Modern society relies on a hidden network of tunnels, pipelines, and underground structures to transport people, cargo, liquids, and gasses from place to place, or to store materials, without disrupting surface activities or intruding on our views of the landscape. This underground infrastructure is taken for granted until an extraordinary event occurs, such as a tunnel collapse or pipeline explosion. Amid the rescue, repair, and restoration efforts, specialists from a variety of disciplines investigate the materials, design, and underground environment of the damaged facility to determine the cause(s) of the failure and appropriate methods of repair.
Collapse of a tunnel may cause injury or death to construction workers, miners, or transit-system riders; settlement of overlying structures and utilities; and disruption of surface drainage or even draining of overlying lakes or rivers. Failure of a major pipeline may result in injury to nearby persons, damage to nearby facilities, and environmental contamination, in addition to expensive service interruptions and physical damage to the pipeline itself. Pipeline failures can cause landslides, sinkholes, and ground settlement. If the failure is associated with ground movement, the need to construct geotechnical stabilization measures may prolong the disruption of service. The reliability of gravity-flow pipelines may be diminished by the effects of ground settlement—example causes include subsidence from mining, petroleum extraction, groundwater withdrawal, or compaction of soft or organic-rich sediment—or by elevation changes due to expansive or collapsible soil.
The performance of tunnels and pipelines relies on their material and structural integrity and their ability to resist external forces. Aging pipelines, like other elements of our infrastructure, are increasingly susceptible to failure. Materials integrity factors often associated with pipeline failures include material defects, improper installation (e.g., welding defects), internal erosion due to a high-energy flow environment, and corrosion—an electrochemical reaction that can manifest as uniform thinning of a pipe wall or as localized pitting. Structural integrity factors include insufficient pipe rigidity or tunnel-support strength to accommodate external soil and traffic loads. Geologic and geotechnical factors that govern soil-structure interaction between a tunnel or pipeline and the surrounding soil and rock include the corrosivity of soil and groundwater, and external forces resulting from unanticipated overburden pressures, improper tunnel or trench shoring, unsuitable pipe bedding or trench backfill, inadequate compaction, soil erosion and piping, and ground movement.
Tunnels and pipelines, because of their long, linear configurations, typically traverse areas of varying topographic, hydrologic, and geologic conditions that subject the structures to different types and magnitudes of external forces. Tunnel and pipeline builders must anticipate the effects of these varying site conditions, as well as existing adjacent structures, during design, construction, operation, and maintenance. External forces are imposed by the in-place surrounding soil, possibly augmented by soil creep, erosion, landslides, earthquake shaking, earthquake-induced permanent ground displacement (e.g., fault rupture, liquefaction and lateral spread, soil densification), and other ground movements.
Exponent’s multidisciplinary scientific and engineering staff is ideally suited for investigations related to construction, performance, and failure of elements of our underground infrastructure. Our mechanical and materials engineers and metallurgists are experts in the integrity of materials used for constructing underground structures. Our structural engineers are experts in the design and overall structural integrity of these structures. And our geologists and geotechnical engineers are experts in the soil, rock, and groundwater that surround and interact with underground structures.
Exponent’s geologists and engineers, working as part of a multidisciplinary team, use a variety of tools to investigate pipeline and tunnel problems, whether they constitute nuisance issues or catastrophic failures.
Our services include:
Emergency response and evaluation of imminent hazards posed by failure of tunnels, pipelines, or other underground structures
- Pre- and post-construction evaluation of the effects of underground construction on adjacent structures
- Field investigation of underground structures, including:
- Pipeline video surveys
- Confined-space inspections
- Surface and underground geologic mapping, emphasizing ground stability, soil corrosivity, and groundwater pathways
- Documentation of ground movement indicators
- Collection of subsurface boring and test-pit data
- Installation and monitoring of instrumentation to detect ground movement
- In-house geotechnical laboratory testing for measuring rock and soil engineering properties
- Engineering analyses of tunnel stability and pipeline integrity
- Pipe stress modeling, pipe material and weld evaluation, non-destructive and destructive pipe testing, corrosion and biochemical testing, collection and preservation of pipeline-failure evidence, fracture analysis
- Condition assessment of pipe in distribution systems
- Service life modeling of distribution/collection systems
- Analysis of the causes of tunnel collapses and pipeline failures, including:
- Evaluation of earthquake hazards
- Evaluation of erosion and flood hazards
- Evaluation and substantiation of, and response to, differing site-condition claims