ISO 10803:2024

International
Standard
ISO 10803
Third edition
Design method for ductile iron pipes
2024-11
Méthode de calcul des tuyaux en fonte ductile
Reference number
© ISO 2024
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Published in Switzerland
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Design procedure . 3
4.1 General .3
4.2 Design steps .3
5 Design for internal pressure . 3
5.1 Design formulae for wall thickness .3
5.2 Design safety factors .4
6 Design for external loads . 4
6.1 Spangler formula .4
6.2 Pipe embedment .7
6.2.1 Types of embedment .7
6.2.2 Types of trenches .8
6.2.3 Embedment properties .8
6.2.4 Spangler modulus of native soils .9
7 Safety check against internal pressure and external loads . 9
7.1 Principle .9
7.1.1 General .9
7.1.2 Method 1: calculate maximum allowable depth of cover from maximum
allowable pipe deflection .10
7.1.3 Method 2: calculate the actual pipe deflection from the actual depth of cover .10
7.2 Total vertical pressure on the pipe.10
7.3 Pressure from earth loads .11
7.4 Pressure from traffic loads .11
7.5 Allowable pipe diametral deflection . 12
Annex A (informative) Dimensions of preferred and other class pipes . 14
Annex B (informative) Examples of calculations for safety check with methods 1 and 2. 17
Annex C (informative) Examples of traffic loads systems .34
Annex D (informative) Soil classification .40
Bibliography . 41

iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 5, Ferrous metal pipes and metallic fittings,
Subcommittee SC 2, Cast iron pipes, fittings and their joints.
This third edition cancels and replaces the second edition (ISO 10803:2011), which has been technically
revised.
The main changes are as follows:
— considering various applicable standards in different countries for the traffic loading, common new
formulae have been developed to enable the calculation of the pressure on pipe due to traffic loads for
any country;
— the previous formula to calculate the pressure on pipe due to traffic loads and the earth loads has no
provision to consider the effect of the settlement of side fill and the effect of native soil; the modified
formula now takes into account the effect of settlement of soil in terms of deflection lag factor and the
effect of native soil by considering the soil modulus of native soil;
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
International Standard ISO 10803:2024(en)
Design method for ductile iron pipes
1 Scope
This document specifies the design of ductile iron pipes used for conveying water, sewerage and other fluids
— with or without internal pressure, and
— with or without earth and traffic loading.
The design method defined in this document is applicable to ductile iron pipes conforming to ISO 2531,
ISO 7186 and ISO 16631.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 2531, Ductile iron pipes, fittings, accessories and their joints for water applications
ISO 7186, Ductile iron products for sewerage applications
ISO 7268, Pipe components — Definition of nominal pressure
ISO 10802, Ductile iron pipelines — Hydrostatic testing after installation
ISO 16631, Ductile iron pipes, fittings, accessories and their joints compatible with plastic (PVC or PE) piping
systems, for water applications and for plastic pipeline connections, repair and replacement
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 7268 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
allowable operating pressure
PFA
P
FA
maximum internal pressure, excluding surge, that a component can safely withstand in permanent service
[SOURCE: ISO 2531:2009, 3.2, modified — The symbol P has been added.]
FA
3.2
maximum allowable operating pressure
PMA
P
MA
maximum internal pressure, including surge, that a component can safely withstand in service
[SOURCE: ISO 2531:2009, 3.17, modified — The symbol P has been added.]
MA
3.3
allowable site test pressure
PEA
P
EA
maximum hydrostatic pressure that a newly installed component can withstand for a relatively short
duration, when either fixed above ground level or laid and backfilled underground, in order to ensure the
integrity and leak tightness of the pipeline
Note 1 to entry: This test pressure is different from the system test pressure, which is related to the design pressure
(3.11) of the pipeline.
[SOURCE: ISO 2531:2009, 3.3, modified — The symbol P has been added.]
EA
3.4
embedment
arrangement and type(s) of material around a buried pipeline, which contribute to its structural performance
Note 1 to entry: See Figure 2.
3.5
bedding
lower part of the embedment (3.4), composed of the lower bedding (if necessary) and the upper bedding
Note 1 to entry: See Figure 2.
3.6
bedding reaction angle
conventional angle used in the calculation model to account for the actual soil pressure distribution at pipe invert
3.7
compaction
deliberate densification of soil during the installation process
3.8
standard proctor density
degree of soil compaction (3.7) using a 2,5 kg rammer and a 305 mm drop
Note 1 to entry: The degree of soil compaction is defined in AASHTO T99.
3.9
deflection lag factor
factor that takes account of the settlement of the sidefill over time resulting in further deflection of the pipe,
till the final equilibrium is reached after pipe installation
3.10
operating pressure
OP
P
O
highest pressure that occurs at a time and at a point in the pipeline when operating continuously under
stable conditions, without surge
3.11
design pressure
maximum operating pressure (3.10) of the pipeline system or of the pressure zone fixed by the designer,
considering future developments but excluding surge

