Study On Consolidation Deformation Properties And Stability Of Silt Roadbed In Seaside Areas

Silt soft clay is widely distributed in littoral expressway foundation. Its consolidation is a popular geotechnical engineering issue. Many roadbed settlement observation tests are carried out to provide valuable data for littoral expressway design and construction. Seaside silt is always under seasonal wave and tide. Coffer dams and back berms are often built in the two sides of a roadbed for convenient construction, resulting in obstructing wave but letting tide come into the top of the silt roadbed through drainage layer, which made great influence on the consolidation process. In our research abundant indoor and outdoor tests were used to thoroughly study the consolidation deformation properties and stability of the seaside silt roadbed.Firstly, the engineering characteristic of the seaside silt taken from Xiamen Haichang was evaluated. The relation between physics and mechanics indexes was analyzed. And many in-situ tests were applied to study the properties of seaside silt. From the comparison of the flat dilatometer test (DMT) and several other in-situ tests, a conclusion can be drawn that the DMT is very suitable for test parameter measurement of seaside silt. Then a method to predict settlement after construction was developed.Secondly, based on large amounts of field observation data, the relation between the thickness of silt, the height of load, the loading methods and the roadbed settlement was discussed in detail. And the influences of coffer dam, tide and precipitation on the consolidation process were studied. An instant settlement formulation of seaside silt was established. The treatment result of surcharge preloading was evaluated.Thirdly, the finite element method model of plain strain sand-wall roadbed was put forward, in which the effect of back berms and tide was considered. The horizontal permeation coefficient of sand-drain roadbed was calculated from the field measurement data and the correspond horizontal permeation coefficient of sand-wall roadbed was ascertained. The calculation result showed that the effect of tide and back berms on the consolidation process is obvious.Finally, the distribution and increasing rule of strength of seaside silt in consolidation process were researched. The relation between the strength and depth is linear before and after consolidation. The strength-increasing rate was different in different horizontal places. The embankment stability and slip surface location is studied. At last the loading rate norm was established.