ASTM International

Chemical Impregnation of Cohesionless Soils

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Existing methods to obtain and test high-quality undisturbed samples of cohesionless soil below the water table depend at some stage on freezing. This limits the range of application to relatively clean sands, and even for those soils the freezing operation is delicate, time-consuming, and costly. Moreover, there is no direct way to check, independently, the effects of the freezing process on the subsequent behavior of the sample. Recognition of these limitations motivated the search for an alternate method, namely, chemical impregnation. After many trials, agar, a natural polymer, has been identified as a potential impregnation material for developing an alternate sampling technique.

Agar powder dissolves readily in water at a temperature of about 85 to 95°C to form a clear solution of low viscosity. On cooling, the solution remains liquid until a gelation temperature of 35 to 40°C is reached, when the mass sets to a rigid gel even at low concentrations, such as 1% or less. The gel does not melt again when immersed in water or during handling, but it can be reliquefied at a temperature above the gelation temperature.

This paper presents the results of tests to examine the suitability of agar as an impregnation material to permit undisturbed sampling of sands below the water table. Field trials were made to demonstrate the feasibility of the impregnation process.

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