COMPARISON OF FOUNDATION IMPROVEMENT EFFECT OF STRENGTHENING AN EXPRESS RAILWAY EMBANKMENT FOUNDATION WITH A SAND LAYER OVER A MUD LAYER BY DIFFERENT METHODS

For an express railway embankment foundation with a thick mud layer underlying a thick top loose sand layer， in order to control only post-construction settlement，which is the best technical and economical treatment method，is still unclear． In this paper，based on in-situ test data of an express railway embankment，numerical simulation was adopt to analyze and compare the improving effect of pre-stressed concrete pipe pile treating both the sand layer and mud layer( PP foundation) ，and jet grouting pile treating only the mud layer ( JP foundation) ． The results showed that because the settlement of the top sand due to compaction was almost completed under construction，the method focused on treating only the mud layer achieved high technical and economical effect． Post-construction settlement of the JP foundation was almost the same as that of PP foundation; JP treating only the mud layer utilized fully the preloading effect of the embankment weight，which made the sand layer became a denser and stable one，while the sand layer still kept loose in the PP foundation，so the JP foundation had higher long-term reliability than the PP foundation under reciprocating load of train; a dense cushion was formed in JP foundation owning to the preloading effect of the embankment weight，which made the top load be carried together by the soil under the cushion and JP，therefore both the length and the stress of the pile were reduced in JP foundation as compared with PP foundation．