Buried Infrastructure & Utilities

RA: Mohammad Katebi (Ph.D. Candidate)

Project Duration: 2016-Present

Collaborators & Partnerships: Dr. James Blatz (Department of Civil Engineering – UofM)

Financial Support: NSERC Discovery Grants &  University of Manitoba, Graduate Enhancement of Tri-Council Stipends (GETS) Programs

Project Description: 

Nowadays, buried pipeline infrastructures are a pre-eminent part of the gas and oil transportation across the country and their integrity has an important impact on the strength of Canada’s economy. In Canada, there are an estimated 242,000 km of gas and oil pipelines. A large proportion of the pipeline system in Canada is decades-old. Pipeline accidents are often environmentally damaging and extremely costly to clean-up and remediate. Also, civil, criminal or regulatory penalties from a pipeline loss of containment may be very high (Oswell, 2016). In Canada, according to the National Energy Board (NEB) database, about 750 incidents have occurred since 2008 along major pipelines, including 454 gas and oil leaks, 25 cases of serious injury, 6 deaths, 13 explosions and 7 cases of adverse environmental effects.

At an early stage of this project, the soil, pipe, and ground movement data collected by Dr. Ferreira (2016) at UofM at Plum River Crossing, Harrowby Assiniboine River valley, and St-Lazare Assiniboine River valley sites in Manitoba is being analyzed. Three research sites were selected that best captured a range of landslide types (translational, rotational), different geological features, and are considered to be high-risk among other parameters considered in the selection process. The Plum River site represents the condition where a gas pipeline is buried parallel to a riverbank slope (a river crossing) that has undergone past riverbank landslide activity and is likely to still be moving. A past riverbank instability encompassing the gas pipeline at the crossing was visaully evident during the initial site visit and the instability is predominantly rotational in nature. The Harrowby and St-Lazare valley sites represent conditions where a gas pipeline transverses a potential landslide area (unstable slope) or a slope undergoing creep movements on a larger scale since the pipelines run along a long valley wall within a deep river valley. The potential for ground movements at the valley sites were deemed to be either translational (assummed to be relatively shallow) or rotational associated with deep seated movements or combination thereof (Ferreira, 2016).

An analytical and numerical study have been performed to interpret the field measurement data (Ferreira, 2016). This study provides meaningful guidelines for future monitoring programs in landslide zones. In addition, the optimum burial depth of pipelines affected by slow downslope ground displacement and temperature variations is recommended.

The other topics, which will be covered in this research project, is the effect of unsaturated soils and the oblique ground movement on the interaction between soil and pipeline. The aim is to present some guidelines to improve the soil-pipeline practice.

This project includes laboratory pullout testing and numerical modeling.

Outcomes:

Katebi M., Maghoul P., Blatz J., 2018. Numerical Analysis of Pipeline Response to Landslides: A Case Study, Canadian Geotechnical Journal, In preparation (to be submitted by June 15, 2018).

Katebi M., Liu H., Maghoul P., Blatz J., 2018. Numerical Analysis of Buried Pipelines subject to Slope Failure and Seasonal Temperature Variation, International Pipeline Conference (ASME), Calgary, Canada.

RA: Hongwei Liu (MSc Student)

Project Duration: 2017-Present

Collaborators & Partnerships: Dr. Ahmed Shalaby (Department of Civil Engineering & Municipal Infrastructure Chair – UofM)

Financial Support: University of Manitoba – Startup Fund

Project Description: 

The buried utilities such as conduits and pipelines are the main part of the infrastructure in urban areas. In cold regions, the effect of frost actions on the structural integrity should be addressed appropriately in the design process of such utilities.  Typically, buried pipelines must be located below the frost depth to avoid frost-induced damage due to differential heave, or freezing of water inside the pipe.  The depth of the frost penetration in Canada can be as deep as 2.5 meters, which increases the construction cost of buried utilities dramatically.  Despite all the efforts in design and operation to prevent buried pipes from the frost damage, pipe failure due to the harsh climate and soil deformations currently costs the City of Winnipeg over $8 million annually.

