| The application of hollow DTH reverse circulation drilling technology in rock and soil drilling engineering is gradually catching people's eyes. It is looked as a new technology after diamond drilling technology and is one of the technologies which have most application scope. The technology of hollow DTH reverse circulation continuous coring drilling is one of directions of DTH drilling technology development. This technology centralizes three items of drilling technology which include DTH fracturing rock, fluent removal by reverse circulation and continuously obtaining sample in drilling. This technology uses double-wall drilling pipe. The compressed air is put into drilling hole through the gap of double-wall drilling pipe, the air which is expelled from DTH is returned to the ground carrying rock grain through the core of double-wall drilling pipe.The technology of hollow DTH reverse circulation continuous coring drilling has been researched by the construction engineering college of JiLin University since"seventh five"periods. The researching is never stopped and now has made this technology at the world advanced level. Now the construction engineering College of JiLin University has successfully accomplished the CGS's project"the research and development of high effective drilling technology under complex strata condition in the west of our country". Its working content is the applying research of hollow DTH coring drilling technology in prospecting for solid mine. This paper is the extended research of the project"the applying research of hollow DTH coring drilling technology in prospecting for solid mine". The contents of research are as follows:1. Based on the theory of percussive drilling, theoretic research on the rock's breaking mechanism of the hollow DTH reverse circulation continuous coring drilling further.2. Using finite element analysis software ANSYS and 3-D modeling software Solidworks make numerical simulation between rock and the bit of hollow DTH reverse circulation continuous coring drilling.3. Designing test device which could simulate the process of percussive-rotary drilling.4. Making experimentation on reverse circulation continuous coring bit with test device.5.Through the theoretic research, finite element analysis and the result of experimentation on action mechanism between rock and the bit of hollow DTH reverse circulation continuous coring drilling,the factors which influence the length of core is analyzed and the structure of the reverse circulation sample drilling bit can be optimized.By the way of combining the theoretic research, the numerical simulation and the experimentation, the mechanism of breaking rock and coring by hollow DTH reverse circulation continuous coring drilling is researched by the numbers.(1) In the aspect of theoretic analysis, the destruct character, dynamic analysis, crack expanding, destruct volume and the relation between the cumulate damage and the impact number of rock under many kinds of loading condition are discussed. Some conclusions are got.1)the character of the rock destruct process under static pressure, impact and both cooperation is bound with increasing of load.2) The time of loading the impact energy when static pressure and impact both cooperate is when the rock breaks in solid, the rock debris are out and the compact entity is pressed fully. The point is in the sect of load–incursive depth curve which slope is negative, and the best loading range can be confirmed by experiment. This loading rule has important directive function for improving the drilling parameter.3) The cut-in force composes by static pressure and impact, and has direct ratio with them. Impact energy in the cut-in force is in the pattern of wave which can be influenced by rock's character and parameter of breaking rock, so the perfect effect of breaking rock in deferent kinds of rock need deferent breaking rock parameter.4) The radial, middle and side cracks are made in the process of cutter in to the rock. The influence of side crack for breaking rock is biggest. The length of them has direct ratio with static pressure Ps and impact energy 2 mV1 ?γγ(1?γ)(hammer's quality and impact velocity) which can be calculated by expression. The expression can become the theoretical gist of optimizing drilling parameter and modifying structure of drilling instrument, and settle the theoretical base of designing the parameter of drilling instrument and drilling from experience to science.5) Initial stress damage by static pressure and impact before impact can reduce the fracture toughness property and rigidity of rock, make the destroy volume and the effect of breaking rock increased.6) Bringing crack in rock needs a critical loading and rock breaking also needs a minimal value. When the loading is less than the value, rock can not be damage. When the loading is bigger than the value, rock destroys in macro scope. When the wave energy between the two values, rock is damaged but can be destroyed by accumulative damage made repeat loading.7) In the friable rock, the perfect loading pattern is static pressure make the rock initial damage, impact make the rock destroyed. This rule explains the parameter which static pressure is assistance and impact is primary is reasonable.8) By analyzing the model of static pressure-cutting cut body and impact-cutting mechanics, base on the size of the impact distance, three situations of impact-cutting are discussed, and expression of every situation are confirmed. The expression settles the foundation on theoretically analyzing the improved pole-patch mix enchase bit.(2) In the aspect of numerical simulation,the action mechanism between bit and rock is simulated by finite element analysis software ANSYS/LS-DYNA first. The key file used in the analysis is also introduced particularly. Some conclusions are got from the analysis.1) The biggest influence in making rock core with reverse circulation continuous coring bit whose type isФ89 is the sphere tooth in the second circle of the bit which destroy the rock first, but isn't the sphere tooth in the center of the bit which solders aslant.2) The analysis result of breaking rock by sphere tooth in second circle which the character of the rock destruct process is bound, accords with the character of the rock destruct process under cooperation of static pressure and impact. It accounts for that there is resemblance between numerical simulation and fact, so the result can be the reference in the qualitative analysis at least.3) The process of breaking rock by sphere tooth in second circle as follows. The concentrative area of stress under the two sphere teeth which is half ball is made first. The Hertz cracks are made along the direction of extending the sphere of stress. Small pit is produced on the surface of rock. Then later the sphere