Japan’s Nation-Wide Electronic Geotechnical Database Systems by Japanese Geotechnical Society
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- Todo, H., Yamamoto, K., Mimura, M. et al. Geotech Geol Eng (2013) 31: 941. doi:10.1007/s10706-012-9562-x
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On October 15, 2010, the Japanese Geotechnical Society (JGS) announced the public release of ‘Nation-wide Electronic Geotechnical Database Systems,’ which provides geotechnical information to the public on the internet. The information the system provides is a collection of ground models at 250 m by 250 m in plan built by using data from various geotechnical information databases. The paper first describes historical development of the geotechnical information databases in Japan, and introduces a 5-year project, ‘Integrated Geophysical and Geological Information Database in Japan,’ led by the National Research Institute for Earth Science and Disaster Prevention (NIED), and participated by the JGS. The paper then presents the JGS’ ‘Nation-wide Electronic Geotechnical Database Systems,’ and describes why such system was proposed and built, followed by the presentation of the examples for possible application of the system.
KeywordsGeotechnical databaseGround modelDatabase linkageInformation communicationUrban geo-informaticsHazard map
The National Institute of Advanced Industrial Science and Technology
The Asian Regional Technical Committee No. 10 for ‘Urban Geo-Informatics’
The Integrated Geophysical and Geological Information Database
The Japanese Geotechnical Society
The Ministry of Education, Culture, Sports, Science and Technology, Japan
The Ministry of Land, Infrastructure, Transport and Tourism, Japan
The Nation-wide Electronic Geotechnical Database Systems
The National Research Institute for Earth Science and Disaster Prevention
Potential of liquefaction
The Public Works Research Institute
The Special Coordination Funds for Promoting Science and Technology
The standard penetration test
The construction of geotechnical information databases in Japan in organized effort started in the 1960s in large cities like Osaka, Tokyo, and Nagoya, which developed on coastal plains underlain by thick Holocene deposits where outcrops are hardly seen. The impetus for building the database was the desire to better understand the stratigraphy and distribution of the post-glacial deposits under rapidly developing metropolises. The first step of the database construction was to collect existing borehole logs and laboratory soil test results then available in print.
The geotechnical information databases typically contain borehole logs, SPT N-values, water levels, borehole location data, and laboratory test data. Some prominent databases also include in situ test data, geophysical investigation data, and surface information such as geological maps. Government organizations normally supply the data sometime after the completion of projects for which geotechnical investigations were performed. A geotechnical investigation is rarely performed for the purpose of database construction in the engineering field.
The geotechnical information databases have rapidly evolved from the paper-based databases to digital databases with the development of the digital and storage technologies from the 1970s. The delivery of the data has changed from paper to floppy disks to CDs to the internet.
Subsurface data accumulated are valuable public intellectual properties.
We should hand over the data to the next generation.
Various departments and organizations should share the information.
The geotechnical data are 4-dimensional property, which vary with time.
While ATC10 was campaigning for the importance of and new vision about the geotechnical information databases, the National Research Institute for Earth Science and Disaster Prevention proposed a 5-year project, the Integrated Geophysical and Geological Information Database (IGGID), and JGS joined the project by setting up a new work team. The team’s mission was to link the existing, independently operating geotechnical information databases to IGGID.
The team came up with the idea of building ground models across the country. Each model represents the ground of 250 m by 250 m in plan and to depths up to 100 m, generally 30–50 m from the ground surface depending on its location. They are built in consideration of types of soil materials and their properties such as strength, deformability, permeability, groundwater, and SPT N-values. The ground models are geometrically simpler and more geotechnical than geological models, which present succession of strata, geological ages, and their distributions. The team also developed the systems to build the models and to publish on the internet. After 5-year effort from 2006 to 2010, JGS published the ground models for 6 cities in Japan on October 15, 2010 on the internet. The ground models for additional 3 cities were published by July, 2012. By 2014 the ground models would cover 18 cities. The systems are useful in various aspects from construction planning to research as described later. The systems could also be the bases for geo-hazard analyses and hazard mapping.
