Analysis of Effects of Deep Braced Excavations on Adjacent Buried Utilities;Final rept. for 1 Apr 02-30 Sep 03

摘要

Ground movements resulting from deep braced excavations impose the risk of damage to adjacent buried pipelines. Accurate assessment of the effects these movements have on pipelines allows potential damage to be avoided or mitigated. A predictive process for determining the stresses occurring in a pipeline adjacent to deep braced excavations is presented. The method can be used to establish rational criteria for determining allowable maximum values for excavation-induced ground movements. The ground movement distribution around the excavated area is predicted using a complimentary error function, an assessment of the maximum ground deformation, and knowledge of the geometry of the excavation. The pipeline is assumed to move with the ground enabling the behavior of the pipeline to be represented by the ground surface movements at its location. Conservative analyses for determining the bending stresses and joint rotations along a pipeline caused by its deformation are established. Allowable values for both the tensile bending stress and joint rotation resulting from the excavation-induced movements are presented for comparison with the computed maximum values. The predictive methodology is applied to three gas mains surrounding a deep braced excavation in downtown Chicago and four cast iron mains from various excavations in Chicago. For these cases, the calculated bending stresses in the pipelines were significantly smaller than allowable values, but the joint rotations were observed to be the more critical case.