Feasibility study on method of rotary jetting pile-formation in firn with melting water in polar regions

Abstract:

It is of great significance to drill across the polar ice sheet and obtain subglacial bedrock samples for revealing the geological environment beneath ice sheet. The upper part of the polar ice sheet is generally covered with highly permeable firn. When drill in the firn， the compressed air and drilling fluid would leak into the surrounding firn if it is not reinforced， resulting in the inability to continue drilling operations. Therefore， it is necessary to seal and reinforce the borehole wall of firn in the process of sampling subglacial bedrocks. In this paper， a method of rotary jetting pile formation with melting water is proposed， and the theoretical analysis and experimental study were carried out. The research results show that in order to obtain a 0.4m borehole in firn， the lifting speed of the grouting pipe should be about 15~30mm/min. When the firn thickness is less than 100m， the temperature loss of meltwater during downward injection is approximately below 16℃. In normal conditions， the amount of water required for pile formation does not exceed 16 m³. In the cold polar environment， piles can be formed in the firn through the method of meltwater rotary jetting and refreezing. At the temperature of -15℃， the time for freezing into piles is approximately 60h.