2 Historical Development of Geotechnical Information Databases in Japan
2.1 Jiban-zu (Borehole Data Book)
Early geotechnical databases in Japan started around 1960 covering coastal and urban areas in large metropolises like Tokyo, Osaka, and Nagoya. They are a sort of borehole data books, called Jiban-zu in Japanese, ‘graphics of ground’ literally in English, and are basically compilations of borehole data, soil cross sections, laboratory soil test results, in situ test results, geophysical exploration results, and description of local geology and topography.
“Borehole Data Book of Osaka Area (Kinki Chapter of Japanese Architectural Institute and Kansai Chapter of Japanese Geotechnical Society 1966)” is one of the earliest of this kind covering the megalopolis areas of Japan. More data books followed later to extend the coverage to provincial cities as well. To date the published borehole data books in Japan cover 34 out of 47 prefectures including Tokyo Metropolitan area. Their major editors often include (a) then Regional Bureaus of the Ministry of Construction, (b) prefecture and municipal governments, (c) JGS, (d) the Architectural Institute of Japan, (e) the Japan Institute of Architects, and (f) the Japan geotechnical consultant association. The latest editions of the borehole data books are “New Borehole Data Book of Tokyo Port (Bureau of Port and Harbor, Tokyo Metropolitan Government 2001)” compiling 5,800 borehole results and “Ground and Construction in Bay Area—Osaka Bay Area as an Example (Research Committee on Ground in Osaka Bay 2002)”, which is the advanced edition of “New Borehole Data Book of Osaka Area (Kansai chapter of the Japanese Geotechnical Society 1993).”
These editions reflect updated information published on the geology and geotechnical engineering as much as possible. The application of the Jiban-zu in Japan increases, and will further increase, to the areas of the environmental impact assessment, such as the evaluation of soil and groundwater contamination. This is especially true after the approval of the Soil Contamination Countermeasures Act (53 of 2002) in May 2002 and its enforcement in February 2003.
Contents of the borehole data books are not standardized and are often different from each other depending on the purposes of publication. Some data book places emphasis on geological conditions, some on the geotechnical characteristics of the ground and some on the data of earthquakes from a viewpoint of disaster mitigation.
Although poor quality data are screened out to some extent in the process of editing, the quality of the data presented may not always be of high standard.
The information presented in the data book might be out-dated. Users need to interpret the data with the latest knowledge.
2.2 Regional Digital Geotechnical Information Databases
The advance of the digital technology such as computer hardware, software, and large storage capacity stimulated the construction of the regional digital geotechnical databases as early as 1980s in the Kansai region, which is one of nine administrative regions consisting of several prefectures. A chamber was formed for the database development with cooperation of government organizations, local municipalities, universities, and geotechnical consultants. For example, the members of the chamber includes the Kansai chapter of JGS, the Kansai Regional Bureau of Ministry of Construction, the Third District Port Construction Bureau of Ministry of Transport, Osaka Prefecture, Kyoto Prefecture, Hyogo Prefecture, Osaka City, Kyoto City, Kobe City, Sakai City, Nishinomiya City, the Kansai Branch of Japan Highway Public Corporation, Hanshin Expressway Public Corporation, the Osaka Branch of Japan Railway Construction Public Corporation, the West Japan Branch of Japan Public Housing Corporation, Osaka Bay Regional Offshore Environmental Improvement Center, Kansai International Airport, Kansai Electric Power Company, Osaka Gas, West Japan Railway Company, NTT (Telecom), Geo-Research Institute, the Osaka Branch of General Contractor’s Association, the Kinki Branch of Japan Civil Engineering Consultants Association, the Kansai Branch of Japan Geotechnical Consultants Association, and universities.
