A Study of the Effects of Geological Conditions on Korean Tunnel Construction Time Using the Updated NTNU Drill and Blast Prediction Model

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.

Composition and consequences of the IntCal20 radiocarbon calibration curve

Radiocarbon calibration is necessary to correct for variations in atmospheric radiocarbon over time. The IntCal working group has developed an updated and extended radiocarbon calibration curve, IntCal20, for Northern Hemisphere terrestrial samples from 0 to 55,000 cal yr BP. This paper summarizes the new datasets, changes to existing datasets, and the statistical method used for constructing the new curve. Examples of the effect of the new calibration curve compared to IntCal13 for hypothetical radiocarbon ages are given. For the recent Holocene the effect is minimal, but for older radiocarbon ages the shift in calibrated ages can be up to several hundred years with the potential for multiple calibrated age ranges in periods with higher-resolution data. In addition, the IntCal20 curve is used to recalibrate the radiocarbon ages for the glaciation of the Puget Lowland and to recalculate the advance rate. The ice may have reached its maximum position a few hundred years earlier using the new calibration curve; the calculated advance rate is virtually unchanged from the prior estimate.

Evaluation of the face advance rate on ground control in the open face area associated with mining operations in Western China

The modern longwall faces in coal bases in Western China are being mined at an increasingly faster rate, yet the consequences of the face advance rate on the ground control and strata movement require further investigation. In this study, two improved physical models with different advance rates are developed to evaluate the roof failure characteristics; the strata movement; the displacement of the strong, massive roof; and the roof movement velocity. The results show that: (i) regular falls of the immediate roof and major falls of the hard roof are observed with the progressive development of the longwall face. Massive fractures on the roof strata extending from the face to the ground surface develop on a major roof fall. (ii) Model I, which has a slower face advance rate, shows a major roof fall interval of 65 m, which is slightly less than the 70 m found by Model II, which advances at a faster rate. Larger strata fractures are observed in Model I, while the gob area of Model II is better filled with waste rock materials. (iii) The displacement and velocity of the hard roof are unnoticeable until a massive roof fall. Maximum displacement occurs on a major roof fall, which is 50 mm for Model I and 30 mm for Model II. The maximum roof movement velocity on a major roof fall is 4.6 cm per min and 5.9 cm per min for Models I and II, respectively.