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Ram weight – Drop height

Ram weight – Drop height. 500 kN´s påle. The capacity of the pile is both a geotechnical and a structural issue. Geotechnical Capacity

joelle-miller
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Ram weight – Drop height

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  1. Ram weight – Dropheight

  2. 500 kN´s påle

  3. The capacity of the pile is both a geotechnicaland a structuralissue

  4. GeotechnicalCapacity The geotechnicalcapacity of a driven pile is the ability of the surroundingsoil and/or the rock to withstandloadswithout harmful movements.

  5. Geotechnicalcapacity The rule of thumb in Sweden for driven piles to set less than 10mm/10bl Concrete piles: 1 kN per cm2 Steel piles: 13 kN per cm2

  6. Geotechnicalcapacity Oftenmuchhighercapacities is used, for concrete piles up to 1,6kN/cm2 and steel piles 22kN/cm2. This require that the pile is driven to solid rock in order to verifycapacity. To verifycapacity 5% to 25% of the piles are normallytested.

  7. Ram weight One condition in order to install the pile to the desired capacity is to have sufficient ram weight. A rule of thumb in Sweden is that for micro piles it is recommended that the piston in hydraulic hammers has a weight at least 2 times the pile weight per meter.

  8. Ram weight – Dropheight In order to mobilizeavailablecapacity the pile final set for the test blow has to be a few millimeters. This requirebothdropheight and ram weight. Rule of thumb: Dropheight 7-8 % of the length of the pile Ram weight 1-1,5 % of desiredcapacity

  9. Ram weight-Dropheight The relationshipbetweenimpactvelocity and dropheight Kinetic Energy = Potential Energy mv2/2 = mgH H = v2/2g or v = √2gH To dropone kg on the toe from one meter is equallypainful as dropping 10kg from the same height. Only the the 10kg hurts for a longer time ;-)

  10. Dropheight Example 1: Calculation of Z (EA/c) steelpipe pile 140mm x 8mm A (Area): 33 cm2 (0,0033 m2) E (Elasticitetsmodul): 210000 MPa c (wavespeed): 5120 m/s Z=210000*106*0,0033/5120=135000 Ns/m= 135 kNs/m

  11. Ram weight-Dropheight If a pile is struck by a impactvelocity of 3 m/s, the force in the pile will be: F = v*Z = 3*135 = 405 kN To achieve this particalvelocity (force) the dropheight has to be: H = v2/2g = 32/2*10 = 0,45 m Due to loss of energy in the cap, cushioning and so forth the dropheight has to be higher

  12. Ram weight –Dropheight If the pile is struck by an impactvelocity of 6 m/s the force in the pile will be: F = 6*135 = 810 kN To achieve this particalvelocity (force) the dropheight has to be: H = v2/2g = 62/2*10 = 1,8 m Due to loss of energy in the cap, cushioning and so forth the dropheight has to be higher

  13. Ram weight-Dropheight Piles driven to solid bed rock the downwardtravelingcompressionwave is superimposedwhichresults in higherstressesthan that induced by the hammer (specially on short piles)

  14. Ram weight – Dropheight The stresses in micro piles are commonlyveryclose to the yeild stress for the test blow. Important that the pile is cutcorrect prior to test and that the hammer is lined up correctly.

  15. Ram weight – Dropheight Example 2: Calculation of Z (EA/c) for a concrete pile (side=235mm) A (Area): 552 cm2 (0,0552 m2) E (Elasticmodulus): 40000 MPa c (Wave speed): 3900 m/s Z=40000*106*0,0552/3900=566000 Ns/m= 566 kNs/m

  16. Ram weight – Dropheight If the pile is struck by an impactvelocity of 3 m/s the force in the pile will be: F=3*566=1698 kN To achieve this particalvelocity (force) the dropheight has to be: H=v2/2g = 32/2*10 = 0,45 m Due to loss of energy in the cap, cushioning and so forth the dropheight has to be higher

  17. Ram weight – Dropheight If the pile is struck with a dropheight of 1,2m the particalvelocitywill be: V= √2gH = √2*10*1,2 = 4,9 m/s The force in the pile willthan be (energylosses are neglected): F=4,9*566=2773 kN, which is equal to a stress of 2,773/0,0552 = 50 MPa. The pile willonlywithstand a few of theseblows!

  18. Ram weight – Dropheight Warning! Modern machinery are oftenequiped with acceleratinghammers. Thesehammerscanquiteeasily over stress the pile.

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