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Publication Number: FHWA-HRT-08-057
Date: November 2008

Long-Term Pavement Performance Computed Parameter: Frost Penetration

CHAPTER 7. FROST PENETRATION ANALYSIS RESULTS

DATA ANALYSIS SUMMARY

Using the E-FROST research analysis tool, all previously processed sections with ER data were reprocessed using the enhanced analysis methodology presented in chapter 4, and new frost depths and layer estimates were determined. In addition to the reinterpretation of the previously processed data, all SMP II sections with ER data that had not been previously analyzed were analyzed using E-FROST, and new frost depths and layer estimates were prepared for the LTPP database upload. The analysis results, as well as the LTPP computed parameters developed under this project, were reviewed thoroughly.

Frost penetration analysis was conducted for 41 LTPP sites from the SMP I and II experiments. The schematic location of LTPP sites used in the frost penetration analysis study is shown in figure 21. Data from 21,953 dates were analyzed, and frost penetration depths were estimated. There were between 2 and 11 years of data analyzed for the different LTPP sites. Detailed frost penetration results were reported in two LTPP computed parameters tables discussed later in this chapter.

This picture shows a map of the lower 48 United States and a portion of Canada with approximate locations of SMP sites analyzed in this study. The sites span from Nevada in the west to Maine in the east, and from Saskatchewan in the north to Arizona in the south. Table 5 of the report lists all the states with SMP sites analyzed in this study.

Figure 20. Picture. Locations of LTPP SMP sites analyzed in this study.

FROST OBSERVATIONS

Observations discovered during the project are described in this section.

Severity of Frost Penetration

Using the results of the frost penetration analysis, average and maximum frost depths were determined, along with the first and the last cold month with freeze conditions for each LTPP site with in-situ measurement data. This information could be used to assess the severity of frost penetration at different LTPP sites.

Maximum freeze depth corresponds to the maximum frost depth for the year with the deepest frost penetration detected during the analysis. Maximum frost depth is used in the design to account for the worst case scenario.

Average maximum freeze depth corresponds to the average of maximum frost depths based on all years used in the analysis and represents average or typical frost penetration conditions.

The first and the last months with freeze conditions are based on the worst case scenario. These months were determined by reviewing frost data for all available years and selecting the earliest month at the beginning of the freeze period and the latest months at the end of the freeze period. A summary of frost determinations is provided in table 6.

Frost penetration profiles generated for all Minnesota, Manitoba, and Saskatchewan sites and site 4018 in New York indicate that frost penetration goes beyond the last interpretation depth. For Arizona site 1024 and Nevada site 0101, the first interpretation depth was lower than the expected frost penetration depth. These cases are noted by starred comments in table 6.

