1. *=srE
ART
208
1989 02/2
Chemicals
:HNICAL INFOMATION
F.RMATT.N
TEKN$F*ED.T
POIYETHYLENE,*,o*ro}3[i[H,::X??llH',?[r*o*
DIMENSIONING PRINCIPLES AND LAYING
INSTRUCTIONS FOR BURIEDPLASTIC PIPES
GENERAL
Plaslic pipes have specific properties and therebyotherdemandson dimensioning calculations and
laying instructions than lor example concrete and steel pipes. ln general the plastic pipes are
flexibte, that is they are deformed under load. This is positive in the rleaning that lhe pipe has the
abilily together with the back-{illing material to cause a horisontal earthpressure lowards lhe side
wall of the pipe, which increase the ability of the pipe to carry the load.
VERTICAL LOAD ON A BURIED PIPE
The important dimensions for a buried pipe are explained in Figure 1. The total vertical load, O, on
the buried pipe is the sum o{ 3 different loads.
O
O
Os
Qr
=Qs+Qr+O",MPa
O,v
= Total vertical load
= Soil load, see Figure 2
= Tralfic load, see Figure 3
= Water load, see Figure 4
The first step is to calculate lhe total vertical load, O, on the pipe. This can be done using the
diagrams in Figure 2 - 4.
Example
1
Consider a llexible pipe ol PEHD that is to be layed at a depth of 6.0 meter. The ground water level
is 4.0 meter below ground level. Determine the totalvertical load on lhe pipe.
Figure 2 gives:
Figure 3 gives:
Figure 4 gives:
Qs = 0.021 + 0.075 = 0.096 MPa
Or= 0
Q* = 0.020 MPa
That is:
Q = 0.096 + 0.020 = 0.1 16 MPa
Neste Chemicals lnt SA/NV
Neste Oy Chemicals
l, Avenue de Bile/Bazellaan,
Neste Polyeten AB
Pr 320
I
PoRVoo
B.I I40 BRUSTLS
sF-06101
Belgium
Finland
Tel. +32 22 44 42 ll
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Tel. +358 !5 lB712
Telex l72l neste sf
5-444 86 STENUNGSUND
Sweden
Tei. +45 303 86 000
Telex 2402 nestepe s

2. DEFORMATION OF A BURIED PIPE
by the lollowing lormula:
a buried pipe can be calculated
The vertical deformation, 8", o{
o
,6v
D
-=
-a
0.083
Es s+uue
mm
= Vertical PiPe delormation'
&,
mm
= Original PiPe diameter,
load, MPa
= Total vertical
supporting soit' MPa' see Figure 5
= S.*nr todulus ol
D
o
Es
,S = Stiffnessfactor =
:t@
T
.
E"
D
/
see Figure 6
Modulus ol elasticity o{ lhe pipe, MPa'
Wallthickness' mm
E
e
is assumed to be
the verticalpipe deformation'
to roSit iiiri''gi' Deiermine
aiproximatety 80 % t*ni"n-.orr.sponds
taved under *,u
,"rnr-.oniition,
i,
e*"ttipiti' frtu-1*i"i" ol compaction
in
6v.
Es = 1.25 MPa
Figure 5 gives:
Figure 6 gives:
at 50 years
E = tgO MPa for Neste NCPE 2467'BL
Now the stiflness laclor, S, can be calculated:
s: 2 .1so (:!':o.oo56
3 1.2s 110 /
6v, can be calculated'
Finally the verlical pipe delormation,
LG
o = 0'1 16 MPa' the Same agin Example
1.
^o
Ov:-
0.116..110.0.083
0.083
D
s+0.122
Eg
1.25.(0.0056+0122)
=
6.6 mm
pipe diameter is then:
The pipe delormation ino/ool originally
6.6
'110
=
60/o
ThedeformationoflhepipeafterbackfillingisrecommendednottoexceedB%,
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3. NESTE
STRAIN IN THE PIPE WALL
lollowing lormulas:
The strain in the pipe wall can be calculated by the
8=6,(#'(+)
is to be used when lhe stitlness lactor,
e
e
D
6,
'w
r=
18
s, is less or equal to 0.012:
= Strain in the PiPe wall
E Wallthickness, mm
= OriginalPiPe diameter' mm
= VerticalPiPe deformalion, mm
e) (?) (+)'(025's+ooo3)
istobeusedwhenthestiflnessfactor,s,isgreaterthan0.0l2:
Es=Secantmodulusofsupportingsoil,MPa,seeFigure5
E
S
pipe, MPa' see Figure 6
= Modulus ol elasticity ol the
factor, see Page 2
= Stiflness
o/o lor HDPE and 2.0 % lor
Allowed initial strain in the pipe wall is 1 .5
M
DPE'
OF BUCK'
ALLOWED PRESSURE ON THE PIPE CONCERNING THE RISK
LING
pipe_lrom collapsing due to buckling' The
The pipe wall must have suflicienl stif{ness to prevent lhe
lormula:
allowed pressure on a flexible pipe can be calculated by the lollowing
,r'
o":
vqOa
F
Er
E
e
D
4 '/-1'E'" /:-*
o/
F 3 /
= Allowed Pressure on the PiPe, MPa
= Factor ol salety
MPa, see Figure 7
= Tangent moduius of supportinO soila
pipe, MPa, see Figure 6
= Modilus of elasticity ol the
= Walllhickness, mm
= Originalpipe diameter' mm
Example 3
ol 6'0 meter' The ground
consider a llexible pipe of NCPE 2467-8L that is to be layed at a depth
is.assumed to be
waler level is 4.0 meter below ground level. The degree of compaction
{illing). Determine the lowest required value of the ratio
io*iratu ty B0 %(correspondinf to loose
"jf and calculate the pipe deformltion 6u/D and the Strain in the pipe wall'
e/D

