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NO DIG BERLIN 2015

Symposium and Exhibition 24 – 27 March

Paper 2-3

SYSTEMATIC COMPARISON OF THE FOUR MAIN NATIONAL

METHODS ASTM F1216, WRC-SRM, DWA-A 143-2 AND 3R-2014 APPLICABLE TO FLEXIBLE LINERS OF BOTH CIRCULAR AND

NON-CIRCULAR CROSS-SECTIONS.

Authors : Olivier THEPOT (Eau de Paris) *, Jean-Michel BERGUE (ASTEE/FSTT) **, Jean-Marie JOUSSIN (FSTT) ***, Dominique Orditz (CSTB) **** *olivier.thepot@eaudeparis.fr ** jean-michel.bergue@wanadoo.fr ***jeanmariejoussin@hotmail.fr **** dominique.orditz@cstb.fr

ABSTRACT: After a brief presentation of the new French recommendation 3R-2014 for the design of liners (published in 2014 by ASTEE Scientific and Technical Association for Water and the Environment), is made a systematic comparison of the four main national established methods ASTM F1216 (USA), WRc-SRM (UK), DWA-A 143-2 (G) and 3R2014 (F) applicable to flexible liners (prefabricated pipes, close-fit, cured-in-place pipes etc...) of both circular and non-circular cross-sections. The aspects compared will include: the characterization of host pipe condition and geometry; characterization of the surrounding ground; liner design characteristics (short and long-term); load cases (groundwater, earth load, traffic etc) and associated liner limit states (ultimate and serviceability); use of closed-form versus numerically (FEA) derived formulae, and of experimentally derived adjustment factors; partial safety factors on loads and material properties, and the degree of integration with Eurocodes. __________________________________________________________________ 1. INTRODUCTION AND BRIEF PRESENTATION OF THE NEW FRENCH RECOMMENDATION 3R-2014 There are several methods of calculation available around the world for designing pipe rehab systems and in particular determining the thickness of liners. Four main established national methods are co-existing in this field: in North America the ASTM F1216 method is normally used, in UK this is the SRM WRc method, in Germany the ATV M127-2, and in France the recent 3R-2014 which are the four main established ones. The existence of several methods is not a problematic situation but the following questions are thus raised: what are the differences between the calculation methods and what are the differences between the results of these calculation methods?

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The recommendations in force in France for pipe rehabilitation techniques design - covering circular and noncircular CIPP, spirally-wound pipes (PVC, PE…profiles), discrete pipes techniques (such as GRP pipes or one-piece panels, PE pipes,…) - are described in the 3R-98 that also proposes a “simplified” design method of gravity flow pipes’s liners published in 1998 by AGHTM (now ASTEE Scientific and Technical Association for Water and the Environment). To meet the market needs and requirements it was necessary to update this method which neglects the mechanical characteristics of the existing pipeline and is only valid for circular systems. The Association ASTEE decided in 2011 to revise the 3R-98 with the following objectives:

to integrate the requirements of new European and international standards published in the meantime,

to propose a method applicable for non-circular linings considering the RERAU research program publication,

to take into account the host pipe to prevent over-design with clear conditions to allow this option.

Among the significant technical advances we can mention:

the characterization of the state of the existing host pipe,

the implementation of an innovating new comprehensive design method applicable for any challenging shape (ovoid, arch shaped, oval, rectangular pipes) and open to computational tools,

some proposed guidelines for application of finite element method (FEM). 2. THE CHARACTERIZATION OF THE HOST PIPE The condition of the host pipe is the basis of the design whatever the chosen method is. The host pipe parameters considered by some or all of the methods include the water tightness, the nature and properties of the material and the cracking geometry, number and location. The different host pipe state definitions are:

ASTM F1216 - Partially deteriorated or Fully Deteriorated;

DWA A143-2 - State 1 (Stable), State II ( Stable - further deformations unlikely), State III (Stable further deformation very likely);

