THE VIBRATORY PILE INSTALLATION TECHNIQUE - Viking

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change M e on the fly, relates to the use of so called ‘resonant free vibro-units’, which minimizethe exposure of the pile from harmful resonant effects during the; start-up and shut downphase.3.2.The axial rigidity assumptionEngineering issues regarding longitudinal effects of vibro-driven piles, normally relates to thequestion whether or not it’s justified to treat the vibrating pile as a rigid body. A vibratory drivenpile can be treated a rigid body if the following ‘rule of thumb’ is fulfilled, in accordance withfigure 6, and the following expression: T/4=(4f d ) -1 ≥t n =4L/c b . With the following phenomenologicalexplanation; a quarter of the time period T of chosen driving frequency f d , should be equal to orgreater than the time t n it takes a stress wave to travel 4L of the vibro-driven pile.Theorethical driving force:F d= F 0+ ξF vT=1/f dtime [s]F o^= ξM e(2πf d) 2t =0 t =T/2 t =Tx=0= W-TF vt =T/8 t n =4L/c bT/4=1/4f dtime [s]Rule of thumbT/4=1/4f d> t n=4L/c bsheet pilePosition: x [ ft ]1c b≅ 16,800 [ ft/s ]x=LFigure 6. Illustration of the ‘rule of thumb’ for the justificationof a rigid body assumption (Viking et al. 2000).3.3. Lateral vibrations and flexibilityAnother important pile-related factor to consider is the lateral vibration and flexibility duringdriving, which normally relates to the use of slender and low-displacement piles such as sheetpiles, and H- and I beams (Viking et al. 2000). However, this neglected pile-related factor canalso be of great concern when driving PCPS concrete piles (Viking et al. 2004).These undesired lateral vibrations during the installation phase normally relates to improperalignment of the driving force F d and axial symmetry line of the pile. Simply, if the clamp does74
not hold the pile correctly, a bending moment M ecc is introduced at the pile head, which mightcause a situation, were the pile-profile vibrates as much laterally as it does axially. Theengineering consequence of neglecting the effects of lateral motion of the pile includes a lowervibro-drivability as well as an increasing amount of induced ground vibrations. Lower vibroabilityas well as higher ground vibrations occurs due to the fact that the pre-installed sheetpiles forming a sheet pile wall are coupled to the next profile being driven into the sheet-pileinterlock. The pre-installed sheet-pile wall acts like the membrane of a load speaker, sendingout laterally induced P-waves, as discussed and visualized (Viking et al. 2000).3.4. Interlock friction force of sheet pilesThe dynamic interlock friction force R c is a sheet-pile related factor, well known to have atremendous impact on both the vibro-drivability as well as generated ground vibrations. Themagnitude of the developed interlock friction force R c is primarily due to presence of soilparticles in the interlocks, but also due to steel-to-steel friction. Other significant factors are; lowmanufacture tolerances of interlocks, re-use of profiles with interlocks in bad shape and/orimpurities in the locks (corrosion and soil), together with mode of operation.The developed magnitude of the friction force r c per unit length during driving appears to be atleast in the range of 69< r c
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Page 7 and 8: The magnitude of the penetration sp
Page 9: 2.6. Accessories and Driving AidesB
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Page 17 and 18: 5.5. Other instrumentationThe relat

THE VIBRATORY PILE INSTALLATION TECHNIQUE - Viking

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