The design of buried pipelines in permafrost regions or artificially frozen grounds requires knowledge of the uplift resistance. The uplift resistance of frozen soil is dependent on soil mechanical properties such as tensile strength, shear strength, and deformation modulus, and those properties are critical for characterizing the plastic yielding zones in the frozen soil around the pipe. Due to the existence of a large amount of unfrozen water, frozen clay soil displays complex mechanical properties which vary with temperatures. Previously, extensive experimental and simulation work has been done on the soil pipe interactions at normal temperatures, but less attention is given to the frozen soil pipe interactions. There are limited researches on frozen clay pipe interactions with the consideration of temperature changes. In this study, finite element analysis is conducted to investigate frozen clay soil-pipe interactions at varying temperatures, where a pipe is simulated as being subjected to vertical load-controlled or vertical displacement-controlled stress path conditions. The temperature-dependent mechanical properties of frozen clay soil are obtained from the literature. Both tensile yielding and shear yielding behavior are included in the modeling and the temperature-dependent yielding surfaces are included in an explicit way. A comparison of results from the Mohr-Coulomb model with tensile cut off and the hyperbolic Drucker-Prager model is presented. The results indicate that hyperbolic Drucker-Prager model is an effective model for analyzing the plastic zones. Under a plane strain condition, the applied hyperbolic Drucker-Prager model gives more conservative uplift resistance-displacement relation when compared with the result from the Mohr-Coulomb model.
Nunavik is a territory in Northern Quebec where 14 communities depend essentially on aerial transportation for their subsistence, economic development, and quality of life. Some airport runways built on permafrost in the late 80s showed worrying degradation signs only a few years after construction. The effect of runway embankments on the thermal regime at the embankment toes and where drainage is deficient, among other things, is well documented throughout the literature. These phenomena, as well as the general permafrost degradation, are amplified by climate changes, especially in northern regions. Because the permafrost degradation is worrying for transportation infrastructure, a project was undertaken to characterize the physical and mechanical properties of some permafrost soils in Northern Quebec, with the objective to assess their creep and thaw sensitivity. Frozen core samples were recovered at seven airstrips and two access roads, and undisturbed specimens were brought back to Laval University geotechnical laboratory. The samples from the most critical and representative study sites were subjected to basic geotechnical characterization along with triaxial creep. The creep tests allowed obtaining estimates of the creep rate for the soils at different deviatoric stress and temperatures. As for the thaw consolidation tests, they allowed estimating the settlements associated with a potential thawing of permafrost for various ice contents. The present paper focuses on the creep behavior. With the available ground thermal regimes and climate change scenarios, the results allow anticipating the thaw and creep settlements for some soils in Nunavik and can be used as part of a global adaptation strategy for infrastructure built on permafrost.
A common road insulation practice in Norway is to use a layer of crushed rock material, which is called a frost protection layer (FPL). The current regulations allow a large variation of particle size distribution into this layer. This paper presents field investigations on frost insulation performance of crushed rock material with three distinct grading. A full-scale test site was built in Roros, Norway, with each FPLs composed of 1 meter of crushed rock aggregates and built as: Ro-3 section was a coarse dense-graded material (0/120 mm), Ro-1 section, a coarse open-graded material (40/120 mm) and section Ro-2, a fine dense-graded material (0/32 mm). The sections were monitored for two winters (2016-17 and 2017-18). The results showed a significant difference in frost penetration and capacities between the sections. For winter 2016-17, the frost depth reached 194, 136, and 175 cm in Ro-1, Ro-2, and Ro-3 sections respectively, for a surface freezing index of 22,630 degrees C.h. For winter 2017-18, the frost depth reached 232, 171, and 209 cm in Ro-1, Ro-2, and Ro-3 sections respectively, for a surface freezing index of 36,683oC.h. The 0/32 mm material provided the best insulation capacity with a frost protection capacity of 443 degrees C.h/cm. The frost protection capacity for the 0/120 and 40/120 mm material were of 253 and 85 degrees C.h/cm respectively. The study showed that fine dense-graded material provided superior frost protection mostly due to the larger amount of water retained that increased latent heat. For similar road design and layer thicknesses, the coarse, well-graded material seemed to be the most cost-effective material adapted to Norwegian regions with F-100 < 28,000 degrees C.h. Coarse, open-graded material should be used in low FI areas, and convection effect should be taken into account.
