Monitoring And Numerical Analysis Of Composite Pile-net Foundation For High-speed Railway

The methods of geogrid reinforced and CFG pile-supported foudation is a new techniquefor foundation treatment developed in recent years. It is the first time to be applied inhigh-speed railway whose design speed is350km/h. It consists of rigid piles, geogrids,cushion and soft soil foundation. The unity of pile, geogrid and soil bear the load together,Because of the soil arching effect, tensioned membrane effect and stress concentration. Thecomposite foundation can not only restrict the side deformation of soft soil, but also give fullplay to the strength an the deformation properties of the soil, in order to effectively improvethe strength of the soft soil foundation, reduce settlement of the soft foundation afterreinforcement, short construction period and lower construction costs.In this paper, based on the test section of a high-speed railway line, experimentalanalysis and numerical simulation were used to study the action mechanism, the deformationrules and the stress distribution rules of the pile-net composite foundation. The main contentsand results are as follows:(1) The previous methods dealing with pile-net composite foundation are outlined. Thecomposition and mechanism of the pile-net composite foundation are summed up.(2)The influencing factor were elicited by the derivation of pile-soil stress ratio. It isincluded of the filling height of the embankment, the angle of internal friction, the pilediameter, the pile spacing, pile-soil different settlement, and so on. In paper, based on the testsection of a high-speed railway line, the variation of pile-soil stress ratio as the change of thefilling height of the embankment, the angle of internal friction, the pile diameter, the pilespacing, pile-soil different settlement were studied.(3) The settlement and the speed of the soft foundation after reinforcement werecalculated by analyzing the field test monitoring and settlement data. The value of settlementis27.34mm. The value of speed is1.9cm/year.It is fully meet the requirements of thesettlement of the soft foundation after reinforcement for high-speed railway. It is verified thatthe composite foundation can not only short construction period, but also reduce settlement ofthe soft foundation after reinforcement. So, this pile-net composite foundation has the valueof promotion.(4)The pile-net composite foundation deformation rules and stress distribution rules ofMohr-Coulomb model were studied using the numerical simulation software. Studies haveshown that: the Reinforced cushion reduced the level of stress and deformation to protect thepile and homogenized vertical stress to reduce the diffeiental settlement. The unity of pile,geogrid and soil bear the load together.