中文摘要：

铁路过渡段是既有铁路提速改造的关键部位,但经过多年运营后过渡段路基构造发生了显著变化。采用轻型动力触探、瑞雷波和E_（vd）等现场勘察方法,对宁启铁路既有铁路过渡段路基的承载特征进行了勘察。瑞雷波仪勘探结合开挖勘察的结果表明：宁启既有铁路过渡段路基典型构造为表层以下有20~30cm厚的水泥改良土硬壳层,30~120cm深度范围是路基最软弱的部位,承载力不能满足提速要求;120cm以下基床层承载力较高,可以满足宁启线提速的暂行规定。硬壳层对E_（vd）值测试影响较大,路肩硬壳层由于冲刷剥蚀变薄,路肩E_（vd）值低于路基中央,统计规律表明,当路肩测试值低于30MPa时,可推断路基中央E_（vd）值比路肩E_（vd）值高30MPa。轻型动力触探勘察结果表明,在90cm深度范围内,大部分测点的承载力低于100k Pa,低于暂行规定中150k Pa标准,承载力低是造成过渡段病害的主要原因,也是过渡段加固的重点部位。

英文摘要：

Railway bridge transition section is a key part in existing railway speed upgrading,while the roadbed structure may have changed significantly after years operation. The transition section roadbed bearing capacity is investigated by light dynamic penetration,Rayleigh wave and dynamic elastic modulus（ E_（vd）） methods in Nanjing-Qidong railway. The detection results of Rayleigh wave and excavation shows that the typical transition section structure including a 20 ~ 30 cm thick hard shell and a soil layer of 30 ~120cm thick which is the weakest parts of roadbed and can not meet speedup requirements. The bearing capacity of the layer beneath the weak layers is high enough for the requirement. Hard shell layer has great influence on the E_（vd）value. The E_（vd）of road shoulder is lower than road central because the hard shell in the shoulder is thin for washing erosion. Statistics shows that when the E_（vd）value of the road shoulder is less than 30 MPa,the E_（vd）value will be 30 MPa higher in the road central than in the shoulder. Light dynamic penetration tests show that the bearing capacity within 90 cm in depth of most testing station is less than100 k Pa,which is lower than the requirement of 150 k Pa for speedup. The weak layer in 90 cm depth range is the main reason causes the transition section disease and it is the key parts of reinforcement.