Table 6. Summary of frost determinations.
STATE CODE SHRP ID Number of years analyzed Average max freeze depth, m Maximum freeze depth, m First freeze month Last freeze month
4 (AZ) 1024 4 * * -- --
8 (CO) 1053 5 0.336 0.374 DEC FEB
9 (CT) 1803 5 0.544 0.794 JAN MAR
16 (ID) 1010 5 0.763 0.864 NOV FEB
18 (IN) 3002 4 1.036 1.213 DEC FEB
20 (KS) 4054 4 1.056 1.056 JAN FEB
23 (ME) 1026 5 1.107 1.819 NOV APR
24 (MD) 1634 4 0.436 0.436 FEB FEB
25 (MA) 1002 2 1.017 1.017 JAN MAR
27 (MN) 1018 5 1.791 2.181*** NOV APR
27 (MN) 1028 5 2.275 2.386*** NOV APR
27 (MN) 4040 5 1.900 2.317*** NOV MAY
27 (MN) 6251 10 2.126 2.308*** NOV APR
30 (MT) 0114 5 1.165 1.256 NOV MAR
30 (MT) 8129 6 0.793 1.082 NOV MAR
31 (NE) 0114 7 0.844 1.173 DEC MAR
31 (NE) 3018 9 1.289 1.679 DEC MAR
32 (NV) 0101 6 ** **
32 (NV) 0204 2 0.612 0.612 DEC JAN
33 (NH) 1001 5 0.954 1.394 DEC MAR
34 (NJ) 0504 3 0.406 0.406 JAN FEB
34 (NJ) 0505 3 0.458 0.458 JAN FEB
34 (NJ) 0506 3 0.608 0.608 JAN FEB
34 (NJ) 0507 3 0.455 0.455 JAN JAN
34 (NJ) 0902 3 0.643 0.668 JAN FEB
36 (NY) 0801 10 0.627 0.988 DEC MAR
36 (NY) 4018 5 1.090 2.102*** DEC APR
39 (OH) 0204 2 0.705 0.705 JAN JAN
39 (OH) 0901 6 0.704 0.776 DEC FEB
42 (PA) 1606 8 0.568 0.771 DEC MAR
46 (SD) 0804 9 1.445 1.998 NOV APR
46 (SD) 9187 4 1.243 1.827 NOV APR
49 (UT) 1001 5 1.557 2.019 DEC DEC
49 (UT) 3011 5 0.553 0.692 DEC FEB
50 (VT) 1002 10 1.020 1.498 NOV APR
56 (WY) 1007 5 0.741 0.999 NOV MAR
83 (MB) 1801 11 2.033 2.13*** OCT MAY
83 (MB) 3802 6 1.798 2.424*** NOV MAY
87 (ON) 1622 5 1.194 1.743 NOV APR
89 (QC) 3015 9 1.316 1.587 NOV MAY
90 (SK) 6405 6 1.999 2.058*** OCT MAY

1 m = 3.28 ft

— No data available.

* First interpreted depth at 0.38 m.

** First interpreted depth at 0.51 m.

*** Possibility of frost beyond the last interpreted depth.

Frost Penetration Profile Characteristics

Using frost estimates computed based on in-situ data, frost penetration profiles were analyzed for each of the 41 LTPP sites for all available years of data. The changes in frost profiles over the cold seasons (fall, winter, and spring) were examined for each available year. The review indicated that even for similar frost depths, the observed profiles varied from site to site and year to year. Hence, knowledge of the maximum frost depth without an understanding of seasonal changes in frost penetration profile would not be enough for accurate characterization of seasonal changes in pavement structural characteristics.

Some of the commonly observed frost penetration profile characteristics were multiple freeze thaw cycles, shallow fall freeze with thaw followed by solid deep freeze with a spring thaw, and solid freeze with spring thaw and refreeze. Figure 21 through figure 23 show examples of each of these commonly observed frost penetration profiles.

This figure shows the frost penetration profile for SMP site 30-0114 for the winter of 2003. The x-axis shows the date, and the y-axis shows the depth in meters. The user-defined date range is from October 5, 2002, to May 3, 2003. There is a legend at the bottom of the form consisting of blue "Freeze" square cells, gray "No Freeze" square cells, and pink "Transition" diamond cells. The profile consists of two freeze states, "Freeze" and "No Freeze." There are six separate areas that are identified as "Freeze" in the penetration profile, separated by areas of "No Freeze."  Maximum freeze depth occurs during the last freeze period, which happens in March, and extends up to 1 m (3.28 ft) in depth.

Figure 21. Chart. Frost penetration profile showing multiple freeze-thaw cycles.

This figure shows the frost penetration profile for SMP site 87-1622 for the winter of 1996. The x-axis shows the date, and the y-axis shows the depth in meters. The user-defined date range is from November 1, 1996, to May 2, 1997. There is a legend at the bottom of the form consisting of blue "Freeze" square cells, gray "No Freeze" square cells, and pink "Transition" diamond cells. The profile consists of two freeze states, "Freeze" and "No Freeze." The frost penetration profile shows three separate shallow freeze areas in November and early December, followed by two weeks of a thaw period. At about December 19, the next freeze period starts and continues to mid April. During this freeze period, frost gradually penetrates reaching a depth of 1.4 m (4.6 ft) by the end of February. At the end of March, the spring thaw starts at the shallow depths, as indicated by "No Freeze" cells, while the soil remains frozen at deeper depths until about April 18.