4 Design procedure
4.1 General
The pipe wall thickness shall provide adequate strength against the internal pressure of the fluid and
against the effects of external loads due to backfill and surcharge, i.e. traffic loadings.
Ductile iron pipes in conformity with ISO 2531 are classified according to their allowable operating
pressure for use in water applications. Ductile iron pipes in conformity with ISO 7186 are for sewerage
applications either under pressure or under gravity. Ductile iron pipes in conformity with ISO 16631 are for
water applications with joints compatible with plastic (PVC or PE) piping systems either under pressure or
without pressure. Using the formulae given in Clauses 5 and 6, the design of buried pipes is performed by
determining:
a) the minimum pipe wall thickness for the allowable operating pressure (PFA); and
b) the allowable depths of cover for the external loads as per procedure given in Clause 7.
NOTE National standards or established calculation methods can be used instead of this document.
4.2 Design steps
The steps for the design procedure for the pipes are given below.
a) Based on the design pressure of the pipeline system, select pressure class of pipe as appropriate in
accordance with ISO 2531 or ISO 7186 or ISO 16631 such that PFA of selected pipe class is higher than
the design pressure.
b) Check the safety against the external loads for the selected pipe class by using appropriate method for
calculating the allowable depth of cover as defined in Clause 7.
c) If the allowable depth of cover is not adequate, select higher pressure class of pipe and repeat steps 4.2 a)
and b) until the allowable depth of cover is acceptable.
NOTE When installed and operated under the conditions for which they are designed, ductile iron pipes, fittings,
accessories and their joints maintain all their functional characteristics over their operating life, due to constant
material properties, to the stability of their cross-section and to their design with high safety factors.
5 Design for internal pressure
5.1 Design formulae for wall thickness
The minimum wall thickness of pipes, e , shall be not less than 3 mm (as specified in ISO 2531) or
min
2,4 mm (as specified in ISO 7186) or 2,2 mm (in accordance with ISO 16631) and shall be determined using
Formula (1):
PS⋅⋅D
FA FH E
e = (1)
min
2⋅+RP ⋅S
()
mFAFH
where
e is the minimum pipe wall thickness to resist hoop stress due to internal pressure, in mm;
min
P is the allowable operating pressure, in MPa (see 5.2);
FA
S is the design safety factor against hoop stress (see 5.2);
FH
D is the nominal pipe external diameter (DE), in mm (see Annex A);
E
R is the minimum ultimate tensile strength of the ductile iron, in MPa (R = 420 MPa as defined in
m m
ISO 2531 or ISO 7186 or ISO 16631).
Nominal wall thickness, e , of the pipe is calculated as given in Formula (2) for pipes conforming to
nom
ISO 2531, ISO 7186 and ISO 16631:
ee + 1,3+ 0,001D (2)
()
nom= min N
where D is the nominal diameter (DN) of pipe, in mm, as defined in Annex A.
N
Nominal pipe wall thicknesses for various classes in accordance with ISO 2531 are given in Table A.1 and
nominal pipe wall thicknesses for pressure and gravity pipe classes in accordance with ISO 7186 are given
in Table A.2.
Nominal pipe wall thicknesses for various sizes in accordance with ISO 16631 are given in Table A.3.
5.2 Design safety factors
The minimum pipe wall thickness, e , shall be calculated with a design safety factor of 2,5 for the maximum
min
allowable operating pressure (i.e. PMA as indicated in ISO 2531 and ISO 7186) and a design safety factor of 3
for the allowable operating pressure (i.e. PFA as indicated in ISO 2531 and ISO 7186).
Field testing of installed ductile iron pipelines shall be done in accordance with ISO 10802 by application of
test pressures up to the allowable site test pressures (i.e. PEA given in ISO 2531 and ISO 7186).
6 Design for external loads
6.1 Spangler formula
The design formula is based on Spangler model (Figure 1), where the vertical pressure, q, is acting
downward and:
— is uniformly distributed at the pipe crown over a diameter;
— is in equilibrium with a pressure, acting upward at the pipe invert, uniformly distributed over the
bedding reaction angle 2α;
— causes a pipe deflection, which gives rise to a horizontal reaction pressure at pipe sides, parabolically
distributed over an angle of 100°.

