EP2084522A1 - Method and device for indicating when to impose axle weight limit on roads - Google Patents

Method and device for indicating when to impose axle weight limit on roads

Info

Publication number
EP2084522A1
EP2084522A1 EP07821433A EP07821433A EP2084522A1 EP 2084522 A1 EP2084522 A1 EP 2084522A1 EP 07821433 A EP07821433 A EP 07821433A EP 07821433 A EP07821433 A EP 07821433A EP 2084522 A1 EP2084522 A1 EP 2084522A1
Authority
EP
European Patent Office
Prior art keywords
ground
conductance
temperature
data
phase
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP07821433A
Other languages
German (de)
French (fr)
Inventor
Gudlaugur JÓNASSON
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Samras Ehf
Original Assignee
Samras Ehf
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Samras Ehf filed Critical Samras Ehf
Publication of EP2084522A1 publication Critical patent/EP2084522A1/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
    • G01D5/16—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying resistance
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D18/00—Testing or calibrating apparatus or arrangements provided for in groups G01D1/00 - G01D15/00
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
    • G01N27/041—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body

Definitions

  • the present invention relates to a method, a device and a system for indicating when to impose or cancel axle weight limit on a road based on the phase condition of the ground of the road construction.
  • a critical condition is as an example when the ground is in thawed condition, or is moving from one frozen phase to a thawed phase. It is well known that when a ground has just moved from frozen to thawed phase it acts as a "sponge" in the first hours or first day after the phase transfer has occurred. When the ground is in such a condition it is extremely sensitive to excessive weights caused by e.g. vehicles. Results show that the damage caused by excessive axle weight limits is approximately 48 times higher when the ground is in this critical condition.
  • the object of the present invention is to overcome the above mentioned problem by providing a method and a device that is capable of monitoring the condition of the grounds of road constructions, thereby providing information relating to the current and the future condition of the roads. This information is then used for imposing or canceling axle weight limit on roads.
  • the present invention relates to a method of indicating when to impose or cancel axle weight limit on a road based on the phase condition of the ground of the road construction, comprising:
  • the conductance measurement can be implemented for determining about the current and/or the future phase condition or phase transformations of the ground at the one or more different depths. Therefore, it is possible to prevent damages caused by excessive weight by e.g. issuing a warning to the road administration in due time and in that way prevent any kind of damages caused by excessive axle weight limits. This will inherently reduce the amount of money invested for preserving the conditions of the road structure enormously.
  • the term road construction can relate to any kind of layered structures, typically the uppermost layers of the ground, e.g. the uppermost 0-100cm of the ground. If the road is an asphalt, the road construction comprises the layers of the ground beneath the asphalt.
  • the method further comprises measuring the temperature of the ground at each respective pair of the conductive elements and using the measure temperature values in conjunction with the measured conductance values over time for determining the current or the future phase condition of the ground of the road construction.
  • the step of utilizing the time evolution of the conductance data for each respective pair of conductive elements comprises determining the slope of the conductance.
  • Phase transformations from one phase to another phase are reflected in abrupt changes in the slope of the conductance, i.e. the conductance can show a sudden increase/decrease over time. Thereby, a very good indicator is provided for determining about the current phase condition of the ground in a very simple manner.
  • the step of determining the slope of the conductance comprises initially performing a filtering step by means of: a) initially measuring two or more conductance data over a given time interval, wherein the conductance data are collected with a pre-fixed frequency, b) determining the average conductance value for the two or more measured conductance data, c) updating the average conductance value at the pre-fixed frequency when a new conductance data is measured, wherein the updating is based on replacing the new conductance data with the earliest measured conductance data and subsequently repeating step b), and subsequently determining the slope between two average conductance values over a pre-fixed time interval.
  • the given time interval can be one hour, and the pre-fixed collecting frequency can be 10 minutes.
  • the step of updating the average conductance value relates to replacing the first measured conductance data with the newest data (like a sequence where the first data is replaced by the newest data, but the number of data in the sequence is preserved), and updating the average value.
  • a "running average” method the scattering in the conductance values is strongly reduced, i.e. a "noise” filtering is applied.
  • the average conductance values are then implemented for determining the slope of the conductance over time.
  • the step of determining the average conductance value for the two or more measured conductance data is adapted to how rapid the phase changes in the ground are.
  • the temperature interval can be adapted to the type of ground, e.g. some grounds can have higher concentration of salinity than other grounds, or the type of the ground can be of completely different nature.
  • the result is therefore that the accuracy of the measurement will be maximized since it will be possible to determine whether the conductance measurements are within the temperature interval or not.
  • the changes are to be interpreted as phase transformation; otherwise the changes are to be interpreted as due to a sudden increase or decrease in the moisture of the ground.
  • the temperature values Tl and T2 enclosing the approximated critical temperature is automatically improved by means of:
  • Tl ' Tc-
  • T2' Tc+
  • T1-T2 surrounding the critical temperature Tc.
  • Tl and T2 are initially set as -1.O 0 C and +1.0 0 C, and the phase change is determined as -0.8 0 C.
  • a user may set
  • 1.0°C and
  • the temperature values Tl and T2 will be updated towards new values, namely Tl 'and T2' that form a new temperature window T2'-T1 ' that surrounds the critical temperature. Additionally, this will result in that the temperature window becomes narrower making the measurement more reliable. This means that where there is an abrupt change in the conductance, one can be certain that this is due to a phase change and not due to other external effects.
  • the indication when to impose or cancel axle weight limit on a road is based on set of rules including: if the temperature of the ground is within the temperature interval and the time evolution of the conductance data shows a negative slope of the conductance over a first time interval, then a sudden decrease in the slope over a second time interval, then a sudden increase in the slope over a third time interval, the phase condition of the ground is moving from a thawed condition to a frozen condition and thereby the axle weight limit of the road construction is to be raised or cancelled.
  • the indication when to impose or cancel axle weight limit on a road is based on set of rules including: if the temperature of the ground is within the temperature interval and the time evolution of the conductance data shows a positive slope of the conductance over a first time interval, then a sudden increase in the slope over a second time interval, then a sudden decrease in the slope over a third time interval, the phase condition of the ground is moving from a frozen condition to a thawed condition and thereby the axle weight limit of the road construction must be lowered to prevent damage.
  • the method further comprises calibrating the measured conductance data to the moisture content in the ground and the load bearing capacity of the ground when the ground is in thawed phase for indicating when to impose axle weight limit of the road construction in thawed phase. In another embodiment, the method further comprises calibrating the measured conductance data to the moisture content and the temperature in the ground and the load bearing capacity of the ground when the ground is in thawed phase for the indicating when to impose axle weight limit of the road construction in thawed phase.
  • the maximum axle weight limit can be determined based on the measured conductance data and other information on the road construction such as the age of the road construction, quality etc.
  • Information about the moisture content in the ground is namely very good indicator for determining the maximum axle weight limit when the ground is in thawed condition. This is of especial advantage when it is known that the ground is in thawed phase, e.g. at +2 0 C, but where the moisture content is still high. In such a situation, the axle weigh limit of the road construction might not yet have reached its maximum limit.
  • Such a calibration would typically comprise measuring the conductance and the temperature to compensate for different salinity and simultaneously measure moisture content and the load bearing capacity and subsequently perform a fitting through the data.
  • the method further comprises monitoring the time evolution of the temperature for predicting about the future phase condition and therefore the future condition of the road construction.
  • the method further comprises adding an intermediate layer between the conductive elements and the ground of the road construction having smaller grain size than the ground of the road construction.
  • an intermediate layer having smaller grain size that the ground of the road construction, the conductivity between the conductive elements will be improved leading to better and more reliable measurement results.
  • the present invention relates to a computer program product for instructing a processing unit to execute the above mentioned method step when the product is run on a computer.
  • the present invention relates to a device for indicating when to impose or cancel axle weight limit on a road based on the phase condition of the ground of the road construction , comprising:
  • an elongated body adapted to be placed into the ground of the road constructions, and • a measuring unit connected to one or more pairs of conductive elements situated along the longitudinal axis of the body for measuring the conductance of the ground between the conductive elements for each respective pair over a time, wherein the time evolution of the conductance data is utilized as input data for determining the current or the future phase condition of the ground.
