Abstract: In order to solve the problems of high loss rate of natural pillars and the inability of traditional artificial pillars to effectively contact roof in hard rock stope， a new pre-stressed expandable pillar was developed by using the volume increase characteristic of the self-developed expandable material after hydration reaction. Based on the laboratory and field industrial tests， the mechanical properties and load bearing mechanism were determined. The test results showed that with the increase of the amount of expandable material in the barrel-type expandable device under constrained conditions， its active support stress increased with a gradually increased increment， and it could reach 500kN under the conditions of full constraint and fully filled with expandable material. The pre-stressed expandable pillar had the advantages of short construction period(about 4h) and large active support stress(about 600kN). When recovering residual pillars in the room-and-pillar mining， the pre-stressed expandable pillars showed strain-hardening bearing characteristics， and the load on natural pillars was successfully transferred to the artificial expandable pillars. Under the conditions of ensuring the stope safety， economic benefit of the test stope increased by 1，700，000 CNY.

Key words: expandable pillar; active support; strain-hardening; pillar recovery; bearing mechanism