However, there are three drawbacks to the anti-permeability
strength that can be identified from this study:
(a) the number of test samples was not enough; (b) the
testing experience is considered insufficient at the current
time and (c) it does not take into account other influencing
factors such as confining pressure, physicochemical
properties, the ratio of sample height to diameter, the
size of the sectional area, porosity and the degree of
saturation. It is worth noting that the confining pressure
must be considered in applying the anti-permeability
strength unless the clay layer is thin like that at the
researched site. If not, results are possibly that the thicker
the engineering field is, the higher the risk is of subsidence
sinkholes developing.