Investigating the effect of overburden on the erodibility of gypsum and anhydrite layers

The presence of soluble layers in the foundation of important structures such as dams, bridges and high-rise buildings, in case of being left untreated, may cause severe problems. These layers may easily be dissolved due to contact with groundwater flow, causing some cavities in the soil and settlement of the structure which in severe conditions may highly damage or ultimately lead to failure of the structure. Since nearly all studies carried out on soluble layers so far, have been concentrated on different factors influencing the solubility of the layers under free field conditions, the effect of overburden which roots from the weight of the structure may have an important and influential role in the phenomenon in many engineering projects. Therefore, to fill the gap in past studies on this topic, investigating the effect of overburden on the rate and types of solubility of the susceptible layers is of great necessity and importance. In the present study, the effect of overburden pressures on solubility and erosion of soluble layers has been assessed and investigated. The circulation tests on cubical gypsum samples taken from a mine in Semnan province, west of Tehran, have been carried out. At the same time, they were subjected to different overburden pressures in a new apparatus developed for this study. Cylindrical holes of different initial diameters from ۶.۵ to ۱۴.۷۵ mm. were cut in the center of samples for the flow passing through and the final diameters of the holes were measured after the electrical conductivity of the flow getting stable during the circulation test. Different flow rates, different overburden pressures and different diameters of holes have been examined and the electrical conductivity was monitored during circulation continuously. Based on the testing results, for relatively large initial hole diameters (eg: ۹ & ۱۲.۵ mm.), the electrical conductivity decreases as the overburden increases. For greater hole diameters the rate of decreasing the electrical conductivity decreases and nearly becomes constant by increasing the overburden. Nevertheless, the variations of electrical conductivity get an unspecific trend by increasing the initial hole diameter and the overburden pressure.

کلیدواژه ها:

Gypsum ، anhydrite materials ، Solubility ، titration ، circulation test ، erodibility ، overburden pressure ، Electrical conductivity