Soft clay stabilisation using lightweight aggregate for raft and column matrices

The stone column technique has been used as a soft ground stabilisation method over the past 30 years by using partial replacement of the compressible soil with a more competent granular material such as stone aggregate and sand. The column filler material in current practice normally consist of sto...

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Main Author:	Zukr, Azhani
Format:	Thesis
Language:	English
Published:	2020
Subjects:	TA Engineering (General) Civil engineering (General)
Online Access:	http://eprints.utm.my/id/eprint/92111/1/AzhaniZukriPSKA2019.pdf.pdf
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spelling	my-utm-ep.921112021-12-31T07:34:41Z Soft clay stabilisation using lightweight aggregate for raft and column matrices 2020 Zukr, Azhani TA Engineering (General). Civil engineering (General) The stone column technique has been used as a soft ground stabilisation method over the past 30 years by using partial replacement of the compressible soil with a more competent granular material such as stone aggregate and sand. The column filler material in current practice normally consist of stone aggregates of 20 mm to 75 mm in diameter. It is compacted into a vertical hole generally of 0.6 meter to 1.0 meter diameters and depths of more than 6 time diameter. The major part of this research is to present the behaviour of stone column group beneath large loaded area through three-dimensional finite element (FE) analysis. Instead of normal aggregate for stone columns, Lightweight Expanded Clay Aggregate (LECA) has the potential to be used as replacement material. By using PLAXIS 3D, LECA columns-raft were modelled as Mohr-Coulomb material and the nonlinear behaviour of soft soil is modelled with Hardening Soil constitutive model. To permit timely analysis in this research and to simulate long term settlement behaviour, drained analysis was adopted to allow for a greater number of sensitivity and parametric analysis to be performed. Parametric study was performed to evaluate the effect of LECA raft thickness (Hr), depth ratio (ß), and area replacement ratio (a) on the settlement performance. The obtained results proved that increasing the thickness of replaced soft clay with compacted LECA layer evidently decreases the settlement, where the performance of settlement improvement up to 40%, 60% and 80% for 1.5 m, 2.5 m and 3.5 m depth of LECA replacement, respectively. The settlement ratio of LECA column was found to be reduced as the column length increases until end bearing condition, where the highest settlement ratio of 4 for a = 0.4 can be achieved. Higher area replacement ratio results in a higher settlement ratio, which indicating that closer spacing provide better improvement. In addition, the replacement of LECA raft on LECA column (LECA columns-raft) significantly decreases the settlement of the soft ground. For higher a with longer columns and thicker rafts provide better settlement improvement. However, LECA columns-raft performance chart can be referred for economic design. Meanwhile, the bearing capacity of LECA raft was found to be increased with increasing of raft thickness. The research indicates that the most controlling parameter in the prediction of LECA columns-raft bearing capacity (qu) is the area replacement ratio, where qu increases considerably with increase of a. The physical modelling was established in laboratory with 1:20 scaling factor to validate numerical analysis. The method can provide even more accurate verification, economical and require less time to perform compare to field testing and full-scale model. The results from physical modelling agree well with numerical prediction where the difference is less than 20% and is considered acceptable. The dimensionless relationship between settlement ratio (S/Suc) against ß was plotted for every a and Hr. Five design charts are proposed for practical engineer to predict the settlement of LECA columns-raft and LECA columns under large loaded area. Two design charts are also developed for LECA raft settlement prediction. It can be referred to as early estimation of settlement ratio according to the thickness of replacement. The reliability of design charts is successfully validated using PLAXIS 3D. 2020 Thesis http://eprints.utm.my/id/eprint/92111/ http://eprints.utm.my/id/eprint/92111/1/AzhaniZukriPSKA2019.pdf.pdf application/pdf en public http://dms.library.utm.my:8080/vital/access/manager/Repository/vital:134427 phd doctoral Universiti Teknologi Malaysia Faculty of Engineering - School of Civil Engineering
institution	Universiti Teknologi Malaysia
collection	UTM Institutional Repository
language	English
