A new exploratory procedure for collecting continuous shear wave velocity measurements via cone penetration testing using a special autoseis source is presented whereby wavelets can be generated and recorded every 1 to 10 s. The continuous-interval seismic piezocone test (CiSCPTu) offers a fast, productive, and reliable means to expedite the collection of downhole shear wave velocity profiles, as well as additional readings on cone tip resistance, sleeve friction, and penetration porewater pressures with depth. A site in Windsor, Virginia, is utilized for illustrating the collection of data, calibration, and post-processing issues arising from large numbers of wavelets that require filtering, windowing, and selection in both time and frequency domain analyses. At the test site, the geology consists of shallow Holocene deposits of clays and sands to 8 m that are underlain by much stiffer calcareous sandy marine clay soils of Miocene age, which extend beyond the termination depths of the soundings at 30 m.Résumé : Cet article présente une nouvelle procédure exploratoire servant à récolter des mesures de vitesse des ondes de cisaillement en continu à l'aide d'essais de pénétration du cône faits avec une source sismique spéciale. Cette procédure permet de générer et enregistrer les ondelettes toutes les 1 à 10 s. L'essai sismique à intervalle continu au piézocône (EPCic) offre une méthode rapide, productive et fiable pour récolter les données de profils de vitesse des ondes de cisaillement de trous de forage, ainsi que des données additionnelles sur la résistance de la pointe du cône, la friction de l'enveloppe et les pressions interstitielles de pénétration avec la profondeur. Un site à Windsor, Virginie, est utilisé pour démontrer les problématiques associées à la collecte de données, au calibrage et traitement des données, lorsqu'un grand nombre d'ondelette nécessitent du filtrage, du fenêtrage, et la sélection dans les domaines d'analyses de temps et de fréquence. La géologie du site d'essai consiste en des dépôts peu profonds d'argiles et de sables de l'Holocène jusqu'à 8 m, déposés sur des sols d'argile marine de calcaire beaucoup plus rigides datant du Miocène qui s'étendent au-delà des profondeurs terminales des environs à 30 m. [Traduit par la Rédaction] Mots-clés : pénétration du cône, essai dans les trous de forage, géophysique, essais in-situ, ondes sismiques, vitesse des ondes de cisaillement.
The Osterberg cell (O-cell) type of bidirectional pile load testing is a modern full-scale proofing method in the realm of performance-based pile design. It is done at considerable cost, not possible on small- to medium-size projects. An economical approach of utilizing the flexible and approximate analytical solution proposed by Randolph has frequently been adopted in the past for evaluating pile settlements under static, unidirectional, top-down axial compression loading. To extend this solution for O-cell loadings, the following adaptations are warranted: (i) appropriate modifications to handle the loadings in two directions and (ii) development of a nonlinear stiffness reduction model, derived from the back-analysis of O-cell pile load tests. Accordingly, a modified analytical solution is presented for the two common cases of O-cell loading arrangements. Using these modified sets of solutions and a well-documented database of O-cell load tests on drilled shaft foundations from different sites, two stiffness reduction models have been developed. The shear wave velocity readings obtained from the hybrid geophysical–geotechnical seismic piezocone tests afford the evaluation of fundamental shear stiffness modulus (Gmax) profiles. These profiles together with the re-arranged modified solution were applied to the axial loads versus displacements (Q–w) from the database of load tests to back-calculate the applicable operational shear stiffness (G) values. Additional sensitivity analyses indicate that pile geometry and soil stiffness profile are the two most significant factors affecting the outcome of this solution. A comprehensive set of step-by-step example calculations is included to explain the procedure for implementing the solution.
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