Permafrost Foundation Research Articles

Investigation of the freeze–thaw states of foundation soils in permafrost areas along the China–Russia Crude Oil Pipeline (CRCOP) route using ground-penetrating radar (GPR)

The China–Russia Crude Oil Pipeline (CRCOP) was built to transport Siberian crude oil across 1030km of frozen ground. The Chinese portion of the CRCOP crosses 441km of discontinuous permafrost zones along the eastern flanks of the Da Xing'anling (Hinggan) Mountains. Significant thaw settlement of some of the pipeline foundation soils has occurred since the pipeline began operating in January 2011. The differential thaw settlement around the pipeline at the transitions between the thaw-settling and thaw-stable zones may lead to displacement or even buckling of the pipeline. To evaluate the engineering safety and long-term stability of pipeline foundations, ground-penetrating radar (GPR) was used to detect the freeze–thaw states of pipeline foundation soils in the permafrost zones. From April 2012 to November 2013, a total of 2780m of GPR profiles and 62 cross-sections (perpendicular to the CRCOP route) were obtained at eight GPR study sites on various terrains and vegetative coverage, with different thermal insulation configurations around the pipe, and with and without thermosyphons installed. The GPR profiles were interpreted and cross-checked with data from drilling, hand-dug pit or trench excavations, and ground temperature measurements. The results showed that the foundation soils around the pipeline were thawing, with maximum thaw depths under the pipeline of about 1.1m to 4.5m from the pipe bottom and increased maximum thaw depths of 0.5m to 3.7m during the period of this study. However, GPR profiles from the areas with dense vegetative coverage, and with pipe insulation of 80-mm-thick extruded polystyrene (XPS), and also with vertical thermosyphons installed, showed that permafrost foundation soils were thermally better protected, with only minor thaw settlement. The thermal states of pipeline foundation soils and the underlying permafrost varied markedly with different terrains. The drainage patterns and engineering activities, especially the heating from operating oil flows at an average annual oil temperature of 7.7°C (with a range of 0.7°C to 20.4°C) along the pipeline route may have been responsible for the extensive and substantial thaw subsidence in the ice-rich permafrost zones. Additionally, there was positive feedback between the thaw subsidence of ground surface in the vicinity of the pipeline route and the thaw settlement of the pipeline foundation soils. The greater the earth surface subsidence, the more surface water ponding and soil disturbances, and even more progressive thawing. Therefore, some measures are recommended for stabilizing the pipeline foundation soils. The research results also indicate that the GPR method is effective, nondestructive, and convenient for evaluating the spatiotemporal extent and development processes of the freeze–thaw states of pipeline foundation soils and the underlying permafrost.

Stochastic analysis of uncertain thermal characteristic of foundation soils surrounding the crude oil pipeline in permafrost regions

For foundation soils surrounding the crude oil pipeline in permafrost regions, the soil properties and the upper boundary conditions are stochastic because of complex geological processes and changeable atmospheric environment. The conventional finite element analysis of thermal characteristics for crude oil pipeline is always deterministic, rather than taking stochastic parameters and conditions into account. This study investigated the stochastic influence of an underground crude oil pipeline on the thermal stability of the permafrost foundation on the basis of a stochastic analysis model and the stochastic finite element method. A stochastic finite element program is compiled by Matrix Laboratory (MATLAB) software, and the random temperature fields of foundation soils surrounding a crude oil pipeline in a permafrost region are obtained and analyzed by Neumann stochastic finite element method (NSFEM). The results provide a new way to predict the thermal effects of the crude oil pipeline in permafrost regions, and it shows that the standard deviations in temperature increase with time when considering the stochastic effect of soil properties and boundary conditions, which imply that the results of conventional deterministic analysis may be far from the true value, even if in different seasons. It can improve our understanding of the random temperature field of foundation soils surrounding the crude oil pipeline and provide a theoretical basis for actual engineering design in permafrost regions.

Evaluation of cooling effects of crushed rock under sand-filling and climate warming scenarios on the Tibet Plateau

Crushed rock has been applied to cool the permafrost foundation on the Tibet Plateau. It is facing the challenges of sand-filling and climate warming. Desertification and climate warming are a definite trend on the Tibet Plateau, which has affected the permafrost and infrastructures. This study investigated the influence of sand-filling and climate warming on the cooling effect of crushed rock on the Tibet Plateau, on the basis of a coupled finite element model of convective heat transfer and heat conduction with phase change. The model is calibrated by field measurements. The field experiment and numerical simulation reveal that natural convection in rock layer only occurs in winter season. With the increasing thickness of sand in rock layer, the critical temperature difference between the sand-free layer increases, and the Ra number decreases, and the natural convection intensity weakens gradually. At the climate warming rate of 0.052 °C a−1, the cooling effect of rock layer can counteract the negative effect of climate warming and raise the permafrost table for about the former 20 years. However, the permafrost will eventually degrade continuously, which means the crushed-rock can't be applied to maintain the permafrost foundation stability anymore under these conditions.

