Consolidation of sensitive clay with vertical drain

The coefficient of consolidation is one of the most important parameters that control the rate of consolidation. Conventional consolidation theories assume that the coefficient of consolidation is constant during the whole consolidation process. In the case of sensitive clay, the coefficient of consolidation is strongly dependent on the level of effective stress of clay. With the dissipation of pore water pressure and the increase of effective stress, the soil structure of the upper subsoil is gradually destroyed downwards and its coefficient of consolidation becomes smaller. At the same time, the coefficient of permeability of the vertical drains drops down because of the kinking or bending effect. The destructured upper subsoil and the kinking of the vertical drain hinder the dissipation of the pore pressure in the lower subsoil. This paper presents a model to describe the above important phenomena during the consolidation of sensitive clay with vertical drain. The solution for proposed model can be obtained by extending the closed-form solution of the consolidation of double-layered ground with vertical drain by the interactive method introducing the concept of the moving boundary and the reduction of discharge capacity of vertical drain. The numerical results obtained from the finite element method package PLAXIS (Ver. 7.2) are adopted to compare those obtained from the present algorithm. Moreover, the rationality of the moving boundary is explained by the distributions of the excess pore water pressure in natural soil zone along the radial direction. Wenzhou airport project is taken as a case study in this paper. The results for the sensitive soil with decaying sand drain agree very well with the in situ measured data. The calculated results can properly explain two general phenomena observed in the consolidation of soft sensitive soil ground with vertical drains: one is that the time to achieve the same consolidation degree is much longer under heavy loading than that under light loading; the other is that the consolidation speed is much slower in the lower subsoil than in the upper subsoil. Finally, it is indicated that the vertical drains can decrease the hindrance effect of the destructured subsoil. Copyright © 2007 John Wiley & Sons, Ltd.

[1]  F. Bouchelaghem,et al.  Real‐scale miscible grout injection experiment and performance of advection–dispersion–filtration model , 2001 .

[2]  C. C. Hird,et al.  Model study of seepage in smear zones around vertical drains in layered soil: further results , 2002 .

[3]  R. Kerry Rowe,et al.  Combined effects of reinforcement and prefabricated vertical drains on embankment performance , 2001 .

[4]  S. J. Ryde,et al.  Modelling consolidation accelerated by vertical drains in soils subject to creep , 2001 .

[5]  Buddhima Indraratna,et al.  Vertical Drain Consolidation with Parabolic Distribution of Permeability in Smear Zone , 2006 .

[6]  Xiaowu Tang,et al.  Consolidation by vertical drains under time‐dependent loading , 2000 .

[7]  Xu-sheng Wang,et al.  Analysis of soil consolidation by vertical drains with double porosity model , 2004 .

[8]  Iichiro Kono.  FINITE ELEMENT ANALYSIS OF A NONSTEADY SEEPAGE PROBLEM , 1974 .

[9]  Guofu Zhu,et al.  Finite element consolidation analysis of soils with vertical drain , 2000 .

[10]  Gholamreza Mesri,et al.  Settlement analysis of embankments on soft clays , 1985 .

[11]  K. Onitsuka,et al.  Consolidation of double‐layered ground with vertical drains , 2001 .

[12]  S. Leroueil,et al.  The permeability of natural soft clays. Part II: Permeability characteristics: Reply , 1983 .

[13]  Hiroshi Yoshikuni,et al.  Consolidation of Soils by Vertical Drain Wells with Finite Permeability , 1974 .

[14]  Balasingam Muhunthan,et al.  NUMERICAL STUDY OF THE FACTORS AFFECTING THE CONSOLIDATION OF CLAY WITH VERTICAL DRAINS , 2002 .

[15]  P. R. Vaughan,et al.  The general and congruent effects of structure in natural soils and weak rocks , 1990 .

[16]  Jian-Hua Yin,et al.  CONSOLIDATION ANALYSIS OF SOIL WITH VERTICAL AND HORIZONTAL DRAINAGE UNDER RAMP LOADING CONSIDERING SMEAR EFFECTS , 2004 .

[17]  Hisao Aboshi,et al.  Kinking deformation of PVD under consolidation settlement of surrounding clay , 2001 .

[18]  V. Choa,et al.  CONSOLIDATION AND PERMEABILITY PROPERTIES OF SINGAPORE MARINE CLAY , 2002 .

[19]  Jun Wang,et al.  An analytical solution of one‐dimensional consolidation for soft sensitive soil ground , 2004 .

[20]  T. S. Nagaraj,et al.  Analysis of Compressibility of Sensitive Soils , 1990 .

[21]  S. Hansbo.  Consolidation of fine-grained soils by prefabricated drains , 1981 .