Abstract
Scouring of soil around large-diameter monopile will alter the stress history, and therefore the stiffness and strength of the soil at shallow depth, with important consequence to the lateral behavior of piles. The existing study is mainly focused on small-diameter piles under scouring, where the soil around a pile is analyzed with two simplified approaches: (I) simply removing the scour layers without changing the strength and stiffness of the remaining soils, or (II) solely considering the effects of stress history on the soil strength. This study aims to investigate and quantify the scour effect on the lateral behavior of monopile, based on an advanced hypoplastic model considering the influence of stress history on both soil stiffness and strength. It is revealed that ignorance about the stress history effect (due to scouring) underestimates the extent of the soil failure wedge around the monopile, while overestimates soil stiffness and strength. As a result, a large-diameter pile (diameter D = 5 m) in soft clay subjected to a souring depth of 0.5 D has experienced reductions in ultimate soil resistance and initial stiffness of the p-y curves by 40% and 26%, and thus an increase of pile head deflection by 49%. Due to the inadequacy to consider the stress history effects revealed above, the existing approach (I) has led to non-conservative estimation, while the approach (II) has resulted in an over-conservative prediction.
Highlights
Scour is a process of soil erosion and can often occur around the foundations of offshore structures [1,2,3,4,5]
Extensive research efforts have been paid on sour effect on pile lateral responses [6,7,8,9], most of these studies have been largely limited to small-diameter piles, with ignorance of the stress history effect under scour conditions
This paper presents a numerical investigation for studying the scour effect on the lateral behavior of monopile, based on an advanced hypoplastic model considering the influence of stress history on both soil stiffness and strength
Summary
Scour is a process of soil erosion and can often occur around the foundations of offshore structures [1,2,3,4,5]. Scour reduces the pile embedded length and changes the stress history of the remaining soils, which significantly influences pile responses and the natural frequency of wind turbines [5]. Extensive research efforts have been paid on sour effect on pile lateral responses [6,7,8,9], most of these studies have been largely limited to small-diameter piles, with ignorance of the stress history effect under scour conditions. The response of the laterally loaded pile under scouring is usually analyzed by two simplified approaches (I): removing the scour layers without changing the strength and stiffness of the remaining soils [7,8], or (II) solely considering the effects of stress history on the soil strength [10,11,12]. The approach (I) ignores the stress history effect due to scouring, which overestimates the undrained shear strength of the remaining soils (as shown in Figure 1), and
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