DWA-A 143-2

1st NO DIG BERLIN 2013 Conference and Exhibition 23 - 26. April 2013

Paper 4-3

German DWA Worksheet A 143, Part 2 – what´s new in structural design of CIPP? CEng Markus Maletz, EUR ING KMG Pipe Technologies, Ursensollen, Germany

SUMMARY Once in the early years of renovation with CIPP liners, many faults (especially buckling 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 been created. Until the publishing in the year 2000 there has been worked on the advisory leaflet M 127, part 2, which have to be used only for the renovation of pipes. Three hostpipe states were defined, which are specified by the client. After over 10 years of successful application, now the leaflet has been revised and published 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 the most successful renovation systems in the non-pressure (= gravity) range. Reasons for this are likely the duration of this processes - the eldest system has been placed in 1971 - and thus the experience with this process and the diversity of this applications. Liners are actually the only renovation process, which are - properly installed – tight to the host pipe, and therefore without a recognizable annular gap. They are built in different profiles, such as circular-, egg-, oval- and rectangleprofiles, closed fit to the wall of the old pipe and the cross-sectional area of the original 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 = Cured In Place Pipe), at least consisting of a tube or hose carrier and a resin (due to EN ISO 11296-4 and EN ISO 11295), optionally with an coated inner film, and/or outer film (or Preliner) and - especially for the larger dimensions with "inert" (no influence to the quality of resin, e.g. with respect to chemical or thermal resistance) additives in the 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 - in rarer cases, using electric resistance heating too. They include also the long introduced 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 each of 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-inpipe, 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 on the construction site. The cold curing of UP and EP resins is a system which is shortening the curing reaction 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 inversely reciprocal to the volume of the mixed-resin behaves. The hardening grade, which is reached immediately after the installation of the cold-hardening resin systems, is below 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 over existing manholes using a winch. By a defined air pressure, the liner is then expanded and pressed against the old pipe. In this state, now a UV lamp (“lightchain”) 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;

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presence of the vault (circular or other profile);

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deformations ≤ 6-8 % (ovality);

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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. This approach was on the safe side, although this paper was meant only for new installation of sewers and pipes. The calculations have been fundamentally separated 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 water pressure (buckling check) and otherwise also with earth-, traffic- and other static surface 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. In September 1999, the (former) working group 1.2.3 of DWA had their last session before the publication of the new leaflet – handle only a few appeals by renovation companies. In January 2000 the new leaflet 127-2 appeared and the "gray zone" of the A 127 had been removed for calculation of liner renovations. Through various research projects and theoretical assumptions, but also try to practice, a calculation methodology was developed, which is now up-to-date and verified by means of the FE (finite element) method. Hostpipe states 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 that correspond 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 and traffic loads are still taken completely by the old pipe. The liner is measured only on groundwater pressure (identified over invert). In that case, if the wall thickness is too low, 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 slight deformations) it is adapted the so-called "arch effect" of the surrounding soil. An intact bedding activates a slight deformation - which follows a crack – and the

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“reaction pressure”. Now the so-called "pipe-soil-system" carries the soil and traffic loads. As in state I, the liner is to be measured simply by water pressure and it is only necessary to prevent the bedding from being damaged by exfiltration and/or infiltration. The state III is characterized by the fact that the existing pipe (or the pipe-soilsystem) is no longer stable for the future. Therefore the liner must additionally carry a water 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 d a + 0.1 m 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 against pressurized groundwater. The M 127-2 has now three reduction factors to be introduced. These consider the following "disturbances" of the old pipe liner geometry: 1. Reduction for a prestrain κv (imperfection, pipe tolerances, etc.), which are specified of 1 % of the liner radius (if there are exact measurements) of the host pipe. If there is no calibration, the value must be 2 % (standard). 2. Reduction for ovality κAr,v (4-hinge-deformation, ovalisation), which is specified with minimum 3 % of the liner radius (Standard). 3. Reduction for a surrounding gap κs between Liner and host pipe of 0.5 % of the liner radius (< DN 800) respectively 0.25 % (≥ DN 800), if there are no greater values, maybe proofed by testing reports (recommendation). All three reduction factors (in combination) mean that the minimum wall thickness increases with unfavorable geometry. Thus, a liner product is selected, which has maybe a high gap, this unfavorable geometry must be compensated by a higher wall thickness. 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 upper diameter 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 stable – possible damages, as leaky pipe connections are suitable, except hairline cracks in the pipe wall are no cracks present. Likewise, even a slight corrosion, such as for concrete pipes may be present.

