مقایسه برخی روش‏های اندازه‏گیری توزیع اندازه ذرات اولیه خاک و ارائه زمان‏های مناسب برای روش چهار قرائت تعیین بافت خاک

نوع مقاله : مقاله پژوهشی

نویسندگان

1 دانشجوی کارشناسی ارشد، گروه علوم و مهندسی خاک، دانشکده مهندسی و فناوری، دانشگاه تهران، کرج، ایران

2 دانشیار گروه علوم و مهندسی خاک، دانشکده مهندسی و فناوری، دانشگاه تهران، کرج، ایران

3 دانشیارپژوهش موسسه تحقیقات خاک و آب، ﺳﺎزﻣﺎن ﺗﺤﻘﯿﻘﺎت، آﻣﻮزش و ﺗﺮوﯾﺞ ﮐﺸﺎورزی، ﮐﺮج، اﯾﺮان

چکیده

برای تعیین توزیع اندازه ذرات اولیه (PSD) در آزمایشگاه‏های خاکشناسی ایران، از روش‏های مختلفی استفاده می‏شود که این امر در بسیاری از شرایط امکان مقایسه نتایج و نیز دقت آنها را دشوار می­کند. پژوهش حاضر برای رسیدن به یک راهکار مشخص که در عین سادگی و ارزان بودن، دقت قابل قبولی نیز داشته باشد، انجام شد. ابتدا با توجه به برخی ویژگی‏های خاک از جمله درصد مواد سیمان‏کننده، 112 نمونه خاک از 16 استان مختلف کشور از کاربری‏ها و اقلیم‏های مختلف تهیه شد. PSD خاک با روش هیدرومتر با و بدون حذف مواد سیمان‏کننده اندازه‏گیری شد. نتایج نشان داد، روش رایج قرائت40 ثانیه و 2 ساعت (Bouyoucos, 1962)، بخش رس را با میانگین خطای مطلق (g/g100) 5/9 درصد نسبت به روش قرائت کامل اندازه­گیری می­کند و در 5/40 درصد از خاک­های مورد بررسی بیش از 10 درصد و در 2/94 درصد از خاکها بیش از 5 درصد بیشتر از مقدار واقعی اندازه­گیری می­کند و با ریز‏بافت شدن خاک میزان انحراف این روش از مقدار واقعی، افزایش می‏یابد. برای رفع مشکل، دو روش چهار قرائتی با طبقه‏بندی انجمن بین‏المللی علوم خاک (ISSS) شامل: الف) قرائت 2 و 10 دقیقه (برای تعیین مرز شن و سیلت) و 6 و 8 ساعت (برای تعیین مقدار رس) و ب) قرائت 2 و 10 دقیقه (برای تعیین مرز شن و سیلت) و 6 و 24 ساعت (برای تعیین مقدار رس)، پیشنهاد شد. روش پیشنهادی قرائت 2 و 10 دقیقه و 6 و 8 ساعت و روش پیشنهادی قرائت 2 و 10 دقیقه و 6 و 24 ساعت به­ترتیب در 1/97 و 2/94 درصد خاک­ها، کلاس بافت را به درستی نشان­ می­دهد و به ترتیب در بیش از 90 و 81 درصد موارد، خطای آنها در تعیین مقدار رس خاک کمتر از 1± درصد می­باشد.

کلیدواژه‌ها


عنوان مقاله [English]

Comparison of Some Methods for Measuring Primary Soil Particle Size Distribution and Introducing Appropriate Times for the Four-Reading Method for Determining Soil Texture

نویسندگان [English]

  • Mortaza Yavari 1
  • Mohammad Hosein Mohammadi 2
  • Karim Shahbazi, 3
1 M.Sc. Student, Dep. of Soil Sciences and Engineering, Faculty of Engineering and Technology, University of Tehran, Karaj, Iran
2 Associate Professor Dep. of Soil Sciences and Engineering, Faculty of Engineering and Technology, University of Tehran, Karaj, Iran
3 Research Associate Professor, Soil and Water Research Institute, AREEO, Karaj, Iran
چکیده [English]

Different methods are used for determination of the primary particle size distribution (PSD) in Iranian soils laboratories, which in many situations makes it difficult to compare results and their precision. This research was conducted to achieve an easy and inexpensive strategy with acceptable accuracy. First, 112 soil samples from 16 different provinces of Iran with a wide range of soils were taken from different climates and land uses. Soil PSD was measured by hydrometer with and without cement removal. The results showed that the common reading method of 40 seconds and 2 hours (Bouyoucos, 1962) measures the clay fraction with an average absolute error of 9.5% as compared to the complete record method. This error was more than 10% in 40.5% of the proposed soils and more than 5% in 94.2% of the soils. The deviation of this method from the actual value is increased as the soil becomes finer. Two four-reading methods with the classification of International Soil Science Association (ISSS) including: a) 2 and 10 minute readings (to measure silt fraction) and 6 and 8 hours (to measure clay fraction), and b) readings of 2 and 10 minutes (to measure silt fraction) and 6 and 24 hours (to measure clay fraction) were suggested to determine the soil texture. The two later methods show the soil texture correctly in 97.1 and 94.2% of the soils, respectively. The error of these two methods for determination of clay fraction is less than % in more than 90 and 81% of the proposed soils, respectively.

کلیدواژه‌ها [English]

  • Particle size distribution
  • Soil Texture
  • Densitometry
  • Hydrometer Method
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