What Does Downhole Test (DHT) Mean?
A downhole test (DHT) is performed in order to determine the physical properties of the soil at the site under investigation. It measures the travel time from the time of wave generation until observed by receiver and predicts the velocity propagation required by elastic waves i.e. compressional and shear wave to propagate through the soil under consideration. While DHT is a lower resolution approach than a crosshole test (CHT), the data analysis of DHT is straightforward and more accurate.
Trenchlesspedia Explains Downhole Test (DHT)
In a downhole test, a wooden board or metal plate is fixed on the ground surface. The metal plate is struck to generate the elastic waves of compression and shear. Receivers set up inside the boreholes observe these waves and record the time taken for these waves to reach from the point of origin to the position where the receivers are placed.
The position of the receivers (depths) is changed and the time required is measured. The data obtained is plotted as depth vs time. The slope of the travel-time curve helps predict the compression and shear wave velocity profiles.