无黏性土中筒型基础静压下沉模型试验研究

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。以往下沉阻力计算多以静力触探的锥尖阻力为基础,考虑渗流对土体有效应力的影响,通过试验确定筒侧壁与端部阻力系数得到最终的下沉阻力,但对于下沉过程中筒-土间的挤压特性及摩擦系数研究较少。本文开展了3种不同厚径比的筒型基础静压下沉模型试验,测量了下沉过程中筒内外侧壁及端部土压力与总的下沉阻力;基于孔穴扩张理论及土塞效应建立了筒内外土压力的计算方法;以地基承载力公式为基础推导了筒端土体阻力的计算方法。研究表明筒型基础下沉过程中筒土间摩擦系数约为0.4,DNV规范推荐的k_f=0.001~0.003仅适用于计算筒外壁摩阻力,实测的筒内壁摩阻力远大于计算值,端阻力系数k_p与土体的有效内摩擦角相关,k_p=1.8时计算值与实测值吻合较好。

Experimental study on static pressure penetration of bucket foundation in cohesionless soil

Bucket foundation is an important foundation type of the offshore structures, especially for off-shore wind turbines. Study on its penetration law is the key to the successful application of this kind of foundation type. Previous method for penetration resistance was based on cone penetration test (CPT) and considered the impact of seepage on the soil effective stress. The resistance coefficient for side wall and tip of the bucket were obtained experimentally, which was used for calculating the final penetration resistance. However, the change rules of the extrusion and the friction between soil and bucket under negative pres-sure were less analyzed. In this paper, three different wall thickness bucket foundation are penetrated by static pressure. Earth pressure inside and outside the bucket wall, as well as the tip resistance and total penetration resistance were measured in the experiments Based on the cavity expansion and soil plug theo-ry, a calculation method of internal and external earth pressure was established, the range of the friction coefficient between soil and bucket was analyzed. According to the bearing capacity formula, a calculation of bucket tip resistance was derived. Studies have shown that coefficient of friction between side wall and the soil is about 0.4 during the penetration process,k_f=0.001~0.003 recommended by DNV(1992) only ap-plies to calculating the outer wall friction resistance, measured inner wall friction resistance is much great-er than the calculated value. Tip resistance coefficient k_p is related to the internal friction angle,calculated value agreed well with the experimental results when k_p=1.8.