Regional geotechnical information databases in Japan (as of March 2012, see Fig. 1 for the locations)
Version 1996, CD, with fee,11,000 boreholes
Version 2003, CD, with fee, with GIS, 13,000 boreholes
2010, distributed to members on the Internet, with fee, 13,400 boreholes
2008, distributed to members on the Internet, with fee, 28,000 boreholes
2010, published as a book including DVD, with fee, 40,000 boreholes
1987, CD to members only, with fee, updated yearly, 40,000 boreholes
2005, CD to members only, with fee, updated irregularly, 20,000 boreholes
2005, CD, with fee, 30,000 boreholes
2.3 Databases by Private Companies and Public Corporations
Private companies and public corporation such as electric power companies, gas utility companies, railway companies, highway companies, geotechnical consulting companies, and soil investigation companies, seem to have their own geotechnical databases for their internal use. However, those data are not disclosed to the public so far. This paper excludes discussion on these databases.
2.4 Municipalities’ Databases
With the Act on Access to Information Held by Administrative Organs (Act No. 42 of 1999) enacted in 1999 and in force in 2001, the central government, prefectures and municipalities started publishing the data they had. However, such move is limited to those having certain amount of budget and personnel. Most of prefectures and municipalities cannot afford providing such services.
There are 1,886 municipalities in Japan including prefectures, cities, towns, and villages. They have two types of geotechnical data: one came from public works such as the construction of roads, sewers, and schools, financed by municipality; the other was the data submitted for building permit by applicants. With the Act on Access to Information Held by Administrative Organs in force in 2001, several prefecture governments and municipalities started releasing their data through the web sites. While the data obtained for the public works are published, the data submitted to the building permits are not disclosed because they are considered private data, not the data owned by the municipalities. Although the disclosure of the geotechnical data by the municipalities are welcome, uncoordinated and unsynchronized publication of the data by each administration with varying format, quality, and reliability are challenging for users, especially for non-professionals.
2.5 Kuni-Jiban by Ministry of Land, Infrastructure, Transport and Tourism
3 Integrated Geophysical and Geological Information Database in Japan
In July 2006 a 5-year, nationwide, inter-agency project, the Integrated Geophysical and Geological Information Database (IGGID), started, led by the National Research Institute for Earth Science and Disaster Prevention (NIED), with the participation of the National Institute of Advanced Industrial Science and Technology (AIST), the Public Works Research Institute (PWRI), Tokyo University, Tokyo Institute of Technology, and JGS. The project was financed by the Special Coordination Funds for Promoting Science and Technology (SCFPST) under the Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT).
Theme 2 is the development of the systems to integrate and coordinates various databases through the internet. JGS took part in Theme 2 to develop the systems to link the existing geotechnical databases that JGS’ local chapters participated in the construction and maintenance. In addition, Theme 2 is to invite prefectures and municipalities to join by connecting their databases to IGGID. The concept of the integration and management is called ‘shared management system,’ which is described below. Theme 3 is to study how to use the database for the earthquake prediction and publicizing potential disaster to local residents.
Integration of various data across the country
Integration of various types of data from the original data (such as borehole logs) to various models (such as geological models and ground models)
Integration of databases from multiple organizations
Integration of data from shallow (less than 100 m) to deep (several kilometres) ground
Integration of qualitative information (such as geological description) to quantitative information (such as property values)
Integration of all the above data via the internet
While users can view the data of any organization at its web site, they can view the data from NIED’s portal site, called Geo-Station, which shows all the data points (locations) on a computer screen from all participating organizations. The borehole points from NIED, AIST, and PWRI complement each other. For example, most of the data of NIED come from prefectures and municipalities, the data of AIST come from other prefectures and municipalities, and the data of PWRI (along roads and rivers as described in Sect. 2.5) originate from the MLIT. Those data are standardized so that the data from various organizations can be viewed, searched, and published in the net work systems. The concept of NIED’s portal site is illustrated in Fig. 7 and more information can be found at the Geo-Station web site (Geo-Station by the National Research Institute for Earth Science and Disaster Prevention 2009).
4 Nation-Wide Electronic Geotechnical Database Systems
4.1 JGS’ Mission in Integrated Geophysical and Geological Information Database
JGS’ mission in the integrated geophysical and geological databases was to link the existing geotechnical databases that the Society’s local chapters were involved for their construction, maintenance, and administration. For this purpose, JGS set up a work team for ‘Shallow Ground Data Base Linkage.’
