The Pore-forming Mechanism Study Of Cam Bit On Percussive-Rotary Extruding DTH Drilling

The DTH hammer percussion-extruding drilling is a high efficiency drilling technology, which can cut-in and crush soil through the impact force produced by hammer. Meanwhile, under the high frequency impact of hammer, the soil can be made liquefy and the original structure of soil can also be destroyed and then the bit will drill forward easily. Comparing with other drilling methods, this drilling technique not only has the rapider construction speed and higher drilling efficiency, but also has the smoothness, stability and good quality of the hole wall. At the same time, it has the merits of compact drilling, vibration drilling and air drilling. So it is widely used in many fields such as geotechnical anchoring engineering and pipe-laying of trenchless technology engineering, and it has good application prospects.At present, conical bit and stepped bit are widely used to carry out the DTH hammer percussion-extruding drilling in the geotechnical anchoring engineering and pipe-laying of trenchless technology engineering. In the low confining pressure or loose ground, it has high efficiency to use conical bit or stepped bit to drill, and also it needs a lower feeding pressure for drilling rig. However, when it drills with the increase of confining pressure or in the medium-hard formation, the drilling speed decreased significantly, sometimes even lead to a phenomenon without any footage, and it also was called for"the pile effect"phenomenon.On the other hand, for normal compacting bit, when it drills the powerful torque of drill rigs was just to be used to overcome the friction between bit and soil, and conquer the effect of water cut adsorption force among the soil, but not to be used to cut-in and crush soil, and this will arise low economical. If the powerful torque were used, the drilling speed and efficiency would be bound to greatly increase.According to the above"pile effect"phenomenon and the need of powerful torque, and on the base of comprehensive analysis of international products and literature, we design a new eccentric cam spinning bit by using experience of soil-rolling device's soil-compacting mechanism for reference. This special bit changes its normal squeeze soil method, which is not like the conical bit to distribute pressure uniformly, but concentrates the pressure on soil. The static pressure, impact force rotary pressure, which were passed by drilling tool from external, have the same effect on soil, so the drilling speed becomes faster. In addition, the soil mainly flows in the radial direction because of the spinning effect caused by cam bit, which is not like the conical bit that squeezes soil below the bit, so the axial stress concentration bulbs will be reduced, thus it can achieve the goal of overcoming"the pile effect"phenomenon.This dissertation is carried out on the combination of Jilin province Science and Technology Bureau project- Study on the basic theory and practice of air drilling fluid mechanics. Based on the Drilling Technology, Rock and Soil Mechanics, Mechanical Principle and Finite Element Analysis and so on, we do lots of research design and analysis soil-squeezing mechanics about the eccentric cam spinning bit systematically, and the main contents are as follow:Firstly, developing an eccentric cam spinning bit structure by using experience of other Countries for reference, and this new novel bit has advantages of high drilling speed and good guidance quality. Designing cam moving curve by its moving discipline, soil was equal to be rotated and squeezed in the radial direction around the bit, and it was beneficial to flow in the radial direction for soil, thus the new cam spinning bit can overcome the problem of"the pile effect"effectively, and is of significance to improve efficiency in DTH hammer percussion-extruding drilling technique in high confining pressure and medium ground.Secondly, the paper uses the finite element analysis software named ABAQUS to establish two-dimensional finite element model, and which is about the course of the DTH extruding drilling processes of cam spinning bit and conical bit. Through setting up Goodman element between bit and soil, the displacement and stress fields of the surrounding soil as well as the stress acting at the bit can be obtained, then the advantages of cam spinning bit has been tested further.Thirdly, designing an eccentric cam spinning bit and testing it outdoors, the experiment results are consistent with the ABAQUS simulation results. The results modeled by ABAQUS show that using three different bit including cam spinning bit, stepped bit, and conical bit in high confining pressure and medium ground, cam spinning bit is the fastest one, next to is stepped bit, and following one is conical bit.The innovations of the papers are as following:Firstly, the new eccentric cam spinning bit overcomes the"pile effect", and improves drilling efficiency greatly. It has a vast application prospect that use eccentric cam spinning bit to carry out DTH hammer percussion-extruding drilling technology in soil strata.Secondly, using ABAQUS to establish finite element model about the course of percussion-extruding drilling and make a comparative analysis of squeeze course on cam spinning bit and conical bit. Meanwhile, it should be further studied and widely used in the field of simulating drilling technology.