Key
1 vertical pressure
2 lateral reaction pressure distribution
3 vertical reaction pressure distribution
Figure 1 — Spangler model
The pipe diametral deflection and vertical pressure at pipe crown based on Spangler model are calculated
from Formulae (3) and (4):
Kq
x
Δ =100 (3)
′
8+SE0,061
qD=+ ⋅qq (4)
LY 12
where
Δ is the pipe diametral deflection, in per cent of external diameter, DE;
K is the deflection coefficient depending on bedding reaction angle, given in Table 1 for each trench
x
type and soil group;
q is the vertical pressure at pipe crown due to all external loads, in MPa;
q is the vertical pressure at pipe crown due to earth load, in MPa;
q is the vertical pressure at pipe crown due to traffic load, in MPa;
S is the pipe diametral stiffness, in MPa;
E′ is the modulus of soil reaction, in MPa;
D is the long-term deflection factor.
LY
Long-term deflection factor (D ) and pipe soil stiffness factor are obtained from Formula (5) and (6):
LY
Dn=+[]10,81()DD− ⋅ (5)
LY LR
′
 E 
 
D
 
L
n= (6)
 ′ 
E
105⋅+S 08,
 
D
 
L
where
D is the deflection lag factor given in Table 1 for each trench type and soil group;
L
n is the pipe-soil stiffness factor;
D is t he reduc t ion f ac tor on long-ter m def lec t ion due to inter na l pressure
R
D =1 , except if the pipeline is to be pressurised to at least 0,3 MPa within one year of buried
R
depth at a depth of less than 2,5 m. In such a case:
P
O
D =−1 , where P is the operating pressure (OP) in pipe in MPa.
R O
S and E′ are obtained from Formulae (7) and (8):
 
e
stiff
E
 
 
 
S = (7)
D
′
EE′= .C (8)
2 L
where
S is the pipe diametral stiffness, in MPa (S can also directly taken from the relevant annexes of ISO
2531 and ISO 7186);
E is the modulus of elasticity of the pipe wall material, in MPa (170 000 MPa for ductile iron);
is the mean diameter of pipe De− , in mm;
D ()
Estiff
D is the nominal pipe external diameter (DE) as specified in ISO 2531 and ISO 7186, in mm;
E
e is the average of the minimum pipe wall thickness of the pipe and nominal wall thickness of pipe,
stiff
in mm, ee=+()e /2 ;
[]
stiffnom min
E′ is the modulus of soil reaction, in MPa;
is the embedment modulus of soil reaction for the selected pipe surround material at the chosen
′
E
level of compaction (see Table 1);
C is the Leonhardt’s coefficient to calculate the effective pipe soil stiffness factor.
L
C is obtained by Formula (9):
L
W
 
t
0,,985+⋅0 544
 
D
 E 
C = (9)
L
 ′ 
W W
   E  
t t
1,,985−⋅0 456 ⋅ −−1
   
   
 
D ′ D
    
E EE E
 
where
W
is the width of trench in mm;
t
is the native soil modulus in MPa, given in Table 2.
′
E
6.2 Pipe embedment
6.2.1 Types of embedment
There are various types of embedments, which are designated into different classes based on configuration,
bedding and side fills. A typical embedment and its various parameters are defined in Figure 2.
Key
1 surface
2 main fill
3 wall of trench
4 direct cover zone (initial backfill)
5 lateral fill (side fill)
6 upper bedding layer
7 haunch zone
8 lower bedding layer
H depth of trench
t
H height of cover
H height of embedment
e
DE outside diameter of pipe
W width of trench
t
Figure 2 — Typical trench embedment

