Investigation of Durability Increasing of the Ripper in Dealing with Hard Boulders

 In mechanized tunneling of soft grounds with boulders, several types of cutting tools are used on the cutter head of the machine. The main cutting tools used in this condition are rippers, disks or a combination of them. In the tunnel of the eastern part of the Mashhad urban railway line 3 project, due to fine grain layers the tunnel section, the main tools used were the rippers. The discs were used only in the cutter head gauge. The addition of a gravel layer containing boulders in the tunnel section has reduced the durability of the rippers and increased the specific excavation energy up to 25%. In order to increase durability, NFM designed rippers were replaced with heavy rippers. In addition, various alloys have been investigated by test and error method. Changes in dimensions and alloy increased the durability if the tools up to 37%. By replacing the NFM designed rippers with heavy rippers, the performance of the rippers have increased from 183 meters to 250 meters. The result of tool replacement in the eastern part of Mashhad urban railway line 3 (about 10 km from the route) shows that the consumption of cutting tools in the boulder area was 10 times the area before the collision with the boulder. In general, 280 tools have been replaced in the investigated boulder area (about 1.7 km), which has resulted in saving about 60 billion rials by using heavy rippers instead of NFM rippers.