Most parts of Manitoba, with freezing indices ranging from 1550 to 3800 degree-days and frost depth as deep as 2.5 m, are susceptible to frost actions, surface heave and eventually distress of the structures. A practical way to control the frost action in a frost susceptible soil is to prevent the penetration of the freezing front through insulation. The low thermal conductivity of insulating materials controls the heat transfer so that the heat is conserved in the soil during winter and the formation of ice lenses is halted. The current practice to design the thickness and width of insulation materials used to protect buried pipes from freezing is based on recommendations provided by manufacturers. In these recommendations, the thickness of insulation is determined by knowing the amount of backfill to be used on top of the insulation and design freezing index (◦C-days), which depends on location of the project.  Also, the total insulation width is calculated by knowing the pipe diameter, design frost depth as well as the insulation depth. In these recommendations, the effects of pore-water phase change and water movement toward the frozen fringe on the geometry of insulation materials are not considered explicitly.

This project has to main objectives:

• The optimum design of the rigid plastic foam insulation in frost susceptible soils: for this purpose, a transient heat and mass transfer model for freezing soil as well as a transient heat transfer model with and without pore-water phase change are implemented to study the thermal regime within the soil during freezing and thawing periods. Results of these analyses are compared in order to highlight the importance of the water movement as well as the pore-water phase change in the heat transfer in the soil. A transient energy balance at the ground surface is used by considering  inputs  such  as  ambient  temperature  and  wind  speed  as  provided  by Environment Canada for typical climate conditions of Winnipeg, Manitoba. Then, the performance of the insulating foam with various backfill materials, insulation length, insulation thickness, distance between pipe and insulation as well as pipe burial depth is  The advanced Nelder-Mead algorithm is implemented to determine the optimum insulation design based on local construction cost and insulation cost.
• The development of a Thermo-Hydro-Mechanical model for freezing soil to assess the effect of frost heave on structural integrity of pavement structure and buried utilities: The serviceability of pavement structures and buried utilities in cold regions can be adversely affected by seasonal frost. The three essential factors for detrimental frost actions are (a) subfreezing temperature, (b) a continual supply of water (a high water table), and (c) presence of frost-susceptible soils. Frost-susceptible soils, e.g. silty soils, have moderate hydraulic conductivity due to their pore size distribution, which promotes capillary flow. In soils with high hydraulic conductivity, e.g., coarse-grained soils, water cannot rise by capillarity to the freezing front while in clayey soils with low hydraulic conductivity, not enough water will get to the freezing front to produce significant heaving. Both the heaving and thawing phases of frost action often lead to cracking of the pavement surface, which results in annual losses in riding quality and a reduction in the life of a pavement. It is an important yearly maintenance task to fill the cracks to keep water out of the base and subgrade. The proposed model is based on the Biot theory and a porosity rate function. The model is validated by comparison with the empirical segregation potential of freezing soil proposed by Prof. Konrad. The model developed in this study will be an asset for the assessment of the structural integrity of infrastructure subject to freezing and thawing cycles.

Outcomes:

Liu H., Maghoul P., Shalaby A., 2018. Optimum Insulation Design for Buried Utilities Subject to Frost Action in Cold Regions Using the Nelder-Mead Algorithm, International Journal of Heat and Mass Transfer (Elsevier), Submitted.

Moussa A., Shalaby A., Kavanagh L., Maghoul P., 2018. Use of rigid geofoam insulation to mitigate frost heave at shallow culvert installations, Journal of Cold Regions Engineering (ASCE), Submitted.

Liu H., Maghoul P., Shalaby A., 2018. Thermo-Hydro-Mechanical Modeling of Frost Heave Using the Theory of Poroelasticity in Frost-Susceptible Soils in Double-Barrel Culvert Sites, Construction and Building Materials (Elsevier), Submitted.