Numerical Studies of Pipeline Uplift Resistance in Frozen Ground

2004 ◽  
Author(s):  
Bill Liu ◽  
Karen Moffitt ◽  
J. F. (Derick) Nixon ◽  
Joe Zhou ◽  
Yuxing Xiao
Keyword(s):  
Numerical Model ◽  
Design Tool ◽  
Frozen Soil ◽  
Frost Heave ◽  
Sensitivity Analyses ◽  
Relative Movement ◽  
Frozen Ground ◽  
Discontinuous Permafrost ◽  
Uplift Resistance ◽  
Load Displacement

A buried pipeline is subject to a variety of internal and external loads, one of which is the load induced by relative movement between the pipeline and the surrounding soils. Frost heave is one of the potential mechanisms that induce the relative movement for buried pipelines of chilled gas. The magnitude of the loads due to frost heave depends upon the amount of heaving and the load-displacement characteristics of the surrounding frozen soils, i.e., the uplift resistance of the soils. Under the sponsorship of Pipeline Research Council International (PRCI), laboratory uplift tests have been carried out to study the load-displacement characteristics of a frozen soil. In parallel, a series of laboratory geo-mechanical tests were conducted to define stiffness, tensile strain limits and time-dependent features of the frozen soil. A numerical model, using the geo-mechanical properties of the frozen soil as input parameters, has been developed. The numerical model is intended to be used as a tool primarily for sensitivity analyses and scaling of the results of the laboratory uplift tests to field operations, which are anticipated to have pipe diameters in a range of 5 to 10 times of the laboratory tests. A description of the numerical model is provided in the paper. The load-displacement relationships and failure mechanisms represented in the numerical model are compared with the measurements and observations made during the laboratory uplift tests (quantitative data on uplift resistance are considered proprietary and will not be presented, but detailed data may be obtained from technical publications of PRCI). After being calibrated, the numerical model can be used for sensitivity analyses, and also potentially used as a design tool for pipelines in discontinuous permafrost.

Experimental Studies of Pipeline Uplift Resistance in Frozen Ground

2004 ◽  
Author(s):  
Bill Liu ◽  
Jack Crooks ◽  
J. F. (Derick) Nixon ◽  
Joe Zhou
Keyword(s):  
Experimental Studies ◽  
Soil Surface ◽  
Mechanical Tests ◽  
Frozen Soil ◽  
Frost Heave ◽  
Frozen Ground ◽  
Frozen Soils ◽  
Uplift Resistance ◽  
Load Displacement ◽  
The Impact

A buried pipeline is subject to a variety of internal and external loads, one of which is the load induced by relative movements between the pipeline and the surrounding soils. Frost heave is one of the potential mechanisms that induce the relative movement for buried pipelines of chilled gas. The magnitude of the loads due to frost heave depends upon the amount of heaving and the load-displacement characteristics of the surrounding frozen soils, i.e., the uplift resistance of the frozen soils. Under the sponsorship of Pipeline Research Council International (PRCI), laboratory uplift tests have been carried out to study the load-displacement characteristics of a frozen soil and to assess the impact of loading rate, ice content and freezing direction. In addition to the measurements of the load and displacement of the pipe, deformations of the soil surface were also monitored at various locations. Parallel to the uplift tests, a series of laboratory geo-mechanical tests were conducted to define stiffness, tensile strain limits and time-dependent behavior of the frozen soil. Examples of the uplift test results are presented in the paper, together with detailed descriptions of soil material and test conditions. It is noted that quantitative data on uplift resistance are considered proprietary and will not be presented in this paper; however, detailed data may be obtained from technical publications of PRCI. Observations during the test with respect to the development of cracks in the frozen soil will be discussed. The load-displacement relationships measured in the uplift tests, together with the geo-mechanical properties of the frozen soil, will be used to the development and calibration of a numerical model, which will be presented in a separate technical paper to IPC2004.

Modelling of pipeline under differential frost heave considering post-peak reduction of uplift resistance in frozen soil

2006 ◽  
Vol 43 (3) ◽  
pp. 282-293 ◽  
Author(s):  
Bipul C Hawlader ◽  
Vincent Morgan ◽  
Jack I Clark
Keyword(s):  
Analytical Solution ◽  
Frozen Soil ◽  
Frost Heave ◽  
Large Strains ◽  
Peak Reduction ◽  
Numerical Predictions ◽  
Discontinuous Permafrost ◽  
Nonlinear Stress ◽  
Uplift Resistance ◽  
Differential Frost Heave

The interaction between buried chilled gas pipelines and the surrounding frozen soil subjected to differential frost heave displacements has been investigated. A simplified semi-analytical solution has been developed considering the post-peak reduction of uplift resistance in frozen soil as observed in laboratory tests. The nonlinear stress–strain behaviour of the pipeline at large strains has been incorporated in the analysis using an equivalent bending stiffness. The predicted results agree well with our finite element analysis and also with numerical predictions available in the literature, hence the simple semi-analytical solution can be considered as an alternative to numerical techniques. A parametric study has been carried out to identify the influence of key factors that can modify the uplift resistance in frozen soil. Among them, the residual uplift resistance has been found to be the important parameter for the development of stresses and strains in the pipeline.Key words: pipeline, frost heave, discontinuous permafrost, semi-analytical solution, uplift resistance, frozen soil.

