بررسی اثر و نحوۀ اختلاط نانورس بر شدت واگرایی روی نمونه‌هایی از خاک‌های لسی استان گلستان

از خاک های لسی در سه منطقۀ شرق و شمال شرق استان گلستان نمونه برداری شد و آزمایش پین هول روی نمونه های با وزن واحد حجم طبیعی (gn) و حداکثر (gdmax) انجام شد و میزان واگرایی آن تعیین شد. پیشنیۀ تحقیق، شواهد صحرایی و نتایج آزمایش های آزمایشگاهی حکایت از واگرا بودن خاکِ مناطقِ نمونه برداری دارد. نتایج نشان می دهد، تراکم خاک باعث کاهش شدت واگرایی می‌شود و نرخ جریان را کم می‌کند، به‌طوری‌که نرخ جریان در نمونه مراوه تپه به میزان 38 درصد، در نمونۀ چشمه لی به‌میزان 13 درصد و در نمونه بق قجه بالا به‌میزان 43 درصد کاهش یافته است. تراکم نمی‌تواند واگرایی خاک را از بین ببرد. افزودن نانورس باعث کاهش شدت واگرایی خاک شده و در غالب موارد خاصیت واگرایی آن را از بین می‌برد. به‌منظور بررسی اثر نانورس روی شدت و کاهش خاصیت واگرایی خاک با نسبت های 5/0، 1، 2، 3، 4 و 5 درصد وزنی نانورس مونت موریونیت افزوده شد. میزان واگرایی نمونه های دارای نانورس در دستگاه آزمون پین هول اندازه گیری شد. هم‌چنین روش اختلاط نانورس با خاک واگرا رفتارهای گوناگونی را در شدت واگرایی و کاهش آن نشان می دهد. نانورس به چهار روش با خاک های مناطق نمونه برداری مخلوط شدند. در روش a ، با تهیۀ گل همگن از خاک و نانورس با هم‌زن برقی کاملاً مخلوط شدند. در روش b، اختلاط خاک لس با نانورس در رطوبت بهینه انجام شد. در روش c. اختلاط خاک لس با نانورس به‌صورت خمیر به‌وسیلۀ هم‌زن دستی انجام شد. در روش d. اختلاط خاک لس با نانورس به‌صورت خشکِ ارتعاشی به‌وسیلۀ لرزاننده الک دانه بندی انجام شد. نتایج بررسی نشان داد که، نسبت وزنی یک درصد نانورس از نظر فنی و اقتصادی مناسب ترین نسبت اختلاط است. با این نسبت وزنی، روش تهیه گل همگن با هم‌زن برقی (روش a) کم‌ترین نرخ جریان را به‌وجود می آورد؛ به‌طوری‌که نرخ جریان از 3/1 میلی لیتر در ثانیه در خاک خالص به 3/0 میلی لیتر در ثانیه در خاک حاوی نانورس در هد 50 میلی متر کاهش می یابد. از این‌رو، می توان گفت این روش مناسب تر است ولی از لحاظ اجرایی کارایی ندارد و روش b مناسب تر است. در روش b نرخ جریان از 3/1 به 55/0 میلی لیتر در ثانیه در همین حد می رسد.

Investigation of the Effect and Mixing of Nano-clay on the Severity of Dispersion on Samples of Loess Soils in Golestan Province

