The relationship between soil lithology and well failure is a function of hydrogeological properties or characteristic of the underlain strata which can be determined using varied groundwater geophysical prospecting methods namely electrical resistivity, Very low frequency electromagnetic fields, seismic refraction etc. A lot of publications both classified and free access are available e.g. Adabanija et al 2008 (Hydrogeology journal). Note however that other hydrogeological factors such as geomorphic and topography also play prominent roles and can be found in this article.

I actually asked the question so that we'll discuss; a survey was carried out and it reveals that the areas where wells and boreholes are drilled through sandy soil and fracture zones have sustainable aquifers for groundwater exploitation, while boreholes that are constructed through CLAYEY formation usually fail, check: Afuwai et al 2015 (Journal of Environment and Earth Science).

Yes, it is possible for boreholes drilled through clay to be dry, whilst deep wells dug through fracture (wet) and sandy formation to be highly productive. It is important to note that clays are not good aquifers whereas sandy clay and clayey sand are better aquifers than clay (relatively). On the other hand, sands are good aquifers hydrogeologically compared with either clay which in this context is more of an aquitard or sandy clay/clayey sand which are admixture of clay and sand depending on which proportion is higher. Furthermore, borehole yields is rather a functions of hydrogeological properties of the aquifers penetrated, fractures inclusive rather than depth.

Yes Adabanija, but rainfall intensity during the month of drilling has a direct influence on failure rates. It is essential that where drillers operate throughout the year, they should develop compensation strategies for seasonal drilling. This is likely to involve drilling to greater depth in wet season, but groundwater levels must be recorded in order to develop appropriate strategies for different geological environments.

Agreed that groundwater table rises during rainy season and drops in dry season. This does not indicate wells that are seasonal will not remain so because of the effect of piezometric pressure. No matter the depth of compensation, water in wells will never rise beyond their piezometric levels. It is also important to note that aquifers are at different depths in the surface and as such different aquifers of varied hydrogeological properties are penetrated. This is why deep sounding is necessary. This is however dependent on the use of the borehole, industrial, domestic or public utility.

The strong correlation among the rainfall regime, the piezometric levels, the rate of movements and the recurrence periods of critical cumulative rainfall on displacement trends are the most important factors.