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Laboratory and field data showed that deep mixed (DM) columns accelerated the rate of consolidation of the soft foundations. Most analyses of consolidation of DM column-improved foundations so far have been based on the elastic theory. In... more
Laboratory and field data showed that deep mixed (DM) columns accelerated the rate of consolidation of the soft foundations. Most analyses of consolidation of DM column-improved foundations so far have been based on the elastic theory. In reality, the DM columns may yield due to the stress concentration from the soft soil and its limited strength. The influence of column yielding on the degree of consolidation of the soft foundation improved by DM columns has not been well investigated. A three-dimensional mechanically and hydraulically-coupled numerical method was adopted in this study to investigate the degree of consolidation of the DM column foundation considering column yielding. A unit cell model was used, in which the soil was modeled as a linearly elastic material. For a comparison purpose, the DM column was modeled as an elastic or elastic-plastic material. This study examined the aspects of stress transfer, settlement, and degree of consolidation of the foundations without or with the consideration of the yielding of the DM column. A parametric study was conducted to investigate the influence of the column yielding on the stress concentration ratio, settlement, and average degree of consolidation of the DM column foundation. The stress concentration ratio increased and then decreased to reach a constant value with the increase of the column modulus and time. A simplified method was proposed to calculate the maximum stress concentration ratios under undrained and drained conditions considering the column yielding. The simplified method based on a composite foundation concept could conservatively estimate the consolidation settlement. An increase of the column modulus, area replacement ratio, and/or column permeability increased the rate of consolidation.
Research Interests:
Foundations constructed on soft soil often require columns to increase bearing capacity and reduce total and differential settlements. Columns can be: (1) flexible (e.g., stone columns and sand compaction columns); (2) semi-rigid [e.g.,... more
Foundations constructed on soft soil often require columns to increase bearing capacity and reduce total and differential settlements. Columns can be: (1) flexible (e.g., stone columns and sand compaction columns); (2) semi-rigid [e.g., deep mixed (DM) columns and jet-grouted columns]; and (3) rigid (e.g., vibro-concrete columns). Research has demonstrated that columns can also accelerate the consolidation of soft foundations by column drainage and stress transfer. In this paper, a three-dimensional, coupled, numerical analysis was adopted to study the consolidation behavior of soft foundations improved with two types of composite columns. For example, a DM column or jet-grouted column can be installed in the middle of the stone column or sand column. In this composite column, the stone column or sand column provides drainage while the DM column or jet-grouted column provides stiffness. Columns and soil in this study were modeled as elastic materials and one quarter of the unit cell was used due to the symmetry. To demonstrate the benefit of the composite columns in accelerating consolidation, two soft foundations improved with stone columns and DM columns were analyzed for comparison purposes. The numerical results show that both column drainage and stress transfer contributed to the acceleration of the consolidation of the soft foundations improved with composite columns. In addition, a parametric study was conducted to evaluate the influence of the stiffness of DM columns on the rate of the consolidation of the soft foundation improved with composite columns.
Research Interests:
This paper presents a numerical analysis of a well-monitored pile–slab-supported embankment for the Beijing–Tianjin high-speed railway in China. Cement–fly ash–gravel piles were used in this project. A coupled twodimensional mechanical... more
This paper presents a numerical analysis of a
well-monitored pile–slab-supported embankment for the
Beijing–Tianjin high-speed railway in China. Cement–fly
ash–gravel piles were used in this project. A coupled twodimensional
mechanical and hydraulic numerical model
was used for this analysis and the results are compared with
the field measurements including settlement, load distribution
between soil and pile, and excess pore pressure. The
numerical model calculated the settlement profile close to
that measured in the field. The proportion of the load
carried by the soil was small thus significantly reducing the
settlement. The stress transfer from the soil to the piles
reduced the excess pore pressure effectively. A parametric
study was conducted to investigate the influence of three
key factors on the performance of the embankment. The
parametric study indicated that the existence of a cushion
reduced the shear force in the slab. The increase in slab
thickness and pile stiffness increased the shear force and
bending moment in the slab. An increase in pile stiffness
reduced the settlement and lateral displacement of the
embankment.
well-monitored pile–slab-supported embankment for the
Beijing–Tianjin high-speed railway in China. Cement–fly
ash–gravel piles were used in this project. A coupled twodimensional
mechanical and hydraulic numerical model
was used for this analysis and the results are compared with
the field measurements including settlement, load distribution
between soil and pile, and excess pore pressure. The
numerical model calculated the settlement profile close to
that measured in the field. The proportion of the load
carried by the soil was small thus significantly reducing the
settlement. The stress transfer from the soil to the piles
reduced the excess pore pressure effectively. A parametric
study was conducted to investigate the influence of three
key factors on the performance of the embankment. The
parametric study indicated that the existence of a cushion
reduced the shear force in the slab. The increase in slab
thickness and pile stiffness increased the shear force and
bending moment in the slab. An increase in pile stiffness
reduced the settlement and lateral displacement of the
embankment.