不同方法加固路堤下上覆砂层下卧淤泥层地基的效果对比

对于高速铁路路堤下上覆松散厚砂层、下卧厚淤泥层的地基,采用何种地基处理方法控制工后沉降更为经济高效尚不清楚。本研究基于某铁路路基的原位测试数据及数值模拟方法对旋喷桩仅加固下卧淤泥层(简称"旋喷桩地基")和预应力管桩加固上覆砂层及下卧淤泥层(简称"管桩地基")两种地基处理方式的效果进行对比。结果表明:由于上覆砂层的压密沉降在路堤填筑施工期间即可完成,仅加固下卧淤泥层的地基处理方法技术、经济效果更佳。"旋喷桩地基"与"管桩地基"相比,虽然总沉降大很多,但工后沉降几乎相同;"旋喷桩地基"充分利用路堤荷载的预压作用使上覆砂层形成密实的稳定土层,而"管桩地基"的上覆砂层仍为松散状态。因此在列车运行往复荷载作用下"旋喷桩地基"具有更高的长期可靠性;"旋喷桩地基"上覆砂层经路堤荷载预压形成密实的"垫层",使其下地基土与旋喷桩分担上覆荷载;与"管桩地基"相比,不仅桩长减短,而且桩身应力降低。

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.