امکان‌سنجی استفاده از دوغاب زیستی برای تثبیت ماسه های روان در مناطق کویری با رویکرد حفاظت از بقایای باستان شناسی

Archaeological sites in desert areas are at risk for destroying and reburied with sand dunes by sand storms. One of the most important issues for archaeologist and conservators in these regions are maintenance of archaeological remains, during the excavation process and after it, There are several sand dune stabilization methods such as mechanical dune stabilization, mulch or protective screen, aerodynamic method and biological fixation (woody and grassy species, planting). However they are mostly expensive and time consuming and may have some harmful effects on environment. In this regard, the bio-grouting technique which produce calcite cements are new approaches to consolidate land in geotechnical engineering. This method has created a potential for archaeological conservation, stabilization procedure for sand dunes or soil. This method works according to the chemical reactions of natural non-pathogenic microorganisms that exist in the soil. The main objective of this research work is to evaluate the possibility of using biological stabilization with calcite-forming bacteria, for consolidating of sand dunes in desert areas with an approach in the conservation of archaeological remains, and archaeological conservation during and after the excavations. In this case sand grains/soil particles are coagulated and make a more dense soil with higher mechanical properties than natural condition. Biological stabilization of sand dunes and soil has been conducted with Sporosarcina Pasteurii Bacteria. When this bacteria supplies with suitable substrates, micro-organisms can catalyze chemical reactions in the subsurface resulting in precipitation of inorganic minerals. These bacteria could microbially catalyze hydrolysis of urea and calcium carbonate reaction when it is cultivated with enough nutritions under proper environmental conditions at laboratory and then it is located on the soil surface with other reactive substances. It results a scaffolding calcite between soil/sand particles. The best reactive environment is achieved at pH 7-9, temperature of 25 °C to examine the depth of penetration of biogrout, a cylindrical mold (PVC) tube (by 1 meter high) is filled with dry sand and consolidates with bio-grouts. The results show that the measured depth of bio-consolidation is 50cm in dry sand. Soil density is 1.6gr/cm3; the permeability of soil is smaller than the normal condition. To control the functional rate and also surface resistance of biogrouted sand, the standard penetration test with 250 g plummet in the dry and wet conditions have been examined. The results of this test show that bio-consolidation was successfully conducted and depth of plummet penetration becomes negligible.