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State II

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

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State III

The host pipe-soil-system is not stable for the future – there are greater deformations and the liner gets additionally soil- and traffic loads.

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Is the state III really critical? It is important to see in the state III, that even after installation of the liner, the old pipe can get further deformations under load. The liner must adapt to these distortions 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 affected only marginally. The liner is loaded mainly by the close-fit component. A lower liner stiffness (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 greater wall thicknesses…" turns out to be wrong. By a rise of groundwater and/or a change in 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 mixed loads 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 old pipe 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 investigations During unclear status, it is necessary to conduct soil tests. This may happen in places that let suggest in the CCTV recording of the sewer, for example cavities, light dynamic probing, or drilling in addition to the pipeline route will be carried out. It can also identify some indication of the groundwater level. There is also the possibility of long-term observations (if available, or possible) to deter-mine, whether the damage profile has changed over time. With increasing deformations certainly the choice of state III is preferable, because then the assumption seems likely that the bedding is disturbed. The experience of the evaluating engineer is very useful here. Thus, for example, in a very flat-lying sewer with longitudinal cracks, have led to the influence of the traffic load due to increased volume of heavy traffic to damage the line, while already such as very deep-lying pipes the damage occurs during installation, and the “dome-effect” has set over the years. Redistribution of soil stresses As an average over old sewers, the rigid pipes usually form after installation stress concentrations over the pipe. The ground tensions are rearranged because of the difference between soil and pipe (see ATV-DVWK A 127, clause 6.1 Redistribution of Soil Stresses).

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a) Rigid pipe

If now a pipe breaks, then the state II is build and the “bedding-reaction-pressure” is activated. A slight deformation is associated with this process. From the previously rigid system, a flexible soft system is made, which releases tensions 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 all damages of liners have been buckling losses. The critical load for the liner is also buckling, which is triggered by levels of ground water, generating a hydrostatic pressure. The distribution of pressure is triangular situated, so you have an increasing water column towards the bottom; the buckling pressure 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 largest radius (= minimal resistance) is located there.

The reasons for buckling may firstly be a false assessment of the liner, coupled with a not exactly known ground water level or other improper curing. In the first case may be concerned, that groundwater, which is infiltrated into the sewer for years, that was used as a type of drainage. After a successful rehabilitation, experience has shown that the ground water level increases, providing the 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, quality assurance, 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 the advisory leaflet M 127 Part 2 has been revised in the last four years and was published in November 2012 as a yellow print. The reasons for raising the status from a leaflet to a worksheet were: -

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Probation of the leaflet M 127-2 in practice. The fact sheet was published in 2000. It has proven itself in practice, even in difficult renovation conditions. This applies to Germany as well as many international projects in which the leaflet 127-2 M was prescribed for the structural design (see the English translation of M 127-2).

Any known claims are mostly attributed on structural defects, inadequate curing or misuse of this information sheet. If cases of damage have occurred, the reasons could be revealed usually with the help of this information sheet. The practicability of the leaflet can also be seen in many training courses for “Certified Sewer Rehabilitation Consultants”, in which practicing engineers learn to control simple CIPP statics due to M 127-2.

A new edition is required, especially due to the concept of partial safety factors for actions (loads) and the resistances (strength and deformation characteristics), which were introduced with the Euro Codes (EC1).Calculation by partial safety factors Table 1: partial safety factors for resistances Pipe material Plastic liner, cured in the sewer Plastic liner, manufactured in a plant (extrusion or other methods) Mortar-liner (regarding of possible notch effects in the materials testing) Stainless steel Resistance, with low effects (e. g. forced deformations of the liner in hostpipe state III

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γM 1,35 1,25 1,50 1,15 1,00

Table 2: partial safety factors for loads Load Constant loads (G) (Soil load, dead-weight, possibly surface load, concentrated area-load) Changing loads (Q) (traffic load, live-loads, groundwater, etc.) Traffic loads with adequate coverage High water (short-term) Internal pressure (incl. pressure surge) Test pressure Changes of temperature Forced deformations 1 2

