Highway construction at Kvithammar-Åsen, mid-Norway: Geotechnical characterization of very sensitive clay deposits

The properties of vast, sensitive clay deposits have been investigated for the construction of the E6 Kvithammar-Åsen highway, north of Trondheim, in mid-Norway. Highway construction included the design of up to 14 m thick road embankments, made possible by stabilization works using lime-cement and vertical drains. Airborne electromagnetic scanning was performed to optimize the field investigation program, which included a large number of total and rotary pressure soundings, CPTU, piezometers, and undisturbed sampling. Advanced laboratory testing was performed to characterize the engineering properties of the clay (i.e., strength, stiffness, and hydraulic properties). In this paper, the properties of the clay deposits were compared to reference data from multiple sites in Norway. The laboratory results indicated that sample disturbance is a key uncertainty, affecting the interpretation of both strength and stiffness parameters. The undrained shear strength ranged approximately from 20 to 120 kPa. The friction angle, interpreted from undrained triaxial tests, was approximately 30°–33°. The overconsolidation ratio ranged from 1 to 6, depending mainly on depth. A correlation with the least scatter for the stiffness parameters was found between the modulus in the overconsolidated range (M₀) and the preconsolidation stress (σ_p'). For samples of quality 1, the average ratio of M₀/σ_p' was 33. In addition, some results from large-scale testing of lime-cement stabilization and road embankments on soft ground are presented. For lime-cement-stabilized clay, the ratio of passive to active maximum shear strength was between 0.45 and 0.95, with an average of 0.67. This ratio is crucial in design. Settlement predictions from the design phase for road embankments on soft soil at Holan agreed with measured values during construction.