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# Buried pipe design by neste

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### Buried pipe design by neste

1. 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 Telex 62270 NCC B Tel. +358 !5 lB712 Telex l72l neste sf 5-444 86 STENUNGSUND Sweden Tei. +45 303 86 000 Telex 2402 nestepe s
2. 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%, fi fi ;'i;;; -i.oia HsTH;'il,.,\$ :*:HiH i":J'.fl:#:ffxilliil? n.autori'e en aucure hgon 1.68e qN *.o. *-p.- tr La pr€*ote dcurcnE!@ ori*nte d(uftn6l'@ I"l-it"i a", ai"*n Erfrndung n en84t n.en8a8e "-fr. "toietio eng"xn t'"'t"'t * :uletie Pd,Tj::ilri:g::.e! ; !ir'iei,i.*,fit c".i" or a " -Y custmer' ou'.."^." d.inYentioro ?:'"11i::"'9: *9a3j15' ]''' brevete:::::':",'::".":;:H;::;;.::::. Erraubnii oder Emplehlunt. 'rtendeift Pa(en(rede einertrlNil..ffdll";;\$'il".".""n mrt x,nat" H:f(un! i,hernehmn. ^ u-r,.,^d irbernehftn' ndh um eine vq Venr:€en --ii r De6(etunt. fijr die wrr e'ne rechllichp uod 5rnd n:ch Beondterr unceruchuns Xiiji"ft^'r'"i'u"rmi(tcrt 'tq'-*ry;ffi.o^""Tlt:".a'*',iljf,ilii,;f;;in;;'t**un6 ohre Uzenr uszuwenen u u'*r'r*' *r' -i";;;;;;';*'""::":.::.-i,"* with :;: liilf fill),T-io*'-'" '''o"'" , - .^^,-^ ili.aat.ni {i orodorli Nesre e re roro possibir ,.;.;5";:***;;\$\$:**ru;.i1":X"ffi::;:".::::tr::i:li"ll;;";i;0,.**cenzae,nlendonoromireindi@ionisiProdo'(liNes'ieer' Uppgirter i daobr:d,
3. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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