DC electrical resistivity tomography (ERT) is increasingly being used to delimit permafrost bodies, but a threshold value to differentiate between frozen and unfrozen ground is needed for data interpretation. Here we compare resistivities measured in peat and silts across a range of temperatures in both the field and the laboratory. ERT surveys were conducted at four sites with instrumented boreholes in the southern NWT (60.9-62.5 degrees N). In the laboratory, remoulded soil samples were wetted to field moisture content, frozen in closed containers, and resistivity was measured across a range of temperatures during thaw. Between 0 degrees C and -0.5 degrees C, the resistivity of peat ranged from approximately 3,000-6,000 Omega m. For frozen silt, maximum resistivities were about 1,000 Omega m while the lowest was 85 Omega m, well below the value typically used to delimit permafrost. The relationship between resistivity and temperature allowed a two-dimensional temperature field to be generated from the tomograms, but predictions were not always consistent due to intra-site differences in moisture content and the presence or absence of segregated ice. This study illustrates the great range of resistivity values possible at temperatures close to 0 degrees C, and demonstrates the importance of validating ERT results for warm permafrost.
In permafrost regions, the movement of water during winter has important implications for hydrology, land use, and infrastructure. Knowledge of winter hydrothermal dynamics in small, extensive tundra stream networks is limited. Climate warming, changing precipitation regimes, and increases in tundra vegetation coverage may delay active layer freeze-back, potentially increasing winter water movement. The primary goals of this research are to improve knowledge of the thermal regime of small stream channels in continuous permafrost, explore the implications of a changing climate and runoff, and describe the influence of infrastructure on channel thermal regime. A program of temperature monitoring in stream channel beds and riparian margins between Inuvik and Tuktoyaktuk is presented here. Preliminary results, if representative of several years, suggest that permafrost is not present at depths shallower than 3.5 m below the bed of a small stream with a contributing area of similar to 30 km(2), and that this layer does not likely re-freeze during winter. This thermal regime may be modified by highway crossings that reduce or eliminate stream snow cover, and the degree of thermal disturbance may be a function of contributing watershed size. This research and further related work have the potential to provide new insight on channel thermal regime and winter hydrology in permafrost regions, offer projections of change in the context of a warming climate, and help inform the design, operation, and mitigation of hydrological issues associated with linear infrastructure in permafrost.
The previous laboratory study of joint electrical resistivity and acoustic velocity measurements is reviewed for both consolidated and unconsolidated permafrost in this paper. The relation of logarithm of resistivity log(R) and P-wave velocity V-p is a concave function. An increase of temperature, fine content, and salinity results in a decrease of both acoustic velocity and electrical resistivity. Electrical resistivity is sensitive to salinity, while acoustic velocity changes substantially near thawing temperature. The joint measurement results could be used to estimate unfrozen water saturation (UWS) based on Archie's law, weighted equation (WE), or Kuster-Toksoz equations (KT). However, the estimated UWS from different methods is not always consistent. The difference can be up to 20%. It might be due to the fact that UWS is not the only parameter influencing the electrical and acoustic properties. In order to obtain consistent UWS, a joint model that combines the electrical effective medium theory (EMT) and the acoustic self-consistent approximation (SCA) is proposed. In this method, UWS and aspect ratio which describes particles shape are found simultaneously from the joint SCA-EMT model. Most of the results from the proposed method are between that of Archie's law and WE method, which indicates that the electrical method might overestimate UWS and acoustic method might underestimate it.
