Abstract
Installation of underground pipelines through unpopulated land situated over pinnacled carbonate bedrock can lead to the development of sinkholes. The formation of sinkholes beneath buried pipelines has the potential of damaging the pipeline and more importantly causing hazardous environmental incidents. This paper presents a case history at a site where significant sinkholes developed within and adjacent to a 400 foot (112 meters) long section of high pressure petroleum pipeline right-of-way that crosses under a local creek in Plymouth Meeting, Pennsylvania. Various geophysical investigation techniques consisting of microgravity, multi-channel analysis of surface waves (MASW), and two dimensional electrical resistivity testing were performed in addition to confirmatory testing borings to effectively evaluate the subsurface conditions at the site. Three options were considered as a solution to the active sinkholes present within the pipeline rightof-way. These options include: 1) subsurface grouting within the right-of-way 2) structurally supporting the pipeline on a deep foundation system or 3) relocating the pipeline to a less sinkhole prone portion of an adjacent property. Following the investigation process, relocating the pipeline in conjunction with pre-installation ground improvements via subsurface grouting represented the most cost-effective, lowest risk solution at the site. Introduction In January 2009 a sinkhole developed below an active petroleum pipeline that crossed under a local creek in Plymouth Meeting, Pennsylvania. Upon initial discovery, it was reported that the sinkhole measured approximately 9 feet (3 meters) in diameter by 9 feet (3 meters) in depth causing the pipeline to be unsupported across a portion of the open void. Representatives of the pipeline company filled in the sinkhole with various materials that ranged from tree stumps to geotextile filter fabric and well-graded aggregates as a temporary solution to the problem. Following the temporary backfill measures, the owner recognized the severity of the problem and the need for the expertise of a geotechnical engineering firm. Initially, a feasibility study was conducted to determine the most cost-effective and best long term solution at the site. The options considered include: 1) subsurface grouting within the right-of-way 2) structurally supporting the pipeline on a deep foundation system or 3) relocating the pipeline to a less sinkhole prone portion of an adjacent property. The first step in the study was to perform a site reconnaissance and a stereographic aerial photograph review. Due to the site being primarily wooded, inconclusive results were found from the aerial photograph review. During the site reconnaissance, the streambed was dry on each side of the pipeline crossing. The stream bed remained dry for approximately 500 to 600 yards (457 to 549 meters) upstream of the sinkhole at the pipeline crossing. Further inspection revealed a large sinkhole had created a disappearing stream condition upstream of the pipeline crossing. Photograph 1 shows the large sinkhole upstream of the pipeline crossing. The overall topography within the pipeline right-of-way slopes gently to moderately downwards toward the creek and sinkhole locations. Photograph 2 shows the area of study within the pipeline right-of-way. The overall topography within the pipeline right-of-way slopes gently to moderately downwards toward the creek and sinkhole locations. Photograph 2 shows the area of study within the pipeline right-of-way. Project Description and Background During low flow conditions, the creek water disappears into the upstream sinkhole leaving the downstream side dry. During periods of steady rainfall, storm water
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Published on 01/01/2017
Volume 2017, 2017
DOI: 10.5038/9780979542275.1108
Licence: CC BY-NC-SA license
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