# Impact Characteristics of a Bidirectional Pneumatic DTH Hammer for Unconsolidated Formations
## 6 Conclusions  
To leverage the advantages of DTH hammer drilling and deal with accidents of drilling tools sticking or burying in unconsolidated formations, a bidirectional pneumatic DTH hammer was designed to drill boreholes using forward impact rotary drilling and retrieve sticking drilling tools from boreholes using a backward impact. A floating gas distribution mechanism was applied to change the impact stroke of the DTH hammer piston. With a larger impact stroke, the piston could impact the drill bit forward with high speeds to drill boreholes. While changing to a smaller stroke, the piston impacts the gas distribution valve backward, and then the upper shaft sleeve breaks rocks above the DTH hammer to help in releasing the sticking drilling tools. According to the structure and operating principle of the bidirectional pneumatic DTH hammer, a physical model was established based on the pneumatic transmission theory. With the SimulationX software, a simulation model was constructed using pneumatic transmission module components. The velocities, displacements, and impact energy of the piston were analyzed, with several main factors being considered including piston mass, the total weight of the DTH hammer, compressed air pressure, and the lifting distance of the inner tube assembly. From the analysis results, an increase in piston mass leads to a decrease in the piston impact frequency and peak impact velocity, but the results show a negligible effect on impact energy. As the total weight of the DTH hammer changes, there is little variation in the piston impact frequency, peak impact velocity, piston displacement, and piston impact energy. While increasing the gas source pressure, the piston impact frequency, peak of impact velocity, velocity  
Figure 17: Field experiments.  
reduction amplitude, piston upward end point, and piston impact energy all increase. For the backward impact process, as the lifting distance increases, the peak impact velocity increases, thereby increasing the acceleration distance. Therefore, a piston mass of 18 kg, total weight of 125 kg, gas source pressure of 2.2 MPa, and lifting distance of 60 mm for the backward impact were recommended. To verify the operating performance of the DTH hammer, a set of bidirectional pneumatic DTH hammers were manufactured and tested in gravel formations. During the experiments, the bidirectional DTH hammer was in good working condition. The maximum drilling rate can reach up to 1.5 m/min, and the actual bit on the bottom time was much shorter than the auxiliary time of adding drill pipes. By lifting the DTH hammer away from the bottom of the borehole and pumping compressed air, the DTH hammer piston can achieve a high frequency backward impact. There are no drilling tools' sticking or burying accidents. The above results indicated that the bidirectional pneumatic DTH hammer can effectively form boreholes in loose formations and deal with drilling tools' sticking or burying accidents.  
Methodology, Y.S.; software, Y.S. and C.L.; investigation, Y.S. and S.H.; writing--original draft preparation, Y.S. and S.H.; writing--review and editing, Y.S. and S.H.; project administration, Y.S.; funding acquisition, Y.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Natural Science Foundation of Anhui Province (2108085 QE210), Natural Science Foundation of the Anhui Higher Education Institutions (KJ2019A0102), Academician Workstation in Anhui Province, Anhui University of Science and Technology (2022-AWAP-05), Major science and technology projects in Anhui Province (202203a07020009, 201903a05020012), and Scientific Research Foundation of AUST.  
Not applicable.  
The authors declare no conflict of interest.