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1st NO DIG BERLIN 2013 Conference and Exhibition23 - 26. April 2013

Paper 4-3

German DWA Worksheet A 143, Part 2 whats new in structural

design of CIPP?

CEng Markus Maletz, EUR INGKMG Pipe Technologies, Ursensollen, Germany

SUMMARY

Once in the early years of renovation with CIPP liners, many faults (especiallybuckling damages) occurred. The first design attempts have been made in the 90's,due to the existing Worksheet A 127 of the German DWA (design for pipes with

digging)the load cases hostpipe stable and hostpipe not safe have beencreated.

Until the publishing in the year 2000 there has been worked on the advisory leaflet M127, part 2, which have to be used only for the renovation of pipes. Three hostpipestates were defined, which are specified by the client.

After over 10 years of successful application, now the leaflet has been revised andpublished in November 2012 as a Worksheet A 143 part 2 (yellow print).

INTRODUCTION

The pipe relining or hose lining, as they will now be called for a long period, are themost successful renovation systems in the non-pressure (= gravity) range. Reasonsfor this are likely the duration of this processes - the eldest system has been placedin 1971 - and thus the experience with this process and the diversity of thisapplications. Liners are actually the only renovation process, which are - properlyinstalledtight to the host pipe, and therefore without a recognizable annular gap.They are built in different profiles, such as circular-, egg-, oval- and rectangle-profiles, closed fit to the wall of the old pipe and the cross-sectional area of theoriginal profile will not decrease very much.

Also the possibilities of use - depending on the process - in sizes from DN 100 up to> DN 2000 shows the universality of these technologies.

Liners are a so-called "locally produced and hardened pipes" (English: CIPP= CuredIn Place Pipe), at least consisting of a tube or hose carrier and a resin (due to ENISO 11296-4 and EN ISO 11295), optionally with an coated inner film, and/or outerfilm (or Preliner) and - especially for the larger dimensions with "inert" (no influence tothe quality of resin, e.g. with respect to chemical or thermal resistance) additives inthe filled resin system. In most cases there are UP resins used for lining, in individual

cases EP or VE resins.

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In the UP resin systems is the reaction or curing fundamentally distinguished in:

- hot water curing, quick curing / cold curing

and

- UV-light curing

The heat curing families include the "classical" methods using hot water or steam - inrarer cases, using electric resistance heating too. They include also the longintroduced system on the market called "quick-hardening" for the heat curing family.

All systems above bring, depending on recipes on the basis of peroxides, with eachof user to user differently defined temperature-time-track (processing- or pot-time),the resin mixture to the reaction and hardening over a defined time period

(tempering); the laminate completely to the finished product, in most cases a pipe-in-pipe, sometimes to a pipe connected to the old liner.

The "quick curing" offers - as the name suggests - a much shorter processing time,which makes it sometimes necessary that the work step "impregnation" is located onthe construction site.

The cold curing of UP and EP resins is a system which is shortening the curingreaction time very much, so that an impregnation is only possible at the job-site.Additionally, the liners to be processed are limited in diameter (max. up to ND 400)and length (up to about 65.0 m), because the pot life of the resin is inverselyreciprocal to the volume of the mixed-resin behaves. The hardening grade, which isreached immediately after the installation of the cold-hardening resin systems, isbelow the final cure, which is only achieved within approximately 30 days.

Before UV-curing, the first step is the installation, usually by pulling in the liner overexisting manholes using a winch. By a defined air pressure, the liner is thenexpanded and pressed against the old pipe. In this state, now a UV lamp (light-chain) with a defined speed is pulled through the liner. By the use of photo catalysts,the resin reacts with the UV light, and hardens. There is usually no peroxide curing;only with thicker laminates ( approx. 12 mm) there will be used a combination!

