Understanding Soil Samples from Split-Spoon Samplers

When collecting soil samples for geotechnical investigations, the method of sampling significantly impacts the quality and nature of the sample obtained. Soil samples can be broadly classified based on whether their in-situ structure and properties are preserved.

Disturbed vs. Undisturbed Soil Samples

• Undisturbed Sample: This type of sample is collected in such a way that the original soil structure, moisture content, and stress conditions are preserved as closely as possible. These samples are essential for laboratory tests that are sensitive to soil structure, such as consolidation tests, shear strength tests, and permeability tests. Special samplers are used to minimize disturbance.
• Disturbed Sample: This type of sample has its original structure significantly altered or destroyed during the collection process. The relative positions of soil particles, the void ratio, and sometimes even the moisture content can be changed. Disturbed samples are still very useful for identification and classification tests, such as grain size analysis, Atterberg limits, specific gravity, and compaction tests.

The Split-Spoon Sampler and Sample Type

The split-spoon sampler is a common tool used during the Standard Penetration Test (SPT). It is a thick-walled, split barrel that is driven into the ground using hammer blows. After driving, the sampler is retrieved, and the split barrel is opened to access the soil sample inside.

The process of driving the relatively thick-walled sampler into the soil using blows causes significant deformation and rearrangement of the soil structure within the sampler. The impact of the hammer, the friction along the sampler walls, and the way the sample is contained in the split barrel all contribute to altering the soil's original structure.

Therefore, the soil sample collected using a split-spoon sampler is considered a disturbed sample. While it is invaluable for identifying soil type, performing classification tests, and determining the number of blows (SPT N-value) which is an index related to soil density or consistency, it is not suitable for tests that require the soil's original structure to be intact.

Based on this understanding, the soil sample collected using a split-spoon sampler is a disturbed type of sample.