Search

Rock Mass Rating (RMR) is a rock mass classification system that is often used to select appropriate excavation methods and rock support systems in tunnel projects. This paper presents a geostatistical method for inferring RMR values quantitatively ahead of excavation of the tunnel face. The study makes full use of geological information exposed on excavated tunnel faces to capture the spatial correlation of rock mass quality and later predicts the RMR value using the kriging method. Predictions are constantly updated during the tunnel construction process. The advantages of the proposed method are as follows: (1) The RMR prediction uncertainty is quantified by accounting for spatial variability and model uncertainty; therefore, the resulting prediction can consider the geological conditions of the worst scenario; (2) The spatial variability of the geological condition is represented as a variogram model that is updated by observation data on the new excavated faces, and as the tunnel advances, the RMR prediction accuracy improves; and (3) The periodicity of geological conditions can be considered in RMR prediction. The proposed method is applied to a rock tunneling project, the Mingtang tunnel in Anhui province, China. The method achieves approximately 80% prediction accuracy; therefore, it has high potential as a tool for predicting RMR information ahead of tunnel face excavation. [ABSTRACT FROM AUTHOR]

This paper presents an automated discontinuity trace mapping method on a 3D surface model of rock mass. Feature points of discontinuity traces are first detected using the Normal Tensor Voting Theory, which is robust to noisy point cloud data. Discontinuity traces are then extracted from feature points in four steps: (1) trace feature point grouping, (2) trace segment growth, (3) trace segment connection, and (4) redundant trace segment removal. A sensitivity analysis is conducted to identify optimal values for the parameters used in the proposed method. The optimal triangular mesh element size is between 5 cm and 6 cm; the angle threshold in the trace segment growth step is between 70° and 90°; the angle threshold in the trace segment connection step is between 50° and 70°, and the distance threshold should be at least 15 times the mean triangular mesh element size. The method is applied to the excavation face trace mapping of a drill-and-blast tunnel. The results show that the proposed discontinuity trace mapping method is fast and effective and could be used as a supplement to traditional direct measurement of discontinuity traces. [ABSTRACT FROM AUTHOR]

According to the planning of Shanghai metro line 10, the interval tunnel from Liyang Road station to Quyang Road station has to cross through the group pile foundation of Shajinggang Bridge on Siping Road. Therefore, how to guarantee the normal traffic function and the safety of bridge structure during the tunneling process becomes a challenge to engineers and technicians. To solve this problem, the pile underpinning technology was recommended for this project. This specific scheme mainly comprises following steps, i.e. ground improvement behind abutment, foundation pit excavation under bridge deck, underpinning pile with raft and cutting pile with shield machine directly, etc. In order to verify the feasibility of this scheme, a series of theoretical analysis and numerical simulation were carried out on the entire construction process to explore the load transfer mechanism of bridge structure. The calculation results show that both the bridge static loads and traffic live loads can be successfully transferred from pile foundation to raft after pile underpinning, and the removal of obstructed piles during tunneling has very limited influence on bridge structure. Furthermore, real-time field monitoring activities, including settlement of bridge deck surface, deformation of surrounding buildings and pipelines, etc. were also conducted to ensure smooth construction. The monitored results agree well with the numerical calculation ones, which prove again that the proposed scheme is reasonable and the calculation results are reliable. [ABSTRACT FROM AUTHOR]