A Shelby tube is an aluminum pipe used to collect and protect soil samples in an undisturbed state for later analysis. It is open on one end and has a cap or tube drive head fitted to the other. The tube is pushed into the soil and then extracted with a sample of the soil intact inside. This tube may then be transported as-is with a threaded sealing cap on the open end or have the sample pushed out and sealed in a purpose made tube for later examination. The purpose of taking soil samples in this way is to preserve the delicate strata or layers and any other defining characteristics of the soil sample intact.
Shelby tubes are typically constructed of a thin walled aluminum material which offers little resistance when inserted into the soil. The tubes are made with a moderate cutting edge on one end and have locking holes or a thread machined into the other. This end of the Shelby tube has a tube drive head locked into place which accepts a tube driving hammer attachment. This tube driving hammer can either be hydraulically or manually operated and drives the tube into the soil. Once the tube is driven into the soil for the required distance it is then extracted again with the undisturbed sample still inside the tube.
At this point, the tube may be sealed with a cap on the open end and transported to the analysis facility or, if the tube is needed for additional samples, the sample can be gently pushed out into a separate PVC or cardboard tube. If the tube is not long enough for the depth of sample required, it can be re-inserted in the same hole and the process repeated. This method of sample taking allows all the subtle layer characteristics of the soil sample to remain intact for accurate analysis. This is not possible with conventional shovel, split core sampler or auger excavation which disturbs the composition of the soil samples taken.
A typical Shelby tube is about three inches (76 mm) in diameter and approximately 10 to 36 inches (254 to 914 mm) in length although different sizes are common for specific applications. The hammer which drives the Shelby tube may either be a hydraulic or manually operated weight which is raised then dropped repeatedly onto a shoulder machined into the hammer attachment. This impact is then transferred to the Shelby tube and drives it into the soil. The shorter Shelby tubes may also be fitted with a simple manual handle which is used to push the tube into the soil without the aid of a tube driver.