Standard Test Method for Measuring Stiffness and Apparent Modulus of Soil and Soil-Aggregate In-Place by Electro-Mechanical Method

Importancia y uso:

4.1 The apparatus and procedure described provides a means for measurement of the stiffness of a layer of soil or soil-aggregate mixture from which a Young's modulus may be determined for an assumed Poisson's ratio. Low strain cyclic loading is applied by the apparatus about a static load that is consistent with highway applications (1).

4.2 This method is useful as a non-destructive method for monitoring or controlling compaction so as to avoid under-compaction, over-compaction or wasted effort. Through an understanding of how stiffness relates to density for a particular material, moisture content and compaction procedure, the stiffness achieved can be related to % compaction in connection with density based compaction control or specifications, for example, to meet the requirements of Method D698 using standard effort or Method D1557 using modified effort.

4.2.1 This method applies to silty and clayey materials containing greater than 20 % fines. In such cases, the relationship between stiffness and dry density or dry unit weight is sensitive to the water content. Water contents should be determined by use of: Test Method D2216, D4643, or D4959. If the determination cannot be made immediately at the time of the stiffness measurements, then soil samples shall be preserved and transported in accordance with Practice D4220, Section 8, Groups B, C, or D soils.

4.2.2 This method is useful in the construction of road bases or earthworks, including the installation of buried pipe (2).

4.2.3 The rapid, non-penetrating nature of this method is suited to production testing, for example, it provides a means of testing that does not necessarily interfere with or delay construction.

4.3 This method is suitable for mitigating the risk of pavement failure. By assuring the relative uniformity of highway subbase, subgrade and base stiffnesses, stresses on the pavement is more uniformly distributed. In this way the life of a pavement is extended and repairs minimized.

4.4 This method is suitable for determining when the surface of a soil or soil-aggregate structure is capable of supporting design loads. This is useful for stabilized fills where the material hardens (stiffens) over time without measurable changes in density or moisture content.

4.5 This test method is suitable for the in-place determination of a Young's and a shear modulus of soil and soil-aggregate mixtures (3, 4). Stiffness, as measured by this method, is related to modulus (5) from an assumption of Poisson's ratio and from the radius of the foot of the apparatus as follows:

where:

K_gr   =   stiffness of the ground layer being measured, MN/m (klbf/in.), R   =   outside radius of the apparatus' foot, m (in.), ν   =   Poisson's ratio, E   =   Young's modulus, MPa (kpsi), and G   =   Shear modulus, MPa (kpsi).

4.5.1 The stiffness and modulus of silty and clayey materials will change with moisture content and can possibly result in hydro-compaction collapse, loss of bearing capacity or loss of effective shear strength. In addition, for silty and clayey materials with significant fines content, higher stiffness does not necessarily assure adequate compaction (6).

Subcomité:

D18.08

Volúmen:

04.09

Número ICS:

93.020 (Earthworks. Excavations. Foundation construction. Underground works)

Palabras clave:

compaction control; in-place modulus; in-place stiffness; in-situ test; non-destructive; production testing; shear modulus; soil stiffness test; stiffness gauge; Young's modulus;