ASTEE 3R2014 - State 1 (Stable or improve), State II ( Stable - further deformations likely), State III (Unstable likely to collapse);

WRc SRM – Type II (no load applied from host pipe) and Type I (lining integral with host pipe)

ASTM F1216 Two host pipe states are considered: “partially deteriorated” or “fully deteriorated”

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Partially deteriorated

Fully deteriorated

Pipe condition Hydraulically compromised Superficial corrosion…

The host pipe lost its hoop and bending stiffness

Evolution in the future

Stable Likely to collapse

Design requirements

Resist groundwater pressure

Resist groundwater + soil pressure + live loads

DWA-A 143-2 Three host pipes states are considered: State I – State II – State III

State I State II State III

Pipe condition Structurally sound

Cracked Low deformations (<3%)

Cracked Large deformations <10%

Evolution in the future

Stable Stable - further deformations are unlikely

Stable but further deformations are very likely

Design requirements

Resist groundwater pressure Resist groundwater + further deformations

ASTEE 3R2014 Three host pipe states are considered: State I – State II – State III

State I State II State III

Pipe condition Hydraulically compromised Superficial corrosion

Cracked Deformations < 10%

The host pipe lost its hoop and bending stiffness

Evolution in the future

Stable or improve

Stable but further deformations are likely

Unstable : likely to collapse

Design requirements

Resist groundwater

Resist groundwater + further deformations

Resist groundwater + soil pressures

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WRc SRM type II The host pipe is in equilibrium at the time of lining and that equilibrium will be preserved by the liner. The host pipe continues to provide support to the surrounding soil and the traffic load. No soil loads are applied to the liner. Design requirement : the lining need only be designed to resist the groundwater effect. 3. THE DESIGN FOR GROUNDWATER Because lining restores hydraulic integrity (water tightness) and because the bond between the lining and the host pipe cannot be relied-on in the long term, it is necessary to consider the effect of external water pressure acting on the lining. Groundwater may percolate through the cracks and act at the interface between the lining and the host pipe. The limit states considered are: buckling (ultimate), strength/material failure (ultimate) and deflection (serviceability). The shape and any imperfections in the geometry can be important especially for resistance to groundwater of non-circular linings. Imperfections are classified in two types: global or local. Global imperfections are uniformly distributed around the perimeter like annular gap. Local imperfections are distributed on a limited angular sector like local intrusion. In all the cases, the distribution of the imperfections in the longitudinal direction is supposed to be constant, that is the most unfavorable configuration.

Dh

Dv

Ovality (four hinges) Gap Local intrusion

g w

2

Figure 2: Global and local imperfections.

These imperfections are not always measurable, and default values must be carefully chosen. In the 3R2014 method, the default value for the gap is 1% of the radius.

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3.1. Circular lining - General buckling For buckling of circular linings ASTM F1216 and WRc SRM are both based on Timoshenko’s solution modified by an enhancement factor of 7.0 (experimentally derived). This can be adjusted for ovality, but not for other imperfections. DWA A1432 is based on Glock’s solution which eliminates the need for the enhancement factor and can consider an annulus gap, wavy intrusion and ovality. ASTEE 3R2014 is based on a closed form analytical solution similar to the Glock’s solution which can consider a wider range of imperfections.

ASTM F1216 / WRc SRM

Based on Timoshenko’s solution modified by an enhancement factor K of 7.0 (experimentally derived)

Global safety factor N of 2.0

Reduction factor for ovality C

Other imperfections cannot be considered (such as gap, intrusion…)

Using « long term modulus » to predict creep-induced buckling.

DWA-A 143-2 SL,d: design ring stiffness

v,s: reduction factor for imperfections

Based on Glock’s solution (closed-form solution)

Eliminates the need for enhancement factor.

