Safe Load Test for Determining the Load Carrying Capacity of an Under-reamed Pile



The load carrying capacity of an under-reamed pile, which is a type of deep foundation, can be determined through various tests. However, the most commonly used method is the safe load test. This test is conducted to evaluate the performance and strength of the pile under load and to ensure that it can safely support the design load.



Explanation:


The safe load test involves applying a gradually increasing load to the pile until it reaches its ultimate capacity or a predefined limit state. The test is typically performed in two stages: the initial loading stage and the main loading stage.



Initial Loading Stage:


During the initial loading stage, a small load is applied to the pile to remove any residual air or water pressure in the soil. This ensures that the load is transferred directly to the pile and not to the surrounding soil.



Main Loading Stage:


In the main loading stage, the load applied to the pile is increased incrementally until the desired load is achieved or the pile reaches its ultimate capacity. The load is usually applied using hydraulic jacks or reaction frames, and the settlement of the pile is measured at each load increment.



Load-Settlement Curve:


The load-settlement curve obtained during the safe load test provides valuable information about the behavior and load carrying capacity of the under-reamed pile. The curve typically exhibits three distinct regions:

1. Elastic Region: In the initial stages of loading, the pile undergoes elastic deformation, and the settlement is directly proportional to the applied load.

2. Plastic Region: As the load increases, the pile enters the plastic region, and the settlement rate starts to increase at a faster rate. This indicates that the soil surrounding the pile is undergoing plastic deformation.

3. Ultimate Load Region: At a certain point, the pile reaches its ultimate load capacity, and the settlement increases rapidly. This signifies that the pile is nearing its failure state.



Safe Load Determination:


The safe load carrying capacity of the under-reamed pile is usually determined based on the allowable settlement criteria specified in the design code or project specifications. The load at which the settlement exceeds the allowable limit is considered the safe load capacity of the pile.



Therefore, the safe load test is used to determine the load carrying capacity of an under-reamed pile by gradually applying loads and measuring the corresponding settlements. The test provides valuable information about the behavior and performance of the pile, ensuring that it can safely support the design load without excessive settlement.