Dynamic Response Of Pile Research Articles

Full-scale field studies of the dynamic response of piles embedded in partially frozen soils

The influence of a frozen soil layer on the dynamic response of full-scale concrete piles subjected to strong horizontal excitation was studied. The study undertaken compares the field observations against the theoretical predictions and provides an insight into the role of the yielded zone (boundary zone) in theoretically matching the field observations. The field measurements are used to postulate empirical relationships that can be used under practical conditions to estimate the magnitude of soil separation around piles embedded in cohesive soils as a function of the maximum vibration amplitude. The tests performed indicate that the presence of a frozen soil layer, even at a modest thickness of less than 0.5 m, can significantly influence the dynamic response of piles; the horizontal stiffness of the pile was increased by one order of magnitude, and its resonant frequency was increased by a factor of four compared to the situation with no frozen soil layer. The qualitative and quantitative findings from this study are considered to have practical applications in the design of piles under similar conditions as well as in providing a field validation of the theoretical solutions that have been developed for analyzing the dynamic response of piles. Key words: dynamics, vibration, piles, full-scale tests, frozen soil, modelling, resonance, soil separation, soil yielding.

Measured Lateral Response of Mass on Single Pile in Clay

The results of dynamic lateral load tests on a cantilevered mass supported by a single 10.75‐in. (273‐mm) diameter steel pipe pile embedded in stiff, overconsolidated clay are presented. These tests were conducted to provide a basis for evaluation of mathematical models that predict the relatively low‐frequency dynamic pile response that is representative of systems in which the primary resonance frequency is controlled by the mass and stiffness of the superstructure. Frequency sweep shear forcing functions were applied at the top of the mass, which simulated a simple structure. The responses of the pilesupported mass, points on the embedded pile, and points in the supporting soil were recorded to determine frequency response functions. Frequency response functions between the applied load and pile cap‐mass were then examined to aid in the identification of the pile‐soil system parameters which most strongly influence response. The measured pile cap frequency response function peak amplitude was 0.0022 in./lb (0.0126 mm/N), or about ten times the static flexibility, and the resonance frequency was approximately 2.2 Hz.

Nonlinear Lateral Dynamic Stiffness of Piles

The effect of nonlinear soil behavior (without slippage of gapping) on the dynamic response of piles subjected to lateral loads is explored, using a finite element model for the soil region adjoining the pile, a consistent boundary matrix at some distance to reproduce radiation effects, and an iterative, equivalent linearization technique to estimate the variation of soil properties with level of strain. Results obtained with this procedure are compared with those that would result from application of the p-y curves and the differences are discussed. (ASCE)