Settlements of spread footing foundations on quick clay stabilized with lime and cement

Abstract

Since the early 70’s ground improvement by use of stabilizing agents such as lime and cement has been widely used for solving geotechnical problems; either as a way to improve slope stability, reduce settlements or vibrations, or to reinforce the inside of braced excavations. On a recently constructed motorway project in south of Trondheim, two bridges were founded with spread footings on a medium stiff, quick Norwegian clay stabilized with lime and cement. The post-tensioned concrete bridges are 78 m and 110 m long, with respectively 4 and 5 spans. In this article, evaluation of various foundation solutions is performed based on cost estimates. This showed that the cost of founding the bridges on stabilized ground to be the most viable alternative. Further, the article discusses the calculation methods used to evaluate settlement properties of the foundations. Settlement measurement is performed for about two years after completion of the structures. A comparison of the calculated deformations and measured settlements is conducted in this work. Settlements are measured to be 3-10 mm after one and a half year, except for one abutment that measured 21 mm of vertical displacements. Then the deformations nearly stop for many of the foundations. The measurements show a higher deformation rate in the first six months after casting of the bridge slab, than expected from the calculations. After some time, the measurements coincide well within the upper and lower bounds in the calculations done in the geotechnical design. Possible reasons for these observations are discussed.