topic	TA Engineering (General) Civil engineering (General)
spellingShingle	TA Engineering (General) Civil engineering (General) Zukr, Azhani Soft clay stabilisation using lightweight aggregate for raft and column matrices
description	The stone column technique has been used as a soft ground stabilisation method over the past 30 years by using partial replacement of the compressible soil with a more competent granular material such as stone aggregate and sand. The column filler material in current practice normally consist of stone aggregates of 20 mm to 75 mm in diameter. It is compacted into a vertical hole generally of 0.6 meter to 1.0 meter diameters and depths of more than 6 time diameter. The major part of this research is to present the behaviour of stone column group beneath large loaded area through three-dimensional finite element (FE) analysis. Instead of normal aggregate for stone columns, Lightweight Expanded Clay Aggregate (LECA) has the potential to be used as replacement material. By using PLAXIS 3D, LECA columns-raft were modelled as Mohr-Coulomb material and the nonlinear behaviour of soft soil is modelled with Hardening Soil constitutive model. To permit timely analysis in this research and to simulate long term settlement behaviour, drained analysis was adopted to allow for a greater number of sensitivity and parametric analysis to be performed. Parametric study was performed to evaluate the effect of LECA raft thickness (Hr), depth ratio (ß), and area replacement ratio (a) on the settlement performance. The obtained results proved that increasing the thickness of replaced soft clay with compacted LECA layer evidently decreases the settlement, where the performance of settlement improvement up to 40%, 60% and 80% for 1.5 m, 2.5 m and 3.5 m depth of LECA replacement, respectively. The settlement ratio of LECA column was found to be reduced as the column length increases until end bearing condition, where the highest settlement ratio of 4 for a = 0.4 can be achieved. Higher area replacement ratio results in a higher settlement ratio, which indicating that closer spacing provide better improvement. In addition, the replacement of LECA raft on LECA column (LECA columns-raft) significantly decreases the settlement of the soft ground. For higher a with longer columns and thicker rafts provide better settlement improvement. However, LECA columns-raft performance chart can be referred for economic design. Meanwhile, the bearing capacity of LECA raft was found to be increased with increasing of raft thickness. The research indicates that the most controlling parameter in the prediction of LECA columns-raft bearing capacity (qu) is the area replacement ratio, where qu increases considerably with increase of a. The physical modelling was established in laboratory with 1:20 scaling factor to validate numerical analysis. The method can provide even more accurate verification, economical and require less time to perform compare to field testing and full-scale model. The results from physical modelling agree well with numerical prediction where the difference is less than 20% and is considered acceptable. The dimensionless relationship between settlement ratio (S/Suc) against ß was plotted for every a and Hr. Five design charts are proposed for practical engineer to predict the settlement of LECA columns-raft and LECA columns under large loaded area. Two design charts are also developed for LECA raft settlement prediction. It can be referred to as early estimation of settlement ratio according to the thickness of replacement. The reliability of design charts is successfully validated using PLAXIS 3D.
format	Thesis
qualification_name	Doctor of Philosophy (PhD.)
qualification_level	Doctorate
author	Zukr, Azhani
author_facet	Zukr, Azhani
author_sort	Zukr, Azhani
title	Soft clay stabilisation using lightweight aggregate for raft and column matrices
title_short	Soft clay stabilisation using lightweight aggregate for raft and column matrices
title_full	Soft clay stabilisation using lightweight aggregate for raft and column matrices
title_fullStr	Soft clay stabilisation using lightweight aggregate for raft and column matrices
title_full_unstemmed	Soft clay stabilisation using lightweight aggregate for raft and column matrices
title_sort	soft clay stabilisation using lightweight aggregate for raft and column matrices
granting_institution	Universiti Teknologi Malaysia
granting_department	Faculty of Engineering - School of Civil Engineering
publishDate	2020
url	http://eprints.utm.my/id/eprint/92111/1/AzhaniZukriPSKA2019.pdf.pdf
_version_	1747818571578212352

Soft clay stabilisation using lightweight aggregate for raft and column matrices

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