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DefinitionsYielding foundation conditions occur when the foundingmaterial and the fill material are expected to settle at equalrates (compressible material). The loading is calculated inaccordancewithTMH7Part2clause2.3.3.2(2).

Unyielding foundation conditionsoccurwhen the foundingmaterial is incompressible (soft rockor hardermaterial).Theloading iscalculated inaccordancewithTMH7Part2clause2.3.3.2(3)and(4).

Trench condition occurswhen culverts are laid in a narrowexcavationandbackfilledtogroundlevel.

Embankment (untrenched) condition occurs when culvertsarelaidatgroundlevelandbackfilledtofinalformationlevel.

ThecombinationsoffoundationandinstallationconditionsusedinTMH7aredefinedas:

Condition 1:Culverts intrenchonunyieldingfoundationwithnoprojection

Condition 2:Culvertsinanembankmentonyieldingfoundation

Condition 3:Culvertsinanembankmentonyieldingfoundationforh>1,7b

Condition 4: Culvertsinanembankmentonunyieldingfoundationforh<1,7b

Where h=fillheightsinmetres b=overalltrenchwidthor,ifinanembankment, overallculvertwidth,inmetres.

AssumptionsThefollowingassumptionsandclausesofTMH7Parts1and2wereusedtocompilethetableabove:

• Aminimumfillheightof300mmovertheculvertunits. Wherethiscannotbeachieved,a100mmreinforced concreteslabmustbeused• StandardtrafficloadingSNABC• Fillmaterialunitweight20kN/m³• Concreteunitweight24kN/m³• Horizontalearthpressure7,8kN/m²permetredepth• UltimateLimitStateLoadfactors.

Maximum Fill Heights

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2100 600 3.3 2.42100 900 3.5 2.62100 1200 3.7 2.72100 1500 75S 3.9 75S 2.82100 1800 4.1 2.92100 2100 4.3 3

2400 600 3.2 2.42400 900 3.4 2.52400 1200 75S 3.5 75S 2.12400 1500 3.7 2.92400 1800 3.8 2.82400 2400 4 3

Culvert Size Foundation conditionsSpan Height 1 and 2 3 and 4(mm) (mm) Class Fill (m) Class Fill (m)

3000 600 3.1 2.43000 900 3.2 2.53000 1200 3.3 2.63000 1500 75S 3.4 75S 2.73000 1800 3.5 2.73000 2400 3.7 2.9

3000 3000 3.1 2.7

3600 600 3.1 2.43600 900 3.1 2.53600 1200 3.2 2.63600 1500 75S 3.3 75S 2.63600 1800 3.3 2.73600 2400 3.5 2.8

3600 3000 3.5 2.7

Forhigherfillheights,productscanbespeciallydesigned.

Culvert Size Foundation conditionsSpan Height 1 and 2 3 and 4

750 300 8.7 4.9750 450 9.2 5.2750 600 10 5.5750 750 10.5 5.8

(mm) (mm) Class Fill (m) Class Fill (m)600 300 10.2 5.6600 450 200S 11 200S 6600 600 12 6.4

900 300 8.6 4.8900 450 9 5.1900 600 175S 9.5 175S 5.3900 750 10 5.6900 950 10.2 5.8

1200 300 7.1 4.11200 450 7.4 4.31200 600 150S 7.7 150S 4.41200 900 8.2 4.71200 1200 8.8 5

1500 300 4.5 2.91500 450 4.7 31500 600 4.9 3.11500 900 5.3 3.31500 1200 5.6 3.51500 1500 6 3.7

100S 100S

1800 600 3.3 2.41800 900 3.6 2.51800 1200 3.8 2.71800 1500 4 2.81800 1800 4.3 2.9

75S 75S

175S 175S

Maximum Fill Heights on Culverts