  • a very simple and advanced device is provided that is capable of collecting the information relating to the conductance of the ground at one or more depths, where the device is adapted to be inserted into the ground in a very user friendly way.
  • the device further comprises temperature sensors for measuring the temperature of the ground at each respective pair of the conductive elements.
  • the device further comprises a processor for determining the phase condition of the ground and for determining the current or the future phase condition of the ground. In that way, the intelligence of the device is increased.
  • the device further comprises a transmitter for transmitting data indicating the current or future phase condition of the ground, or the conductance values over time along with the temperature values to an external processing unit via a communication channel.
  • a typical implementation would be to send the data to the road administration via the internet, fiber optic cable, telephone line and the like, wherein the road administration then notifies e.g. the police about the condition of the road construction.
  • the one or more pairs of conductive elements comprises parallel arranged plates or cylinders isolated from each other integrated into the elongated body such that the plates are exposed at the periphery of the outer surface of the elongated body.
  • the present invention relates to a system for indicating when to impose or cancel axle weight limit on a road based on the phase condition of the ground of the road construction , comprising:
  • a measuring unit connected to one or more pairs of conductive elements situated along the longitudinal axis of the body for measuring the conductance of the ground between the conductive elements for each respective pair over a time
  • Figure 1 shows a device according to the present invention for indicating when to impose or cancel axle weight limit on a road based on the phase condition of the ground of the road construction
  • Figure 2 shows a closer view of the device in Fig. 1,
  • Figure 3 is an example of a temperature curve for one temperature sensor as a function of time t
  • Figure 4 is an example of a conductance curve as a function of time t
  • Figure 5 shows an example of a conductance curve as a function of time t
  • Figures 6 - 8 illustrate various scenarios illustrating graphically how the conductance is changing over time when the temperature is within the temperature window T 1-T2,
  • Figure 9 shows a method according to the present invention of indicating when to impose or cancel axle weight limit on a road based on the phase condition of the ground of the road construction
  • Figure 10 show an example of how to present the result of the above graphically and in a user friendly way.
  • Figure 1 shows a device 100 according to the present invention for indicating when to impose or cancel axle weight limit on a road 130 based on the phase condition of the ground of the road construction 110.
  • the device comprises an elongated body 108 adapted to be placed into the ground of the road construction 110, at least one pair 103-107 of conductive elements 101-102, a measuring unit (M U), and in one embodiment temperature sensors 113 placed at each respective pair 103-107 for measuring the temperature at of the pairs 103-107.
  • the term road construction 110 can relate to any kind of layered structures, typically the uppermost layers of the ground 110, e.g. the uppermost 0-100cm of the ground. If the road is asphalt 130, the road construction 110 is the layers of the ground beneath the asphalt 130.
  • an intermediate material or a filling material between the device 100 (i.e. the elongated body 108) and the ground of the road construction 110 (not shown here).
  • Such an intermediate material is preferably a material having a grain size that is smaller than the grain size of the ground of the road construction 110. This may e.g. be a clay, or silt and the like.
  • Figure 12 depicts a graph showing on the upper vertical axis a grain size diameter that was used during the measurement and the percentage of the silt having such grains size diameter on the left vertical axis. As an example, figure 12 depicts that 20% of the material has approximately a diameter of 0.125mm or less, 50% of the material has a diameter of 0.6mm or less, and 98% of the material has a diameter of 4mm or less.
  • the temperature sensors 113 are not essential for the present invention since the time evolution of the measured conductance is sufficient to determine the current or the future phase condition of the road construction 110. However, a situation can occur where there is a sudden increase or decrease in the moisture in the road construction 110 due to e.g. rain, where such a sudden increase can lead to a sudden change in the conductance. It is of course possible to distinguish a sudden change in the conductance cause by phase transformation from a sudden change caused by e.g. rain. However, here below, it will be assumed that temperature sensors are implemented at each respective pair 103-107.
  • the device 100 comprises five pairs 103-107 of conductive elements lOla-lOlc, 102a- 102b, temperature sensors 113 placed at each respective pair for measuring the temperature at the pairs 103-107 and a measuring unit (M U) 111 connected to each respective element 101-102.
  • the conductive elements lOla-lOlc, 102a- 102b is isolated from each other and placed so that the ground 110 acts as a contact carrier between the plates for each respective pair.
  • the conductive elements are integrated into, or mounted to the elongated body 108 such that the plates are exposed at the periphery of the outer surface of the elongated body.
  • the surrounding ground 110 therefore acts as a contact carrier.
  • the measuring unit (M U) 111 comprises a power source, preferably AC power source applied over each respective pair wherein the conductance of the ground is measured for each respective pair over time.
  • the AC current generator sends AC current through the ground. This current is feed through a resistor. The voltage drop over the resistor indicates the conductance of the ground. The voltage is measured by analog to digital converter. In this example, five measurements of the conductance values are measured over time and each measurement is associated with the temperature value measured by the temperature sensors placed at each respective pair.
  • the phase condition of the road construction 110 will then be determined for each respective pair 103-107. Since the pairs 103-107 are placed at different depths, a depth profile of the phase conditions is obtained.
  • the uppermost layers are the layers that are of particular relevance.
  • the elongated body is made of isolating material such as a plastic material, or any metal or metal alloy material (here it is of course ensured that the conductive plates are isolated from the elongated body).
  • the main role of the elongated body is more or less to host the pairs 103-106 and to be robust against corrosion and other factors since it is to be placed into the ground for eventually several years.
  • the device 100 further comprises a processor (P) 115 for utilizing the conductance data and the temperature data for determining the current phase condition of the ground, or for estimating the future phase condition of the ground.
  • the determination of the phase condition is based on set of rules, which will be discussed in more details later.
  • the device 100 further comprises a memory 114 such as ROM, RAM, DRAM, SRAM and the like for storing among other things the set of rules and the measured data.
  • a memory 114 such as ROM, RAM, DRAM, SRAM and the like for storing among other things the set of rules and the measured data.
  • the device 100 further comprises a transmitter (T) 112 for transmitting data e.g. the measuring data to an external server, or information relating to the current or the future phase condition of the ground.
  • T transmitter
  • Figure 1 further illustrates a system 120 according to the present invention for determining an axle weight limit for a road construction 110 based on the phase condition of the ground, wherein the system 120 comprises the above mentioned device 100 and an external server 121, which in an embodiment may include said processor (P) 115, a receiver (R) 123 and said memory 114.
  • the external server 121 may e.g. be a server at the road administration.
  • the above mentioned processing steps are performed at the server side where the receiver (R) 123 receives data transmitted over a communication channel 122 relating to the measured conductance over time along with the measured temperature values.
  • the communication channel can be a wireless communication channel 122, e.g. the internet, or be fiber optic cable, telephone line and the like.
  • the external server 121 may also be adapted to receive already processed data from the device 100 where data relating to the current or the future phase condition of the ground are transmitted over to the server 121.
  • the server acts as an alert unit (A U) 124 that is adapted to issue a warning about the condition of the road construction.
  • the alert unit (A U) 124 can simply be a telephone, where an operator at the road administration issues a warning by e.g. calling the police and request for that the road construction in this are is to be closed.
  • the alert unit (A U) 124 may comprise an automatic unit that issues, based on the received or the processed data, a warning 131 relating to critical condition of the road construction 110.
  • Figure 2 shows a closer view of the device 100 in Fig. 1, where the two pairs of conductive elements 101 a- 101c, 102a- 102b that are exposed at the periphery of the outer surface of the elongated body 108 such that the ground 110 surrounding the body acts as a contact carrier between the plates for each respective pair.
  • the conductance values 203, 204 are measured over time by the measuring unit (M U) 111 along with the measured temperature values 201, 202 for each respective pair 103, 104.
  • M U measuring unit
  • These data are the processed by the processor (P) 115, which as mentioned here above can be comprised in the device 100, or at the external server 121.