Requirements for the use of CIPP are:

- hydraulic sufficient cross-section before renovation;

- presence of the vault (circular or other profile);

- deformations 6-8 % (ovality);

- thermal and chemical resistance of the selected resin system;

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(GERMAN) STRUCTURAL DESIGN ASPECTS

General

Before publication of the leaflet M127-2 static assessments have been carried out

according to the DWA worksheet A127, because of lack of a missing standard. Thisapproach was on the safe side, although this paper was meant only for newinstallation of sewers and pipes. The calculations have been fundamentallyseparated in "old pipe not safe" and "old pipe secure."

Under the assumption of a consolidated soil (E1= E2= E3= E4) and simplifications,such as the friction on the walls (in a trench fault), the liners were rated on waterpressure (buckling check) and otherwise also with earth-, traffic- and other staticsurface loads (e.g. container, foundations, pools).

First thoughts of the DWA were in 1993 that there is a difference of the system

(which was generally used) of a damaged pipe impaired in the surrounding soil. InSeptember 1999, the (former) working group 1.2.3 of DWA had their last sessionbefore the publication of the new leaflethandle only a few appeals by renovationcompanies. In January 2000 the new leaflet 127-2 appeared and the "gray zone" ofthe A 127 had been removed for calculation of liner renovations.

Through various research projects and theoretical assumptions, but also try topractice, a calculation methodology was developed, which is now up-to-date andverified by means of the FE (finite element) method.

Hostpipe s tates

In the (new) leaflet, it is no longer distinguished between the load case "stable" and"not stable" according to ATV-M 143, part 3, and it defines three host pipe states thatcorrespond to all the "old" state "stable":

- state I

- state II

and

- state III

In the state I, which is not different from the previous load case "stable", soil andtraffic loads are still taken completely by the old pipe. The liner is measured only ongroundwater pressure (identified over invert). In that case, if the wall thickness is toolow, it can cause a buckling of liners in the invert (circular profiles).

In state II is assumed that (even with a cracked pipe, which may also have slightdeformations) it is adapted the so-called "arch effect" of the surrounding soil.An intact bedding activates a slight deformation - which follows a crackand the

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reaction pressure. Now the so-called "pipe-soil-system" carries the soil and trafficloads. As in state I, the liner is to be measured simply by water pressure and it is onlynecessary to prevent the bedding from being damaged by exfiltration and/orinfiltration.

The state III is characterized by the fact that the existing pipe (or the pipe-soil-system) is no longer stable for the future. Therefore the liner must additionally carry awater column and the soil- and traffic loads. It may (or may not) lead to thicker liners,as in the two cases above.

If there is no existing groundwater, it is to be considered a minimum load of da+ 0.1m water column over invert (1.5 m) in state I and II.

In the relevant "main states" I and II, is now made a buckling check againstpressurized groundwater. The M 127-2 has now three reduction factors to beintroduced. These consider the following "disturbances" of the old pipe liner

geometry:

1. Reduction for a prestrain v(imperfection, pipe tolerances, etc.), which arespecified of 1 % of the liner radius (if there are exact measurements) of thehost pipe. If there is no calibration, the value must be 2 % (standard).

2. Reduction for ovality Ar,v(4-hinge-deformation, ovalisation), which is specifiedwith minimum 3 % of the liner radius (Standard).

3. Reduction for a surrounding gap sbetween Liner and host pipe of 0.5 % ofthe liner radius (< DN 800) respectively 0.25 % ( DN 800), if there are nogreater values, maybe proofed by testing reports (recommendation).

All three reduction factors (in combination) mean that the minimum wall thickness in-creases with unfavorable geometry. Thus, a liner product is selected, which hasmaybe a high gap, this unfavorable geometry must be compensated by a higher wallthickness.

A direct comparison of a liner between the "old" calculation due to A 127 (buckling)and the state I to M 127-2 has shown that for circular profiles, especially in the upperdiameter range (> ND 600) and at higher ground-water exercise, a reduction of the

minimum wall thickness can be achieved up to 14% - a positive aspect of the "new"rule.

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System sketches and examples

State I

The host pipe is stablepossible damages, as leaky pipe connections are suitable,except hairline cracks in the pipe wall are no cracks present. Likewise, even a slightcorrosion, such as for concrete pipes may be present.

