Stability analysis of a mini-disc equipped boom type tunneling machine

In today's world, hundreds of kilometers of galleries/tunnels are being constructed. Since high rates of urbanization and demand of infrastructure has also increased, tunnels need to be excavated in the quickest and safest way. Moreover, the mining activities will be operated near the urban areas and because of this, the contractors tend to chose the underground mining methods to avoid causing environmental impact. Mainly there are two methods in underground excavation: drilling and blasting method and mechanical excavation. These methods are selected depending on tunnel dimensions, tunnel geometry, length of tunnel, geological and rock mechanical condition, ground water level, vibration restrictions and allowed ground settlements. The drilling and blasting method is still the most typical method for medium to hard rock conditions. It can be applied to a wide range of rock conditions. Some of its features include versatile equipment, fast start-up and relatively low cost tied to the equipment. On the other hand, the cyclic nature of drilling and blasting excavation method cause low speed of excavation. Blast vibrations and noise also restrict the use of drilling and blasting method in urban areas. Mechanical excavation has some advantages over the drilling and blasting method. This method is safer and more environmental friendly operations. The muck size in mechanical excavation is uniform thus haulage cost is lower than drilling and blasting methods. This method is suitable for selective mining and continuous operations. For all these advantages mechanical excavation has became a rival of drilling and blasting method in 20th and 21st century. The machinery in mechanical excavation is mainly divided two parts, full face excavation machineries and partial face excavation machineries. The full facel excavation machines are TBMs, EPBs, micro-tunneling machines. The partial face machines are roadheaders, hydraulic hammer, continous miners. Roadheaders has an exceptional place among those other excavation machines. It has lower initial costs than the full-face excavation machinery. They are also flexibly equipped to excavate galleries in various shapes. On the other hand, they are not suitable for hard and abrasive rock conditions and are more preferable for excavating stable rocks with low to medium hardness. This disadvantage is an obstacle to usage of roadheader widely. The main reason why roadheaders can not be used in abrasive and hard conditions is the cutting tools of roadheaders. Drag bits and chisel bits are used in the cutter heads of roadheaders. These bits wear out very rapidly or suffer total structure failure. Moreover roadheaders can not handle the forces in hard conditions and these reaction forces are causing stability problems of roadheader. To overcome this problem, the bigger and more powerful roadheaders are produced, however the power of machine and the size of machine is direct proportional. The bigger size of these machines eliminate the mobility and flexibility feautures of roadheaders. For these reasons, the researchers are studying on new technologies for using the roadheaders in hard rock without increasing the machine size. These technologies are mainly focused on cutterheads and rock cutting tools. For example, water jets are used on the cutter heads of roadheaders for increasing the efficency of cutting and new materials like PDC for cutting tools to reduced the wear ratio of the bits. The researchers has considered using disc cutters on the roadheaders cutting heads. If disc cutters could be utilized on a roadheader, the application of this type of excavator could be extended into harder rocks. While disc cutters are too big, they occupy too much mounting space and require thrust levels much higher than roadheaders can handle. Because of this , reseachers have developed mini-disc cutters for using in cutter heads in boom type tunneling machines. On the other hand, the changes in the structure of machines and the cutter heads cause changes in reaction forces that is applied on roadheader and also these changes stability of the roadheaders Stability has got a direct effect on the efficiency of cutting and safety of excavation, because of these, stability analysis must be well performed. The study aims to establish the stability analysis for mini-disc equipped roadheader cutterheads that are designed for using in hard and abrassive conditions. The study first introduces the mechanical excavation systems, classification of mechanical excavation machines and places they are used and then general features, structures and types of boom type tunneling machines states. After that cutter tools types that is used on cutting heads in boom type of tunneling machines and the cutting theories of these cutters are explained. The parameters of designing cutter heads are explained and type of the cutting head are stated, dynamic and kinematical features demonstrating the machine integrity are mentioned. Selection factors of the boom type tunneling machine is explained . The stabilility of boom type machine which is one of the selection factor is important for the efficiency and safety in excavation operations and the method to make stability analysis of boom type tunneling machines (BKM) and obtain numerical values, is stated. Stability analyses are divided mainly two parts, stability analyses of longitudinal cutter head (BEP) and stability analyses of transversal cutter head (BED). The stability analysis of BEP is contained 4 different stability state (turning around the vertical axis, turning to side, turning to back, sliding of the machine). These states are analysed in four cutting mode, sumping, overcutting, undercutting, lifting, lowering. The stability analysis of BED is also contained 4 different stability state but these states are analysed in 4 different cutting mode, sumping, arcing, lowering and lifting. Then based on these stability states, a computer program which is based on C++ programing language, are used for analysing the stability of boom type tunneling machine all of the face or the specific point in the face. Then the implementation of one of the newest cutting tool type, mini-disc cutter and the laboratory testing and performance evaluation of a mini-disc equipped cutter head that is performed by Colorado School of Mines Earth Mechanics Institute (EMI), is presented. 3 mini-disc equipped cutter heads were designed for excavating highly abrasive hard welded tuff. These design are stated as original design, modified design and final design. Following extensive compute modeling and performance analysis that was conducted by EMI, a 920 mm (36 inch) cutterhead (final design) featuring thirty six 125 mm (5 inch) cutters are fabricated for testing in the laboratory. The tests were performed by using horizantal drill rig that allow sumping and lowering modes. The cutter heads are designed for using on Voest Alpine AM 105 transverse boom type tunneling machine. Mini-disc were found to excavate the welded tuff in a high efficient manner both in the sumping and shearing (lowering) modes. No cutter wear of failure was observed. The cutter head was found to efficiently excavate welded tuff with thrust, torque and power requirements well below the capabilities of the AM 105 by EMI. The stability analysis of these test was performed by using the methods explained above in this study. Three design mini-disc equiped cutter heads and original dragbit head that is used on AM105, were analysed. The parameters of tunnel, machine and the forces ,that effects boom of the machine, were used for analysis. The analyses were performed for all positions in face and all modes of cutting.The result of these analysis of all four cutter heads were discussed. The comparision between these cutter heads and the cutter heads design relations to performance on the face based on stability were established in consideration of analysis results. The minumum and negative values of stability on the face was stated. To conclude, this study states that the cutting efficiency can not estimated by only cutting tests, machine dynamics such as stability are also important. The stability analysis should be performed for estimation efficiency. Moreover the study is proved that every little changes in cutter head design directly effects the stability and the stability has also direct affect to efficiency.