Behaviour of skirt footings of gravity offshore platforms is simulated by means of large seale laboratory tests. The studies include static loading tests of rigid plate with flat ribbed elements (skirt) and penetration tests of wedge-shaped rib fragments (simulation of platform operation and installation, respectively).
One of the possible ways to improve the performance of footings of gravity offshore platforms is the installation of additional ribbed elements – "skirts". Their height (the depth of penetration) is determined by many factors, such as the installed weight of the platform, occurrence and thickness of soft soils in upper layers of the soil base, combinations and magnitudes of loads acting on the platform etc. Presence of the skirts at the footing poses additional problems, among which the most important are as follows: - assessment of the rib penetration forces, that stipulates the number and the height of the ribs, depending on the platform installed weight, and specifies volume, capacity and operation mode of the ballasting system during installation of the platform; - determination of forces, acting on the ribs due to vertical, lateral and angular displacements of the platform; - analysis of bearing capacity and stress-strain state of the soil base during the operation of the platform. This paper presents some results of large scale laboratory tests, carried out on the experimental soil set-up of Moscow Civil Engineering Institute with a purpose of studying the behaviour of the soil base in the course of the skirt penetration and during operation of the skirted gravity structure subjected to combined loading. The studies included tests of a rigid steel 2mx2m plate with flat ribbed elements 0.2m high under the action of static loads (vertical and horizontal forces and moment) and 1.5m high rib fragment penetration tests.