The work team does not have authority over other independent database operators and could not force them to link their databases to a new system the work team was going to develop. Under these circumstances, the work team invited representatives from the JGS’ 9 local chapters to join in, because the local chapters are deeply involved in the administration of the regional geotechnical information databases as described earlier. The work team also had seats for the representatives from NIED, AIST, and PWRI.
The systems the work team was going to build should be such that the independently operated other databases would willingly join. After a year of discussion, the work team proposed to build NEGDS, which is essentially a collection of ground models with each size of 250 m by 250 m in plan to a maximum depth of 100 m. The systems can electronically construct, save, modify, and display the models. The information contained there can be viewed and downloaded from the internet.
It is difficult to simply connect the existing borehole databases through the internet, because the existing databases are very much different in their construction, systems, data structures, data contents, and data quality. It is also very difficult to use such data coming from variety of databases with different contents and systems. It is important for a user that interpretation and quality of the data are unified at a certain standard, and the nation-wide database linkage should be user-friendly.
The research results funded by the Special Coordination Funds for Promoting Science and Technology (SCFPST) have to be open to the public. This condition makes many operators of the databases difficult to participate to the systems if the systems were to simply link the existing databases, because all the data linked to the systems have to be disclosed. Such disclosure is not acceptable for those who had supplied data with prior confidential agreement not to disclose the data due to ownership of the data, copy rights, and information on private properties. Some of the databases contained the data that were supplied with the conditions that data can be used for research only, and cannot be released to the public. These databases cannot join the systems that simply link various databases.
In order to overcome the above obstructions to use raw data such as individual borehole data, the work team decided to make ground models by interpreting all the available raw data. By making the ground models, the problems of the ownership and copy rights can be skipped. At the same time, the systems can provide quality information on the ground conditions by using only reliable data based on good knowledge of local geology. Such model will be much user-friendly to the public than just providing raw data from various existing databases.
4.2 Coverage of NEGDS in Japan
Since its publication, NEGDS has often been cited in mass media as a tool for the public to check the ground conditions under their own houses and to be aware of potential natural disasters related to the ground, especially after the Great East Japan Earthquake Disaster on March 11, 2011. However, the coverage areas are still few, and the data contents at present are limited to soil types and SPT N-values only. Interpretation of the data requires judgement by professionals, and the public is advised to consult with the professionals.
4.3 The Systems
4.3.1 Overview of the Systems
4.3.2 Information Contained in NEGDS
The system is intended to contain any type and any amount of data, such as borehole logs, laboratory test results, in situ test results, soil-cross sections, primary and secondary wave velocity logging (PS) data, geological description, changes in groundwater level with time, groundwater quality, ground settlement with time, and others. At present, the system contains borehole logs only.
4.3.3 Construction of NEGDS
A standard 250 m grid map published by Geographic Survey Institute of Japan is used.
The location for the model to be constructed is selected.
Ground model is constructed using borehole data available nearby in consideration of topography and geology. For making the ground model, the systems developed by the work team are used to assist construction of a ground model from the existing digital databases.
The construction of the ground models requires setting up local teams of specialists who have good knowledge of local ground conditions. The team consists of geotechnical engineers, geologists, and specialists for topography and land formation from geotechnical consulting companies, universities, geotechnical investigation companies, for example. As of March 2012, there are 18 local specialist teams at 18 cities shown in Fig. 9.
The models can be modified anytime by the local teams if and when additional boreholes become available. The users can download the information contained in the model, but cannot modify the published models.
4.3.4 Tests Against Various Ground Conditions and Improvements of Systems
Ground conditions for trail construction of NEGDS
Typical large alluvial plain
Reclaimed ground, steeply sloped ground
Peat, volcanic ash
Fan, sloped ground
Valley tributary etching terrace
Natural and artificial sand ground
NEGDS has to include all types of soils distributed in Japan. During the trials, additional soil types were included in the systems. However, the present systems are incapable of representing all the soil types in Japan, for example, the volcanic ash. The pyroclastic flow deposits distributed near Sapporo, Hokkaido, and near Kagoshima, Kyushu, have a few distinct appearances such as original pyroclastic flow deposits, deposits of falling ash, and redeposition of those deposits after erosion, each having totally different geotechnical properties. The representation of these different types of materials needs to be developed in NEGDS.