Figure 22. Chart. Frost penetration profile showing shallow freeze cycles in the fall followed by solid deep freeze with spring thaw.

This figure shows the frost penetration profile for SMP site 27-4040 for the winter of 1994. The x-axis shows the date, and the y-axis shows the depth in meters. The user-defined date range is from November 1, 1994, to May 30, 1995. There is a legend at the bottom of the form consisting of blue "Freeze" square cells, gray "No Freeze" square cells, and pink "Transition" diamond cells. The profile consists of two freeze states, "Freeze" and "No Freeze." The frost penetration profile shows one solid freeze area with a shallow thaw area, followed by refreeze for a few days and then another thaw. The freeze period starts at the end of November and continues to mid May. During this freeze period, frost gradually penetrates reaching the depth of 2 m (6.56 ft) by mid March. From late March through mid April, the spring thaw starts and progresses to the depth of 0.9 m (2.95 ft), as indicated by "No Freeze" cells, while the soil remains frozen at deeper depths. A brief refreeze occurs in mid April, followed by another long thaw period. During this second thaw period, thawing starts from the top and takes about 1 month to thaw gradually to the bottom of the frozen layer.

Figure 23. Chart. Frost penetration profile showing solid freeze with partial spring thaw and refreeze.

Table 7 summarizes typical frost penetration characteristics observed for each SMP site. To describe frost penetration profile characteristics, frost depth was characterized as shallow, medium, or deep. A shallow frost depth was defined between 0 m and 0.6 m (0 ft and 1.97 ft); a medium frost depth was defined between 0.6 m and 0.9 m (1.97 ft and 2.95 ft); and a deep frost depth was defined for frost that penetrated 0.9 m (2.95 ft) or more. Since these definitions are subjective, the seasonal maximum frost depth is also reported in the table for each site. Furthermore, the depth of the top of the first unbound layer was different for each SMP site, which occasionally limited frost determination at shallow and medium depths where the first unbound layer was placed below the expected freeze depth. The information in table 7 could be used to infer the typical frost penetration characteristics for LTPP SMP sites.