Permafrost and thermal interfaces from Normal Wells pipeline ditchwall logs

1991 ◽  
Vol 28 (5) ◽  
pp. 738-745 ◽  
Author(s):  
J. F. Derick Nixon ◽  
R. Saunders ◽  
J. Smith
Keyword(s):  
Color Change ◽  
Input Parameter ◽  
Data File ◽  
Frozen Soil ◽  
The Arctic ◽  
Frozen Ground ◽  
The North ◽  
Discontinuous Permafrost ◽  
Geophysical Surveys ◽  
Thermal Interfaces

During the construction of the Normal Wells pipeline by Interprovincial Pipeline Ltd. in the early 1980s, a continuous ditchwall log was created during ditching for pipeline burial. The ditch was typically 1.2 m deep and stretched continuously from Normal Wells in the Canadian Arctic to Zama Lake in northern Alberta, a total distance of 869 km through the discontinuous permafrost zone. The ditch was logged by experienced geotechnical field personnel every 50–100 m, depending on changing conditions. Every transition from unfrozen to frozen soil was logged based on visual criteria such as color change, visual presence of ice or moisture in the ditchwall, etc. Recently, the authors have carefully studied the ditchwall records and compiled a data file containing all of the relevant data pertaining to permafrost distribution. This provided a unique opportunity to study the amount and distribution of permafrost along a continuous transect through discontinuous and sporadic permafrost regions in Arctic Canada. The number of thermal interfaces per kilometre is an extremely important input parameter for studies relating to pipeline frost heave and thaw settlement in the Arctic. In addition, a knowledge of the percentage of frozen ground is important when deciding whether to operate a gas or pipeline above or below freezing. The number of frozen–unfrozen interfaces have been summarized in the paper by pipeline spread and geological terrain unit. The overall percentage of frozen ground decreases from up to 95% in the north to a low of around 16% at the south end of the study area, as might be expected. The number of interfaces typically varies between about one and three per kilometre, with the highest number occurring in some of the organic terrain units in the southern discontinuous zone. Finally, comparisons are made with the amount of permafrost and number of interfaces as logged by electrical geophysical surveys carried out and published in advance of pipeline construction. There is reasonable agreement in terms of the overall amount of frozen ground; however, the geophysical surveys may have overestimated the number of thermal interfaces in some areas. Key words: ditch logs, permafrost, Normal Wells, pipeline, thermal interfaces, frozen ground.

scholarly journals Numerical analysis of temperature fields around the buried arctic gas pipeline in permafrost regions

2020 ◽  
pp. 248-248
Author(s):  
Xinze Li ◽  
Huijun Jin ◽  
Yanjing Wei ◽  
Zhi Wen ◽  
Yan Li ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Ambient Air ◽  
Gas Pipeline ◽  
Frozen Soil ◽  
Temperature Fields ◽  
Frost Heave ◽  
Positive Temperature ◽  
Discharge Temperature ◽  
Discontinuous Permafrost ◽  
Permafrost Table

Based on one planned arctic natural gas pipeline engineering which will cross continuous, discontinuous, sporadic and non-permafrost areas from north to south, with different pipeline temperatures set, a thermal model of the interaction between pipeline and permafrost is established to investigate the influence of pipelines on the freezing and thawing of frozen soil around pipeline and thermal stability of permafrost. The results show that different pipeline temperatures influence the permafrost table greatly. Especially in discontinuous permafrost areas the permafrost table is influenced in both positive temperature and negative temperature. The warm gas pipeline of 5?C could decrease the value of permafrost table about 1 to 3 times pipe diameter and aggravate the degradation of permafrost around pipeline; -1?C and -5?C chilled gas pipeline can effectively improve the permafrost table and maintain the temperature stability of frozen soil , but the temperature of soils below pipeline of -5?C decreases obviously, which may lead to frost heave hazards. In terms of thermal stability around pipeline, it is advised that transporting temperature of -1?C is adopted in continuous permafrost area; in discontinuous permafrost area pipeline could operate above freezing in the summer months with the station discharge temperature trending the ambient air temperature, but the discharge temperature must be maintained as -1?C throughout the winter months; in seasonal freezing soil area chilled pipeline may cause frost heave, therefore pipeline should run in positive temperature without extra temperature cooling control.

