We conducted hydrostatic experiments on a basalt specimen in both dry and saturated conditions. The investigated icelandic basalt is characterized by a bimodal porosity, i.e., cracks and equant pores. The elastic properties -bulk moduli in our case- were investigated under high pressure through two experimental methods: (1) a classical one using ultrasonic P- and S-waves velocities (frequency 106 Hz), (2) and a new one, using oscillation tests (frequency 10-2 Hz). In dry condition, experimental data show no significant difference between high (HF) and low (LF) frequency bulk moduli. However, in saturated conditions, two effects are highlighted : a physico-chemical effect evidenced by a difference between drained and dry moduli, and a squirt-flow effect evidenced by a difference between HF and LF undrained moduli. We try to predict such a frequency dispersion from a theoretical point of view. An effective medium with cracks and pores is used for calculating the HF bulk and shear moduli. The LF moduli are obtained by taking the HF dry moduli and substituting into Gassman's equations.


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