Wersäll, C., Massarsch, K. R. och Bodare, A. (2009)
Planering och Övervakning av
Sprängningsarbeten i Bebyggda
Områden. Bygg och Teknik, vol. 101 nr 1.
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SAMMANFATTNING
Infrastrukturprojekt i tätbebyggda områden kräver ofta omfattande sprängningsarbeten, där vibrationsnivåer många gånger styr hela projektets ekonomi och tidplan. Sprängning projekteras och utförs ofta med ledning av praktisk erfarenhet från tidigare projekt, men skulle kunna göras mer effektiv genom bättre förståelse av vågutbredningen i berg och jordlager. En annan viktig frågeställning är risken för skador, som kan uppstå vid dynamisk påverkan i byggnader eller undermarksanläggningar, såsom tunnlar. I många fall används riktvärden enligt svensk sprängstandard, som är framtagen för konventionella vibrationsproblem. Till skillnad från exempelvis tågtrafik eller anläggningsarbeten, har endast begränsade forskningsinsatser hittills ägnats åt sprängningsproblematiken. I artikeln redovisas nya kunskaper om vågutbredningen och dynamisk samverkan mellan sprängningsinducerade vibrationer och tunnlar i berg. Detta kan utnyttjas för säkrare och kostnadseffektiv sprängning i tätbebyggda områden.

Massarsch, K. R. and Fellenius, B. H. (2008)
Ground Vibrations induced by Impact Pile Driving. Keynote Lecture, International Conference on Case Histories in Geotechnical Engineering. Arlington, 2008.
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ABSTRACT
The importance of vibration problems induced by pile driving is addressed and guidelines for establishing limiting vibration levels with respect to buildings with different foundation conditions are presented. Basic concepts of pile dynamics and stress wave measurements, which are widely used for the determination of driving resistance and bearing capacity of impact-driven piles, provide important information about ground vibration caused by pile penetration. Dynamic hammer properties and geometry as well as the driving process are important for ground vibration emission from the pile. It is shown that the energy-based, empirical approach, which is still widely used by practicing engineers, is too crude for reliable analysis of ground vibrations and can even be misleading. The main limitations of the energy approach are the assumption that driving energy governs ground vibrations, the omission of geotechnical conditions and soil resistance, and the uncertainty with regard to input values.

Three types of ground waves are considered during pile driving: spherical waves emitted from the pile toe, cylindrical waves propagating laterally from the pile shaft, and surface waves, which are generated by wave refraction at the ground surface at a critical distance from the pile. These three wave types depend on the velocity-dependent soil resistance. The most important factor for analyzing ground vibrations is the impedance of each system component, i.e., the pile hammer, the pile, and the soil along the shaft and at the pile toe. Guidance based on geotechnical conditions is given as to the selection of appropriate impedance values for different soil types.

A theoretical concept is presented, based on a simplified model, considering the strain-softening effect on wave velocity in the soil, which makes it possible to predict the attenuation of spherical and surface waves and of cylindrical waves generated at the pile toe and the pile shaft, respectively. The concept is applied to define k-values, which have been used in empirically eveloped models and correlated to type of wave and soil properties.

An important aspect of the proposed prediction model is the introduction of the vibration transmission efficacy, a factor which limits the amount of vibration force that can be transmitted along the pile-soil interface (toe and shaft). Results from detailed vibration measurements are compared to values calculated from the proposed model. The comparison is very good and suggests that the new model captures the important aspects of ground vibration during penetration of the pile into different soil layers. Finally, based on the presented model, factors influencing the emission of ground vibrations during impact pile driving are discussed.