Bedding Type, Trench Depth
Theory of determining Bedding Type, Trench Depth:



W      Design load (KN)
Fs      Safety Factor, assumed to be 1.25
Pn      Crushing strength of the pipe (KN)
Fm      Bedding factor
Wc      Narrow trench load (KN) Design
Wc'      Wide trench load (KN) Design
Wc"      Weight of trench backfill
Wcsu      Traffic and other transient surcharge loads (KN)
œ      Until pressure due to vehicle load
Ww      Water load {pipe content} (KN)
H      The cover depth (m)
Bd      Effectěve width of trench
Bc      External diameter of pipe
Cd      Narrow trench load coeffieient
Cc      Wide trench load coefficient
Y      Weight of soil (Backfill) , assumed to be 19.6 KN/m3
ku      The product of the Rankin coefficient of active soil pressure and the coefficient of internal friction of the soil , it's maximum value of 0.19 since this is the most unfavourable condition
ku'      The product of the Rankin coefficient of active soil pressure and the coefficient of soil friction between the trench wall and the fill , value 0.13 is often taken for general design purpose in mixed soil unless other wise as stated.
rsd      Settďement ratio
p      Projection ratio

The product of the settlement deflection ratio and the projection ratio (rsd p):
For pipe dia. up to 300mm = 0.7
For pipe dia.350mm and greater = 0.5.
ku rsd Load coefficent Cc
0.19 +0.5 Cc = 1.50(H / Bc)-0.07
0.19 +0.7 Cc = 1.59(H / Bc)-0.09
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