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Publication Number: FHWA-RD-03-088
Date: November 2003

Introduction to The LTPP Information Management System (IMS)

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The Seasonal Monitoring Program (SMP) study is designed to measure the impact of daily and yearly temperature and moisture changes on pavement structures and the response to loads. Sixty-three sites were selected from the GPS and SPS studies and were monitored for temperature and moisture, and at higher than normal intervals for distress, deflection, and longitudinal profile. Measurements specific to sections in the SMP were made using the following devices:

The data collected from these devices are stored in the tables contained in the SMP module. All other data collected at sites within the SMP, but not specific to sites in the SMP, are stored in the usual tables external to the SMP module. For example, deflection measurements on SMP test sections are stored in the MON_DEFL series of tables.

At the inception of the SMP program, subsurface time-domain reflectometry and electrical resistivity measurements were taken on a nominal monthly cycle. In the latter part of the SMP program, selected sites were instrumented to take these measurements daily and, in some cases, subdaily to capture changes caused by rainfall. The only way to identify the sites with these types of daily measurements is to inspect the contents of the tables containing these data.

In addition to the raw data as collected, several computed parameters are included that reduce the raw data into values in engineering units. All of the raw data used to calculate the computed parameters are included in the database.

10.1 DATA TABLES

10.1.1 Ambient Temperature and Precipitation

The ambient temperature and precipitation data collected from the onsite weather stations are stored in the SMP_ATEMP_RAIN series of tables.

SMP_ATEMP_RAIN_HOUR: This table contains the average hourly temperature and the total hourly precipitation. Temperature or precipitation data in this table may be null if an instrumentation error was discovered. The hour at the end of the averaging period is stored in the ATEMP_RAIN_TIME field in 24-hour military-style text format. The date of the measurement is stored in the SMP_DATE field in a native date format.

SMP_ATEMP_RAIN_DAY: This table contains the average, minimum, and maximum ambient air temperatures over the course of a day; the times at which the minimum and maximum temperatures occurred; and the cumulative precipitation. These values are computed directly from the SMP_ATEMP_RAIN_HOUR table when at least 18 hours of data exist for a day.

10.1.2 Subsurface Temperature

Subsurface temperatures are stored in the SMP_MRCTEMP_* series of tables (MRC is the manufacturer of the type of thermistor used by the LTPP program).

SMP_MRCTEMP_AUTO_HOUR: This table contains the vast majority of subsurface temperature data. It includes average hourly temperatures at a series of depths; however, it must be linked to SMP_MRCTEMP_DEPTHS using the THERM_NO field (and the STATE_CODE and SHRP_ID for the section) to determine the depth at which the temperature was recorded.

SMP_MRCTEMP_MAN: This table contains the remainder of the subsurface temperature data. Its format is very similar to SMP_MRCTEMP_AUTO_HOUR; however, it contains manual temperature measurements taken when the automatic temperature monitoring equipment was out of service. Like SMP_MRCTEMP_AUTO_HOUR, it must be linked to SMP_MRCTEMP_DEPTHS to determine the depth at which the temperature was measured.

SMP_MRCTEMP_AUTO_DAY_STATS: This table contains the average, minimum, and maximum subsurface temperatures over the course of a day and the times at which the minimum and maximum temperatures occurred. These values are based on either the minute-by-minute readings recorded by the data logger or are computed from the averages stored in the SMP_MRCTEMP_AUTO_HOUR table when recomputation of the daily statistics is needed for adjustments, and like that table, it must be linked to SMP_MRCTEMP_DEPTHS to determine the depth at which the temperature was measured.

SMP_MRCTEMP_DEPTH: This table contains the depths at which each temperature probe at an SMP section was installed and the date of installation. The primary use of this table is to link to other SMP_MRCTEMP_* tables, using the STATE_CODE, SHRP_ID, and THERM_NO fields, to determine the depth corresponding to a temperature reading. In some rare cases, STATE_CODE, SHRP_ID, and THERM_NO do not resolve to a unique depth because the thermistors were reinstalled at slightly different depths at some point after the initial installation. In these cases, the link must be further refined using the INSTALL_DATE field.

10.1.3 Subsurface Moisture Content

The LTPP SMP uses time-domain reflectometry (TDR) to measure subsurface moisture content. A description of the process is located in chapter 2 of the Seasonal Monitoring Program Guidelines.

SMP_TDR_AUTO_MOISTURE: This table contains the volumetric and gravimetric moisture contents calculated using TDR (the dry densities used to convert volumetric to gravimetric moisture content are located in SMP_MOISTURE_SUPPORT). The depths at which these moisture contents were calculated can be determined by linking to SMP_TDR_DEPTHS_LENGTHS using STATE_CODE, SHRP_ID, and TDR_NO. Further information on the calculation of these computed parameters can be found in An Input for Moisture Calculations-Dielectric Constant From Apparent Length, Publication No. FHWA-RD-99-201.