  • Figure 3 is an example of a temperature curve 300 for one temperature sensor as a function of time t, where the vertical axis is the temperature T and the horizontal axis is the time.
  • the critical temperature for the ground Prior to placing the above mentioned device 100 into the ground the critical temperature for the ground must be estimated as precisely as possible. This estimation is based on various parameters, e.g. the ratio of different ions and salinities in the ground, or their absolute values.
  • a temperature window 301 is then defined around this critical temperature so that Tl ⁇ Tc ⁇ T2, where Tc is the critical temperature.
  • One way of estimating the critical temperature is to calibrate the device 100 prior to implementing it, i.e. make measurements where the ground moves from frozen phase to thawed phase, and vice verse, and compare the theoretical result of the determined phase condition discussed here above with the measured results. If e.g. there is not a consistency in the theoretical and the measure results it could be an indicator that the temperature interval is not correct, or narrow enough. In that way, the temperature interval can be adjusted until the theoretical results are consistent with the measured result.
  • Figure 4 is an example of a conductance curve 400 as a function of time t for temperature T larger than T2, i.e. T>T2.
  • the measurements may in this case be implemented to estimate the load bearing capacity and the moisture of the ground. This may be done by calibrating the conductance measurement to measured moisture measured by any type of hygrometer for a number of different moisture concentrations, and thereby link the conductance and preferably the temperature to the moisture concentration, for increasing the accuracy. This may e.g. be done by measuring the conductance and the temperature and simultaneously the moisture content in the ground for each respective depth and subsequently perform a fitting through the data so that the resulting fitting function is the moisture as a function of the conductance data.
  • Information about the moisture content in the ground is namely highly relevant for determining the maximum axle weight limit when the ground is in thawed condition.
  • the measured moisture content can be very helpful in determining in what phase condition the ground is if the initial temperature of the ground lies within the temperature interval when the unit is installed for first time. If the ground is e.g. in a frozen phase the moisture content is low, whereas if the ground is in thawed phase the moisture content is high.
  • the phase is determined with maximum accuracy after the temperature has traveled from T>T2 to T ⁇ T2 or T>T1 to T ⁇ T1.
  • the conductance measurement can also be calibrated to the bearing capacity by measuring the load bearing capacity using any kind of bearing capacity gauge and simultaneously measure the conductance and/or the temperature of the ground.
  • the conductance values may be determined and linked the measured load bearing capacity, by e.g. fitting the data so that the resulting fitting function gives the load bearing capacity as a function of the conductance and/or the temperature. This is of especial advantage when it is known that the ground is in thawed phase, e.g. at +2 0 C, but where the moisture content is still high.
  • Figure 5 shows an example of a conductance curve 500 as a function of time t for a temperature T ⁇ T1.
  • the ground is in frozen condition meaning that the axle weight limit may be raised or even be at it's maximum level.
  • Figures 6 - 8 illustrate various scenarios illustrating graphically how the conductance is changing over time when the temperature is within the temperature window T1-T2, i.e. here T1 ⁇ T ⁇ T2.
  • the interpretation of these graphs can be based on "IF-THEN" rules.
  • the change in the slope is an abrupt change.
  • the threshold values are preferably adjustable for each sensor. This sudden change in the slope indicates that there is a phase change in the ground where the ground is moving from a thawed phase towards a frozen phase.
  • a very good indicator for conforming that this is actually due to a phase transformation, and not a sudden increase in the moisture content, is to monitor the time evolution of the temperature, because during a phase transformation the temperature remains constant. Accordingly, the "IF-THEN" rule for this scenario is interpreted in the following way:
  • phase is changing from frozen phase to thawed phase
  • -ground is critical.
  • the conductance 800 remains substantially constant the ground is either in a frozen condition or in a thawed condition, which can be determined by measuring the temperature or the moisture content in the ground. As mentioned previously, if the moisture content is "low” or below a given threshold value, the phase condition is frozen, whereas if the moisture content is above the threshold value the phase condition is thawed.
  • Figure 9 shows a flowchart of a method according to the present invention of indicating when to impose or cancel axle weight limit on a road based on the phase condition of the ground of the road construction.
  • One or more pairs of conductive elements are placed into the ground of the road construction (Sl) 901, and the conductance of the ground between the conductive elements for each respective pair is measured as a function of time (S2) 902.
  • S3 903 it is preferred to initially estimating the critical temperature of the ground where the measurements take place (S3) 903 and defined a temperature interval that encloses the critical temperature.
  • the temperature interval is a narrow interval, e.g. between "-0.2°C"-"+0.2°C", or "-0.1°C"-"+0.1°C", but this is highly dependent on the salinity of the ground, and the type of the ground.
  • the time evolution of the conductance data for each respective pair is then used for determining the current or the future phase condition of the ground (S4) 904, based on e.g. said set of rules. In an embodiment, this is done by determining the slope of the conductance by implementing so-called "running average” method, where initially measuring two or more conductance data over a given time interval, wherein the conductance data are collected with a pre-fixed frequency. The average conductance value for the two or more measured conductance data is then determined. As an example, if the sequence of the measured conductance data is: 0.25; 0.32; 0.28;0.29;0.28;0.31, where the time interval between two adjacent measurements is 10 minutes, then first determined average value is 0.288.
  • a new conductance value When a new conductance value is measured, i.e. every 10 minutes it replaces the first value, i.e. 0.25 is deleted and the new value comes as a first value in the sequence.
  • the new value if the new value is 0.33, the new sequence becomes: 0.32; 0.28; 0.29; 0.28; 0.31; 0.33 and the average value is updated.
  • the conductance curves in Figs. 6-8 may accordingly comprise such average conductance values.
  • Such a "filtering" process decreases the scattering in the conductance and therefore makes the calculations of the slope of the conductance more reliable.
  • the calculations of the slope may be performed every 5 hours, where e.g. the first and the last average conductance value may be used for determining the slope.
  • the temperature of the ground at each respective pair is measured at the conductive elements for eliminating scenarios where the conductance shows an abrupt change to enhanced moisture concentration in the ground, and not due to phase transformation. This may e.g. be done by monitoring whether the temperature is constant during the abrupt changes, since such a stable condition would indicate that there is a phase transformation.
  • the measured conductance data are calibrated to the moisture in the ground for linking the conductance data to the moisture (S5) 905 and to the load bearing capacity of the ground for linking the conductance data to the load bearing capacity (S6) 906.
  • This may e.g. be done by measuring the conductance and simultaneously the moisture content in the ground for each respective depth and subsequently perform a fitting through the data so that the resulting fitting function is the moisture as a function of the conductance data.
  • Information about the moisture content in the ground is namely highly relevant for determining the maximum axle weight limit when the ground is in thawed condition.
  • Figure 10 show an example of how to present the result of the above graphically and in a user friendly way, where the vertical axis represents the depth of said pairs into ground, and the horizontal axis different dates (e.g. 1. feb. 2006, 1. marc. 2006 etc.).
  • the white area may e.g. represent where the moisture concentration is below a given threshold value, and the temperature is above T2 of said temperature limit shown in Fig. 3.
  • the vertical lines may represent a frozen phase condition, and the horizontal lines could indicate limit axle weight limit due to high moisture for T>T2, or the horizontal lines could indicate that the road construction is in a critical condition.
  • Figure 1 Ia-I Ic shows an example of a freeze /thaw period, measured by a single device 100 (see in Fig. 1).
  • Figure 11a depicts the temperature of the of the ground of a road construction as a function of time
  • Fig. 1 Ib depicts the conductance resulting from Fig. 1 Ia as a function of time
  • Fig. l ie depicts the resulting graph bar indicating the different phase conditions as a function of time.
  • the temperature curve in Fig. 11a lies is within Tl ant T2.
  • the sudden change in the slope of the conductivity curve in Fig. 1 Ib towards a lower value indicates a phase change occurring from thawed phase to frozen phase.
  • This beginning of the phase change is thus the beginning of the frozen phase condition, indicated by the beginning of the vertical bar graph 1102 in Fig. l ie. From that moment the bar graph shows frozen phase, vertical lines throughout the interval tc.
