Abstract
The interface behavior between a caisson and the surrounding soil plays an important role in the installation of suction caissons as foundations for offshore wind turbines. A series of shear tests were carried out using a modified direct shear apparatus to study the interface shear behavior between sand and concrete. Sand samples with three particle size ranges (0.63–1.25 mm, 1.25–2.5 mm, 2.5–5.0 mm) and concrete plates with different relative roughness were used to explore the influence of the relative roughness parameter (Rn) and mean particle size (D50) on shear behavior. The responses from the pure sand shear test are also discussed for comparison. Test results show that the higher the relative roughness (Rn), the greater the maximum shear stress (τmax) appeared. The interface shear stress was weaker than that of the pure sand test. Furthermore, the interface friction angle (φ) of sand–concrete was closely related to the relative roughness of the concrete surface. Under the same conditions, the interface friction angle (φ) increased with relative roughness due to the effect of sand particles breakage and redistribution. By contrast, the effect of the mean particle size (D50) on the interface friction angle (φ) was less significant. However, for the pure sand shear test, the friction angle (φ′) obtained from the traditional shear test apparently increased with D50, indicating that the friction angle was more affected by D50 in the pure sand test than in the interface shear test.
Highlights
Suction caissons are widely used in offshore foundations for offshore wind turbines because of their great cost-saving advantages, less expensive installation equipment, shorter installation periods and being more environmentally friendly, as shown in Figure 1a [1,2,3,4,5,6,7]
The shear stress gradually increased with the horizontal displacement at the beginning until it became relatively constant after a certain amount of displacement
The Rn values in these two references are defined by the method of Uesign et al [45], which was almost the same with a modified poured-sand method [35]. This indicates that the shear performance of the sand–concrete interface is similar to that of the sand–mild steel interface. This may be because this study describes post-peak shear behavior; these two references by Dietz and
Summary
Suction caissons are widely used in offshore foundations for offshore wind turbines because of their great cost-saving advantages, less expensive installation equipment, shorter installation periods and being more environmentally friendly, as shown in Figure 1a [1,2,3,4,5,6,7]. Suction caissons are usually large, hollow, cylindrical steel or concrete structures with an upturned bucket shape. The interaction behavior between the caisson and the surrounding soil has a significant impact on the installation of suction caissons [8,9,10]. Neglecting the interaction between the caisson and the surrounding soil or assuming a fully rough surface will cause the design or construction to be inconsistent with reality [11].
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