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State II

The host pipe-soil-system is stableas damage may occur e.g. longitudinal cracks,in combination with a low deformation, proofed by a verified bedding which isconfirmed (for example by dynamic drop penetration testing or even long-termobservation).

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State III

The host pipe-soil-system is not stable for the futurethere are greater deformationsand the liner gets additionally soil- and traffic loads.

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Is the s tate III really crit ical?

It is important to see in the state III, that even after installation of the liner, the oldpipe can get further deformations under load. The liner must adapt to thesedistortions of the old pipe, because his pipe stiffness is usually lower than the

stiffness of the old pipe. In this way, the liner of the old pipe-soil-system is affectedonly marginally. The liner is loaded mainly by the close-fit component. A lower linerstiffness (reduced wall thickness and/or E-Modulus) may be beneficial in this case.

This shows, that the slogan: "I calculate only in host pipe state III, then I get greaterwall thicknesses" turns out to be wrong. By a rise of groundwater and/or a changein the existing pipe-soil-system, however, an increase of frictional effects is possible.This would then apply the criteria for dimensioning by host pipe state II. For mixedloads is a compromise between flexibility and stiffness of the liner to be found.

The calculation model for the host pipe state III consists of a spring system. The

longitudinal cracks in the old pipe will be idealized in the theoretical model of the oldpipe to be as eccentric joints. This can now be solved using Finite Element Analysis(FEA), but there are only a few FEA models to calculate state III.

Further invest igat ions

During unclear status, it is necessary to conduct soil tests. This may happen inplaces that let suggest in the CCTV recording of the sewer, for example cavities, lightdynamic probing, or drilling in addition to the pipeline route will be carried out. It canalso identify some indication of the groundwater level.

There is also the possibility of long-term observations (if available, or possible) todeter-mine, whether the damage profile has changed over time. With increasingdeformations certainly the choice of state III is preferable, because then theassumption seems likely that the bedding is disturbed. The experience of theevaluating engineer is very useful here. Thus, for example, in a very flat-lying sewerwith longitudinal cracks, have led to the influence of the traffic load due to increasedvolume of heavy traffic to damage the line, while already such as very deep-lyingpipes the damage occurs during installation, and the dome-effect has set over theyears.

Redistr ibut ion of soi l stresses

As an average over old sewers, the rigid pipes usually form after installation stressconcentrations over the pipe. The ground tensions are rearranged because of thedifference between soil and pipe (see ATV-DVWK A 127, clause 6.1 Redistribution ofSoil Stresses).

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a) Rigid pipe

If now a pipe breaks, then the state II is build and the bedding-reaction-pressure isactivated. A slight deformation is associated with this process.From the previously rigid system, a flexible soft system is made, which releasestensions to the surrounding soil.

a) flexible pipe

By means of renovation, the flexural soft system will be kept.

Experiences / Damages

The experiences of renovations over the last years have shown that mostly alldamages of liners have been buckling losses.

The critical load for the liner is also buckling, which is triggered by levels of groundwater, generating a hydrostatic pressure. The distribution of pressure is triangularsituated, so you have an increasing water column towards the bottom; the bucklingpressure is greatest at the invert. In circular profiles at this point also occur the

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damages. Egg-shaped sewers form the buckle in the spring line, because the largestradius (= minimal resistance) is located there.

The reasons for buckling may firstly be a false assessment of the liner, coupled witha not exactly known ground water level or other improper curing.

In the first case may be concerned, that groundwater, which is infiltrated into thesewer for years, that was used as a type of drainage. After a successfulrehabilitation, experience has shown that the ground water level increases, providingthe water can find no other way.

In the second case, the construction management is required to identify the curing

procedures the liner strictly adhered to. Through a carefully planned strategy, qualityassurance, these errors can be avoided.

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CHANGES FROM M 127-2 TO A 143-2 (yellow print)

With over 10 years of successful application theadvisory leaflet M 127 Part 2 has been revised in thelast four years and was published in November 2012 as

a yellow print.