SMP_TDR_AUTO: This table contains a flat representation of the TDR waveform. The measured reflected waveform is sampled at 245 intervals and stored in the WAVP_1 through WAVP_245 fields. The distance interval between samples is recorded in the DIST_WAV_POINTS field. This table is only useful to the analyst who is interested in reinterpreting the raw TDR data.

SMP_TDR_MANUAL_DIELECTRIC: This table contains dielectric constants interpreted from TDR measurements recorded on paper strip charts during installation of SMP instrumentation. The protocol for interpretation of the manual TDR measurements is stored in LTPP Directive SM-28.

SMP_TDR_AUTO_DIELECTRIC: This table contains the dielectric constant interpreted from the waveforms stored in SMP_TDR_AUTO and several intermediate calculations.

SMP_TDR_DEPTHS_LENGTHS: This table contains information on the physical characteristics of the TDR probes, including the depth at which the probe is installed, the length of the probe, and its installation date. The primary use of this table is to link to other SMP_TDR_* tables, using the STATE_CODE, SHRP_ID, and TDR_NO fields, to determine the depth corresponding to a moisture reading. In some rare cases, STATE_CODE, SHRP_ID, and TDR_NO do not resolve to a unique depth because the thermistors were reinstalled at slightly different depths at some point after the initial installation. In these cases, the link must be further refined, using the INSTALL_DATE field. A secondary use of this table is to determine the length of the TDR probe, which is necessary when reinterpreting the TDR data.

SMP_TDR_MOISTURE_SUPPORT: This table contains the dry density of soils sampled from areas adjacent to each of the TDR probes. These data are primarily useful for converting volumetric moisture contents to gravimetric moisture contents. For some samples, gradation and plastic limit data are also available.

SMP_DRY_DENSITY: This table is an alternate source of soil dry density data. Data are limited to one dry density per SMP site, with the test conducted on samples obtained from approximately 1 m below the pavement surface. In practice, the utility of this table is limited because of low data availability.

SMP_GRAV_MOIST: This table contains the results of laboratory gravimetric moisture testing of materials sampled adjacent to each TDR probe at the time of installation.

10.1.4 Frost Penetration

The LTPP SMP uses a combination of subsurface temperature and electrical resistivity to estimate frost penetration. The soil resistivity probes used by the LTPP program are all identical; however, the data have been collected in slightly different ways, as described below.

SMP_ERESIST_MANUAL_CONTACT: This table contains manually collected voltage and current, and the calculated resistance between adjacent electrodes on the probe. This resistance is the contact resistance. The depths of the electrodes can be determined by linking ELECTRODE_START and ELECTRODE_END to ELECTRODE_NO in the SMP_ERESIST_AUTO_ABF table.

SMP_ERESIST_MAN_4POINT: This table contains the manually collected voltage and current, and the calculated bulk resistivity of the material around the probe using the four-point method. This process is described further in chapter 2 of Seasonal Monitoring Program Guidelines. The depths of the electrodes across which these measurements were made can be determined by linking EAMP_START and EAMP_END to ELECTRODE_NO in the SMP_ERESIST_AUTO_ABF table.

SMP_ERESIST_AUTO: This table contains automatically collected voltage data between adjacent electrodes on the probe. Since the current associated with this voltage varies over time, the absolute contact resistance cannot be calculated. However, significant changes in voltage with depth at a given time can be used to indicate changes in the freeze state of the soil. The depths of the electrodes across which these measurements were made can be determined by linking ELECTRODE_START and ELECTRODE_END to ELECTRODE_NO in the SMP_ERESIST_AUTO_ABF table.

SMP_ERESIST_AUTO_ABF: This table contains data from the ABF data logger that is automatically calibrated using an internal resister (these calibrations are stored in SMP_ERESIST_ABF_RES_VA). Therefore, unlike SMP_ERESIST_AUTO, both the voltage and the contact resistance are available from this table.

SMP_ERESIST_ABF_RES_VA: This table contains automatic calibration data from the ABF data logger. Both the total voltage applied by the data logger and the voltage drop across the internal calibration resister are available. Generally, this table is only of use to the analyst who wishes to recalculate the contact resistance data stored in SMP_ERESIST_AUTO_ABF.

SMP_ERESIST_DEPTHS: This table contains the depths at which each resistivity probe at an SMP section was installed and the date of installation. The primary use of this table is to link to other SMP_ERESIST_* tables, using the STATE_CODE, SHRP_ID, and ELECTRODE_NO fields, to determine the depth corresponding to a resistance or resistivity reading. In some rare cases, STATE_CODE, SHRP_ID, and THERM_NO do not resolve to a unique depth because the probes were reinstalled at slightly different depths at some time after the initial installation. In these cases, the link must be further refined using the INSTALL_DATE field.

