Vibratory driving is today the most common installation method of sheet piles. The knowledge of the induced ground vibrations is however still deficient. This makes predictions of the vibration magnitudes difficult to carry out with good reliability.
To avoid exceeding the limit values, resulting in stops of production, or that vibratory driven sheet piles are discarded for more costly solutions, a need for increased knowledge of the vibration process is imminent. With increased knowledge, a more reliable and practical prediction model can be developed.
The aim of this study is to analyze measured data from a field study to increase the understanding of the induced vibrations and their propagation through the soil. The field study was performed in Karlstad in May 2010, where a trial sheet piling prior to an extension of Karlstad Theatre was carried out.
During the trial sheet piling, two triaxial geophones were mounted at the ground surface at two different distances from the sheet piles, to measure the vibration amplitude. The field test is associated with some limitations. Only four sheet piles were driven, with one measurement per sheet pile. Some measurements were less successful and some parameters had to be assumed. This limits the accuracy but still provides some interesting results.
Another aim is to compare the measured values to existing models for predicting vibrations from piling and sheet piling operations. There are today several prediction models available, which however often provide too crude estimations or alternatively are too advanced to be incorporated in practical use. Two basic empirical prediction models are compared to the measured values in Karlstad, where the first is one of the earliest and most well known models and the other is a later development of the first model.
The purpose of this comparison is to evaluate these models to contribute to the development of a new prediction model. The results show that the earlier model greatly overestimates the vibration magnitude while the later developed model provides a better estimation.
A literature study is performed to gain a theoretical background to the problem of ground vibrations and how they are related to the method of vibratory driving of sheet piles. The analysis considering the field study and prediction models is mainly performed by using MATLAB to obtain different graphical presentations of the vibration signals.
The conclusions that can be drawn from the results are that the focus of vibration analysis should not always be the vertical vibration components. Horizontal movements of the sheet pile might be introduced, e.g. by the configuration of the clamping device, which generates additional vibrations in horizontal directions. The soil characteristics influence the magnitude of the vibrations. As the sheet pile reaches a stiffer soil layer, the vibration magnitude increases. A realistic and reliable prediction model should take the characteristics of the soil into account.
Author: Lidén, Märta