A Study on Friction Resistance of Pipe Pile Subjected To Tension Load in Sand

Pile foundations often used to transfer structural loads into deeper layers. On granular soils shaft resistance is an important factor bearing capacity of axially loaded, especially when the pile is subjected to tensile loading. Tensile forces apply on the pile holding the position of ship repair, basements, pumping stations, waterworks structures which are under water. In addition, transmission lines towers, tall chimneys, submerged platforms, masts, and other similar structures that are built on piles, in exposed disturbing moments resulting from wind, earthquakes and sea waves. In such structures, disturbing moments transferred, in some piles for pressure and other piles for tensile load. So, study the behavior of these piles and also effective parameters on the tensile capacity of is very important. Bearing the applied tensile loads on structures is one of the important applications of deep foundations, especially piles. Tensile capacity of these foundations is often produced by the frictional resistance in soil-pile interface. Piles are deep foundations which have considerable acceptance because of multi-applications. Understanding the behavior of piles and prediction of their tensile capacity is so important. In the last three decades various theories have been created regarding the behavior of piles under different loading conditions. The validity of these theories is evaluated by comparing the test results on models or structures piles with the predictions of theoretical. The field tests are Perfect scale and highly desirable, but often costly and difficult. For this reason, laboratory experiments are used to study the behavior of piles under tensile load. But to consider real conditions of the area, especially coastal sites, can be installed the piles in the soil that have been used to study the tensile behavior of piles. The reliability of tension test results in the homogeneous soils and the impact of surface layers of sand in providing friction force are special cases that have not been tested in real conditions of the site. Different methods are developed to achieve safe, constructible and economic design, such as analytical, experimental and in-situ methods, but in some cases they are still subjected to limitations. These methods can’t neither determine tensile capacity of pipe piles in coastal sand nor examine behavior of them. Since jacking technique is recommended for achieving improved soil properties and eliminating the deficiencies of other installation methods, so investigation of its effect is important. In this method, after jacking the piles with hydraulic jacks, the piles are arbitrarily tested under compressive loading to determine their compressive bearing capacity and then their tensile capacity is determined based on ASTM D-3689 procedure. After reading test data, the ultimate tensile capacity of piles were determined using tensile capacity criteria and then compared with analytical results. Tensile behaviors of piles at large displacements are also investigated and required force for larger pull out displacements were measured. The results showed that determined uplift capacities are more than analytical results and sand compaction due to pile installation can increase frictional resistance. It also revealed that the tangential criterion is determinant to obtain ultimate tensile capacity in most piles.