Technischer Bericht NTB 86-13

In this report the results are presented of swelling, permeability and shrinkage tests on quartz sand-bentonite mixtures. The bentonites used were those previously investigated, i.e. the Na-bentonite MX-80 and the Ca-bentonite Montigel. The selected quartz sand exhibited a steep grading curve in the range 1 to 1.5 mm. The bentonite content was 35 % and 45 % respectively of the mass of the dry quartz sand.

Measured swelling pressures are represented in function of the dry density of the bentonite included in the pores. The test results were in good agreement with those of the tests on pure bentonite.

Measurements of the hydraulic conductivities of the studied quartz-bentonite mixtures gave average values in the range 2 to 3 × 10^-10 m/s. These values are about 10⁴ times higher than those measured on pure bentonites.

Compared with pure bentonite, the amounts of shrinkage measured on bentonite-quartz sand mixtures are very low, especially on mixtures with Montigel. For the examined domain, the secondary shrinkage s' of the compacted specimen can be calculated with the formula s' = s ⋅ w ⋅ ρdo / ρw, where s = 20 ± 4 % for mixtures with MX-80 and s = 5 ± 2 % for mixtures with Montigel. Considering the measured shrinkage amounts we can assume that, with the chosen bentonite contents and the achieved dry densities, an intergranular contact between the sand grains has been reached. In the tests with previous free swelling in a humid room, the amounts of shrinkage are higher. In this case mixtures with Montigel gave higher values then those with MX-80.