بررسي آزمايشگاهي تأثير نانورس بر فرسايش داخلي خاكهاي واگرا در سدهاي خاكي

فرسايش داخلي در سدهاي خاكي از عوامل تهديدكننده پايداري است. وجود خاك‌هاي واگرا در هسته سد باعث تشديداين پديده مي گردد. در اين پژوهش از نانورس كه سازگار با محيط زيست مي باشددر جهت كنترل فرسايش داخلي در خاك­هاي واگرا استفاده شده است. بدين منظوردر آزمون فرسايش حفره‌اي مقادير 5/0، 1، 5/1 و 3 درصد نانورس و زمان­هاي عمل­آوري 1، 2، 7، 14 و 28 روز و در سه گراديان هيدروليكي 05/7، 96/7 و 05/11 همچنين اثر اين ماده افزودني بر خواص خميري خاك مورد بررسي قرار گرفته است. نتايج نشان مي­ دهد كه افزودن نانورس به خاك باعث افزايش شاخص نرخ فرسايش و كاهش فرسايش‌پذيري خاك مي­ شود به گونه ­اي كه فرسايش‌پذيري خاك از گروه نسبتاً سريع در خاك شاهد به گروه نسبتاً آرام تغيير پيدا مي ­كند. در زمان عمل‌آوري 1 روز مقدار بهينه نانورس 1 درصدودر دو زمان عمل‌آوري 2 و 7 روز 5/1 درصد مشاهده شد. همچنين در گراديان‌هاي هيدروليكي بزرگتر تأثير نانورس در كاهش فرسايش بيشتر مي­ باشد به گونه­ اي كه در گراديان هيدروليكي 05/11 شاخص نرخ فرسايش به ميزان 6% نسبت به گراديان 05/7، افزايش نشان داده است. با افزايش زمان عمل­ آوري، شاخص نرخ فرسايش افزايش پيدا كرده، كه در مدت زمان 28 روز ميزان افزايش شاخص نرخ فرسايش به ترتيب در گراديان‌هاي هيدروليكي 05/11، 96/7 و 06/7 برابر 8/23% ، 4/23% و 3/20% ، نسبت به خاك شاهد مي‌باشد. همچنين افزودن%1 نانورس باعث افزايش خواص خميري وافزودن 2% درصد نانورس باعث كاهش خواص خميري خاك نسبت به نمونه شاهد شده است.

The phenomenon of internal erosion in embankment dams is one of the threats to their stability and the presence of Dispersive Clayey soils on the embankment dam is one of the exacerbating and one of the reasons that causes internal erosion which is associated with dam damages. Basically, Dispersive Clayey Soils in the vicinity of moisture and saturation will highly lose resistance Due to the presence of Na+. Due to the mentioned fact, stabilization of these soils seems to be of essential importance for the sake of making proper embankment of hydraulic projects. One way for soil amendment and confronting soil erosion is the injection of additives. In this research, nanoclay (montmorillonite) has been used as a modern and eco-friendly additives for controlling internal erosion in Dispersive soils. nanoclay materials had particle size ranges of 1–2 nm and specific surface area value of 220–270 m2/g . The dispersion ratio of soil was equal to 86%. In order to investigate the erodibility values, samples containing 0, 0.5, 1, 1.5 and 3 (weight percent) of dry soil were tested by Hole Erosion Test. After determining the optimal percentage of nanoclays, effects of hydraulic gradient (i= 7.05, 7.96, 11.05) and processing time (t= 1, 2, 7,14, 28 day) on erodibility of samples containing the optimum amount of nanoclays and also the effect of optimal amount of nanoclays on atterberg limits of soil were investigated. Experiment results on Dispersive Clayey Soils without nanoclay showed that the index of erosion rate of soil was in the fairly fast group. The results show that adding nanoclay to soil increases the index of erosion rate and decreases soil erodibility. So that the erosion of the soil changes from fairly fast group in the control soil to laminar group. At the processing time of 1 day, the optimum amount of nanoclay in reducing erosion was obtained 1% and the index of erosion rate was 4.33. The optimum amount of nanoclay in the processing times of 2 and 7 days was observed equal to 1.5% and the index of erosion rate was 4.85 and 4.72, respectively. It was also observed that in larger hydraulic gradients, the effect of nanoclay in reducing erosion is more. In addition for optimal amount of nanoclays with increasing hydraulic gradient and processing time, the index of erosion rate increased and sample’s erodibility decreased. So that, in the hydraulic gradient equal to 11.05, the index of erosion rate increased by 5%. Also the index of erosion rate has increased with increasing processing time. So, at the processing time of 28 days, the amount of increasing in the index of erosion rate in hydraulic gradients equal to 11.05, 7.96 and 7.06, is 23.8%, 23.4% and 20.3%, to the control soil, respectively. Also adding the optimum amount of nanoclays because of absorbing water, has expands atterberg limits of soil. So that with adding 1 percent nanoclays increased liquid limit (about 4 percent), plastic limit (about 4.2 percent) and plastic index (about 3 percent) of dispersive clayey soil and adding 2 percent nanoclays decreased atterberg limits of soil, compared to the control sample.