Table 7. Typical frost penetration profile characteristics for LTPP SMP sites.
State or province State code SHRP ID #of years w/ data Frost profile description
Fall (Sept 21–Dec 21) Winter (Dec 22–Mar 20) Spring (Mar 21–June 21)
Arizona 4 1024 3 No Freeze* No Freeze* No Freeze*
Colorado 8 1053 3 No Freeze Multiple Shallow Freeze-Thaw Cycles (up to 0.37 m) No Freeze 
Connecticut 9 1803 4 No Freeze Shallow or Medium freeze-thaw (up to 0.79 m) No Freeze
Idaho 16 1010 3 Possible Medium Freeze-Thaw Re-freeze (up to 0.66 m) Multiple Shallow or Medium Freeze-Thaw Cycles (up to 0.86 m) No Freeze 
Indiana 18 3002 2 Medium Freeze-Thaw Multiple Medium to Deep  Freeze-Thaw Cycles  (up to 1.21 m) No Freeze 
Kansas 20 4054 3 No Freeze  Multiple Medium to Deep  Freeze-Thaw Cycles (up to 1.06 m) No Freeze 
Maine 23 1026 4 Shallow freeze-thaw re-freeze (up to 0.55 m) Continuous Deep Freeze (up to 1.82 m) Prolonged Deep Thaw (up to 1.77 m)
Manitoba 83 1801 9  Deep Freeze, possibly preceded by  Shallow Freeze w/ Thaw (up to 1.72 m) Continuous Deep Freeze (up to 2.13 m)*** Deep Freeze, Shallow Thaw followed by Re-freeze, Prolonged Deep Thaw (up to 2.13 m)***
Manitoba 83 3802 4  Deep Freeze (up to 1.31m) Continuous Deep Freeze (up to 2.42 m)*** Deep Freeze, Shallow Thaw followed by Re-freeze, Prolonged Deep Thaw (up to 2.42 m)***
Maryland 24 1634 4 No Freeze  Shallow freeze-thaw (up to 0.44 m) No Freeze 
Massachusetts 25 1002 2 No Freeze Deep Freeze w/ Thaw, followed by Medium Freeze w/ Thaw (up to 1.02 m) No Freeze 
Minnesota 27 1018 4 Medium to Deep Freeze (up to 1.83 m) Deep Freeze, Shallow Thaw followed by Re-freeze (up to 2.18 m) Prolonged Deep Thaw (up to 2.13 m)
Minnesota 27 1028 3  Deep Freeze, possibly proceeded by Medium Freeze w/ Thaw. (up to 1.83 m) Continuous Deep Freeze (up to 2.39 m)*** Deep Freeze, Possible Shallow Thaw followed by Re-freeze, Prolonged Deep Thaw  (up to 2.39 m)***
Minnesota 27 4040 3  Deep Freeze  (up to 1.20 m)  Deep Freeze, Possible Shallow Thaw followed by Re-freeze   (up to 2.32 m)***  Prolonged Deep Thaw  (up to 2.3 2m)***
Table 7. Typical frost penetration profile characteristics for LTPP SMP sites—continued.
State or province State code SHRP ID #of years w/ data Frost profile description
Fall (Sept 21–Dec 21) Winter (Dec 22–Mar 20) Spring (Mar 21–June 21)
Minnesota 27 6251 8 Deep Freeze (up to 1.85 m) Deep Freeze, Possible Shallow Thaw followed by Re-freeze (up to 2.31 m)*** Prolonged Deep Thaw (up to 2.31 m)***
Montana 30 0114 4 Multiple Shallow/Medium Freeze-Thaw Cycles or Deep Freeze Multiple Medium/Deep Freeze-Thaw Cycles or Deep Freeze with Shallow Thaw and Re-freeze (up to 1.26 m) Possible Deep Freeze and Thaw (up to 0.95 m)
Montana 30 8129 3 Medium Freeze (up to 0.83 m) Multiple Medium/Deep Freeze-Thaw Cycles (up to 1.08 m) No Freeze
Nebraska 31 0114 6 Medium Freeze w/ Thaw (up to 0.67 m) Multiple Medium/Deep Freeze-Thaw Cycles (up to 1.17 m) No Freeze
Nebraska 31 3018 8 Possible Deep Freeze (up to 1.2 2m) Deep Freeze (up to 1.68 m) No Freeze
Nevada 32 0101 5 No Freeze** No Freeze** No Freeze**
Nevada 32 0204 1 No Freeze Multiple Shallow Freeze-Thaw Cycles (up to 0.61 m) No Freeze
