JOB REPORT

Surface miners biting their way through granite.

Routing operations in granite for a Japanese link road

In Japan, road builders are often confronted with ground that contains high percentages of granite. Blasting is usually not an option, however, because of the extremely high population density in the Land of the Rising Sun.

Because of the risk potential involved, blasting is not permitted when building roads, railway lines or motorways in the immediate vicinity of residential areas. Dust, noise pollution and, most importantly, damaging vibrations need to be kept to an absolute minimum during the construction work. It is not surprising, therefore, that surface mining is an application that is much in demand.

Blasting was precluded also when building a link road between two new housing estates, as the route was to lead through a hill with houses and factory buildings on both sides and with overhead power supply lines crossing the building site.

Following analyses on the cuttability of the hard granite material and the costs involved, the Japanese contractor decided to use surface miners 2500 SM, 2600 SM and 3500 SM from Wirtgen to carry out the routing operation. Depending on the hardness of the rock to be cut, the Wirtgen surface miners – powered by 1,000 HP engines – achieved production rates of between 70 and 600 cubic metres per hour in 9-hour shifts.

Cutting tool consumption also varied depending on rock hardness. At times, the construction crew needed to replace no more than 10 to 30 tools per hour. To avoid extremely high – and sometimes excessive – wear and tear on the cutting tools, the surface miners were equipped with special tools with particularly long and robust carbide tips developed by Wirtgen’s system partner Betek.

The surface miners from Wirtgen cut their way through the hard granite step by step, creating an embankment with a specified slope of 45° and a level surface that was perfectly suitable for trafficking during the subsequent stages of the construction work.