What type of boring involves using a 2-inch to 4-inch diameter pipe with a water jet to extract soil?

The correct answer relates to the technique known as wash borings, which are specifically designed to facilitate the sampling and extraction of soil using a water jet, often through a pipe that is typically between 2 inches and 4 inches in diameter. This method involves the injection of water at high pressure to aid in loosening and suspending the soil, allowing for the efficient extraction of soil samples. The water not only helps in the removal of soil but also aids in the transportation of the soil particles up through the pipe, providing a clear understanding of the various soil layers encountered during the boring process.

The use of water reduces the risk of soil collapse during the boring operation, making this technique particularly advantageous in soft or loose soil conditions where traditional methods may struggle. Wash borings are often employed in geotechnical investigations to assess sub-surface conditions accurately.

In contrast, dry sample borings do not utilize water, which means they rely on a different technique for soil retrieval, while auger borings involve a screw-like mechanism for extracting soil without water. Test pits involve excavating trenches to analyze soil layers directly, rather than boring or drilling for samples. All these methods offer distinct advantages and drawbacks, but for the specific process defined in the question, wash