Types of Pile Testing
1. Pile Integrity Test
2. Dynamic load Test
1. Pile Integrity Test:
A pile is a slender element cast in the ground or driven into it. Since pile construction as well as the final product are mostly invisible, engineers have often questioned their integrity, i.e. their compliance with project drawings and specifications. In fact, experience has shown that in piles, of all kinds flaws may occur. The purpose of integrity testing is to discover such flaws before they can cause any damage.
Indirect methods, or imaging, were first developed in the early 1970s. These include three distinct methods:
● Nuclear radiation, or gamma-gamma method.
● Short wave (ultrasonic) acoustic method.
● Long wave (sonic) acoustic method.
A pile integrity test (also known as low-strain dynamic test, sonic echo test, and 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.
Pile integrity testing using low-strain tests such as the TDR (Transient Dynamic Response) method, is a rapid way of assessing the continuity and integrity of concrete piled foundations.
The Test Measures:
● Pile length, or depth to anomalies.
● Pile head stiffness.
● Pile shaft mobility, which is dependent on pile section and concrete properties
The software also produces computer simulations and impedance profiles of the test result, to analyse in detail any intermediate pile shaft responses.
2. Dynamic Load Test:
Dynamic load testing is a method to assess a pile's bearing capacity by applying a dynamic load to the pile head (a falling mass) while recording acceleration and strain on the pile head. Dynamic load testing is a high strain dynamic test which can be applied after pile installation for concrete piles. For steel or timber piles, dynamic load testing can be done during installation or after installation.
The procedure is standardized by ASTM D4945-00 Standard Test Method for High Strain Dynamic Testing of Piles. It may be performed on all piles, regardless of their installation method. In addition to bearing capacity, Dynamic Load Testing gives information on resistance distribution (shaft resistance and end bearing) and evaluates the shape and integrity of the foundation element.
Pile and Test Preparation:
Dynamic load test on piles is carried out by fixing strain sensors and accelerometers to the sides of the test pile below 1.5 times of pile diameter or higher from the pile head top and then connecting them with PDA.
Test pile should be extended to 1.6 times pile diameter after chipping top loose concrete.
In the case of the liner pile, two openings(300mm x 300mm) shall be left below 1.5 times of pile diameter from the top of the pile head for sensor fixing.
Input Parameters Dynamic Load Test on Piles:
1. Pile No.
2. Date and time of test
3. The pile length below gauges (LE)
4. The adopted pile wave speed at the pile head and the overall wave speed
5. The wave return time (2L/c)
6. The pile modulus at the transducer location
7. The pile specific weight
8. The pile area at the transducer location (AR)
9. The pile impedance
10. The Case Method damping factor(Jc)
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