  • this temperature interval i.e. tc
  • the temperature curve in Fig. 1 Ia is below Tl.
  • the next phase change takes place in the interval td, where the temperature curve in Fig. 11a lies within Tl and T2.
  • the phase change in Fig. 1 Ib changes abruptly towards a lower slope value and a phase change (ps) occurs from frozen phase to thawed phase.
  • the bar graph 1103 in Fig. l ie from interval td shows critical condition, where the horizontal lines throughout the interval te indicate high moisturized not frozen state of the ground.
  • the bar graph in Fig. l ie shows a non critical condition as the conductivity in Fig. l ib has dropped down under a given threshold value and the temperature in above T2.
  • the temperatures Tl and T2 may be detected automatically. In one embodiment, this is done by detecting the face change based on the conductivity measurement (Fig. 1 Ib). By detecting a phase change through the abrupt change in the conductance as previously discussed the phase change (pc) temperature Tc is registered in the moment where the phase change takes place.
  • and Tl Tc-
  • the deltaTl and deltaT2 are selected as 1.O 0 C.
  • a user of the device may self decide the values of deltaTl and deltaT2.
  • the new temperature window becomes Tl ' ⁇ Tc ⁇ T2'.

Abstract

This invention relates to method, a device and a system for determining indicating when to impose or cancel axle weight limit on a road based on the phase condition of the ground of the road construction. One or more conductive elements placed into the ground for measuring the conductance of the ground as a function of time. Based on the time evolution of the conductance the current or the future phase condition of the ground is determined.

Description

METHOD AND DEVICE FOR INDICATING WHEN TO IMPOSE AXLE WEIGHT LIMIT ON ROADS
FIELD OF THE INVENTION
The present invention relates to a method, a device and a system for indicating when to impose or cancel axle weight limit on a road based on the phase condition of the ground of the road construction.
BACKGROUND OF THE INVENTION
Road systems play a key role for the infrastructure in any modern society. Every year an enormous amount of money is invested for preserving the conditions of the roads. It has been reported in the literature that 40% and up to 90% of the total early damage on road sections occurs during spring thaw. This is of course highly dependent between countries, where in some countries the temperature variations are large, whereas in other countries these variations are less.
One way of minimizing the costs for preserving the conditions of the roads is to lower the weight limit of the roads when the condition of the road is "critical". A critical condition is as an example when the ground is in thawed condition, or is moving from one frozen phase to a thawed phase. It is well known that when a ground has just moved from frozen to thawed phase it acts as a "sponge" in the first hours or first day after the phase transfer has occurred. When the ground is in such a condition it is extremely sensitive to excessive weights caused by e.g. vehicles. Results show that the damage caused by excessive axle weight limits is approximately 48 times higher when the ground is in this critical condition.
It is therefore of crucial importance to be able to know when the ground is proceeding from the frozen phase to the thawed phase for predicting when the substrate is or will be sensitive to excessive weigh limits in order to enable to impose weight limits when measurements show a risk of damage from excessive weight. BRIEF DESCRIPTION OF THE INVENTION
The object of the present invention is to overcome the above mentioned problem by providing a method and a device that is capable of monitoring the condition of the grounds of road constructions, thereby providing information relating to the current and the future condition of the roads. This information is then used for imposing or canceling axle weight limit on roads.
According to one aspect the present invention relates to a method of indicating when to impose or cancel axle weight limit on a road based on the phase condition of the ground of the road construction, comprising:
• placing one or more pairs of conductive elements into the ground of the road construction,
• measuring the conductance of the ground between the conductive elements for each respective pair over a time, • utilizing the time evolution of the conductance data for each respective pair of conductive elements as input data for determining the current or the future phase condition of the ground.
Since the conductance over time reflects the different phases or phase transformations, the conductance measurement can be implemented for determining about the current and/or the future phase condition or phase transformations of the ground at the one or more different depths. Therefore, it is possible to prevent damages caused by excessive weight by e.g. issuing a warning to the road administration in due time and in that way prevent any kind of damages caused by excessive axle weight limits. This will inherently reduce the amount of money invested for preserving the conditions of the road structure enormously. The term road construction can relate to any kind of layered structures, typically the uppermost layers of the ground, e.g. the uppermost 0-100cm of the ground. If the road is an asphalt, the road construction comprises the layers of the ground beneath the asphalt.
In an embodiment, the method further comprises measuring the temperature of the ground at each respective pair of the conductive elements and using the measure temperature values in conjunction with the measured conductance values over time for determining the current or the future phase condition of the ground of the road construction.
This can be of particular advantage since the scenario can occur where the sudden abrupt in the conductance over time is due to sudden increase or decrease in the moisture concentration when the ground is in thawed condition. By additionally measuring the temperature it is possible to distinguish whether a sudden abrupt in the conductance over time is due to phase transformation of the ground or is due to a sudden increase in the moisture in the ground. As an example, if the sudden abrupt in the conductance occurs at 1O0C the temperature values would indicate that this is not due to a phase transformation, whereas if the abrupt would occur at e.g. -0.050C the temperature value would indicate that this is indeed due to a phase transformation of the ground.
In an embodiment, the step of utilizing the time evolution of the conductance data for each respective pair of conductive elements comprises determining the slope of the conductance.
Phase transformations from one phase to another phase are reflected in abrupt changes in the slope of the conductance, i.e. the conductance can show a sudden increase/decrease over time. Thereby, a very good indicator is provided for determining about the current phase condition of the ground in a very simple manner.
In an embodiment, the step of determining the slope of the conductance comprises initially performing a filtering step by means of: a) initially measuring two or more conductance data over a given time interval, wherein the conductance data are collected with a pre-fixed frequency, b) determining the average conductance value for the two or more measured conductance data, c) updating the average conductance value at the pre-fixed frequency when a new conductance data is measured, wherein the updating is based on replacing the new conductance data with the earliest measured conductance data and subsequently repeating step b), and subsequently determining the slope between two average conductance values over a pre-fixed time interval.
As an example, the given time interval can be one hour, and the pre-fixed collecting frequency can be 10 minutes. This means that six conductance data are collected every hour, and the average conductance value for these six data is then calculated. The step of updating the average conductance value relates to replacing the first measured conductance data with the newest data (like a sequence where the first data is replaced by the newest data, but the number of data in the sequence is preserved), and updating the average value. By implementing such a "running average" method the scattering in the conductance values is strongly reduced, i.e. a "noise" filtering is applied. Subsequently, the average conductance values are then implemented for determining the slope of the conductance over time. This gives a much more reliable slope values than if the slope between two conductance values would be determined. Since change in the conductance typically occurs very slowly, it may be preferred to calculate the slope over a time interval that is somewhat larger than the given time interval, e.g. every five hours if the given time interval is one hour.
In an embodiment, the step of determining the average conductance value for the two or more measured conductance data is adapted to how rapid the phase changes in the ground are.
Accordingly, where the changes in the conductance are fast it will be preferred to calculate at more frequent rate the average conductance value than where the changes in the conductance are slower. In an embodiment, the method further comprises approximating the critical temperature of the ground and based thereon defining a temperature interval deltaT=T2-Tl enclosing the approximated critical temperature.
In that way, the temperature interval can be adapted to the type of ground, e.g. some grounds can have higher concentration of salinity than other grounds, or the type of the ground can be of completely different nature. The result is therefore that the accuracy of the measurement will be maximized since it will be possible to determine whether the conductance measurements are within the temperature interval or not. As an example, if the above mentioned abrupt changes in the conductance occur within the temperature window, the changes are to be interpreted as phase transformation; otherwise the changes are to be interpreted as due to a sudden increase or decrease in the moisture of the ground.
In one embodiment, the temperature values Tl and T2 enclosing the approximated critical temperature is automatically improved by means of:
• utilizing the conductance data for estimating the critical temperature Tc, the estimate being based on monitoring where an abrupt change occurs in the conductance, the temperature at the instant of the abrupt change being used as the estimating for the critical temperature Tc,
• defining a deltaTl value and deltaT2 values,
• calculating improved values Tl ' and T2' to replacing the Tl and T2 values via the equations: Tl '=Tc-|deltaTl | and T2'= Tc+|deltaT2|.
