sokoll, O.: Profilierte Großrohre aus Kunststoff – Praxiserfahrungen und Prüfkonzepte; final report of the IKT - Institute for Underground Infrastructure by order of the Ministry for Environment and Nature Protection, Agriculture and Consumer Protection of NRW (Oktober 2005).

[6] Berger, C.; Lohaus, J.: Zustand der Kanalisation, Ergebnisse der DWA-Umfrage 2004; KA -Abwasser, Abfall (2005), Issue 5, pp. 528-539.

[7] Company information bauku - Troisdorfer Bau- und Kunststoff GmbH, Wiehl-Drabenderhöhe.

[8] Company information Frank & Krah Wickelrohr GmbH, Schutzbach.

[9] Company information Henze GmbH, Troisdorf.

[10] Regulations of the Deutschen Vereinigung für Wasserwirtschaft, Abwasser und Abfall e.V. (DWA), Standard A 127: Statische Berechnung von Abwasserkanälen und -leitungen, 3rd edition, Hennef, GFA (August 2000).

[11] Falter, B.; Holthoff, F.: Statiken für profilierte Rohre; Report of the Münster University of Applied Sciences / Department of civil engineering by order of the IKT - Institute for Underground infrastructure; Münster (November 2004, unpublished).

[12] Regulations of the Deutschen Vereinigung für Wasserwirtschaft, Abwasser und Abfall e.V. (DWA), Standard A 127: Statische Berechnung von Abwasserkanälen und -leitungen, 3rd edition, Hennef, GFA (August 2000).

[13] Falter, B.; Holthoff, F.: FEM-Berechnungen zum Beulverhalten von außen profilierten Rohren der Nennweite DN 300; Report of the Münster University of Applied Sciences / Department of civil engineering by order of the IKT - Institute for Underground infrastructure; Münster (September 2004, unpublished).

[14] Falter, B.; Holthoff, F.: FEM-Berechnungen zum Beulverhalten von profilierten Rohren der Nennweite DN 2000; Report of the Münster University of Applied Sciences / Department of civil engineering by order of the IKT - Institute for Underground Infrastructure; Münster (September 2004, unpublished).

Dipl-Ing Oliver Sokoll
IKT – Institut für Unterirdische Infrastruktur gGmbH
Exterbruch 1
45886 Gelsenkirchen
Tel.: 0209 17806-26
Fax: 0209 17806-88
E-Mail: info@ikt.de
Internet: www.ikt.de