CYCLIC PILE LOAD TEST ON MODEL PILES IN SAND

Abstract

Piles are vertical or slightly slanting structural foundation members, having relatively small cross-sectional dimensions With respect to their length. They are introduced into the soil and transmit the loads and forces acting on the superstructure to the subsoil. The length, method of installation, and way of acting of piles can vary greatly, and thus they are easily adaptable to various conditions and requirements. Conducting a load test on a pile to determine its ultimate or safe load carrying capacity is indeed a costly and time-consuming enterprise. However, as stated earlier, it is the most reliable means of determining the load carrying Capacity of a pile, since, as a deep foundation; a pile passes through a number of different layers of soil with varying sometimes uncertain properties. Hence, in spite of the cost, time and effort, one may have to resort to a load test in many instances where one may be doubtful whether calculation by static or dynamic formulae would be sufficiently reliable. In fact, in most piling jobs, it is usual to stipulate that load test should be conducted on one pile, if not more. The load test on pile involves measuring deflection against loads applied in stages till the soil fails under the load. The data is plotted as a cyclic load settlement curve from which the ultimate load carrying capacity is interpreted. When a pile is loaded by an axial load at ground level, initially the applied load is distributed as friction load within a certain length of the pile measured from its top. When the pile is loaded first the load is taken by surface of pile in entire length. This is due to friction of surface this is called skin friction. After that the load of superstructure is taken by the base of pile in case of cohesionless soil. This resistance of pile is known as tip resistance. It is only after the full length of the pile develops frictional resistance at a certain stage of loading, that a part of the load is transferred to the soil at the base as point load. With the increase in load at the top after this stage, both the frictional as well as point loads increase. The frictional load attains a maximum value at a certain load level and will not further increase upon increase in axial load. But the point load still keeps on increasing till the soil at the base fails in local shear. The total settlement S of a pile obtained from a pile load test comprises of two components, namely, elastic settlement, Se and plastic settlement Sp. Piles are vertical or slightly slanting structural foundation members, having relatively small cross-sectional dimensions With respect to their length. They are introduced into the soil and transmit the loads and forces acting on the superstructure to the subsoil. The length, method of installation, and way of acting of piles can vary greatly, and thus they are easily adaptable to various conditions and requirements. Conducting a load test on a pile to determine its ultimate or safe load carrying capacity is indeed a costly and time-consuming enterprise. However, as stated earlier, it is the most reliable means of determining the load carrying Capacity of a pile, since, as a deep foundation; a pile passes through a number of different layers of soil with varying sometimes uncertain properties. Hence, in spite of the cost, time and effort, one may have to resort to a load test in many instances where one may be doubtful whether calculation by static or dynamic formulae would be sufficiently reliable. In fact, in most piling jobs, it is usual to stipulate that load test should be conducted on one pile, if not more. The load test on pile involves measuring deflection against loads applied in stages till the soil fails under the load. The data is plotted as a cyclic load settlement curve from which the ultimate load carrying capacity is interpreted. When a pile is loaded by an axial load at ground level, initially the applied load is distributed as friction load within a certain length of the pile measured from its top. When the pile is loaded first the load is taken by surface of pile in entire length. This is due to friction of surface this is called skin friction. After that the load of superstructure is taken by the base of pile in case of cohesionless soil. This resistance of pile is known as tip resistance. It is only after the full length of the pile develops frictional resistance at a certain stage of loading, that a part of the load is transferred to the soil at the base as point load. With the increase in load at the top after this stage, both the frictional as well as point loads increase. The frictional load attains a maximum value at a certain load level and will not further increase upon increase in axial load. But the point load still keeps on increasing till the soil at the base fails in local shear. The total settlement S of a pile obtained from a pile load test comprises of two components, namely, elastic settlement, Se and plastic settlement Sp.