Thus, it is possible to automatically narrow the temperature window T1-T2 surrounding the critical temperature Tc. As an example, assuming Tl and T2 are initially set as -1.O0C and +1.00C, and the phase change is determined as -0.80C. A user may set |deltaTl |=1.0°C and |deltaT2|=1.00C. Based on the above, it follows that T2=0.20C and Tl=-1.8 0C, i.e. a narrower temperature window is obtained. Accordingly, in case there is a swift in the critical temperature such that e.g. critical temperature falls nearly outside or outside the temperature window T2-T1, the temperature values Tl and T2 will be updated towards new values, namely Tl 'and T2' that form a new temperature window T2'-T1 ' that surrounds the critical temperature. Additionally, this will result in that the temperature window becomes narrower making the measurement more reliable. This means that where there is an abrupt change in the conductance, one can be certain that this is due to a phase change and not due to other external effects.
In an embodiment, the indication when to impose or cancel axle weight limit on a road is based on set of rules including: if the temperature of the ground is within the temperature interval and the time evolution of the conductance data shows a negative slope of the conductance over a first time interval, then a sudden decrease in the slope over a second time interval, then a sudden increase in the slope over a third time interval, the phase condition of the ground is moving from a thawed condition to a frozen condition and thereby the axle weight limit of the road construction is to be raised or cancelled.
In that way, a very advanced and precise indicator is provided indicating when to bring down the axle weight limit or to cancel the axle weight limit.
In an embodiment, the indication when to impose or cancel axle weight limit on a road is based on set of rules including: if the temperature of the ground is within the temperature interval and the time evolution of the conductance data shows a positive slope of the conductance over a first time interval, then a sudden increase in the slope over a second time interval, then a sudden decrease in the slope over a third time interval, the phase condition of the ground is moving from a frozen condition to a thawed condition and thereby the axle weight limit of the road construction must be lowered to prevent damage.
Since such a condition indicates that the ground is extremely sensitive to excessive axle weights it is possible to lower the axle load limit in due time, and therefore prevent damages caused by excessive axle weight limits.
In one embodiment, the method further comprises calibrating the measured conductance data to the moisture content in the ground and the load bearing capacity of the ground when the ground is in thawed phase for indicating when to impose axle weight limit of the road construction in thawed phase. In another embodiment, the method further comprises calibrating the measured conductance data to the moisture content and the temperature in the ground and the load bearing capacity of the ground when the ground is in thawed phase for the indicating when to impose axle weight limit of the road construction in thawed phase.
In that way, the maximum axle weight limit can be determined based on the measured conductance data and other information on the road construction such as the age of the road construction, quality etc. Information about the moisture content in the ground is namely very good indicator for determining the maximum axle weight limit when the ground is in thawed condition. This is of especial advantage when it is known that the ground is in thawed phase, e.g. at +20C, but where the moisture content is still high. In such a situation, the axle weigh limit of the road construction might not yet have reached its maximum limit. Such a calibration would typically comprise measuring the conductance and the temperature to compensate for different salinity and simultaneously measure moisture content and the load bearing capacity and subsequently perform a fitting through the data.
In an embodiment, the method further comprises monitoring the time evolution of the temperature for predicting about the future phase condition and therefore the future condition of the road construction.
This can e.g. be based on considering what value the temperature is approaching, e.g. where will the temperature be within the next 12 hours. Based thereon the future phase conditions of the ground can be predicted and therefore it is possible to be well prepared to critical conditions of road constructions.
In one embodiment, the method further comprises adding an intermediate layer between the conductive elements and the ground of the road construction having smaller grain size than the ground of the road construction. Thus, by using such an intermediate layer having smaller grain size that the ground of the road construction, the conductivity between the conductive elements will be improved leading to better and more reliable measurement results.
According to another aspect, the present invention relates to a computer program product for instructing a processing unit to execute the above mentioned method step when the product is run on a computer.
According to still another aspect, the present invention relates to a device for indicating when to impose or cancel axle weight limit on a road based on the phase condition of the ground of the road construction , comprising:
• an elongated body adapted to be placed into the ground of the road constructions, and • a measuring unit connected to one or more pairs of conductive elements situated along the longitudinal axis of the body for measuring the conductance of the ground between the conductive elements for each respective pair over a time, wherein the time evolution of the conductance data is utilized as input data for determining the current or the future phase condition of the ground.
Thereby, a very simple and advanced device is provided that is capable of collecting the information relating to the conductance of the ground at one or more depths, where the device is adapted to be inserted into the ground in a very user friendly way.
In an embodiment, the device further comprises temperature sensors for measuring the temperature of the ground at each respective pair of the conductive elements.
In an embodiment, the device further comprises a processor for determining the phase condition of the ground and for determining the current or the future phase condition of the ground. In that way, the intelligence of the device is increased. In an embodiment, the device further comprises a transmitter for transmitting data indicating the current or future phase condition of the ground, or the conductance values over time along with the temperature values to an external processing unit via a communication channel.
A typical implementation would be to send the data to the road administration via the internet, fiber optic cable, telephone line and the like, wherein the road administration then notifies e.g. the police about the condition of the road construction.
In an embodiment, the one or more pairs of conductive elements comprises parallel arranged plates or cylinders isolated from each other integrated into the elongated body such that the plates are exposed at the periphery of the outer surface of the elongated body.
According to yet another aspect, the present invention relates to a system for indicating when to impose or cancel axle weight limit on a road based on the phase condition of the ground of the road construction , comprising:
• an elongated body adapted to be placed into the ground of the road constructions, and
• a measuring unit connected to one or more pairs of conductive elements situated along the longitudinal axis of the body for measuring the conductance of the ground between the conductive elements for each respective pair over a time,
• a processor for utilizing the time evolution of the conductance data for each respective pair of conductive elements as input data for determining the current or the future phase condition of the ground,
• a transmitter for transmitting either the measured conductance data and the temperature data, or the data indicating the phase condition of the ground to the external server, • a receiver for receiving the transmitted data, and
• an alert unit for alerting about the current or the future phase of the road construction.
The aspects of the present invention may each be combined with any of the other aspects. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which
Figure 1 shows a device according to the present invention for indicating when to impose or cancel axle weight limit on a road based on the phase condition of the ground of the road construction,
Figure 2 shows a closer view of the device in Fig. 1,
Figure 3 is an example of a temperature curve for one temperature sensor as a function of time t,
Figure 4 is an example of a conductance curve as a function of time t,
Figure 5 shows an example of a conductance curve as a function of time t,
Figures 6 - 8 illustrate various scenarios illustrating graphically how the conductance is changing over time when the temperature is within the temperature window T 1-T2,
Figure 9 shows a method according to the present invention of indicating when to impose or cancel axle weight limit on a road based on the phase condition of the ground of the road construction, and
Figure 10 show an example of how to present the result of the above graphically and in a user friendly way.
DESCRIPTION OF EMBODIMENTS
Figure 1 shows a device 100 according to the present invention for indicating when to impose or cancel axle weight limit on a road 130 based on the phase condition of the ground of the road construction 110. The device comprises an elongated body 108 adapted to be placed into the ground of the road construction 110, at least one pair 103-107 of conductive elements 101-102, a measuring unit (M U), and in one embodiment temperature sensors 113 placed at each respective pair 103-107 for measuring the temperature at of the pairs 103-107. The term road construction 110 can relate to any kind of layered structures, typically the uppermost layers of the ground 110, e.g. the uppermost 0-100cm of the ground. If the road is asphalt 130, the road construction 110 is the layers of the ground beneath the asphalt 130.
To enhance the conductance between the conductive elements 101a,b, 102a,b and the surrounding ground or soil it may be preferred to provide an intermediate material or a filling material between the device 100 (i.e. the elongated body 108) and the ground of the road construction 110 (not shown here). Such an intermediate material is preferably a material having a grain size that is smaller than the grain size of the ground of the road construction 110. This may e.g. be a clay, or silt and the like.
