80 % of silts abundantly contained in the Yellow River water rapidly deposit at the River estuary. From previous investigation

it was found that the topsoils on the tide flat of Yellow River delta have been in a nonuniform consolidation state. In order to reveal the mechanism of aforementioned phenomena

a series of experiments were conducted on the tide flat of Diaokou delta-lobe which lies in the north of Yellow River delta. The fluid sediments imitating the rapidly deposited seabed silts were made in situ

and the fluid sediments were promptly filled into a one-meter deep pit excavated at the tide flat. By field-testing methods

such as static cone penetration test

field vane shear test and pore water piezometer test

the variation of strength and pore water pressure are measured at real time. It is shown from the testing data that the consolidation speed of the rapidly deposited seabed silts measured by water piezometer in situ is much quicker than the speed calculated through the Terzaghi’s one-dimensional consolidation theory. It is also shown that after consolidation compression had completed

the strength of such silts increased unequally along the depth continuously. Thus the rapidly deposited silts present a nonuniform consolidation state and a quasi-overconsolidated state

which is similar to undisturbed soils of the Yellow River estuary. Analyses show that the formation of such quasi-overconsolidated state and nonuniformity changes of strength along depth are attributable to the coupling effects of wave and tide loading and that long-term effect of wave loading which can cause the accumulation of excess pore water pressure within certain depth is the fully convincing evidence to form the crust layer of tide flat topsoil at the Yellow River estuary.