Abstract
Soil improvement can be enhanced significantly when combining the two well-known methods, i.e., prefabricated vertical drains (PVDs) and deep cement mixing (DCM) columns. While this approach has been proved to be effective through recent site studies, there is a lack of rigorous theoretical methods to model the coupled effects of PVDs and DCM columns on soil behavior. This paper hence aims to propose a novel analytical solution for consolidation of soft ground stabilized by the combined PVDs-DCM columns. The solution is developed with radial drainage, in which the effects of smear zone, well resistance, and nonlinear behavior of permeability and compressibility during the consolidation process are simultaneously considered. The proposed solution is verified by comparing itself with field data and previous theoretical solutions. The results indicate promising outcomes from the proposed model considering its good agreements with field data and other solutions. Subsequently, key parameters affecting the performance of composite PVDs-DCM foundation are investigated using the proposed solution. The results show that the effects of the compression modulus and cross-section area of DCM columns on consolidation rate are prevalent over their hydraulic conductivity. The discharge capacity of PVDs significantly affects the short-term bearing capacity of the DCM columns. The study offers significant values to industry applications via the newly proposed model and parametric assessment.
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The data presented in the paper are presented in the main text. The results were understood from figures, tables which mentioned in this article.
Abbreviations
- a s :
-
area improvement ratio (\({a}_{s}={A}_{col}\text{/}A\))
- A :
-
area of influent zone (unit cell) (m)
- A s :
-
area of soil in influent zone (unit cell) (m)
- A col :
-
cross-section area of DCM column (m)
- A DCM :
-
area of DCM zone in influent zone (m)
- A w :
-
area of PVD in influent zone (m)
$$b=\frac{{r}_{e}}{{r}_{sm}}$$ - C c :
-
compression index
- c col :
-
is cohesion of column material
- C k :
-
a constant used to reflect the decrease in permeability as the void ratio changes during consolidation
- c u :
-
undrained shear strength of the clay
- C r :
-
recompression index
- D col :
-
diameter of DCM column
- DCM:
-
deep cement mixing
$$d=\frac{{r}_{s}}{{r}_{D}}$$ - d e :
-
diameter of unit cell (m)
- d sm :
-
diameter of the smear zone (m)
- d w :
-
diameter of the drain (m)
- e o , e :
-
void ratio
- e o :
-
initial void ratio
- E s :
-
compression modulus of soil (kPa)
- E col :
-
compression modulus of DCM column (kPa)
- E w :
-
compression modulus of PVD (kPa)
- F :
-
factor
- FEM :
-
finite element method
$$f=\frac{{r}_{e}}{{r}_{D}}$$ - H :
-
thickness of soft clay layer (m)
- h 1 and h 2 :
-
thickness of upper and lower clay layer (m)
- k col :
-
coefficient of permeability of DCM column (m/s)
- k h :
-
coefficient of permeability in radial direction (m/s)
- k s :
-
coefficient of permeability in smear zone (m/s)
- k w :
-
coefficient of permeability of drain (m/s)
- k wo :
-
initial value of kw (m/s)
- n :
-
drain spacing ratio, (\(n=\frac{{r}_{e}}{{r}_{w}}\))
- n s :
-
stress concentration factor, \({n}_{s}={\sigma }_{col}\text{/}{\sigma }_{s}\)
- OCR :
-
overconsolidation ratio.
- q r :
-
water flow in unit cell (m.3/s)
- q w :
-
discharge capacity of drain (m.3/year)
- r :
-
radius (m)
- r e :
-
radius of the unit cell (m)
- r sm :
-
radius of the smear zone (m)
- r w :
-
radius of the drain (m)
- r D :
-
radius of the DCM zone in unit cell (m)
- S c :
-
final consolidation settlement (m).
- s :
-
smear ratio (\(s=\frac{{d}_{sm}}{{d}_{w}}\))
- PVD:
-
prefabricated vertical drain
- P ( t) :
-
external load with time (kPa)
- Q ult ,col :
-
ultimate bearing capacity of DCM column in short term (kN)
- Q ult , col ( t ) :
-
ultimate bearing capacity of DCM column according to time (kN)
- u :
-
excess pore water pressure (kPa)
- \({\overline{u} }_{r}\) :
-
average excess pore water pressure in unit cell (kPa)
- \({u}_{o}\) :
-
initial excess pore water pressure (kPa)
- \({\overline{u} }_{w}\) :
-
average excess pore water pressure at drain (kPa)
- \(\overline{U },{\overline{U} }_{1},{\overline{U} }_{2}\) :
-
degree of radial consolidation (%)
- z :
-
depth (m)
$$\alpha :=\frac{{k}_{h}}{{k}_{sm}}$$$$\beta :=\frac{{k}_{h}}{{k}_{col}}$$ - \({\varepsilon }_{v}\) :
-
vertical strain at any depth
- \({\gamma }_{sat}\) :
-
unit weight of saturated soil (kN/m.3)
- \({\gamma }_{w}\) :
-
unit weight of water (kN/m.3)
- \({\sigma }_{v}\) :
-
total stress (kPa)
- \({\sigma }_{h}\) :
-
lateral pressure (kPa)
- \({\sigma }_{vo}^{^{\prime}}\) :
-
initial vertical effective stress of soil (kPa)
- \({\tilde{\sigma }}_{vo}^{^{\prime}}\) :
-
average value of initial vertical effective stress of composite foundation (kPa)
- \({\tilde{\sigma }}_{s}^{^{\prime}}\),\({\sigma }_{v}^{^{\prime}}\) :
-
vertical effective stress of soil (kPa)
- \({\tilde{\sigma }}_{vo}^{^{\prime}}\) :
-
average value of vertical effective stress of composite foundation (kPa)
- \(\Delta {\sigma }_{v}\) :
-
total of external load (kPa)
$$\lambda :\text{ } = \frac{{E}_{s}}{\overline{E} }$$
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The support of this research by the Industrial University of Ho Chi Minh City is gratefully acknowledged.
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Nguyen, BP., Nguyen, T.T., Nguyen, T. et al. Analytical model for consolidation and bearing capacity of soft soil stabilized by combined PVD-deep cement mixing columns. Bull Eng Geol Environ 82, 286 (2023). https://doi.org/10.1007/s10064-023-03287-0
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DOI: https://doi.org/10.1007/s10064-023-03287-0