Figure 12 depicts a graph showing on the upper vertical axis a grain size diameter that was used during the measurement and the percentage of the silt having such grains size diameter on the left vertical axis. As an example, figure 12 depicts that 20% of the material has approximately a diameter of 0.125mm or less, 50% of the material has a diameter of 0.6mm or less, and 98% of the material has a diameter of 4mm or less.
The temperature sensors 113 are not essential for the present invention since the time evolution of the measured conductance is sufficient to determine the current or the future phase condition of the road construction 110. However, a situation can occur where there is a sudden increase or decrease in the moisture in the road construction 110 due to e.g. rain, where such a sudden increase can lead to a sudden change in the conductance. It is of course possible to distinguish a sudden change in the conductance cause by phase transformation from a sudden change caused by e.g. rain. However, here below, it will be assumed that temperature sensors are implemented at each respective pair 103-107.
As shown in this embodiment, the device 100 comprises five pairs 103-107 of conductive elements lOla-lOlc, 102a- 102b, temperature sensors 113 placed at each respective pair for measuring the temperature at the pairs 103-107 and a measuring unit (M U) 111 connected to each respective element 101-102. The conductive elements lOla-lOlc, 102a- 102b is isolated from each other and placed so that the ground 110 acts as a contact carrier between the plates for each respective pair. In an embodiment, the conductive elements are integrated into, or mounted to the elongated body 108 such that the plates are exposed at the periphery of the outer surface of the elongated body. The surrounding ground 110 therefore acts as a contact carrier. In one embodiment the measuring unit (M U) 111 comprises a power source, preferably AC power source applied over each respective pair wherein the conductance of the ground is measured for each respective pair over time. The AC current generator sends AC current through the ground. This current is feed through a resistor. The voltage drop over the resistor indicates the conductance of the ground. The voltage is measured by analog to digital converter. In this example, five measurements of the conductance values are measured over time and each measurement is associated with the temperature value measured by the temperature sensors placed at each respective pair. The phase condition of the road construction 110 will then be determined for each respective pair 103-107. Since the pairs 103-107 are placed at different depths, a depth profile of the phase conditions is obtained. Here, the uppermost layers are the layers that are of particular relevance.
In an embodiment, the elongated body is made of isolating material such as a plastic material, or any metal or metal alloy material (here it is of course ensured that the conductive plates are isolated from the elongated body). The main role of the elongated body is more or less to host the pairs 103-106 and to be robust against corrosion and other factors since it is to be placed into the ground for eventually several years.
In an embodiment, the device 100 further comprises a processor (P) 115 for utilizing the conductance data and the temperature data for determining the current phase condition of the ground, or for estimating the future phase condition of the ground. In an embodiment, the determination of the phase condition is based on set of rules, which will be discussed in more details later.
In an embodiment, the device 100 further comprises a memory 114 such as ROM, RAM, DRAM, SRAM and the like for storing among other things the set of rules and the measured data.
In an embodiment, the device 100 further comprises a transmitter (T) 112 for transmitting data e.g. the measuring data to an external server, or information relating to the current or the future phase condition of the ground.
Figure 1 further illustrates a system 120 according to the present invention for determining an axle weight limit for a road construction 110 based on the phase condition of the ground, wherein the system 120 comprises the above mentioned device 100 and an external server 121, which in an embodiment may include said processor (P) 115, a receiver (R) 123 and said memory 114. The external server 121 may e.g. be a server at the road administration.
In the embodiment, the above mentioned processing steps are performed at the server side where the receiver (R) 123 receives data transmitted over a communication channel 122 relating to the measured conductance over time along with the measured temperature values. The communication channel can be a wireless communication channel 122, e.g. the internet, or be fiber optic cable, telephone line and the like. The external server 121 may also be adapted to receive already processed data from the device 100 where data relating to the current or the future phase condition of the ground are transmitted over to the server 121. In this case, the server acts as an alert unit (A U) 124 that is adapted to issue a warning about the condition of the road construction. The alert unit (A U) 124 can simply be a telephone, where an operator at the road administration issues a warning by e.g. calling the police and request for that the road construction in this are is to be closed. The alert unit (A U) 124 may comprise an automatic unit that issues, based on the received or the processed data, a warning 131 relating to critical condition of the road construction 110.
Figure 2 shows a closer view of the device 100 in Fig. 1, where the two pairs of conductive elements 101 a- 101c, 102a- 102b that are exposed at the periphery of the outer surface of the elongated body 108 such that the ground 110 surrounding the body acts as a contact carrier between the plates for each respective pair. As illustrated graphically, the conductance values 203, 204 are measured over time by the measuring unit (M U) 111 along with the measured temperature values 201, 202 for each respective pair 103, 104. These data are the processed by the processor (P) 115, which as mentioned here above can be comprised in the device 100, or at the external server 121.
Figure 3 is an example of a temperature curve 300 for one temperature sensor as a function of time t, where the vertical axis is the temperature T and the horizontal axis is the time. Prior to placing the above mentioned device 100 into the ground the critical temperature for the ground must be estimated as precisely as possible. This estimation is based on various parameters, e.g. the ratio of different ions and salinities in the ground, or their absolute values. A temperature window 301 is then defined around this critical temperature so that Tl<Tc<T2, where Tc is the critical temperature. An example of a temperature interval is where Tl=-0.2°C and T2=+0,2°C. This temperature is preferably adjustable.
One way of estimating the critical temperature is to calibrate the device 100 prior to implementing it, i.e. make measurements where the ground moves from frozen phase to thawed phase, and vice verse, and compare the theoretical result of the determined phase condition discussed here above with the measured results. If e.g. there is not a consistency in the theoretical and the measure results it could be an indicator that the temperature interval is not correct, or narrow enough. In that way, the temperature interval can be adjusted until the theoretical results are consistent with the measured result.
Figure 4 is an example of a conductance curve 400 as a function of time t for temperature T larger than T2, i.e. T>T2. Here the ground is in a thaw phase condition. The measurements may in this case be implemented to estimate the load bearing capacity and the moisture of the ground. This may be done by calibrating the conductance measurement to measured moisture measured by any type of hygrometer for a number of different moisture concentrations, and thereby link the conductance and preferably the temperature to the moisture concentration, for increasing the accuracy. This may e.g. be done by measuring the conductance and the temperature and simultaneously the moisture content in the ground for each respective depth and subsequently perform a fitting through the data so that the resulting fitting function is the moisture as a function of the conductance data. Information about the moisture content in the ground is namely highly relevant for determining the maximum axle weight limit when the ground is in thawed condition.
Also, when starting with the measurements, the measured moisture content can be very helpful in determining in what phase condition the ground is if the initial temperature of the ground lies within the temperature interval when the unit is installed for first time. If the ground is e.g. in a frozen phase the moisture content is low, whereas if the ground is in thawed phase the moisture content is high.
The phase is determined with maximum accuracy after the temperature has traveled from T>T2 to T< T2 or T>T1 to T<T1. By spanning the temperature in that way one has passed the different phase conditions/transformations and knowing the actual phase condition at each respective time point one can perform a calibration for the future measurements.
The conductance measurement can also be calibrated to the bearing capacity by measuring the load bearing capacity using any kind of bearing capacity gauge and simultaneously measure the conductance and/or the temperature of the ground. As an example, the conductance values may be determined and linked the measured load bearing capacity, by e.g. fitting the data so that the resulting fitting function gives the load bearing capacity as a function of the conductance and/or the temperature. This is of especial advantage when it is known that the ground is in thawed phase, e.g. at +20C, but where the moisture content is still high.
Figure 5 shows an example of a conductance curve 500 as a function of time t for a temperature T<T1. In this scenario, the ground is in frozen condition meaning that the axle weight limit may be raised or even be at it's maximum level.
Figures 6 - 8 illustrate various scenarios illustrating graphically how the conductance is changing over time when the temperature is within the temperature window T1-T2, i.e. here T1<T<T2. The interpretation of these graphs can be based on "IF-THEN" rules.