Internal stresses in frozen ground

1985 ◽  
Vol 22 (3) ◽  
pp. 413-416 ◽  
Author(s):  
P. J. Williams ◽  
J. A. Wood
Keyword(s):  
Temperature Gradient ◽  
Key Words ◽  
Field Studies ◽  
Frozen Soil ◽  
Phase Relations ◽  
Frost Heave ◽  
Internal Stresses ◽  
Frozen Ground ◽  
Mechanical Constraints

Small transducers that were inserted 1.2 cm apart in a frozen soil subjected to a temperature gradient have shown differences in pressure of more than 0.1 MPa. The pressures are generated by growth of ice lenses taking place against the resistance of the surrounding frozen soil.The observations, which are compatible with reports by others from various field studies, illustrate the importance of both the thermodynamic and mechanical constraints on the process of frost heave and the development of frost heave pressures. Key words: frozen ground, frost heave, frost heave pressures, phase relations, internal stresses.

Frost heave – pipeline interaction using continuum mechanics

1983 ◽  
Vol 20 (2) ◽  
pp. 251-261 ◽  
Author(s):  
J. F. Nixon ◽  
N. R. Morgenstern ◽  
S. N. Reesor
Keyword(s):  
Continuum Mechanics ◽  
Applied Pressure ◽  
Soil Mass ◽  
Structural Member ◽  
Frozen Soil ◽  
Frost Heave ◽  
Flexible Pipe ◽  
Frozen Ground ◽  
Frost Heaving ◽  
Differential Frost Heave

As a chilled pipeline crosses a transition from frozen to unfrozen ground or shallow permafrost, a differential frost heave problem may develop causing strains in the pipe. Soil–structure interaction models that are currently available to handle this problem concentrate on the pipe as the dominant structural member and represent the soil mass as a series of unconnected springs. This paper considers the soil to be an elastic or nonlinear viscous continuum and imposes a nonlinear boundary condition to represent the frost heaving soil and the dependence of frost heave on applied pressure. The pipe is assumed to be a completely passive structural member and the soil strains at the pipe elevations are studied. The dependence of the maximum pipe strains on the length of the heaving section and on the thickness of frozen ground beneath the pipe have been established for a typical set of soil and frost heaving conditions. It is found that, for the conditions studied, when the thickness of shallow permafrost or frozen soil is greater than about 7–8 m, the strains that a flexible pipe experiences are less than the strain criteria currently in use on many pipeline projects. Keywords: frost heave, pipeline, interaction, stress analysis, finite elements, continuum mechanics, thermo-elasticity.

scholarly journals Effects of preferential flow on snowmelt partitioning and groundwater recharge in frozen soils

2019 ◽  
Vol 23 (12) ◽  
pp. 5017-5031 ◽  
Author(s):  
Aaron A. Mohammed ◽  
Igor Pavlovskii ◽  
Edwin E. Cey ◽  
Masaki Hayashi
Keyword(s):  
Soil Moisture ◽  
Groundwater Recharge ◽  
Preferential Flow ◽  
Frozen Soil ◽  
Time Lags ◽  
Runoff Generation ◽  
Frozen Ground ◽  
Soil Matrix ◽  
Frozen Soils ◽  
Flow Through

Abstract. Snowmelt is a major source of groundwater recharge in cold regions. Throughout many landscapes snowmelt occurs when the ground is still frozen; thus frozen soil processes play an important role in snowmelt routing, and, by extension, the timing and magnitude of recharge. This study investigated the vadose zone dynamics governing snowmelt infiltration and groundwater recharge at three grassland sites in the Canadian Prairies over the winter and spring of 2017. The region is characterized by numerous topographic depressions where the ponding of snowmelt runoff results in focused infiltration and recharge. Water balance estimates showed infiltration was the dominant sink (35 %–85 %) of snowmelt under uplands (i.e. areas outside of depressions), even when the ground was frozen, with soil moisture responses indicating flow through the frozen layer. The refreezing of infiltrated meltwater during winter melt events enhanced runoff generation in subsequent melt events. At one site, time lags of up to 3 d between snow cover depletion on uplands and ponding in depressions demonstrated the role of a shallow subsurface transmission pathway or interflow through frozen soil in routing snowmelt from uplands to depressions. At all sites, depression-focused infiltration and recharge began before complete ground thaw and a significant portion (45 %–100 %) occurred while the ground was partially frozen. Relatively rapid infiltration rates and non-sequential soil moisture and groundwater responses, observed prior to ground thaw, indicated preferential flow through frozen soils. The preferential flow dynamics are attributed to macropore networks within the grassland soils, which allow infiltrated meltwater to bypass portions of the frozen soil matrix and facilitate both the lateral transport of meltwater between topographic positions and groundwater recharge through frozen ground. Both of these flow paths may facilitate preferential mass transport to groundwater.

