ارزیابی هم خوانی روش های مختلف تعیین پایداری ساختمان خاک برای برآورد فرسایش پاشمانی

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشجوی دکتری گروه علوم خاک، دانشکده کشاورزی، دانشگاه صنعتی اصفهان، اصفهان، ایران

2 گروه علوم خاک، دانشکده کشاورزی، دانشگاه صنعتی اصفهان، اصفهان، ایران

3 گروه علوم خاک، دانشکده مهندسی و فناوری کشاورزی، دانشگاه تهران

چکیده

پایداری خاکدانه‌ها یکی از عوامل مهم اثرگذار بر فرسایش خاک است. هدف از انجام این پژوهش مقایسه روش‌های مختلف برآورد پایداری خاکدانه‌ها، شامل اندازه‌گیری پاشمان، الک تر و مقاومت برشی اندازه‌گیری‌شده با فروسنج مخروطی اُفتان برای برآورد فرسایش پاشمان است. برای این منظور، 28 نمونه خاک با ویژگی‌های اولیه متفاوت از نظر بافت، آهک و ماده آلی از خاک‌های سطحی استآن‌های اصفهان و چهارمحال بختیاری جمع‌آوری شد. میزان پاشمان (S) با دستگاه شبیه‌ساز باران، مقاومت برشی (τ) با فروسنج مخروطی اُفتان و میانگین وزنی قطر خاکدانه‌ها (MWD) و میانگین هندسی قطر خاکدانه‌ها (GMD) با استفاده از الک تر اندازه‌گیری شدند. نتایج همبستگی بین روش‌های مختلف نشان داد میزان پاشمان با τ و GMD همبستگی منفی و معنی‌دار و τ با GMD و MWD همبستگی مثبت و معنی‌دار داشت. نتایج نشان داد که S عمدتاً به توزیع اندازه ذرات، MWD و GMD به کربن آلی، و τ هم به توزیع اندازه ذرات و هم به کربن آلی خاک وابسته است. برای ارزیابی کارآیی روش‌ها در خاک‌های متفاوت، خاک‌های مورد مطالعه با استفاده از روش K-means در محیط نرم‌افزار MATLAB بر اساس ویژگی‌های اولیه خوشه‌بندی شدند. مقایسه میانگین بین خوشه‌ها با استفاده از آزمون حداقل تفاوت معنی‌دار (LSD) در قالب طرح کاملاً تصادفی انجام شد. نتایج مقایسه میانگین نشان داد هر سه روش، روند تغییرات پایداری خاکدانه در گروه‌های مختلف را به طور مشابه برآورد می‌کنند؛ بنابراین روش‌های ذکرشده به‌جای یکدیگر قابل‌استفاده هستند و فروسنج مخروطی اُفتان را می‌توان به عنوان یک روش درجا برای اندازه­گیری پایداری خاکدانه در برابر فرسایش پاشمانی معرفی کرد.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Evaluation of different methods of soil structural stability determination for predicting splash erosion

نویسندگان [English]

  • Hamid Kelishadi 1
  • Mohammad Reza Mosaddeghi 2
  • Shamsollah Ayoubi 2
  • Hossein Asadi 3
1 PhD Student, Department of Soil Science, College of Agriculture, Isfahan University of Technology, Iran
2 Department of Soil Science, College of Agriculture, Isfahan University of Technology, Isfahan , Iran
3 Soil Science Department, University of Tehran
چکیده [English]

Introduction Soil erosion is one of the major obstacles to sustainable development. A large part of Iran has an arid and semi-arid climate, without vegetation with suitable density or even completely without vegetation. Therefore, many parts of the country face high erosion and soil losses. Previous studies showed an increased trend of soil erosion in Iran. Because in situ measurement of soil erosion at the farm or watershed scale is expensive and time-consuming, estimation of soil erosion from easy and ready parameters can be useful. It is well-known that aggregate stability can affect soil erosion. There are many methods developed to measure soil aggregate stability, but there is no specific method that can be used for a wide range of soil types under different land uses. This study was done to compare different methods of aggregate stability determination (i.e., splash rate measurement, shear strength measured with fall-cone penetrometer and wet sieving).
Materials and Methods Twenty-eight soil samples with different textures, equivalent calcium carbonate, and organic matter were collected from surface soil layers in Isfahan and Chaharmahal-va-Bakhtiari provinces. Particles size distribution of studied the soil was measured. Very coarse sand (VCS), coarse sand (CS), medium sand (MS), fine sand (FS) and very fine sand (VFS) were measured according to ASTM sieves. Also, four components of silt (0.035-0.05, 0.02-0.035, 0.01-0.02 and 0.002-0.01 mm) were measured according to Stock's law by the pipette method. Geometric mean diameter and geometric standard deviation of particles were calculated by Shirazi and Boeresma (1984) relations. Soil splash rate (S) was measured with rainfall simulator, near-saturated soil shear strength (τ) was determined using the fall-cone penetrometer, and mean weight diameter (MWD) and geometric mean diameter (GMD) of soil aggregates were measured by the wet sieving.
Results and Discussion The results of this study showed that the sand, silt and clay contents were, respectively, in the ranges of 1.5-51%, 34-73% and 11-35% in the studied soils. Most of the sand particles belonged to the FS and VFS (0.05-0.25 mm) fractions and most of the silt fraction was in the very fine silt (0.002-0.01 mm) fraction. The range of organic matter was 0.08 to 8.8% and calcium carbonate equivalent varied in the range between 10% and 63%.
Generally, soil aggregate stability was low and splash erosion was high in the studied soils. The results showed that S showed significant correlations with sand, silt, and geometric mean diameter and geometric standard deviation calculated using all particle fractions, VCS, CS, MS, FS, fine silt and very fine silt. Soil shear strength (τ) had significant correlations with silt, very fine silt, geometric mean diameter and geometric standard deviation. The GMD and MWD had significant correlations with soil organic carbon. The results showed that S had significant and negative correlations with τ and GMD, and there were significant and positive correlations between τ with GMD and MWD. The S was mainly dependent on particle size distribution, while GMD and MWD mainly depended on soil organic carbon. However, both particle size distribution and soil organic carbon would affect τ. This finding might be justified by differences between mechanisms which are responsible for particles detachment. The energies induced by raindrop impact and slaking are the main forces and mechanisms responsible for detachment of particles in splash erosion and wet sieving tests, respectively while the cohesive forces between particles mainly govern soil strength in the fall-cone penetrometer test. The studied soils were clustered based on intrinsic soil properties (i.e., texture, CaCO3 and organic carbon) by using K-means method in MATLAB software, in order to evaluate the capability of different methods in different soil groups. The least significant difference (LSD) test was used in a completely randomized design for mean’ comparisons between the clusters. The mean comparison results showed that the three methods similarly predicted the variation of aggregate stability in different soil clusters. The results of clustering showed that the soil cluster with high organic matter, silt and clay contents and low sand content was more stable than other clusters.
Conclusion Three methods similarly predicted the variation of aggregate stability in different soil groups; therefore, the methods might be used alternatively for aggregate stability determination. Fall-cone penetrometer can be introduced as an in situ method for evaluation of aggregate stability against splash erosion.

کلیدواژه‌ها [English]

  • Aggregate stability
  • Fall-cone penetrometer
  • Splash erosion
  • Multiple rainfall simulator
  • Wet sieving
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