Construction site inventory with drones

The current year is a time of hard work on the development of Polish infrastructure. We are still constructing long segments of expressways and motorways, in near future more and more railway projects are about to start. With such a big scale of investment, the advantages of drones become more clearly visible. UAVs help in decision making and management during the construction and they are also indispensable in crisis situations like breach of contract with the general contractor. We describe our experience from S3 Nowa Sól – Legnica construction site. The task III, Kazimierzów – Lubin Północ was abandoned by the Italian contractor Salinini. The construction inventory was carried out for the General Directory for National Roads and Highways (GDDKiA). In this project, in addition to standard procedures, we had to take into consideration the mining subsidence.

S3 Kazimierzów – Lubin Północ construction segment (Google Earth)

Drone based construction site inventory – advantages

Many companies have realised the benefits of surveying construction site inventory carried out by UAVs. In this case, the work was submitted to us by the General Directory for National Roads and Highways. After the agreement was terminated with the general contractor, the need for rapid measurement of the whole construction site appeared. The data was gathered for the documentation purpose as well as to serve as an attachment to the new tender procedure.

The real and significant problem in this type of investment is the discrepancy between the declarations and factual state. Mostly the subcontractors suffer and the state loses money. When drones are applied, the end product is a continuous digital terrain model, in which we can clearly see if the works were realised or not. Furthermore, the model can be directly compared to the road project which enables to control whether the works were conducted correctly. In case of the S3 expressway, the most important task was to determine the factual works progress so that the companies taking part in the new tender can conduct detailed contract valuation.

The area of most significant surface deformation

The area of most significant surface deformation

Particular conditions in mining areas

The dense cloud or a model is a significant factor facilitating the preparation of documents in every segment of the construction – hydrologists can control the slopes, ditches and ponds, road constructors can determine the progress in building embankments and road surface, and bridge constructors can see the progress in engineering structures. The stockpile volumes of aggregates can be easily calculated. On the other hand, it is a proof in court cases for the Directorate.

The construction between Lubin and Pokowice is interesting for one more reason: it is located in the area influenced by mining activity of KGHM (copper mining company). It means that the surface subsides around 0,5 m per year. Despite the obvious influence on the surroundings, it determines special procedures on the construction site. Without continuous surveying monitoring it would not be possible to conduct works according to the project. In this case, when calculating any volumes, we must consider the value of subsidence trough. Here again the drones are a big advantage. Thanks to continuous model we can precisely model the subsidence trough and make exact calculations.

The experience shows that the exact construction inventory gives measurable benefits for all parts. The situation on S3 is exceptional but more and more frequently we conduct works for general contractors before they submit the tender offer, with our models they can calculate their offer more accurately.