Stress compacted bentonite

Compacted bentonite blocks were manufactured by compacting statically in appropriate moulds a crushed bentonitic rock under vertical stresses of 40-45MPa. The average values of water content and dry density of all the manufactured blocks are 14.4% and 1.69 g/cm , respectively. 

The space between the drift and the heaters is fdled by blocks of compacted bentonite with a smectite content in the range of 88%-96%. The test is heavily instrumented with measurements of temperatures, relative humidity (equivalent to total suction), pore pressures, displacements, and stresses. 

Three tests on bentonite compacted at an initial dry density of 1.7 g/cm with its hygroscopic water content have been performed at different temperatures (20, 40 and 60 °C), following the suction and stress paths indicated in Figure 4. In the first step, under a vertical load of 0.1 MPa, the suction of the sample was equalised to 14 MPa (due to mechanical limitations of the cell, this is the maximum suction that can be controlled). Afterwards, keeping this suction constant, the vertical load was increased up to 5 MPa. Under this vertical load, suction was decreased by steps until... 

Figure 5 shows the volume change measured in the samples loaded at different temperatures keeping their water content constant. As it has been observed in saturated materials, the temperature increases the compressibility of the bentonite. A certain reduction in the size of the elastic domain with the temperature can be observed (Hueckel Borsetto 1990), despite the fact that the vertical stresses applied are smaller than the compaction load. 

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