Profiling of weathered argillaceous limestone rock with MWD data from advanced drilling for tunnelling along Wu-Kai expressway in Chongqing, China

Abstract

Advanced drilling was employed for the ongoing excavation of a tunnel on Wu-Kai Expressway in Chongqing, aiming to characterize the ground condition ahead of the tunnel face and avoid potential geohazards. Measurement While Drilling (MWD) system and the hydraulic rotary crawler drilling machine are used for the advanced drillhole in the weathered argillaceous limestone rock mass. However, the MWD data exhibits random variations in penetration rate and cannot be correlated with ground conditions. In addition, there is little MWD data on the weathered argillaceous limestone with time-series algorithm in relevant open literature. This paper presents further analysis of the MWD data, resolves the random variation issue in penetration rate, and re-interprets the MWD data along three advanced drillholes in this tunnel project. The re-calculated penetration rate with the time-series algorithm for each drillhole is a stepped function of the drillhole depth. The constant penetration rates for the different homogeneous zones can be further correlated with the weathering degrees of the rock and compared with those from other five ground sites with different ground conditions in China and London. The findings of the paper can enhance the general applicability of MWD data for accurate profiling of weathered argillaceous limestone rock mass for safe tunnelling.