Wuhan-guangzhou Passenger Line Pile - Net Composite Foundation Of Internal Forces And Deformation Monitoring And Finite Element Analysis

The pile-net composite foundation is an effective method to improve and strengthen weak foundation of soft soil, which bear the loads through the interaction among the piles, the geo-grid, the cushion layer. When high-speed railway is built on soft soil foundation, the pile-net composite foundation can solve the two technology difficulties effectively, which is the residual settlement control and Stability of embankment.On the basis of somebody else have worked, methods such as testing in laboratory and in the field, theory analysis, numerical simulation, etc. were used to study the working performance and strengthened effects of the pile-net composite foundation by theory discussion and practice analysis, which was applied in the special railway line for passenger transport. The main achievement and conclusion are as follows:(1) according to the on-the-spot geological condition and the design scheme, the monitor section was choosed rationally and the scientific monitoring scheme was made to monitor in an all-round way the development laws of the foundation settlement, section settlement, horizontal displacement, soil pressure and pile-soil stress ratio, stress on the pile, geo-grid strain, etc. in the pile-net composite foundation.(2) After analyzing the 3 monitor sections on-the-spot, which the periods of building and press in advance last for 216 days and the whole building height was 6.2 meters, the results were as follows:①The settlement of the foundation increased as the height of the building at the same time. It basically kept steady after been pressed in advance for 152 days. And the measured biggest settlement of the foundation varied between 12.92 millimeters and 13.79 millimeters.②The horizontal displacement decreased as the depth increased, and the measured horizontal displacement varied between 29 millimeters and 74.8 millimeters. The biggest horizontal displacement appeared at the depth between 1.5 meters and 2 meters. It was showed that there was no horizontal displacement at the depth of 10 meters and the deeper place was the same. ③The pile-soil stress ratio increased as the height of the building at the same time, which varied from 1.6 to 5.4. After the embankment were finished, the pile-soil stress ratio tends towards stability gradually, which varied from 4.4 to 6.2.The results above have proved that the pile-net composite foundation is effective in controlling the settlement.(3) Based on the principle of replacement rate of equivalent area, the treatment of plane strain was applied to turn the piles into the limitless long wall along the longitudinal line.The interaction of contact between piles, geo-grid and soils was simulated by interface unit without thickness. And the finite element software for rock and soil engineering was applied to simulate the pile-net composite foundation.(4) After compared the monitor results on-the-spot with the results of finite element calculation, it showed that the vary law of numerical simulation was the same as the measurement results, which were the foundation settlement, horizontal displacement, pile-soil stress ratio, stress on the pile, geo-grid force, etc. So the rationality of the model was verified.(5) Take the finite element model above, and change the parameter for thickness and the elastic modulus of the cushion layer, elastic modulus of the soils between piles, interval among piles. The influence law and influence degrees to the settlement in the pile-net composite foundation, the pile-soil stress ratio, axle stress on piles and geo-grid force was analyzed with the factors above.