ETL 1110-3-446

20 Aug 92

C-3. Thrust Blocks for Horizontal Bends. Refer to paragraph C-7

for sketches. The size of thrust block is calculated by;

ATB $ FS[T -- f(WS + WTB)]/(SZRKP

where;

ATB = area of thrust block,

T

f

with type of soil; refer to Table C-1,

WTB = weight of thrust block,

(S = unit weight of soil,

Z **= **embedment depth to bottom of thrust block,

R **= **reduction factor applied to Kp (reference 4),

FS = factor of safety,

KP = coefficient of passive pressure for undisturbed soil of

trench sidewall, preferably determined using the log-spiral

method (reference 4).

In the absence of information regarding maximum allowable

displacement of pipe and pipe joints, use Ko instead of RKP. The

above formula is then;

ATB $ FS[T - f(WS + WTB]/(S Z K0

where;

Ko = coefficient of at-rest pressure.

For a conservative approach, the term f(Ws + WTB) may be neglected

resulting in either ATB $ FST/(S Z R KP or; ATB $ FST/(S Z K0.

C-4. Thrust Blocks for Vertical Bends. Refer to paragraph C-B

for sketches.

C-4.l. The size of thrust block for upward directed thrust is

calculated by;

VTB $ FS(Ty -- WW - WJ -WS)/(C

where;

VTB = volume of thrust block,

Ty = vertical component of thrust force=2PA Sin 0/2 Cos 0,

WW = weight of water in joint,

WJ = weight of pipe joint,

(c = unit weight of concrete, and

FS = Factor of Safety.

For a conservative approach, the terms WW, WJ, and WS, may be

neglected resulting in VTB $ FSTy/(C.

C-3