Abstract
To analyze the influence of stone column installation on the enhancement of soft ground and to reveal the physical aspects of the soil-pile interaction (SPI) mechanism, the stone column installation process is fully simulated by the three-dimensional continuous-discrete coupling (CDC) method for the first time. The stone column is simulated by particles in a discrete domain, the soft foundation and hammer are simulated by solid elements in a continuum domain, and the soil-pile interface and soil-hammer interface are simulated by coupling faces. Four installation effects, including the bottom enlargement effect, the branch effect, the heave effect and the penetration effect, are found during the installation process through the analysis of the displacement and stress field of the soft soil around the stone column. The bottom enlargement effect and the branch effect help improve the bearing capacity of the soft foundation, the heave effect helps to offset the ground subsidence, and the penetration effect reflects the penetration of the particles into the soft soil as they are punched by the hammer. Parametric studies of the stone backfill show that the average particle size, the friction coefficient and the bond strength ratio are linearly positively correlated with the displacement of the soil around the stone column, but the displacement of the soil decreases with a negative power law as the particle stiffness ratio increases. These research results are helpful for evaluating the influence of the stone backfill and the installation process on the reinforcement effect of the soft ground and for improving the accurate design and control level of soft ground strengthened by stone columns.
Highlights
Stone columns are cost effective and environmentally friendly; they are widely used to improve the soft ground formed by river alluvial, lacustrine sediment and marine deposition to increase the bearing capacity, accelerate the consolidation and reduce the long-term settlement of soil foundations
It can be seen that after the stone column is filled in the late stage, after the soil around the pile is compacted, the soft soil will further take the borehole as the center and escape to the surface of the ground, which is called the “heave effect.”14 Under the influence of the heave effect, the soil around the stone column has an upward displacement, which helps to offset the settlement deformation of the ground surface
This paper proposes for the first time a continuousdiscrete coupling method for simulating the installation process of stone columns to address the response of a composite foundation subjected to the impacts of a column hammer
Summary
Stone columns are cost effective and environmentally friendly; they are widely used to improve the soft ground formed by river alluvial, lacustrine sediment and marine deposition to increase the bearing capacity, accelerate the consolidation and reduce the long-term settlement of soil foundations. Indraratna et al. and Ngo et al. proposed a continuous-discrete coupling method to analyze the load-deformation behavior of a single stone column installed in clay but did not consider the installation process. Tan et al. used the discrete element software UDEC and the finite difference software FLAC to carry out the continuousdiscrete coupling simulation of a stone column enhanced foundation and studied the stress and strain localization of the soft soil around the stone column; the software failed to simulate the compaction effect of the stone backfill. The mechanism of the soil-pile interaction (SPI) during stone column installation is studied by a three-dimensional continuum-discrete coupling method, and the influence of the layered installation process, as well as the mesoproperties of the backfill, on the reinforcement effect of the soft foundation is analyzed. The layered installation process of a stone column is simulated, and the effect of the SPI and the mesomechanical parameters of a stone column on the reinforcement effect of the soft soil around the pile is analyzed
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