The work team’s initial intention to define the surface deposits by only geological history such as Holocene deposits did not work well, because foundation bearing layers that are often older than the Holocene are excluded. Also, there are places of thin Holocene deposits underlain by soft Pleistocene deposits or places of loose ground even in Pleistocene deposits. Instead of setting a uniform rule for a boundary, the work team decided to fix the target zone depending on local engineering practice such as foundation depth and bearing layers of piles. For example, SPT N-value of 30 within Holocene sand deposits is used to define the bottom boundary of the models in Niigata, while SPT N-value of 50 either in Holocene or Pleistocene deposits is used in Tokyo.
4.3.5 Viewer for Assembled Models
The work team developed viewers (Sub-systems 2 and 4 in Fig. 10) in order to view the ground conditions after a number of the ground models of 250 m by 250 in plan have been digitally accumulated. The viewer has the following functions:
Description of geological and topographical background
The viewer has an explanatory section describing local geological conditions and sedimentation environment, especially Pleistocene to Holocene period together with micro-topographic conditions. It is important for the users to have knowledge of the local geology and topography before viewing the ground models.
Function to pinpoint a location on a map on computer screen
Function to draw a soil cross section
Where the user wants to view a soil cross section, the user can draw a line on a map displayed on a computer screen (shown as line A-B in Fig. 15), and a separate window appears with a soil cross section along the line as shown in Fig. 15.
Function to display depths to foundation bearing layers
Function to show soil types at different depths
4.3.6 Internet Connection
Once connected to JGS’ server through the internet, a user is guided to select a city and can look at the figures like those presented above by manoeuvring buttons on the screen. The web site is accessible from all countries, but only displayed in Japanese for the time being. There is a message box for users to submit comments to the work team, who is currently operating NEGDS. This is Subsystem 3 in Fig. 10.
4.3.7 Archiving Non-digital Data
There are a lot of old geotechnical databases in Japan published as borehole data books containing borehole logs, soil cross sections, laboratory data, in situ test data, and other geophysical investigation data as described in Sect. 2.1. With passing time after their publication, they were forgotten, lost, abandoned, or buried under piled documents. Before they are completely gone, the work team attempted to archive those data. The intention of providing the archiving function in NEGDS is to collect and save those old, non-digital data, which are difficult to digitise and incorporate into NEGDS at present. If they are collected and archived, these data could one day in future be incorporated into NEGDS. Subsystem 5 in Fig. 10 represents this function.
The final form of the archives is collection of PDF files produced by scanning old borehole data books, and other information on the ground conditions such as geotechnical literature and construction records. As the first step, the work team conducted the survey for the old borehole data books with the following information: title, ownership/publisher, area coverage, number of boreholes, and permission for archiving. The survey data will be, as the next step, published on the internet.
5 Merits and Application of NEGDS
There are merits and possible application of NEGDS in the geotechnical engineering as follows.
Merits for researchers on geotechnical properties of soils
The systems can provide geotechnical information on urban areas, which is important subject for the researchers of geotechnical engineering. A new research area on soil properties may grow because the systems, covering the entire Japan, make it possible to compare properties of similar soil types with similar depositional environment, the same depositional age, but in different localities. Conventionally, most of researches on soil properties have concentrated on soils in particular areas familiar to them. It is expected that such comparative studies of soil properties provide more in-depth understanding of properties of local soil deposits.
Merits for practicing geotechnical engineers
Using the systems, practicing geotechnical engineers in Japan can understand potential problems and risks for proposed structures anywhere when they plan geotechnical investigations, because the system can provide the ground conditions at any part of in Japan. They can also obtain literatures or case records of similar problematic ground conditions in other areas.
