20685

۲۰۶۸۵

بررسي اثر مويينگي بر مقاومت برشي ماسه فيروزكوه

كارشناسي ارشد

ژئوتكنيك

93-94

۱۳۹۶/۰۷/۲۹

دكتر حسين صالح زاده

عمران

تأثير مكش بافتي بر رفتار برشي خاك از آن جهت كه نقش تعيين كننده اي در مدلسازي ژئوتكنيكي دارد، همواره مورد توجه پژوهشگران در اين زمينه بوده است. در اين پژوهش به تأثير مكش بافتي بر پارامترهاي مقاومت برشي خاك ماسه اي پرداخته شده است. براي مشاهده تأثير مكش بافتي بر پارامترهاي مقاومت برشي (چسبندگي و زاويه اصطكاك داخلي)، نمونه هايي از ماسه سيليكاتي با درصد رطوبت اوليه و در نتيجه مكش هاي بافتي متفاوت، بر اساس منحني مشخصه آب - خاك و منحني تراكم ساخته شدند. نمونه هاي خاك بر اساس شرايط اوليه مورد نظر در جعبه دستگاه برش مستقيم به صورت استاتيكي متراكم شدند. روي نمونه هاي آماده شده، آزمايش برش مستقيم در حالت غير اشباع صورت گرفته بر اساس نتايج آزمايش ها، منحني تغييرات تنش برشي بر حسب جابه جايي افقي در تنش هاي قائم متفاوت رسم شد و درباره نتايج آن بحث شد؛ نتايج نشان داد تغييرات ميزان رطوبت و در نتيجه تغييرات مكش بافتي اوليه نمونه هاي خاك، تأثير قابل توجهي بر پارامترهاي مقاومت برشي خاك غير اشباع ندارد.

1398/01/26

Effect of Capillary on Shear Strength of Silicate Sand

10/21/2017 12:00:00 AM

The effect of matric suction on shear strength of soil, because of its dominant role in geotechnical modelling, has received the attention of researchers in this filed. This research is focused in investigating the effect of matric suction on shear strength of a coarse soil. The physical properties of the soil are determined. The filter paper method is performed to extract the soil water characteristic curve. In addition to its simplicity, one of the major advantages of this method is the vast range of suctions can be measured by it. Specimens were compacted at identical void ratio with different water contents. Suctions are inferred from empirical relations that relate the suction to the measured moisture content of filter paper which has been in contact with soil sample. In order to examine moisture content effects on shear strength parameters (cohesion and friction angle) of the sand, soil samples are prepared with different moisture content and consequently different matric suctions with respect to soil water characteristic curve. The specimens with different initial moisture contents are statically compacted at dry density of 1.3 gr/cm'into direct shear test mould. Direct shear tests are conducted in unsaturated state. After applying vertical stress the samples are left at least for 2 hours to allow the equalization of internal stresses. Based on experimental data the shear stress is plotted against horizontal displacement in different vertical stresses and moisture contents and the results and analysed and discussed. The effective stress equation proposed by Bishop (1959) is used to interpret the results. The effective stress parameter x in each moisture content is calculated by the equation suggested by Khalili & Khabbaz (1998) using the air entry suction extracted from SWCC curve. The results reveal that strength parameters do not substantially change at different moisture contents. The negligible changes in strength parameters may be attributed to slight changes in pore water pressure during shearing experiment. Such changes in pore pressure during shearing would be eliminated in constant suction consolidated drained experiments.