scholarly journals Joint Acoustic and Electrical Measurements for Unfrozen Water Saturation of Frozen Saline Soil

2020 ◽  
Author(s):  
Chuangxin Lyu ◽  
Thomas Ingeman-Nielsen ◽  
Seyed Ali Ghoreishian Amiri ◽  
Gudmund Reidar Eiksund ◽  
Gustav Grimstad
Keyword(s):  
Electrical Resistivity ◽  
Water Content ◽  
Electrical Resistance ◽  
Water Saturation ◽  
Acoustic Velocity ◽  
P Wave ◽  
Unfrozen Water ◽  
Unfrozen Water Content ◽  
P Wave Velocity ◽  
Hydrate Bearing Sediments

<p><strong>Abstract. </strong>The climate change has aroused great concern on the stability and durability of the infrastructure installed on permafrost, especially for frozen saline clay with a large amount of unfrozen water content at subzero temperature. The joint electrical resistivity and acoustic velocity measurements are conducted for frozen saline sand and onsøy clay with 50% clay content and 20~40 g/L salinity in order to determine the unfrozen water content. A systematic program of tests involves the saline sand with different salinity, natural onsøy clay with the variable of temperature and freezing-thawing cycles and reconstituted onsøy clay with distinctive density and salinity. The data analysis of measurement results in combination with previous joint measurements for frozen soil resolves the effect of temperature, salinity, soil type and freezing-thawing cycles on the acoustic and electrical properties. 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. We also find that both natural and reconstituted clay with similar water content and salinity show quite different acoustic velocity and electrical resistivity, which indicates that ice crystal structures are distinctive between natural and reconstituted samples. Besides, P-wave velocity is much more sensitive to the fabric change or induced cracks than electrical resistance during freezing-thawing cycles.  In the end, acoustic models like the weighted equation (Lee et al., 1996), Zimmerman and King’s model (King et al., 1988) and BGTL (Lee, 2002) are applied to the UWS estimates based on P-wave velocity and electrical models like Archine’s law are adopted based on electrical resistance. Both estimated UWS from different methods is not always consistent. The difference can be up to 20%.</p><p><strong>Keywords:</strong> Frozen Saline Clay, Acoustic Velocity, Electrical Resistance, Unfrozen Water Saturation</p><p>References:</p><p>King, M. S., Zimmerman, R. W., & Corwin, R. F. (1988, May). Seismic and Electrical-Properties of Unconsolidated Permafrost. Geophysical Prospecting, 36(4), 349-364. https://doi.org/10.1111/j.1365-2478.1988.tb02168.x</p><p>Lee, J. S. (2002). Biot–Gassmann theory for velocities of gas hydrate-bearing sediments.</p><p>Lee, M. W., Hutchinson, D. R., Collett, T. S., & Dillon, W. P. (1996). Seismic velocities for hydrate-bearing sediments using weighted equation. Journal of Geophysical Research: Solid Earth, 101(B9), 20347-20358. https://doi.org/10.1029/96jb01886</p><p> </p>

Permafrost Mapping with Electrical Resistivity Tomography: A Case Study in Two Wetland Systems in Interior Alaska

2020 ◽  
Vol 25 (2) ◽  
pp. 199-209
Author(s):  
Christopher H. Conaway ◽  
Cordell D. Johnson ◽  
Thomas D. Lorenson ◽  
Merritt Turetsky ◽  
Eugénie Euskirchen ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Water Content ◽  
Electrical Resistivity Tomography ◽  
Time Lapse ◽  
Research Area ◽  
Acquisition Time ◽  
Unfrozen Water ◽  
Resistivity Tomography ◽  
Interior Alaska ◽  
Unfrozen Water Content

