crosshole

Crosshole refers to a geotechnical and hydrogeological technique as well as the borehole arrangement used in such work. In its common testing sense, crosshole testing involves placing measurement instruments in two or more boreholes that intersect or run in close proximity, and transmitting acoustic energy from one borehole to another to probe the material between them.

The method, often called crosshole sonic testing or crosshole seismic testing, uses a transmitter in one borehole to generate mechanical waves (typically P-waves and S-waves) and receivers in adjacent boreholes to record the arriving signals. By analyzing travel times and wave amplitudes along multiple paths, engineers can determine the in-situ velocities of seismic waves and, from that, estimate dynamic elastic properties such as shear and Young’s moduli and Poisson’s ratio for the rock or soil mass between the holes. Crosshole data can also be used for tomographic imaging to produce a regional view of velocity distribution and to identify anomalies, fractures, voids, or zones of degraded rock quality.

Applications include assessment of rock and soil stiffness for tunnels, caverns, dams, and foundations; evaluation of rock mass quality and integrity around underground openings; and support design, grouting planning, or monitoring for stability and safety. The technique requires access to suitable boreholes and careful coupling of transducers to the surrounding material; it is relatively high-cost and time-consuming and provides high-resolution information only in the region between the boreholes studied.

See also: borehole geophysics, sonic logging, tomography, non-destructive testing.