پژوهشنامه حمل و نقل

پژوهشنامه حمل و نقل

بررسی مشخصات درجا و سه‌محوری دینامیکی خاکهای آبرفتی غیرچسبنده با تمرکز بر عمق لایه فرسایش سطحی

نوع مقاله : مقاله پژوهشی

نویسنده
عطا آقایی آرایی
دانشیار، مرکز تحقیقات راه، مسکن و شهرسازی، تهران، ایران
10.22034/tri.2024.464667.3254
چکیده
این مقاله مشخصات درجا صحرایی سه نمونه خاک ماسه ای غیرچسنده و یک نمونه خاک لای شامل تعیین مقاومت الکتریکی و سرعت امواج به روش لرزه نگاری  شکست مرزی و درون گمانه و مقایسه آن با نتایج سه محوری دینامیکی را بررسی می ‌کند. بیشترین و کمترین مقادیر مقاومت الکتریکی به ترتیب مربوط به خاک SM گمانه BH8 و خاک ML گمانه BH34 است. مقاومت الکتریکی "لایه فرسایش سطحی" در بخشهای سطحی به ترتیب حدود 2 و 3 برابر حداقل مقادیر آن در کل عمق گمانه 30 متری به ترتیب برای خاکهای ماسه ای SM یا SW و ML است. سرعت موج برشی "لایه فرسایش سطحی"، حداکثر  نصف متوسط سرعت موج برشی کل لایه 30 متری است. ضخامت "لایه فرسایش سطحی" براساس سرعت موج برشی روش شکست مرزی تا عمق 9/3، 8/2، 7/1و 2/7 متر به ترتیب برای خاک SW گمانه BH32، SM گمانه BH3، SM گمانهBH8  و ML گمانه BH34  است که داده های مقاومت الکتریکی، با تفاوت حدود 30% ضخامت­های مذکور را تایید می‌کند. سرعت موج برشی بدست آمده روش شکست مرزی و روش درون گمانه ایزنتروالی به ترتیب معرف مقادیر سرعت در جهت افقی و طولی و به نوعی معرف تخمینی از بیش تحکیم یافتگی نمونه درجا است. در ادامه روی مصالح متراکم شده SM گمانه BH8 با رطوبت ساخت بهینه و شرایط نیمه اشباع و اشباع کامل، آزمایش‌های نوسانی دینامیکی با دستگاه سه‌محوری بزرگ‌مقیاس طبق ASTM D3999 انجام شد. نمونه ها تحت تحکیم همسان و  غیرهمسانی ( / ) مختلف و  برابر 1، 2 و  5 و  فرکانس‌های 5/0، 1، 2، 5 و Hz10 آزمایش شدند. با توجه به تفاوت قابل ملاحظه‌ بین مقادیر و  مصالح ماسه ای از جمله SM گمانه  BH8با نتایج موجود در ادبیات فنی، لزوم انجام آزمایش برای دستابی به منجنی های مناسب مورد تاکید است. تطابق نسبتاًخوبی بین داده­های صحرایی سرعت موج برشی متوسط از سطح روش درون گمانه با متوسط مقادیر نمونه آزمایشگاهی سه‌محوری تحت تحکیم غیرهمسان برقرار است.
کلیدواژه‌ها
آبرفت
غیرچسبنده
مقاومت الکتریکی
سرعت موج‌
مدول برشی
نسبت میرایی
غیرهمسانی
فرکانس‌
مونوتونیک پسانوسانی
لایه فرسایش سطحی

موضوعات

عنوان مقاله English

Investigating the In-situ Characteristics and Dynamic Behavior of Non-cohesion Alluvium Soils with a Focus on the Depth of the Surface Erosion Layer

نویسنده English

Ata Aghaei Araei
Associate Professor, Road, Housing and Urban Development Research Center, Tehran, Iran
چکیده English

This paper presented the in-situ characteristics of three non-cohesion alluvium soils and one slity soil, including the determination of electrical resistance and waves velocity using seismic-reflection and Downhole method, and comparing its result with dynamic triaxial results. In general, the highest and lowest electrical resistance values are related to SM soil of borehole BH8 and ML of BH34 borehole , respectively. The electrical resistance of the "surface erosion layer" in the surface sections is about 2 and 3 times the minimum values in the whole borehole depth of 30 meters respectively for SM or SW and ML soils. The shear wave velocity (V_S) of the "surface erosion layer" is half the average shear wave velocity of 30 m depth ( V_S30). In general, the thickness of the "surface erosion layer" based on VS of the seismic-reflection method are 3.9, 2.8, 1.7 and 7.2 m, respectively, for SW of BH32, SM of BH3, SM of BH8, and ML of BH34 borehohes, which, mentioned thicknesses, are confirmed by the electrical resistance data, with a difference of about 30%. The V_S obtained by the seismic-reflection method and the Downhole method respectively represent the velocity values in the horizontal and longitudinal directions and in a way represent the estimated overconsolidation of the in-situ sample. In the following, on the compacted SM of borehole BH8 materials under semi and full saturation conditions, dynamic cyclic tests ASTM D3999 were performed, using large triaxial equipment. Specimens were teted under σ_3^'equal to 1, 2 and 5〖kg/cm〗^2, under isotropic and unisotropic consolidation (σ_1^'/σ_3^') and loading frequencies of 0.5, 1, 2, 5 and 10 Hz. Due to the significant difference between G/G_max-γ and D-γ values of sand materials, including SM of BH8 borehole, with the results available in the technical literature, the necessity of conducting these tests is emphasized.

کلیدواژه‌ها English

Alluvium
Non-Cohesion
Electrical Resistance
Wave Velocity
Shear Modulus
Damping Ratio
Anisotropic
Frequency
Post-Cyclic Monotonic
Surface Erosion Layer
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