In fact, huge number of ground anchors with concrete frame are used to protect landslide of slope in cold regions, which may have a serious risk of rupture or pop out of wires due to over tensioned and loosening caused by frost heave and thaw settlement of slope. Center hole type load cells are generally used to monitor tension force of wires at ground anchor head, which have not been effectively used to cover wide area of slope because they are expensive, large, and heavy to deal. Authors are developing a new monitoring system of anchored slope protections making use of small, light, and low-cost MEMS inclinometer and wireless communication device, which might be replaceable with the direct measurement of wire tension using large load cells. Tension force of anchored wires is calculated using precise data of inclination angle of anchored concrete frame obtained by sensors fixed near to anchor head. The frame inclination data are telecommunicated by wireless through communication base nearby to display on web site in real time. Monitored data in field, laboratory test results using model frame, and FEM analysis are shown in the paper, which support the system is highly practical to know real time condition of slope stability, and to judge optimal time of re-tense of wires effectively in minimum number.
The Heart River drains approximately 3,360 square miles in southwest North Dakota, flowing through the city of Mandan, ND, before entering the Missouri River near Bismark, ND. Flood protection and irrigation projects have been constructed over the years in the Heart River basin, including the Heart Butte Dam constructed in 1949 by the U.S. Bureau of Reclamation approximately 100 miles upstream of Mandan. While this altered the hydrology of the basin slightly by providing storage, irrigation opportunities, and increasing evaporation, the Lower Heart River can cause both open water and ice jam flooding in the city of Mandan. Flood protection levees have been constructed over time in Mandan starting in 1959 with improvements added in 1963 and in 1989. An effort to provide increased flood protection and to re-certify the levee system in Mandan to Federal Emergency Management Agency (FEMA) protection levels is being undertaken by the Lower Heart Water Resource District. The effort included a reanalysis of the historic discharge and stage records of the USGS gage at the upstream edge of the city. An analysis of past ice jamming events, river and floodplain geometry, and ice jam mechanics found that there is a peak discharge for which an ice jam can remain in place and that this discharge varies depending on river location and local geometry. The analysis indicated that the 1% annual exceedance probability ice jam discharge is 42,000 cfs, but the peak discharge for which an ice jam could remain in place varied between 15,000 and 25,000 cfs depending on river location. The paper describes the analysis techniques used to develop the combined stage frequency values for the levee recertification.
Construction of highway embankments vary in thickness along its planned alignment to maintain horizontal and vertical road geometry requirements. In regions of continuous permafrost, however, the thickness of the overlying embankment greatly impacts the thermal regime of the frozen foundation soil. Thick embankments, exceeding 5 m, usually provide considerable thermal insulation where the frozen soil used to construct the embankment remains frozen in the core, while thin embankments, usually less than 2 m thick, can contribute to permafrost degradation. Climate boundary conditions also play a significant role in the thermal performance of these embankments. In order to study the thermal impact of embankment thickness on permafrost degradation and thermal embankment performance, test sections along the newly-constructed Inuvik-Tuktoyaktuk Highway in the Northwest Territories, Canada, were instrumented with thermistor strings to measure temperature readings at different locations in the embankment fill and foundation soil. This paper presents the results of the monitored temperature for two phases of instrumentation in April 2015 and April 2017 for the thick and thin embankments, respectively. Thermal numerical modelling using site climate data showed considerable agreement with field values and provides confidence for future performance prediction.
