Maridal Culvert, Norway - Field Tests I

The Maridal Culvert is a part of the Ring Road around Oslo. The culvert is a box culvert and has a total length of approximately 340 meters. The culvert is constructed with 2 by 2 traffic lanes.Three sections have been instrumented with strain gauges. A total of 42 points have been instrumented using 4 different types of strain gauges. Cracking occurred in most of the walls cast on a hardened concrete slab. The number of cracks on a 15 meters section varies between 3 and 10 depending on the wall thickness, time of the year for execution, formwork removal etc. Most of the cracks were detected when the formwork was removed.Time of removal has varied a lot, from the following day after casting to up to one week. And cracks have occurred. But all cracks have narrow crack widths. Normal crack width has been 0.1-0.2 mm. The only wall without cracks, is the one were heating cables have been used in the slab. In the top slabs and top part of the walls, no cracks have been detected. There was good correlation between the welded strain gauges and the Geokon vibrating wire strain gauges. And the correlation was improved when a corrected temperature dilation coefficient, found in laboratory tests, was used. The Geokon vibrating wire strain gauge is simple to handle and install, and at slightly lower cost than the welded strain gauge. From a practical and economical point of view, we intend to continue with this kind of instrument for future measurements.