Borings for observation well, such as the one shown in Figure 3.21, are normally

Question

Borings for observation well, such as the one shown in Figure 3.21, are normally sealed ith an impervious cap near the ground surface. This cap prevents significant quantities of surface water from seeping into the well. For convenience, manufacturers supply a pel letized clay that has been dried and formed into 10-mm diameter balls. The driller pours these balls into the boring and adds water. As the clay absorbs the water, it expands and seals the boring. What type of clay would be Would other clays produce less satisfactory results? Why? ther most appropriate for this purpose? Why?

Explanation / Answer

Bentonite clay would be the most appropriate clay for this purpose.

Bentonite contains the clay mineral called montmorillonite. When it is mixed with water it in the boring well it swells and becomes gell like, thus sealing the boring tight. Because of its gell like and plastic nature when mixed with water it does not flow or get washed away thus acting as a good sealant. As known clay has very low permeability it works as a very good sealant.

Other types of clay would not provide the satisfactory result as they would get washed away due rains and also although these clays they would not seal the boring because they are not expansive as the bentonite clay.

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