Reduction factors for three imperfections (gap, wavy intrusion, ovality) with minimum values g: 0,5%, w: 2,0%

Account for the coupled effect gap + ovality

One-lobe buckling mode

ASTEE 3R2014 EIL,d: design flexural stiffness EAL,d: design axial stiffness

p: reduction factor for imperfections

Based on a fully closed-form analytical solution.

Eliminate the need for enhancement factor.

Reduction factors for several imperfections (gap, intrusion, ovality) with minimum values g: 1%.

Account for the coupled effect gap + ovality

One-lobe buckling mode (k = 1)

32

2 1

1 1

LK E Cp

NSDR

0,8

La,d v,s L,d

L

rkrit p 2,62 S

t

0,6 0,4

L,d L,d0,4

cr,we,d p 2,2

EI EAp 0,97 k

r

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Calculation of the Buckling pressure - numerical comparison between the four methods The four methods give almost the same results thanks to an appropriate choice of the imperfections (see figure…).

3.2. Circular lining - Material failure (stress calculation) For material failure of circular linings under groundwater ASTM F1216 considers an elliptical ring under uniform load. DWA A1432 uses a combination of precalculated chart based on finite element analysis and equations. ASTEE 3R2014 uses a fully closed form analytical solution. The WRc SRM method does not consider material failure. 3.3. Non Circular lining For buckling of noncircular linings WRc SRM type II uses a simple design method for egg-shaped and oval linings (however this is unsafe for 2x1 Egg and oval sections), ASTM F1216 does not consider this. DWA A143-2 uses an equivalent circular lining for 3x2 egg shapes and recommends FEA for other shapes. ASTEE 3R2014 uses a fully closed form analytical solution (shapes must be convex). The ASTEE method compares well to FEA analysis.

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3.4. Summary of ASTEE 3R2014’s non circular design

Calculable shapes

Shapes must be convex

Shapes are classified in two categories: o Critical (circular, egg shaped, horseshoe shaped linings…) o Sub-critical (oval shaped, rectangular…)

The use of laser profiler is strongly recommended

Critical and sub-critical linings

(a) Critical (b) Sub-critical

(a) Critical shape: the lobe span decreases. (b) Sub-critical shape: the lobe span increases.

Critical liners can buckle under external pressure, sub-critical cannot but are far more deformable.

0.01 0.02 0.03 0.04 0.05 0.06

10

20

30

40

50

60

Deflection(mm)

Pressure (MPa)

Buckling

point

pcr=0.054 MPa

(a) (b)

CriticalSub

Critical

(a)

R=1200

(b)

The figure 4 illustrates the difference between critical and sub-critical shape. The mechanical characteristics of these 2 shapes are identical (same thickness and same modulus). Their height and their width are also identical, but differ on the side curvature. The curvature is infinite for the shape a) and equal to 1.5 time the height for the shape b). The graph on the right of the figure shows the deflection at the middle of the straight section calculated with the finite element method for the two shapes. One can see that the deflection curve of the shape b) shows a bend where the pressure is maximum (this is the buckling pressure) and after the bend, the stiffness becomes negative which causes the instability. For the shape a) there is no bend, the deflection increases continuously with the pressure and the stiffness decreases. It is also obvious that the stiffness of the shape a) is much lower than the stiffness of shape b).

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The design for non-circular critical shapes (egg-shape, horseshoe shape…)

Figure 8: Critical shapes.

The calculation method is based on an analytical solution (Thépot, 2000) which extends Glock’s analysis to non-circular lining. The shape must be convex, comprising a succession or arcs tangent at their points of contact. The buckling pressure is given by the following formula:

0,6 0,40,4

cr,we p,g 0,4 1,8

EI EAp 2,02 k

P r

where k is the number of lobe (1 or 2), P is the mean perimeter of the lining, r is the radius of the arc where the lobe develops, EI is the flexural stiffness and EA is the

compressive stiffness of the wall, p,g is the reduction factor of the critical pressure due to the initial gap.

