Model Tests of Gravity Platforms. I: Description

Five model tests were performed to qualify the concept of a monobase gravity platform for the Troll Field in the North Sea. These tests were designed to simulate the conditions for a platform situated in deep water $(\simeq 330m)$ and on soft clay. The program included one static, one static after cyclic, and three cyclic model tests. A description of the procedures and selected test results are presented. The results provide a basis for a critical evaluation of the foundation design procedures presently used for offshore gravity structures in the North Sea. The results indicate that cyclic loading results in a reduced static bearing capacity, cyclic bearing capacity is lower than static bearing capacity, the cyclic stiffness, decreases with number of cycles, and for the relatively large moment arms employed, cyclic rotation is the dominant displacement mode. The results also show that for the conditions of these tests, design storm compositions with the largest cyclic load first, followed by decreasing cyclic loads, may be more critical than the traditional design storm composition with increasing cyclic loads (largest load last).