Nonlinear analysis of coupled temperature-seepage problem of warm oil pipe in permafrost regions of Northeast China

This study investigated the influence of an underground warm oil pipe on the stability of the permafrost foundation in Northeast China on the basis of a coupled mathematical model of heat transfer and seepage and the finite element method. The thawing cycles around a non-insulated oil pipe and around an oil pipe packaged with insulations of three different thicknesses were analyzed. The results show that in the case of the non-insulated pipe, the maximum thawing depth under the pipe exceeded 8 m after 30 years of operation. Further, the maximum thawing depth decreased significantly after the pipe was insulated. The thawing cycle of the permafrost foundation expanded and shrank alternately between the warm and cold seasons. The range of thermal influence of the warm oil pipe on the upper active layer was much smaller than that on the lower permafrost foundation in the vertical direction. Among the different insulation thicknesses examined (5 cm, 8 cm, and 10 cm), the 8-cm-thick insulation was found to be sufficient to keep the permafrost foundation stable when the oil temperature was maintained at 15 °C. Insulation of the underground warm oil pipe can help maintain the stability of the permafrost and reduce the disturbance of the permafrost environment.

Main Problems and Solutions on Design and Construction of Qinghai-Tibet DC Transmission Project in Permafrost Region

The Qinghai-Tibet direct-current transmission project crosses the high-altitude permafrost region of the Qinghai-Tibet plateau. The permafrost foundation is characterized by being poor in thermal stability, rich in underground ice, very sensitive to climate warming, and strong in water-thermal activity. The foundation of the transmit electricity engineering therefore faces great challenges including tower foundation type selection and design, permafrost protection in the process of foundation construction and long-term stability. Based on an analysis of the geological engineering conditions and principal geological engineering problems of the project, a study is carried out on the design and construction problems of the transmission tower foundations in the permafrost region, the systematic analysis is also made regarding the main solutions to these problems with consideration of tower foundations long-term stability. This study will provide a theoretical basis and technical guide for design and construction of transmission lines in the permafrost region, and a reference for construction of transmission line projects in similar regions in China or even in the world.

Review of Effectiveness and Costs of Strategies to Improve Roadbed Stability in Permafrost Regions

This paper reviews the effectiveness and costs of strategies to improve roadbed stability in permafrost regions, based on a synthesis of literature findings. Roadbeds in permafrost regions experience instability when the embankment loading and its heat absorption properties degrade the permafrost foundation. A variety of engineering strategies are used to mitigate this effect. The review summarizes the rationale, effectiveness, and costs of four types of strategies, namely those that control roadbed thawing, cool the roadbed, insulate the roadbed, and reduce roadbed fill weight. The literature reveals that strategies to control roadbed thawing, insulate the roadbed, or reduce roadbed fill weight do not reverse the long-term degradation of permafrost foundations. Strategies that cool the roadbed by implementing air convection embankments, ventilation ducts, thermosiphons, heat drains, or combinations of these are effective in reducing embankment temperatures and stabilizing the roadbed. Costs vary by geographic and climatic conditions and the proximity of materials to the construction site. Reported data suggest that conducting normal maintenance is less expensive than implementing roadbed cooling strategies, but maintaining serviceability may not be feasible.

Environmental heterogeneity and community structure of the Kobuk River, Alaska, in response to climate change

The Kobuk River runs west along the southern Brooks Range from Gates of the Arctic National Park in Alaska, USA, to the Chukchi Sea. It is highly vulnerable to changes in climate due to its sub-Arctic location, unique geography, and permafrost foundation. Combined with its pristine condition, these qualities make the Kobuk an ideal system upon which to build a conceptual model for predicting ecosystem effects of climate change. We constructed a conceptual ecosystem model for the Kobuk River synthesizing surveyed baseline hydrologic, geomorphic and biotic conditions with literature on Arctic rivers. While the mainstem Kobuk has limited biological productivity, it provides spawning habitat and connectivity for large resident and migratory fish that rely upon off-channel habitat for food resources. System function is dependent largely on intermittent pulse flows that connect riverine habitats, allowing periods of late summer high productivity in off-channel habitat. Spring break-up and hill slope processes are critically important for maintaining habitat complexity and inter-connectivity. Climate change models predict the region will experience a disproportionate increase in average winter air temperature relative to summer temperatures, in the number of ice-free days, and in annual rainfall. Our conceptual model predicts that changes to fish and invertebrate populations on the Kobuk River will result not from physiological responses to increased temperatures, but rather to shifts in two main physical drivers: 1) spring break-up intensity, resulting in changes to scour rate and sediment deposition; and 2) discontinuous permafrost melt, resulting in widespread heterogeneous zones of active layer thickening and thermokarsting. The interaction of these two drivers offers four potential scenarios of geomorphic change in the system and four dramatically different biological outcomes. This model should help managers and scientists evaluate the magnitude and direction of ecosystem changes as they occur within the Kobuk system and potentially other sub-Arctic river systems.