The design for non-circular sub-critical shapes (oval-shape, horseshoe shape, rectangular…)

3x2 Egg-shape

General Egg-shape

Horseshoe-shape

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Figure 9. Sub-critical shapes. The calculation method for sub critical lining is based on an analytical solution (Thépot 2001). This method gives an explicit solution for the pressure function of the maximum deflection at the center of the lobe which is a serviceability requirement (normally 2 or 3% of the “straight” section but a different value may be used).

Comparisons with F.E.A.

Excellent agreement for the critical buckling pressure.

Fairly good agreement for stress and deflection.

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3.5. Summary of WRc type II design for NC liners

Based on bending formulae of straight beam. The calculated deflection is less than 3% of the "straight" section length. Buckling is not checked, failure by bending is considered as the predominant mechanism. Two conditions must be verified:

Bending stress: 2

1 340 LH s t l

Maximum deflection: 3

2 236 LH R E t l

Where: H1 : Head water limited by the permissible stress; H2 : Head water limited by the permissible deflection; EL : Long-term elastic modulus; sL : Long-term permissible bending stress. R = 1 for curved/egg shape, R = 0,5 for straight/oval shape l: critical length, t : thickness. The following conditions must be verified:

1 2,Min H H H

where H is the design head of water.

Comparisons with F.E.A.

3x2 egg shaped : OK

2x1 egg shaped : Unsafe, the design head of water may be higher than the buckling head.

Flat egg shaped (oval) : Unsafe (see example below)

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Example : GRP oval shaped (Thépot 2001) EL=5000 MPa, t = 30 mm, l = 1000 mm sL=60 MPa,

Minimum Head of water: WRc : 15,9 m > very optimistic/risky! F.E rtesults : 2,8 m (for 3% of deflection) 4. THE DESIGN FOR THE OTHERS LOADS (SOIL LOADS, TRAFFIC) For other loads ASTM F1216 the liner is designed as if it were placed directly in the surrounding soil with only the buckling limit state considered. DWA A1432 uses a Winkler model for state III. ASTEE 3R2014 for state II (cracked pipe) uses a design model based on Law and Moore in which the stiffness of the liner is neglected.

ASTM F1216 – The design approach for the “Fully deteriorated pipe”

The liner is designed as if it were placed directly in the surrounding soil.

Only one limit state considered: buckling.

Unique “box equation”.

Soil modulus plays a major role.

Approach not very realistic and not automatically on the safe side.

DWA-A 143-2 – The design model for the host pipe state III

0

10

20

30

40

50

60

0% 1 % 2 % 3% 4% 5 % 6 % 7% 8 % 9 % 1 0%

re la t iv e d e f le c t io n ( % )

Pre

ss

ure

(k

Pa

)

A n a ly t ica l re s u lts

F E r e s u lts

Pressure - deflection

E1

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Sophisticated (second-order analysis) Winkler model (the surrounding soil is modelled with springs).

The loads history is ignored: all the loads are applied in one time to the “liner-pipe-soil system”.

Soil modulus plays a major role

Pre-calculated chart available, or dedicated software.

ASTEE 3R2014 –The design model for the host pipe state II (cracked pipe)

Based on M. Law & I.D. Moore works.

The stiffness of the liner is neglected.

The response of the liner-damage pipe-soil system can be separated into two interaction components:

o Interaction between the cracked pipe and the soil o Interaction between the liner and the cracked pipe

The soil stiffness controls the pipe deflection.

