The Vertical Holding Capacity Of Marine Anchors In Sand And Clay Subjected To Static And Cyclic Loading

Abstract

ABSTRACT The purpose of this investigation was to experimentally measure and then to evaluate the influence of different loading conditions on the vertical holding capacity of marine anchors embedded in a saturated sand and in a saturated clay. Small and medium scale indoor laboratory and outdoor tests employing controlled static and cyclic loading patterns were conducted. The experimental data was utilized to develop the presented design curves. PREVIOUS INVESTIGATIONS The prediction of the vertical holding capacity of an anchor comprises a soil-structure interaction problem. The early theories for this prediction were based on assumed simple shapes for the failure surfaces. The concepts of the friction cylinder and the weight of cone methods, for example, are WBll described by Baker and Konder (1966). It is generally agreed that the observations of the shapes of the failing soil masses do not match either of these simple shapes and. Furthermore that these methods usually overestimate the holding capacity of deeply embedded anchors. Baker and Konder (1966) considered theoretical failure mechanisms for a plate anchor. They recognized that the failure mechanisms for shallow and deep embedment cases were different. A shallow case exists when the depth of cover is the limiting factor which controls the holding capacity; otherwise, a deep case exists. Bemben and Kalajian (1969) agree with this differentiation between failure mechanisms. Balla (1961) and Mariupol'skii (1965) each developed theoretical equations, for shallow case failures, which were each tied to model test observations of the breaking out soil mass. Mariupol'skii (1965) and Vesic (1969) each developed theoretical equations, for deep and shallow cases respectively, which were based upon cavity expansion principles. Balla introduced the relationship, A, between the depth, D, and the diameter, B, of the anchor such that: (Mathematical equation available in full paper) Sutherland (1965) investigated model anchor tests in sands and related the holding capacity stress on the anchor surface, qf' to a breakout factor, N, which is dependent upon the friction property of the sand, and which is related to the surcharge effective stress existing prior to the placement of the anchor, yD, by the equation: (Mathematical equation available in full paper) Meyerhof and Adams (1968) used a similar total stress analogy, qu where the breakout factor, N, is applied to the undrained shear strength, c, of a cohesive soil and where reference is made to the surcharge total stress existing prior to the placement of the anchor by the equation: (Mathematical equation available in full paper) If the holding capacity stress on the anchor surface, qu, should happen to be related to the undrained shear strength, c, of a cohesive soil by a breakout factor, NU' but not to any surcharge stress term, then these authors note that the latter relationship is then expressed by the equation: (Mathematical equation available in full paper) Two reviews of these and other previous works, which are all concerned with static loading, were recently presented by Kalajian (1971) and Kupferman (1971).