تاثير تزريق باكتري در كاهش سرعت فرسايش ماسه

Effect of Biogrouting in Reducing the Erosion Rate of Sand

روش زيست- تزريق، روشي نوين در مسايل ژيوتكنيك و اصلاح خاك بر مبناي رسوب كربنات كلسيم با استفاده از باكتري است. در اين پژوهش از باكتري Sporosarcina pasteurii براي كنترل فرسايش ماسه‌ي سيليسي استفاده شده است. همچنين از آزمايش XRD براي بررسي رسوبات ايجادشده بر روي نمونه‌ها و از دستگاه تابع فرسايش براي بررسي پارامتر فرسايش‌پذيري استفاده شده است. باكتري و محلول اوره به همراه كلسيم كلرايد به طور جداگانه بر روي نمونه‌ي ماسه تزريق شده و به مدت 24 ساعت به حالت اشباع در آمده است. سپس محلول‌ها از انتهاي نمونه با استفاده از پمپ، تخليه شده‌اند. در اين پژوهش تاثير هوادهي در داخل باكتري و محلول اوره، كه به صورت اشباع بر روي سطح ماسه قرار گرفته است، بر روي پارامترهاي فرسايش‌پذيري مورد ارزيابي قرار گرفته است. نتايج نشان داده است كه ضريب فرسايش‌پذيري ماسه تا 2 برابر در حالت تزريق به همراه هوادهي نسبت به حالت بدون هوادهي كاهش پيدا مي‌كند. همچنين تكرار تزريق نيز مورد ارزيابي قرار گرفته و ضريب فرسايش‌پذيري تا ??? كاهش پيدا كرده است. بنابراين اعمال هوادهي و همچنين تكرار تزريق باكتري و محلول كلسيم كلرايد باعث افزايش عملكرد روش زيست- تزريق در كنترل فرسايش خاك مي‌شود.

The simplest soil improvement processes are compaction and drainage. Other processes include improving the gradation of particle size and adding binders to weak soils. There are various treatment techniques available to improve the condition of poor or unstable ground by altering the nature of the soil in-situ. These methods are used when replacement of the in-situ soil is impractical because of physical limitations, environmental concerns, or is too costly. Biogrout is a new method in geotechnical problems and can induce soil improvement on microbial induced calcium carbonate precipitation (MICP). Biogrout may provide new opportunities for cost-effective and environmentally friendly processes. Bacteria produce the urease enzyme. This enzyme converts urea into ammonium and carbonate; finally producing calcium carbonate. The calcium carbonate forms a bridge between the sand grains, which increases the strength of the soil. In this study, the Sporosarcina pasteurii bacteria were utilized, an aerobic bacterium which exists pervasive in natural soil deposits, in order to control silica sand erosion. An XRD test was performed to evaluate the calcium carbonate precipitation. Erodibility parameters were obtained by erosion function apparatus (EFA). The test result consists of the erosion rate versus shear stress curve, and the slop of the curve is the erodibility coefficient, which represents the resistance of soil to erosion. Bacterial optical density (OD600) was 1 (8×107 cell/ml) and cementation included 0.5 M urea and 0.5 M calcium carbonate in all of samples. Bacteria and cementation were separately injected in soil and saturated for 24 hours, then, drained from the soil. The effect of aeration in the bacteria and cementation saturated in soil was investigated and results show that the sample with aeration decreased the erodibility coefficient twice as much as the sample without aeration. A repeat of grouting was investigated too and a reduction of erodibility coefficient was observed up to 95% for sample D (bacteria and cementation were injected twice at an interval of 5 days) Consequently, biogrouting shaving appropriate performance for is shown to have an appropriate performance in the control of sand erosion and can be used in the control of pier, contraction and abutment scour.