Which drilling method is considered best for hard rock?

Cable Tool Drilling is considered the best method for hard rock due to its ability to provide efficient penetration and rock removal. This technique employs a heavy steel bit that is repeatedly dropped and raised, using the weight of the drill string to break the rock. The action allows for effective borings in very hard and dense material, making it suitable for geological formations that resist penetration by other methods.

One of the defining characteristics of Cable Tool Drilling is its capacity to handle difficult and abrasive rock without the issues that can arise with other methods, such as excessive wear on equipment or inefficient drilling rates. The method also allows for the retrieval of rock samples, which can be beneficial for assessing geological conditions.

In contrast, other methods like Reverse Circulation Drilling, Direct Push Drilling, and Auger Drilling may be more appropriate for different conditions and materials. For instance, Reverse Circulation is used primarily for faster drilling in softer formations and has limitations when it comes to very hard rock. Direct Push may lack the necessary force and is typically more applicable in unconsolidated materials or soft formations. Auger Drilling, while effective in some scenarios, is not designed for hard rock and can struggle to create the necessary boreholes in these tougher geologies.