Performance of roadheaders in low strength pyroclastic rocks, a case study of cold storage caverns in Cappadocia

Roadheaders are one of the mechanical excavators widely used in mine roadway excavation or tunneling projects. Therefore, researchers have usually investigated the performance of roadheaders only for these working areas. However, roadheaders can be also used in excavations of the other underground spaces which can be designed as cold storages, hotels, restaurants etc. In Cappadocia region, cold storage caverns (CSC) are excavated also by roadheaders and CSCs are generally constructed in tuff formations that are very soft, homogeneous, and can be carved out easily. The use of roadheaders for the excavation of CSCs may show some different characteristics in mining and tunneling projects. For example, the excavated formations are generally accepted as massive and since the drainage problem, water is not used during the excavations of CSCs. For such reasons, the performance of a roadheader may differ from the estimated performance calculated in the previous models. In this study, field performance of roadheaders were analyzed in eight different CSCs excavated in low strength pyroclastic rocks, in Cappadocia region. The excavation performance and cutter consumptions of the road headers were recorded in detail and the instantaneous cutting rates (ICRs) of the machines were determined. The Cerchar abrasivity tests and physico-mechanical tests were carried out on the core samples collected from the project areas. Relationships between field ICRs and results of physico-mechanical tests were analyzed. Based on the uniaxial compressive strength (UCS), a new site specific model for predicting roadheader performance was proposed for low-strength rocks with up to 10 MPa UCS. The ICRs of the roadheaders were calculated using some previously developed empirical models and compared with the field performance of the roadheaders and the results of the newly developed model. Similarly, a new model based on the Cerchar abrasivity index (CAI) for predicting cutter consumption rate of roadheaders was proposed to excavate low-strength tuffs. The amount of cutter consumption was also calculated using some previous models for each CSC project and compared with the field data.