Abstract
This paper analyses the construction time and advance rate of a 3 km long drill and blast tunnel under various geological conditions using an upgraded NTNU drill and blast prediction model. The analysis was carried out for the five types of Korean tunnel supports according to the rock mass quality (from Type 1, meaning a very good rock mass quality; to Type 5, meaning a very poor rock mass quality). Four kinds of rock properties, as well as the rock mass quality, for each tunnel support type were applied to simulate different geological conditions based on previous studies and the NTNU model. The construction time was classified into five categories: basic, standard, gross, tunnel and total, according to the operation characteristics to more effectively analyse the time. In addition, to consider the actual geological conditions in tunnelling, the construction times for the three mixed geological cases were analysed. It was found that total construction time of a tunnel covering all the operations and site preparations with a very poor rock mass quality was more than twice that of a tunnel with a very good rock mass quality for the same tunnel length. It is thought that this study can be a useful approach to estimating the construction time and advance rate in the planning or design stage of a drill and blast tunnel.
Highlights
In tunnel construction, it is typical to compare the advantages and disadvantages of two major methods, drill and blast (D&B), and TBM, in the planning or design stage
The second step is to set up the tunnel sizes, such as the cross-sectional area, perimeter length of a tunnel, round length, etc., as well as the tunnel support types based on a Korean tunnel specification
The analysis was carried out for the five types of Korean tunnel supports according to rock mass quality, ranging from Type 1 through to Type 5, and four kinds of rock properties, as well as the rock mass quality for each tunnel support type, were applied to simulate different geological conditions based on the previous studies and the NTNU model
Summary
It is typical to compare the advantages and disadvantages of two major methods, drill and blast (D&B), and TBM, in the planning or design stage. The construction time is an important factor in the selection of the construction scheme (number of construction lots and intermediate construction access) and the construction method (excavation method, lining system) [2]. The D&B method is a very flexible and adaptable process with respect to the excavation of intermediate cross sections or cross sections of any shapes and sizes, and it has advantages in installing the various types of primary rock supports such as shotcrete, wire-mesh, rock-bolt and forepoling. D&B has a short time-mobilisation, as standard equipment is used during the excavation, and has a lower advance rate (performance rate) in most cases, compared to the TBM technology [13]
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