Recently I posted an article about mapping underground utility infrastructure in cities and regions around the world. The most recent notable efforts in the regard are Las Vegas, which is creating a 3D model of underground and above ground infrastructure and implementing new regulations to ensure that accurate location information about underground facilities is captured, and the Region of Lombardy in Northern Italy, which has mandated that ground penetrating radar (GPR) be used by all municipalities in the region to capture location for all underground infrastructure. But to date these efforts have been limited to municipalities or regions.
At Geospatial World Forum 2014 in Geneva I was made aware of a project to map underground infrastructure on a national scale. Pascal Berteaud, Director General, French National Institute of Geographic and Forest Information (IGN), referred to a large ten year, multi-billion euro project involving IGN and France's utilities to map all of France's underground utility infrastructure in 3D to an accuracy of 40 cm (about 16 inches).
Berteaud discussed IGN's extensive use of geoinformation and innovative technologies like 3D building information modeling (BIM) for development activities in France. Geospatial information is the basis for optimization of mobility and transport, real-time information about assets, and intelligent road reference systems. In this context Berteaud emphasized that accurate 3D location is essential for effectively managing underground infrastructure and mentioned that France is developing a 3D model for its underground infrastructure and is employing advanced technologies in the project.
Accuracy of location of underground structures
The motivation for this project is a new regulation that was promulgated on 15 February 2012 titled Decree relating to excavations near underground, overhead or underwater transmission or distribution networks.
Project managers of proposed construction projects are required to send a statement of the proposed work including a polygon delineating the area affected to the operators of utility networks operating in the area.
In return operators of utility networks must provide to the project managers plans of their underground networks in the area indicating the accuracy of the geographical location of different structures of their networks classified according to three accuracy classes.
For this purpose the Decree defines three levels of cartographic accuracy for underground structures;
Class A: if the maximum uncertainty of location indicated by the utility operator is less than or equal to 40 cm
Class B: if the maximum uncertainty of location indicated by the utility operator is greater than that for Class A and less than or equal to 1.5 meters
Class C: if the maximum uncertainty of location indicated by the utility operator is greater than 1.5 meters , or if the operator is not able to provide the location.
The Decree states that uncertainty in the geographical location of a structure is considered likely to jeopardize the construction project or significantly impact the technical or financial conditions of its implementation when the geolocation of the structure is classified in accuracy classes B or C. For structures falling in this category, the utility operator is required to initiate a process to reduce this uncertainty to achieve the goal of class A as quickly as possible.
Furthermore, if further investigation (typically potholing) of some structures by the contractor is required, the cost of the investigations is assigned as follows
- The construction contractor assumes the entire cost when the structures are assigned by the operator to accuracy class B and further investigation reveals that the actual classification is found to be Class B or Class A
- Half of the cost of the investigation is to be borne by the operator when the structures are assigned by the operator to accuracy class C;
- All of the cost is to be borne by the operator when the structures have been assigned by the operator to accuracy class B and when the result of further investigation reveals that the actual classification is accuracy class C
Surveying underground infrastructure
Construction contractors are required to survey all new and changed underground structures. These surveys must satisfy certain conditions.
Location coordinates of structures in an open trench must be reported by a ceritified provider (in North America I assume this would be a registered surveyor). If remote detection technology such as GPR is employed, the firm performing this work is not required to be certified, but a certified provider must be involved in georeferencing the data.
Whatever the method of measurement used , direct or remote, the accuracy of the reported locations must be accuracy class A.
For each structure the data recorded must include
- Name of the project manager of the site
- Name of the company that provided the location information
- Name of the certified provider responsible for georeferencing
- The maximum measurement uncertainty (differentiating , where appropriate , x, y, and z )
- In the case of remote detection, the type of measurement technology used.
The data must be shared with the operator.