Abstract
In the present research, two real-time rock strength determination models based on the drilling parameters were studied. Firstly, a discrete element software named Particle Flow Code in 2 Dimensions (PFC2D) was used to analyze the applicability of rock drillability index and drilling specific energy, in which graded particle assemblies were created to simulate the rock behaviour. In the numerical models, Weibull distribution was used to randomize the bonds between particles and make the assembled rock model with different heterogeneity. The drilling process of a PDC (polycrystalline diamond compact) cutter was modelled in two steps: horizontal linear rock cutting and vertical pressing-in progress. From the horizontal linear rock cutting process, the peak cutting forces were obtained and vertical pressing-in process outputs the relationship between normal force and cutting depth. Subsequently, the methods for calculating rock drillability index and drilling specific energy were proposed in the discrete element model. Then, the relationship between the calculated indexes and rock strength was investigated (supported with the regression analysis). Moreover, the effect of rock heterogeneity, along with error comparison between the above two indexes, were discussed. The results showed that the rock drillability index is more accurate than drilling specific energy in rock strength assessment (The error is about 10% smaller).
Highlights
The information about the surrounding rock’s geological conditions plays a vital role in the design of the support of the coal mine roadways
ROCK DRILLABILITY INDEX AND DRILLING SPECIFIC ENERGY FOR SINGLE PDC CUTTER As stated in Section 1, rock drillability index and drilling specific energy are obtained based on in-situ tests, while, this work is to study the rock breaking process by a single PDC cutter, it is necessary to simplify these two rock strength assessment methods
(2) In the process of horizontal linear rock cutting, as the cutting depth increases, the drilling specific energy has a slight upward trend. This phenomenon can indicate that an increase in thrust to a certain extent will reduce the efficiency of rock breaking, which in turn will increase the drilling specific energy
Summary
The information about the surrounding rock’s geological conditions plays a vital role in the design of the support of the coal mine roadways. There are currently many methods to detect geological conditions, such as geological radar, electrical survey system, and advanced drilling technology. The most commonly used method for detecting the geological conditions in the geoengineering is advanced drilling technology which can obtain the core, making it the most direct and accurate geological prediction method. Geological radar and electrical survey system are indirect methods to detect the geological conditions. They are limited by underground observation conditions and the influence of the roadway environment, making them have the disadvantage of multi-solution. Their detection accuracy needs to be further improved. The applicability of the two methods will be discussed by numerical modelling
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