In Figure 6, the conductance 600 decreases steadily (there are of course typically fluctuations in the conductance values) for time interval tl wherein the average slope value for this time interval is si, then the slope changes abruptly to much lower slope value s2 (s2«sl) subsequently maintains steady, and then again the slope changes abruptly to higher slope value s3 (s3»s2). The fact that throughout this plot the slope is negative indicates that the ground was in thawed condition and is moving to a frozen condition. Here it might be important to define a threshold value for defining whether or not a change in a slope is to be interpreted as an "abrupt change". For simplicity, if the slope value becomes lower than "-1", and e.g. sl=-0.1, s2=-l.l and s3=-0.09, then the change in the slope is an abrupt change. The same applies for the scenario in Fig. 7. The threshold values are preferably adjustable for each sensor. This sudden change in the slope indicates that there is a phase change in the ground where the ground is moving from a thawed phase towards a frozen phase. A very good indicator for conforming that this is actually due to a phase transformation, and not a sudden increase in the moisture content, is to monitor the time evolution of the temperature, because during a phase transformation the temperature remains constant. Accordingly, the "IF-THEN" rule for this scenario is interpreted in the following way:
IF sl»s2«s3 AND
T2<T<T1 THEN
-the phase is changing from thawed phase to frozen phase, -ground the axle weight limit is to be raisen.
Here it is important to note that if the time evolution of the conductance is similar as shown in here, but the temperature measurements is below Tl such a sudden change will not be interpreted as a phase change.
In Figure 7, the conductance 700 is increasing steadily for time interval tl wherein the average slope value for this time interval is si, then the slope changes abruptly to much larger slope value s2 (s2»sl) subsequently maintains steady, and then again the slope changes abruptly to lower slope value s3 (s3«s2). Accordingly, the "IF-THEN" rule for this scenario is interpreted in the following way:
IF sl«s2»s3 AND T2<T<T1
THEN
-the phase is changing from frozen phase to thawed phase, -ground is critical.
As mentioned above, it is important to note that such a sudden increase in the slope can be due to a sudden increase in the moisture in the ground. Therefore, if the time evolution of the conductance is similar as shown in here, but the temperature measurements is above T2 such a sudden change will not be interpreted as a phase change, but due to increase moisture content in the ground.
In Figure 8, the conductance 800 remains substantially constant the ground is either in a frozen condition or in a thawed condition, which can be determined by measuring the temperature or the moisture content in the ground. As mentioned previously, if the moisture content is "low" or below a given threshold value, the phase condition is frozen, whereas if the moisture content is above the threshold value the phase condition is thawed.
Figure 9 shows a flowchart of a method according to the present invention of indicating when to impose or cancel axle weight limit on a road based on the phase condition of the ground of the road construction.
One or more pairs of conductive elements are placed into the ground of the road construction (Sl) 901, and the conductance of the ground between the conductive elements for each respective pair is measured as a function of time (S2) 902. In an embodiment, it is preferred to initially estimating the critical temperature of the ground where the measurements take place (S3) 903 and defined a temperature interval that encloses the critical temperature. Preferably, the temperature interval is a narrow interval, e.g. between "-0.2°C"-"+0.2°C", or "-0.1°C"-"+0.1°C", but this is highly dependent on the salinity of the ground, and the type of the ground.
The time evolution of the conductance data for each respective pair is then used for determining the current or the future phase condition of the ground (S4) 904, based on e.g. said set of rules. In an embodiment, this is done by determining the slope of the conductance by implementing so-called "running average" method, where initially measuring two or more conductance data over a given time interval, wherein the conductance data are collected with a pre-fixed frequency. The average conductance value for the two or more measured conductance data is then determined. As an example, if the sequence of the measured conductance data is: 0.25; 0.32; 0.28;0.29;0.28;0.31, where the time interval between two adjacent measurements is 10 minutes, then first determined average value is 0.288. When a new conductance value is measured, i.e. every 10 minutes it replaces the first value, i.e. 0.25 is deleted and the new value comes as a first value in the sequence. As an example, if the new value is 0.33, the new sequence becomes: 0.32; 0.28; 0.29; 0.28; 0.31; 0.33 and the average value is updated. The conductance curves in Figs. 6-8 may accordingly comprise such average conductance values. Such a "filtering" process decreases the scattering in the conductance and therefore makes the calculations of the slope of the conductance more reliable. As an example, the calculations of the slope may be performed every 5 hours, where e.g. the first and the last average conductance value may be used for determining the slope.
In an embodiment, the temperature of the ground at each respective pair is measured at the conductive elements for eliminating scenarios where the conductance shows an abrupt change to enhanced moisture concentration in the ground, and not due to phase transformation. This may e.g. be done by monitoring whether the temperature is constant during the abrupt changes, since such a stable condition would indicate that there is a phase transformation.
In an embodiment, the measured conductance data are calibrated to the moisture in the ground for linking the conductance data to the moisture (S5) 905 and to the load bearing capacity of the ground for linking the conductance data to the load bearing capacity (S6) 906. This may e.g. be done by measuring the conductance and simultaneously the moisture content in the ground for each respective depth and subsequently perform a fitting through the data so that the resulting fitting function is the moisture as a function of the conductance data. Information about the moisture content in the ground is namely highly relevant for determining the maximum axle weight limit when the ground is in thawed condition.
Figure 10 show an example of how to present the result of the above graphically and in a user friendly way, where the vertical axis represents the depth of said pairs into ground, and the horizontal axis different dates (e.g. 1. feb. 2006, 1. marc. 2006 etc.). The white area may e.g. represent where the moisture concentration is below a given threshold value, and the temperature is above T2 of said temperature limit shown in Fig. 3. The vertical lines may represent a frozen phase condition, and the horizontal lines could indicate limit axle weight limit due to high moisture for T>T2, or the horizontal lines could indicate that the road construction is in a critical condition.
Figure 1 Ia-I Ic shows an example of a freeze /thaw period, measured by a single device 100 (see in Fig. 1). Figure 11a depicts the temperature of the of the ground of a road construction as a function of time, Fig. 1 Ib depicts the conductance resulting from Fig. 1 Ia as a function of time and Fig. l ie depicts the resulting graph bar indicating the different phase conditions as a function of time.
As shown in Fig. 11a, in the time interval ta the temperature is above T2 and the conductivity in Fig. 1 Ib is below a given threshold for this time interval. This is reflected in the white area 1101 in Fig. l ie showing non critical condition.
In the interval tb, the temperature curve in Fig. 11a lies is within Tl ant T2. The sudden change in the slope of the conductivity curve in Fig. 1 Ib towards a lower value indicates a phase change occurring from thawed phase to frozen phase. This beginning of the phase change is thus the beginning of the frozen phase condition, indicated by the beginning of the vertical bar graph 1102 in Fig. l ie. From that moment the bar graph shows frozen phase, vertical lines throughout the interval tc. In this temperature interval (i.e. tc) the temperature curve in Fig. 1 Ia is below Tl.
The next phase change takes place in the interval td, where the temperature curve in Fig. 11a lies within Tl and T2. For this time interval, the phase change in Fig. 1 Ib changes abruptly towards a lower slope value and a phase change (ps) occurs from frozen phase to thawed phase. From that moment the bar graph 1103 in Fig. l ie from interval td shows critical condition, where the horizontal lines throughout the interval te indicate high moisturized not frozen state of the ground. In the interval tf the bar graph in Fig. l ie shows a non critical condition as the conductivity in Fig. l ib has dropped down under a given threshold value and the temperature in above T2.
The temperatures Tl and T2 may be detected automatically. In one embodiment, this is done by detecting the face change based on the conductivity measurement (Fig. 1 Ib). By detecting a phase change through the abrupt change in the conductance as previously discussed the phase change (pc) temperature Tc is registered in the moment where the phase change takes place. A deltaTl and deltaT2 are selected such that on one hand the Tcis added and on the other hand subtracted such that T2=Tc+|deltaT2| and Tl=Tc-|deltaTl|. The advantage of doing so it that if e.g. T2=1.0°C and T I=- LO0C but later results show that the phase change occurs at Tc=-0.8°C, the temperature Tl and T2 will be automatically corrected. This may either be done via a computer program when it is run on a computer or via a pre-programmed processor. As an example, T I=- 1.O0C and T2=+1.0°C, and the phase change occurs at Tc=-0.8°C. The deltaTl and deltaT2 are selected as 1.O0C. Thus, the automatic correction Tl ' and T2' in Tl and T2 will result in that T2'=-0.8°C+1.0°C=+0.2°C and Tl '=-0.8°C-1.0°C= -1.80C. A user of the device may self decide the values of deltaTl and deltaT2. Thus, the new temperature window becomes Tl '< Tc<T2'.
