The Mechanics of Inflatable Anchors Embedded in Soils

Temporary anchors are often used during offshore construction to provide support for temporary structures or to secure underwater construction equipment to the seabed. An inflatable anchor system that is inexpensive, reusable and has several uses would be desirable for offshore applications. This thesis investigates the mechanisms of an inflatable anchor system embedded in sand and clay.;Next, the anchor behavior during pullout in soft clay is interpreted using a coupled FE model. A series of scaled mode pullout tests performed on an inflatable anchor embedded in soft clay is modeled using the coupled FE model, which accounts for the non-linear stress-strain response of the clay and inflatable membrane, consolidation of clay and geometric non-linearity of the rubber membrane. Two simplified methods are developed to estimate the pullout capacity of inflatable anchors embedded in soft clayey soils. The first method uses radial consolidation theory and an undrained FE model which is zoned to account for increase in undrained shear strength of the clay after inflation; The second method treats the anchor as an equivalent plate anchor and uses cavity expansion theory, radial consolidation theory and plate anchor bearing capacity solutions to estimate this pullout capacity.;A series of laboratory tests performed on Clarke Sideroad (CS) sand, rubber membrane and rubber-sand interface are described. The tests are used to characterize: (i) the shear strength and stress-strain characteristics of the CS sand used in the pullout tests, (ii) the nonlinear stress-strain parameters for the rubber membrane, and (iii) the rubber-to-sand interface shear strength properties. The data from the laboratory tests are used to derive engineering parameters for both CS sand and the rubber membrane for use in the FE analysis of the anchor load-displacement response during pullout.;A series pullout tests conducted on an inflatable anchor system embedded in both dry and submerged CS sand is described. The pullout tests included constant pressure tests, constant volume tests and tests with multiple inflation cycles prior to anchor pullout. The pullout tests were performed to examine the influence of embedment depth, inflation pressure and disturbance of the sand adjacent to the anchor on the pullout response. In addition, the tests provide experimental data that are used to develop and verify a numerical model for simulating the mechanical response of inflated anchors in sand.;First, the pullout behavior in sand is examined using an elastoplastic finite element (FE) model that accounts for non-linear soil behavior, deformation of the inflatable membrane and soil-anchor interaction. Scaled physical model test results are studied with the FE model to identify the dominant factors affecting the pullout capacity of this type of anchor system.;The measured pullout response of the anchor tests in sand is interpreted using full geometric non-linear FE analyses. The stress-strain response of the sand was modeled using either: (i) linear elasticity coupled with Mohr-Coulomb plasticity; or (ii) A Lade single hardening constitutive model, which accounts for non-linearity of stress-strain response prior to failure. The inflatable membrane was modeled using a nonlinear hyperelastic model.;Finally, based on the geometric non-linear FE model and scaled model tests, a simplified method is developed for estimating the pullout capacity of inflatable anchors in sand. It is shown that the pullout capacity of the inflatable anchor can be estimated using cavity expansion theory and plate anchor theory supplemented by the effective anchor depth derived from the scaled model tests and FE model. A design chart has been complied to set the relationship between the embedment ratio and the cavity expansion factor.;Keywords: Inflatable anchor, pullout mechanism, cavity expansion, pullout capacity,' effective length, soil-anchor interaction, single hardening model, material non-linearity geometric nonlinear analysis, finite element analysis...