Using the improved true triaxial testing system SPAX-2000, the static and dynamic drainage consolidation tests on muck are carried out. And then the mechanical responses of muck are investigated at different impact loading frequencies of 1 Hz, 8 Hz and 16 Hz and different confining pressures of 200 kPa, 250 kPa and 300 kPa. With combining the triaxial shear tests, this paper studies the undrained strength development of muck under different consolidation conditions. The experimental results are drawn as follows. (1) At the same impact loading frequency, the shearing strength of the specimen continuously increases as confining pressure increases. The increasing confining pressure also can result in an increase in the spherical stress and the volumetric strain increase, effectively promoting the specimen drainage consolidation. (2) Under the same confining pressure, there is a threshold of impact loading frequency. When the frequency is lower than the threshold, with the increase of impact load frequency, the axial strain gradually tends to become smaller, and vice versa. (3) At the instant of the impact, the volumetric strain is negative and characterized by volumetric expansion. The development law of volumetric strain is in agreement with that of pore water pressure at tamping moment in a field test. The fact is confirmed that a negative growth in pore water pressure would occur as the muck with high water content is subjected to the impact.