An electrical resistivity and temperature piezocone penetration test (RTCPTu) was carried out in ice-rich permafrost near Umiujaq, Nunavik, Quebec, Canada, to assess the permafrost cryostratigraphy. A penetrometer with temperature and piezometer sensors and electrical resistivity module was used for this RTCPTu. Signal processing of RTCPTu logs and forward modelling to simulate the response of the electrical resistivity module penetrating in ice-rich layered medium were performed to discriminate the ice lenses from the layers of frozen silt within permafrost. The cryostructure of permafrost, made of a complex sequence of ice lenses and layers of frozen silt, induces very noisy RTCPTu logs. Ice-rich permafrost is characterized by extremely variable values of cone resistance, friction ratio, pore pressure, and electrical resistivity. Based on the wavelet analysis of RTCPTu logs, the wavelengths of electrical resistivity are shorter than the ones of cone resistance, friction ratio, and pore pressure while all these sensors penetrated the same ice-rich layered medium. As found from forward modelling of the response of an electrical resistivity module penetrating in a resistive ice lens of different thicknesses embedded in conductive frozen silt, the variations in electrical resistivity as a function of depth are more complex than the ones of cone resistance, friction ratio, and pore pressure. This complex response is due to the four electrodes of the electrical resistivity module which are alternately in contact with the ice lens inducing complex electrical current flow and potential induction in this ice-rich layered medium. Knowing the simulated responses of the electrical resistivity module penetrating in ice-rich layered medium, the ice lenses, and layers of frozen silt in ice-rich permafrost were discriminated using cross-correlation between the electrical resistivity log and these simulated responses. Therefore, the cryostratigraphy of permafrost and ice content per penetrated linear meter of 42% were assessed from this RTCPTu.
Permafrost is generally sustained in tundra lakes beneath water depths less than 2/3 of the maximum ice thickness. Few talik development models consider areas of shallow water even though widespread talik development beneath shallow water may result from environmental change. In thaw lakes where frost does not penetrate the lake bottom, talik development has been successfully predicted using models such as the Stefan solution based on mean annual lake-bottom temperatures (T-lb). In the nearshore zone of the tundra lakes of Old Crow Flats, YT, frost penetrates the lake bottom sediment in early winter, yet T-lb are greater than 0 degrees C and permafrost sustainability is controlled by the thermal offset. This research assessed whether the Stefan solution can provide reasonable estimates of talik development under such conditions. We compared model results to talik depths measured by water-jet drilling along transects perpendicular to four receding shores. The Stefan solution predicted talik depth and shape well where seasonal freezing and thawing of the sediment was limited in duration by rapid subsidence of the lake bottom beneath maximum lake-ice thickness. Prediction accuracy increased when talik depth was calculated in two stages to reflect an increase in T-lb once the lake bottom subsided to depths exceeding maximum lake-ice thickness. The Stefan solution was ineffective where shore erosion was slow (<0.2 m a(-1) over 50 years) and water depth was shallow (<0.5 m) over an extended area near shore, because variations in snowpack thickness determined permafrost sustainability and degradation rates, resulting in irregular talik geometry.
Winter roads in Canada, which comprise over-land and over-ice segments, account for approximately 10,000 km of roadways. Operator experience has shown that over-ice segments often limit the operating window for winter roads—reducing the time available to haul essential goods to isolated communities and to service the private sector (e.g. mining, forestry). The operating windows for over-ice segments have generally decreased in time with a warming climate. When a floating ice cover incorporates a reinforcing element, it may better resist fracture propagation and breakthrough, and may thus better support vehicle traffic. Ice cover reinforcement could be applied to weak links in a winter road, i.e. segments known to be unreliable, or to help close off open leads in a river. Ice reinforcing elements may include wood pulp, steel cables, timbers, natural fibers, and geomembranes among many other options. Such microscopic and macroscopic ice reinforcement techniques have been tested in the past by various research groups. This paper reviews established ice reinforcement methods, proposes criteria for selecting appropriate methods, and presents preliminary results of testing on reinforced ice. In addition to strength characteristics, the environmental compatibility, the constructability, and stakeholder acceptability are primary screening criteria for reinforcement selection. Four-point beam testing has been initiated on reinforced ice samples. These tests confirm an increase in breakthrough resistance, but not an increase in strength, which may have to do with a weakly bonded surface at the ice/reinforcement interface.
