无黏性土中筒型基础负压下沉模型试验

筒型基础是海洋结构物特别是海上风力机的重要基础型式之一，其下沉阻力的研究是该种基础型式成功应用的关键。目前对于无黏性土中下沉负压的计算方法主要有以静力触探为基础的(CPT-Based)方法与基于贯入过程中筒体受力平衡的解析方法，但计算结果与工程实测数据均存在偏差。开展了3种不同厚径比筒型基础的负压下沉模型试验，测量了下沉过程中筒内外侧壁、端部土压力以及周围土体的孔压变化；分析了2种方法中计算参数对结果的影响，给出了推荐的参数取值范围；根据实测孔压与数值模拟结果建立了临界负压计算公式。研究表明：砂土中筒型基础负压下沉时筒土间摩擦系数约为0.2，推荐CPT-Based方法中的外侧摩阻力系数为0.002 6～0.007 0，内侧摩阻力系数为0.001，端阻力系数为0.2～0.6；解析法中侧向土压力系数介于静止土压力系数与被动土压力系数之间，端阻力承载系数为40；考虑土体渗透破坏保护机制的临界负压计算公式可以有效地提高筒型基础下沉控制的临界负压，更加接近实际情况。

Model test of bucket foundation suction installation in cohesionless soil

Bucket foundation is an important foundation type of offshore structures, especially for offshore wind turbines. Study on its penetration law is the key to successful application of this kind of foundation type. Previous methods for penetration suction are CPT-Based method and analytical calculation method, which are based on cone penetration test (CPT) and force balance in the penetration process, respectively. However, results from previous methods deviate from practical engineering data. In this paper, three bucket foundations with different wall thicknesses were penetrated by suction pressure. Earth pressure and pore pressure inside and outside the bucket wall, as well as the tip resistance were measured in the experiments. The influence of key parameters on the two calculation methods was analyzed and reasonable suggestions were given. According to measured pore pressure compared with numerical simulation analysis, a critical pressure calculation formula is established. Studies have shown that coefficient of friction between side wall and the soil is about 0.2. For CPT-Based method，outside-wall friction parameter kf is in the range of 0.002 6? 0.007 0；inside-wall friction parameter kf is 0.001; tip resistance coefficient kp is in the range of 0.2?0.6. For analytical calculation method, lateral earth pressure coefficient K should be between the stationary earth pressure coefficient and passive earth pressure coefficient, and tip resistance coefficient Nq is 40. The critical suction pressure formula based on protection mechanism for seepage failure can effectively increase the critical suction pressure，which is close to the actual situation.