A composite sample is a representative mixture of all soil within a soil mass to be investigated or of the material contained in a stockpile or windrow of soil excavated from a trench. A test sample is obtained from a composite sample by quartering (to be explained later) in the laboratory.

To take composite samples from test pits, trenches, or power shovel cuts, take the following steps:

1. Remove any overburden or surface soil that is to be wasted.

2. Shave off loose and dried soil to obtain a fresh surface for taking the sample.

3. Excavate a channel of uniform cross section from top to bottom, and deposit the soil onto a quartering cloth, canvas, or tarpaulin, as shown in figure 15-6.

Collect and bag all material removed to ensure that the sample contains the correct proportions. To take composite samples from auger holes, collect all material excavated from the hole after first removing the over-burden. When taking representative composite samples from stockpiles or large windrows, take particular care. When material is dumped on large piles, the coarse material tends to roll to the bottom, leaving the finer material on the top. To compensate for this, take the sample from a full height strip after clearing the surface. To sample from a small windrow, excavate and bag material from a short section, as shown in figure 15-7.