Consolidation states of silty soils in tidal flats of Yellow River estuary by in-situ testing

The sediments in the Yellow River estuary rapidly deposit in the estuarine area. Under the action of waves and tidal waves, the surface sediments are in an over-consolidated state. However, it is found that the pre-consolidation pressure of silty soils in the Yellow River estuary calculated by the Casagrande graphic method is usually too high. In order to find out the consolidation states and estimate the pre-consolidation pressure of silty soils reasonably, a series of tests are conducted on the tide flat of Diaokou delta lobe. The fluid sediments imitating the rapidly deposited seabed silts are made in situ, and then promptly filled into a one-meter deep pit excavated at the tide flat. Through the in-situ testing methods such as the static cone penetration tests, field vane shear tests and pore water pressure tests, on the basis of long-term observation, the consolidation processes and states of the undisturbed soils of the tidal flat and testing pit soils are studied in the range of 1.0 m in depth. It is shown that the consolidation speed of the rapidly deposited pit silty soils are very fast under the effective gravity stress, after consolidation compression is completed, the strength of such soils still increase unevenly with the development of time, exhibiting high-low-subhigh non-uniform consolidation characteristics along the depth. After 16 months, the pre-consolidation pressures of the undisturbed soils and testing pit soils further increase, the characteristics of non-uniform consolidation and structure are enhanced continuously. According to the actual consolidation states of the testing pit soils after the self-weight compression consolidation is completed and the indexes of physical and mechanical properties of the undisturbed soils, the results of the Casagrande graphic method are too great, so it is more reliable to estimate the pre-consolidation pressures of the undisturbed soils and testing pit soils by using the static cone penetration tests and field vane shear tests. Meantime such in-situ testing methods provide a new way to determine the consolidation states of soils.