γF 1,35 1,50 1,35 1 1,10 2 1,50 1,20 1,10 1,10

Only allowed in hostpipe state III and coverage’s of h > 2 · ND and h > 1,5 m 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 temperature change) there are special combination safety factors ψ (see A 143-2). The characteristic material values of the liners (index: k) are divided by the value of γM (reduction) and the actions (loads) multiplied by the value of γF (raise). The resulting values are now the so-called “design values” (index: d) – the structural calculation is now be done with that items. In contrast to the former method of calculation, the load will not be increased up to the 2-times load (global safety factor γ = 2.0), but only up to the γF-times load. The calculated stresses and deformations are now also design values, and must be compared with the (design-) strengths. Thus, the evidences of the tensile and compressive stresses are as follows:

max  d /  fB,d  1,0

min  d /  C , d  1,0 The resulting deformations, calculated with γF = γM = 1.0, represent the proof of usability. The verification of stability results to:

pe, d / crit pe, d  1,0 A liner is optimal exploited when the ratios move as close to the 1.0 - in contrast to the 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 MPa σfB,k = 18.0 MPa σC,k = 50.0 MPa Resistances: due to table 1 follows γM = 1.35 – the design values are: EL,d = EL,k / γM = 1400 / 1.35 = 1037 MPa σfB,d = σfB,k / γM = 18.0 / 1.35 = 13.3 MPa σC,d = σC,k / γM = 50.0 / 1.35 = 37.0 MPa Loads: due to table 2 follows γF = 1.50 – the design value is: pe,d = EL,k · γF = 3.50 m · 1.50 = 5.25 m · 10.0 kN/m³ = 52.5 kN/m² (= 0.0525 MPa) Note: most of the diagrams in the worksheet A 143-2 are created with design values. Be care of reading!

Poisson´s Ratio When a sample object is stretched (or squeezed), to an extension (or contraction) in the direction of the applied load, it corresponds a contraction (or extension) in a direction perpendicular to the applied load. The relation between these two values is the Poisson's ratio. If the quantity of the Poisson’s ratio is proofed by an external lab, it´s allowed using this value in the stiffness equation:

   em  EI   S L   12  1   ²    d m 

3

SL = Stiffness Liner EI = Young´s modulus μ = Poisson´s ratio em = mean thickness of composite dm = mean diameter liner

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

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Note: in the German version of the stiffness equation there is the mean diameter substituted by the mean radius. So, the values for the stiffness’s differ by factor 8!

Hostpipe 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, the concrete 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 the springlines there is no pressure transfer possible – the evidence of the pressure zones in the old pipe must be passed. There are great discussions in Germany at the moment, whether we need this state or not. There are a lot of objections made by practical working engineers and we will see, what happens.

New traffic load model The traffic loads for calculations in hostpipe state III are now made by the EC1, due to DIN FB 101 for heavy 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-stresses caused by the traffic on the surface. The usage of LM2 or 3 is only interesting for exceptional loads. The “classical” German heavy truck SLW60 (and also SLW30 & Lkw12) is now history! Note: if there are soil coverage’s ≤ 1.5 m you have to do a fatigue-check for your material! At the moment, no CIPP manufacturer made these tests… What else? Beside the news described above, there are also some less interesting items in the new worksheet: -

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a common reduction factor κv,s in state II (incl. diagram) egg shape profiles:  local prestrain → ωv = 0,5 % + ωAr,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: “realistic” material 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 Germany – in this advisory leaflet you will find design tables for a “special” load case: -

hostpipe state II local limited prestrain of 2 % of rL in 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 due to A 143-2! Nearly all manufacturers of CIPP in Germany have agreed and have formed so called “Liner Design Groups, LDG”. There are now twenty groups for SF- and GF-liners (UP-, EP-resins) and every group has its own table – as input you need only the diameter and the groundwater lever over invert and you will get 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 the products in very easy technical way. In Germany, the M 144-3 has the state of “Additional Technical Terms and Conditions (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 lot of experiences with this calculation method. It is proofed by FEA calculations and there were almost no damages; caused by the design itself. The new A 143-2 is now an actual standard for designing CIPP and other renovation methods – but during the “yellow print phase” there are also still a lot of discussions in details. The usage of the rule did not become easier than the old one – so it´s necessary that only highly specialized engineers are working with this standard! Please note, that the “old” ATV-DVWK M 127, part 2 is still valid for the structural design of liners and the usage of the new DWA A 143, part 2 is desired. The inclusion of the new worksheet in your “personal” renovation-contracts is possible.

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