The typical reactions that are obtained in this testfor various types of soils are described below.1. Very highly plastic soils (CH). The pat cannot bebroken or powdered by finger pressure.2. Highly plastic soils (CH). The pat can be brokenwith great effort, but cannot be powdered.3. Medium plastic soils (CL). The pat can bebroken and powdered with some effort.4. Slightly plastic soils (ML, MH, or CL). The patcan be broken quite easily and powdered readily.5. Nonplastic soils (ML, MH, OL, or OH). The pathas little or no dry strength and crumbles or powderswhen picked up.ROLL OR THREAD TESTThis test is performed only on the material passinga No. 40 sieve. First, you mix a representative portionof the sample with water until it can be molded or shapedwithout sticking to your fingers. This moisture contentis referred to as being just below the sticky limit.Next, prepare a nonabsorbent rolling surface byplacing a sheet of glass or heavy wax paper on a flator level support. Place the sample on this surface andshape it into an elongated cylindrical shape. Thenattempt to roll the cylindrical sample rapidly into athread approximately 1/8 inch in diameter (fig. 16-6).If the moist soil rolls into a thread, it has someplasticity. The number of times it can be rolled into athread without crumbling is a measure of the degreeof plasticity of the soil. Materials that cannot be rolledin this manner are nonplastic or have extremely lowplasticity.Figure 16-6.-Roll or thread test.The results of this test indicate the following:1. High plasticity (CH). The soil can be moldedinto a ball or cylinder and deformed under firm fingerpressure without crumbling or cracking.2. Medium plasticity (CL). The soil can be molded,but it cracks or crumbles under finger pressure.3. Low plasticity (CL, ML, or MH). The soilcannot be lumped into a ball or cylinder withoutbreaking up.4. Organic material (OL or OH). The soil forms asoft, spongy ball or thread when molded.5. Nonplastic soil (ML or MH). The soil cannot berolled into a thread at any moisture content.From the thread test, the cohesiveness of thematerial near the plastic limit may also be described asweak, firm, or tough. The higher the soil is on theplasticity chart, the stiffer the threads are as they dry outand the tougher the lumps are if the soil is remolded afterrolling.RIBBON TESTThe ribbon test is performed only on the materialpassing the No. 40 sieve. The sample prepared for usein this test should have a moisture content that is slightlybelow the sticky limit. Using this material, form a rollof soil about 1/2 to 3/4 inch in diameter and about 3 to5 inches long. Place this material in the palm of yourhand and, starting at one end, flatten the roll, forming aribbon 1/8 to 1/4 inch thick. This is done by squeezingit between your thumb and forefinger (fig. 16-7).Handle the sample carefully to form the maximumlength of ribbon that can be supported by the cohesiveproperties of the material. If the soil sample holdstogether for a length of 6 to 10 inches without breaking,the material is then considered to be both highly plasticand highly compressive (CH). If the soil cannot beribboned, it is nonplastic (ML or MH). If it can beribboned, it is nonplastic (ML or MH). If it can beribboned only with difficulty into short lengths, the soilis considered to have low plasticity (CL). The roll testand the ribbon test complement each other in giving aclearer picture of the degree of plasticity of soil.WET-SHAKING TESTThe wet-shaking test is performed only on thematerial passing the No. 40 sieve. In the preparation ofa portion of the sample for use in this test, enoughmaterial to form a ball of material about 3/4 inch in16-18
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