Research On Bearing Capacity Of Square Perforated Mudmats On Soft Clay

As a shallow foundation,mudmat is widely used to support various temporary or semi-permanent submarine structures.However,in some practical situations,the large bearing equipments lead to the bulky and heavy mudmat,which is not convenient for transportation,installation and recycling.Therefore,the mudmat structure is optimized to a certain extent to be perforated.In addition,the use of perforated mudmat can also save steel consumption and reduce engineering cost in some cases where the volume of equipment is large but the required bearing capacity of foundation is not high.At present,the research on the perforated mudmat is still in the initial stage in China,and only a few foreign studies on the uplift and vertical bearing capacity in recent years.Thus,based on the research results and methods of bearing capacity of different foundations summarized by predecessors,this paper systematically studies the bearing capacity of square perforated mudmat on the undrained saturated clay.These provide important basis for the rapid design,bearing capacity check and stability judge of square perforated mudmats in actual engineering.The main work and conclusions are as follows.(1)Based on the upper bound theorem,the upper bound solution of the vertical ultimate bearing capacity of perforated mudmat is derived,which is related to the perforation ratio,the number of perforations and the soil parameters.Compared with the existing research results,it shows that the formula deduced by the upper bound theorem can reflect properly the influence of these parameters on the vertical ultimate bearing capacity.(2)The finite element software ABAQUS is used to study the influence of perforations on the bearing capacity of foundation.The results show that perforations are able to increase the vertical,horizontal and moment ultimate bearing capacity of mudmats.And with the increase of perforation ratio,the nature of the failure mechanism changes under vertical and moment loads.Furthermore,the influence of the number and shape of perforations on the bearing capacity are investigated.It is concluded that as the perforation ratio increases,the difference of the uniaxial ultimate bearing capacity becomes more distinct with the increase of the number of perforations.When the perforation ratio is small,the number of perforations has almost no effect on the uniaxial ultimate bearing capacity.But when the perforation ratio becomes large,increasing the number of perforations to a certain extent can improve the vertical and horizontal ultimate bearing capacity of perforated mudmats.For the moment capacity,with increasing perforation ratio,the perforated mudmats with 4 perforations are the worst,while the perforated mudmats with 16 perforations are the best.Comparing the pure uniaxial capacity of perforated mudmats with circular and square holes,it is found that the vertical and horizontal bearing capacity of perforated mudmats are not affected by the shape of the perforations when the perforation ratio and the number of perforations are fixed.However,in the case of a large perforation ratio,the perforated mudmats with circular holes have a slightly better uniaxial moment capacity.(3)A numerical study on the relationships between the perforation ratio R and the pure uniaxial capacity is also investigated.The results show that uniaxial vertical capacity and uniaxial horizontal capacity of perforated mudmats decrease linearly with the increase of perforation ratio on the undrained saturated homogeneous clay.In order to clearly show the relationship between uniaxial vertical,horizontal,moment and torsional capacity and the perforation ratio,the expressions are proposed when the number of perforations is 1 and 0?R?0.64.Displacement-controlled swipe tests and constant-ratio displacement probe tests are carried out to investigate the variation of undrained capacity under biaxial loading with the perforation ratio.The failure envelopes of perforated mudmats with different perforation ratios on undrained saturated clay in V-H,V-M,V-T,V-H-M,H_x-H_y,M_x-M_y,T-H and T-M space are established.By judging the relative position of the actual combined loadings and the relevant failure envelopes,the safety status of foundations can be determined.