Influence of loading rate on pile capacity in unsaturated sand

When in-situ tests are performed to determine the ultimate capacity of a pile after the installation, quite a lot of types of tests are available. The following tests are generally used, in order from most used method to least used method: the static testing method, dynamic testing methods, pseudostatic and statnamic testing methods. During a pseudostatic (or statnamic) test the pile is loaded with a ~ 70-150 ms loading pulse. In comparison with the dynamic test this loading regime is about 20 times as long, in comparison with the static test this is very short lasting. The difference in loading regime is influencing the bearing capacity of the pile. In literature two main phenomena for the change in bearing capacity are recognized: the excess pore pressures and the loading rate. In the typical Dutch situation the end bearing piles are situated in the Pleistocene sand layer, so the influence of the loading rate in non-saturated and saturated sand are of interest. From literature is concluded that the effect of the loading rate on the strength and stiffness properties for dry sand are small, but for the rate effect on the shaft friction no conclusive answer could be found. Therefore a series of model scale tests are performed to investigate the influence of the loading rate on the bearing capacity