Computational & Technology Resources
an online resource for computational,
engineering & technology publications 

CivilComp Proceedings
ISSN 17593433 CCP: 81
PROCEEDINGS OF THE TENTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING Edited by: B.H.V. Topping
Paper 266
Evaluation of the Soil Initial Tangent Moduli (E0,G0) by the Shear Wave Propagation Method J. Bencat
Department of Structural Mechanics, Civil Engineering Faculty, University of Zilina, Slovakia J. Bencat, "Evaluation of the Soil Initial Tangent Moduli (E0,G0) by the Shear Wave Propagation Method", in B.H.V. Topping, (Editor), "Proceedings of the Tenth International Conference on Civil, Structural and Environmental Engineering Computing", CivilComp Press, Stirlingshire, UK, Paper 266, 2005. doi:10.4203/ccp.81.266
Keywords: soil dynamics, nondestructive determination of soil parameters, wave propagation, elastic moduli.
Summary
Initial tangent moduli of soils can be measured in the field or in the laboratory. If only
lowamplitude strains occur (strain less then 0.001 percent), the key soil parameters are the initial
tangent moduli (G_{0},E_{0}). The most direct field method and box test method for determining initial
tangent moduli is seismic testing. Shear and constrained moduli are evaluated directly from shear
(V_{s}) and compression (V_{p}) waves velocities, respectively, using the theory of viscoelasticity.
In the impactseismic method (ISM), body wave velocities are commonly evaluated from visual determinations of times of arrival of the waves at receivers or by timedetermination techniques based on correlation and spectral analysis. It is common practice in the seismic methods (ISM) to use a linear sourcereceiver array with one or two receivers located at a distance 1 (m) from source, Bencat & Stehlíková [2]. Other techniques based on correlation and spectral analysis theories can be employed to determine body wave velocities in the ISM test (as well as other seismic tests such as the crosshole and the downhole method). This approach offers benefits in two areas. First, interval velocities have fever potential errors than direct velocities. Second, the techniques can be fully automated. Furthermore, the retrieval of additional information such as strain rate effects and material damping is possible evaluate, e.g. via the spectral analysis. Records obtained from the shear wave velocity measurements by an ISM test at a box soil media are analysed as an application of the traveltime determinations explained above. Details of the box set up, and equipment used can be found in reference Bencat [1]. The time records of wave motion are obtained with two vertical acceleration transducers. The time interval obtained from first arrival of the shear wave is t = 29,29 msec. This corresponds to a shear wave velocity V_{s} = 94,23 ms^{1} and modulus for subgrade material (MS: = 1735 kg/m^{3}, w = 13.9%, v = 0.3) E_{0} = 40,05 MPa. The maximum value of the crosscorrelation function (CCF) of the two time records is occurs at time t* = 29,40 msec. The shear wave velocity calculated with this time is V_{s} = 93,87 ms^{1} and modulus E_{0} = 39,75 MPa. The phase of the crossspectral function (CROSSESD PHASE) is discussed in the paper along with the coherence function and the energy crossspectrum (CROSSESD MAGNITUDE). For a signal with no background noise, the coherence function (CF) should have a value of one at any frequency if the system is considered linear. Comparison between mean value of the statistical value colection of all corresponding static moduli (E_{s}), from the Static Loading Tests (SLT) and seismic resilient moduli (E_{s}) at the layer of soil under investigation (MS, test T 113/6) gives ratio E/E_{s} = 2.35. There were evaluated ratios E_{0}/E_{s} for each layer of the soils creating a corresponding combination of the subballast and subgrade in the box using the procedure described above in Bencat et.al. [1]. The ratio between the dynamic moduli (E_{D}),from the Dynamic Loading Tests (DLT) and the static moduli (E_{D}/E_{s}) and between the initial tangent and the static resilient moduli (E_{0}/E_{s}) for an individual of soils in the box test (layer) combination are given in the paper. Techniques to determine travel times of the body waves in geotechnical seismic testing have received little attention. Travel times are required to calculate the shear wave velocities from which the initial tangent moduli (G_{0},E_{0}) are determined. With the advent of portable signal processing equipment (e.g. BruelKjaer Portable PULSE 3560 MASystem) or portable PC with relevant software (e.g. DISYS or DAS16) other techniques for traveltime determination, such as those based on correlation and spectral analysis, can also be implemented in the field. References
purchase the fulltext of this paper (price £20)
go to the previous paper 
