Search

Inclined pile foundations are commonly adopted in the support of wharf, harbor, bridge, and wind turbine structures. In the context of offshore wind turbines, inclined piles are typically arranged symmetrically around a circle with an elevated pile cap above sea level, referred to as an elevated pile-cap foundation. However, limited research exists on the impedances of inclined pile foundations with elevated pile caps. In this study, a theoretical model was developed that incorporates a homogeneous soil half-space and an inclined pile foundation with an elevated pile cap. The pile and soil half-space were modeled as Euler-Bernoulli beams and linear-elastic continuum, respectively. The soil's contribution to the pile's dynamics was represented by the receptance matrix, established at discrete interactions points along the pile's embedded section. The effects of the rake angle and scour depth on the dynamic impedances of the inclined pile foundation with an elevated pile cap were investigated. It was observed that the peak frequency of impedance shifts to a lower value as the scour depth increases; whereas the peak frequency shifting effect is less prominent when the rake angle changes. The impedance of the elevated pile-cap foundation is more sensitive to the pile's rake angle compared to the scour depth. [ABSTRACT FROM AUTHOR]

In offshore engineering, marine clays, which are widespread in the southeastern coastal areas of China, may be subjected to two-way cyclic stresses. To experimentally investigate the effects of the two-way cyclic stress with low-stress amplitude on the cyclic behavior of soft marine clay, a series of triaxial tests is performed on intact marine clay from Zhoushan covering various values of the cyclic stress ratio (CSR) and confining pressure (p′0). Several useful conclusions are inferred: First, the double-amplitude axial strain (εDA), dynamic axial modulus (E), and energy dissipation (W) increase with the CSR. Second, under the same CSR, the value of εDA is independent of p′0. The values of E and W increase with increasing p′0 during cyclic loadings, whereas the normalized modulus and normalized energy are independent of p′0. Third, an allowable CSR is proposed based on the strain behavior and energy concept. Based on the experimental results, two equations are established to predict the dynamic axial modulus and double-amplitude axial strain. [ABSTRACT FROM AUTHOR]

Influence of the depth and location of perforation, direction and magnitudes of in situ stresses, wellbore angle, and pumping pressure is investigated numerically for the hydraulic fracture. 3D models of rock formation with vertical, inclined or horizontal wells containing semi‐circular crack are analyzed to obtain both KI and the minimum pumping pressure. By computing the magnitude and sign of the T‐stress it is demonstrated that hydraulic fracture path is generally stable except for a very limited situations in which the vertical well is subjected to the lowest in situ stresses. The minimum horizontal in situ stress has the most dominant role in controlling the hydraulic fracture. A direct relationship between KI and T was obtained for different ranges of in situ stresses and some relations were presented for estimating the critical stress intensity factor at the onset of hydraulic fracture and minimum injection pressure in terms of the applied in situ stresses. Highlights: Influence of in situ stresses, well orientation and perforation size on KI and T values.Determining the minimum pumping pressure in terms of in situ stresses and well type.Stability analysis of hydraulic fracture path for vertical‐oblique‐horizontal wellbores.Obtaining direct relationships between KI and T by changing in situ stresses. [ABSTRACT FROM AUTHOR]