Testing of Falling Weight Deflectometer Device Designed for Evaluating the Soundness of Pavements
- Contributing to proper pavement maintenance through FWD testing
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The combined length of roads in Japan has reached approximately one million kilometers, and in order to adequately manage the roads within a limited budget, it is very important to appropriately evaluate pavement soundness and implement maintenance and repair based on evaluation results.
Pavement cross sections are studied by digging or other ways to evaluate pavement soundness, but such methods involve the destruction of pavement and are also costly and time consuming. In recent years, many field investigations have been conducted using a vehicle (Figure 1) equipped with a Falling Weight Deflectometer (FWD) designed for conducting non-destructive testing.
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The FWD is a device (Figure 2) consisting of weights and multiple deflection sensors that is capable of evaluating pavement soundness based on the measured values obtained by measuring the deflection of the pavement surface generated when a weight is dropped on it. Investigation results data from FWDs is used to select appropriate maintenance and repair methods in accordance with the pavement state.
In Japan, as of 2020 a total of about 50 FWDs are currently in operation. If FWDs are not properly maintained, it may not be possible to obtain accurate measurement values as measured values will vary between vehicles. Since FWD investigation results data is used as the basis for selecting pavement maintenance and repair methods etc., it is necessary to ensure that there is no difference in measurement results from vehicle to vehicle.
PWRI established an FWD testing facility (Figure 3) to perform calibration and testing of FWDs and has been conducting FWD testing at the request of FWD owners since 2010. In the testing, values measured with an FWD (including impact loads and deflections measured at the sensors) are compared with those measured by the reference measuring devices in the test facility to confirm the accuracy of the measurements obtained from the FWD. PWRI issues certificates (Figure 3) to vehicles that pass the testing to certify that a vehicle is capable of performing accurate measurements.
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(Contact: Pavement Research Team)
Development of a Risk Communication Tool to Raise Public Awareness of Flood Risk
1. Development of a Virtual-Reality Flood Simulation Tool
In recent years, various types of information have been provided in advance to reduce flood disaster damage. However, it has not necessarily been utilized effectively, thus not leading to appropriate evacuation actions and consequently resulting in considerable human damage. One reason for this to keep happening is the lack of public awareness that flood disasters can happen to anyone. To address this issue, ICHARM has been developing a virtual-reality (VR) flood simulation tool as part of its research project aiming at helping each individual become able to make proper decisions and take proper actions in time of flooding. This tool is intended to raise public awareness of floods by providing a simulated flood experience to all people who have never experienced a flood disaster.
The simulation scenario consists of the following scenes (Figure 1): (1) The simulation starts from a daily life situation in which the user is in the living room on the 1st floor of a house; (2) A river near the house overflows, and the water flows over the road in front of the house; (3) The water level increases further, and the water comes into the house; and (4) The water reaches the ceiling in the 2nd floor. With a VR headset on, the user can experience a simulated flood virtually, freely viewing in all directions - front, back, left, right, up and down. You can watch an introductory video at the following URL:
(http://www.icharm.pwri.go.jp/activities/movie_collection/index_j.html)
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2. Verification of Effectiveness of the VR Flood Simulation Tool
On April 19, 2019, an open house was held by the National Institute for Land and Infrastructure Management (NILIM) and the Public Works Research Institute (PWRI). In this event, we conducted a flood simulation workshop using the VR tool. A total of 111 visitors tried out the new technology and answered a ten-question questionnaire designed to see whether a virtual flood experience helps people increase their awareness towards floods. Of the respondents, people in their 40s accounted for the largest portion, about 26%, followed by people in their 30s making up about 17%. The following is an overview of the results of the questionnaire survey.
When asked whether they were scared in the virtual-reality flood simulation, about 90 percent surveyed answered yes (Figure 2).
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Before experiencing the flood simulation, the visitors were asked whether they worried about floods in the rainy or typhoon season each year. After the simulation, they were asked if they worried about floods in the coming rainy or typhoon season. The comparison of the replies shows that the number of people worrying about floods almost doubled after experiencing the flood simulation (Figure 3).
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In addition, a cross-tabulation was performed between the level of concern about floods after experiencing the flood simulation and the replies to the question about whether or not they will check a flood hazard map when they get home. The result shows that the higher the level of concern, the higher the percentage of respondents who answered that they would check a hazard map (Figure 4).
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In summary, these findings lead us to speculate that the simulated flood experience with the VR tool has improved the participants' interest in and awareness of floods. ICHARM continues to study and test approaches for effective and efficient risk communication to convince people that flood disaster risk reduction is their own affair, thereby contributing to the prevention and mitigation of flood disaster damage in the future.
