Gypseous soils are distributed in many regions in Iraq and other countries. Large damages that affect structures founded and constructed in or on them occur mainly due to the dissolution of the cementing gypsum. The change in porosity with time is studied herein. Laboratory oedometer permeability leaching tests are conducted using sandy soils with gypsum contents greater than sixty percent brought from Khan-Thare, Iraq. Analyses reveal a high effect of dissolution of gypsum on the settlement of structures founded on them.