Application Of Bidirectional T-shaped Deep Mixing Column Supported Ground In Lianyungang-yancheng Railway

The investigation site was located in Guanyun section as a part of Lianyungang-Yancheng railway project in Jiangsu Province,China.Both of the laboratory and in-situ tests indicated that the subsoil in Guanyun section was unfavorable for railway construction,and therefore,the ground improvement is required.The Deep Mixing Method was used in Guanyun Section which is a coomon way to improve the soft ground.The traditional deep mixing(DM)column and the innovative T-shaped deep mixing(TDM)column were constructed in two test sites.Exhaustive data have been collected and analyzed,and some fingdings have been made:(1)A series of numerical models,including one DM column and ten TDM columns,were created based on the data obtained from Lianyungang-Yancheng railway project to investigate the effect of the shape of enlarged upper part of single TDM column on its performance.The strain softening of soil-cement material was taken into consideration through the User Defined Subroutine Field in ABAQUS.The volume,column length and the diameter of the lower column body were kept the same through all models so that the evaluation is more persuasive.The ultimate bearing capacity and the residual bearing capacity after failure were recorded to investigate the performance of single column.Some findings and suggestions are presented about the best shape of enlarged upper part of TDM columns.(2)The bidirectional rotating technology used by TDM columns is found to be more efficient when supporting embankments over soft ground compared with the traditional single rotating technology which conventional DM columns often use.For instance,the soil and cement can be mixed more uniformly so that the unconfined compressive strength of the TDM column is higher than that of the DM column.There were nine test sites of railway embankment supported by TDM columns and conventional DM columns.The measured data of these test sites were studied including the surface settlement,stress concentration ratio,column efficacy,excess pore pressure,lateral displacement.The results indicated that the TDM column can bear higher proportion of load induced by the embankment and control the load in supported layer rather than transferring them into soft underlying layer.Therefore,the consolidation of TDM column-supported railway embankment is faster and its final settlement is lower than DM column-supported one.(3)The settlement of different layers was calculated and the final settlement of two sites were predicted using the hyperbolic fitting method.The final settlement and consolidation coeefieicients of composite foundations were also calculated through laboratory tests and insitu tests.The empirical relationships between the calculated results with the predicted results were developed to offer references for following projects with similar backgrounds,so that the settlement and the consolidation rate can be predicted before construction.