Standard Test Methods for Crosshole Seismic Testing of Soil and Rock

Importancia y uso:

5.1 Crosshole seismic tests provide data about the seismic wave velocities of subsurface stratigraphic materials between boreholes as a function of depth at a site (1).3 Seismic wave velocities are directly related to the important geotechnical elastic constants, which are essential input parameters in geotechnical foundation designs. Such parameters are used in both analyses of soil behavior under both static and dynamic loads where the elastic constants are input variables into the models defining the different states of deformations such as elastic, elasto-plastic, and failure. Another important use of derived shear wave velocities in geotechnical design is in the liquefaction assessment of soils. Examples of the use of the derived P-wave and S-wave velocities are summarized as follows:

5.1.1 For input into static/dynamic analyses;

5.1.2 For computing shear modulus, Young's modulus, and Poisson's ratio (provided density is known or assumed);

5.1.3 For determining Seismic Site Class using the appropriate Building Code; and

5.1.4 For assessing liquefaction potential.

5.2 Fundamental assumptions inherent in the test methods are as follows:

5.2.1 Horizontal layering is assumed.

5.2.2 Snell’s law of refraction applies to P-waves and S-waves and to the velocities derived from crosshole tests. If Snell’s law of refraction is not considered in the analysis of Crosshole Seismic Testing data, the report shall so state. In that case special attention shall be given whenever high velocity layers are adjacent to low velocity layers, since waves can refract through the high velocity layers and arrive sooner than the direct waves (2).

5.2.3 Strong amplitude Total Internal Reflections (TIRs) will be present where higher velocity materials are adjacent to the layer under investigation (see Fig. 1). They arise when the incident angle exceeds the critical angle; as a result of which reflection coefficients become complex, which in turn leads to distortions in the reflected source wave (4). TIRs can significantly distort the desired direct travel path source wave and , if detected, should be documented in the test report.

Note 1: The quality of the result produced by this standard is dependent on the competence of the personnel performing it and the suitability of the equipment and facility used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some, but not all, of those factors.

Subcomité:

D18.09

Referida por:

D5782-18, D5195-21, D7400_D7400M-19, D5220_D5220M-21, D5872_D5872M-18, D5783-18, D8381_D8381M-21, D5784_D5784M-18, D6031_D6031M-24, D5781_D5781M-18, D5875_D5875M-18, D6286_D6286M-20, D0420-18, D6429-23, D5777-18, D7128-18

Volúmen:

04.08

Palabras clave:

accelerometers; compression waves; geophones; machine foundations; seismic waves; shear waves; wave velocity ;