Deflection of Large Diameter Butterfly Valves in Fat Clays

As water supply demands continue to increase, many agencies have an increased demand for larger pipelines to carry water over longer distances. As the diameter of these pipelines increase, the deflection behavior of the pipeline, valves, and fittings becomes an increasingly important consideration. In the case of butterfly valves, potential deflections can lead to seal and operational issues. Traditional reinforced concrete encasements are commonly used to control these deflections, but they can be costly and may lead to stress concentrations at the encasement edges for certain soil types. For this study, alternative encasements of a 96-in. diameter butterfly valve are considered for fat clay foundation soils of various stiffness. A numerical analysis is conducted using finite-difference modeling with FLAC (Version 7.0) to study the soil-structure interaction. The results are correlated with a concurrent analysis in STAAD (Version 8i) to verify and calibrate the results. The analysis considers the sensitivity of the results to a variety of geotechnical and structural variables, including various cemented backfill materials, foundation material types, and the length of the encasement. The paper presents the results of the analysis, a summary of the findings, and recommendations for consideration when using alternative encasements for large diameter pipelines. Supporting figures demonstrating the model response and sensitivity for geometry and encasement-type variables.