Surface-based 2D electrical resistivity tomography (ERT) surveys were used to characterize permafrost distribution at wetland sites on the alluvial plain north of the Tanana River, 20 km southwest of Fairbanks, Alaska, in June and September 2014. The sites were part of an ecologically-sensitive research area characterizing biogeochemical response of this region to warming and permafrost thaw, and the site contained landscape features characteristic of interior Alaska, including thermokarst bog, forested permafrost plateau, and a rich fen. The results show how vegetation reflects shallow (0–10 m depth) permafrost distribution. Additionally, we saw shallow (0–3 m depth) low resistivity areas in forested permafrost plateau potentially indicating the presence of increased unfrozen water content as a precursor to ground instability and thaw. Time-lapse study from June to September suggested a depth of seasonal influence extending several meters below the active layer, potentially as a result of changes in unfrozen water content. A comparison of several electrode geometries (dipole-dipole, extended dipole-dipole, Wenner-Schlumberger) showed that for depths of interest to our study (0–10 m) results were similar, but data acquisition time with dipole-dipole was the shortest, making it our preferred geometry. The results show the utility of ERT surveys to characterize permafrost distribution at these sites, and how vegetation reflects shallow permafrost distribution. These results are valuable information for ecologically sensitive areas where ground-truthing can cause excessive disturbance. ERT data can be used to characterize the exact subsurface geometry of permafrost such that over time an understanding of changing permafrost conditions can be made in great detail. Characterizing the depth of thaw and thermal influence from the surface in these areas also provides important information as an indication of the depth to which carbon storage and microbially-mediated carbon processing may be affected.

Active layer and bedrock mapping in permafrost with Electrical Resistivity Tomography and Induced Polarization – A case study from Svalbard 

2021 ◽  
Author(s):  
Asgeir Kydland Lysdahl ◽  
Sara Bazin ◽  
Andreas Olaus Harstad ◽  
Regula Frauenfelder
Keyword(s):  
Electrical Resistivity ◽  
Physical Properties ◽  
Water Content ◽  
Active Layer ◽  
Electrical Resistivity Tomography ◽  
Unfrozen Water ◽  
Resistivity Tomography ◽  
Unfrozen Water Content ◽  
Run Off ◽  
Permafrost Soils

<div> <p> </p> <p>Design and construction of infrastructure in frozen permafrost soils demands for detailed investigation of the ground characteristics prior to the construction process. Variations in ground temperature affect the physical properties of permafrost, such as amount of unfrozen water content and ice content. In addition, aggradation and degradation of permafrost induce changes of its physical properties. Ground-based Electrical Resistivity Tomography (ERT) and Induced Polarization (IP) surveying can be used to characterize near-surface ground conditions to a few tens of meters depth, especially when calibrated by boreholes. </p> </div><div> <p>Measured electrical resistivity is temperature‐dependent, which makes ERT a suitable tool in permafrost investigations. The temperature dependence is most pronounced for temperatures below freezing point. Electrical resistivity rises exponentially during freezing, when unfrozen water content within a substrate decreases. The electrical resistivity is, thus, very sensitive to phase changes between water and ice and we usually observe a lack of resistivity contrast at lithological interfaces. Direct translation from resistivity to lithology is, therefore, seldomly possible in permafrost. While ERT is successful for mapping the active layer, further interpretation of resistivity profiles is thus impeded by the lack of resistivity contrast within the permafrost. Indeed, the lithological structures are hidden by the strong resistivity of the frozen layer. By adding complementary information, IP measurements can help separate effects due to freezing and lithology. The IP effect can be measured in the time-domain, simultaneously with the ERT measurements, and with the same equipment. The IP effect occurs after abruptly interrupting the current flow between the current electrodes. The voltage across the potential electrodes does not drop to zero instantaneously, but  decays exponentially. The decay time can be used to estimate the chargeability of the ground. </p> </div><div> <p>Here, we present three examples where combined ERT- and IP-surveying was used to detect the interface between sediments and bedrock within permafrost soils, and to investigate potential environmental hazards related to run-off paths from existing and planned landfills. Study sites were an active landfill near the town of Longyearbyen, and two potentially new landfills near Longyearbyen and Barentsburg, respectively (the latter one for surplus masses resulting from coal mining). As permafrost traditionally had been seen as a natural flow barrier for such landfills, understanding its degradation owing to climate change was considered key in the planning of future sites. Eight profiles were carried out in September 2018, when expected active layer thicknesses were at their maxima. Two-dimensional inversion was performed with the commercial software RES2DINV for the resistivity data and Ahrusinv for the chargeability data.  </p> </div><div> <p>The results of our case studies show the benefit of simultaneous ERT- and IP-measurements, to both map active layer depths and determine sediment depths in permafrost areas. They also gave valuable insights in understanding potential environmental hazards related to run-off from the landfill, as a consequence of water entering the landfill in the summer period. ERT/IP surveys are flexible and relatively easy to deploy. The technique is non-destructiv and is, therefore, also suitable for maintenance studies in vulnerable arctic Tundra environments. </p> <p> </p> </div>

