Research On Multi-process No-circulation Foundation Drilling Techniques

The history, status and problems are analyzed of auger boring. Studies and experiments demonstrate that multi-process no-circulation foundation drilling techniques can be used to drill a variety of formation such as soil, sand, silt, rock. In addition, multi-process auger-boring can be carried out in a borehole with different methods and accessories to achieve economy, high ROP, and environment protection, providing energy-saving and environment conservation. The process has changed the traditional method of one bit and one method in one borehole.The multi-process no-circulation foundation drilling techniques is highly adaptable to various formations, and drills faster than the conventional methods by 2 to 4 times. It drills holes ranging from 0.5m to 2.5m for various foundation piles without limitation of foundation types and sites. There is no circulation in drilling with only a little amount of mud for wall protection without pollution to the environment. It is economical and environment-friendly. It produces little settlements at the bottom, less disturbance and erosion of mud to the walls. It provides a high rate of quality boreholes and meets requirements of various foundation piles.A total of 11 series in 4 categories of no-circulation foundation drilling techniques have been designed through studies. BSS and AGS auger-boring tools of different structures are selected to drill different soil and formation with different water contents. For boulder formation, special designed BSG can be used. For rock formation, either BSR, AGR, or CB, CAB can be used.Detailed analysis is made of four categories of drilling tools with study and design of the key elements. The design of the closing and opening mechanism is reliably simplified for auger boring tools with different designs of the bottom plates employed in respect of different formation. A tray-type reinforcement device is incorporated into the auger bit and a ROP limit and fixed cutting device into the auger bit for permafrost. Tests have proved that the above-mentioned structural designs are reliable and contribute a lot to increase in ROP and service life.Also a CBA local air reverse circulation tool is designed with the required air pressure and consumption calculation formula given. Field tests demonstrate that the formula is proper with ROP 2 to 4 times higher than other tools and max. ROP up to 1.83m/h in medium weathered sandstone and 0.8m/h in slightly weathered sandstone.Examination and design have also been made of the auger type under-reaming tools, in particular, design of the torque-transfer mechanism of the rock under-reaming bit, the box-type structure of the reaming wings, swivel-type bottom plate, which has tackled the difficulty of the strength problem in design of rock under-reaming tools. Field tests indicate that the auger-type under-reaming tools can be used in construction of under-reamed piles in various formations.