Vibratory Pile Research Articles

Mathematical model for vibratory pile driving : Dicker, D Proc 5th Engineering Mechanics Division Speciality Conference, Wyoming, 1–3 Aug 1984P305–307. Publ New York: ASCE, 1984

Mathematical model for vibratory pile driving : Dicker, D Proc 5th Engineering Mechanics Division Speciality Conference, Wyoming, 1–3 Aug 1984P305–307. Publ New York: ASCE, 1984

A study of vibratory driving in granular soils

Two types of vibratory pile driving have been identified by the Authors termed respectively ‘slow’ and ‘fast’ vibrodriving. The occurrence of slow or fast motion is determined by the initial soil density, pile diameter, displacement amplitude and acceleration of vibration. Slow vibrodriving is concluded to be the most widely encountered and the paper, therefore, concentrates on this type of motion. A theory and interactive computer simulation of the case of slow vibratory driving has been developed. The motion is considered to be that of a rigid body subject to viscous—Coulomb side and elasto—plastic end resistance under a combined sinusoidal excitation and static surcharge force. Experimental verification of the theory has been by means of tests on a fully instrumented 0·745 kW (1 hp) model in dry cohesionless soils. The need for further research work to quantify soil resistance and the dependence of this on displacement amplitude and frequency of vibration is stressed. The Authors recommend that this information is obtained from full scale tests using a prototype designed on the basis of the information provided by the present research work. Deux types de battage de pieux vibratoire ont été identifiés par les auteurs et désignés respectivement par vibrobattage ‘lent’ et vibrobattage ‘rapide’. La ‘lenteur’ ou la ‘rapidité’ du mouvement est déterminée par la densité initiale du sol, le diamètre du pieu, l'amplitude du déplacement et l'accélération des vibrations. Selon les conclusions, le type de vibrobattage ‘lent’ est celui qui se rencontre le plus fréquemment et l'article se concentre donc sur ce type de mouvement. Une théorie et une simulation interactive sur ordinateur du cas du vibrobattage ‘lent’ ont été mises au point. Le mouvement est envisagé comme étant celui d'un corps rigide soumis à une résistance visqueuse, type Coulomb et extrémité élastoplastique, sous l'action simultanée d'une surcharge statique et d'une excitation sinusoïdale. La théorie a été vérifiée expérimentalement par des essais sur un modèle 0·745 kW (1 HP) à instrumentation complète dans des sols secs sans cohésion. L'article insiste sur la nécessité d'effectuer des recherches supplémentaires pour quantifier la résistance du sol et sa dépendance avec l'amplitude du déplacement et la frequence de vibrations. Pour obtenir ces renseignements, les auteurs recommandent d'effectuer des essais a l'échelle à l'aide d'un prototype réalisé sur la base des renseignements obtenus à partir des travaux de recherches actuels.

Pile driver noise control—costs and benefits

The results of a Construction Engineering Research Laboratory project sponsored by EPA's Office of Noise Abatement and Control is reported here. The costs for feasible pile driver noise control methods were investigated. Noise control methods studied were: (1) substitution of a vibratory pile driver, (2) substitution of a pneumatic cushioned unit (Chelminski), and (3) silencing of a standard unit. Average costs for substituted units are as much as 110% higher than the cost of standard units, while the cost for a retrofitted silenced unit increases only 20%. Maximum pile driver sound levels are reduced about 29 dB by use of the substitute unit, and about 18 dB using a retrofitted silenced unit. The reduction in construction site one-hour equivalent sound level Leq (1), for either a substitute unit, or the retrofitted unit is only 11 dB. Thus, if only pile driver noise control is being considered, outfitting a standard unit with a well-designed muffler and enclosure is the most cost-beneficial approach for construction site noise reduction. A cost-benefit demonstration is to take place at a Corps of Engineers flood control project in Iowa. The resulting field data will be presented, if available.

Vibrations Associated with Pile Driving

The developed prediction equation relating peak particle velocity and scaled energy can be used to predict expected maximum levels of vibrations from pile driving. Peak particle velocity can be utilized as a criterion for safe levels of vibration. Vibration levels can be reduced by various means such as pre-coring, or selection of low-displacement piles. However, reducing transmitted vibrations by reducing hammer energy may be an unwise solution. Increasing pile impedance may be a more judicious means of reducing pile driving vibrations. Finally, the effects of pile driving vibrations in densifying cohesionless soils may be more significant to adjacent structures than any vibrations transmitted directly to those structures; unfortunately such soils also favor the use of vibratory pile drivers and extractors.

Vibroflotation and Terra-Probe Comparison

The most widely used techniques for deep vibratory compaction of cohesionless soils are Vibroflotation and Terra-Probe. The Vibroflotation process consists of penetrating the soil with a horizontally vibrating probe and simultaneously saturating and vibrating the soil as the probe is extracted. The Terra-Probe process consists of driving and retracting a 30-in.(760-mm) diam open-ended steel pipe with vertical vibrations induced by a vibratory pile driver. Three test patterns with different probe spacings were compacted with 100-hp Vibroflot probes and three test patterns were compacted by Terra-Probe. Each test pattern was compacted to a depth of 35 ft (11m). Static cone penetration tests and standard penetration tests were conducted in each test pattern before and after compaction. The average change in relative density within each test pattern was obtained by measuring the volume of sand added and the subsidence of the ground surface. The test results indicate that Vibroflotation compacted a greater volume of soil per probe penetration than Terra-Probe, the latter, however, working faster.

New Method for Deep Sand Vibratory Compaction

Densification of saturated cohesionless soils is now feasible by using a vibratory pile driving device and a tubular probe suspended from a crane boom and by driving and extracting the probe material on certain modular spacings to achieve a required density. Preprobe and post-probe soil explorations using the Standard Penetration Test can verify the results. The method is a fast and economical means of compaction having applications also in land reclamation and some liquefaction situations. It can also be used in subaqueous compaction. The parameters of this method’s soil range and its full penetration depth effectiveness have not yet been fully determined.

Densification of Sand for Drydock by Terra-Probe

Sand fill placed through 70 ft (21.3 m) of water to a depth of 35 ft (10.7 m) was densified for support of the walls and floor of a large fully relieved drydock by the use of the Foster Terra-Probe method vibratory pile driver and probe. The operation was, in general, successful. Compaction varied with probing patterns, depth of fill, proximity of original bottom, entrapped silt, and other factors. Control was by the Standard Penetration Test. About 60 borings were made to check compliance with specifications which required an unusually high degree of densification. The paper documents the compaction operation and considers the various factors influencing the results. Initial settlement of the structure is noted as minor. It is concluded that the method is effective provided its limitations are recognized.