Interaction of the augercast micropiles with permafrost

Abstract

Owing to the current extensive exploration of the continuous permafrost zone which takes up no less than 25% of the entire land area and over 60% of the territory of the Russian Federation, the necessity arises to search for innovative construction technologies in view of bases and foundation engineering carried out in the cryolithozone.The article studies one of such technologies, i.e. the pile foundations built on permafrost employing the cement grout injection into the pre-drilled hole. The article reveals the investigation findings pertaining to the interaction of micropiles with permafrost. The investigation objective is to determine the mechanical and thermophysical properties of interaction for the micropile cement body with permafrost.Within the scope of the investigation presented herein a series of tray tests of the scaled augercast pile models in permafrost was carried out to assess their ability to withstand static pressing loads simultaneously measuring the temperatures in depth, as well as proceeding with the laboratory testing of mechanical and thermophysical properties of the injected cement grout, and thermal engineering calculations to determine the nature of thermal interaction of the micropiles with permafrost.Obtained are the values of the load-bearing capacity of the augercast piles and resistance of frozen non-saline soils to sustain the shear over the adfreeze surface with the cement body of the augercast piles; generated are the graphs of the temperature fluctuations in the course of the cement grout consolidation. The strength values for the cement body of the augercast piles built in permafrost are recorded. The time required to ensure the cement grout hardening to prevent its freezing is estimated; the temperature required for the cement grout used for injection is also determined.In consequence of the investigation, the recommendations are provided with respect to the augercast piles construction in the cryolithozone.