New Hampshire 33 1001 4 Possible Shallow Freeze w/ Thaw (up to 0.33 m) Multiple Medium/Deep Freeze-Thaw Cycles or Single Deep Freeze (up to 1.39 m) Possible Thaw (up to 1.19 m)
New Jersey 34 0504 3 No Freeze Multiple Shallow Freeze-Thaw Cycles (up to 0.41 m) No Freeze
New Jersey 34 0505 3 No Freeze Multiple Shallow Freeze-Thaw Cycles (up to 0.46 m) No Freeze 
New Jersey 34 0506 2 No Freeze Medium Freeze-Thaw (up to 0.61m) No Freeze
New Jersey 34 0507 3 No Freeze Shallow Freeze-Thaw (up to 0.46 m) No Freeze
New Jersey 34 0902 3 No Freeze Multiple Shallow/Medium Freeze-Thaw Cycles (up to 0.67 m) No Freeze
New York 36 0801 7 Multiple Shallow Freeze-Thaw Cycles (up to 0.48 m) Multiple Shallow to Deep Freeze-Thaw Cycles or Single Deep Freeze (up to 0.99 m) Possible Multiple Shallow Freeze-Thaw Cycles (up to 0.28 m)
New York 36 4018 4 No Freeze Multiple Shallow to Deep Freeze-Thaw Cycles or Single Deep Freeze (up to 2.10 m)*** Possible Shallow Freeze-thaw or Prolonged Deep Thaw (up to 2.10 m)***
Table 7. Typical frost penetration profile characteristics for LTPP SMP sites—continued.
State or province State code SHRP ID #of years w/ data Frost profile description
Fall (Sept 21–Dec 21) Winter (Dec 22–Mar 20) Spring (Mar 21–June 21)
Ohio 39 0204 2 No Freeze Medium Freeze-Thaw (up to 0.71 m) No Freeze
Ohio 39 0901 6 Possible Medium Freeze (up to 0.57 m) Multiple (B) Shallow to Medium Freeze-Thaw Cycles (up to 0.78 m) No Freeze
Ontario 87 1622 4 Multiple Shallow Freeze-Thaw Cycles (up to 0.42 m) Single Deep Freeze or Multiple Deep Freeze-Thaw Cycles (up to 1.74 m) Possible Shallow Freeze-Thaw, Prolonged Deep Thaw (up to 1.69 m)
Pennsylvania 42 1606 8 Multiple Shallow Freeze-Thaw Cycles (up to 0.42 m) Multiple Shallow to Medium Freeze-Thaw Cycles (up to 0.77 m) No Freeze
Quebec 89 3015 6 Shallow to Medium Freeze-Thaw followed by Deep Freeze (up to 1.03 m) Deep Freeze, Shallow Thaw followed by Re-freeze (up to 1.54 m) Prolonged Deep Thaw, Possible Deep Freeze (up to 1.59 m)
Saskatchewan 90 6405 3 Shallow Freeze-Thaw, followed by Deep Freeze (up to 1.80 m) Continuous Deep Freeze (up to 2.06m)*** Deep Freeze, Multiple Shallow Thaw & deep Re-freeze periods, Prolonged Deep Thaw (up to 2.06 m)***
South Dakota 46 0804 7 Medium Freeze-Thaw, followed by Medium to Deep Freeze (up to 1.24 m) Deep Freeze, Possible Shallow Thaw followed by Re-freeze (up to 2.00 m) Deep Freeze, Possible Shallow Thaw followed by Re-freeze, Prolonged Deep Thaw (up to 1.95 m)
South Dakota 46 9187 2 Multiple shallow Freeze-Thaw Cycles followed by Medium to Deep Freeze (up to 1.02 m) Deep Freeze, Multiple Shallow Thaw followed by Re-freeze Cycles up to 1.83 m) Medium to Deep Freeze, Shallow Thaw & Re-freeze periods, Prolonged Thaw (up to 1.63 m)
Utah 49 1001 3 Mid Depth to Deep Freeze (up to 2.02 m) No Freeze  No Freeze 
Utah 49 3011 3 No Freeze Period Multiple Shallow to Medium Freeze-Thaw Cycles (up to 0.69 m) No Freeze 
Vermont 50 1002 8 Multiple Shallow to Medium Freeze-Thaw Cycles (up to 0.64 m) Multiple Shallow to Deep  freeze-thaw cycles, Possible Continuous Deep Freeze (up to 1.50 m) Possible Deep Thaw (up to 1.40 m)
Wyoming 56 1007 3 Multiple Shallow Freeze-Thaw Cycles (up to 0.49 m) Multiple Shallow to Deep  Freeze-Thaw Cycles (up to 1.00 m) No Freeze 

