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STUDY ON DESIGN METHODS OF HORIZONTALLY LOADED LARGE-DIAMETER MONOPILE IN CLAY
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摘要: 本文针对静力荷载作用的情况，对比了4种黏土中水平受荷大直径单桩的设计方法，包括基于p-y弹簧模型的API规范方法，以及新近发展的基于p-y弹簧模型的
Zhang et al.(2017b) 、基于双弹簧模型的Wang et al.(2020) 方法以及基于三弹簧模型的Fu et al.(2020) 方法。考虑两种大直径单桩常用的长径比(L/D=5和10)，通过与三维有限元结果比较，对现有设计方法进行了对比，分析了不同参数对预测结果的影响。结果表明：(1)对于大直径单桩的水平位移和转角，现行API规范的预测值最大，而Wang et al.(2020) 方法预测值最小; (2)Fu et al.(2020) 方法不仅考虑了桩底剪力及桩身摩擦造成的分布力矩，还能够有效捕捉初始剪切模量与土体延性对水平响应的影响，还因此具备其余方法所不具备的优势; (3)采用Fu et al.(2020) 方法时，桩土界面粗糙系数α越大，桩身位移与转角越大，且长径比越小影响越显著，而与桩身分布力矩有关的缩放系数ξp2的影响则相对有限，当L/D≥10时其影响可以忽略。Abstract: This paper compares four design methods of horizontal loaded monopile under monotonic loading in clay. They include API method based on p-y spring model,Zhang et al.(2017b) method based on p-y spring model,Wang et al.(2020) method based on double-spring model,andFu et al.(2020) method based on triple-spring model. Two typical length-diameter ratios of large diameter monopile(L/D=5 and 10) are considered. The four methods are analyzed by comparing with the results of 3D finite element analysis. The influence of different parameters on the prediction results is discussed. The results show that:(1)For the deflection and rotation of a large diameter monopile,the current API method is the most conservative,whileWang et al.(2020) method provides the lowest predictive results. (2)Fu et al.(2020) method not only incorporates the shear force at pile tip and the distributed moment along the pile induced by frictional resistance,but also is capable of capturing the effects of initial shear modulus and soil ductility on horizontal response,which makes it superior to the other three methods; (3)In the design of monopile usingFu et al.(2020) method,the larger the interface roughness coefficient α is,the greater the pile deflection and rotation are. The influence is more significant with larger length-diameter ratios. The effect of coefficient ξp2 related to the distributed moment along the pile is relatively limited,which is negligible for L/D≥10.-
Key words:
- Monopile /
- Horizontal load /
- Clay /
- Finite element analysis /
- Design method
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图 2 水平受荷桩分析方法示意图
a. API规范法; b. Zhang et al.(2017b)方法; c. Wang et al.(2020)方法; d. Fu et al.(2020)方法
Figure 2. Analysis methods for pile under horizontal load
图 3 黏土中水平受荷大直径单桩三维有限元模型(L/D=5)
Figure 3. Three-dimensional finite element model of monopile under horizontal load in clay(L/D=5)
图 5 不同方法结果对比
a. L/D=5，H=2000kN，M=60000kN ·m; b. L/D=10，桩顶H=5000kN，M=150000kN ·m
Figure 5. Comparison of results on different methods
图 6 初始剪切模量Gmax的影响
a. L/D=5，H=1200kN，M=36000kN ·m; b. L/D=10，H=5000kN，M=150000kN ·m
Figure 6. Influence of initial shear modulus Gmax
图 7 破坏塑性剪应变γfp的影响
a. L/D=5，H=1200kN，M=36000kN ·m; b. L/D=10，H=5000kN，M=150000kN ·m
Figure 7. Influence of plastic shear strain on failure γfp
图 8 不同α条件下预测结果的对比
a. L/D=5，H=5000kN; b. L/D=10，H=10000kN
Figure 8. Comparison of prediction results under different α
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