Study On Settlement Control Of Composite Foundation Of Heavy-haul Railway High Embankment In Collapsible Loess Area

ABSTRACT:Lime-soil Compaction Pile is one of the most common and effective foundation treatment methods used in collapsible loess area. The new heavy-haul railway Dazhun to Shuohuang railway contact line was built in loess area. The main foundation treatment methods are Dynamic Compaction and Lime-soil Compaction Pile respectively. Whether the design standard of Lime-soil Compaction Pile in the past is enough for new heavy-haul railways needs to be studied further. In this paper, selecting the contact line, through load test, basic indoor soil test, SPT, settlement monitoring, numerical analysis method, the effectiveness of Dynamic Compaction and Lime-soil Compaction Pile was studied. The main research contents of this paper are as follows:(1)The principle of Dynamic Compaction and Lime-soil Compaction Pile and their applications in the contact line was studied. In order to better understand the elimination of collapsibility, effective reinforcement depth and bearing capacity of foundation, load test, basic indoor soil test and SPT tests were conducted before and after foundation treatment process. The results of the tests have shown that Lime-soil Compaction Pile can effectively eliminate the collapsibility and improve the bearing capacity of foundation soil; The effective reinforcement depth of Dynamic Compaction is5-7m, Dynamic Compaction can effectively eliminate the collapsibility and improve the bearing capacity of shallow foundation soil.(2)The bearing capacity of foundation have also been analyzed if the axel load were increased from22t to25t, it showed that the affection had been mainly appeared in roadbed and the roadbed design was still acceptable.The settlement of a20m highfilling embankment was monitored, the settlement value of the subgrade center is about18cm and most of the consolidation settlement of the foundation and subgrade had finished during filling. Slowing down filling would help to control foundation settlement.(3)Based on the foundation treatment design scheme of a20m high embankment section of the line, Lime-soil Compaction Pile finite element models were established basing on ABAQUS. The influences of pile length, pile diameter, pile space, pile elastic modulus and elastic modulus of soil around pile on foundation settlement were analyzed respectively; it had shown that pile length is the main control parametres of settlement control. According to the analysis results, optimized foundation treatmen schemes were put forward, and the effectiveness of foundation settlement control had been verified.