Study On The Settlement Of Composite Foundation At Backfill-Pond Region In Dezhou-Dajiawan Railway

With the development of nation’s economy, increasing density of road network has indicated a new trend in railway construction nationwide. There has been a lot of research on settlement prediction and controlling of soft soil subgrade, however, little study was reported on train crossing special section like pond. It is necessary to go deep into settlement prediction and controlling of pond region. Furthermore, because of the difference between the backfill material and the structure of natural foundation, as well as the variety of the height of embankment fill, has become a key to control the differential settlement of the subgrade construction in those areas which pass the ponds.Composite foundation of Dezhou-Dajiawan railway which crossed pond region was taken as research object in this paper. By means of analyzing geological survey data, theoretical calculation and numerical simulation, the settlement law of backfill foundation crossing pond region was introduced in detail, and optimized scheme was raised up. Research contents and results were listed as follows:(1) Adopting numerical calculation method, the central basement settlements of horizontal differential section, intermediate deep water section and external section of pond foundation were compared and analyzed. Conclusions were drawn that significant differential settlements existed longitudinally, maximum in intermediate deep water section and minimum in external section. Conclusion that lateral differential settlements existed was drawn from lateral comparison of horizontal differential section of foundation;(2) The pond backfill foundation was backfilled based on the pond foundation, and it showed mainly inhomogeneity of stratum. By means of theoretical calculation and numerical calculation method, the central basement settlements of horizontal differential backfill section, intermediate deep water backfill section and external section of natural pond foundation were compared and analyzed. Conclusions were drawn that significant differential settlements existed longitudinally, maximum in horizontal differential backfill section and minimum in intermediate deep water backfill section. Conclusion that lateral differential settlements existed was drawn from lateral comparison of horizontal differential backfill section of foundation;(3)The influence of pile length, pile spacing and filling soil character on differential settlement controlling of pond backfill composite foundation and pond composite foundation was studied;(4)Based on influence factors, two controlling schemes of differential settlement of composite foundation were raised up, and pond backfill composite foundation was better than pond composite foundation. Details are as follows:1) Remain pile length and pile diameter the same, reducing pile spacing can control differential settlement effectively;2) Increasing pile length or reducing pile spacing of thicker layer of soft soil foundation can control differential settlement effectively;3) Choose soil whose engineering character was similar to in-situ soil as fillings to reduce discrepancy of stratum, and then control differential settlement.