(Contact: Water-related Hazard Research Group)
Development of Techniques for Supporting Deicing Agent Application
The road surface in cold, snowy regions sometimes becomes slippery in winter because moisture on the surface freezes or snow is packed down. The road administrator controls the road surface by using snow plows and chemical spreading vehicles. In recent years, however, operators of this equipment have decreased in number due to depopulation, and skilled operators have also decreased or have been aging. Under resource-constrained circumstances due to the tight fiscal situation of the national government, road management is required to be implemented more efficiently than before.
In view of this, the Civil Engineering Research Institute for Cold Region (CERI) has been developing techniques for spreading deicing agent by a single operator, even when that operator is less experienced. Currently, deicing agent is spread by a team of one driver and one operator.
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Specifically, CERI has developed a system for supporting the application of deicing agent and has been conducting experiments to verify the effectiveness and safety of application operation under the system. In this system, a control interface is set in front of the driver´s seat. The interface has 1) functions for providing information on what road sections should receive deicing agent and how much they should receive, in order to support decision-making regarding deicing agent application, and 2) functions for supporting application which is controlled manually, automatically, or by voice commands (Photo 1.)
Operators have used the control interface in tests conducted to understand the effectiveness and issues regarding the provision of information. It was found that because of the information provided, the operators were able to discern the road surface condition more quickly than before and were better able to determine whether the surface was frozen or wet. However, because the information was provided on a screen, the percentage of operation hours that operators gazed at the road and at their surroundings decreased significantly, which
was understood as a potential safety problem (Figure 1.)
The accuracy of application was verified with versus without application support and by using different support types. When no application support was provided, the distance between the actual application point and the specified point of application varied most widely. The distance between these two points varied less widely when application support was provided (Figure 2).
These test results indicate that the support system helps to save labor and to optimize application operation.
In the future, the system for supporting the application of deicing agent will be further improved and tests by operators will be conducted for the purpose of enhancing the accuracy of application.
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(Contact: Traffic Engineering Research Team, Civil Engineering Research Institute for Cold Region, CERI)
Research on the Control of Subsidence in Large-scale Farming Fields on Peatland
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1. Subsidence of agricultural peatland
Peat is composed of dead plant material that has accumulated over time, and it is distributed around rivers and lakes in cold regions. Because peat has a high void content, an increase in the load exerted on peat leads to the compaction of these voids and thus to decreases in the volume of the peat. The shrinkage of peat due to drying and the loss of organic matter due to decomposition also result in reductions in peat volume. It is well known that on peatland used for farming, field drainage results in ground subsidence. Immediately after field drainage, the groundwater level in the field drops, so the buoyancy that had acted on the soil layer also decreases. Consequently, the load on the peat under the groundwater surface increases, and the volume of peat is reduced. Over an extended period of time, peat above the groundwater level dries out, decomposes and is lost, which leads to a reduction in the volume of peat and the subsidence of the field. Ground subsidence is greater for crop fields than for paddy fields, even in the case of adjacent fields (Figure 1.) This difference in the ground subsidence is caused by the fact that while a high water level is maintained in a paddy field during the farming period, the water level in a crop field is lowered by drainage.
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2. Differential subsidence in large-scale fields, and mitigation measures
The small-scale fields have been combined into large-scale field in agricultural peatland in Hokkaido for labor savings and enhanced efficiency. Peaty farmland undergoes uneven subsidence, which causes surface unevenness. This phenomenon is called differential subsidence. It is known that large-scale fields tend to be subject to significantly differential subsidence. When the field surface is uneven, the ponding depth is uneven in paddy fields, and the wetness/dryness is not uniform on the surface of crop fields; thus, rice and crops do not grow uniformly. The Rural Resources Conservation Research Team has been conducting research with the aim of elucidating the state and controlling factors of subsidence in large-scale field on peatland as well as proposing measures for mitigating ground subsidence and differential subsidence. Differential subsidence took place in a field where observations have been conducted (Figure 2.) That differential subsidence is likely to have been associated with the irregular distribution of groundwater levels, which varied depending on the slope of the underdrainage and with the non-uniformity of the peat properties in the field. A paddy field and a crop field are sometimes combined into create a large-scale field. Because the land-use history and the way the large-scale field was developed might relate to the special variation of peat properties, research is being conducted to clarify the causal relationship between these factors and differential subsidence.
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As an important measure for mitigating ground subsidence in an entire field as well as for mitigating differential subsidence, the groundwater level in the field should not be lowered excessively. A groundwater level control system is to be installed into large-scale paddy field in farmland consolidation. It is expected that ground subsidence can be mitigated by controlling the groundwater level with this system (Figure 3.) Our team has also been working on verifying the mitigation of ground subsidence through the control of the groundwater level.
(Contact:Rural Resources Conservation Research Team, CERI)