# Dynamic Properties of Calcareous Sands from Urban Areas of Abu Dhabi
## 3 Experimental Program and Methodology  
Four (4) cylindrical undisturbed sand specimens (10 by 20 cm) were collected from boreholes advanced at different locations of the capital city (Abu Dhabi). The specimens were also collected from different depths of the boreholes. Routine geotechnical tests such as moisture content, index densities, and gradation analysis were also conducted. Table 1 presents important properties of the materials representing the specimens. The specimens were extruded after splitting the tubes in halves and were then placed on the bottom plate. A rubber membrane was installed and a vacuum applied after attaching the top plate and O-rings. The specimen was allowed to consolidate in drained conditions before conducting dynamic testing. All tests were performed with cyclic triaxial (CT) equipment provided by VJ Tech (UK), following the ASTM standard (ASTM D3999-91, [20]). The bottom and top platens of the CT were fitted with bender elements (BE) of maximum input frequency of 10 kHz for low strain evaluation of Vs. Each specimen was tested at different effective confining pressures and in consolidated drained conditions. At each confinement, BE measurements were performed at an input frequency of 5 kHz due to better response at this frequency. At least 10 signals were stacked to enhance the signal-to-noise ratio. The measurements were repeated by inverting the polarity for better detection of shear wave arrivals. The Vs was finally calculated from the ratio of distance between the elements and the time interval between the trigger and first arrival. Figure 1 presents the typical time histories of the signals recorded at the receiver (Rx). Typical Fourier spectra were also presented for the analysis of wavelength-to-specimen size ratios (e.g., [PERSON] et al. [6]; [PERSON] et al. [19]). The energy of the propagating pulse was concentrated between 3 and 6 kHz, as shown in Figure 1b. The calculated wavelengths ranged from 3 to 10 cm, which ensured the presence of at least one wavelength within the distance (20 cm) between the transmitter and receiver to avoid near field effects (e.g., [PERSON] [21]; [PERSON] [22]). BE measurements were taken at seven confinements of 30, 40, 60, 80, 100, 120, 140 kPa. Figure 2 presents the typical receiver signals for some of the confinements. CT testing was performed at 40, 100 and 140 kPa in displacement (stroke) control mode. The displacement was increased incrementally to measure the dynamic properties at different strain levels. An input signal of 1 Hz with 10 cycles was used in all tests to obtain raw hysteresis loops. The time signals of load and displacement were fitted with a simulated signal to generate symmetrical loops for further analysis (e.g., [PERSON] et al. [23]). Figure 3a,b presents the measured and fitted signals for typical cyclic triaxial data. Figure 3c presents the comparison of hysteretic loops from measured and fitted signals. The load and displacement amplitudes in Figure 3a,b are normalized for clarity. The dynamic properties as a function of shear strain levels were then fitted with hyperbolic model presented in Equation (1).