30 June 2001
PROCEDURE FOR DETERMINING THE MODULUS OF ELASTICITY OF
UNBOUND GRANULAR BASE AND SUBBASE COURSE MATERIALS
a. Relationships. The procedure is based on relationships developed for the resilient modulus
of unbound granular layers as a function of the thickness of the layer and type of material. The
modulus relationships are shown in Figure J-1. Modulus values for layer n (the upper layer) are
indicated on the ordinate, and those for layer n + 1 (the lower layer) are indicated on the abscissa.
Essentially linear relationships are indicated for various thicknesses of base- and subbase-course
materials. For subbase courses, relationships are shown for thicknesses of 102, 127, 152, 178,
and 203 millimeters (4, 5, 6, 7, and 8 inches). For subbase courses having a design thickness of
203 millimeters (8 inches) or less, the applicable curve or appropriate interpolation can be used
directly. For a design subbase-course thickness in excess of 203 millimeters (8 inches), the layer
should be divided into sublayers of approximately equal thickness and the modulus of each sublayer
determined individually. For base courses, relationships are shown for thicknesses of 102, 152,
and 254 millimeters (4, 6, and 10 inches). These relationships can be used directly or by
interpolation for design base course thicknesses up to 254 millimeters (10 inches). For design
thicknesses in excess of 254 millimeters (10 inches), the layer should also be divided into sublayers
of approximately equal thickness and the modulus of each sublayer determined individually.
b. Modulus Values. To determine modulus values from this procedure, Figure J-1 is entered
along the abscissa using modulus values of the subgrade or underlying layer (modulus of layer
n + 1). At the intersection of the curve applicable to this value with the appropriate thickness
relationship, the value of the modulus of the overlying layer is read from the ordinate (modulus of
layer n). This procedure is repeated using the modulus value just determined as the modulus of
layer n + 1 to determine the modulus value of the next overlying layer.
a. Thickness. Assume a pavement having a base-course thickness of 102 millimeters
(4 inches) and a subbase-course thickness of 203 millimeters (8 inches) over a subgrade having a
modulus of 69 MPa (10,000 psi). Initially, the subgrade is assumed to be layer n + 1 and the
subbase course to be layer n. Entering Figure I-1 with a modulus of layer n + 1 of 69 MPa
(10,000 psi) and using the 203-millimeter (8-inch) subbase course curve, the modulus of the
subbase (layer n) is 127.5 MPa (18,500 psi). In order to determine the modulus value of the base
course, the subbase course is now assumed to be layer n + 1 and the base course to be layer n.
Entering Figure J-1 with a modulus value of layer n + 1 of 127.5 MPa (18,500 psi) and using the
102 millimeter (4-inch) base-course relationship, the modulus of the base course is 248 MPa
(36,000 psi). Modulus values determined for each layer are indicated in Figure J-2.
b. Design Thickness. If, in the first example, the design thickness of the subbase course had
been 305 millimeters (12 inches), it would have been necessary to divide this layer into two
152-millimeter- (6-inch-) thick sublayers. Then, using the procedure described above for the
second example, the modulus values determined for the lower and upper sublayers of the subbase