scholarly journals Electrical Conductivity-Based Estimation of Unfrozen Water Content in Saturated Saline Frozen Sand

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Zejin Lai ◽  
Xiaodong Zhao ◽  
Rui Tang ◽  
Jinhong Yang
Keyword(s):  
Electrical Conductivity ◽  
Electrical Resistivity ◽  
Water Content ◽  
Freezing Point ◽  
Salt Content ◽  
Free Water ◽  
Conductivity Measurement ◽  
Unfrozen Water ◽  
Essential Difference ◽  
Unfrozen Water Content

The salinity of the pore solution is closely associated with the unfrozen water content and can be reflected by variation in electrical conductivity in frozen soils. However, the influence of salinity was not considered in the existing models for estimation of unfrozen water content based on electrical conductivity measurement, and a model considering the effect of salt content was therefore developed to estimate the change of unfrozen water content of saline sands with variation of salt content (0%, 0.2%, and 1%). The unfrozen water content and the electrical resistivity were measured by nuclear magnetic resonance (NRM) and using resistance test equipment under a temperature ranging from 25°C to −15°C, respectively. The results indicated that the model using a cementation exponent expressed by a piecewise function with respect to temperature can produce a reasonable estimation on the content of unfrozen water. There was an essential difference between nonsaline and saline frozen sands in the increase of electrical resistivity due to the different reduction rates of unfrozen water content. The variation of electrical resistivity in nonsaline sand was mainly caused by the decrease of free water when temperature was higher than the freezing point and adsorbed water when temperature was lower than the freezing point, whereas the reduction of free water in two stages was the main reason for the variation of electrical resistivity in saline sand. The results and data obtained provided a basis for further developing a novel approach to measure the unfrozen water content in the field.

scholarly journals Semiempirical Correlation between P-Wave Velocity and Thermal Conductivity of Frozen Silty Clay Soil

2021 ◽  
Vol 2021 ◽  
pp. 1-7
Author(s):  
Yadong Ji ◽  
Kaipeng Zhu ◽  
Chao Lyu ◽  
Shidong Wang ◽  
Dianyan Ning ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Wave Velocity ◽  
Clay Soil ◽  
P Wave ◽  
Unfrozen Water ◽  
Silty Clay ◽  
Geothermal Systems ◽  
Unfrozen Water Content ◽  
P Wave Velocity ◽  
Silty Clay Soil

In this study, the thermal conductivity and P-wave velocity of silty clay soil with different water contents are investigated through experiments at different temperatures, and a theoretical correlation between thermal conductivity and wave velocity is established. With temperature decline, the unfrozen water content is reduced and frost heave cracks propagate in soil samples. The variations in thermal conductivity and P-wave velocity are summarized as four phases. The freezing temperature of silty clay soil is between −2°C and −4°C. There is an inversely proportional relationship between thermal conductivity and P-wave velocity for silty clay soil at temperatures below freezing. The experimental results show that the theoretical correlation can well explain the relationship between P-wave velocity and thermal conductivity. These findings provide a possibility for determining the thermal conductivity easily and quickly in geothermal systems and underground engineering projects.

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