## 3 Test Arrangement and Procedure  
During the preparation stages, the soil samples were trimmed to produce cylindrical specimens with a final diameter of 70 mm. The height of the specimens, either 140 or 100 mm, was chosen considering the estimated effective stresses in situ and the consistency of the samples. For softer soil samples from shallower depths, problems were encountered with the performance of the mini oscillators at the lowest effective stress, particularly during oscillation with small shear stresses. To remedy this, the specimen height was adjusted to 100 mm to increase the resonant frequency and address the issues with the mini oscillators, following an approach similar to that of [PERSON] and [PERSON] [55]. The effect of specimen height on the measured \(G\) was tested in advance to confirm the validity of the results on specimens with a lower height to diameter ratio. Before and after testing, specimens were measured and weighed to determine water content and density [56; 57]. Throughout the test, the vertical displacements of the specimen were measured using an internal transducer. The specimen volume was determined considering the final volume and the corresponding volume change during each consolidation stage. The specimen diameter was calculated assuming a perfect cylindrical shape, with constant radial strains over the entire height. After inserting the specimen into the RC device, a low isotropic effective stress was applied, and the soil was saturated by increasing the back pressure. After the saturation stage, the vertical displacements were measured. Figure 4: An example of the frequency response curve. Each specimen was subjected to at least four consolidation stages, including isotropic and anisotropic conditions. In the first consolidation stage, an isotropic consolidation was performed in which the effective stress was set close to the horizontal stress under field conditions. The estimated coefficient of lateral earth pressure at rest \(K_{0}\) was approximately 0.5 for all samples; therefore, to simplify the procedures, the value 0.5 was used for all tests. In the second consolidation phase, an isotropic consolidation was performed with an effective stress corresponding to the stress \(p^{\prime}\) under field conditions. In the third consolidation stage, anisotropic consolidation was carried out with an effective vertical stress corresponding to the field conditions and a horizontal stress set at 0.5 times the effective vertical stress. In the fourth consolidation stage, a further isotropic consolidation was performed with an effective stress corresponding to the effective vertical stress under field conditions. To investigate the effect of the stress state on the stiffness at small strains, some specimens were subjected to additional isotropic consolidation stages with stresses 2 or 4 times higher than the fourth consolidation stage. After each consolidation stage, both BE and RC tests were performed. The BE test was repeated three times with different frequencies of the transmitter (input signal) (black line in Figure 1). For each BE test, the transit time was determined, and then the shear modulus was calculated. The final result was calculated from the average of the three measurements. After the BE test, an RC test was carried out under undrained conditions. The excess pore water pressure \(\Delta u\) during the vibrations was measured using a pore pressure transducer. Unfortunately, BE tests could not be performed on all soil samples due to equipment problems. In the cases labelled RCBE in Table 2, both BE and RC tests were performed. In cases when only the RC test was performed, the sample is labelled RC.