PSI - Issue 72

Boris Folić et al. / Procedia Structural Integrity 72 (2025) 286 – 293

291

Fig.9. (a) Approximate calculation of soil-cassion resistance. Without self weight of cassion. Coff.of sefty on tg a is onli 1.

In the previous approximate calculation, the dimensions of the RC diaphragm of the caisson and the soil conditions that satisfy and do not satisfy the requirements of the caisson’s stability are presented. Changes in influence in the arch for moving supports can be calculated tabularly. 4. Passive resistance of the soil due to the friction force between the wall and the soil Due to the appearance of friction between the wall and the soil, the Rankine wedge of passive soil resistance has an addition, an area next to the wall that is assumed to be in the form of a logarithmic spiral. Also due to friction in the case of passive soil resistance, there is a (deflection) rotation of the resultant, in relation to the normal to the wall, by an angle δ, Fig. 8. That angle δ expressed in relation to φ is usually about 1/3 to ½.

Fig. 10. Passive earth pressure , model with friction between wall and soil; (a) vertically immovable wall (b) vertically movable wall. By Milović (1987), or Maksimović (2005) .

The pneumatic caisson is by definition watertight, in order to enable dry work inside the caisson. The movement of the wall (RC diaphragm) is possible only if the watertightness of the caisson is preserved, several years after construction, and if the thrust force is greater than the vertical force of its own weight. To the extent that the thrust force occurs, in this case, it affects the reduction of the intensity of the vertical component. Measurements after the rehabilitation showed that the right caisson moved downwards by about 10 cm and rotated. So there is no upward movement of the wall, unless the center of rotation is in the center of the caisson, then one end moves down and the other moves up. A small digression, with deep foundations it is assumed that the point of rotation is in the axis of the foundation, but the point of rotation can be located, under, in or above the foundation. As we can see in Fig. 10b, the Rankine wedge can be extended to the junction with the wall, and the resistance calculated with a smaller wall height. The passive resistance of the soil due to upward movement of the wall is shown in Fig. 10b, but in this case movement of the rear part of the caisson can occur only if the center of rotation is near the center of the caisson. The force acting on the RC diaphragm due to passive resistance, with the influence of friction between the wall and the ground (Fig. 10a) for the data from Fig. 8 left, (φ=40 ֩̊ ) where δ/φ=0.50, is 11724.9 kN/m. If we compare with the value from Fig. 8 left, 5564.08 kN/m, we can conclude before the flood if the model with and without the