Effects of the physico-mechanical properties of low-strength pyroclastic rocks on cutter wear of roadheaders

Abstract

Construction projects that use mechanical excavators such as tunnel boring machines (TBM) or roadheaders generally result in high costs due to cutter wear. Cold storage caverns (CSC) are one area where roadheaders are used, but excavations of CSCs show different characteristics than tunneling and mining excavations. The effects of the physico-mechanical properties of low - strength, pyroclastic rocks (tuffs) on the wear of roadheader cutters were investigated during the excavation of CSCs in the Cappadocia region of Turkey. The excavated tuffs containing 13–19% quartz had low uniaxial compressive strength (UCS), ranging from 3.14 to 13.17 MPa. Field excavation performance parameters were continuously recorded for one week on two similar roadheaders and 14 different CSCs projects. The average field cutter consumption rate (CCRField), defined as cutter material loss per excavation of 1 cubic meter rock, was calculated for each CSC. Physico-mechanical tests were performed on the rock samples collected from the CSC project areas. Additionally, sieve analyses were performed on the excavated rock materials to determine their coarseness index (CI) and mean particle size (d(50)). The calculated average CCR values were statistically analyzed with some physico-mechanical properties of rocks, in-situ Schmidt hammer hardness (SHHIn-situ), CI and d(50). Negative correlations were found between CCR and each of the UCS values, Brazilian tensile strength (BTS), point load strength (Is(50)), SHHIn-situ, CI and d(50), and a positive linear correlation was found only with the water contents of the rocks. All of these relationships were found to be dependent on crushing of the excavated materials in fine sizes, blockage of cutters by filling of the fine materials into the space between the holder and cutters and adherence of fine materials to the cutters and cutterhead, as affected by water/moisture and clay contents. This study, whose results apply to studies in the Cappadocia region of Turkey, showed that the CCRField of roadheaders decreased as the strength of rocks increased. These relationships specifically apply to easy-cutting tuffs with very low strength and high water content.