In-situ tests programme
The in-situ test includes:
- A static vertical load test (axial compression test) of a single steel pile in sand.
- A static vertical load test (axial compression test) of a group of five steel piles in sand.
The tests will be executed according to the principles of European Standards.
The description of the piles used for in-situ tests:
The piles are composed of a steel pipe d133 mm with the 4 mm wall thickness, closed on the bottom. The total length is about 5 m, but only L=4 m of it is pressed into the soil.
In the case of the group of piles, their heads will be connected with a pile cap, according to figure 1.
Fig. 1. Diagram of the pile group arrangement
The assumed maximum load value for a single pile is 250 kN. The ultimate vertical test load Fu = 250x1.4 x1.2 = 420 kN (factors of 1.4 and 1.2 are required in EN standards);
The load will be applied gradually, at one-hour intervals until reaching the maximum load. The increment will be 25% of SWL, i.e. 62.5 kN. Then, the load will be decreased gradually again, at 15-minute intervals. This time, the increment will be 50% of SWL, i.e. 125 kN. The loading scheme for the single pile loading test is presented in Fig. 2 and for the group of piles in Fig. 3. and the values are presented in Table 1 and Table 2 respectively.
Fig. 2. Loading program of the single pile test
Table 1 Loading steps for axial compression test for a single pile
|Step||Load||Duration of step, min||Total duration, min|
Fig. 3. Loading program of the pile group
|Step||Load, kN||Duration of step, min||Total duration, min|
As required in the Standards, the pile head displacements and the applied load will be recorded at least at the following time intervals:
- Loading steps: 0, 2, 5, 10, 15, 20, 25, 30, 40, 50, and 60 min,
- Unloading steps: 0, 5, 10 and 15 min (plus at 30 min for total unloading).
Reaction frame description
A reaction frame is used to transfer the load applied to the tested piles.
The special ballasts are used to anchor the reaction frame as presented in Fig. 4. The ballast provides about 1500 kN of dead load.
The load cell and hydraulic jack system will be installed on the pile top.
Fig. 4. Pile test stand with reaction frame
Test equipment installation
For the axial compression test, the following equipment will be put in place:
- 2 vertical (for the single pile test) or 4 vertical (for the group of piles test) linear transducers (range 150 mm) at the pile top to measure the displacement of the head during the loading test; these sensors are fixed on reference beams independent of the reaction frame.
- 2 horizontal linear displacement transducers (range 25 mm) at pile head (or on the cap) in order to measure the horizontal displacement of the pile head during the loading test; these sensors are also fixed on the reference beam.
- A load cell is placed between the main reaction beam and the hydraulic jack.
- 10 to 50 strain gauges
Taking into account the number of sensors, the acquisition of the data will be carried out via Data Acquisition System connected to a computer. These transducers allow measuring displacements with an accuracy of at least 0.01mm.