Study On Creep Tests And Numerical Analysis Of Sandy Slate Coarse-grained Soils In High Embankment

At present, high-speed railway is vigorously constructed in China. High embankment appears inevitably, because obstacles need crossed, such as alpines and vales. With good compaction and high shear strength properties, coarse-grained soil is widely used in subgrade engineering of the high-speed railway. Settlement-time question is particularly prominent in high embankment. To solve this problem, this article combined with the project "Key Technology Study of High-speed Railway Subgrade in Difficult Mountainous Area" supported by China Railway Corporation, took sandy slate coarse-grained fillings of high embankment in Hunan Zhijiang North Station of Shanghai-Kunming passenger line as research subjects, and then studied the fillings’creep deformation through a large number of theoretical studies, laboratory tests, field tests and numerical simulation. The main contents and conclusions are as follows:(I)Combining with settlement deformation mechanism and engineering features of high-filled subgrade, creep experimental study on sandy slate coarse-grained fillings was carried out by a large compressive oedometer. Tests showed that the fillings had the creep attenuation characteristics. Based on the creep tests, the establishment of creep constitutive model of coarse-grained soils was depth discussed. Creep model was selected or builded to reflect creep deformation features of coarse-grained soils.A computer program was written to identify the creep model parameters with improved Gauss-Newton method. Finally, it found that H-K model can well reflect the creep characteristics of the coarse-grained soil.(II)Designing coarse-grained soil samples under different water content or particle composition or degree of compaction, compression creep tests and creep orthogonal experiment were conducted. Using H-K model, it analyzed creep factors’impacts on the long-term settlement of high embankment. The results showed that without considering other factors, it can reduce the long-term settlement of high embankment by using dry or saturated coarse-grained fillings, or using coarse-grained fillings, of which the ratio of coarse and fine content is70:30, or increasing compaction coefficient of coarse-grained fillings. The orthogonal experiment was showed that the primary and secondary sequence of creep various factors is compaction coefficient as the main factor, then particle composition and moisture as the minor factor.(Ⅲ)The article conducted field settlement observation of high embankment by using single-point settlement gauges, and discovered that under filling height of twelve meters, the sandy slate coarse-grained fillings’ post construction settlement, which occurred three months after the completion of roadbed construction, was about20%of the final accumulated settlement. Under the VC++compiler environment, the H-K model was carried out secondary development of FLAC3D. And then adopted FLAC3D to calculate creep settlement of two high embankment sections in DK369+618and DK369+440of the Shanghai-Kunming passenger line. By comparison, numerical values were in good agreement with the measured values. That verified the reasonableness of the H-K model and its parameters. Finally, numerical analysis was carried on creep factors, and obtained conclusions were similar with the compression creep tests.