Abstract
Locked sand is a material with unusual geomechanical properties (Dusseault - Morgenstern 1979): rela- tively high unconfined compressive strength, high internal fric- tion angle but very low tensile strength. These properties arise from the lack of permanent cement, andinterlockedstructure of quartz grains.
At least some of the locked sands are load stabil- ized, which means that load protects sand from disintegration. In the Czech Republic the load stabilized sands were not studied with the exception of Střeleč LockedSand(Bruthans et al. 2014).
The purpose of this paper is to introduce several load stabilized sandsites in the Czech Republic, andto describe their properties, namely long-term stability of underground passages, and at the simultaneously time, rapid weathering and erosion of the same material on the ground surface.The presence of loadstabilizedsandwas testedat Nevřeň and Hosín sites on kaolin sandstone, where extensive mine passages were created, which did not collapse when flooded (Figs 1, 2), and Střeleč, Rudice and Běleč sites in quartzose sandstone (Ta- ble 1). Buckland/Reigate site in Englandwas usedfor comparison.
Sands were sampled by low speed dry drilling with a diamond core bit 80 mm in diameter. Material characteristics were tested by flooding the cores by three different ways (Fig. 3): A) flooding the core with free sides; B) flooding the core with a cylindrical side wrappedin foil (-10 kPa compressive stress); C) flooding the core in foil in concrete sleeve (not penetrating the sample).
Sandstone shouldbe stable in all three cases. On the contrary, common sand should disintegrate into angle of repose under all three cases.Only load stabilized sand should decay in the first case, but it should be stable under cases B and C as outer stress avoids disin- tegration of sand structure by slaking (Fig. 3; Bruthans et al. 2014).