Laboratory Testing on High-Sodium Nondispersive Clays as Related to the Repair of a Clay Dam in Algeria

A 10-km-long homogeneous dam needed repair before filling as extensive cracking and slides occurred soon after completion. In order to design the repair, two sorts of clays were investigated: a gray plastic expansive clay constituting the old dam and a red sandy clay for the repair works. After Soil Conservation Service (SCS) tests and chemical analyses on the saturation extract, dispersiveness of the gray clay was feared, but pinhole tests proved it to be nondispersive. This allowed substantial savings on the design of the repair.

The red clay, after SCS tests and chemical analyses on the saturation extract, should not be dispersive. Pinhole tests gave dispersive reactions on air-dried specimens but nondispersive reactions on specimens at natural moisture content. Correlatively, the sodium content in the saturation extract decreases while calcium and magnesium content increases when air drying the red clay.

The conclusion may be that dispersiveness of a clay is more a result of the sodium that adheres to the clay particles than the sodium dissolved in the pore water.