Research On Static And Dynamic Characteristics Of The Low Liquid-limit Silt In The Subgrade Of The Heavy Haul Railway

Abstract:Heavy Haul Railway is a major thoroughfare of energy transport in China, the increased traffic leads to the increased axles and the increased marshalling, which will inevitably lead to the increases of the dynamic load amplitude, the load frequency and the load last period in the subgrade, but the existing Heavy Haul Railway were constructed with a low standard (common railway specification), even the subgrade was filled with the low liquid-limit silt. Research has shown that deficiencies and changes of the acquired service environment led to the multi-disaster in the existing Heavy Haul Railway embankment, which directly affects the subgrade bearing performance and the long-term stability, so an evaluation and reinforcement study of the existing Heavy Haul Railway embankment service state is urgent where the study of the static and dynamic characteristics of the subgrade filling is basic. This paper relies on the national863project, through static and dynamic triaxial tests, a comprehensive study about the static and dynamic characteristics of fine grained soil in ShuoHuang railway has gained. The main research contents and results are as follows:(1) By direct shear tests and static triaxial tests, gained the value of the static strength parameters c、φ, and the law of the value change with its moisture content and compaction factor:CD experiments show that the static strength parameters increases with the increase of compaction factor. The stress-strain curve of samples under different confining pressures has nonlinear hardening characteristics. The shearing peak value increases with the increase of the confining pressure and the compaction factor. UU tests showed that the value of the cohesion c increases then decreases with the increase of the saturation, increases with the increase of the compaction factor. The value of the internal friction φ value decreases with the increase of the saturation, increases with the increase of the compaction factor.(2) In order to study the deformation characteristics of the low liquid limit silt under repeated train load, sustained triaxial vibration test were conducted, before the test, reasonably determine the soil properties (saturation, compaction factor), initial static stress state (confining pressure, consolidation ratio) and dynamic loads (dynamic amplitude, frequency, vibration times) and other experimental parameters, then analysis of these parameters impact features on the vibration times accumulated plastic strain relations:under the same test conditions, the accumulated plastic strain has a positive correlation with the increased frequency, the increased stress and the increased saturation; has a negative correlation with the increased consolidation ratio; has a negative correlation with the increased vibration frequency in the overall relationship, but in the stable condition, with the increase of vibration times, the accumulated plastic strain remains unchanged.(3) Using Monismith index formula, semi-logarithmic formula, Zhang empirical formula and the Boltzmann equation for the fitting of the "stable" and "destructive" accumulated plastic strain curve. The results showed that:the Boltzmann equation fit the "stable" strain curve best, and the parameter a is the maximum accumulated plastic strain; the "destructive" curve should be fitted best by using the Monismith index formula.(4) Dynamic triaxial strength tests found that the saturation and the number of vibrations significantly affect the liquefaction stress ratio: saturation increases, liquefaction stress ratio decreases; destruction week decreases, liquefaction stress ratio increases. The dynamic internal friction angle φd and the dynamic cohesion cd of saturated soil increases with the increases of the compaction factor, while in the non-saturated soil, the law of the effect between them are not obvious.(5) An analysis about the change characteristics of the saturated soil dynamic pore pressure has been made:found that vibration times significantly affect the pore pressure, pore pressure increases with the increase of the vibration times until the damage; Compaction factor affected the relationship between the pore water pressure ratio and the vibration frequency ratio (ud/σ3～N/Nf)significantly. Dynamic elastic modulus triaxial test found that:The larger the confining pressure is, the greater the corresponding dynamic elastic modulus are; the larger the confining pressure is, the greater the reduced rate of the dynamic elastic modulus are; The larger the consolidation ratio is, the greater the corresponding dynamic elastic modulus are; The larger the compaction factor is, the greater the corresponding dynamic elastic modulus are.