HomeMy WebLinkAboutWTR2703554.2CONCRETE BLOCKING SIZING PROCEDURE
A. GENERAL
THE AMOUNT OF CONCRETE REQUIRED TO ANCHOR HORIZONTAL BENDS,
TEES, AND DEAD ENDS DEPENDS ON THE STRENGTH OF THE SOIL. THE
METHODS OF PLACING CONCRETE TO KEEP THE JOINT ACCESSIBLE IS
SHOWN IN FIGURE 1, THE AREA IN SQUARE FEET OF CONCRETE WHICH
MUST BEAR AGAINST THE SIDE OF THE TRENCH IS FOUND BY DIVIDING
THE THRUST IN POUNDS SHOWN IN TABLE 1 BY THE SAFE BEARING LOAD
OF THE SOIL AS SHOWN IN TABLE 2.
B. CRITERIA
1. THE SIZING PROCEDURE IS FOR HORIZONTAL OR DOWNWARD
THRUST ONLY.
2. HEIGHT OF THE THRUST BLOCK MUST BE EQUAL TO OR LESS
THAN 1/2 THE DEPTH FROM THE GROUND SURFACE -0 THE BLOCK
BASE.
3. THE THRUST BLOCK BEARING FACE IS APPROXIMATELY
RECTANGULAR.
4. THE CONCRETE BLOCKING SHALL BE AS PER APWA
SPECIFICATION 74-2.14.
C. SYMBOLS
D = OUTSIDE DIAMETER OF PIPE IN FEET
T = THRUST IN POUNDS AT THE FITTING (TABLE 1)
SBL = SAFE BEARING LOAD IN POUNDS/SQ. FT. (TABLE 2)
H = DEPTH OF TRENCH IN FEET
W = WIDTH OF TRENCH IN FEET
A = AREA OF CONCRETE WHICH MUST BEAR AGAINST
THE SIDE OF THE TRENCH IN SO. FT.
HM = MAXIMUM HEIGHT OF THE THRUST BLOCK IN FEET
DC = DEPTH OF THE CONCRETE THRUST BLOCK TO
BEARING SURFACE IN FEET
LM = MAXIMUM LENGTH OF THE THRUST BLOCK IN FEET
GROUND SURFACE
h �d
Hm h
- 2 +
BLOCK BASE
DC
W
D. CALCULATION EQUATIONS
1. Area of Concrete (A) = Thrust (In Pounds = T
Safe Bearing Load (In Pounds/Sq. Ft.) SBL
2. Maximum Height of Thrust Block (Hm) = Depth of Trench in Feet = h
2 2
(Width of Trench in Feet) -
3. Depth of Concrete Thrust Block = (Outside Diameter of Pipe in Feet) - W-d
2 2
4. Maximum Length of Thrust Block (Lm) - Area of Concrete = A
Maximum Height Hm
5. Required Amount of Concrete (Cu. Yd.) = (Height x Depth x Length) x 0.03704
- (Hm x Lm x Dc) x 0.03704
E. EXAMPLE
1. Problem:
Calculation of the amount of concrete required to block a 90` bend in an 8"
C.I. water main; the normal operating pressure in the pipe will be 65 psi
and the soil condition in the area indicates sand and gravel.
2. Solution:
- Maximum testing pressure (See Table 1) = 300 psi.
- Outside diameter of 8" pipe = 9.05 in. = 9.05/' 2
- Go to Table 1: The testing pressure of 300 psi, we see
that the thrust on a 90' bend is 21,360 pounds.
CAP
TEE
22-1/2'
45' BEND
- Go to Table 2: Table 2 gives the safe bearing load for
sand and gravel: 3,000 lbs./sq. ft.
- Go to Figure 1: figure 1 indicates the position
of the concrete for blocking the 90' bend.
- Go to the specifications of the project and find
depth of trench (h) = 4 feet
- Width of trench (W) = 3 feet
With the above assembled information,
we proceed to the final calculations:
- Area of Concrete (A) = Thrust = 21,360 = 7.12 sq ft.
Safe Bearing Load 3,000
Depth of Trench in Feet
- Maximum Height of Thrust Block (Hm) _ _ h _ 4 _ 2
- 2 - 2 - 2.0 ft.
