| Sallow geothermal energy is green and renewable sources of energy. It doesn't only have a wide distribution and a large reserve, but also is clean, environmentally-friendly and reproducible. Further, its exploring doesn't be affected by using areas and the seasons. Vigorously developing and exploiting sallow geothermal energy has major significance for satisfying the energy need of all the world, improving energy structure, alleviating environmental pollution, fulfilling the target on energy conservation and reduction of pollutant emissions of all countries and promoting the sustainable development of eco.At the same time, developing an effect environmental drilling method, just applying to geothermal hole, is very important. Then, the drilling technology of percussion-compact DTH hammer solves this drilling problem, and builds a strong foundation for exploiting and widely using sallow geothermal energy. Additionally, the drilling technology of percussion-compact DTH hammer also has a wide field of application with good prospects on geotechnical anchor engineering, no open-digging laying pipeline engineering and pile foundation engineering.Percussion-compact DTH hammer is an effect environmental drilling technology, and design on exterior structure of percussion-compact DTH hammer is the key. The exterior structure of percussion-compact DTH hammer contacts with soil around during the process of percussion-compact-rotary drilling. Therefore, the optimum design on exterior structure will improve drilling effect of percussion-compact DTH hammer.This paper just based on "Research on applying of an effect environmental drilling technology in exploring of sallow geothermal energy". After analysis on the effect environmental drilling technology of soft formation, mechanical model and finite element model of soft formation and exterior structure of DTH hammer were built and analyzed on numerical simulation. The forming reasons of "pile effect" were analyzed through dynamic simulation methods. Cam spinning bit, outer and tail structures were optimum designed, and the theory of surface non-smooth was applied to outer structure design. Based on experimental data, the parameters of exterior structure of the CJ-130 percussion-compact DTH hammer were defined. All these played an important part in exploiting the sallow geothermal energy. The main research contents and conclusions contain:1. Based on the theory of damage of soil body, combining the dynamic character of soil under live-loading, the forming reason of "pile effect" was analyzed from mechanism, and the numerical simulation of the "pile effect" was done, during which its forming process was observed. The continuous dynamic simulation of optimized nine multiple diameter drill pressing soil was analyzed, and then, the same analysis on Cam spinning bit was completed. The difference of pressing soil mechanism between these two drills was compared. Next, comparative trials were completed among circular cone bit, multiple diameter drill and cam spinning bit. The results showed that cam spinning bit had the top drilling effect, multiple diameter drill takes second place, and circular cone bit was the last. The reason of the cam spinning bit with high effect was conclude combining simulation and experiment. Given this, some improvements of cam spinning bit were done. I designed five cam spinning bits, including buttons well-distributed front cam spinning bit, buttons spiral-distributed front, unilateral channelized, double sided channelized and spiral-distributed channelized.2. Based on the result that outer tube effects on drilling efficiency is three times than that of drill, the outer tube structures, such as different angels of oblique edge, different slenderness ratios, different numbers and places of wide diameter, effects on drilling depth were calculated by use of ANSYS/LS-DYNA. The results deduced the best parameters. That is, the angel of oblique edge was 20°, the slenderness ratio of one wide diameter was 1.54, the slenderness ratio of two wide diameters(front-middle) is 1.42, the slenderness ratio of two wide diameters(front-back) is 1.35, and the slenderness ratio of three wide diameters is 1.15. All these drilling efficiency were higher than that of the same diameter outer tube.3. On the base of theory researches and numerical simulations, looping type test pieces of outer tubes were manufactured, and test-bed was built. Many compared experiments were made, including the angel of oblique edge, the slenderness ratio and the numbers and places of outer tube with one wide diameter, outer tube with two front-middle wide diameters, outer tube with two front-back wide diameters and three wide diameters. The end results deduced the best angel of oblique edge was 20°, the range of wide diameter was 2～4mm, the range of the slenderness ratio was 1.4～1.6. And the reasonable number of wide diameter is 1～2. The three wide diameters will be not consided.4. Test piece of outer tube withΦ34mm was secondary manufactued. Together with looping and matrix, it was made new sample of two or three sections joined. And the second compared experiments were made. As is shown from the results, the synergic parameters of exterior structure of the CJ-130 percussion-compact DTH hammer provided reliable test data for the following research. That is, the angel of oblique edge was 20°, the diameter of wide section isΦ134mm,the length is 201mm,the number of wide section is one and it situated at the bottom.5. Optimum designs on rear axle housing, castellated shaft and air Distributor of tail structure of percussion-compact DTH hammer were researched. As a result, the function of axial alignment self-locking came true in the tail structure. And it solved the discontinuous-"working on and off" problem of percussion-compact DTH hammer. In other words, continuous and effect drilling was carried out. At the same time, the simulate theory of surface non-smooth was applied to the surface design of outer structure. Then, experiment on exterior structure with non-smooth simulation surface was made. The results showed that drill with simulation surface of steel pit, and outer tube and tail structure with simulation surface of notch would help to improve drilling efficiency.The main innovation points in this paper contain:1. The forming process of "pile effect" was dynamic simulation analyzed by the non-linear finite element solver ANSYS/LS-DYNA, whose calculation is explicit, aided with implied. The drilling process of nine multiple diameter drill, cam spinning bit and the wide diameter outer tube were simulated by the same means.2. Optimum design on exterior structure of percussion-compact DTH hammer was done, borrowing ideas from pipe boots structure. The parameters of wide diameter outer tube were determined from numerical simulation and experimental research. And the drilling efficiency was improved.3. Flank spline, transferring from circumference direction, was applying to the tail structure of percussion-compact DTH hammer. So it solved the discontinuous problem of percussion-compact DTH hammer. The simulate theory of surface non-smooth was applied to the surface design of outer structure. The simulation surface helped to improve drilling efficiency of percussion-compact DTH hammer.
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