Large diameter steel pipe field test using controlled low strength material and staged construction modeling using 3-D nonlinear finite element analysis

Field test of buried pipes, monitoring the pipe in different trench conditions is extremely valuable in predicting the displacement of the pipe during construction stages and during its lifetime. The field instrumentation monitors the circular displacements and strains of a buried steel pipe with an outside diameter (O.D.) of 84in. and 0.375in. thickness in three different trench profiles using controlled low strength material. For the first case, the trench width is the O.D. plus 36in., and CLSM is used as embedment up to 30% of the O.D. In the second case, the trench width is the O.D. plus 36in., and CLSM is used as embedment up to 70% of the O.D. In the third case, the trench width is O.D. plus 18in., and CSLM is used as embedment up to 70% of the O.D. From the CLSM to the top of the pipe, ordinary local soil is used and compacted to 95% standard proctor density. Approximately 5ft. of backfilling is added for all cases. The tests provide guidance for the finite element modeling and are an important study in predicting the structural performance of buried steel pipes.;The finite element analysis developed is a three dimensional (3D) nonlinear finite element model of steel pipe coupled with CLSM and compacted soil. The finite element model consists of the pipe and soil interaction during the staged construction of embedment and backfill. The model considers the at rest lateral pressure and the lateral effect of soil compaction on the pipe-soil structure. Different trench conditions are modeled by varying the in-situ soil stiffness for the trench wall, and trench width. The finite element model developed simulates the load-deformation results of a buried steel pipe in different trench conditions and was verified by the field test results. After developing the nonlinear finite element model for steel pipes and verifying the results with field test, the model can be used to predict pipe performance under varying backfill and loading conditions.