Construction on permafrost foundations: Lessons learned from the Qinghai–Tibet railroad

In allusion to the problems of the frozen soil engineering geology, the roadbed stability with climate change in construction of the Qinghai–Tibet Railway (QTR), this paper provides overview of the frozen soil engineering problems before and during the QTR constructions. Based on the experiences and lessons learned from the road construction in permafrost areas, the authors recommended that the principle of “positive cooling” of the railroad roadbed by lowering permafrost temperatures should be used in the design of the QTR, rather than that of “passive protection” of permafrost through increasing thermal resistance of the roadway, such as simply increasing fill thickness and/or using thermal-insulation materials. This is especially important for the road sections in warm, ice-rich permafrost areas. In addition, this paper reviews several methods for “cooled roadbed” by controlling radiation, convection and conduction through modifying roadway structure and using different fill materials. Meanwhile, the authors also provide information on some existing problems and future monitoring programs along the QTR.

Experimental validation of passive permafrost cooling systems

In areas of warm permafrost, the thawing of interstitial ice in the permafrost layer can cause man-made infrastructure to suffer from thaw settlement damage and failure. For highway and railway embankments, thermosyphons and air convection embankment (ACE) layers are two methods that can be used to reduce embankment and foundation soil temperatures and prevent thaw settlement. These techniques utilize the low air temperature during winter to enhance freezing of the foundation soils and maintain the thermal integrity of the permafrost foundation. In the present paper we report on the application of these techniques in a full-scale field application, carried out as part of a new road building project near Fairbanks, Alaska. Three separate cooling techniques were utilized in the project, including hairpin thermosyphons, horizontal ACE layers, and ventilated shoulders in three different configurations. Each of the three configurations was instrumented with a thermal monitoring system in an effort to evaluate the cooling effectiveness and predict the long-term impact on underlying permafrost temperatures. This paper describes the cooling systems that were used in the project including the thermal monitoring system, and presents performance results for the first year of operation.

In Situ Test on Cooling Effectiveness of Air Convection Embankment with Crushed Rock Slope Protection in Permafrost Regions

An experimental air convection embankment (ACE) was constructed in Beiluhe on the Qinghai-Tibet Plateau during 2001–2003, using coarse (5–8 and 40–50 cm), poorly graded crushed rock fill material on the slope of embankment with thick ground ice permafrost foundation, which should be called the air convection embankment with crushed rock slope protection (ACE–CRSP). The highly permeable ACE–CRSP installation was designed to test the cooling effectiveness of ACE–CRSP concept in an actual railway project. Ground temperature data were collected from test sections on the railway with thermistor sensor strings. The results showed that the mean ground temperature under the layer of the crushed rock with coarse particle diameter of 40–50 cm was lower than that under one with finer particle diameter of 5–8 cm, and the fluctuating range of temperature under the former was bigger than that under the latter. It was obvious that the maximum thaw depth was raised under the layer of crushed rock with coarse particle diameter of 40–50 cm, which resulted from the stronger cooling effectiveness of air convection during the winter. The amount of heat exchange also showed that the absorbed cooling energy of the foundation, under the layer of the crushed rock with coarse diameter, was larger than that with finer diameter.So, we believe that the cooling effectiveness of the crushed rock layer with coarse diameter was stronger than that one with finer diameter.

