Refer again to figure 15-33. In this figure, you see the values of G~, G., and G~ that were obtained using the correction factor (K). Now, if you were to disregard K and recalculate, you would obtain values of the following: G. = 2.7939, G= = 2.6638, and Gm = 2.4471. As you can see, these values, obtained without the correction factor, are hardly different than the values obtained with the correction factor. Therefore, unless unusually accurate precision is required, the correction factor may be disregarded.

As you previously learned, fine-grained soils are not classified under the Unified Soils Classification System on the basis of grain size distribution. They are, instead, classified on the basis of plasticity and compressibility. The Atterberg limits are laboratory classification criteria used for classifying fine-grained soils. As an EA3, you will be responsible for the performance of the Atterberg limits test.

A clay or related fine-grained soil, when dry or nearly dry, has a semisolid consistency. As moisture content increases, a point is reached where the material has a plastic (putty like) con-sistency. This point is called the PLASTIC LIMIT (PL). As moisture content continues to increase, the material remains plastic over a certain range. However, at a point called the LIQUID LIMIT (LL), the consistency of the material finally changes to semiliquid.

The upper and lower limits of the plastic range (that is, the liquid and plastic limits) are called ATTERBERG LIMITS. These limits were named after a Swedish scientist who developed the concept of the limits. The liquid limit (LL) is simply the moisture content (WL) at the upper limit of the plastic range, expressed as a percentage. The plastic limit (PL) is the moisture content at the lower limit of the plastic range.

Figure 15-34 shows equipment for determining the Atterberg limits of a soil sample. The LIQUID LIMIT TESTING DEVICE consists of a brass bowl mounted on a box type of apparatus. When you turn the crank, the apparatus elevates the bowl containing the sample and then drops it downward a specific distance onto the hard-rubber anvil of the testing device. Each of these drops is called a BLOW. We will explain the pur-pose of the procedure as we describe the test.