Effect of permeability variation with depth on soil resistance to Caisson penetration

Moura Mehravar, Ouahid Harireche, Amir M. Alani

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Suction-induced seepage is pivotal to the installation of caisson foundations in sand. Indeed, Pressure gradient generated by the imposed suction inside the caisson cavity cause an overall reduction in the lateral soil pressure acting on the caisson wall as well as caisson tip resistance. This transient loosening of soil around the caisson wall helps caisson penetration into the seabed. However, these effects must be controlled to avoid soil failure due to critical condition such as piping which may cause the installation process to fail because of instability of the soil plug trapped inside the caisson cavity. Therefore, in order to have a safe installation process the soil conditions, especially soil resistance and critical condition to piping must be predicted and controlled during entire installation procedure.
In this paper, the effects of excess pore water pressure gradients due to applying suction on soil resistance in homogenous sandy soil and isotropic heterogeneous seabed profile is addressed. For this purpose a simple finite difference model is used to solve the normalised seepage problem. In order to apply the results to any size of the caisson, the problem dimensions are scaled with regard to the caisson radius. The results show that a predication of soil resistance based on constant permeability in the seabed profile with varying permeability by depth is non-conservative, due to an overestimated reduction in effective stress under suction-induced seepage.
Original languageEnglish
Title of host publicationProceedings of the 22nd UK National Conference of the Association for Computational Mechanics in Engineering
EditorsAkbar Javadi, Mohammed S. Hussain
Pages77-80
Number of pages4
Publication statusPublished - 2014
Event22nd ACME Conference on Computational Mechanics - Exeter, United Kingdom
Duration: 2 Apr 20144 Apr 2014

Conference

Conference22nd ACME Conference on Computational Mechanics
Abbreviated titleACME 2014
CountryUnited Kingdom
CityExeter
Period2/04/144/04/14

Fingerprint

Caissons
Soils
Seepage
Pressure gradient
Sand

Keywords

  • suction Caisson installation
  • varying permeability with depth
  • soil resistance
  • normalised seepage problem

Cite this

Mehravar, M., Harireche, O., & Alani, A. M. (2014). Effect of permeability variation with depth on soil resistance to Caisson penetration. In A. Javadi, & M. S. Hussain (Eds.), Proceedings of the 22nd UK National Conference of the Association for Computational Mechanics in Engineering (pp. 77-80)
Mehravar, Moura ; Harireche, Ouahid ; Alani, Amir M. / Effect of permeability variation with depth on soil resistance to Caisson penetration. Proceedings of the 22nd UK National Conference of the Association for Computational Mechanics in Engineering. editor / Akbar Javadi ; Mohammed S. Hussain. 2014. pp. 77-80
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abstract = "Suction-induced seepage is pivotal to the installation of caisson foundations in sand. Indeed, Pressure gradient generated by the imposed suction inside the caisson cavity cause an overall reduction in the lateral soil pressure acting on the caisson wall as well as caisson tip resistance. This transient loosening of soil around the caisson wall helps caisson penetration into the seabed. However, these effects must be controlled to avoid soil failure due to critical condition such as piping which may cause the installation process to fail because of instability of the soil plug trapped inside the caisson cavity. Therefore, in order to have a safe installation process the soil conditions, especially soil resistance and critical condition to piping must be predicted and controlled during entire installation procedure. In this paper, the effects of excess pore water pressure gradients due to applying suction on soil resistance in homogenous sandy soil and isotropic heterogeneous seabed profile is addressed. For this purpose a simple finite difference model is used to solve the normalised seepage problem. In order to apply the results to any size of the caisson, the problem dimensions are scaled with regard to the caisson radius. The results show that a predication of soil resistance based on constant permeability in the seabed profile with varying permeability by depth is non-conservative, due to an overestimated reduction in effective stress under suction-induced seepage.",
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Mehravar, M, Harireche, O & Alani, AM 2014, Effect of permeability variation with depth on soil resistance to Caisson penetration. in A Javadi & MS Hussain (eds), Proceedings of the 22nd UK National Conference of the Association for Computational Mechanics in Engineering. pp. 77-80, 22nd ACME Conference on Computational Mechanics, Exeter, United Kingdom, 2/04/14.

Effect of permeability variation with depth on soil resistance to Caisson penetration. / Mehravar, Moura; Harireche, Ouahid; Alani, Amir M.

Proceedings of the 22nd UK National Conference of the Association for Computational Mechanics in Engineering. ed. / Akbar Javadi; Mohammed S. Hussain. 2014. p. 77-80.

Research output: Chapter in Book/Report/Conference proceedingConference contribution

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T1 - Effect of permeability variation with depth on soil resistance to Caisson penetration

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AU - Harireche, Ouahid

AU - Alani, Amir M.

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N2 - Suction-induced seepage is pivotal to the installation of caisson foundations in sand. Indeed, Pressure gradient generated by the imposed suction inside the caisson cavity cause an overall reduction in the lateral soil pressure acting on the caisson wall as well as caisson tip resistance. This transient loosening of soil around the caisson wall helps caisson penetration into the seabed. However, these effects must be controlled to avoid soil failure due to critical condition such as piping which may cause the installation process to fail because of instability of the soil plug trapped inside the caisson cavity. Therefore, in order to have a safe installation process the soil conditions, especially soil resistance and critical condition to piping must be predicted and controlled during entire installation procedure. In this paper, the effects of excess pore water pressure gradients due to applying suction on soil resistance in homogenous sandy soil and isotropic heterogeneous seabed profile is addressed. For this purpose a simple finite difference model is used to solve the normalised seepage problem. In order to apply the results to any size of the caisson, the problem dimensions are scaled with regard to the caisson radius. The results show that a predication of soil resistance based on constant permeability in the seabed profile with varying permeability by depth is non-conservative, due to an overestimated reduction in effective stress under suction-induced seepage.

AB - Suction-induced seepage is pivotal to the installation of caisson foundations in sand. Indeed, Pressure gradient generated by the imposed suction inside the caisson cavity cause an overall reduction in the lateral soil pressure acting on the caisson wall as well as caisson tip resistance. This transient loosening of soil around the caisson wall helps caisson penetration into the seabed. However, these effects must be controlled to avoid soil failure due to critical condition such as piping which may cause the installation process to fail because of instability of the soil plug trapped inside the caisson cavity. Therefore, in order to have a safe installation process the soil conditions, especially soil resistance and critical condition to piping must be predicted and controlled during entire installation procedure. In this paper, the effects of excess pore water pressure gradients due to applying suction on soil resistance in homogenous sandy soil and isotropic heterogeneous seabed profile is addressed. For this purpose a simple finite difference model is used to solve the normalised seepage problem. In order to apply the results to any size of the caisson, the problem dimensions are scaled with regard to the caisson radius. The results show that a predication of soil resistance based on constant permeability in the seabed profile with varying permeability by depth is non-conservative, due to an overestimated reduction in effective stress under suction-induced seepage.

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Mehravar M, Harireche O, Alani AM. Effect of permeability variation with depth on soil resistance to Caisson penetration. In Javadi A, Hussain MS, editors, Proceedings of the 22nd UK National Conference of the Association for Computational Mechanics in Engineering. 2014. p. 77-80