Merits for the public
Based on the soil information obtained from the systems, the public can easily get advices on potential troubles related to the ground from professionals when they plan to buy land or houses. Liquefaction, ground subsidence, and slope movements are examples for the potential troubles. The NEGDS model information may have certain influence to the public. Misinterpretation of the models may lead to improper perspective on the ground conditions and false awareness of potential geotechnical problems and geo-hazards.
It is advisable for the public to consult with the professionals for interpretation of the models, because judgement for potential troubles needs a little technical knowledge and geotechnical practice. When a 250 m grid cell is selected on the map shown on a computer screen, a ground model comes out in a separate window with soil types (sand or clay) and SPT N-values at every 1 or 2 m depth to the bottom of the model, as shown in Fig. 15. With such information, geotechnical professionals are able to tell potentials for liquefaction, ground subsidence, and other geo-hazards that the public is normally concerned with. Since more information is attached to the model, such as ground water levels and various test results, the professionals can analyze potential problems in detail if judged necessary.
It is emphasized that the model represents average ground conditions of a 250 m by 250 m area, not the ground conditions at a pin point location, where the ground conditions may differ significantly from the average ground conditions. In that context, the ground models NEGDS provides are preliminary information on the ground conditions. The models are not suitable for actual foundation designs, and building authorities do not grant building permits without geotechnical investigation results obtained at pin-point locations.
Quality evaluation of data contained in geotechnical information databases
The trial application during the development of NEGDS as described in Sect. 4.3.4 immediately made it evident that a lot of faulty data was contained in many existing databases, which are seemingly subjected to rigorous screening procedures and supposedly very reliable databases. For example, ground elevations are missing, groundwater levels are absent, and soil types of reclaimed ground are unavailable. Furthermore, a single borehole was doubly registered at different locations and at different elevations. About 1 % of total 30,000 registered boreholes in Kyushu Geotechnical Information Database were found to be not reliable. As one of the advantage of NEGDS, questionable data are excluded as much as possible during modelling procedure by the local specialist teams as described in Sect. 4.3.3 because each borehole data is checked by comparing with the surrounding ground conditions and nearby borehole data, while only an individual borehole data is checked in case of a usual borehole database without reference to surrounding data. Thus NEGDS provides ground models with reliable data only.
Application to Liquefaction Hazard Maps
Application to Seismic Hazard Map
Figure 19 shows that surface particle velocities are low in the eastern part of Tokyo, which corresponds to low-lying area as shown in topographic features in Fig. 14. The places where the peak particle velocities are high in Fig. 19 correspond to the edge of the terrace ground seen in Fig. 14 where mouths of valleys are present with soft organic deposits.
How to present to the public the prediction of the velocity, acceleration, and displacement during earthquakes is another issue. Publication of such prediction should not confuse the public and should not send wrong messages. Such publication should be combined with public awareness programme for potential seismic risk, and social education for correct knowledge of shaking prediction and preparedness for possible seismic disaster.
Application to Regional Geotechnical Study
Since the NEDGS provides basis for 3 dimensional grid model of the ground, geotechnical studies for broad areas such as earthquake response of the ground, ground settlements, and groundwater flow in prefecture sizes may advance using, for example, finite element analyses. Of course three dimensional finite element analyses for the ground under vast extent of land consisting of various topographic features, various geological formations, and various soil and rock materials requires tremendous volume of reasonably accurate data, as well as high-specification computers.
6 Challenges for Further Development
There are challenges for the further development of NEGDS in addition to the problems described earlier.
Funding problems for sustainable development of NEGDS
Even after the NEGDS project supported by national fund completed in 2010, JGS continues expanding the coverage areas and maintaining the systems until March 2014 without outside financial support. The current work is supported by volunteers of JGS members from various parts of Japan. Permanent arrangement for the financing is challenging for continuing further expansion of the coverage areas and the on-line delivery of the data.
Organization for further development of NEGDS
In order to continue building the database systems beyond the 5-year funding period, the work team proposed to set up a study organization to continuously build and maintain NEGDS. The study organization will consist of nine regional panels at each regional chapter of JGS and the central panel at the head-quarter of JGS.
