The concept and the testing method of dynamic pile testing and the rationale, preparation, data collection, and data processing of the low-strain reflection wave method are described. In addition, some of the disadvantages inherent to low-strain detection and experiences related to the correlation between detection data and pile realities are discussed.

In order to reveal the mechanical properties of the subgrade fillers, they are studied by screening test of coarse-grained soils, compaction test and large-scale triaxial test in the track-subgrade model in high-speed rail laboratory of Central South University. The experimental results show that the coarse particle content for filler of the bottom layer is larger than that of the underlying embankment. The optimum water content of the filler of the bottom layer is less than that of the underlying embankment, while the maximum of dry density is similar, All samples have shown strain hardening characteristic, the higher the confining pressure is, the more obvious the strain hardening characteristic is. the volumetric strain of samples changes from shear contraction to shear dilation with the increment of axial strain. The cohesion and internal friction angle for filler of the bottom layer is greater than that of the underlying embankment. The tangent modulus for filler of the bottom layer is larger than that of the underlying embankment, and with the confining pressure increases, the difference also increases.

One-way shearing test of the coarse-grained soils and the reinforced earth was carried out under different normal stresses. The one-way shearing curves of coarse-grained soils and reinforced earth are similar. The changed curves of normal direction deformation with the shearing distance of coarse-grained soils and reinforced earth are also similar. Trend of the curve for the normal direction deformation and the reinforced earth is shrink at first and then expand continually. Under different vertical stresses, the difference of the curve for the normal direction shift and the reinforced shift is larger. Compared with raw coarse-grained soils, the cohesive force (c) of the reinforced earth increased, but the angle internal friction (φ) decreased for the reason that the articulation effect between the grilling, and the coarse-grained soils was reduced in the progress of shearing. So, the anti-shearing strength was decreased.