Pile Integrity Test
Pile Integrity test is the test to assess the integrity of the pile foundation In order to know the condition of the integrity of the pile structure. As the pile found that the condition is not perfect than the criteria used for acceptance, it may affect the ability of its capacity to withstand the bearing capacity as well. The pile integrity test method investigated by using stress wave such as the Low Strain Integrity Test (Seismic Test), Side Echo Test, and Single Shock End Test and Cross Hole Sonic Logging Test is the method which using Ultra Sonic Pulse Test in Inspection.
Low Strain Integrity Test (Seismic Test)
Low strain integrity test is one of the methods for assessing the condition of piles or shafts. It is cost-effective and not very time-consuming. This method is covered under ASTM D5882 Standard Test Method for Low Strain Integrity Testing of Piles.
The test is based on wave propagation theory. The name "low strain integrity test" stems from the fact that when a light impact is applied to a pile it produces a low strain. The impact produces a compression wave that travels down the pile at a constant wave speed. Changes in the cross-sectional area - such as a reduction in diameter - or material - such as a void in concrete - produce wave reflections.
This procedure is performed with a handheld hammer to generate an impact, an accelerometer or geophone placed on top of the pile to be tested to measure the response to the hammer impact, and a data acquisition and interpretation electronic instrument.
Moreover, This Scope of work in low Strain integrity test has been certified according to ISO9001:2015 standard which is the first and only testing company in Thailand that is certified in this section.
Side Echo Test
The Side Echo Test is a modified method from the normal sonic echo test (seismic test). The purpose of this testing is applied to evaluate the integrity condition and length of the pile foundation when foundation tops are not accessible.
Due to the foundation top cannot access, the excavation beside the foundation pile is required until the pile side is accessible. The transfer block (steel block 500 ×500×250 mm.) shall be attached to the side of the test pile by expansion bolt.
This block is used to transfer the compression wave down to the pile. Before testing the tri-axial accelerometer geophone shall be attached beside the pile at approximately 0.15-0.20 cm. below the transfer block. After that, the transfer block is struck by the handheld hammer in the vertical direction. The movement of the pile, caused by hammer impact stress wave and subsequent reflection is measured by the above mention sensitive accelerometer. The acceleration signal is converted to velocity and presented on screen as a function of time. All results are stored for use in reports.
Single Shock End Test
Single Shock End Test is the advanced method compare with Conventional Low strain Seismic Test for testing the integrity of the pile foundation. In the Conventional seismic test, the basic concept in the analysis of the result is base on Time-Based Techniques. The interpretation result displays the relation between pile head velocity, the depth of pile structure, and a Non-Instrument hammer generates the impact pulse. While in the Shock Testing the impact pulse stress wave is generated by using an Instrument hammer which can record the signal in both pile head velocity and force versus depth.
The frequency response method uses modern computational techniques to analyze the composite waveform. The information obtained by using Shock Testing is shown in the list below:
1. Impact quality and concrete quality near the pile top
2. Pile defect along the investigated length
3. Approximated pile length (if possible)
4. Characteristic mobility (M) and Pile head dynamic Stiffness (E’)
Cross Hole Sonic Logging Test
Cross hole sonic logging is a method to verify the structural integrity of drilled shaft and other concrete piles. This method is covered under ASTM D6760. The method is considered to be more accurate than sonic echo testing in the determination of structural soundness of concrete within the drilled shaft inside of the rebar cage. This method provides little indication of concrete soundness outside the cage.
Cross Hole Acoustical Testing normally requires steel (preferred) or PVC access tubes installed in the drilled shaft and tied to the rebar cage. Before the rebar cage is placed in the hole, the access tubes are attached to the interior of the rebar cage. The cage is then lowered into the hole and the concrete is placed. Steel tubes are preferred over PVC tubes because studies have shown that PVC tubes tend to de-bond from the concrete due to the heat of the hydration process of concrete.
The tubes are filled with water as an intermediate medium. After curing for 7-14 days, a sound source and receiver are lowered, maintaining a consistent elevation between source and sensor. A signal generator generates a sonic pulse from the emitter which is recorded by the sensor. Relative energy, waveform, and differential time are recorded and logged. This procedure is repeated at regular intervals throughout the pile and then mapped. By comparing the graphs from the various combinations of access tubes, a qualitative idea of the structural soundness of the concrete throughout the pile can be gleaned.