Pile Testing, Pile Integrity Test and Crosshole Sonic Logging Techniques during the Construction

Piles are often tested at great expense and effort, as results are critical in verifying foundation design parameters and formulating remedial actions when needed. As such, the data has to be recorded with a high degree of accuracy and integrity. 

Benefits of Pile Testing

• Increased quality assurance
• Cost effective
• Can test a greater number of piles
• Operate to standards
• Tests are carried out quickly

A pile integrity test (also known as lowstrain 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.

During the construction of deep foundations there are different circumstances that are likely to affect the final shape of piles that tend to affect the designed depth, cross section and material quality. For quality control assurance of these elements pile integrity test (PIT) is often used.

Pile Integrity Test (PIT) as a method that involves the impact of a hammer on the head of the pile generating a low strain compression wave that propagates along the pile and afterwards is reflected at the bottom of the pile, or where there are changes of impedance related with variations in cross section or density of the material.

Importance of Pile integrity tester plays an efficient role during or after construction.

The Pile Integrity Tester is available in 4 models, with one (PIT-X and PIT-V) or two (PIT-X2 and PIT-FV) channels of data acquisition:

PIT-X and PIT-X2 are small and light, and read data from wireless accelerometers.

PIT-V and PIT-X read velocity data from a single accelerometer and analyze data in the Time Domain; this is sufficient for most integrity tests

PIT-X2, used in 2 velocity mode, enables the tester to analyze data from 2 accelerometers; this may be useful for determining unknown foundation length.

PIT-FV reads data from one (traditional) accelerometer and one instrumented hammer or from two accelerometers. It permits force and velocity analysis in the Frequency Domain for a more thorough evaluation of the integrity of the foundation and allows the investigation of defects near the pile top. PIT-FV may also be used to assess of the depth of an unknown foundation.

Construction planning adopts a completeness with a wll planned strategies and techniques, considering the equipment effect also. An another testing factor is involved in the construction area i.e Crosshole sonic Logging.

Crosshole Sonic Logging (CSL) is the most accurate and reliable technique for assessing the integrity of deep foundation elements constructed on-site from concrete or grout. The crosshole sonic lo gging method is normally applied as a quality assurance (QA) technique for newly placed drilled shafts and auger cast piles, but can also be applied to slurry walls, mat foundations, and mass concrete pours.

Secant pile walls are formed by a series of interlocking drilled shafts. Primary piles without reinforcement are built first. The gaps are filled  by secondary reinforced piles, which overlap the primary ones . The concrete of the primary pile is often chosen to be weaker than for ordinary piles to facilitate drilling.

Standard pile drilling rigs are used for construction Crosshole Sonic Logging (CSL) was until now limited to be applied within the reinforcement cage of a single pile. Thus there is no possibility to check the integrity of the primary piles before excavation. Even if high standards are applied, the construction sometimes fails, e.g. at unexpected soil in homogeneities.