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برآورد خصوصیات فیزیکی و خمیری خاکهای رسی مارنی تبریز بر اساس عدد spt
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نویسنده
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علیزاده مجدی علیرضا ,دبیری روزیه
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منبع
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زمين شناسي مهندسي - 1398 - دوره : 13 - شماره : 3 - صفحه:485 -510
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چکیده
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آزمون نفوذ استاندارد (spt) یکی از متداولترینترین آزمایشها در تحقیقات ژئوتکنیک است. در این تحقیق با استفاده از نتایج آزمایش نفوذ استاندارد، برآورد خصوصیات خمیری و فیزیکی خاکهای رسی باروش های آماری بررسی شده است. محدودۀ بررسی شده مربوط به انواع لایه های رسی و مارنی در شهر تبریز واقع در شمالغرب ایران است. دو گمانه ماشینی حفاری شده و آزمایش نفوذ استاندارد بههمراه سایر آزمونهای آزماشگاهی برای تعیین همۀ خصوصیات خمیری و فیزیکی روی نمونههای تهیه شده انجام شد. با استفاده از نتایج پژوهشهای پروژههای مهم موجود در منطقه، بانک اطلاعاتی مشتمل بر 107 سری از خصوصیات لایههای منطقه تهیه شد. ضریب همبستگی اسپیرمن بین خصوصیات فیزیکی و خمیری خاک شامل درصد رطوبت طبیعی، درصد ریزدانه و درصد ذرات رسی، حد روانی، حد خمیری، دامنۀ خمیری، شاخص استحکام، فعالیت، تخلخل اولیه، وزن مخصوص خشک و تنش موثر قائم با عدد نفوذ استاندارد تصحیح شده تعیین شد. 8 رابطۀ تجربی موجود برای برآورد نفوذ استاندارد تصحیح شده با دادههای این تحقیق صحتسنجی شد. برای این روابط عموماً نتیجه ضعیف از نظر ضرایب آماری شامل ضریب تبیین (r2)، خطای ریشه میانگین مربعات (rmse) و شیب خط رگرسیون(cr) بهدست میآید. با استفاده از رگرسیون غیرخطی و بر اساس دادههای تحقیق حاضر، هشت رابطۀ تجربی جدید بررسی و پیشنهاد شد. ضریب تبیین، خطای ریشه میانگین مربعات و شیب خط رگرسیون برای روابط پیشنهادی نسبت به روابط موجود بهبود یافته است. ضرایب آماری برای مناسبترین رابطه بهمنظور برآورد شاخص استحکام خاک با استفاده از نفوذ استاندارد تصحیح شده حدود 0.7 با خطای 129/0 بهدست آمد. همچنین دو رابطه برای همبستگی تنش موثر قائم و عمق نمونه با نفوذ استاندارد تصحیح شده پیشنهاد شد.
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کلیدواژه
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عدد نفوذ استاندارد، خصوصیات خمیری، خاکهای مارنی رسی تبریز، روابط تجربی
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آدرس
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دانشگاه آزاد اسلامی واحد تبریز, گروه مهندسی عمران, ایران, دانشگاه آزاد اسلامی واحد تبریز, گروه مهندسی عمران, ایران
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Estimation of Physical and Engineering Properties of Clayey Soils According to Standard Penetration Test: A Case Study of Tabriz Clayey Marl
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Authors
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Alizadeh Majdi Alireza ,Dabiri Rouzbeh
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Abstract
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IntroductionThe standard penetration test (SPT) is one of the most common tests in geotechnical investigations. The results of this test are known as a simple, inexpensive, and tangible criterion in geological and geotechnical engineering. Many computational methods and engineering judgments depend on the results of this test. In this research, estimation of physical and engineering properties of clay soils was carried out using statistical methods based on standard penetration test results. The scope of this case study is related to a variety of clayey soils in Tabriz (the northwest of Iran). The existing relationships were confirmed based on database of this study. After statistical analysis of the database, eight relationships including single and twovariable associations have been proposed to estimate the physical and engineering properties with better performance using nonlinear regression.Material and MethodsDifferent types of clayey silt and marl layers spread in Tabriz were included for the purpose of this study. The geological age of these layers dates back to the Miocene and Pliocene era. This research was conducted in two sections of the field and analysis. Two machine boreholes were drilled, and, based on ASTM, a standard penetration test with other laboratory tests were performed on the soil specimens in order to determine the physical and plasticity properties. According to the results of this study and the existing data, a total of 107 series were prepared. Based on the soil properties, 11 variables were selected including the fine grain percentage (FGP), liquid limit (LL), plastic limit (PL), percentage of clay particles (C), plastic index (PI), consistency index (CI), activity (A), dry unit weight ( gamma;d), natural moisture content (wn), initial void ratio (eo), and effective vertical stress ( sigma;'v). The standard penetration tests were run for each meter in drilled boreholes. The results of this test were corrected according to NCEER method. The correlation between the variables and corrected standardized penetration test results (N60) were studied by Spearman ranking coefficient. Verifications of the existing eight experimental relationships between standard penetration and other soil properties, proposed by Kayabasi (2015) and Hoshmand et al., (2012), were checked out using the findings and data of the present study. The linear, exponential, logarithmic, and exponential regressions between each variable and N60 were investigated using SPSS software, version 16. The best regression with the highest R2 for each variable was selected. Eight new relationships were proposed. Performance of the suggested relationships was compared with the existing relationships.Results and DiscussionThe findings of the current study could be summarized as:1. The clay soils of the studied area in Tabriz were classified into four categories including CH, MH, CL, and ML according to USCS classification. The range of changes in plastic index and liquid limits of the samples were 9.19 ~ 45% and 29 ~ 77%, respectively. The corrected standard penetration test results (N60) changed from 9 to 28 showing that soil compression was low to high.2. The highest positive and negative Spearman correlation coefficients were related to the consistency index (+0.772) and moisture content (0.759), respectively.3. The existing empirical relationships, based on the database of this study, were found to have better statistical coefficients in terms of consistency index, activity, moisture percentage, and fine grained percentage. In term of sample depth, the experimental relationship, showed the lowest statistical coefficient.4. Four singlevariable and twovariable relationships were proposed by nonlinear regression analysis. Using these relationships, clay soil properties including activity, moisture content, fine grain percentage, and consistency index were estimated based on N60. In addition, two relations were proposed between sample depth (D) and vertical effective stress ( sigma;'v) with N60. The statistical coefficients of the suggested relationships were better than the existing empirical relationships. The proposed relationship of estimating the consistency index with coefficient (R2) of 0.673 and regression line slope of about 1 had the best performance.ConclusionIn general, the main objective of this study was to investigate the correlation between physical and plasticity properties of clay soils and N60 on Tabriz clayey soils. Clay soils of the present study included various silty and marl layers. Sufficient correlation was observed between the physical and engineering properties of clay soils and N60. The validation of the existing experimental relationships based on A, wn, FGP, and D resulted in weak statistical coefficients (R2 <5) employing the database of the current study. Six new experimental relationships were proposed to estimate A, FGP, wn, and CI as well as two correlations of N60 with effective stress and sample depth. Generally, the results have been revealed that the statistical coefficients of the proposed relationships were improved compared with the existing relationships. The most suitable relationship was the estimation of soil consistency index (R2~70) and root mean square error (RMSE=129). Finally, due to the novelty of this research topic, verification and development of the proposed relationships for the soils has been recommended in other areas.
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Keywords
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Empirical equation ,Plasticity properties ,Standard penetration test ,Tabriz clayey marl
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