QUALITY EVALUATION OF MONOPILE HIGH STRENGTH CONCRETE IN MARINE BRIDGE FOUNDATION (KEY IJP************854)

• Saurav Kumar, Chaitanya Mishra

Abstract

Monopile is the most common form of foundation employed under offshore or Marine works. These foundations are subjected to millions of repeated load cycles from the wind and waves of varying magnitude leading to accumulated displacements and changes in soil-pile stiffness. The purpose of this study was to investigate the behavior of Quality Evaluation of Monopile High strength Concrete in Marine bridge foundation. Monopiles, cylindrical steel structures driven into the seabed or riverbed, have gained prominence as a foundation solution due to their cost-effectiveness, ease of installation, and environmental benefits. This paper explores the design considerations, construction methodologies, challenges, and advancements in utilizing monopiles for such critical infrastructure projects. Through case studies and technical discussions, the paper aims to provide valuable insights for engineers, researchers, and policymakers involved in marine and bridge engineering projects. The investigation was divided into two parts: the first part is studying the long-term behavior through the reduced scale model test, and the second to analyse the short-term behavior using the Finite Element analysis. The findings of three monotonic and seventeen cyclic load tests performed in the laboratory on medium dense sand and dense sand were presented in this thesis. The experimental investigations discussed the effect of asymmetric two-way cyclic loads on the rate of accumulated displacements and changes in soil-pile stiffness. The overall conclusion of this research was that the monopile foundation experiences a higher reversal of accumulated displacement at relatively low load amplitude with an increasing number of cycles. As the monopile was subjected to irrecoverable displacement at the initial cycles and recoverable displacement with an increasing cycles on both serviceability and fatigue loading conditions. Under asymmetric two way cyclic loading with c -1.3, the reversal of accumulated displacement was 49% higher than the symmetric two-way cyclic loading with c -1 at around cycle number N 2150. It is observed that a more severe problem occurs under asymmetric two-way loading conditions. The non-linear response was observed for both test series, first lateral cyclic secant stiffness increases with a higher rate, and then the rate of increasing got decreased with an increasing number of cycles, but it did not get stabilized. This indicates a gradual increase in soil-monopile system stiffness in each cycle owing to sand densification. The linear regression analysis was also performed to fit the conventional degradation parameter using the minimum number of critical constraints that includes the loading conditions and the flexibility parameter of soil-pile system. In this study, an attempt has been made to examine the influence of embedded length on monopile behavior using finite element analysis. The centrifuge test carried out on a monopile embedded in sandy soil was used to validate the constituent model (Hardening soil model with small-strain stiffness). The numerical studies were performed on a 6m diameter monopile by varying the load amplitude and embedded length ratios (LD 4, 5, and 6). The monopile was subjected to two-way symmetric lateral cyclic loading with an amplitude of 30%, 40%, and 50% of the monotonic ultimate capacity of the pile. The difference between the measured displacement of numerical analysis and the centrifuge test varies by 27%. The similar trend irrespective of the values, and the monopile response under cyclic loading was observed from the load displacement curve, which indicates that the measured accumulated displacement increases drastically for the first load cycle. For a given embedded length, the lateral displacement was observed to increase with an increase in load amplitude. Also, the load amplitude was observed to cause a linear increase in the accumulated displacements.