An Application of Resonant Column along with Bender Elements Tests for Assessing Dynamic Properties and Liquefaction Potential of Sand

Abstract

For determining the response of foundation soils subjected to different kinds of vibrations emerging from (i) an occurrence of an earthquake, (ii) movements of trains over railways tracks, (iii) running of vehicles over roads, and (iv) continuous running of different types of the vibratory machines such as turbines, generators, and reciprocating engines, it is essential to know the dynamic properties of soils at different levels of strains and stresses. The resonant column and bender element tests have been extensively used over past few decades by numerous researchers for evaluating the dynamic properties of soils in a strain range of 0.0001 % to 0.1 %. In the present thesis, the resonant column and the bender elements tests have been employed to determine the dynamic properties (namely, elastic moduli and damping ratio) of not only soils (sand) but even for metal specimens as well to check the applicability of the tests for very stiff specimens. With a provision of continuous excitations, it was also attempted to extend the usage of the resonant column apparatus to examine the liquefaction potential of a fully saturated sand specimen. In addition, an attempt has also been made to introduce an automated predominant frequency-based approach to predict very accurately the arrival times of the waves while interpreting the bender elements tests results. From the study of the received bender elements signals, it has been noted that, due to the presence of near field effects, it becomes a little difficult task to measure accurately the arrival point of the shear wave. The different available procedures in literature to mark the arrival times of the shear wave often require manual intervention and are often prone to errors. Therefore, it was aimed to develop an automated method to identify the time of the arrival of the shear wave. In the proposed method, the predominant frequency of the received signal was first evaluated and then, with the help of the sliding Fourier transform approach, the arrival time of the shear wave was identified. The main advantage of the proposed approach is that the method can be fully automated by following the algorithm which can be easily coded into a computer program, and it eliminates any manual judgement while determining the travel time. The proposed automated approach was applied to the bender element tests performed on dry and saturated sands by varying the input frequency of the signal, confining pressure, and void ratio. The results obtained from the proposed method were found to be very promising and were noted to be consistent with the data obtained on the basis of the resonant column tests