Zakkende grond op ankers

Abstract

The graduation thesis focuses on providing insight in the consequences of subsiding ground on soil anchors. With the years, the bars of an anchored sheet pile walls for example, can be unfavourably loaded due to subsiding soil. As a result of these lateral loads, the bar will deform and elongate, causing the stresses to increase. The applicability of the current design method of CUR 166 is limited. Hereby referring to using it for determining the deformation of anchors in common situations, such as inclined anchors crossing multiple layers of soil. Because of the ambiguities and limitations of this method, the report will verify and modify the design method of CUR 166. While looking at the issues regarding subsiding soil, distinction will be made between the soil behaviour around the anchor and the way in which the anchor bar deforms due to the soil load. As a way of gaining insight in the consequences of subsiding soil on anchors, Deltares has conducted model tests on small sized bars and measured the resulting loads. By simulating these tests with Plaxis 2D has the way subsiding soil loads the bars been defined. In contrast to the current method of CUR 166, the value of the shear strength should depend on the drained or undrained behavior of the soil. The result is an almost constant value for the factor to determine the load with, this in contrast to the currently used variable / unclear factor. The subsidence process loads the anchor laterally and causes it to deform. A new design method (vernieuwde rekenmethode) has been created in order to approximate the deformation and stress–strain curve of the anchor with along the free anchor length. This method is applicable for a wide range of situations, including the loading of inclined anchors crossing multiple layers of soil. The current method uses an elastic calculation to verify the stresses with the regulations. The possibilities of using a plastic calculation have been researched. Due to the displacement controlled nature of subsiding soil loading the bar, can the bending moments be absorbed by the yielding of the bar. As long as the curve of the yielding anchor bar is not obstructed by supports, the rotational capacity of the anchor will be sufficiently large to allow for yielding of the steel. In Plaxis 2D and 3D has the applicability of an embedded pile as an anchorage been researched in order to verify it with the vernieuwde rekenmethode. When comparing the different methods, it can be concluded that the resulting increase in axial anchor force due to subsiding soil, defined with the CUR 166, is conservative compared to the Plaxis simulation and the vernieuwde rekenmethode.