4. level is at
when the ground water
by the risk o{ buckring
is determined
The required wartthict(ness
it's highest Point'
t;=
at 50 vears
Fisure
ilFi Neste NCPE 2467'BL
gives:
Figure 6
t-sl f= 2.0
as in Example 1 '
b"!'o.t't 6 MPa, the same
1s:":::
i;i
",
Formula 1 gives:
0116=
+
F5'1'g0-)'"'
(J
+
=28o/o
(tJ; (#)"=oo28
0'03' This
should no be p'etow
recommended that e/d
example'
rigu" al iu to oL used in this
itis
handring or the pipe
As a security due to
ic-orresponding
means thar pipe crass
2
is calculated as in Example
The pipe delormation
,;5-;;';;;
ii
. = L.
3
6v
4"
=
D
190
(0.031)3
=
o'oo3o
1.25
0.116
1.rs
0.083
=
0.062
=
6.20/o
o.oo3o+o'122
since the stiflness ractor,
wa, c11 be carcurated.
strain in the pipe
Now linary the
page 3'
t"t"'t'i" itio Ot used' see
0.012 the lollowing
t = 6'0.031 '0'062 = 0'0115 =
1'15%
pipe wall'
initial strain in the
This is below the allowed
s' is ress
rhan

5. NESTE
Figure
Ground level
Ground water level
D:
UV:
ft=
O:
H=
Original pipe diameter, mm
Vertical piPe deformation, mm
Distance between the ground water level and
the pipe center, rn
Total vertical load, MPa
Height of fill above the PiPe, m
1

6. Figure 2
05, MPa
0.15
0.10
Ground water level
belo-w the PiPe.
r-v
-r--1
ll
0.05
/t
-/
Ground r ater level
above th pipe
I
I
I
g
B
H,M
Soil pressure vs height of backfilling

7. NESTE
Figure 3
Traffic load from 14 ton distributed
on 2 wheels with a distance of 1.g m
14 ton
Q1, MPa
0.04
1-
jQ,
0.03
4tF
I
ii
I
:
I
0.01
,
I
I
H,m
Traffic pressure vs height of backfilling.
With a height of backfilling above 3 m the contribution
from traffic load to the totalvertical load on the pipe
normally negligeabel.
is

8. Figure 4
1 bulo-j g',-^"1
l"uol'
Ground water pressure vs head of ground water
for ground water level above the pipe.

9. NESTE
Chemicals
Figure 5
E5, MPa
//
-t'
5:i,"J-ffi
---
--+-€
012345
67
H,M
Secant modulus of supporting soil vs height of backfilling
for non-cohesive filling material i.e' sand and grave!
r - -.
Ground water levelat ground level
Ground water levelbelow pipe
% Filling from ground levelwith shovel
80 % Corresponds loose filling and almost no compaction (dumping from truck)
75
85 oh Corresponds soft comPaction
90 % corresponds hard compaction (under areas with heavy traffic
done with a machine)
9

