| Building offshore wind turbine in complicated and bad ocean surroundings,such as silt and silty sand, the bucket foundation has high anti-overturning stability, low construction cost and reusable etc. advantages, which means it has broad prospects. To achieve controlling each compartment individually, Bulkheads are necessary here, which can strengthen the stability of towing, and provide the chance to achieve meticulous balancing control. The bucket foundation is with a close cover and an open button. During and after its sinking, there is a pump to suck water out from the cover of the bucket. By the negative pressure, the soil consolidates. The influence of bulkheads and soil consolidation on the bearing capacity is usually ignored during the design of bucket foundation, but bulkheads and soil consolidation do have impacts on the bearing capacity and characters of bucket foundation.The main contents and results of this thesis are as following:(1) A comparative model experiment with or without bulkheads is set on the same steel bucket. Obtain the results of load-displacement curve under horizontal load( including bending moment) and vertical load, and the distribution of the soil pressure of the inner, outer and upper side of the bucket. Numerical analysis is settled at the same time. Comparing the bearing modes of bucket with or without bulkheads,it comes to a result that shows the influence of bulkheads on the bearing character and the mechanism. The experimental and numerical results show: under vertical load, the capacity of bucket with bulkheads is of 8.8% higher than the bucket without, the bulkheads share the bearing capacity of the cover and sidewall, especially cutting the cover's bearing capacity. under horizontal load, bulkheads provide large pulling resistance, increase the horizontal and bending ultimate bearing capacity 20.2%,decrease the ultimate horizontal displacement and angle. In a word, bulkheads can not only improve the stability among towing, but also increase the ultimate bearing capacity of offshore wind turbine foundation during the operation..(2) A three dimensional numerical model considering coupled fluid flow and stress is developed, simulate the process of suctioning water out and soil consolidating. The results show: after 2.5 days of vacuum consolidation, the settlement, negative pore pressure and void ratio are dramatically different from those results after 1 day consolidation, but similar to those after 4 days consolidation. So we take 2.5 days as the most economical and efficient time for lasting the negative pressure. After 2.5 days of consolidation, the settlement levels off 0.2m, negative pore pressure expands widely and void ratio dramatically decreases from 1.248 to 1.061.(3)Analyzing the influence of vacuum stabilization of soil on the bearing characters. The results show: Vacuum consolidation makes the contacts between bucket and soil more tightly, disengaging radios under ultimate loads between the cover of bucket and the soil drop dramatically. Under separate loading,42.6% of vertical designed bearing capacity, 129.2% of horizontal designed bearing capacity,69.6% of bending designed bearing capacity, 4.4% of vertical ultimate bearing capacity, 61.3% of horizontal ultimate bearing capacity and 99.1% of bending ultimate bearing capacity increase. Under compound loading, the V-M?V-H?V-H-Mfailure envelope of foundation with soil consolidated or not is different, the one without soil consolidation is in the outer side of the other. |
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