Interaction of cast-in-place piles with soil under type II collapsibility conditions

Conclusions

1. Under the given and similar hydrogeologic conditions, the settlements of piles fully cutting through the collapsible mass and sunk 2–12 m into the noncollapsible soils, when the pile bearing capacity under the external load is satisfied, are practically equal to the ground surface settlements in the pile site.

2. For long-term soaking of the soils from the top, the low position of the depth at which soil compression starts under the action of the dead weight of the mass (it is in the range 14–16 m), and the development of compression deformations in the noncollapsible layers, which prevents detachment of the upper soil zone from the piles, are essential under the given conditions.

3. For increase in the pile length from 24 to 31 m and support on denser soil layers (alluvial clays), the soil base resistance and the additional load caused by the soil mass action increase correspondingly, but the pile settlements remain practically unchanged.

For substantial reduction of the possible absolute pile settlements with prolonged soaking of the soils under the given hydrogeologic conditions, the pile length should be increased by about 20 m. However, for establishment of the foundation dimensions it is extremely important to compare the allowable and possible differential settlements of adjacent foundations, which are comparatively small under the given conditions.