SMP_FREEZE_STATE: This table contains the computed parameters necessary to determine whether the pavement layers at a given depth are frozen or not. It includes resistivity and contact resistance extracted from SMP_ERESIST_MAN_4POINT and SMP_ERESIST_MAN_CONTACT, the daily average temperature extracted from SMP_MRC_TEMP_AUTO_DAY_STATS, and a determination of the freeze state of the soil based on these values. Information on the calculation of these computed parameters can be found in Freeze-Thaw Monograph for LTPP, Publication No. FHWA-RD-98-177.

SMP_FROST_PENETRATION: This table contains an estimation of the upper and lower boundaries of the frozen layer based on the computed parameters in the SMP_FREEZE_STATE table.

10.1.5 Depth to Water Table

The LTPP SMP uses an observation well (this well is sometimes called an "observation piezometer" for reasons relating to the permitting process for drilling wells) to determine if the depth of the water table is within approximately 5 m from the pavement surface. In many cases, the observation well did not extend to the water table.

SMP_WATERTAB_DEPTH_MAN: This table contains manual observations of the distance from the pavement surface to the water table.

SMP_WATERTAB_DEPTH_AUTO: This table was originally developed to contain automated readings of the water table depth; however, such readings were never obtained. Therefore, this table contains no data.

10.1.6 Surface Elevation Data

Surface elevation measurements using a rod-and-level surveying method are taken at each SMP site at the time of FWD testing. Measurements are taken at the location of each FWD test and are referenced to a frost- and swell-free benchmark

SMP_ELEV_AC_DATA: This table contains surface elevation measurements for asphalt-surfaced SMP sections. At each longitudinal location, elevation measurements are typically taken at the pavement edge (PE), outer wheel path (OWP), midlane (ML), inner wheel path (IWP), and inner lane edge (ILE). To determine the actual transverse locations of these measurement points, this table must be linked to SMP_ELEV_AC_OFFSET using STATE_CODE, SHRP_ID, and SMP_DATE.

SMP_ELEV_AC_OFFSET: This table contains the transverse offset of the elevation measurement locations stored in SMP_ELEV_AC_DATA. In addition, it also contains a text description of the equipment used to conduct the elevation survey.

SMP_ELEV_PCC_DATA: This table contains surface elevation measurements for PCC-surfaced SMP sections. At each longitudinal location, elevation measurements are typically taken at the pavement edge (PE), midlane (ML), and inner lane edge (ILE). To determine the actual transverse locations of these measurement points, this table must be linked to SMP_ELEV_PCC_OFFSET using STATE_CODE, SHRP_ID, and SMP_DATE.

SMP_ELEV_PCC_OFFSET: This table contains the transverse offset of the elevation measurement locations stored in SMP_ELEV_PCC_DATA. In addition, it also contains a text description of the equipment used to conduct the elevation survey.

10.1.7 Joint Opening and Faulting

Joint opening and faulting measurements are typically collected concurrently with FWD testing at the same locations as where the load-transfer tests are conducted. The joint opening is measured using snap rings installed in the joint, while faulting is measured using a Georgia-style faultmeter (as done with standard LTPP distress surveys).

SMP_JOINT_FAULT_DATA: This table contains joint faulting measurements for PCC-surfaced SMP sections. At each longitudinal location for which FWD load-transfer testing is conducted, joint faulting is measured at the pavement edge (PE), midlane (ML), and inner lane edge (ILE). To determine the actual transverse locations of these measurement points, this table must be linked to SMP_JOINT_FAULT_OFFSET using STATE_CODE, SHRP_ID, and SMP_DATE.

SMP_JOINT_FAULT_OFFSET: This table contains the transverse offset of the joint fault measurement locations stored in SMP_JOINT_FAULT_DATA.

SMP_JOINT_GAUGE_DATA: This table contains joint opening measurements for PCC-surfaced SMP sections. At each longitudinal location for which FWD load-transfer testing is conducted, the joint opening is measured at the pavement edge (PE), midlane (ML), and inner lane edge (ILE). To determine the actual transverse locations of these measurement points, this table must be linked to SMP_JOINT_GAUGE_OFFSET using STATE_CODE, SHRP_ID, and SMP_DATE.

SMP_JOINT_GAUGE_OFFSET: This table contains the transverse offset of the joint opening measurement locations stored in SMP_JOINT_GAUGE_DATA.

10.1.8 Additional SMP Tables

SMP_LAYOUT_INFO: When using SMP data, it is critical to know the locations at which the measurements were taken. SMP_LAYOUT_INFO is the source for much of this information, including the location of the instrument hole where the TDR, thermistor, and resistance probes were installed, and the locations of the piezometer and the weather observation instrumentation. Longitudinal and transverse locations for joint opening and faulting, and surface elevation measurements are located in other tables within the SMP module, as described elsewhere in this chapter.

SMP_COMMENTS: This table contains a wealth of information regarding irregularities in data collection. Equipment failure, unusual weather conditions such as flooding of an adjacent river, and anything else out of the ordinary will be recorded in this table. These data are keyed to the section ID, date of occurrence, and the table in which the effected data is stored.

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