Mixed-Grained Till in Pavement Structures; A Field and Laboratory Study
The road network in Sweden has historically been constructed using rock fill and natural gravel. More than 75 per cent of the land surface of Sweden is covered by glacial till and greater utilization of site-won material will not only reduce transportation costs but will also promote better sustainability of natural assets.
The objective of this study was to investigate the possibility of using mixed grained till at higher levels in the pavement, i.e. as part of the sub-base layer. The potential of till material was investigated by means of a laboratory programme comprising standard tests, static and dynamic triaxial tests and field tests involving the measurement of bearing capacity, density and water content.
The aim of the tests performed was to study how changes in saturation affect design properties and seasonal variation in saturation in a completed pavement structure.
This work shows that the use and application of till material can be increased, as till under specified conditions has good engineering properties. However, the mechanical properties of till were found, as expected, to be highly dependent on the water content of the material. The results not only indicate a threshold stress state but more importantly a threshold water content, beyond which the material rapidly develops large, permanent deformations. This water content limit occurs below full saturation due to pore pressure built up during the accelerated dynamical triaxial testing.
The threshold state with no or only small permanent deformations is affected by the water content, stress situation, fine content of the material and degree of compaction (density) etc. Design properties of the till material therefore need to be evaluated under the present conditions within the structure and its seasonal variations.
Design properties for the till material are proposed for applications that ensure unsaturated conditions, which together with evaluated stress limits show that no or only small deformations occur if the material is placed at a depth of 0.6 m
permanent deformation behaviour