Analysis of Soil Disturbance Associated with Mandrel-Driven Prefabricated Vertical Drains Using an Elliptical Cavity Expansion Theory

Ghandeharioon, Ali; Indraratna, Buddhima; Rujikiatkamjorn, Cholachat

doi:10.1061/(asce)gm.1943-5622.0000027

Cited by 47 publications

(24 citation statements)

References 18 publications

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“…3 times lower than the surrounding undisturbed region. Using cavity expansion theory, Ghandeharioon et al (2010) demonstrated that a conical shape of the smear zone would be more realistic than an assumed cylindrical shape. However, an equivalent cylindrical shape could still provide the same consolidation response based on the equivalent area method and it was concluded that the radius of the smear zone is about 3 .…”

Section: Introductionmentioning

confidence: 99%

Soil disturbance analysis due to vertical drain installation

Indraratna

Perera

Rujikiatkamjorn

et al. 2015

Proceedings of the Institution of Civil Engineers - Geotechnica

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The installation of drains creates a disturbed region known as a smear zone where the change in the clay structure affects the horizontal permeability and compressibility. The parameters required to characterise the smear effect are the extent of the smear zone and the ratio of the horizontal coefficient of permeability in the undisturbed zone and in the smear zone. Only limited studies have been carried out on different aspects of soil disturbance due to driving vertical drains and its effects on the subsequent consolidation. In this paper the disturbed zone around a rectangular mandrel was characterised using soil samples obtained from the soft clay layer at various locations beneath an embankment built at Ballina, Australia, where vertical drains were installed. By determining the change in the coefficient of permeability, the water content and volume compressibility across the smear zone, the effects of soil disturbance on consolidation due to the installation of drains can be quantified using the available numerical model. Disciplines Engineering | Science and Technology StudiesThe installation of drains creates a disturbed region known as a smear zone where the change in the clay structure affects the horizontal permeability and compressibility. The parameters required to characterise the smear effect are the extent of the smear zone and the ratio of the horizontal coefficient of permeability in the undisturbed zone and in the smear zone. Only limited studies have been carried out on different aspects of soil disturbance due to driving vertical drains and its effects on the subsequent consolidation. In this paper the disturbed zone around a rectangular mandrel was characterised using soil samples obtained from the soft clay layer at various locations beneath an embankment built at Ballina, Australia, where vertical drains were installed. By determining the change in the coefficient of permeability, the water content and volume compressibility across the smear zone, the effects of soil disturbance on consolidation due to the installation of drains can be quantified using the available numerical model.

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Section: Introductionmentioning

confidence: 99%

Soil disturbance analysis due to vertical drain installation

Indraratna

Perera

Rujikiatkamjorn

et al. 2015

Proceedings of the Institution of Civil Engineers - Geotechnica

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“…2 shows a unit cell with external radius r e , drain radius r w and smear zone radius r s : Depending on the soil stiffness, the size and shape of the mandrel, and the installation method, the extent of the smear zone (r s ) can usually be estimated as r s ¼ (2 to 3)r m , where r m is the equivalent radius of the mandrel (Hansbo, 1981). Ghandeharioon et al (2010) showed that the driving of the mandrel does follow the theory of lateral cavity expansion in a nonlinear manner. Weber et al (2010) showed that a very clearly structured smear zone was observed from environmental scanning electron microscope photographs.…”

Section: Development Of Governing Equation For Non-darcian Flowmentioning

confidence: 99%

“…However, for short vertical drains with larger drain spacing, the contribution from c v will become increasingly relevant, and this is to be captured as future work where short prefabricated vertical drains can still be used effectively, for example under rail tracks, as demonstrated by Indraratna et al (2010). (c) Lateral soil displacements based on elliptical cavity expansion theory (ECET) have been recently analysed (Ghandeharioon et al, 2010); however, for simplicity, the mathematical formulations related to ECET have not been incorporated in the current analysis. (d ) The non-Darcian flow equation adopted in this study is similar to Hansbo (2001) and Sathananthan & Indraratna (2006).…”

Section: Model Limitations and Future Recommendationsmentioning

confidence: 99%

Vertical drain consolidation with non-Darcian flow and void-ratio-dependent compressibility and permeability