10. Flgure 6
MODULUS OF ELASTICITY, E, FOR DIFFERENT
NESTE PIPE GRADES
NCPE
210 MPa (50 year value)
NCPE
2467-BL
190 MPa (50 year value)
NCPE
10
2467
2418
185 MPa (50 year value)

11. NESTE
Chemicals
Figure
7
E,, MPa
7
I
^"."-
_L^"{:]_
'oo'
qQ
qo'
/-t---
I
I
I
^ro(
. ?(o:-
Jr-.'
lno*ff
6
H,m
Tangent modulus of supporting soil vs height of backfilling
for non-cohesive filling material i.e. sand and gravel
Ground water level at ground level
r orQ;ound water level below pipe
- oh Filling
ground level with shovel
from
75
80 o/o Corresponds loose filling and almost no compaction
(dumping from truck)
%
Corr:asponds soft compaction
90 o/o Corresponds hard compaction (under areas with heavy traffic done with a machine)
85
11

12. Flgure 8
RECOMMENDED DIMENSIONS FOR BURIED HDPE PIPES
Ref. Swedish Slandard SS 3403
ISO PIPE SERIES
Swedsh designation
OUTER DIAMETER
s-16
L-2
s-12.5
s-10
T:4
E-16
W.ALL
,
WALL
WALL
40
3.0
3.0
50
3.0
3.0
75
3.0
3.0
90
3.0
3.5
110/ -
3.4
4.2
160
4.9
6.2
9.5
20.0
6.2
7.7
11.9
250
7.7
9.6
14.8
2<tr
9.7
12,1
18.7
404
12.3
15.3
oe -,
500
15.3
19.1
29.6
630
19.3
24.1
37.2
/
6.6
ln lhis Swedish Standard "Pipes and f itlings ot PE for buried sewers and discharge systems inside
buildings" the minimum wall thickness is 3.0 mm, due to handling of the pipe during the laying
operation.
12

13. NESTE
HDPE PIPES IN SANDYSOIL
Recommended pipe class under different
laying depths and traffic load
Local Streets
Sporadic heavy
traffic
Open areas
Carparks
Height of
backfilling
(m)
'-a
s12.
s12.5
1.0
2.0
Main roads
lntensiv heavy
tratfic
s10
s-16
3.0
s12.5
4.0
s12.5
5.0
6.0
s10
"
s10
s10
Backfilling with rnacadam, 4-16 mm
Backfillinng with excavations
lf no sand or macadam is available make the trench broader at least 2D on each
side of the pipe.
13

14. HDPE PIPES IN CTAYSOIL
Recommended pipe ctass under different
laying depths and traffic load
Height of
backfilling
Open areas
Carparks
Local streets
sporadic heavy
traffic
(m)
Main roads
lntensive heavy
traffic
'!
1.0
s10
2.0
3.0
tr,
..1
l
4.0
sl0
"ll.*
s1o
I
I
sro
5.0
6.0
-'-
'
*r
Backfiiling with macadam, 4-16 mm
Backfilling with excavations
Backfillingwithsandandgravel, 0_16mm
-,-
"
lf no sand or macadam is avairabre make the trench
broader
at least 2 D on each side of the pipe.
t4
-'-

15. NESTE
HDPE PIPES IN LOOSE CLAYSOIL
Recommended pipe class under different
laying depths and traffic load
Height of
backfilling
Open areas
carparks
(m)
Localstreets
sporadic heavy
traffic
Main roads
lntensiv heavy
traffic
s10
1.0
2.0
sl0
s10--
s10
3.0
4.0
5.0
6.0
'
*.
"'
Backfilling with macadam,4-16 mm
Backfilling with excavations
Backfilling with sand an gravel, 0-16 mm
lf no sand or macadam is available make the trench broader
at least 2-D on each side of the pipe.
15

16. LAYING OF PE SEWAGE PIPES
1.
Preparation of narrow trench'
2.
Sand or gravel bedding
3.
Firm bottom supporting
4.
lnilial backlilling around sides
5.
Protective backfilling. No hard compacling above the pipe
6.
Final backfilling with compacting
Proper laying is lhe last step in making a reliable sewage system.
lf no sand or gravel is available as backfilling material make the trench broader at least 2 D
on each side of the pipe
i6