LiDAR Survey: An Essential Step in the Construction of National Highways

From planning to construction and project management, LiDAR has many uses. It helps out in soil work computations, multiple alignment identification, and topographic survey for DPR generation.

LiDAR Survey: An Essential Step in the Construction of National Highways
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LiDAR Survey: An Essential Step in the Construction of National Highways

The importance of accurate surveys in DPR (Detailed Project Planning) cannot be over-emphasized. Accurate details before construction like finished road level, original ground level, and high water level (above which road should stay) have to be calculated and measured to avoid a massive amount of cutting and filling losses. If something goes out of the plan, it is a massive loss to the government and contractor. 

Why should levels of the road be visualized correctly?

Accurate and a better survey in DPRs are very critical. It reduces the cost of the project and avoids wastage of construction material before, after, and during the construction. A precise survey reduces the time of completion and delivers quality output. It considers various safety aspects like slopes, floods, and the life of the road. 

LiDAR mandatory for DPRs: MORTH

Ministry of Road Transport and Highways (MORTH) has made LiDAR survey mandatory for DPRs. Depending on the use, any LiDAR survey can be done, i.e., with the mobile LiDAR, Aerial Mobile LiDAR, or any better technology. 

The deliverables include raw DGPS data for the entire Highway, point cloud data including adjoining areas of interest, Topo map of scale 1:1000, contour map at 50 cm interval, and cross-section of Highway in *.dwg format. 

The accuracy obtained from the LiDAR survey for DPRs must be horizontal 5 cm or better or 50 points per sq m. 5cm and 10 points per sq m for aerial survey. Also, DGPS can be used for establishing accuracy and checking point survey. 

LiDAR: Useful in Different Stages

From planning to construction and project management, LiDAR has many uses. It helps out in soil work computations, multiple alignment identification, and topographic survey for DPR generation. The progress of construction and it’s monitoring have a significant role in the LiDAR survey.

To take advantage of the LiDAR data, it is essential to choose the right technology for the right project. Recent successful examples of Mobile LiDAR survey by ICT, are projects like Shimla to Mataur of NH-88, Karwar-Gajendragad project, and survey for the physical condition of the NH Toll Operate Transfer (TOT) covering five states (combined with drone videography). 

Nakuru-Nyahururu-Nyeri- Marua road (B5) project by ICT was done using Aerial LiDAR for 192 km road length. A drone survey for developing greenfield alignment was done in Rajasthan-Punjab for 25 km (Jalandhar-Bhatinda-Ajmer project). 

Overall total 2108 km length has been surveyed successfully by recent LiDAR projects by ICT. 

Why is Ground survey sometimes combined with the LiDAR survey?

LiDAR survey has the required accuracy coupled with the ground survey. The surveyor can easily revisit data to get more information. Getting 3D images is another advantage that makes the visualization more clear and easy. 

The ground survey helps in fixing of control points and covers the shadow areas for surveying. Culverts are not easy to fix using cloud point data, but a ground survey can help out. 

In areas like hilly terrain, many stretches have to be repeated manually. A high error is there in dense vegetation, U-turns to negotiate steep slopes; a ground survey coupled with LiDAR can avoid repetitions in these cases.  

A data bank to avoid repeated survey

Ravi Shankar, president of ICT Delhi, compares LiDAR data to a data bank that can avoid repeated surveys. “ It’s good. It’s happening, it gives us things much faster, but there are a lot of gaps, and we need to fill them”, he says. 

A better understanding of LiDAR functions and limitations to consultants is required to increase its usage. It is also important for analysts to understand the terrain variables in a better way.

To increase the use of digital data in DPRs, a component of the Ground survey must progressively reduce, and the cost must be optimized with time. There is a need to improve the quality and speed of processing cloud point data. 

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