The release of water from hydropower plants into downstream rivers is primarily driven by electricity demand, creating sub-daily fluctuations in flows, a phenomenon known as hydropeaking. In Southwestern Yukon, the Aishihik plant releases most of its annual volume during the winter, when non-controlled rivers are at their lowest levels. Massive volumes of water released during that period of the year may be enhancing freeze-up ice jams and associated flooding. The present study uses a multi-method approach that includes signal treatments to characterize the influence of water releases from the Aishihik plant on river discharge at selected downstream gauging stations. Overall, this study shows that water releases from the Aishihik plant significantly influence the Dezadeash River discharge at a station located approximately 50 km downstream. The average Dezadeash River discharge is approximately double what its natural level would be during the winter. The effects of hydropeaking from the plant are clearly observable in the Dezadeash discharge sub-daily time series, even during months when plant operations are limited. During the winter, the Alsek River discharge, measured at a station located at more than 150 km from the plant, is also influenced by the Aishihik hydropower plant. The lack of data availability at that station did not allow for an estimation of the degree to which winter discharge may exceed its natural regime.
Maintenance costs have risen since 1996 along the northern Dempster Highway, especially for snow clearing. The purpose of this paper is to investigate the wind regime of the region and determine its association with increased maintenance activities. Hourly wind speed and direction were measured at four sites near the territorial border crossing (YT km 465/NT km 0) for July 2006-December 2018 at the Environment Canada Rock River station (YT km 457) and February 2014 to July 2018 at YT km 421, NT km 8.5, and NT km 51.5. Wind speeds were classified according to the Beaufort Scale and wind type: calm (force 0-1), breeze (2-6), gale (7-9), and storm (10-12). The mean winter wind speed was highest at Rock River (4.1 m/s), followed by km 8.5 (2.4 m/s), km 421 (2.3 m/s), and km 51.5 (2.1 m/s). At all sites the mean wind speed was lower in winter than summer, but the highest winds were measured in the winter. At Rock River, 9.1% of observations were for gale or storm winds, considerably more than at kms 8.5 (0.5%), 51.5 (0.1%), and 421 (1.1%). In Yukon the dominant and strongest winds were easterly off Richardson Mountains, while in the NT the dominant winds were southwesterly, but more variable in direction. There were no apparent increases in winter wind speeds over the period of record. Although Rock River experienced the strongest winds throughout the year, it exhibited the same seasonal trends in wind speed as the other locations. The dominant easterly wind direction at Rock River was consistent with km 421. The valley near Rock River is well nicknamed Hurricane Alley.
Gas pipeline transportation crossings (trench method) under the large rivers with destructive spring flood and intensive ice jams involves very different safety hydro-technical issues of operation. Such as changing the riverbed, the banks destruction, the new channels formation, erosion, and formation of alluvial sedimentation. For the effective application of the remote control method of underwater gas pipelines for the purpose of operational inspection of its technical condition it is necessary to improve the methodical of GPR application. Low-frequency linear GPR with a frequency of 50 MHz and 100 MHz (OKO-2, Logis-GEOTECH Company) to study the water surface of the Lena River depth up to 20 meters are applied. A special device for waterproof of antennas is developed. And also, if it necessary, a special equipment to submersibility the antennas to a depth of 1 meter is constructed. The paper presents the results of the survey of the operated main gas pipeline in the period 2014 to 2017, including monitoring of changes in the conditions of occurrence, as well as determining the exposure of the pipeline due to the erosion of the banks after the destructive spring flood. For the first time, the technology of changing the orientation of the receiving and transmitting antenna are applied to increase the search area of the pipeline in the bottom sediments at a depth of more than 8 meters, which is also disclosed and described in the paper. Experimentally proved the effectiveness of the GPR using in the inspection of gas pipelines at river crossings with a depth of more than 10 meters, buried in the sediments with a capacity of more than 6 meters. The method of increasing the search area of pipelines is developed.
