Thus, the main process should be considered tixotropic hardening of clay soil surrounding the pile.
With a short -term appendix of the vertical load (namely, these conditions and take place in static tests), under the edge of the pile, an area of excess hydrostatic pressure is formed, which cannot instantly resolve.
Therefore, it remains to assume that there is a redistribution of internal forces between the tip and the side surface. The relative displacement of the pile causes a complete mobilization of superficial friction forces, which can be determined by measuring the effort necessary to extract it.
The value of surface lateral friction when extracting the pile or when it is immersed is approximately the same for cylindrical piles. If the hound -shaped piles are tested, it is natural that the resistance value during extraction will be much less than when pressed. In this case, the value of the resistance of the pile of the pile during its extraction cannot be larger than atmospheric pressure in the vacuum formed under the end of the pile. In the experiments, this value is quite small in comparison with the stresses that occur in the case of the application to the piles of pulling out the efforts.
The resistance to pulling out the pile largely depends on the speed of this process, which, as will be shown below, can give an idea of the nature of the flowing thixotropic changes in various clay soils. For the test, a special stand was made, which allows to determine the vertical pulling force with the measurement of the movement of piles from each stage of the load with an accuracy of 0.01 mm.
The pulling force on the piles was transmitted by steps with a constant speed depending on the consistency of the soil. When testing piles in pastes with a consistency of 6 = 0-G-0.5, pulling speed y = 250 g/min, and with a consistency of 6 = 1.0 it was 100 g/min.