Shear Strength of a Synthetic Transparent Soft Clay Using a Miniature Ball Penetrometer Test

This article is concerned with the properties of Laponite colloids, which are being used as a transparent surrogate for soft natural clays. Laponite is a synthetic smectite clay similar to natural hectorite clay that is made of magnesium lithium phyllosilicate (MLPS). The effect of aging on the shear strength of transparent soft clay formed from MLPS and water is presented in this article. A miniature ball penetrometer (MBP) was developed for this study. MBP tests were used to measure the shear strength of samples at three different concentrations of MLPS in water. Sodium pyrophosphate was used to slow down the flocculation of MLPS by altering its rheology, thus improving the transparency of higher MLPS concentration samples. Parameters that were studied included the water quality, aging, penetration rate, penetrometer geometry, and repeatability. The strength of clays made of MLPS was found to increase with MLPS concentration, depth, and penetration rate. Water quality had little effect on strength or transparency. Equations to predict the strength of MLPS based on constituents, age, and stress, as well as the effect of rate of loading, are proposed. The performance of the MBP test was also investigated. It showed excellent repeatability, although the shear strength measured was dependent, to some degree, on the penetrometer's dimensions as well as the rate of loading.