Experimental Studies Of Bit Rock Interaction For Rock Mechanical Parameters Indentification In Rotary Drilling

Drilling,as the initial stage of the rock-bit interaction in hard rock excavations,has a significant role in rock identification since drilling parameter changes would provide too much potential rock information.Drilling would therefore become a new in-situ rock mechanical parameters assessment technique in underground construction and mining.The goal of this study was attempted to present rock-bit interaction mechanism and the relationship between drilling parameters and the excavated rock mechanical parameters in rotary drilling.A serial of indentation tests and rotary cutting tests were first conducted on various rock samples with different drilling conditions(such as rock angles,thrust,and rotary speed)by a rotary drilling machine.Correlation analysis together with high-speed video analysis was carried out to understand the rock-bit interaction process and the influence of drilling parameters on rock fragmentation.In-situ drilling test were then performed using a modified drilling process monitoring system on a concrete hole to propose an index for rock strength recognition.A case study of Dehou reservoir,Yunnan Province was finally performed to show the capacity of this drilling process monitoring system in rock mechanical parameters identification.The main results are as follow:A 3D bit-rock fragmentation model by compression crack propagation was proposed to reveal rock-bit interaction mechanism and the relationship between maximum thrust and crack length on basis of indentation test results.Results also indicated that fragmentation efficiency obtained from spherical indenter are much higher than that of the conical indenters.Additionally,a high loading rate and brittleness could also lead a high rock fragmentation efficiency.During the rock cutting,the cutter shows a helicoidal trajectory in rock because of the simultaneous indentation and cutting process.It also found that there is a positive linear correlation between torque and thrust.While the magnitude of this linear slope is affected by the cutter movement condition,but not by the rotation speed.Specifically,a higher linear slope means lower rock drillability in the rotary stage.Additionally,a comprehensive analysis of the empirical relationships between rock mechanism parameters and drilling parameters has shown that rock compressive strength and tensile strength contribute significantly to the mass rock fragments and size of rock fragments respectively.According to the results of in-situ drilling tests,it has been proven that the newly drilling process monitoring system is suitable for field application because of improvement of sensors,data processing capacity including data noise reduction,data cleaning,and rock mechanical information identification by processed drilling data.The slope of the linear relationship between thrust and penetration rate per revolution could be used to define the strength parameters of stratification because it is only related to rock intrinsic specific energy and friction coefficient.Additionally,a modified specific energy model was proposed to obtain the optimal specific energy on basis of the relationship between drilling parameters and specific energy.The lessons learned in the Dehou reservoir permit us to define an effective comprehensive approach for delineating the general characterization of karst zones between two boreholes and locations of potential conduits for grout flow along the borehole.The proposed DBN model,trained by data collected using this comprehensive approach,could map the relationship between strata information and grouting quantities to show the capacity of this drilling process monitoring system in karst identification.