Scribd
Upload
119 views3 pages

Thrust Block Design Guide

The document summarizes the design of a thrust block for a 900mm diameter water main operating at 11kPa pressure. It calculates the horizontal thrust of 53.48 tonnes and compares it to the lateral resistance provided by the weight and friction of the thrust block, soil, and earth. The total lateral resistance of 113.16 tonnes provides a factor of safety of 2.19, which is acceptable. It specifies using 10 bars spaced at 200mm centers in the thrust block, providing over 5kg/m2 of reinforcement.

Uploaded by

Shankar Murthy
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
119 views3 pages

Thrust Block Design Guide

The document summarizes the design of a thrust block for a 900mm diameter water main operating at 11kPa pressure. It calculates the horizontal thrust of 53.48 tonnes and compares it to the lateral resistance provided by the weight and friction of the thrust block, soil, and earth. The total lateral resistance of 113.16 tonnes provides a factor of safety of 2.19, which is acceptable. It specifies using 10 bars spaced at 200mm centers in the thrust block, providing over 5kg/m2 of reinforcement.

Uploaded by

Shankar Murthy
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 3

APPENDIX 6.

DESIGN OF THRUST BLOCKS


To design a thrust block for 900mm diameter main conveying water at 11k)'!J "

pressure(p).
The deviation angle a is 450 and density of concrete is 2300 kgs/m3• Soil Jt"'m!li

assumed to be 1800 kgs/m3 and angle of internal friction $ = 300 •


Assume minimum cover of earth is 600 mm. Cohesion is 0 for sandy soils.

HORIZONTAL THRUST: F =2 pA Sin a/2

Cross sectional area A = (n/4) (90/ = 6364 sq. ems.


Sin a/2 = 0.382
F= 2 (11) (6364) (0.382) (1O-~ = 53.48 Tonnes
(i) Lateral resistance to counteract the horizontal thrust

Weight of thrust block = 3.2M x 3.2 M x 3.2 M x 2.3 = 75.36 tonnes


Weight of water in the pipe = 0.785 x (0.9)2 x 1 x 3.2 = 2.03 tonnes
Weight of earth = 0.9 x (3.2) (0.6) (1.8) = 3.11 tonnes

Total Weight 80.50 tonnes

Total force available considering frictional


resistance of soil = 80.5 (0.3) = 24.15 tonnes
(i~ Lateral resistance of soil against the block:

fp = y. (H) 2 .L. 1 + Sin () + 2CHL 1 + Sin ()


2 1 - Sin () 1 - Sin ()

1.8 (3.2) 2 (3.2) (1.5) = 88.47 tonnes


2 0.5
i II) Lateral resistance of soil when the thrust block is free to yield away from the
soil mass i.e.) the portion of projected pipes :-

fa = 1 -
ys h -----
Sin e _ 2C ~ 1 -
-----
Sin e
I + Sin e I + Sin e

= (1.8)(0.9) (0.5) = 0 .54 tonnes


--"'" 1.5

Total lateral resistance = 24.15 + 88.47 + 0.54 = 113.16 tonnes/m2

Total horizontal thrust = 53.48 tonnes


I;actor of safety = 113.16/53.48 = 2.19 which is O.K.

t minimum surface reinforcement in all thrust blocks shall be 5 kgs/sq.m(as per IRG
2 Article 306.4). The spacing of these bars is not to exceed 500mm. Hence provide 10
. 200 c/c which is more than 5 kgs/sqm.
r 3200
t
8
tD
lATA.
E41HH CUSHION
IJIscharge thr<
••• •
I Materialof pi,
l)iameter of 1
ickness of
0
0
GO
tatic Head
N
200 c/c ....
ngth of p
'otal Head·
10#0200ct;
lead & oth(
esign head
~
........ : :..- ... ...
~" ,' tIDospheri
§ 200 c/c CB.W) •
~o
= Absol
SECTIONJ _1

10# 200 'Ie


(B. )

You might also like