Study On Uplift Behaviour Of Perforated Mudmat In Saturated Soft Clay

Mudmat is a type of shallow foundation used to support various temporary and semi-permanent subsea structures such as pipeline end manifolds(PLEMs)and pipeline end terminations(PLETs).In general offshore industry,mudmat is usually perforated to reduce uplift resistance on soft clay.However,no theoretical solutions have been established to determine bearing capacity factors for perforated mudmat.In this paper,the uplift behavior of mudmat is studied.The effects of perforation ratio,effective width,non-homogeneity ratio and skirt length on uplift resistance are revealed by small scale model tests,FEM and Upper Bound solutions.Therefore,theoretical solutions of uplift resistance of surface mudmat and skirted mudmat are obtained,respectively.The main research content and innovative achievements are as follows:(1)The influence of perforation ratio and effective width on the uplift behaviour of mudmat is studied.Six different perforated forms are designed to perform in model tests of uplift behavior on soft clay.FEM stimulates model tests and in-situ tests.Study shows that when h/B is less than 0.2,uplift resistance decreases with bigger perforation ratio and smaller effective width.However,when h/B is equal to 0.2,uplift resistance may decrease with larger effective width under the same perforation ratio.(2)Failure mechanism under uplift force is created from FEM results.Upper bound solutions of perforated mudmat are obtained under different perforation ratio,effective width,non-homogeneity ratio and h/B.Results are compared with model test results and centrifuge test results.(3)FEM simulates the condition of soil plug obstructed ratio in perforation area.Study shows that 20%~50% increase in uplift resistance occurs because of 100% obstruction in perforation area.The ability of soil plug obstructed ratio increasing uplift resistance would be weakened with higher non-homogeneity ratio.(4)FEM simulates circular and square perforation under the same perforation ratio and effective width.Study shows that circular perforation leads to lower uplift resistance.Moreover,with higher non-homogeneity ratio,circular perforation is more efficient in reducing uplift resistance.