IntroductionThe dispersivity phenomenon occurs due to the dissolution of some of the ions in clay soils or against the shear stress of normal water flow in cohesionless soils. Water surface flows in low slopes cause surface erosion of dispersive soils. Dispersivity in the soil starts from a point and gradually expands; the starting point can be the holes from the activity of the animals, the existing cracks or the growth path of the roots of the plants. There is a lot of field evidence to recognize the dispersivity of the loess soils. In field investigations, soil dispersivity can be detected according to the following parameters: geological origin of the loess soil, mineralogical composition, gradation, drainage pattern, slaking of agglomerates, specific morphology, high permeability, geographical area (length and width relative to origin), soil color, relationship between slope and soil erosion, precipitation, erosion of column cracks, heeling, mud flowing runoff and the presence of salt crystals in loess soils. In terms of sedimentological characteristics and engineering geological properties, Golestan loesses have been dispersed in three areas 1, 2 and 3, which are consistent with the loesses of clay, silt, and sand types, respectively.Material and methodsLoess soils in three regions of east and northeast of Golestan province were sampled. Sampling was conducted in two forms of waxcoated agglomerates and metallic cylindrical tubes. Depth of sampling follows the foundation of the buildings located on the Mehr Housing site and the Cheshme Lee village, varying from 0.5 to 2 meters. On the path of the Beqqeje Bala village, sampling was carried out from the path trench. After transferring to the laboratory, samples were subjected to gradation testing, Atterberg limits test to determine the unit weight of the volume and density.The pinhole test was done on samples with the unit weight of normal volume (gn) and maximum volume (gdmax) and its rate of dispersion was determined. The research background, field evidence and the results of laboratory experiments indicate the dispersion of soil sampling areas. The results show that soil compaction reduces the severity of dispersion and decreases the flow rate, so that the flow rate has decreased in the Maravehtapeh sample by 38%, in the Cheshmeli sample by 13% and in the Beqqeje Bala sample by 43%. Compaction cannot eliminate the dispersion of soil. Adding nanoclay decreases the severity of soil dispersion and eliminates its dispersion properties in most cases.In order to evaluate the effect of nanoclay on severity and to decrease the dispersion property of soil with ratios of 0.5, 1, 2, 3, 4 and 5 wt%, of Montmorillonite Nanoclay was added.The nanoclay used in the present research was selected from the SigmaAldrich America Company called montmorillonite nanoclay and was purchased from its domestic representative, i.e. Iranian Nanomaterials Pioneers Company. The product has a density of 300 to 370 kilograms per cubic meter and a particle size of between 1 and 2 nm. The specific surface area of the nanoparticle is about 250 square meters per gram. Its color in normal light and in 1 to 2% moisture is yellow to yellowish buff.Results and discussionThe rate of dispersion of samples with nanoclay was measured in Pinhole Test Apparatus. Also, the method of mixing nanoclay with dispersive soil shows different behaviors in severity of dispersion and its reduction. Given that the specific surface of nanoclay is high and this property can include the whole surface of soil grains as a sticky coating and increase soil cohesion, the mixing method is practically one of the most important steps in examining the effect of nanoclay on soil stabilization. At ratios of 0.5, 1, 2, 3, 4 and 5 wt% of nanoclay, nanoclay was mixed with soils of sampling regions by four methods:In the method A, they were completely mixed with the preparation of a homogeneous mud from soil and nanoclay via an electric mixer.In the method B, mixing of loess soil with nanoclay was performed in optimum water content.In the method C, mixing of loess soil with nanoclay was conducted in the form of dough by hand mixer. In the method D, mixing of loess soil with nanoclay was carried out in the form of vibration dry by grading sieve shaker.After mixing with nanoclay in the desired method (four methods A, B, C, D), the samples were first stored in sealed plastic containers for 24 hours. Then, the samples containing nanoclay were reconstructed in cylindrical mold of the pinhole device with the unit weight of maximum dry volume and moisture of two percent higher than the optimum moisture content and a hole was created in the middle of it. The samples remained in this position for 24 hours, and then the test was performed. Testing was carried out on each sample according to the standard D464793, and flow rate reading was done over a period of two minutes to 18 minutes.ConclusionThe conclusion of this study shows that the three loess samples taken have a dispersivity potential and the flow rate is low in the unit weight of maximum volume, but the dispersivity potential does not eliminate. Adding nanoclay with any weight ratio reduces the flow rate and eliminates the soil dispersivity potential.The results of this survey showed that 1% nanoclay weight ratio is technically and economically the most appropriate mixing ratio. With this weight ratio, the method of preparing homogeneous mud with an electric mixer (method A) produces the lowest flow rate, so that the flow rate from 1.3 ml per second in pure soil to 0.3 ml per second in the soil containing nanoclay is reduced by 50 mm. Therefore, it can be said that this method is more suitable, but it is not operationally efficient and the method B is more appropriate. In the method B, the flow rate reaches from 1.3 to 0.55 ml per second.