Crosshole seismic testing

Crosshole seismic testing is carried out to supply information about elastic properties of soil and rock. These data are used in earthquake resistant design analyses for structures, liquefaction potential study, site development and dynamic machine foundation design. This is the best method in determining longitudinal and shear velocity profile. One can calculate the elastic modulus, shear modulus, Poisson’s ratio, assessment of fundamental period (To), amplification factor of ground (A) for earthquake resistant design for structures from shear wave and primary wave velocity.

sketch-of-crosshole-seismic-testing

                 A sketch of crosshole seismic testing

To perform crosshole seismic testing, we need two to three boreholes. Borehole diameter after casing is from 70 to 100 mm, and cased by PVC pipe. Between borehole-wall and and casing is grouted by grout mixture which formulated to closely the density of the surrounding in situ material after sodification and not affected to the measured result. Borehole deviation survey must be conducted to determine accurately the horizontal distance between borings for deep crosshole seismic testing.

A borehole impacter source is capable of generating shear wave and primary wave is lowered into borehole along with one or couple of 3-axis borehole geophones at the same elevation in the other boreholes. Horizontal distance between boreholes is typically about 3 to 5m.

Crosshole data tabulation

                                                            Crosshole data tabulation

Depend on the project requirement, data are calculated in table form or processed by SeismicCross software. Fieldwork, processing and interpretation of crosshole seismic testing are carried out in accordance with ASTM D 4428/ D 4428M.: Standard test methods for Crosshole Seismic Testing.