The reasons for raising the status from a leaflet to aworksheet were:

- Probation of the leaflet M 127-2 in practice. The factsheet was published in 2000. It has proven itself inpractice, even in difficult renovation conditions. Thisapplies to Germany as well as many internationalprojects in which the leaflet 127-2 M was prescribedfor the structural design (see the English translation

of M 127-2).

- Any known claims are mostly attributed on structural defects, inadequate curingor misuse of this information sheet. If cases of damage have occurred, thereasons could be revealed usually with the help of this information sheet.

- The practicability of the leaflet can also be seen in many training courses forCertified Sewer Rehabilitation Consultants, in which practicing engineers learnto control simple CIPP statics due to M 127-2.

A new edition is required, especially due to the concept of partialsafety factors for actions (loads) and the resistances (strengthand deformation characteristics), which were introduced with theEuro Codes (EC1).Calculation by partial safety factors

Table 1: partial safety factors for resistances

Pipe material M

Plastic liner, cured in the sewer 1,35

Plastic liner, manufactured in a plant (extrusion or other methods) 1,25

Mortar-liner (regarding of possible notch effects in the materials testing) 1,50

Stainless steel 1,15

Resistance, with low effects (e. g. forced deformations of the liner inhostpipe state III

1,00

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Table 2: partial safety factors for loads

Load F

Constant loads (G)(Soil load, dead-weight, possibly surface load, concentrated area-load)

1,35

Changing loads (Q)

(traffic load, live-loads, groundwater, etc.)

1,50

Traffic loads with adequate coverage 1,35

High water (short-term) 1,10

Internal pressure (incl. pressure surge) 1,50

Test pressure 1,20

Changes of temperature 1,10

Forced deformations 1,101

Only allowed in hostpipe state III and coverages of h > 2 ND and h > 1,5 m2

Valid only for approach of the long-term e-module, see also 6.4.1.1.

For some load combinations (e. g. groundwater in combination with a temperaturechange) there are special combination safety factors (see A 143-2).

The characteristic material values of the liners (index: k) are divided by the value ofM(reduction) and the actions (loads) multiplied by the value of F(raise). Theresulting values are now the so-called design values(index: d)the structuralcalculation is now be done with that items.

In contrast to the former method of calculation, the load will not be increased up tothe 2-times load (global safety factor = 2.0), but only up to the F-times load.

The calculated stresses and deformations are now also design values, and must becompared with the (design-) strengths.

Thus, the evidences of the tensile and compressive stresses are as follows:

0,1/max , dfBd

0,1/min, dCd

The resulting deformations, calculated with F= M= 1.0, represent the proof ofusability.

The verification of stability results to:

0,1/ ,, dede pcritp

A liner is optimal exploited when the ratios move as close to the 1.0 - in contrast tothe earlier statement, "... greater safety 2 ...".

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Example

CIPP, Synthetic Fiber liner (felt), impregnated with UP resin, hostpipe state II,hW,inv,k= 3.5 m groundwater lever over invert.

Characteristic values

EL,k= 1400 MPafB,k= 18.0 MPaC,k= 50.0 MPa

Resistances: due to table 1 follows M= 1.35the design valuesare:

EL,d= EL,k/ M= 1400 / 1.35 = 1037 MPafB,d= fB,k/ M= 18.0 / 1.35 = 13.3 MPaC,d= C,k/ M= 50.0 / 1.35 = 37.0 MPa

Loads: due to table 2 follows F= 1.50the design valueis:

pe,d= EL,k F= 3.50 m 1.50 = 5.25 m 10.0 kN/m = 52.5 kN/m (= 0.0525 MPa)

Note: most of the diagrams in the worksheet A 143-2 are created with design values.Be care of reading!

Poi ss on s Ratio

When a sample object is stretched (or squeezed), to an extension (or contraction) inthe direction of the applied load, it corresponds a contraction (or extension) in adirection perpendicular to the applied load. The relation between these two values isthe Poisson's ratio.

