Design of Reaction System for 1500 mm diameter Test Pile

The following are the main elements in the design of reaction system for 1500 mm diameter test pile.

 

  •   Design of Reaction Anchor.

 

  •   Design of Dywidag Bars.

 

  •   Design of cross beam.

 

Anchor Design

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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)       =             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

 

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

 

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.