**AASHTO R 75**:16(2020) Standard Practice for Developing a Family of Curves.

1.1. AASHTO R 75 practice provides a process for developing a family of curves using multiple individual moisture—density relationships (curves) developed according to T 99 or T 180.

1.2. The values stated in SI units are to be regarded as the standard.

2. REFERENCED DOCUMENTS

2.1. AA SHTO Standards:

• T 99. Moisture—Density Relations of Soils Using a 2.5-kg (5.5-Ib) Rammer and a 305-mm

(12-in.) Drop

• T 180, Moisture—Density Relations of Soils Using a 4.54-kg (lO-Ib) Rammer and a 457-mm

(18-in.) Drop

3. TERMINOLOGY

3. 1. Definitions:

3.1 .1. family of curves—a group of soil moisture—density relationships (curves) determined using T 99 C T 180. which reveal certain similarities and trends characteristic of the soil type and source.

3.1.2. spine—smooth line extending through the point of maximum density—optimum moisture content of a family of moisture—density curves.

4. SIGNIFICANCE AND USE

4.1. All curves used in a family must be developed using a single Method: A, B. C, or D of T 99 or T 180.

4.2. Curves are plotted on a graph; the family is developed by drawing a smooth line through the maximum density/optimum moisture points. At least three curves are required to form a single family.

4.3. Generally, it will be found that higher unit mass soils assume steeper slopes with maximum dry densities at lower optimum moisture contents, while the lower unit mass soils assume flatter, mor gently sloped curves with higher optimum moisture contents (Figure 1).

5. DEVELOPING A MOISTURE-DENSITY FAMILY OF CURVES

5.1. Sort the curves by Method (A, B, C, or D of T 99 or T 180). At least three curves are required per family.

5.2. Select the highest and lowest maximum dry densities from those selected to assist in determining the desired scale of the subsequent graph.

5.3. Plot the maximum density and optimum moisture points of the selected curves on the graph.

5.4. Draw a smooth, “best fit,” curved line through the points creating the spine of the family of curves (Figure I).

5.5. Remove maximum density and optimum moisture points that were not used to establish the spine.

5.6. Add the moisture—density curves associated with the points that were used to establish the spine. It is not necessary to include the portion of the curves over optimum moisture.AASHTO R 75 pdf download.