If the quantity of the Poissons ratio isproofed by an external lab, its allowed usingthis value in the stiffness equation:

3

112

m

mIL

d

eE

S

SL= Stiffness LinerEI= Youngs modulus = Poissons ratioem= mean thickness of compositedm= mean diameter liner

Typical values for glass fiber liners are 0.25 and for synthetic fiber liners 0.35the symbol is (beside ) also known as and the unit is [-].

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Note: in the German version of the stiffness equation there is the mean diametersubstituted by the mean radius. So, the values for the stiffnesssdiffer by factor 8!

Hos tpi pe state IIIa

Additionally to the hostpipe state III there is a suggestion for a new state: IIIa.

In this hostpipe condition there is a significant body formation. Furthermore, theconcrete quality of the old pipe is C8/10 (e.g. determined from drill cores) and the

masonry strength worse than II and / or there are unfavorable soil parameters. In thespringlines there is no pressure transfer possiblethe evidence of the pressurezones in the old pipe must be passed.

There are great discussions in Germany at the moment, whether we need this stateor not. There are a lot of objections made by practical working engineers and we willsee, what happens.

New traf f ic load m odel

The traffic loads for calculations inhostpipe state III are now made bythe EC1, due to DIN FB 101 forheavy loads on bridges, of 2003.

The load system is called UDL & TS(UDL = Uniformly Distributed Load,TS = Tandem System).

The main situation is the LM1 (load

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model 1) and the new A 143-2 delivers some diagrams to determine the soil-stressescaused by the traffic on the surface. The usage of LM2 or 3 is only interesting forexceptional loads. The classical German heavy truck SLW60 (and also SLW30 &Lkw12) is now history!

Note: if there are soil coverages 1.5 m you have to do a fatigue-check for yourmaterial! At the moment, no CIPP manufacturer made these tests

What else?

Beside the news described above, there are also some less interesting items in thenew worksheet:

- a common reduction factor v,sin state II (incl. diagram)- egg shape profiles:

local prestrain v= 0,5 % + Ar,v/10 in state II

two different substitute radii in state II and III (proofed by FEA) coefficient tables for normal egg shape profiles

- annex D: realisticmaterial properties for SF- and GF-liners- evidence of the hostpipe compression zones- changes in annex A6, regarding the determination of the critical vertical load in

state III (crit qv)

and much more.

DESIGN TABLES DUE TO DWA M 144, PART 3

Please do not confuse the A 143-2 with the new M 144-3 in Germanyin thisadvisory leaflet you will find design tables for a specialload case:

- hostpipe state II- local limited prestrain of 2 % of rLin the invert of a circular pipe (normal egg

shape profiles: 0.8 % of rLK)- four-hinge-deformation of 3 % of rL(normal egg shape profiles: in the crown)- annular gap of 0.5 % of rL(normal egg shape profiles: crown radius)- substitute circle for normal egg shape profiles: 0.6 H (stability proof)

In all other cases, there must be done a structural design dueto A 143-2!

Nearly all manufacturers of CIPP in Germany have agreed andhave formed so called Liner Design Groups, LDG. There arenow twenty groups for SF- and GF-liners (UP-, EP-resins) andevery group has its own tableas input you need only thediameter and the groundwater lever over invert and you willget the cured thickness of every liner on the (German) market.

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A great advantage for the contracting authority is, that they can compare theproducts in very easy technical way.

In Germany, the M 144-3 has the state of Additional Technical Terms andConditions (ZTV)and is mandatory for new contracts.

SUMMARY

In the last 12 years of using the M 127-2 advisory leaflet, there have been made a lotof experiences with this calculation method. It is proofed by FEA calculations andthere were almost no damages; caused by the design itself. The new A 143-2 is nowan actual standard for designing CIPP and other renovation methodsbut during theyellow print phase there are also still alot of discussions in details.

The usage of the rule did not become easier than the old oneso its necessary that

only highly specialized engineersare working with this standard!

Please note, that the oldATV-DVWK M 127, part 2 is still validfor the structuraldesign of liners and the usage of the new DWA A 143, part 2 is desired. Theinclusion of the new worksheet in your personal renovation-contracts is possible.