6.2.2 Types of trenches
There are following types of trenches.
a) Trench type 1: embedment dumped.
b) Trench type 2: embedment with very light compaction, greater than 75 % standard proctor density.
c) Trench type 3: embedment with light compaction, greater than 80 % standard proctor density.
d) Trench type 4: embedment with medium compaction, greater than 85 % standard proctor density.
e) Trench type 5: embedment with high compaction, greater than 90 % standard proctor density.
6.2.3 Embedment properties
Embedment properties depend on the type of embedment and compacted density (see 6.2.2 for type of
trenches). Embedment properties i.e. value of deflection coefficient (K ), compaction density, embedment
x
′
soil modulus ( E ) and deflection lag factor (D ) for various embedment classes are given in Table 1.
2 L
The bedding reaction angle depends on the installation conditions (bedding, sidefill compaction) and on the
′
pipe diametral deflection. The embedment modulus of soil reaction, E , depends on the selected pipe
surround material at the chosen level of compaction and the trench type.
′
In the absence of the applicable standards or other data, the values of E indicated in Table 1 can be used at
the design stage for five trench types and for six soil groups as defined in Annex D for the pipe surround
material. A preliminary geotechnical survey should be carried out to facilitate identification of the soil and
′
proper selection of E values. The final value of modulus of soil reaction, E′ is calculated as per the formulae
defined in 6.1.
′
Table 1 — Pipe embedment properties (values of K , D and E )
x L 2
Trench type 1 2 3 4 5
Placement of em- Very light com- Medium compac-
Dumped Light compaction High Compaction
bedment paction tion
Standard proctor
a
density of sidefill, >75 >80 >85 >90
%
Bedding reaction
30° 45° 60° 90° 150°
angle (2α)
K 0,108 0,105 0,102 0,096 0,085
x
D D D D D
′ ′ L ′ L ′ L ′ L ′ L
E (MPa) and D E E E E E
2 L 2 2 2 2 2
(MPa) (MPa) (MPa) (MPa) (MPa)
Soil group A 4 1,5 4 1,5 5 1,25 7 1,0 10 1,0
Soil group B 2,5 3,0 2,5 2,5 3,5 2,0 5 1,5 7 1,25
Soil group C 1 3,0 1,5 2,5 2 2,0 3 1,5 5 1,25
Soil group D 0,5 4,5 1 4,0 1,5 3,5 2,5 3,0 3,5 2,0
b b b b b
Soil group E - - - - -
b b b b b
Soil group F - - - - -
a
Depending on the type of test of soil and its moisture content, a standard proctor density of 70 % to 80 % should normally be
achieved by simply dumping the soil in the trench.
b
′
Use an E value of 0 unless it can be ensured that a higher value is achieved consistently.
6.2.4 Spangler modulus of native soils
The stiffness of the native soil in which the pipeline trench is excavated is important for the design of ductile
′
iron pipes. The stiffness of the native soil is measured in terms of the Spangler modulus E (see Table 2),
′ ′
which in combination with the soil modulus, E , is used to calculate the overall modulus of soil reaction, E .
′
Table 2 — Guide values of Spangler modulus of native soils ( E , in MPa)
Soil type Very dense Dense Medium dense Loose Very loose
Gravel > 40 15 to 40 9 to 15 5 to 9 3 to 5
Sand 15 to 20 9 to 15 4 to 9 2 to 4 1 to 2
Clayey, silty sand 10 to 15 6 to 10 2,5 to 6 1,5 to 2,5 0,5 to 1,5
Clay Very hard 11 to 14
Hard 10 to 11
Very stiff 6 to 10
Stiff 4 to 6
Firm 3 to 4
Soft 1,5 to 3
Very soft 0 to 1,5
SOURCE: BS 9295:2020, Table 27, reproduced with permission.
7 Safety check against internal pressure and external loads
7.1 Principle
7.1.1 General
Two methods can be used for safety check of pipe class against external loads and internal pressure. Both
the methods are based on Spangler formula (6.1) and their results are valid for the following conditions:
— minimum allowable depth of cover is equal to 2 times DN;
— for calculated depth of cover more than 6 meters, adequate structural pipeline design engineer
recommendations should be considered as per the actual site conditions;
— the pipe deflection in percentage shall not exceed the value defined in 7.5.
In method 1, the allowable depth of cover is calculated based on the maximum allowable pipe deflection.
In method 2, the actual deflection of the pipe is calculated based on the actual depth of cover. Examples of
calculation with methods 1 and 2 are given in Annex B. Examples of national traffic load systems are given
in Annex C.
In any case, it is presupposed that the height of cover complies with the project specifications and local
regulations for traffic loading (type of load and lading pattern), the safety of people and shielding, and anti-
freeze prevention.
