Foundation Testing

1. Static Pile Load testing using Kentledge / Load Frame method

In Static pile load test the load is most commonly applied via a jack acting against a reaction beam, which is restrained by an anchorage system or by jacking up against a reaction mass (“Kentledge” or dead weight). The anchorage system may be in the form of cable anchors or reaction piles installed into the ground to provide tension resistance. The nominated test load is usually applied in a series of increments in accordance with the appropriate Code, or with a pre determined load testing specification for a project. Each load increment is sustained for a specified time period, or until the rate of pile movement is less than a nominated value.

Static load testing methods are applicable to all pile types, on land or over water, and may be carried out on either Working piles or sacrificial Preliminary piles. Trial piles are specifically constructed for the purpose of carrying out load tests and therefore, are commonly loaded to failure. Testing of working piles however, is limited to prove that a pile will perform satisfactorily at the serviceability or design load, plus an overload to demonstrate that the pile has some (nominated) reserve capacity. All the systems are designed to allow easy interfacing with our range of jacking and testing equipment.

2. High-strain Dynamic Pile Testing using specialized 8-channel, PDA equipment imported from Pile Dynamics Inc., U.S.A.

Attempts to determine the pile capacity using dynamic analysis date back to the 19th century. ‘Hiley’s or other formulae were widely used to predict the pile capacity and decide the pile termination for driven piles. Dynamic formula considers the energy of the pile driving hammer and the set of a pile to estimate the pile capacity. Numerous studies have concluded that their predictionaccuracy is poor. A major limitation of dynamic formula in the context of driven piles is the fact that they cannot predict hammer efficiency and stresses during driving. The dynamic formulae do not take into account the changes in soil stratum and are not applicable to bored piles. These limitations are overcome by the High Strain

Dynamic Pile Tests (HSDPT) which is sometimes referred as ‘PDA (pile driving analyzer) Test’. In case of driven piles the pile capacity derived from HSDPT generally shows satisfactory agreement with that measured by static load test (Rausche et al., 1985). The HSDPT also offers the following advantages:

• Piles can be tested in a day resulting time saving,
• HSDPT requires very little space,
• Structural integrity of the pile is verified,
• It is possible to broadly estimate the frictional and end bearing resistance of the piles.

3. Low-strain Pile Integrity tests using customized equipment imported from Pile Dynamics Inc., U.S.A.

Low Strain Impact Integrity Testing is a non-destructive pile testing method for integrity assessments of augered cast-in-place piles, drilled shafts or driven concrete or timber piles. If major defects exist, test results may be interpreted to estimate their magnitude and location. Test results may also be used to estimate pile length. Because of their simplicity, speed of execution and relatively low cost, these integrity tests may be performed on 100% of the piles on a given a job site.

Pile Integrity Testing has been routinely used worldwide for many years; it is standardized by ASTM D5882 - Standard Test Method for Low Strain Impact Integrity Testing of Piles.

4. Cross-hole Sonic Logging tests using customized equipment imported from Pile Dynamics Inc., U.S.A.

Crosshole sonic logging (CSL) is a method to verify the structural integrity of drilled shafts and other concrete piles. The CSL 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.

Also known as Crosshole Acoustical Testing, CSL 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 CSL 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 CSL tubes are preferred over PVC tubes because studies have shown that PVC tubes tend to debond from the concrete due to the heat of hydration process of concrete, resulting in erratic CSL test results.

The tubes are filled with water as an intermediate medium. After curing for 3-7 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.

5. Parallel Seismic Tests: Determination of unknown pile length using customized equipment imported from Olson Engineering, U.S.A.

The Parallel Seismic (PS) method is a not pile testing and is applied to determine the lengths of deep foundations where foundation tops are not accessible, or when the piles are too long and slender (such as H piles or driven piles) to be tested by Impact Echo, Pile Integrity Testing, Sonic Echo/Impulse Response techniques. In addition, the PS method can provide information about the soil below the foundation bottom for geotechnical testing

Parallel Seismic involves hitting any part of the structure that is connected to the pile or foundation (or hitting the foundation itself, if accessible) and receiving compressional and/or shear waves travelling down the foundation by a hydrophone or a geophone receiver.