چكيده به لاتين
The experience of pile driving projects failing in carbonate soils reveals the need for a more detailed study of the behavior pattern of the vertical bearing capacity of piles in these types of soils. Due to their calcareous structure, carbonate soils have their own characteristics such as high crushing and compaction, which behave differently from silicate soils. This thesis has investigated the laboratory study of the vertical bearing capacity of the pile wall and tip in the carbonate soils of Hormoz, Hengam, Qeshm and silicate soils of Firouzkouh 161, with two percentages of compaction of 30 and 80% in the dry state. The experiments were conducted using an innovative pneumatic long odometer and a 10 x 10 cm direct cutting device. The long odometer is able to simulate the friction process between the metal pile wall and the soil with good approximation on a laboratory scale. This is done by determining parameters such as the soil lateral pressure coefficient at rest (K0) and the effective vertical stress (𝞂´v) that are used in calculating the wall strength. Also, the direct shear device, with its high repeatability and ease of sample preparation, provides the necessary conditions for determining the shear strength parameters, including the interface friction angle (δ), which is used in wall friction calculations. It was observed that the unit resistance of the metal pile wall in Hormoz soil, compared to Firoozkouh 161 soil in contact with a rough surface, decreases by 23% for 80% density and by 21% for 30% density. Also, for the smooth metal surface, these values are 29% and 23%, respectively. This decrease is due to the occurrence of the crushing phenomenon in carbonate soil particles, which causes a sharp decrease in the metal-soil interface friction angle and can make the bearing capacity in this type of soil less than that of silicate soils with similar conditions. The results obtained were also compared with the values suggested by authoritative regulations such as API and ARGEMA and it was found that these values are less than the final limits set by the regulations. The bearing capacity of open-ended pile tips can be evaluated using the stresses measured by the end pressure gauge of the odometer cell and converting these data to the total capacity, using logarithmic spirals of the failure surface. Also, the use of the analytical method of hole expansion allowed the numerical calculation of this parameter and the results were compared with laboratory data. This difference was observed to be 15% for Hormoz soil with a density of 80% and 14% for a density of 30%. Therefore, the odometer device has performed well in measuring the pile tip resistance. The bearing capacity of the pile tip in two soils, Hormoz and Firouzkouh 161, was also evaluated and it was observed that this parameter can be reduced by up to 27% in dense soil due to increased stress and by up to 24% in loose soil. The reason for this is due to the breakage of particles, which leads to a change in the size and shape of the grains, and as a result, the soil structure is removed from its original state. Also, these values were less than the limiting numbers of the regulations. Therefore, designers should take this into account in calculating the pile tip resistance.
The evaluation of the most important indicator of carbonate soils, namely the crushing parameter (Br), was carried out in all experiments using the Hardin method. Percentage changes in this parameter play an important role in better understanding the behavior of this type of soil and identifying high-pressure areas such as the shear zone. It was observed that with increasing density, calcium carbonate percentage and pressure on the soil, crushing increases, and with increasing sample height, shear rate and friction angle, crushing decreases. Also, the shear rate was examined using a concept called the sensitivity coefficient (β). The results showed that with increasing shear rate, the time required for particle displacement decreases and the sensitivity coefficient becomes a smaller number.
By presenting new results and comparing them with existing recommendations, this research has contributed to a better understanding of the behavior of carbonate soils and their application in construction projects such as installing piles in coastal areas, and can be a useful guide for the design and implementation of these projects.
