| The pile-net composite foundation combines the advantages of horizontal reinforcement of cushion and bidirectional reinforcement of pile foundation,has the characteristics of good reinforcement effect,low construction cost and short construction period,and is widely used in the foundation treatment engineering of deep soft soil areas.At present,there are few experimental studies on settlement characteristics of pile-net composite foundation under different pile foundation layout and pile cap setting conditions.In this paper,the settlement characteristics of geography-cement mixing pile composite foundation are studied by means of indoor model test,numerical simulation and field monitoring.(1)Through the indoor model test of four kinds of reinforced materials in different pile foundation layout and pile cap Settings,the variation rules of parameters such as overall settlement of foundation,differential settlement of pile and soil,stress ratio of pile and soil,strain of reinforced materials and axial force of pile body were explored.The results show that the overall settlement of pile-net composite foundation and the differential settlement of pile-soil increase with the increase of loading time,and the settlement of the foundation edge is slightly larger than that of the middle part of the foundation.The stress ratio of pile-soil increases gradually with the loading process.The strain value of three-way geogrid is larger than that of two-way geogrid and one-way geogrid,and the strain value of three-way geogrid is smaller than that of three two-dimensional geogrid.The axial force of pile body increases first and then decreases from pile top to pile bottom,and the neutral point is close to the lower part of pile body.Under the same upper load,the geogrid,as the reinforced material of cushion,has a better control effect on settlement change than the three-way geogrid,bidirectional geogrid and unidirectional geogrid.The settlement control effect of pile foundation is slightly better than that of square layout.The setting of pile cap on pile top can effectively improve the bearing capacity of composite foundation.(2)Midas GTS finite element software was used to analyze and calculate the variation rules of various parameters during the 365-day loading period,and the specific influence rules of each parameter on the settlement characteristics of composite foundation were obtained through comparative analysis with the monitoring data of indoor model test.The results show that the variation rules of the parameters in the first stage within 7.3 days are basically consistent with the results of the indoor model test,which verifies the effectiveness of the indoor model test.Based on the analysis of the variation law of loading time in 365 days,it is found that the settlement of geographiccement mixing pile composite foundation increases steadily and becomes stable around 120 days after loading.Compared with the model test,the stress ratio of pile-soil increases first and decreases at the later stage of loading.Among the 2d plane reinforced materials,the tensile effect of three-way geogrid under the action of load is the most significant.The axial force of the pile body first increases and then decreases along the pile body downward,but the neutral point is closer to the top of the pile than the results of the indoor model test.(3)According to the results of model test and finite element analysis,the geography-cement mixing pile composite foundation method is adopted to treat the foundation of three test sections on site.The settlement monitoring data show that the post-construction settlement control effect of the geographic-cement mixing pile network composite foundation construction treatment method is good,which meets the settlement control requirements of the project and brings into play the significant engineering benefits. |
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