THE VIBRATORY PILE INSTALLATION TECHNIQUE - Viking

More documents

Recommendations

Info

2.1.3. Driving frequencyf d is specified by the revolution per second of the eccentric weights [Hz], sometimes alsospecified as revolution per minute n [rpm]. Another common expression is revolution in radiansper second ω [rad/s]. The three different ways can be combined as follows: ω =2πf d =2πn/60.time [s]ω [rad/s]F oω = 2πf dF o^F v= ξM e( 2πf d) 2F da.) Driving force F dvs. timeT=1/f dDriving force: F d25% . M e50% . M e75% . M e100% . M eb.) Peak value of F dvs. M eand f dFigure 2. Driving force as a function of changed frequency and eccentric moment.2.1.4. System efficiencyξ which is applied to the dynamic part, (centrifugal force F v ), of the theoretical expression of thedriving force F d (see equation below). Since the actual driving force F d delivered to the pile headwill always be less than the theoretically rated.The theoretical peak amplitude of the driving force F d in [kN] can be assessed by the followingexpression.F d = F o + ξF v = F o + ξM e ω 2 = F o [kN] + ξ [-] M e [kg-m] (2πn) 2 [rpm] 22.2. Parts and type of vibro-unitsThe main parts of modern vibro-units consist of the following parts.Bias mass; a part of the vibrator that’s also called ‘suppressor housing’ which is the nonvibratingpart of the unit. It connects to the exciter block via elastomers pads that isolate thedynamic motion of the exciter block from being transmitted to either crane line or leader mast,which connects, to the bias mass. To the bias mass are also electrical cables, hydraulic hosesmast connected.Elastomer pads (or springs); connects and at the same time isolates the non-vibrating part fromthe vibrating part of the vibro-unit.Exciter block; contains the rotating eccentric weights, gearbox and hydraulic motor, whichcombined generates the sinusoidal motion and centrifugal force of the vibrator.Clamp; at the bottom of the vibro-unit, which forms the rigid connection between pile and vibrounit.Used to transfer the generated force and motion, (preferably ‘axially’), to the pile profile.The clamp must be adapted to the size of the vibro as well as to the shape of the pile.Five different types of vibratory drivers (free or leader mounted) can be distinguished, based onapplied driving frequency (f d [Hz]) and eccentric moment (M e [kg-m]), see Table I.Table I. Type of modern vibratory drivers/extractors.68
TypeFrequencyrange[rpm]Eccentricmoment M e[lb-in.]Max F vforce[tons]Displacementamplitude S p[in.]1.) Standard20,835 517 1.26< 1,800frequency2.) High520 – 3,980 45 - 303 0.51 – 0.87> 1,800frequency3.) Variable866 – 4,670 67 - 371 0.55 – 0.671,800 - 2,400eccentricity4.) Excavator90 – 1,125 8 - 56 0.24 – 0.791,800 - 3,000mounted5.) Directional♣ ♣ ♣force ♣ 1,800 - 2,400♣ Still not commercially available, but considered as the next generation of vibratory drivers.2.3. type of vibratory drivers/extractors2.31. Standard frequencyStandard frequency are still the vast majority of vibro-units in use today since they combine afrequency range that interacts properly with most soils, and generates sufficient displacementamplitude to penetrate denser sub-surface strata’s. These units are primarily used for heavypiles and large toe resistance such as concrete and large steel pipe piles. They are at the sametime the simplest, but also the most powerful, since they are able to generate both the highestdriving force and displacement amplitude due to being equipped with the largest eccentricweights.2.3.2. High frequencyThese units are the second generation of vibrators. They were primarily developed to meet thehigher demands of reduced transmission of harmful ground vibrations to neighboring structures,which can cause undesirable settlements. This was accomplished by using higher drivingfrequencies (>30 Hz). However, these units are not as powerful as standard units, they are alsoless successful in overcoming large toe resistance compare to standard units since they do notgenerate as high displacement amplitudes.2.3.3. Variable eccentricityAlso known as resonant-free vibrators, are the third generation, and they distinguishesthemselves through their ability to start up and stop without resonant vibrations. This isaccomplished by adjusting the eccentric moment on the fly, (read adjusting the displacementamplitude on the fly). These units are considered as the “state of the art equipment” in theapplication of the vibratory installation technique to drive piles. Their applications areadvantageous in densely populated areas or city centers and for the use on vibration-sensitivejobs: i.e. near old buildings and/or hospitals with sensitive equipment (computers)…2.3.4. Excavator mountedRefers to vibro-units that are typically quick and easy to connect to the excavator boom of abackhoe with a swivel connection after that the bucket is removed. The small excavatormounted vibro-units uses normally both the existing electric circuit and hydraulic system of thebackhoe. The excavator-mounted unit is used for small or remote jobs where a cost effectivemethod is needed to vibrate a few piles. They are also ideal for low height applications andwhere a long reach is required to vibrate sheets, beams or casings.69
Page 3: to the three above mentioned engine
Page 7 and 8: The magnitude of the penetration sp
Page 9 and 10: 2.6. Accessories and Driving AidesB
Page 11 and 12: not hold the pile correctly, a bend
Page 13 and 14: intuitively the direction and varia
Page 15 and 16: 5. Vibratory pile monitoringIf corr
Page 17 and 18: 5.5. Other instrumentationThe relat

THE VIBRATORY PILE INSTALLATION TECHNIQUE - Viking

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?