# Dynamic Characterization of Cohesive Material Based on Wave Velocity Measurements
## 4 Conclusions
It must be always kept in mind, that even when using the same identification method, reading points differed with the laboratory [22]. The scatter in the S-S method was definitely smaller in comparison to another method. Presented results show and confirm observations made by previous researchers [6; 22], acknowledging the status of the start-to-start method as the most prevalent and consistent method for the determination of travel time. With reference to the dependence of the dynamic behavior of clayey material on various factors, the following conclusions can be drawn:  
* The data show that the input signal frequency, in particular frequencies, which are below the level of \(T\) = 0.1 ms, does not significantly affect the stiffness values obtained by both adopted identification methods. The decrease in frequency results in greater dependence on frequency. * The best measurements of travel time for the tested soils were received at the frequencies of the input signal in the range of 50 to 20 kHz. In most of the considered cases, the greatest values of the dynamic parameters were obtained when the frequencies from this range were applied. * Mean effective stress has a visible influence on the seismic wave velocities and on the elastic modulus of the examined soils. * There are linear relationships between the mean effective stress and the small strain shear modulus and the small strain modulus of elasticity. * The compression waves propagate through the analyzed clayey material with far larger velocities than in the case of shear waves; at certain pressure levels, these velocities can be even up to 10-times larger. * The dynamic Poisson's ratio for the tested cohesive soils is almost constant, being approximately equal to 0.46. * The dynamic Poisson's ratio linearly increases with the decrease of the shear modulus. * Concerning the unloading process, it profitably affects the stiffness of silty clays. The dynamic properties rise in their values, from 8% to 16%, owing to unloading. Based on the results as described above, the standard procedure for the BE tests was proposed here in order to obtain appropriate test results in the present conditions. The authors discussed the important issue regarding the applied sciences, precisely the seismic research and dynamic response of porous material due to dynamic loads, such as earthquakes, traffic loads or machine vibrations. They attempted to characterize the dynamic properties of a fine-grained material, whose average porosity is approximately 0.44. This differs from the commonly-encountered in the literature dynamic characteristics of granular materials, non-cohesive soils, with a larger porosity value, described for example in [53; 54]. The authors used generally-applied laboratory tests in order to investigate a still new material, as well as to expand the knowledge of the interpretation of this new material's results. The acquired knowledge of the behavior of the tested material should be verified in the process of modeling, using an appropriate model, such as the one proposed in [55]. The discussion about the results obtained was carried out with the valuable support of [PERSON] (LNCMI--Laboratoire National des Champs Magnetiques Intenses, Toulouse, France). [PERSON] was the inventor of the research presented in this paper. [PERSON] and [PERSON] conducted the described research and also performed geotechnical laboratory studies. [PERSON] and [PERSON] prepared the manuscript. [PERSON] and [PERSON] performed the analysis of the tests results. [PERSON] consulted the research program and proofread the manuscript. The authors declare no conflict of interest.