1 m = 3.28 ft

* First interpreted depth at 0.38 m.

** First interpreted depth at 0.51 m.

*** Possibility of frost beyond the last interpreted depth.

Comparison with Historical Non-LTPP Frost Data

The computed maximum frost penetration depths were compared to the historical frost penetration values, as published in the climatic maps developed by NOAA(1) and Environment Canada.(2) Data from the historical maps were interpolated to the LTPP site locations. The results of the comparison are shown in figure 24.

The figure is an x-y scatter plot, with a solid diagonal line of equality going from the lower left to upper right corner. In addition, the solid diagonal line has three parallel dashed lines: one short-dashed and two long-dashed. The short-dashed line is located just to the right of the solid line and represents the Average Difference (AD) between the U.S. and Canadian sites. The two long-dashed lines are equidistance from the AD line in opposite directions. These two lines represent the AD plus and minus 2 times the standard deviation. The x-axis shows the LTPP predicted frost depth in meters, and the y-axis shows the historical frost depth in meters. The individual points are represented by diamonds for the U.S. sites and triangles for the Canadian sites. The points are spread around the line of equality with only two outliers located outside of the low long-dashed line, indicating good overall agreement between LTPP and historical maximum frost depth predictions.

1 m = 3.28 ft

Figure 24. Graph. Comparison of frost penetration depths.

The graph in figure 24 shows a good overall agreement between LTPP and historical maximum frost depth predictions. Some of the differences can be attributed to the fact that, while comparisons are provided for the same region, the historical values are not site-specific and that local variations are possible due to factors such as soil type, moisture content, altitude, and land development. In addition, for Canadian sites, some inaccuracies could result from estimation of frost depth from the freezing index data provided on the climatic map. For the three Canadian sites shown in the upper-right corner on the graph, LTPP frost penetration profiles indicate the possibility of frost beyond the last interpreted depth; however, the full frost depth cannot be established as no LTPP measurements are available at these lower depths.

The extreme frost predictions for U.S. sites provided on the NOAA map are based on longer monitoring period than the LTPP frost predictions; hence, covering more seasons where extreme conditions could occur. Table 8 contains data used in the analysis.

Table 8. Comparison of average frost depth for LTPP SMP sites.
STATE_CODE SHRP_ID Number of years analyzed LTPP maximum freeze depth, m Historic maximum freeze depth, m
4 (AZ) 1024 4 * 0.250
8 (CO) 1053 5 0.374 0.875
9 (CT) 1803 5 0.794 1.167
16 (ID) 1010 5 0.864 1.125
18 (IN) 3002 4 1.213 0.875
20 (KS) 4054 4 1.056 0.750
23 (ME) 1026 5 1.819 1.792
24 (MD) 1634 4 0.436 0.390
25 (MA) 1002 2 1.017 1.240
27 (MN) 1018 5 2.181*** 1.917
27 (MN) 1028 5 2.386*** 2.042
27 (MN) 4040 5 2.317*** 2.245
27 (MN) 6251 10 2.308*** 2.250
30 (MT) 0114 5 1.256 1.500
30 (MT) 8129 6 1.082 1.500
31 (NE) 0114 7 1.173 1.000
31 (NE) 3018 9 1.679 1.031
32 (NV) 0101 6 ** 0.600
32 (NV) 0204 2 0.612 0.500
33 (NH) 1001 5 1.394 1.531
34 (NJ) 0504 3 0.406 0.750
34 (NJ) 0505 3 0.458 0.750
34 (NJ) 0506 3 0.608 0.750
34 (NJ) 0507 3 0.455 0.750
34 (NJ) 0902 3 0.668 0.750
36 (NY) 0801 10 0.988 1.208
36 (NY) 4018 5 2.102*** 1.208
39 (OH) 0204 2 0.705 0.875
39 (OH) 0901 6 0.776 0.875
42 (PA) 1606 8 0.771 0.938
46 (SD) 0804 9 1.998 1.667
46 (SD) 9187 4 1.827 1.688
49 (UT) 1001 5 2.019 0.625
49 (UT) 3011 5 0.692 0.833
50 (VT) 1002 10 1.498 1.625
56 (WY) 1007 5 0.999 1.475
83 (MB) 1801 11 2.13*** 2.670
83 (MB) 3802 6 2.424*** 2.670
87 (ON) 1622 5 1.743 1.710
89 (QC) 3015 9 1.587 2.130
90 (SK) 6405 6 2.058*** 2.790

