ETL 1110-3-446
20 Aug 92
L = restrained pipe length, one leg,
P = internal pressure of pipe,
A = internal cross--section of pipe,
2 = angle of deflection of bend,
Ff = unit frictional force f(2 We + Wp + WW),
R = reduction factor,
(S = unit weight of soil,
Z = depth of embedment,
Kp = coefficient of passive pressure,
Do = outer diameter of pipe,
We = weight of earth on pipe,
Wp = weight of pipe,
Ww = weight of water in pipe,
f = as defined in paragraph C-3, and
Fs = Factor of Safety.
In the absence of information regarding maximum allowable
displacement of pipe and pipe joints, use K0 instead of RKp. The
above formula is then;
L $ Fs(PA tan 0/2)/Ff + 0.5 (S Z Ko Do)
where, K0 = coefficient of at-rest pressure. If movement is
permitted, the reduction factor CR) must be determined by a
geotechnical engineer.
C-6.
Trenching and Backfilling.
Trenching and backfilling is specified in CEGS 02222 to
include bedding, if required, initial backfill to at least one
foot above pipe, and final backfill to ground surface. This is
shown in Figure C-8.
The backfilling, or laying condition as it is sometimes
called, has relevance on the reduction factor (R) used to develop
the partial passive soil pressure for the restrained joint
conditions. Use only cohesionless materials, if at all possible,
as bedding, initial backfill, and final backfill.
C-7. Thrust blocks for horizontal bends are shown in Figures C-
9, C-10, C--1l and C-12.
C-8. Thrust blocks for vertical bends are shown as follows. For
thrust vertically upward see Figures C-13 and C-14, and for
thrust vertically downward see Figure C-15.
C-7
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