http://www.engineeringnews.co.za/articl ... 2011-04-08
Aerial surveys for three greenfield railways completed
By: Henry Lazenby
8th April 2011
Land surveyor Southern Mapping Company reports that it was contracted to survey three significant greenfield railway routes in Africa in recent months.
The company makes use of the latest light detection and ranging (Lidar) lasers to undertake aerial surveys that form the front-end work of greenfield projects.
Zanaga to Point-Noire (Congo)
The company reports that it has finished surveying a 500 km railway in the Republic of the Congo, between Zanaga and the Port of Ponte-Noire during February.
Southern Mapping Company project manager Colin Ord says that the survey was undertaken for an iron-ore miner, which owns mining rights to what is reported to be the largest deposit of iron-ore in the world.
“The mining area is about 500 km from the nearest and only point of exit, which is Pointe-Noire. “We completed aerial surveys of the mining area before moving on to the port. “We then surveyed a potential railway route between the two points,†Ord says.
However, once the data from the survey was processed and submitted to the client, it was discovered that the terrain is unsuitable for a railway. Ord explains that the client had certain specifications regarding the design of the railway.
“The client intends to run extremely long and heavy trains, in the region of 2 km in length, down to the coast, and has precluded the construction of tunnels along the route for safety and operational reasons. “If a train were to derail inside a tunnel, it would be an expensive and logistical nightmare to dig out the wreck.
“This requirement also rules out steep gradients, and dictates large-radius curves to be constructed in extremely challenging terrain. The design team is instructed to build bridges across the difficult terrain only,†he points out.
Further, Ord says that the surveying team was given only a 2 km broad reserve in which to find a route, which made finding a viable route of 500 km a significant challenge. After reviewing the initial data, the client contracted the company again to survey the area for an alternative route, which was completed during February.
The geographic information was again submitted and a suitable railway is now being designed.
Cameroon (Mbalam mine to new Atlantic port)
Meanwhile, Southern Mapping Company MD Peter Moir reports that the company completed surveying another 500 km railway from an iron-ore mine in the neighbouring Republic of Cameroon to the nearest port, at the end of last year.
“Australia-based Sundance Resources, which is developing the Mbalam mine, plans to connect the mine with a new port, south of Kribi, on the Atlantic Ocean with a railway line,†he says.
On its website, Sundance reports that the Mbalam Iron Ore project comprises a proposed port, a railway, a mine and a processing plant, and a second mine, a processing plant and a railway spur of about 60 km to the Republic of Congo. Mining studies are at an advanced stage, with the aim of establishing a Joint Ore Reserves Committee-compliant mining reserve and definitive feasibility study for the project by the end of March.
The miner believes the region has the potential to support iron-ore production of over 100-million tons a year.
Tete to Nacala
Further, Southern Mapping Company was also involved in surveying a railway route from Tete, located in the Moatize coalfield in Mozambique, to Nacala. The shortest route traversed Malawi. The $500-million project was initiated by the Mozambican government to transport coal along this important corridor. The railway is expected to be complete by 2015.
Meanwhile, regarding the challenges the company had to deal with while undertaking the surveys in the Congo, Moir points out that, when one undertakes long-distance surveys, it is challenging to determine accurate datum points, owing to the earth’s curvature. This is compounded by the often unreliable information being supplied by the surveyor general’s office at certain locations.
He says Africa presents some unique challenges, as various certifications are needed to legally fly an aeroplane abroad, and the responsible inspectors are not always available to undertake the certifications when needed.
Further, the weather also interferes with the surveying team’s work, especially in Africa’s tropical regions. Procuring aviation fuel is another challenge within rural African regions. The team often flies long distances and fuel is not always readily available.
Southern Mapping Company air operator Steve Weitz adds that the dense rainforests in the tropical regions make it extremely challenging to plot accurate datum points of the earth’s contours.
“It was challenging to obtain results in the dense jungles of the Congo, as we were only able to bounce coordinate lasers off the ground about once every 5 m, despite firing the laser at 200 000 pulses a second,†he says.
Advanced Technology
Moir explains that the company is able to accurately map areas by flying an aircraft in cross sections along the planned route. The aircraft is equipped with sophis-ticated equipment, including a sensitive global positioning system that records the precise location every second.
Further, the aircraft is equipped with an inertial measurement unit that takes 200 readings a second of the attitude of the aircraft to determine its position at any given point. This helps to accurately interpret the data.
Further, the Lidar laser fires at 200 000 pulses a second, resulting in 200 000 coordinates a second being recorded of the terrain below. “Whatever the laser hits below is reflected in the data, including trees and rocks,†Moir explains.
The system is accurate to within millimetres.
Another integral feature of the technology is its ability to take high-resolution photographs of the terrain below, which is later draped over the three-dimensional model of the terrain, created by the laser.
“The information is then fed into software that can automatically find the most appropriate route, according to the specifications of the project,†Moir concludes.
Edited by: Chanel de Bruyn