scholarly journals Experimental and analytical study of seismic site response of discontinuous permafrost

2016 ◽  
Vol 53 (9) ◽  
pp. 1363-1375 ◽  
Author(s):  
Behrang Dadfar ◽  
M. Hesham El Naggar ◽  
Miroslav Nastev
Keyword(s):  
Shear Wave ◽  
Site Response ◽  
Free Field ◽  
Frozen Soil ◽  
Shaking Table ◽  
Experimental Program ◽  
Small Scale ◽  
Seismic Site Response ◽  
Discontinuous Permafrost ◽  
Spectral Accelerations

Seismic site response of discontinuous permafrost is discussed. The presence of frozen ground in soil deposits can significantly affect their dynamic response due to stiffer conditions characterized by higher shear-wave velocities compared to unfrozen soils. Both experimental and numerical investigations were conducted to examine the problem. The experimental program included a series of 1g shaking table tests on small-scale models. Nonlinear numerical analyses were performed employing FLAC software. The numerical model was verified using the obtained experimental results. Parametric simulations were then conducted using the verified model to study variations of the free-field spectral accelerations (on top of the frozen and unfrozen soil blocks) with the scheme of frozen–unfrozen soil, and to determine the key parameters and their effects on seismic site response. Results show that spectral accelerations were generally higher in frozen soils than in unfrozen ones. It was found that the shear-wave velocity of the frozen soil as well as the assumed geometry of the blocks and their spacing have a significant impact on the site response.

Geothermal modeling of soil or mine tailings with concurrent freezing and deposition

1998 ◽  
Vol 35 (2) ◽  
pp. 234-250 ◽  
Author(s):  
JF (Derick) Nixon ◽  
Nick Holl
Keyword(s):  
Snow Cover ◽  
Mine Tailings ◽  
Frozen Soil ◽  
Freezing And Thawing ◽  
Frozen Ground ◽  
Geothermal Model ◽  
Winter Time ◽  
Upper Boundary ◽  
Good Agreement

A geothermal model is described that simulates simultaneous deposition, freezing, and thawing of mine tailings or sequentially placed layers of embankment soil. When layers of soil or mine tailings are placed during winter subfreezing conditions, frozen layers are formed in the soil profile that may persist with time. The following summer, warmer soil placement may not be sufficient to thaw out layers from the preceding winter. Remnant frozen soil layers may persist for many years or decades. The analysis is unique, as it involves a moving upper boundary and different surface snow cover functions applied in winter time. The model is calibrated based on two uranium mines in northern Saskatchewan. The Rabbit Lake scenario involves tailings growth to a height of 120 m over a period of 24 years. At Key Lake, tailings increase in height at a rate of 1.3 m/year. Good agreement between the observed position of frozen layers and those predicted by the model is obtained. Long-term predictions indicate that from 80 to 200 years would be required to thaw out the frozen layers formed during placement, assuming 1992 placement conditions continue. Deposition rates of 1.5-3 m/year give the largest amounts of frozen ground. The amount of frozen ground is sensitive to the assumed snow cover function during winter.Key words: geothermal, model, tailings, freezing, deposition.

Impact of seasonally frozen soil on germinability and antioxidant enzyme activity of Picea asperata seeds

2009 ◽  
Vol 39 (4) ◽  
pp. 723-730 ◽  
Author(s):  
Jihong Qin ◽  
Qing Liu
Keyword(s):  
Oxidative Stress ◽  
Antioxidant Defense ◽  
Germination Rate ◽  
Antioxidant Defense System ◽  
Antioxidant Enzyme Activity ◽  
Frozen Soil ◽  
Defense System ◽  
Frozen Ground ◽  
Subalpine Zone ◽  
Picea Asperata

In the subalpine zone of the Qinghai–Tibetan Plateau of China, Dragon spruce (Picea asperata Mast.) is commonly used for reforestation. The aim of the present work was to study the effects of seasonally frozen soil on the germination of P. asperata seeds and to investigate whether these effects were associated with resumption of the antioxidant defense system. The nonfrozen treatment resulted in near failure of germination (1%) and was associated with relatively high levels of hydrogen peroxide (H2O2) and low activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxide (APX). Germination of P. asperata seeds at 10 cm under the seasonally frozen soil was higher than that at 5 cm by 26%; this higher germination rate was associated with the recovery of SOD, CAT, and APX activities. The levels of malondialdehyde (MDA) in seeds from seasonally frozen treatments were higher than those in the nonfrozen treatment, implying greater lipid peroxidation and that frozen seeds might have suffered from oxidative stress. The results indicate that seasonally frozen soil facilitated the germination of P. asperata seeds and that germination was closely related to the resumption of antioxidant enzymes activity. Overall, these findings suggest that the disappearance of seasonally frozen ground caused by global warming might result in failure of regeneration of P. asperata.

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