Determination of settlement of pile foundations by load test method, equipment required, procedure and reporting of results in discussed.
Equipment for Pile Settlement Determination TestVarious types of equipments are required for determination of settlement of pile foundations. Following is the list of equipment required: (a) Kentledge, anchor piles or other anchorages supported or installed at suitable locations to provide adequate reactions against jacking. (b) A load-measuring device which shall consist of a load column, pressure cell, or other appropriate system, calibrated before and after each series of tests, or whenever adjustments are made to the device, or at time intervals recommended by the manufacturer of the equipment. (c) Four deflectometers accurate to 0.025 mm. (d) Precision levelling equipment accurate to 0.25 mm. (e) A reference frame for supporting deflectometers and providing a datum for deflectometer measurements. (f) Working platforms. (g) Screens and protection from exposure to conditions which may affect the test. (h) Hydraulic loading equipment.
Procedure of Pile Settlement Determination Test
The procedure before testing shall be as follows:(a) The kentledge, anchor piles or other anchorages shall be installed. The centre of each anchor pile shall be at least 2 m or three times the pile diameter, whichever is greater, from the centre of the pile to be tested and from the centre of any adjacent pile. (b) If required, the pile to be tested shall be extended from cut-off level to ground level. The strength of piles at joints shall not be less than any normal section of the pile. (c) A temporary square pile cap designed by the Contractor shall be constructed. (d) Working platforms, screens and protection shall be installed. (e) The reference frame shall be set up on supports which are at least 2 m or three times the pile diameter, whichever is greater, from the test pile and anchor pile. The four deflectometers shall be mounted on the reference frame to measure the deflection of the four corners of the temporary pile cap.
Fig: Pile load test for Burj Khalifa (Dubai)
Procedure: Pile Load Test
The procedure for the pile load test shall be as follows:(a) Preliminary piles shall be tested to not less than twice the working load of the pile or other loads stated in the Contract. Working piles shall be tested to not less than 1.8 times working load. Reductions for group or boundary effects shall not be made in determining the test loads. (b) Test loads shall be applied and removed in three stages as stated in Table - 1. (c) Unless otherwise permitted by the Engineer, the test loads shall be applied in increments, and removed in decrements, of 25% of the working load. Increments of load shall not be applied until the rate of settlement of the pile is less than 0.1 mm in 20 minutes. (d) The full test loads for Stage I shall be applied in increments and shall then be maintained for at least 24 hours after the rate of settlement has reduced to less than 0.1 mm per hour. The test loads shall be removed in decrements and the recovery of the pile determined before loading is resumed. (e) The procedure stated above in (d) shall be repeated for Stage II loading. (f) The procedure stated above in (d) shall be repeated for Stage III loading unless the Engineer instructs the loading to be maintained for a longer period. (g) The settlement of the pile shall be measured at hourly intervals or other intervals agreed by the Engineer. The settlement of the pile under each increment and decrement of loading shall be measured. The exact times at which increments are applied and decrements are removed shall be recorded. Settlements shall be measured and times shall be recorded in the presence of the Engineer. (h) The level of the reference beam shall be checked at regular intervals agreed by the Engineer during the test.
Table – 1: Test loading stages
|I||25% max. test load|
|II||50% max. test load|
|III||100% max. test load|