ISRM International Symposium - EUROCK 2020, Trondheim, Virtual, Norway, 14 - 19 June 2020
© International Society for Rock Mechanics and Rock Engineering Norwegian Group for Rock MechanicsSometimes performance (productivity) of the Raise Boring Machines (RBMs) could be low due to incorrect machine selection and improper application of operational parameters such as pushing / pulling force and rotational speed, of which should be arranged according to properties of the excavated rock mass. By considering these critical subjects especially in the feasibility and planning stages of mine and tunnel projects, performance of RBMs should be investigated sufficiently to avoid the loss of money and time. In addition, stability of the raise-bored shafts is another critical subject that directly affects the long-term use of the shafts. The excavated ground should have a sufficient quality to allow a freestanding and unsupported excavation. Some lessons learnt about the performance evaluation and stability assessment of the raise-bored shaft in the Efemcukuru Gold Mine in Turkey are briefly highlighted in this case study. The final diameter of the shaft is 2.44 m and the length of shaft is 73.4 m. First of all, the study gave an insight on the stability problems in soft and crushed ground. The drilling / excavation of this ground in this shaft (13% of total length of shaft) was performed in a short time with a favorable performance. Stability assessment indicated that a collapse could occur due to low raise bore quality index (QR<1) in the soft and crushed section of the ground. Another important finding was that water inflow in this ground could create stability problems during rainy seasons. As a short-term solution, grouting could be considered in this ground. However, the casing support system could be taken in consideration for a long-term solution to prevent any collapse and water inflow in upper levels of the shaft.