The following are the main elements in the design of reaction system for 1500 mm diameter test pile.
- Â Design of Reaction Anchor.
- Â Design of Dywidag Bars.
- Â Design of cross beam.
Anchor Design
The test load                =         1.5 x W.L = 1.5 X 21800 = 32700 KN (Comp.)
No. of anchors               =         24 Nos.
Load / Anchor               =         32700 / 24   = 1362.50 KN
Diameter of anchor strands      =     15.20 mm
According to FIP Code
Grade of anchor strand          =         1570 /1770 N/mm2
Allowable load/ strand           =         1.770 X 130 / 1.60   = 144 KN/ strand
No. of strand/ anchor            =         1362.50/144   = 9.46  =  10
Provide 10 Nos. of Strands / anchors
Total No. of strands               =         24 x 10 = 240 Nos.
Load on one strand                =         32700 / 240 = 136.25 KN < 144 KN (safe)
Total length of anchor ‘L’ = 25.60 m.
Proposed 10 Nos. strands (15.24 mm dia) of 24 anchors located as shown in the sketch.
Design For Grout Body Length
Load per anchor                     =         32700 / 24 KN  = 1362.50 KN
Safety factor                          =         2
Ultimate anchor load             =         1362.50 x 2 = 2725 KN
Required grout length(Lo)Â Â Â Â Â Â =Â Â Â Â Â Â Â Â Â Â Â Pu / ( Ao x sigma )
Nominal diameter of strands             =         15.20 mm
Perimeter = Ao = 0.0152 x p = 0.048 m
Proposed No. of strands                                =         10
Lo       =                2.725 MN / ( 10 x 0.048 x 1.0 MN/m2)     =         5.68 m
Provide grout body of 10.00 m long
GROUT – Ground Interaction
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Ultimate anchor load                  =         2725 KN
Proposed length of grout body                     =         10.00 m
According to B.S- 8081 – 1989– fig. 60 (conservative).
The skin friction capacity for medium dense sand  = 300 – 800 KN/m2
Considering an ultimate skin friction capacity of 600 KN/m2
Use 1500 mm diameter casing for drilling of anchor.
Pult = 0.15 x p x 10.00 x 600 KN/m2 = 2827 KN/anchor >2725 KN (safe)
Elastic Elongation Of Anchor
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Max. load / anchor                 =         1362.50 KN
Elastic elongation                   =         I          =      (P x L) / ( E x A )
P                  =  Anchor Load              =      1362.50 KN
L                  =  Free Length of Anchor =     25.60 – 10 =15.60KN
E                  =  Young’s Modulus       =     200 KN
No. of strands            =         10 Nos.
Area of strands          =      (10 x 15.202 x p) / 4  = 1810 mm2
Max. elongation         =      (1362.50 x 15600 ) / 200 x 1810  = 58.72mm
Dywidag Bar Design
Dywidag bars are used to transfer the load from the anchor to the cross beam.
The Dywidag bars of steel grade 1080/1230 N/mm2
Total Test load           =         32700 KN
The working load of 36 mm dia. Bar with a F.O.S. of 1.6 = 783 KN (Data sheet attached)
No. of 36 mm Dywidag bars required  = 32700 / 783  = 41.76 = 42 Nos.
No. of Anchors                                  =         24 Nos.
No. of Dywidag Bar / Anchors        =         2 Nos.
Total No. of Dywidag bars  = 24 x 2  = 48 Nos. > 42 Nos. (safe)
Design of Cross Beam
The cross beam is capable to provide a reaction of 4000 tons to test piles. Since test load is only 3270 tones the cross beam is adequate to provide reaction load to the test pile.