Air Convection Embankment for Roadways: Field Experimental Study in Alaska

During 1996—1997, an experimental air convection embankment (ACE) was constructed in Fairbanks, Alaska, using very coarse [1- to 6-in (25- to 150-mm)], poorly graded, crushed rock fill material on top of icerich permafrost foundation. The highly permeable ACE installation was designed to test the cooling effectiveness of the ACE concept in an actual roadway project. Using thermistor sensor strings, temperature data were collected from the ACE test section and an adjacent control section. Results showed that the ACE technique can be used to generate a passive cooling effect. This effect manifested as a depression of mean annual temperature at the base of the ACE cross section compared with mean embankment surface temperatures. The data indicated that this thermal offset is on the order of 7°F (Δ = 4°C) for this installation. The measured data also showed that mean annual temperatures are generally near or above the freezing value in the upper portion of the ACE embankment but significantly below freezing at the base. The temperature offset caused a gradual cooling of the foundation soil beneath the embankment with maximum base temperatures that have decreased from more than 40°F (4.4°C) to near freezing during the 5-year measurement period. Within a few more years of operation, it is anticipated that the permafrost table will move up into the base of the ACE cross section, completely eliminating any seasonal thaw in the foundation soil below and thus preventing future subgrade thaw–consolidation.

Monitoring of thermal and mechanical interactions between a structure and its permafrost foundation bed

The problem of the development of geotechnical systems that eliminate thermal pollution of the geological medium is discussed. It is confirmed that their creation is possible only under conditions whereby an inverse relation between the structure and geological medium is provided for on the basis of monitoring. An example of the solution of this problem in Vorkuta is cited, and prospects for the use of monitoring as a component part of structural engineering are described.

Combined method for electric thawing of permafrost foundation beds

Combined method for electric thawing of permafrost foundation beds

Method for determining deformability of permafrost foundations before and after thawing : Panov, S I; Iushin, I I US Army Cold Regions Research and Engineering Lab translation TL 638, July 1977, 6P

Method for determining deformability of permafrost foundations before and after thawing : Panov, S I; Iushin, I I US Army Cold Regions Research and Engineering Lab translation TL 638, July 1977, 6P

Temperature conditions of dams constructed on a permafrost foundation

Temperature conditions of dams constructed on a permafrost foundation

An Analysis of the Performance of a Warm-oil Pipeline in Permafrost, Inuvik, N.W.T.

The data collected at a warm-oil test pipeline at Inuvik. N.W.T. are analyzed making use of the theory of thaw–consolidation proposed by Morgenstern and Nixon. The observed pore pressures, settlements, and rate of melting in the thawing permafrost foundation have been compared with their corresponding theoretical predictions. Bearing in mind the natural variability of ice-rich permafrost deposits, the agreement between prediction and observation is extremely encouraging. As the data collected at this test facility form the only completely documented case history of a thawing foundation in permafrost published to date, this comparison between theory and actual performance is valuable in establishing a level of confidence in the application of the theory of thaw–consolidation.

Performance of a 48-in. Warm-oil Pipeline Supported on Permafrost

An experimental pipeline loop, 2000 ft (609.8 m) long and 4 ft (1.22 m) in diameter, was constructed on the Mackenzie Valley Pipe Line Research Limited test site near Inuvik, N.W.T. Oil at 160 °F (71 °C) was circulated through the loop from February 1971 until January 1972 and performance of the continuous gravel berm and intermittent pile bent support systems and ice-rich permafrost foundation monitored.Instrumentation was placed on and around the pipeline to measure settlement and temperature. Site climatological data were also compiled. Settlement and other movements were monitored by periodically taking elevations at the ground surface and on survey rods attached directly to the pipe. Temperatures were measured using both resistance thermal device (R.T.D.) and thermistor type sensing elements. Measured changes in the foundation soil thermal regime were compared with performance as predicted by a two-dimensional thermal simulator model.The observed pipeline loop performance is discussed and compared with predictions for both foundation thawing and settlement. Applicability of the thermal simulator model used and the support piling behavior is also discussed.

Regulation of the thermal effect of a building on a permafrost foundation bed

Regulation of the thermal effect of a building on a permafrost foundation bed

Dikes on permafrost foundations in northern Manitoba

The development of hydro-electric power within the areas of low relief of northern Canada often requires long dikes to impound a reservoir. Much of this region lies within a zone of discontinuous permafrost, and dike design must allow for foundations varying from soft alluvial materials which will settle during or shortly after construction, to frozen strata with a high ice content which will settle as the ice thaws due to heat loss from the reservoir.This paper describes the approach to design and construction of dikes for the Kettle Generating Station in northern Manitoba, and includes a description of the instrumentation installed in an attempt to correlate the relationship between the rate of thawing of the permafrost and the rate of drainage of free water from the foundation.

Airfields on Permafrost

In this paper the author outlines the special problems of constructing airfield pavements on permafrost foundations. Particular attention is devoted to problems of construction in areas of discontinuous permafrost, the importance of non-frost-susceptibility soils is shown, and means of combating degradation of pavements are carefully explained. The effects of frost loosening on subgrade soil compaction are outlined.