ارزیابی کارایی روش سیمانی سازی زیستی در مقاوم سازی ماسه های روان به منظور مقابله با فرسایش بادی

نوع مقاله : پژوهشی اصیل (کامل)

نویسندگان
حمیده غفاری
سید محمد علی زمردیان
دانشگاه شیراز
چکیده
فرسایش بادی و به­تبع آن پدیده ریزگرد با وجود همه راهکارهای مقابله با آن، امری اجتناب‌ناپذیر است. بنابراین بررسی و بکارگیری روش‌های نوین جهت مقابله با این پدیده طبیعی که بیشتر منشأ فرامنطقه­ای دارد بایستی بیشتر موردتوجه واقع گیرد. در همین ارتباط در این پژوهش از یک روش نوین و سازگار با محیط زیست که از باکتری­های موجود در خاک به منظور بهبود خواص فیزیکی خاک استفاده می­کند بهره­گرفته شده است. بنابراین از گونه­ای خاص باکتری با نام علمی Sporosarcina Pasteurii، با قابلیت تولید آنزیم اوره­آز که موثر در فرآیند رسوب میکروبی کربنات کلسیم می­باشد، به بررسی میزان مقاومت فشاری خاک در برابر فرسایش بادی پرداخته ­شد. در همین راستا، از یک دستگاه نفوذسنج جیبی به منظور کمی­سازی میزان مقاومت فشاری خاک، و همچنین یک دستگاه تونل باد، به منظور شبیه سازی میزان فرسایش پذیری گونه­های خاک­ در طیف وسیعی از سرعت باد (با دامنه 1-20m/s)استفاده گردید. به منظور در نظر گرفتن شرایط فیزیکی و شیمیایی خاک بر میزان بازدهی این روش، از دو گونه خاک ماسه سیلیسی با دانه­بندی متفاوت و همچنین یک گونه خاک ماسه­ای با منشا کربناته استفاده شده است. پارامترهای مورد بررسی شامل زمان­های نگهداشت 3، 7، 14، 20 و 28 روز، تزریق مجدد محلول باکتری و سمنتاسیون با فاصله زمانی 6 روز و همچنین تأثیر شرایط محیطی بر میزان اثرگذاری باکتری در خاک می­باشد. همچنین از تست SEM برای بررسی ریزساختاری خاک­ها قبل و بعد از بهسازی استفاده شد. نتایج حاصل از بکارگیری دستگاه نفوذسنج نشان داد که مقاومت فشاری خاک به صورت معنادار با زمان افزایش می­یابد که بیشترین مقاومت در ماسه کربناته به میزان 84 kPa حاصل شد. ماسه سیلیسی با توزیع دانه‌بندی ریزتر مقاومت فشاری بیشتری نسبت به گونه دیگر آن نشان داد. همچنین این نتایج نشان داد که تزریق مجدد، تأثیر افزاینده‌ای به صورت معنادار در مقاومت فشاری خاک به ‌خصوص در ماسه سیلیسی به اندازه 190% در دوره 28 روزه دارد. نتایج حاصل از شبیه­سازی میزان فرسایش در دستگاه تونل باد نشانگر عملکرد بسیار مناسب این روش در بهسازی خاک و ایجاد لایه مقاوم سطحی نسبت به فرسایش می­باشد به گونه­ای که هیچ گونه فرسایشی در دامنه سرعت­های موجود مشاهده نگردید.

کلیدواژه‌ها

موضوعات

عنوان مقاله English

Investigating Performance of Biocementation Method in Stabilization Sand Dunes for Dealing with Wind Erosion

نویسندگان English

hamideh ghaffari
Seyed Mohammad Ali Zomorodian
Shiraz University
چکیده English

Wind erosion and the phenomenon of Dust with all of its controlling methods is serious problem. This phenomenon lead environment degradation and fugitive dust storms. So, Study and use of the new methods to control this natural phenomenon is essential. In this study, the novel and environmental friendly method of soil biological stabilization was investigated with using an abundant bacterial species founding in nature and soil deposits. The scientific name of this bacterium is Sporosarcina Pasturii (PTCC 1645) and uses as the urease-positive bacterium. This bacterium produce urease enzyme which converts urea to ammonium and carbonate, resulting in the precipitation of calcite crystals that bridge the soil particles. In this study a mixture of cementation and bacterial-cell solutions uniformly sprayed onto the exposed top surfaces of the soils. The concentration of bacterial-cell solution was quantified in terms of its optical density at 600nm wavelength (OD600) which equal 1.5 (that is, approximately 1.5×108 bacterial cells·ml−1). The prepared equimolar urea–calcium chloride cementation solution included nutrient broth (3g.l-1), ammonium chloride (10g.l-1) and sodium bicarbonate (2.12g·l-1) prepared at 0.5M concentration. The mixture volume sprayed onto each specimen was equal to 1.5Vv (where Vv is the pore voids volume of the topmost 3-mm thick layer of the 20–mm deep loose sand tray-specimens). The bench scale experimental programme presented investigates the proposed technique’s effectiveness for stabilisation of two clean, angular to sub-angular medium silica sands and carbonate silty sands with different gradations (sand t60 and sand t90 with size ranges of 0.125–0·50 and 0.075–0.85mm, respectively and carbonate sand with size ranges of 0·001–0·85mm, and mean particle size (D50) values of 0.28, 0.24 and 0.20 mm, respectively), the time-dependent (retention time 3, 7, 14, 20 and 28 days) compressive strength development for the crustal sand layer following single- and double-MICP (with interval of 6 days) spray treatments, as well as wind tunnel experiments under the condition of wind velocity of 20 ms-1. The effect of dew formation on crustal compressive strength development with curing period and the efficiency of the MICP treatment for the outdoor environment compared to laboratory-controlled test conditions. A pocket penetrometer was used to determine the compressive strength of soils. Significant improvements in the Compressive strength of the treated soil samples were observed. The results show improving compressive strength with time. The highest compressive strength in the carbonate sand was obtained equals to 84 kPa. Silica sand with finer size distribution has shown more compressive strength than two other soils. Also the results showed that double-MICP spray treatments of the bacteria solution and cementation was more effective than single- MICP spray treatments in the compressive strength of soils, especially in the silica sand equals to 190% in a curing period of 28 days. Also, the cured MICP-treated crustal sand layer was stable to 20 m·s−1 winds that demonstrating the potential of biological stabilisation via the MICP process as an appropriate option for dealing with desertification and motion of sandy soil deposits.

کلیدواژه‌ها English

Wind Erosion
Sporosarcina Pasteurii
compressive strength
Pocket Penetrometer
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مهندسی عمران مدرس
دوره 22، شماره 1
فروردین و اردیبهشت 1401
صفحه 35-51