What type of material should be used to fill the hole in the sand cone method?

The sand cone method is a widely used field test for determining the in-place density of soil. In this method, a hole is excavated in the soil, and the volume of that hole is measured by filling it with a material that is free-flowing and has a known density. Free flowing sand of a known density fulfills these criteria perfectly, as it can easily fill the void and will not clump or compact in the hole, allowing for an accurate measurement of volume.

Using sand that is specifically characterized by known density ensures that any calculations regarding the density of the soil can be performed accurately. This is crucial in determining the moisture content and compaction of the area being tested. The specific gravity and uniformity of the sand contribute to reliability, making it an ideal choice for this testing method. Other materials like clay or gravel may not provide the same level of consistency in filling the hole or may change density under pressure, which can lead to inaccurate readings.