7.1.2 Method 1: calculate maximum allowable depth of cover from maximum allowable pipe
deflection
From Spangler Formula (3), the value of q can be re-formulated as below:
′
Δ×+()80SE,061
q= (10)
100K
x
Where q is basically a function of H (allowable depth of cover) after all other constants are known. The
method consists in calculating q with all terms on the right-side equation, then extracting the maximum
allowable depth of cover (H ) from q, in the following steps:
max
a) calculate the value of S;
b) calculate the value of E’;
c) calculate the maximum allowable pipe defection, Δ ;
max
d) calculate the value of q;
e) formulate q , q and q as a function of H;
1 2
f) calculate the value of H .
max
7.1.3 Method 2: calculate the actual pipe deflection from the actual depth of cover
From spangler Formula (3) the actual pipe deflection is calculated as below:
100Kq
x
Δ=
80SE+ ,061 ′
The method consists in calculating the actual deflection Δ with all terms on the right-side formula, then
actual
checking if the actual deflection is lower than the allowable pipe diametral deflection, in the following steps:
a) calculate the values of q , q and q;
1 2
b) calculate the value of E′;
c) calculate the value of S;
d) calculate the value of Δ ;
actual
e) calculate the value Δ ;
allowable
f) check if Δ is lower or equal to Δ . If not, use higher class pipe and repeat till the calculated
actual allowable
value in step d) is lower than the value in step e).
7.2 Total vertical pressure on the pipe
The total vertical pressure, q, acting at pipe crown is the sum of the components shown in Formula (11):
qD=⋅qq+ (11)
LY 12
where
q
is the pressure from earth loads;
q
is the pressure from traffic loads;
D
is the long-term deflection factor as defined in 6.1.
LY
NOTE Special considerations are required in case the pressure from traffic loads, q , is greater than that from
normal static loads applied to the ground surface or in the case of any abnormal surface loading.
7.3 Pressure from earth loads
Pressure from earth load, q shall be calculated using Formula (12) from the weight of the earth prism
immediately above the pipe:
qH=0,001γ (12)
where
q
is the pressure at pipe crown, in MPa;
γ is the unit weight of the backfill, in kN/m ;
H is the height of cover (distance from pipe crown to ground surface), in m.
A preliminary geotechnical survey should be carried out to determine the actual unit weight of the backfill.
The unit weight of the soil of 20 kN/m is covering a vast majority of soils. In the absence of other data, it can
be used for general design purposes.
7.4 Pressure from traffic loads
The design formula is based on the Boussinesq model (Figure 3).
Key
H height of cover
Q pressure of wheel
P pressure on pipe
Figure 3 — Boussinesq model
The value of q shall be calculated using Formula (13). This formula has been derived from Boussinesq
theory and further approximation.
qa=⋅0,001 ϕ⋅⋅p (13)
2 ff
where
q
is the pressure at pipe crown, in MPa;
φ is the dynamic impact coefficient, given in Table 3.
a
is a correction factor to take into account the pressure spread over the pipe cross-section;
f
p
is an approximation for the maximum stress under wheel loads and wheel contact areas.
f
Table 3 — Suggested values of φ for various types of vehicle
Vehicle φ
Heavy vehicle 1,2
Medium vehicle 1,4
Light vehicle 1,5
a and p are obtained using Formula (14) and (15):
f f
09,
a =−1 (14)
f
4⋅+HH
09, +
11,(D)
3 5
 
 2  2
 
   
 
F 1 3 F 1
 
A   E  
p = 1− +⋅ ⋅ (15)
 
f
∑
22 i 22
   
r ⋅π π ⋅H
r r
     
A
A E
   
1+ 1+
   
 
   
H H
       
 
 
where
H is the height of cover, in m;
D is the mean diameter of pipe in m;
i is the wheel number;
F the load of the wheel passing directly above the pipe crown;
A
F the load of the wheel passing at a distance r from the vertical of the pipe crown;
E E
r , r are auxiliary radii for the traffic loads, in m.
A E
NOTE The parameters r and r are based on wheel loads of national and/or local applicable standards and
A E
regulations. Examples are given in Annex C.
7.5 Allowable pipe diametral deflection
The allowable pipe diametral deflection, Δ , can be taken from relevant annexes of ISO 2531, ISO 7186
max
and ISO 16631. These values provide sufficient safety against yield bending strength of the pipe wall, lining
deformation, joint leak tightness and hydraulic capacity of the pipe. However, national standards and/or the
manufacturer's catalogues can introduce more stringent limitations, for instance 3 % for cement mortar
linings.
For each DN, the allowable pipe diametral deflection, Δ , is the lowest of the following:
max
a) Δ , which provid
...