بررسي آزمايشگاهي ظرفيت باربري شمع هاي مخروطي در خاك هاي ماسه‌يي تحت بارهاي استاتيكي قايم

Experimental Study of Bearing Capacity of Tapered Piles in Sandy Soils under Vertical Static Loads

مطالعاتي كه تاكنون بر روي شمع ها صورت گرفته است، عموماً بر روي شمع هاي استوانه‌يي بوده است. پژوهش‌هاي محدودي كه بر روي شمع هاي مخروطي انجام شده است، بيان گر مزيت اين نوع شمع‌ها از نظر ظرفيت باربري و سختي است. در اين نوشتار به مقايسه‌ي ظرفيت باربري 4 نوع شمع مخروطي با زاويه هاي مختلف در ماسه‌ ريزدانه‌ي گردگوشه معروف به ماسه‌ بادي يزد و ماسه‌ شكسته‌شده به روش مصنوعي تحت نيروي استاتيكي كه بر روي دستگاه نيروسنجي قرار گرفته اند، در محيط آزمايشگاهي پرداخته شده است. با داشتن بار سر، نوك و جداره‌ي شمع، نمودار متناظر با نشست براي نيروهاي حاصل ترسيم و ظرفيت باربري تعيين شده است. نتيجه‌ي حاصل‌شده بيان‌گر اين امر است كه شمع 45/2 درجه در ماسه‌ شكسته‌شده به روش مصنوعي بيشترين ظرفيت باربري را دارد و در ماسه‌ بادي با افزايش زاويه‌ي مخروط‌شدگي، ظرفيت باربري كاهش مي يابد.

All structures are built on foundations which are used to transfer loads from structures to the bearing stratum. In certain cases, where shallow foundations are not suitable for transferring loads, deep foundations such as pile foundations are used. It is worth mentioning that in most cases, cylindrical piles have been used. However, past research revealed that the bearing capacity and stiffness of tapered piles are more than their cylindrical equivalents. There has been limited experimental research carried out on the bearing capacity of tapered piles, and most studies in this area are based on numerical analysis. Results of the above mentioned research indicate that there is a relationship between the tapered angle and the bearing capacity of the piles. In this study, the bearing capacity and settlement of tapered piles using different tapered angles have been studied. Four different tapered angle piles were installed in two different soils, namely; fine grain sand (regionally named Yazd Windy Sand), and a fabricated coarse angular sand. Using a load cell at the tip of the pile, the transmitted load to the pile base has been measured and the load transferred by skin friction calculated by subtracting the base load from the whole applied load. The results demonstrated a relationship between tapered angle and bearing capacity, which have been compared with their cylindrical equivalents. Available recommended methods have been used to deduce the ultimate bearing capacity of piles from load- settlement curves. Based on acquired results, piles with a 2.45 degree of tapered angle in fabricated coarse angular sand have the maximum bearing capacity. Furthermore, in fine sand, the ultimate bearing capacity reduces with tapered angle after an optimized angle.