| The gravity spread foundation is one of the widely used foundation forms for onshore wind turbine in China,it has good bearing capacity,simple force transmission and the advantages of geological adaptability;however,it also has two problems of a large amount of concrete and the high cost of maintenance;according to these two problems,a new spread circular foundation was proposed,which connects the upper tower with prestressed anchor bolt,the current research on the new type of spread foundation is at the beginning,,this article is to explore the mechanical characteristic and anti overturning performance of this basic form through theoretical analysis and field structure test.Based on similarity theory,the 1:5 scaled model is made for the prototype spread foundation,combined with the characteristics of external loads of wind turbine,which can be concluded as a combined load of vertical,horizontal and moment for spread foundation.the most unfavorable load calculation of 1.0V+1.5H+1.5M was calculated.A bidirectional composite loading system was presented and prove the feasibility by theory,numerical simulation and experiment means.The loading system can be flexibly matched according to the change of load combined value.At the same time,considering the boundary conditions of the foundation of wind turbine in operation,the foundation soil with the same property as the field is made.The hierarchical loading mode of 0.1 to 1.5 times value of H-M standard combination is adopted in the test,the horizontal force matched with the H-M is applied by the classification.The vertical force is the self weight of the superstructure and it is kept unchanged during the loading process.Experimental results prove that area of foundation for carrying the maximum bending moment is at the position near the bottom pillar,it cracked when loading grade was 1.3,final crack width in normal the use of limit state within the range of other locations without cracks and breaking,is consistent with the finite element simulation results;the maximum tensile steel plate bottom radial reinforcement tensile stress in 1.3 stage loading grade,when the sudden increase,that the cracking of concrete,reinforced by radial bear the main force.foundation displacement is in a reasonable range,average tilt rate is 2.665 per thousand,less than the corresponding hub height limit;according to the distribution of the measured pressure at the bottom of the basement,area ratio of the foundation bottom removed soil is between 16.5% and 25% within the allowable index,soil shear failure does not occur.The test results show that this basic form has good bearing capacity and anti overturning property,which provides some reference for the design of spread foundation for onshore wind turbine. |
