DT325 Driven Casing SPT (OTE) Overview

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The Geoprobe® 3.25 Out-the-End System (OTE) gives drillers the ability to collect continuous soil samples as well as complete standard penetration testing using the same outer rod string and drill rods from the inner rod string. This process is designed to be fast and productive while delivering excellent quality data for geotechnical engineers. With this system, there is no need to use hollow stem augers, mud rotary, or drive and wash - which are all more time consuming and not as easy on the operator. This system can be run on any Geoprobe® direct push or combination machine with an automatic drop hammer.

To begin the first interval, the tooling is setup. A 3.25 inch OTE cutting shoe is installed on the 3.25 inch probe rod that will be the outer casing. The inner sample sheath is then setup. A DT325 OTE retainer is installed onto a PVC liner, which is then placed into the DT325 sample sheath. A DT325 OTE drive head is installed on the opposite end of the sheath.

The sheath assembly is now installed into the outer 3.25 casing. An OTE centering drive cap and 3.25 inch drive cap are added to the rod string. The whole assembly is then driven to depth. The inner rod string is removed with the winch and Geoprobe® Spring Assisted Swivel Lift Cap to reveal the first soil sample. The DT325 OTE retainer and liner are removed from the sample sheath. Once complete, additional samples can be taken through the rod string until the desired depth is reached or standard penetration testing can begin. AWJ drill rods are used as the inner rod string with both methods.

The same outer casing is used for standard penetration testing. The inner string consists of the Geoprobe® Interlocking Split Spoon Sampler, AWJ inner rods, and an automatic drop hammer drive cap. Using the automatic drop hammer, a sample is taken. It is then retrieved from the rod string using the Geoprobe® Spring Assisted Swivel Lift Cap. The SPT sample is then finished.

With this system, the driller has the option to continue soil sampling or completing additional standard penetration testing at various intervals.

The Out-the-end (OTE) SPT system has gained favor with drillers and engineers. The ability to collect continuous soil samples more quickly — pushing the casing versus completing traditional geotechnical drive and wash — has created business advantages for companies utilizing the OTE system. It is lightweight, fast, and does not require drilling fluid.

For more information, visit our website or call us at 785-825-1842.