of stress becomes flat and long and continuances period of time. Little elastic distortion in rock makes. Then the radial cracks become along the direction of stress extending with the stress around the sphere teeth increasing. Because the rock is in the plastic state after in the elastic state and the radial cracks expands to the surface of rock, the volume destroy of rock comes on. This is the process of making and developing the concentrative area of stress for second time in picture of stress. Then another bound circulated process begins until the loading process ends. Uninstall process is the phases of side cracks making and developing which can make at the area has big remnant stress and extend the direction of stress extending. From the way of remnant stress distributing, there is a trend which the side cracks extending to the bottom of the rock core. Although it makes in the first time, the cracks can run through at a moment with accumulative damage in rock making time after time, and the rock core break completely.4) Analyzing the process of bit breaking rock with big impact work, there are concentrative areas of stress which extend inside around the rock core and which make for stress adding at the center of two sphere teeth in the rock. The process of rock core breaking with big impact work can be guessed as follows. The cracks which makes around the rock core can produce small shiver first, then the cracks in the center of rock core can produce big breaking, but the rock core may be short because the position of cracks in center is not deep. It means long rock core can not be made in big impact work.5) Along with the increasing of impact work, the size of concentrative area of stress becomes big, which can reach the size of stress making the cracks need easily. And also along with the run-through between the concentrative area of stress around rock core and the concentrative area of stress making for stress adding, the cracks run through faster, namely the rock core makes faster but is not long.6) For reducing the influence of this kind of bit making rock core, two new bits are designed. They are the bit with two cone-shaped sphere teeth solder in center protuberant and the bit with pole and patch mix enchasing.7) Comparing the analysis of the new bits with the analysis result of the actual bit, the influence in making rock core by new bit changes, because the shape and size of the concentrative area of stress for breaking rock is different. There is advantage for increasing the length of rock core. It means the two bits with new structure should be tried and experimented more in aspect of increasing the length of rock core.(3) In the aspect of experiment, for researching the influence which the impact work, impact frequency, drilling pressure, rotate speed, structure of bit and shape of tooth to the effect of breaking rock and the length of rock core, opening out the mechanism and process of breaking rock with impact-revolving drilling, validating the result of definite analysis, the experiment device which can simulate the impact-revolving drilling for breaking rock is designed. This device uses the actual bit and can be control by man whose parts is designed considering the influence in experiment result. This device is the basic for experimenting go on wheels.The experiment using the reverse circulation coring bit and the experimental device for simulating the impact-involving drilling, in which the rock core has border, proves the experimental device can simulate the actual drilling state.The experiment with deferent rock proves the theory of accumulative damage in theoretic analysis and the character of rock breaking, validates the deduction in simulative analysis. The deduction is that the second circle teeth in the bit have big influence in making rock core, the structure of bit must be improved and the mechanism of making rock core must be changed radically. The process of making rock core in deferent impact work proves the deduction in simulative analysis with deferent impact work. Because the cracks make and develop making by the concentrative area of stress, the breaking of rock core becomes and the length of rock core determines by the situation of the crack making. The long rock core becomes not easy in the condition which the bit has old structure.The innovative key point of this paper is as follows.1. The finite element analysis software ANSYS/LS-DYNA for analyzing the nonlinearity dynamics is used to simulative analyze the action mechanism between bit and rock first. And the key file used in the analysis is introduced particularly.2. By the way of combining the theoretic research, the numerical simulation and the experimentation, the process and mechanism of breaking rock and coring by hollow DTH reverse circulation continuous coring drilling is explained, especially the process of making rock core.3. The experiment device for simulating the state of breaking rock by impact-involving drilling is established. This device uses the actual bit and can be control by man. Through the experiment of reverse circulation bit whose type isΦ89, proves the device can simulate the actual drilling state.4. For increasing the length of rock core, two new bits are designed. They are the bit with two cone-shaped sphere teeth solder in center protuberant and the bit with pole and patch mix enchasing. This kind of research is not found interiorly, is a creative work, and must be perfected more.The theoretical study on action mechanics between rock and bit under the condition of impact-involving drilling is elementary. For simplifying the model during numerical simulation, just the sphere teeth contacting with rock is considered. But the action mechanism between bit and rock is very complex in real case. In order to simulate the action process of bit and rock actually, the sequence of reach tooth breaking rock must be analyzed particularly, and the 3D model of bit and rock in the hole must be found. Then analysis can be made considering static pressure, impact load, cornering force together working. But restrict with the development of computer technology, this simulation can not be done, need to be discussed and researched more deeply. The experiment device of researching the impact-involving drilling is basic in the aspect of experiment. The testing and operation must be improved to make the test function completer and the operation simpler.Because the time is short, the research of making rock core with deferent parameter and bit is elementary, need more discussion and experiment. In a word building precise mathematic model to realize the numerical calculation exactly needs abundant deep particular research, gets a mass of data which needs many scientists put their efforts insistently.
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