Certain specific details of the disclosed embodiment are set forth for purposes of explanation rather than limitation, so as to provide a clear and thorough understanding of the present invention. However, it should be understood by those skilled in this art, that the present invention might be practiced in other embodiments that do not conform exactly to the details set forth herein, without departing significantly from the spirit and scope of this disclosure. Further, in this context, and for the purposes of brevity and clarity, detailed descriptions of well- known apparatuses, circuits and methodologies have been omitted so as to avoid unnecessary detail and possible confusion.
Reference signs are included in the claims, however the inclusion of the reference signs is only for clarity reasons and should not be construed as limiting the scope of the claims.

Claims

1. A method of indicating when to impose or cancel axle weight limit on a road (130) based on the phase condition of the ground of the road construction (110), comprising:
• placing (901) one or more pairs (103-107) of conductive elements (101-102) into the ground of the road construction,
• measuring (902) the conductance of the ground between the conductive elements (101-102) for each respective pair over a time, • utilizing the time evolution of the conductance data for each respective pair of conductive elements as input data for determining (904) the current or the future phase condition of the ground.
2. A method according to claim 1, further comprising measuring the temperature of the ground at each respective pair of the conductive elements and using the measured temperature values in conjunction with the measured conductance values over time for determining the current or the future phase condition of the ground.
3. A method according to claim 1 or 2, wherein the step of utilizing the time evolution of the conductance data for each respective pair of conductive elements comprises determining the slope of the conductance.
4. A method according to claim 3, wherein the step of determining the slope of the conductance comprises initially performing a filtering step by means of: a) initially measuring two or more conductance data over a given time interval, wherein the conductance data are collected with a pre-fixed frequency, b) determining the average conductance value for the two or more measured conductance data, c) updating the average conductance value at the pre-fixed frequency when a new conductance data is measured, wherein the updating is based on replacing the new conductance data with the earliest measured conductance data and subsequently repeating step b), d) and subsequently determining the slope between two average conductance values over a pre-fixed time interval.
5. A method according to claim 4, wherein determining the average conductance value for the two or more measured conductance data is adapted to how rapid the phase changes in the ground are.
6. A method according to any of the preceding claims, further comprising approximating (903) the critical temperature of the ground and based thereon defining a temperature interval deltaT=T2-Tl enclosing the approximated critical temperature.
7. A method according to claim 5 or 6, wherein the temperature values Tl and T2 where T2>T1 enclosing the approximated critical temperature are automatically improved by means of:
• utilizing the conductance data for estimating the critical temperature Tc, the estimate being based on monitoring where an abrupt change occurs in the conductance, the temperature at the instant of the abrupt change being used as the estimating for the critical temperature Tc,
• defining a deltaTl value and deltaT2 values, and
• calculating improved values Tl ' and T2' to replacing the Tl and T2 values via the equations: Tl '=Tc-|deltaTl | and T2'=|Tc+deltaT2|.
8. A method according to any of the preceding claims, wherein indicating when to impose or cancel axle weight limit on a road is based on set of rules including: if the temperature of the ground is within the temperature interval and the time evolution of the conductance data shows a negative slope of the conductance over a first time interval, then a sudden decrease in the slope over a second time interval, then a sudden increase in the slope over a third time interval, the phase condition of the ground is moving from a thawed condition to a frozen condition and thereby the axle weight limit of the road construction is to be raised.
9. A method according to any of the preceding claims, wherein indicating when to impose or cancel axle weight limit on a road is based on set of rules including: if the temperature of the ground is within the temperature interval and the time evolution of the conductance data shows a positive slope of the conductance over a first time interval, then a sudden increase in the slope over a second time interval, then a sudden decrease in the slope over a third time interval, the phase condition of the ground is moving from a frozen condition to a thawed condition and thereby the axle weight limit of the road construction must be lowered to prevent damage.
10. A method according to any of the preceding claims, further comprising calibrating the measured conductance data to the moisture content in the ground (905) and the load bearing capacity of the ground (906) when the ground is in thawed phase for indicating when to impose axle weight limit of the road construction in thawed phase.
11. A method according to any of the preceding claims, further comprising calibrating the measured conductance data to the moisture content and the temperature in the ground (905) and the load bearing capacity of the ground (906) when the ground is in thawed phase for indicating when to impose axle weight limit of the road construction in thawed phase.
12. A method according to any of the preceding claims, further comprising monitoring the time evolution of the temperature for predicting about the future phase condition and therefore the future condition of the road construction.
13. A method according to claim 1, further comprising adding an intermediate layer between the conductive elements (101-102) and the ground of the road construction (110) having smaller grain size than the ground of the road construction (110).
14. A computer program product for instructing a processing unit to execute the method steps as claimed in any of the claims 1-12 when the product is run on a computer.
15. A device (100) for indicating when to impose or cancel axle weight limit on a road (130) based on the phase condition of the ground of the road construction (110), comprising:
• an elongated body (108) adapted to be placed into the ground of the road constructions (110), and
• a measuring unit (111) connected to one or more pairs of conductive elements (101-102) situated along the longitudinal axis of the body for measuring the conductance of the ground between the conductive elements for each respective pair over a time, wherein the time evolution of the conductance data (203, 204) is utilized as input data for determining the current or the future phase condition of the ground.
16. A device according to claim 15, further comprising temperature sensors (113) for measuring the temperature of the ground at each respective pair (103-107) of the conductive elements (101-102).
17. A device according to claim 15 or 16, further comprising a processor (115) for determining the phase condition of the ground and for determining the current or the future phase condition of the ground of the road construction (110).
18. A device according to any of the claims 15 - 17, further comprising a transmitter (112) for transmitting data indicating the current or future phase condition of the ground, or the conductance values over time along with the temperature values to an external processing unit via a communication channel.
19. A device according to any of the claims 15 - 18, wherein the one or more pairs of conductive elements (101-102) comprises parallel arranged plates or cylinders isolated from each other integrated into the elongated body such that the plates are exposed at the periphery of the outer surface of the elongated body (108).
20. A system (120) for indicating when to impose or cancel axle weight limit on a road (130) based on the phase condition of the ground of the road construction (110) , comprising:
• an elongated body (108) adapted to be placed into the ground of the road constructions, and
• a measuring unit (111) connected to one or more pairs of conductive elements situated along the longitudinal axis of the body for measuring the conductance of the ground between the conductive elements for each respective pair over a time,
• a processor (115) for utilizing the time evolution of the conductance data for each respective pair of conductive elements as input data for determining the current or the future phase condition of the ground,
• an external s erver (121),
• a transmitter (112) for transmitting either the measured conductance data and the temperature data, or the data indicating the phase condition of the ground to the external server,
• a receiver (123) for receiving the transmitted data, and
• an alert unit (124) for alerting about the current or the future phase road construction.
EP07821433A 2006-10-17 2007-10-17 Method and device for indicating when to impose axle weight limit on roads Withdrawn EP2084522A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IS8554 2006-10-17
PCT/EP2007/061068 WO2008046846A1 (en) 2006-10-17 2007-10-17 Method and device for indicating when to impose axle weight limit on roads

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EP2084522A1 true EP2084522A1 (en) 2009-08-05

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US6401742B1 (en) * 1999-11-08 2002-06-11 Dean L. Cramer Moisture sensor and irrigation control system
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DE10052892A1 (en) * 2000-10-25 2002-05-08 Christian Edlhuber Device and method for determining a snow profile, and system herewith for determining the avalanche probability
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