The regional panels (1) back up development of local geotechnical databases within their region, (2) study local soil conditions and geology with the assistance of geotechnical databases, (3) research how to use the databases, and (4) build and maintain the local portion of NEGDS.
The central panel (1) backs up the regional panels in the development of local geotechnical databases, (2) coordinates cooperation among the regional panels, (3) backs up the study of the local soil conditions and geology with the assistance of geotechnical databases, (4) assembles NEGDS based on the those each regional panel has constructed, and (5) coordinates linkage of NEGDS to the Integrated Geophysical and Geological Information Database (IGGID).
Data contents that the geotechnical information database should have
Quality evaluation of the data
Function the database should provide
Application of the databases
Issues related to digital networking of the databases
Issues related to ownership, copy rights, and use right of the data
Privately obtained data submitted to the authorities as a part of building permit
Means to collect private companies’ data as described in Sect. 2.3
Maintenance and administration of the databases
Responsibility of each party involved in various aspects of the databases
Problems related to modelling
Discontinuous planes such as faults, line structures like river dykes, and localized landforms and ground need better way of expressions.
The presently published models, which are the results of the trial development, are limited to central parts of 9 cities as shown in Fig. 9 and contains soil types and SPT N-values only, although the models are designed to contain as many and as much information as possible, as described in Sect. 4.3.2. As the coordinated construction of the models all over Japan has just started, the public can expect much more development of the quality and quantity of the models.
User education is necessary for correct interpretation of the models as more various types of geotechnical data are to be contained.
Continuous improvement of ground models and the systems
The systems allow modifying the ground models from time to time when new borehole data are available. A permanent organization such as the local panels as discussed above is required to continuously modify the ground models. The updating of the models is necessary when the topographic conditions have changed, like reclamation, filling, and excavation. The change of the groundwater levels should also be incorporated into the models.
The paper introduces Japan’s NEGDS, which JGS built aiming at linkage, collaboration, and corporation of various databases in Japan. The systems, although still rudimentary in data contents, were published on the internet on October 15, 2010 and have received attention of mass media as a tool for the public to check the ground conditions.
NEGDS can electronically construct, save, modify, and display the ground model of 250 m by 250 m in plan. The information is available to the public through the internet. The presently published models are limited to central parts of 9 cities and contain very limited source of information such as soil types and SPT N-values.
The systems provide opportunities for researchers to compare properties of similar soil types with similar depositional environment, the same depositional age, but in different localities in Japan. Such comparative studies of soil properties provide more in-depth understanding of properties of local soil deposits.
Practicing geotechnical engineers in Japan can understand potential problems and risks for proposed structures anywhere and they can incorporate such knowledge when they plan geotechnical investigations. As the systems provide geotechnical information in general, detailed geotechnical investigations are necessary at pin-point locations when designing foundations, excavations, slopes, and retaining walls. The ground models NEGDS provides are preliminary information on the ground conditions and are not suitable for actual foundation designs.
The NEGDS provides information, albeit in general, for preliminary judgement of potential geo-hazard such as liquefaction, earthquake shaking, ground subsidence, and slope movements.
The public can easily get advices on potential troubles related to the ground from professionals when they plan to buy land or houses. The public is advised to consult with the professionals for interpretation of the models. User education is necessary for correct interpretation of the data, as NEGDS become more popular in the public.
Potential application of NEGDS includes liquefaction hazard maps, seismic shaking hazard maps, estimates of ground subsidence in broad area, and groundwater flow maps. Advance of these application requires extensive research on model parameters.
Stable funding method is being sought in order to expand coverage areas of NEGDS, to improve data contents in each model, updating the existing models, and to research various applications.
For the continuous development of NEGDS as well as local geotechnical databases, an organization consisting of the central panel and nine regional panels was proposed to set up. NEGDS models need to be improved and refined to more accurately represent the ground conditions. Data contents have to be improved.
The authors are grateful to Geo-Research Institute, who developed the computer software of the systems under the supervision of JGS’ work team, ‘Shallow Ground Data Base Linkage.’