Pipelines are the lifelines of modern infrastructure, transporting oil, gas, water, and other resources across vast distances. While much focus is placed on pipeline materials and design, the importance and impact of surrounding soils on pipeline safety should not be ignored. Geotechnical engineers ensure pipelines are designed to withstand various soil conditions, ground movements, and external forces.

Pipeline failures, which can lead to environmental disasters and significant economic losses, often stem from poor soil-pipe interaction, that is, how the pipe and soil interact under stresses such as landslides, thermal expansion, and seismic activity. Forensic geotechnical engineers play a critical role in determining the causes of these failures, especially regarding how soil conditions were assessed during the design and construction phases.

How Geotechnical Engineers Address Forensic Pipeline Failure Challenges

1. Proper Determination of Soil Strength

Pipeline stress analysts generally perform pipe stress analysis using the soil strength values provided by geotechnical engineers. These values indicate the stress level the soil can tolerate without undergoing excessive deformations.

Geotechnical engineers often provide conservative values to provide a margin of safety by judiciously applying factors to overestimate the load-bearing capacity of the soils. However, overestimating the load-bearing capacity too much can result in excessive deformation or even failure of the pipe in extreme conditions. Conversely, underestimating the soil’s load-bearing capacity can result in using an overdesigned pipe.

In circumstances where pipe failures do occur, forensic geotechnical engineers investigate whether the soil strength was assessed adequately and whether the design team overestimated the load-bearing capacity of the soils in the pipe zone. The results of these investigations affect legal proceedings and provide insight for future design and remedial work.

2. Forensic Site Investigations

Root cause analysis (RCA) is the most essential part of pipeline failure cases as it helps determine the underlying cause of the failure. This is critical to resolving legal disputes and preventing future failures. For this analysis, forensic geotechnical engineers play an essential role in determining whether the soil conditions were appropriately assessed during the design phase.

In many failure cases, the behavior of surrounding soil, including movement due to downward forces, seismic events, and thermal expansion, must be thoroughly considered during the design phase. A lack of understanding of soil-pipe interaction at the outset of design can lead to buckling, excessive pipe deformation, and/or ruptures. Detailed subsurface investigations, such as soil composition tests and stress-deformation analysis, help forensic geotechnical engineers determine whether the pipeline was designed to handle the soil conditions it experienced.

3. Analysis of Various Probable Scenarios

Pipelines typically pass through different geological terrains, from flat zones with soft or loose soils to sloped rocky terrains with seismic hazards. High groundwater levels can also be a challenge in some sections. Each terrain presents specific challenges for the design and construction of the pipeline.

Because the design of pipelines needs to be consistent with the geologic terrain, the shear strength of the soil is a key factor in assessing pipe movement on sloping areas. In contrast, soil dilatancy (the tendency of soil to expand when sheared) must be accounted for in seismic zones to prevent excessive stresses on the pipeline during an earthquake.

In forensic analysis, evaluating how different failure scenarios could have contributed to a pipeline’s performance allows engineers to pinpoint the root causes of failure and implement better designs for the future.

4. Selection of Pipeline Installation Method

Choosing the appropriate pipeline installation method for some sections of the pipeline route can be critical to ensuring long-term performance and stability, whereas selecting an improper installation method could lead to failure. For example, selecting an open-cut installation method instead of horizontal directional drilling (HDD) in an area with deep organic deposits can increase the likelihood of upheaval buckling and pipeline failure.

The proper selection of bedding, padding, and backfill materials, especially around pipe haunches, is imperative to providing pipe support and preventing excessive stresses on the pipe. Similarly, pipeline zone materials must be compacted to an acceptable level to ensure long-term stability. Joint misalignments or improper grading during installation can also affect the pipeline’s integrity and increase the risk of damage due to soil movement, traffic loads, and/or thermal effects.

The Role of Communication in Preventing Pipeline Failures

The RCA of failures associated with geotechnical engineering often reveals a lack of communication between geotechnical engineers and pipeline stress analysts. Geotechnical engineers perform geotechnical investigations to study soil behavior, whereas stress analysts focus on the pipe’s load-bearing capacity.

If these two teams fail to communicate effectively, misjudgments about soil strength or pipeline load-bearing capacity may result in unexpected pipeline failures. Overestimated soil strength parameters, for example, may lead stress analysts to under-design a pipeline for the range of forces applied to it during its lifespan. Conversely, where the soil is assumed to be weaker than it actually is, the pipeline may be overdesigned, leading to unnecessary costs and more rigidity. Effective communication between geotechnical engineers and pipeline stress analysts is crucial to mitigating risks associated with pipeline failures due to a lack of design for site-specific conditions

Forensic Geotechnical Engineers in Legal Cases

Forensic geotechnical experts are critical in legal disputes related to pipeline failures. Geotechnical engineers hired as forensic experts for pipeline failure cases conduct inline inspections and forensic subsurface investigations to assess whether soil properties were correctly determined and whether all scenarios of soil-pipe interaction were considered. Data collected from the site is used to reconstruct the events that led to the failure and determine whether the design and installation phases followed the applicable standards and contract documents. These findings are key to resolving disputes and determining each party’s liability. Forensic engineers may make future recommendations for improvements based on their findings.

The Essential Role of Geotechnical Engineers in Pipeline Design and Failure Analysis

Geotechnical engineers play a critical role in the pipeline design and forensic analysis of pipeline failures associated with soil and terrain conditions. The risk of pipeline failures can be significantly reduced through site-specific assessment of soil strength parameters, an informed selection of the pipeline installation method, and effective communication between geotechnical engineers and pipeline stress analysts. Forensic geotechnical experts provide the technical insight to resolve pipeline failure-related legal disputes and ensure the long-term performance of future design and improvements.

Contact the Author for further information:

Peyman Tabatabaei is a professional engineer with 20 years of experience. He has been appointed as an engineering expert or assisted the named expert on numerous occasions. Peyman’s expertise is in civil and geotechnical investigation, which includes front-end engineering design (FEED), detailed design, construction, and consulting engineering. He supports clients in the analysis of retaining and shoring walls for deflections, settlement analysis of foundations, failure analysis of dams, road structure failure root cause analysis, and geotechnical-related failures of pipelines. 

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References

Oswell, J. M. (2021). Soil Mechanics for Pipeline Stress Analysis (2nd ed.). Calgary, Alberta, Canada: Naviq Consulting Inc.

Tsatsis, A., Gelagoti, F., & Gazetas, G. (2018). Performance of a buried pipeline along the dip of a slope experiencing accidental sliding. Géotechnique, 68(11), 968–988.

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