Lesson 2/Learning Event 4
Low Plasticity (CL, ML, or MH). The soil cannot be lumped together into a ball without
completely breaking up.
Organic Materials (OL or OH). Soils containing organic materials or mica particles will form
soft spongy threads or balls when remolded.
Nonplastic Soils (ML or MH). These cannot be rolled into a thread at any moisture content.
FIGURE 19. THREAD TEST
Description of Cohesiveness
From this test, the cohesiveness of the material near the plastic limit may also be described as weak,
firm, or tough. The higher the position of a soil on the plasticity chart, the stiffer are the threads as they
dry out-and the tougher are the lumps if the soil is remolded after rolling.
The sample prepared for use in this test should have a moisture content slightly below the "sticky limit."
The sticky limit is the lowest water content at which the soil will adhere to a metal tool. Using this
material, form a roll of soil about 1/2 to 3/4 inch in diameter and about 3 to 5 inches long. Place the
material in the palm of the hand and, starting with one end, flatten the roll, forming a ribbon 1/8 to 1/4
inch thick by squeezing it between the thumb and forefinger. The sample should be handled carefully to
form the maximum length of ribbon that can be supported by the cohesive properties of the material. If
the soil sample holds together for a length of 8 to 10 inches without breaking, the material is then
considered to be both highly plastic