Application of decision tree to selection of MTBM for adverse geological conditions

So many potential risks can be identified for application of trenchless technology especially using microtunneling methods. Unexpected changes in ground conditions, such as encountering boulders, tree roots, ground water and man-made structures such as old foundations are the principal geotechnical risks, which affect the selection of an appropriate microtunnel boring machine. On the other hand, the performance of each microtunneling technique will differ while encountering such conditions. Hence, predicting the potential hazards provides a better safety and risk management plan. In this study, a couple of potentially hazardous situation, which are commonly associated with ground conditions, were identified and investigated. A decision tree aid methodology was proposed based on geotechnical risk assessment for selection of proper microtunneling technique. Based on the approach the most appropriate microtunneling technique has the minimum risk level either before or after hazards mitigation measures. In order to check the efficiency of the approach in practice, selection of microtunnel boring machine for Hamadan sewerage pipeline project was evaluated. Accordingly, an earth pressure balance (EPB) MTBM was selected for the project.