# Effect of Rock Abrasiveness on Wear of Shield Tunnelling in Bukit Timah Granite
## 1 Introduction
[PERSON] [6] showed the relationship between the wear coefficients of 17 inch disc cutters and _CAI_, as illustrated in Figure 1.  
Figure 1: Relationship between wear coefficient and Cerchar Abrasivity Index (_CAI_). The relationships between geological parameters and cutter life were determined by [PERSON] et al. [7]. Their findings indicate that intact rock properties, including Vickers hardness number of the rocks (VHNR) and uniaxial compressive strength (UCS), exhibited the highest level of correlation with cutter life. [PERSON] et al. [8] introduced a rolling indentation abrasion test (RIAT) for rock abrasiveness. RIAT is designed to replicate actual wear behaviour more accurately than other more commonly used methods can, in the context of boring hard rock tunnels. [PERSON] et al. [9] investigated the effect of the cutterhead design of TBM face cutters on cutter consumption based on the data from six projects. [PERSON] et al. [10] developed a wear model for analysing disc cutters based on the wear mechanism and motion analysis of the cutter rings. They found that the cumulative wear depth and advance distance are correlated linearly. As tunnelling progresses, the wear rate varies, owing to variations in geotechnical or operating parameters. Several studies have been conducted on slurry pipe wear in relation to mining, dredging, paper and pulp, sewage pumping, and agricultural waste industries [11], but few have been conducted on slurry shield TBMs. The wear of slurry discharge pipes can be evaluated based on the wear rate. The wear rate (\(wr\)) is defined as the ratio of the degree of pipe wear, in mm (\(p\)), over a given period to the advance distance of TBM, in m (\(d\)), and it is expressed as follows:  
\[wr\ [\mathrm{mm}/\mathrm{m}]=\frac{p\ [\mathrm{mm}]}{d\ [\mathrm{m}]}, \tag{4}\]  
The wear rate is proportional to the flow velocity, volume, size, and shape of the material used in the slurry. A power-law relationship describing the slurry flow velocity is one of the most commonly used expressions, as follows [12]:  
\[wr\propto V^{n}, \tag{5}\]  
where \(V\) is the slurry flow velocity, and \(n\) is the power index based on the material and other variables, and its value ranges between 1 and 4 for slurry pipes. [PERSON] [13] proposed that the annual wear rate (mm/year) is related to the slurry particle diameter and slurry transport speed, as follows:  
\[wr(\mathrm{mm}/\mathrm{year})=6.1d^{2.15}V^{3.7}, \tag{6}\]  
where \(d\) is the slurry particle diameter, in mm, and \(V\) is the slurry transport speed, in m/s. In this study, the effect of rock abrasiveness on the wear of disc cutters and slurry discharge pipes was examined. The radial wear of disc cutters and the thickness of slurry discharge pipes were measured at a slurry shield TBM site in Singapore. The wear of the disc cutters was assessed considering the wear coefficient of a 19 inch disc cutter. The relationships between the weathering grade of Bukit Timah granite and the wear coefficient of disc cutter rings were investigated, and the correlation between _CAI_ and wear coefficient of disc cutters was determined. In addition, the average wear rates of slurry discharge pipes for Bukit Timah granite were estimated through pipe thickness measurements. Based on the weathering grade of the Bukit Timah granite, the relationship between the wear coefficients of the disc cutters and the wear rates of slurry discharge pipes was investigated. Finally, the relationship between the slurry discharge velocity and the wear rate was derived.