The deflection controls the strain in the liner. 5. GLOBAL AND PARTIAL SAFETY FACTORS ASTM F1216 and WRc SRM use global safety factors of 2.0. DWA A1432 and ASTEE 3R2014 use partial safety factors which when multiplied together typically give a value ≈ 2.0. They do however disagree on whether groundwater loading is considered a permanent or variable action. 5.1. Partial safety factors for actions The safety factors on actions conform to European standards (Eurocode NF EN 1990, NF EN 1991 and NF EN 1997). Groundwater is considered as a permanent action in NF EN 1990/NA and 1997/NA but a variable action in …

Local

Bending

Fractured

Host pipe

BackFill

Overburden

pressure

Flexible

Live load (traffic)

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DWA-A 143-2 ASTEE 3R2014

Earth pressure (permanent action)

1,35 1,35

Groundwater 1,5 1,35 (NF EN1990/NA –1997/NA)

Traffic loads 1,5 (1,35*) * If coverage > 1,5 m and 2xDN

1,35 (NF EN 1990/A1:2005)

Other variable loads

1,5 1,5

5.2. Partial safety factors for material properties (resistances)

DWA-A 143-2 ASTEE 3R2014

Cure in place linings - Flexural stress - Young modulus

1,35 1,5*

Manufactured (prefabricated) linings - Flexural stress - Young modulus

1,25 1,2

*The value of the safety factors has been set to 1,5 to retrieve the old global safety

factor of 2,0 1,5x1,35 on the buckling pressure due to groundwater. For the DWA-

A 132 the same reasons give a value of 1,35 because 2,0 1,35x1,5 ! 5. CONCLUSION The description of each of the four considered methods - ASTM 1216, WRc, DWA A143-2 and 3R2014 - show significant differences between some of them on the covered area, the developed calculation models and the safety design approach that finally indicate some divergences in the calculation figures. 3R-2014 method which is the last to be published offer: • As the DWA and WRc a field of application expanded notably in relation to the ASTM (circular only). • A more satisfactory approach to the risk of buckling than the WRc for shapes that deviate from that of the ovoid 3 x 2 and partly the DWA (only for non-standard forms) in the case of non-circular. • As the DWA a complete consideration of safety Eurocodes.

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6. REFERENCES RERAU (2004). Restructuration des collecteurs visitables - Guide technique - Tome 2. Edition Tec et Doc - Lavoisier.

DWA-A 143-2 (2012). Sanierung von Entwässerungssystemen außerhalb von Gebäuden Teil 2: Statische Berechnung zur Sanierung von Abwasserleitungen und –kanälen mit Lining- und Montageverfahren.

ASTEE (2014). Nouvelles recommandations pour le dimensionnement de la réhabilitation par chemisage et tubage des réseaux d’assainissement. TSM, N°10, octobre 2014. ASTM F1216-09 (2009). Standard Practice for Rehabilitation of Existing Pipelines and Conduits by the Inversion and Curing of a Resin-Impregnated Tube. WRc Sewerage Rehabilitation Manual (2001) 4 th edition. WRc, Swindon, Wiltshire SN5 8YF (UK). Falter B. (1997). Structural analysis of sewer linings. Trenchless Technology Re-search. Vol. 11, N°2, 27-41. Glock D., (1977). Behavior of liners for rigid pipeline under external water pressure and thermal expansion, Der Stahlbau, Vol. 46, No. 7, 212-217. Gumbel,J.E. (1983). Analysis and design of buried flexible pipes. Ph.D. dissertation. Department of Civil Engineering, University of Surrey, Guildford, England, 1983. Thépot O. (2000). A new design method for non-circular sewer linings. Tunnelling and Underground Space Technology. Vol. 15, N°1, 25-41. Law M., Moore I.D. (2007). Numerical modeling of tight fitting flexible liner in damaged sewer under earth loads. Tunnelling and Underground Space Technology. Vol. 22, 655-665. Thépot O., Joussin J.M. (2007). The structural Design of Large Non-Circular GRP Prefrabricated Liners. International No Dig Rome. Moore I.D. (2009). Specialised design considerations for liners in gravity flow pipes. Trenchless International – January 2009. Thépot O. Bergue J.M., Orditz D., Joussin J.M., (2014). New design for gravity flow pipes – French recommendations 3R-2014 . International No Dig Madrid

Thépot O. (2001). Structural design of oval-shaped sewer linings. Thin-Walled Structures. Vol. 39