Research On Bearing Capacity Of Mudmat Foundation For Underwater Production System Under Multi-Dimensional Loading

The mudmat foundation is an important part of the subsea production system in the deep sea oil and gas exploitation.It is a support structure for components such as subsea wellheads,manifolds,and manifold terminals to withstand the forces generated by the oil pipelines and crossover pipes in different directions.Because of the uncertainty in the direction and size of these forces,the mudmat foundation is subjected to multi-dimensional and complex loadings.In this paper,the bearing capacity characteristics of mundmat in multi-dimensional loading spaces are studied.Limit analysis,small scale model tests,centrifuge tests and numerical calculations are used to study the influence of mudmat shapes,skirts and perforations on the bearing capacity and uplift force of mudmat foundation both in one-dimensional and multi-dimensional loading spaces.Also this paper put forward two kinds of new mudmat infrastructure with high-efficiency bearing capacity.The main research contents and results are as follows:(1)The bearing capacity of mudmat in one-dimensional and multi-dimensional loading spaces are studied.The upper bound solutions of rectangular and circular mudmat foundations under the uniaxial loading of V,H and M are deduced.Based on the Hansen formula and Vesic formula,the formulae of the envelope of the bearing capacity of two-dimensional V-H and V-M loading spaces are proposed.It was found that the shape of mudmat has a great influence on the bending and torsion bearing capacity when subjected to one-dimensional loading,and the normalized envelopes of mudmat foundation in different shapes have good consistency.Uniform formulas for the envelopes of mudmat foundations with different shapes are proposed.(2)The failure mode of the perforated mudmat foundation under vertical loading is revealed,and the upper bound solution considering perforation rate is deduced.Small-scale model tests and numerical calculation methods are used to study the effects of the perforation rate,number of perforations,and the shape of perforations of mudmat on the vertical bearing capacity.The results show that the perforation rate do have the greatest influence on the vertical bearing capacity of both single-perforated and multiple-perforated mudmat foundations and the shape of the perforation has little effect.For the multiple-perforated mudmat foundation,there exist an optimum number of perforation s,when the perforation rate is constant.(3)The bearing capacity of mudmat in one-dimensional and two-dimensional loading spaces are studied.The height of the skirt has great influence on the unidirectional bearing capacity of the skirted mudmat foundation,and the influence of the number of skirts is small;in the two-dimensional V-H and V-M loading spaces,the bearing capacity envelope expands outward with the increase of d/B.However,the normalized envelopes does not change with d/B.(4)The small scale model test and the centrifuge test method are used to explore the uplift characteristics of the mudmat foundation.The test results show that: with the increase of the uplift loading rate,the uplift force and the super-hole pressure increase exponentially,and at the same time,the ratio of the uplift force provided by the super-hole pressure to the overall uplift force shows an inverse S-shape curve;Compared with perfotation shape and perfotation number,the influence of perfotation rate is the most obvious on the uplift characteristics of the mudmat foundation.