Where a sub grade has lower natural stiffness modulus. The minimum permitted sub grade surface modulus is 30 MPa (approx. The following equation shall be used where California bearing ratio (CBR) is used in the estimation of short-term and/or long-term subgrade stiffness modulus: The subgrade surface modulus is used in the pavement foundation design.įor widening schemes, where the subgrade is consistent across the width of the existing carriageway and the proposed widening, use of the in situ long-term subgrade surface modulus of the subgrade below the existing carriageway may be used for design purposes.ĬBR is traditionally used as indirect test for sub grade strength. Other considerations include drainage and durability. Pavement foundations are designed on the basis of practical minimum layer thicknesses for construction, protection of the subgrade during construction and long-term provision of support to the overlying pavement layer. This is required both during construction and during the service life of the pavement. The main function of a pavement foundation is to distribute the applied vehicle loads to the underlying subgrade, without causing distress in the foundation layers or in the overlying layers. Note: The top pavement bound layer consists of surfacing, binder course and base course.
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