Geoprobe Systems® 6x8 sonic sampling provides the operator a larger area to work with than the traditional 4x6 method. The operator can obtain a larger diameter sample if desired, but this casing combination is typically used to provide a larger hole, such as to set a monitoring well. When telescoping one casing over another it is important to consider your main objective to determine sampling size.
Conventional Sonic Sampling
Geoprobe Systems® conventional sonic sampling systems provide a wide range of casing sizes and bit configurations. Conventional sonic sampling consists of driving your lead core barrel (sample collection) first and then overcasing it with a larger size casing. Once the larger casing has reached the same depth of the core barrel, the core barrel is removed, sample extruded, core barrel sent back down the middle of the larger casing and advanced out the end collecting another sample. Again, the larger casing is advanced to the same depth as the core barrel. This process is repeated to the depth desired. A long established casing configuration for this is using a 4 in. core barrel overcased with a 6 in. casing (4 x 6 Sonic Sampling). Other sonic configurations follow in this manner with larger inner and outer casing sizes.
Geoprobe® sonic casings have been uniquely designed with conventional sonic sampling in mind. When telescoping one casing over another, (such as 4x6) it is important to consider the spacing (annulus) between the telescoping casings. Geoprobe® sonic casing is designed so that each incremental casing is sized with bit clearances, and annular space in mind. If there is too little annulus between casings, certain soils can cause them to lock up and become stuck together. If there is too much annular space between casings, then excessive water is needed to flush the soil between the casings. The Geoprobe® sonic casing family has been uniquely designed so that each incremental casing size works efficiently with the next. Notice the similarities in the annular space between the casing sizes in the diagram. This results in a very efficient combination of casings for use in conventional sonic sampling applications such as 4x6, 6x8, or 8x10.