Nonlinear deformations of the compacted soil base under the broadening of piles in punched holes

Abstract

The peculiarity of piles in punched holes with broadening (PPH), performed according to the technology of foundations in rammed pits, is considered to be a high load-bearing capacity compared to traditional driven piles. At the same time, from the long-term practice of using the PPH, the actual excess of the calculated settlement is noted. This is due to a significant excess of pressure of the order of 1,000-3,000 kPa under the widening of the pile over the calculated resistance of the compacted soil layer. This makes it necessary to calculate such a foundation for the second group of limit states, taking into account the nonlinearity within the limits of the calculated allowable pressure. The article compares three methods of calculating settlement taking into account non-linearity: according to the tables of the standard, the methods of N.V. Ornatsky and M.V. Malyshev. It is noted that the methods do not always correspond to the actual work of the foundation in the ground, which can reduce the reliability of calculations. The authors proposed to modernize the existing methods of calculating settlement due to the peculiarities of the work of the PPH. In the calculation scheme of the PPH, to determine the settlement, it is necessary to take into account the soil layer with an increased modulus of deformation created during the punching of the well and the formation of broadening. Zones of marginal equilibrium develop with a margin within the boundaries of the compacted layer under broadening. It is proposed to take into account the nonlinear dependence of soil deformations on stresses within the specified boundaries, and to take into account the remaining deformations of the compressible thickness in a linear formulation. Taking into account the non-linearity in the determination of settlement leads to an increase in the reliability of the application of the piles in question, especially in weak clay water-saturated soils, and in relatively strong soils allows us to confirm the reliable use of PPH.