Footing Stability of Jack-up Rig in the Layered Soil

Punch-through is the main factor that affects the footing stability of jack-up rig in the layered soil. Geological condition that can cause a footing to experience a punch-through failure includes sand or strong clayey soil layer of limited thickness overlying a weaker clayey soil layer. The paper introduces two methods to obtain the possibility of punch-through failure and deduces the equation of calculation. The two methods are applied in one case that shows the result is consistent. In this case, the factor of stability based on different calculation method varies from 0.3 to 0.5 and the footing penetration is about 7.1m, which approaches the actual penetration. It is recommended to calculate the ultimate bearing capacity of a strong stratum overlying a weaker clayey layer in order to evaluate the possibility of punch-through failure and footing penetration. Other factors affecting the footing stability such as scour and dynamic load are also discussed.