Spontaneous corrugation can occur at intersections on snowy and icy roads due to the repeated passage of moving vehicles. Corrugation adversely affects driving safety due to reduced friction between the wheels and road; it can also cause passenger discomfort and transform crosswalks into unstable surfaces for pedestrians. Because the causes and timing of spontaneous corrugation remain poorly understood, effective countermeasures cannot be applied to prevent its formation. In this study, we installed time-lapse cameras at an intersection in Sapporo, Japan, to observe the formation of corrugation in two consecutive winters (2015-2017). To determine the relationship between corrugation and environmental conditions, we obtained meteorological data from the observatory closest to the intersection and recorded the temperature distribution on the road using a thermographic camera. Our analysis showed that a threshold amount of fresh snowfall was necessary for corrugation. The air temperature required for corrugation was between 0 and -2 degrees environment, snow, temperature, vehicle, washboard road C. Surface snow showed a tendency to thaw due to energy provided by heat transfer from the chassis of vehicles; thus, corrugation emerged at the headstream side of the traffic flow, where vehicles frequently stopped for red lights. As a result, corrugation can be predicted by forecasting environmental conditions. We also initiated a social network survey, where participants were asked to upload photographs of corrugation on snowy and icy roads to a website, along with the time and location. An analysis of these corrugation events and the associated environmental conditions supported our results. This study will contribute to improving the safety of winter travel in regions where spontaneous corrugation is common.
Following four years of construction, a new open-pit to access a diamondiferous kimberlite pipe (A21 Pipe), was officially opened at the Diavik Diamond Mine on August 20, 2018. The site is located approximately 300 km northeast of Yellowknife, NT, in a zone of continuous permafrost. The A21 Pipe is in a depression just offshore of South Island in Lac de Gras that had developed a through talik. A 2,200 m long ring dike was constructed to allow dewatering of the depression and to mine the kimberlite pipe by open-pit mining. Near the lake shore, the rockfill dike is founded on permafrost, whereas in deeper waters, the foundation is on unfrozen lakebed sediments and till over bedrock. A cut-off wall was installed to reduce seepage through the dike and its unfrozen foundation. Within the section of the dike founded on permafrost, the frozen soil and bedrock are used as a hydraulic barrier. It was therefore essential to understand the extent of the permafrost into Lac de Gras, especially on the South Abutment, where the water is shallow, and the lakebed topography forms a complex-shaped submerged peninsula with talik under the permafrost. Boreholes and geophysical surveys were used to estimate the extent of the talik and provide input for the design. During the initial phase of construction, extensive ground temperature monitoring and detailed observations were used to verify the extent of permafrost assumed in the design. These measures helped with the understanding of the complex ground thermal regime and provided information on the thermal behaviour of the foundation required to guide some of the construction decisions, such as the required initiation of active freezing by the use of thermosyphons or the timing of the placement of additional dike embankment construction material to accurately lock in winter frost and protect the permafrost from thawing.
In this paper, we present a numerical modelling approach that simulates the melting of an ice-filled rock discontinuity. Using a finite element model, we implement an ablation process to simulate the thawing of ice and removal of the resulting meltwater, assuming a well-drained system, under specific environmental conditions defined by appropriate boundary conditions. By extending an earlier version of an ablation model, we demonstrate the importance of the strength loss due to melting ice in a rock mass discontinuity that is influenced by convective and conductive heat transfer. The results from the numerical model provide input for analytically computing the tensile strength of the ice-rock interface to further characterize the strength of ice-filled discontinuities.
An LNG storage tank in Fairbanks, Alaska, is one of the first LNG storage tanks constructed on permafrost soils that has been designed as an at-grade foundation. An at-grade mat foundation was selected for this tank over the typical pile supported foundations due to the seismic hazards at the site. Above-grade construction activities for the LNG storage tank were planned to occur over an 18-month period. The construction included a large poured concrete mat foundation, which generated significant heat during curing and had the potential of impacting the underlying permafrost. In addition, the outer concrete tank shell was planned to be heated over the next year to facilitate construction of the inner steel tank. An active cooling system installed below the storage tank was designed, constructed, and used to maintain the permafrost, thereby mitigating the thermal impacts of tank construction activities. Thermal finite element modeling of the system was performed before construction to develop an adequate design. During construction, soil temperature measurements were collected at and above the level of the active cooling system to monitor system effectiveness. Comparisons between the modeled and actual soil temperatures are compared and an evaluation of the active cooling system is presented.
