TEST PROCEDURES FOR THE DETERMINATION OF THE DYNAMIC SOIL CHARACTERISTICS

TEST PROCEDURES FOR THE DETERMINATION OF THE DYNAMIC SOIL CHARACTERISTICS - Printable Version

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TEST PROCEDURES FOR THE DETERMINATION OF THE DYNAMIC SOIL CHARACTERISTICS - TAFATNEB - 08-30-2013

Accurate prediction of railway induced vibration and assessment of the efficiency of vibration mitigation measures within the RIVAS project requires detailed knowledge of the dynamic soil characteristics.
Within the frame of the project, it is assumed that the soil can be modelled as a layered elastic halfspace, where the material properties vary only in the vertical direction, and that small strain behaviour prevails in the case of railway induced vibrations with relatively low amplitude. Within each layer, linear elastic isotropic constitutive behaviour is assumed; anisotropic constitutive behaviour would better represent the formation process, but is not generally used in state-of-the-art numerical models and geophysical prospection methods. Apart from the layer thickness, five parameters need to be determined for each layer: the shear and dilatational wave velocity, the material damping ratios in shear and dilatational deformation, and the mass density. The depth upto which these parameters should be investigated depends on the lowest frequency of interest and on the soil profile (stiffness). After a brief description of wave propagation in elastic media and the dependence of the constitutive soil behaviour on the strain level, the report discusses classical laboratory and in situ tests, which results can be used for soil characterization and a first estimate of dynamic soil characteristics based on empirical relations. Main emphasis is going to a detailed description of small strain dynamic laboratory tests and seismic in situ tests that can be used to determine dynamic soil characteristics.
The report concludes with a recommended course of action to determine dynamic soil characteristics within the frame of the RIVAS project, which is minimally based on a study of geological maps and historical geotechnical investigations, a first estimate of dynamic soil characteristics using empirical relations, soil characterization (e.g. mass density) using classical soil mechanics tests and seismic in situ testing (a combination of surface wave and seismic refraction methods). If budget permits, it is further recommended to perform an intrusive in situ test (cross-hole, up-hole, down-hole or SCPT) in order to enhance profiling depth and resolution, as well as to perform dynamic laboratory tests on undisturbed samples to determine complementary dynamic soil characteristics and to evaluate their strain dependency.
It is emphasized that, within RIVAS, estimations of dynamic soil characteristics based on empirical relations cannot replace their determination by means of in situ or laboratory tests. It is further recommended that impact loads are also measured when performing seismic in situ tests, so that the transfer functions of the soil are available and can be used for validation of the dynamic soil characteristics derived from the test.

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