# Dynamic Characterization of Cohesive Material Based on Wave Velocity Measurements
## 1 Introduction
The first person to use piezoceramic elements bonded to shear plates was probably [PERSON] [13; 14]. His idea was to measure the velocity of the shear wave in materials, such as clay and sand. In 1978, [PERSON] [15] proposed the introduction of piezoceramic bender elements to determine S-wave velocity in the laboratory. Other scientists, like [PERSON] and [PERSON] [16], described the incorporation of BE for geotechnical laboratory testing in the 1980s. The appeal of the BE technique lies in its apparent simplicity: one of the transducers is excited at one end of a specimen by a single pulse excitation, and the second, located at the other end of a specimen, is receiving it. The time required for this process can be simply read off from an oscilloscope. On the basis of this value, shear wave velocity can be obtained [17]. Therefore, BEs are an inexpensive and versatile solution, which can be used for laboratory seismic measurement. Furthermore, their capabilities of monitoring the process of stiffening with effective stresses, namely cementation, load stabilization, curing or consolidation, are particularly appealing [18]. However, there is a critical drawback connected with a BE test that contributes to many errors, namely the determination of the travel time. A number of researchers, including [PERSON] and [PERSON] (1995), attempted to use various methods in order to find the arrival time in order to reduce the degree of subjectivity [19]. In 2005, [PERSON] and [PERSON] [20], as well as [PERSON] _et al._[21] reported a method of travel time determination, by performing a bender element test. Nevertheless, there are still some differences between the first arrival of the S-wave and the preferred input wave. Therefore, the BE technique still needs to be verified with respect to how reliable it is, when it comes to calculation of the arrival time [2; 22]. The intention of the authors of this paper was to recognize the dynamic characteristics of the cohesive medium through the performance of the BE tests on this material, _i.e.,_ clayey soil, obtained from the area of Warsaw, the capital of Poland, at various effective confining pressures under saturated conditions. Two methods, namely peak-to-peak and start-to-start, were used to determine the travel time using the BE technique. The \(\upsilon_{S}\) was calculated on this basis. Subsequently, shear modulus (\(G\)) was obtained using the value of shear wave velocity. Additionally, the authors used piezoceramic elements to determine compression wave velocity (\(\upsilon_{P}\)). Furthermore, they tried to evaluate the values of dynamic Poisson's ratio (\(\
u_{d}\)). The dynamic Poisson's ratio of soil deposits is a matter that has attracted rather little attention so far [23]. Nevertheless, it significantly affects stresses, strains, wave propagation characteristics in a mass of soils and other important types of soil deposit behavior during dynamic excitation [4]. In this paper, \(\upsilon_{d}\) was calculated from the results of measurements of longitudinal and shear wave velocities in seismic exploration and then used to establish [PERSON]'s modulus (\(E\)). The authors also studied the possible impact of unloading on the received values of elastic modulus.