| Our country has a vast land and soft soil from various sources.The biggest characteristics of this kind of soft soil are high water content,large pore ratio,low shear strength,high compressibility,low permeability,long-term settlement.In recent years,more and more highway construction,some projects have to pass through soft soil areas.Soft foundation treatment has become one of the key factors affecting the quality of expressway construction projects.Composite foundation,which can give full play to the advantages of pile-soil bearing capacity,has been widely used in the treatment of soft foundation,and has become a common way of expressway soft foundation treatment.As a new type of composite foundation,composite foundation bidirectionally reinforced by geocell and stone columns has been gradually applied in practical engineering,but its calculation theory lags behind engineering practice,especially the research under traffic load is still less.Due to the lack of in-depth research on the action mechanism of bidirectional reinforcement composite foundation under traffic load,it is easy to cause the deviation in the understanding of bearing mechanism of composite foundation and the error in settlement calculation or prediction.Therefore,it is necessary to conduct a systematic and in-depth study on the load-bearing deformation mechanism of bidirectional reinforced composite foundation under traffic load.Therefore,with the support of the General project of National Natural Science Foundation of China,this paper takes composite foundation bidirectionally reinforced by geocell and stone columns as the research object,and combines theoretical analysis,laboratory test and numerical simulation to conduct in-depth research on it.First of all,through consulting a large number of domestic and foreign literature on composite foundation and traffic load,analysis of composite foundation bearing characteristics and traffic load characteristics,and then through literature analysis and combined with the conditions of the laboratory,select sinusoidal load as dynamic load to simulate traffic load.Then,the action mechanism of geocell and stone columns under traffic load is discussed.On this basis,the load transfer law and interaction characteristics of composite foundation bidirectionally reinforced by geocell and stone columns under traffic load are analyzed,and the action mechanism of bidirectional reinforcement is revealed.Secondly,according to the similarity theory,two sets of model tests are designed for simple low embankment soft soil foundation and composite foundation bidirectionally reinforced by geocell and stone columns,and the test results are analyzed.Combined with the experimental phenomenon and results,the bearing and deformation characteristics of composite foundation bidirectionally reinforced by geocell and stone columns under traffic load are analyzed.The results show that under traffic load,the settlement growth rate of composite foundation bidirectionally reinforced by geocell and stone columns is much lower than that of pure soft soil foundation,and the final settlement amount is also much lower than that of pure soft soil foundation.Laying cushion in foundation,especially geocell cushion,can well homogenize stress,reduce stress concentration and improve bearing capacity of the foundation.The pile and soil stress near the traffic load source is relatively large,and the gravel pile bears most of the load and the stress concentration is obvious.With the increase of traffic load time,the pile-soil stress ratio fluctuates in a certain range,but eventually tends to be stable.With the increase of traffic load cycles,the excess pore water pressure increases,and the excess pore water pressure far away from the load source is small and not significantly affected by the load.Finally,the ABAQUS finite element software is used to carry out numerical simulation analysis of bearing characteristics of composite foundation under different traffic loads,and the bearing characteristics of different types of composite foundation under traffic loads are obtained.The results show that under the same load,the settlement of pure soft soil foundation is the largest,followed by geocell reinforced composite foundation,and the composite foundation bidirectionally reinforced by geocell and stone columns has the best treatment effect.The bidirectional reinforced composite foundation has no obvious inhibition on the lateral displacement of embankment slope.Under dynamic load,the pile-soil stress ratio of composite foundation bidirectionally reinforced by geocell and stone columns is obviously smaller than that of stone columns composite foundation due to the stress diffusion of geocyte composite layer,and the fluctuation of pile-soil stress ratio tends to be stable after traffic load is applied,which is consistent with the law of indoor model test. |