1 m = 3.28 ft

* First interpreted depth at 0.38 m.

** First interpreted depth at 0.51 m.

*** Possibility of frost beyond the last interpreted depth.

Comparison with Previous LTPP Frost Estimates

When comparing the results of the current frost penetration data analysis to the previous results, the following improvements can be noted:

LTPP FROST DATA TABLE DESCRIPTIONS

As a result of this data analysis effort, two tables were created for inclusion in the LTPP database. The proposed computed parameter tables (CPT) are based on the existing LTPP frost CPT tables with changes and additions made as a result of the current frost penetration analysis study.

These tables have the same names as in the previous LTPP database releases and are defined as follows:

These new tables contain freeze state interpretations for all the available temperature and ER data collected during the SMP I and II experiments. As such, the intent of these tables is to replace the existing SMP_FREEZE_STATE and SMP_FROST_PENETRATION tables.

Summaries of the information included in the CPT frost tables are provided in table 9 and table 10.

Table 9. Summary of information included in the revised table SMP_FREEZE_STATE.
Data element or parameter DESCRIPTION
STATE code State code
SHRP ID SHRP identification code
SMP date Date corresponding to SMP data collection
Interpretation depth number Depth number where freeze state is interpreted, increasing from top downward.
Interpretation depth Middepth between electrodes used in the freeze state interpretation, measured for pavement surface; two consecutive electrodes are used in voltage and contact resistance measurements and four in resistivity.
Interpreted freeze state Interpreted freeze state at the interpret depth: F-Freeze, N-No-freeze, T-Transitional (or partial freeze).
Interpretation basis Code indicating the basis for freeze state interpretation: 1. Freeze state based on temperature data using 0 oC freezing isotherm, not forced. 2. Freeze state determined by the analyst after reviewing the temperature, electrical resistivity, and moisture data trends. 3. Temperature data is not available. Freeze state determined by the analyst from ER and moisture.
Normalized resistivity Electrical resistivity of the soil at the measurement depth, relative to the extreme values measured at that depth.
Normalized resistance Electrical resistance of the soil at the measurement depth, relative to the extreme values measured at that depth.
Normalized voltage Voltage drop of the soil at the measurement depth, relative to the extreme values measured at that depth.
Soil temperature Average soil temperature of the day, calculated at the interpretation depth. This could either be based on interpolation of measured values, or derived using EICM.
Temperature source Source of the temperature data used in freeze state interpretation: (1) based on measured, (2) derived using EICM.
Table 10. Summary of information included in the revised table SMP_FROST_PENETRATION.
Filed name DESCRIPTION
STATE code State code
SHRP ID SHRP identification code
SMP date Date corresponding to SMP data collection
Frozen layer Code for interpreted frozen layer number. A value of zero indicates no frozen layers.
Top depth number Serial number for the starting depth (top) of a frozen layer, increasing from pavement surface downward.
Bottom depth number Serial number for the ending depth (bottom) of a frozen layer, increasing from pavement surface downward.
Freeze from Starting (top) depth (meter) of a frozen layer, measured from the pavement surface.
Freeze to Ending (bottom) depth (meter) of a frozen layer, measured from the pavement surface.
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