How to install a concrete thrust block (SABI Vol 6)

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THRUST BLOCK SIZING
The calculation of the size of a thrust block is directly dependent on a number of factors including the fitting type, pipe size, the
operating pressure of the pipeline and the prevailing soil type where the thrust block is required . Soil types, such as clay and
sandy loam have an extremely low bearing capac ity, therefore in these soil types, thrust block sizing has to be increased in order
to be effective.
6.5.1 Reducer
6.5.4 Sluicevalve 6.5.5 End ca p
_
concrete
thrust block
6.5.2 Tee
Trench
m 7T!77T71
Redu(er, VoMlselc
The following table is a general guideline to thrust block sizing and is based on a PN 9 (9 bar) operating pressure in a medium
loam soil. Needless to say, higher operat ing pressures and other soil types will result in different sizing. The sizeof the thrust block
in m 2 is determined by the area (AxB) of the vertical bearing face.
GUIDELINE TO THRUST BLOCK SIZING
(recommended minimum sizes)
Pipe size (DN ) 90° Bends (AXB) 45 ° Bends (AXB) Tees (AXB) End caps, valves,
mm m m m reducers (AxB) m
50-90 0.20 x 0.20 0.20 x 0.20 0.25 x 0.25 0.25 x 0.60
110 0.30 x 0.30 0.30 x 0.25 0.30 x 0.30 0.30 x 0.60
125-140 0.30 x 0.45 0.30 x 0.30 0.30 x 0.45 0.30 x 0.70
160 0.30 x 0.60 0.30 x 0040 0.30 x 0.30 0.30 x 0.30
200 0.45 x 0.70 0.30 x 0.70 0045 x 0.60 0.45 x 0 .80
250 0.60 x 0.60 0.60 x 0.60 0.45 x 0.80 0.45 x 0.85
315 0.60 x 1.30 0.60 x 0.90 0.60 x 0.90 0.60 x 1.00
355 0.80 x 1.50 0.60 x 1.20 0.60 x lAO 0.60 x 1.40
400 1.00 x 1.60 1.00 x 1.20 0.80 x 1.50 0.80 x 1.50
Note : For further detoils refer to the DPI Plcstics technical manual.
It is highly recommended that the calculation of the final thrust
block sizing is carried out by the system designer, who will
have the required formulae as well as the ability to determine
the bearing capacity of the soil along the pipeline route. The
procedure described below is a step by step guide to the
installation of a thrust block on a 110 x 90° PVC long radius
bend, PN 9. Once the thrust blocks have been completed, it
is essential to allow the concrete to set long enough before
commissioning of the pipeline . This is to achieve sufficient
strength to counter the end thrust forces being exerted by the
operating pressure within the pipel ine.
SABII AUGUST/SEPTEMBER 2014 27