ETL 1110-3-446
20 Aug 92
TABLE C-l
Friction Coefficient for Concrete Cast on Soil
(reference 4)
Interface Materials
Coefficient, f
Mass concrete on the following foundation
materials:
Clean sound rock
0.70
Clean gravel, gravel--sand mixtures, coarse
sand
0.55 to 0.60
Clean fine to medium sand, silty medium
to coarse sand, silty or clayey gravel
0.45 to 0.55
Clean fine sand, silty or clayey fine to
medium sand
0.35 to 0.45
Fine sandy silt, nonplastic silt
0.30 to 0.35
Very stiff and hard residual or
preconsolidated clay
0.40 to 0.50
Medium stiff and stiff clay and silty clay
0.30 to 0.35
C-4.2. The size of thrust block for downward directed thrust is
calculated by;
ATB $ FSTY/qS
where;
ATB = bottom area of thrust block,
Ty = vertical component of thrust force,
qS = allowable bearing capacity of soil, and
FS = Factor of Safety.
C-4.3. There is also a horizontal component of thrust (Tx) in
vertical bends. The sizing of thrust block for the horizontal
component is calculated by the same formula used for horizontal
bends, except the term T is replaced by Tx = 2PA Sin 0/2 Cos 0.
C-4.4. These are shown in Figures C-4, C-5, C-6 and C-7.
C--5. Restrained Joints. There are several approaches to this.
They all calculate the length of pipe to be restrained on both
sides of the joint. The length to be restrained may be determined
by;
L $ FS(PA tan 2/2)/(Ff + 0.5 R (S Z Kp Do)
where;
C-4
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