Abstract:A set of comprehensive rock test s , including unjacketed hydrostatic compression test of rock , measure2 ment of elastic wave velocities under confining pressure and pore pressure , and the decane modulus determination , are performed. The effective modulus of composite medium can be calculated by effective medium theory , such as RVH , Hashin2Sht rikman bounds , and self2consistent approximation. The static Biot coefficient is larger than the dynamic one. They are all related to porosity and decrease with the confining pressure. A Biot′s coefficient model is built .