Depth of Concrete Thrust Block (Dc)
Width of Trench in Feet (W) - Outside Diameter of PIN (d
- = - 3 0.75 1.13 ft.
2
-
2 Area of Concrete
- Maximum Length of Thrust Block (Lm) _
Height of Concrete
= A = 7.12 = 3.56 ft.
Hm 2.0
- Required Amount of Concrete = (Height x Depth x Length) x 0.03704
_ (Hm x Lm x Dc) x 0.03704
2.0 x 3.56 x 1.13) x 0.03704
= 0.30 cu. yd.
TABLE 1
Size
Pressure
PSI
Thrust at Fittings in Pounds
Tees
90°
45'
22-1 /2"
11-1 /4"
Dead Ends
Bend
Bend
Bend
Bend
3"
300
2,120
3,000
1,630
830
430
4"
300
3,780
5,370
2,910
1,470
750
6"
300
8,500
12,000
6,510
3,320
1,700
8"
300
15,100
21,360
11,550
5,880
3,020
10"
275
21,620
30,570
16,540
8,430
4,330
12"
250
33,930
48,000
25,950
13,260
6,780
14"
250
46,200
65,370
35,340
18,030
9,240
16"
225
45,250
64,000
34,620
17,650
9,050
18"
200
50,900
72,000
38,940
19,860
10,180
20"
200
62,840
88,900
48,080
24,520
12,560
24"
200
90,480
127,980
69,200
35,320
18,100
30"
200
141,370
199,960
108,150
55,140
28,280
36"
200
203,580
287,950
155,740
79,400
40,720
TABLE 2
Safe Bearing Loads in Lb./Sq. Ft.
The safe bearing loads given in the following table are for
horizontal thrusts when the depth of cover over the pipe
exceeds 2 feet.
Safe Bearing Load
SOIL Lb. per So. Ft.
*Muck, peat, etc. 0
Soft Clay 1,000
Sand 2,000
Sand and Gravel 3,000
Sand and Gravel Cemented with Clay 4,000
Hard Shale 10,000
*In muck or peat, all thrusts shall be restrained by piles or
tie rods to solid foundations or by removal of muck
or peat and replacement with ballast of sufficient
stability to resist thrusts.
FIGURE 1
NOTE: FOR CONVEX VERTICAL BENDS BLOCKING
SEE APWA STANDARD PLAN NO. 73.
90' BEND
3/4" SQUARES
AS INDICATED -
RAISE-1 /2"
WIDE BORDER
10"
9„
8-3/4" 5/8"
1- 1/4" 1/2" -1 2"
3 4" _T
8"
N
CAST IRON RING AND COVER
2'- 0 "
CONCRETE
CLASS 3000
12"o
FIBER JOINT
PACKING
45° (1/8) BEND
z EJE
„A„
nC DClll IIDCfI
WOOD BLOCKING
CASING DETAIL
A
PIPE
SIZES
B
CASING
SIZES
CASING
WALL
THICKNESS
6"
12"
1/4"
8"
16"
1/4"
10"
20"
1/4"
12"
24"
1/4"
14"
28"
1/4"
16"
32"
1/4"
NOTE:
NYLON PIPE SPACERS MAY BE
USED IN LIEU OF WOOD BLOCKING
SECTION A -A
)NC. END SEAL
EX CPLG.
SING PIPE "B" 0
STD. STEEL PIPE
"B" STD. WALL STEEL CASING PIPE
PIPE FLANGE
STAINLESS STEEL BAND AS SPECIFIED
FOR EACH LENGTH OF BLOCKING
MAX. SPACING 8 FEET.
WOOD BLOCKING SHALL BE
CONTINUOUS EXCEPT AT JOINTS
NTS NTS
Clean Out 3 Pipe Casing
7
NTS
10
Blocking Sizing Procedure 1 1
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NO. DATE REVISION
12/11/09 PERMIT SET
SHFFT TITI.F
UTILITY
DETAILS
12 C090125-02
JOB NO.:
SSN
DRAWN:
DARDS SLG
CHECKED:
4/12/10
DATE:
SHEET NUMBER:
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