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Pile tests

Static pile load tests

High strain static and dynamic load tests are the basic method for measuring pile bearing capacities on the site. Each of them can be used for testing reinforced concrete piles as well as compressed, timber, steel or combined piles. Pile cross-section can be constant or variable along the pile length. While static measurements are considered as most precise, dynamic test loading allows for a free choice of a test pile and determining pile bearing capacity with sufficient engineering precision. The results of such tests may be used in designing provided that the tests are performed on test piles prior to final piling or as as-built measurements.

Static Load Test (SLT) are considered as most precise method for measuring pile bearing capacities. Their results may be used for verifying the calculations models used in the geotechnical design of piles. The results of SLTs performed on test piles, prior to the final piling, may be directly used in designing. SLTs allow for determining the geotechnical bearing capacity and settlement/uplift of a single pile after time t that has collapsed from the moment of the pile is driven/installed in the ground. SLTs are measurements of displacement (settlement/uplift) of pile head s loaded with variable load Q.

The tests are performed as maintained load tests (MLT). The analysis of the obtained Q-s curve allows for:

• in ultimate limit state (ULS):

- determining the design geotechnical bearing capacity of tested pile Rd (ULS) in the Q-s curve funtion, e.g. in accordance to PN-83/B-02482;

- determining the geotechnical ultimate bearing capacity of pile R, and then determining the design bearing capacity Rd through dividing the ultimate bearing capacity R by the correct safety factor γ, e.g. in accordance to PN-EN 1997-1-1 (EC7);

• in serviceability limit state (SLS), determining total settlement/uplift, both variable and permanent, under the expected service load conditions.

SLTs may be performed as compression and tension tests as well as recurrent tests. Loads are applied with a hydraulic cylinder mounted between the tested pile and the retaining structure. Based on the cylinder characteristics, pressure measurements allow for determining the load acting on a pile, whereas the digital and/or displacement cells make it possible to continuously monitor the pile head position caused by the applied load.

Aarsleff performs SLTs with max. loads of 4,000kN based on the provisions of PN-83/B-02482, PN-EN 1997-1, ISSMFE Subcommittee on Filed and Laboratory Testing, Axial Pile Load Test, Suggested Method. ASTM Journal, June 1985, pp. 79-90 or technical specifications included in designs

Dynamic pile load tests

High strain static and dynamic load tests are the basic method for measuring pile bearing capacities on the site. Each of them can be used for testing reinforced concrete piles as well as compressed, timber, steel or combined piles. Pile cross-section can be constant or variable along the pile length. While static measurements are considered as most precise, dynamic test loading allows for a free choice of a test pile and determining pile bearing capacity with sufficient engineering precision. The results of such tests may be used in designing provided that they are performed on test piles prior to final piling or as as-built measurements.

Dynamic load tests (DLTs) are based on the measurements of strain (with strain transducers) and acceleration (with accelerometers) in piles caused by their dynamic installation into the ground. The preparation for a dynamic load test consists in equipping the opposite sides of a pile with two pairs of sensors – a strain transducer and accelerometer – in order to avoid the bending impact, as the hammer blows rarely occur precisely in the pile axis. During the test the cells are linked to a data logger, which may be connected to a PC. In the course of the test the pile is driven into the ground and simultaneously the signals from the cells are recorded. Usually the signal obtained from one hammer blow is used for further data processing. From strain values, force in pile F is calculated as F = EAε, and from a acceleration values, velocity is determined as v = ∫αdt. The results are analyzed with one of methods available, such as CASE or CAPWAP.

The preparation of a pile for DLT (assembly of the cells with bolts and connection of the data logging equipment) and the test itself usually take up to 20 minutes. Depending on the method of analysis, the results of DLTs are the ultimate pile baring capacity and resultant displacement (CASE) or ultimate bearing capacity of pile toe and pile shaft, bearing capacity distribution on the pile shaft length and relation between the load and settlement of the tested pile. The results of DLTs should be correlated to the results of SLTs performed for a driven/installed piles in corresponding soil conditions (for another pile in a foundation or on the basis of previous SLT data). Aarsleff performs DLTs in accordance with the provisions of PN-EN 1997-1-1 oraz ASTM D 4945 Standard Test Method for High-Strain Dynamic Testing of Piles or technical specifications included in designs.

Pile integrity tests

The main objective of pile integrity testing is the quality assessment of precast piles installed into the ground. Pile integrity tests are performed as high-strain and low-strain impact tests. In case of precast RC piles, the high-strain method is applied, which is one of the results of DLTs. The piles for integrity testing are chosen on the basis of the Driving Records. For piles formed in the ground the low-strain method should be used, such as the Pile Integrity Test (PIT). This test allows for determining in detail the size, length and location of possible pile damage. As a result, the percentage of damaged area is calculated in relation to the total area of the cross-section.

Aarsleff performs dynamic pile integrity tests as high-strain dynamic tests for precast RC piles and as PITs for piles formed in the ground, in accordance with ASTM D 5882-07 Standard Test Method for Low Strain Impact Integrity Testing of Deep Foundation or technical specifications included in designs.