Research On Mechanism, Technology And Calculation For Constructing Roads On Very Soft Subsoil Using Large Scale Silt-Filled Geotubes

With the rapid development of economy in eastern area in China, there have been great demount for land. In Tianjin Binhai New Area and other coastal areas, large scale reclamation of land from sea water has been taking place. It has been known that one of the key technique for this kind of reclamation is to construct roads and dikes on very soft subsoil for hydraulic filling and soil improvement. This thesis present a technique using large scale silt-filled geotubes to construct roads and dikes on very soft subsoil by displacing consolidating the soft subsoils. The new technique is based on laboratory tests, mechanism analysis and finite element simulation, and proved to be efficient, quick and economical by engineering practice. The content and achievement of this thesis can be concluded as follows:(1) Based on the laboratory test results, it is found that the silt can be used as the material to fill the large scale geotubes to replace the coarse and middle size sands. This will bring about tremendous economic benefits to the places such as Tianjin Binhai New Area where the sand source is rare.(2) In combination with practical engineering, the structural configuration and construction technology are presented. The procedure for calculating the depth of displacement by the geotubes is put forward according to the soil mechanics theory and the caracteristics of very soft clay. The calculation method for estimating the consolidation degree and settlement of the subsoil of the road is studied based on the Barron's consolidation theory.(3) In order to calculate the tensile stress in the sheet of geotube, a interative procedure is established according to the force equilibrium conditions and geometry conditions, with which the filling pressure, tube hight and the tensile developed in the tube material can be related. This approach can be used to design both the fully inflated geotubes and the flat geotubes.(4) A practcal project is demonstated in Nanjiang Harbor, with which the details of construction process and construction controlling methods are studied to form the technical code for the purpose of expanding use of this technique.(5) A finite element model is established to simulate the procedure of using geotubes to construct road and dike on very soft clay, with which the stability of the road/dike, the pore water distribution and the consolidation displacement can be computed.