Walker¹,

Indraratna²,

Rujikiatkamjorn³

2012

Géotechnique

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Vertical drains increase the rate of consolidation in soft soils by facilitating faster dissipation of excess pore water pressure through short, horizontal drainage paths. This paper presents an analytical solution for nonlinear radial consolidation under equal-strain conditions incorporating smear but ignoring well resistance. Three aspects of non-linearity are considered: (a) non-Darcian flow, (b) a log-linear void-ratio-stress relationship; and (b) a log-linear void-ratio-permeability relationship. The analytical solution to non-linear radial consolidation can explicitly capture the behaviour of both overconsolidated and normally consolidated soils. For non-linear material properties, consolidation may be faster or slower when compared with the cases with constant material properties. The difference depends on the compressibility/ permeability ratios (Cc/Ck and Cr/Ck), the preconsolidation pressure and the stress increase. If Cc/Ck < 1 or Cr/Ck < 1 then the coefficient of consolidation increases as excess pore pressures dissipate, and the corresponding rate of consolidation is greater. Vertical drains increase the rate of consolidation in soft soils by facilitating faster dissipation of excess pore water pressure through short, horizontal drainage paths. This paper presents an analytical solution for non-linear radial consolidation under equal-strain conditions incorporating smear but ignoring well resistance. Three aspects of non-linearity are considered: (a) non-Darcian flow, (b) a log-linear void-ratio-stress relationship; and (b) a log-linear void-ratio-permeability relationship. The analytical solution to non-linear radial consolidation can explicitly capture the behaviour of both overconsolidated and normally consolidated soils. For non-linear material properties, consolidation may be faster or slower when compared with the cases with constant material properties. The difference depends on the compressibility/ permeability ratios (C c /C k and C r /C k ), the preconsolidation pressure and the stress increase. If C c /C k < 1 or C r /C k < 1 then the coefficient of consolidation increases as excess pore pressures dissipate, and the corresponding rate of consolidation is greater.

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“…1(a)). The experimental procedures are explained elsewhere by Ghandeharioon et al (2010). The clay sample was extracted from a low-lying flood plain consisting of highly compressible and saturated estuarine clay from the coastal town of Ballina, NSW, from a depth of 2 m. It is a dark grey, silty and highly plastic clay with a specific gravity of 2·6 and a natural water content of 94%.…”

Section: Experimental Set-up and Proceduresmentioning

confidence: 99%

Pore pressure based method to quantify smear around a vertical drain

Choudhary

Indraratna

Rujikiatkamjorn

2016

Géotechnique Letters

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Radial consolidation testing of Ballina clay (New South Wales, Australia) was carried out using a large-scale consolidometer 650 mm in diameter. In this study, the characteristics of the smear zone were evaluated on the basis of hydraulic gradient changes derived from the measured excess pore pressure data in the radial direction. The extent of the smear zone determined using this technique is compared with past approaches, where the variations in water content and lateral permeability were adopted to evaluate smear. The approach proposed herein based on the change of hydraulic gradient coincides with the previous two methods, and the smear zone could be established at almost 2·5 times the effective mandrel diameter. A good agreement is also found between the theoretical radial consolidation predictions, after incorporating the smear zone characteristics and the measured time-settlement curve. The proposed method for the determination of smear zone extent can be carried out during consolidation with minimum disturbance to soil, provided a sufficient number of pore pressure transducers are installed. It also eliminates the need for a number of soil samples and high-quality soil sampling technique after the installation of the drain. Radial consolidation testing of Ballina clay (New South Wales, Australia) was carried out using a large-scale consolidometer 650 mm in diameter. In this study, the characteristics of the smear zone were evaluated on the basis of hydraulic gradient changes derived from the measured excess pore pressure data in the radial direction. The extent of the smear zone determined using this technique is compared with past approaches, where the variations in water content and lateral permeability were adopted to evaluate smear. The approach proposed herein based on the change of hydraulic gradient coincides with the previous two methods, and the smear zone could be established at almost 2·5 times the effective mandrel diameter. A good agreement is also found between the theoretical radial consolidation predictions, after incorporating the smear zone characteristics and the measured time-settlement curve. The proposed method for the determination of smear zone extent can be carried out during consolidation with minimum disturbance to soil, provided a sufficient number of pore pressure transducers are installed. It also eliminates the need for a number of soil samples and high-quality soil sampling technique after the installation of the drain.

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Analysis of Soil Disturbance Associated with Mandrel-Driven Prefabricated Vertical Drains Using an Elliptical Cavity Expansion Theory

Cited by 47 publications

References 18 publications

Soil disturbance analysis due to vertical drain installation

Soil disturbance analysis due to vertical drain installation

Vertical drain consolidation with non-Darcian flow and void-ratio-dependent compressibility and permeability

Pore pressure based method to quantify smear around a vertical drain

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