Study on consolidation state of silty soils in tidal flat of Yellow River estuary by in-situ test

The sediment of the Yellow River mouth rapidly deposits in the estuary area. Under the action of waves and tidal waves loading, 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 state and estimatie the pre-consolidation pressure of silty soils reasonably, in this paper a series of experiments were conducted on the tide flat of Diaokou delta-lobe. The fluid sediments imitating the rapidly deposited seabed silts were made in situ, and then promptly filled into a one-meter deep pit excavated at the tide flat. By the in-situ test methods such as static cone penetration test, field vane shear test and pore water pressure test, on the basis of long-term observation, the consolidation process and state of undisturbed soils of tidal flat and testing pit soils were studied in the range of 1.0m depth. It was shown that the consolidation speed of the rapidly deposited pit silty soils were very fast under the effective gravity stress, after consolidation compression was completed，the strength of such soils still increased unevenly with the development of time, presented a high-low-subhigh non-uniform consolidation characteristics along the depth. After 16 months, the pre-consolidation pressure of undisturbed soils and testing pit soils further increased, the characteristics of non-uniform consolidation and structure enhanced continuously. According to the actual consolidation state of testing pit soils after the self-weight compression consolidation was completed and the index of physical and mechanical properties of undisturbed soils, the results of Casagrande graphic method are too great, it is more reliable to estimate the pre-consolidation pressure of undisturbed soils and testing pit soils by static cone penetration test and field vane shear test. Meantime such in-situ testing methods provides a new way to determine the consolidation state of soils.