مطالعه آزمايشگاهي تاثير رفتار هيسترسيس هيدروليكي بر ظرفيت باربري كاليفرنيا يك مخلوط ماسه رسي تراكم پذير غيراشباع

Experimental investigation on the influence of hydraulic hysteresis on the California Bearing Ratio of an unsaturated deformable clayey sand

در اين پژوهش به بررسي آزمايشگاهي تاثير پارامترهاي نسبت تخلخل اوليه، درصد رطوبت، مكش بافتي، درجه اشباع و هيسترسيس هيدروليكي بر روي ظرفيت باربري كاليفرنيا يك مصالح روسازي پرداخته شده است. براي اين منظور، مقدار سي بي آر يك خاك مخلوط ماسه رسي در بازه اي از مقادير نسبت تخلخل اوليه بر روي بازه هاي تر و خشك شدگي منحني مشخصه آب – خاك اندازه گيري شده است. آزمايش هاي تر شدگي سي بي آر بر روي نمونه هاي خاك متراكم و تر شده در بازه اي از مقادير نسبت تخلخل و درصد رطوبت اوليه انجام پذيرفت. نمونه هاي خاك مورد استفاده در آزمايش هاي خشك شدگي نيز ابتدا مطابق با روند و پارامترهاي نمونه هاي مورد استفاده در آزمايش هاي تر شدگي ساخته شده و بعد از خشك نمودن يكنواخت آن ها با استفاده از تكنيك هوادهي مقادير سي بي آر آن ها اندازه گيري شده است. بر پايه نتايج آزمايشگاهي، ظرفيت باربري كاليفرنيا خاك مورد مطالعه با افزايش مقادير تراكم اوليه و مكش بافتي خاك افزايش يافته است. ليكن نتايج آزمايشگاهي حاكي از كاهش مقدار سي بي آر خاك مفروض با افزايش درجه اشباع خاك مي باشد. با عنايت به مشاهدات آزمايشگاهي در يك مكش بافتي مفروض، ظرفيت باربري خاك مورد مطالعه داراي مقادير كمتري بر روي بازه هاي خشك شدگي نسبت به بازه هاي تر شدگي بوده است. اين روند هيسترتيك مشاهده شده در تغييرات سي بي آر، با توجه به رفتار هيسترسيس هيدروليكي منحني مشخصه آب – خاك بيان شده است.

Many of the past experimental research on the design of road pavement layers was confined to the behavior of saturated pavements materials. Among the experimental studies to determine the road layers properties, California bearing ratio (CBR) has been one of the most common and applicable parameter for determination of the resistance of roads subgrade in both design and practical purposes. An extensive amount of research exist in the literature that explains the behavior of California bearing ratio of saturated soils. However, any change in the degree of saturation of subgrade materials and in particular different hydraulic response in wetting and drying paths can affect the CBR value of a pavement material. In compare to the extensive previous studies on the California bearing ratio of soils, this phenomenon is rarely concerned in the previous studies. The goal of this laboratory research is to examine the influence of the initial compaction void ratio, moisture content, degree of saturation, matrix suction and hydraulic hysteresis on the California bearing ratio of a pavement material. To this end, California bearing ratio of sandkaolin mixture was measured in a range of initial void ratios and initial water contents along drying and wetting portions of the soilwater characteristic curve. The CBR tests along wetting paths was performed on the soil sles that were dynamically compacted and wetted in a range of initial void ratios and initial water contents. The CBR tests for drying paths was also carried out on the soil sles that were compacted identically to the sles used in wetting tests, but they were air dried for seven days before CBR measurements. The air drying process was achieved from the both ends of soil sles as to maintain a homogenous moisture distribution thorough the soil. This was experimentally verified by measuring the moisture contents of top, middle, and bottom portions of the specimens. The CBR values of soil sles were measured within the loading speed of 1.2 mm/min both for wetting and drying paths. According to the laboratory results, it is observed that the CBR value is increased within the increment of initial soil compaction and matrix suction. Based on the results, it is also observed that the value of California bearing ratio of the understudying soil is decreased within increment of the degree of saturation and initial moisture content of the soil. The experimental data also revealed that the California bearing ratio of the pavement material along the drying and wetting paths are not identical, and for a given suction, the CBR values for drying paths possess lower values than the wetting paths. This hysteretic trend for the change of CBR along drying and wetting paths is explained with regard to the hysteretic behavior of the soilwater characteristic curve.