超短桩处理无砟轨道深厚含砾黏土试验研究

Experimental Research on the Treatment of Deep Gravel Clay in Ballastless Track by Ultra-short CFG Pile

研究目的:硬塑含砾黏土属于中等压缩性黏土,深厚含砾黏土作为无砟轨道地基,其稳定性没有问题,但是如何进行地基处理,研究成果不多。按照传统观念,高速铁路无砟轨道地基遇到类似土时最大处理深度达到30 m,地基处理的费用较高,能否采用短桩等较轻的处理措施来满足工后沉降的要求,值得研究。本文拟通过超短桩处理深厚含砾黏土地基的现场原位试验,确定地基的沉降、深层沉降、侧向位移、土压力等变化规律,为高速铁路无砟轨道深厚含砾黏土地基处理积累经验。研究结论:(1)含砾黏土地基厚度26 m、路堤填高7 m,采用6 m的超短桩处理,可以在填筑到位后满足无砟轨道工后沉降的要求,采用短桩等相对较弱的地基处理方案,对于优化高速铁路中等压缩土地基处理方案意义巨大;(2)深厚含砾黏土地基的总沉降量较小,最大约为8.7 cm,其地基的沉降具有快速收敛的规律,填筑完成时发生的沉降占总沉降的比例达到84.7%~86.4%,对控制工后沉降非常有利;(3)含砾黏土短桩复合地基桩土应力比随着荷载的增加而增大,荷载稳定后桩土应力比平均值为2.9,地基土体承担了约80%的土压力;(4)本研究成果可为高速铁路中等压缩性土的地基处理提供借鉴和参考,并为相关规范的编制积累数据。

Research purposes: The hard plastic gravelly clay belongs to the medium compressibility clay. As the ballastless track foundation, the deep gravelly clay has no problem in stability. However, there are few research results on how to deal with the foundation. According to the traditional concept, the maximum treatment depth of high-speed railway ballastless track foundation is 30 m when it meets similar soil, and the cost of foundation treatment is high. It is worth studying whether the lighter treatment measures such as short piles can be used to meet the requirements of post-construction settlement. Based on the in-situ test of the treatment of deep gravel clay foundation with extra-short pile, the change rules of foundation settlement, deep settlement, lateral displacement, and earth pressure are determined to accumulate experience for the treatment of deep gravel clay foundation of ballastless track of high-speed railway.Research conclusions:(1)When the gravel clay foundation is 26 m thick and the embankment is 7 m high, the ultra short pile of 6 m can meet the requirements of post-construction settlement of ballastless track. It is of great significance to optimize the medium compression foundation treatment of high-speed railway.(2)The total settlement of the deep gravel clay foundation is small, the maximum settlement is about 8.7 cm, and the settlement of the foundation has the law of rapid convergence. When the filling is completed, the settlement accounts for 84.7%~86.4% of the total settlement, which is very beneficial to control the post-construction settlement.(3)The pile-soil stress ratio of composite foundation with short pile increases with the increase of load. The average value of pile-soil stress ratio after load stabilization is 2.9, and the foundation soil also bears about 80% of the earth pressure.(4)The research results can provide basis and reference for the foundation treatment of medium compressibility soil of high-speed railway, and accumulate data for relevant specifications.