Trenching and Excavation Safety (Part 3)

Testing the Soil

There are three ways to test the soil:


  1. In order to determine the unconfined comprehensive strength of the soil, a penetrometer is used. To use the penetrometer simply collect an uncompressed handful of the soil and push the penetrometer into it up to the indicator ring. The reading on the penetrometer is in tons per square foot (tsf). The reading, when compared to the classification above will let you know which type of soil you have.

    (image from You can purchase the pocket Penetrometer from this website)

  2. The Torvane Soil Test (aka “shear vane”) measures shear rather than unconfined comprehensive strength. To use it, simply push the vane end of the Torvane into the soil sample and turn the dial until it breaks free. Read the number on the dial and multiply the number by 2 in order to get the unconfined comprehensive strength.

    (image from You can purchase the Torvane from this website)
  3. The final method utilizes only your thumb to test the soil sample. To do this, simply push your thumb into the sample and measure the depth of penetration. A penetration of less than the length of your thumb nail (¼”or less) is probably a type A soil, a penetration that is the depth of the thumb nail (between ¼” and ¾”) is probably a type B soil and a penetration the is greater than the depth of your thumb nail (greater than ¾”) is probably a type C soil.