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Modelling of a vacuum consolidation project in Vietnam

Ground improvement technique by prefabricated vertical drain (PVD) in combination with vacuum preloading is widely used to facilitate consolidation process and reduce residual settlement. However, this technique seem hardly be estimated by both analytical method and numerical method because it has complex boundary conditions (such as vacuum pressure changing with time). Moreover, lateral displacements caused by this technique are also significant problem. Numerical modelling may be an effective design tool to estimate behavior of soft soil treated by this method, however it needs to have a proper calibration of input parameters. This paper introduces a matching scheme for selection of soil/drain properties in analytical solution and numerical modelling (axisymmetric and plane strain conditions) of a ground improvement project by using Prefabricated Vertical Drains (PVD) in combination with vacuum and surcharge preloading. In-situ monitoring data from a case history of a road construction project in Vietnam was adopted in the back-analysis. Analytical solution and axisymmetric analysis can approximate well the field data meanwhile the horizontal permeability need to be adjusted in plane strain scenario to achieve good agreement. In addition, the influence zone of the ground treatment was examined. The residual settlement was investigated to justify the long-term settlement in compliance with the design code. Moreover, the degree of consolidation of non-PVD sub-layers was also studied by means of two different approaches. | Nguyen Trong Nghia. Journal of Science Ho Chi Minh City Open University 9 2 67-84 67 MODELLING OF A VACUUM CONSOLIDATION PROJECT IN VIETNAM NGUYEN TRONG NGHIA1 1Ho Chi Minh City Open University Vietnam Corresponding author email nghia.nt@ou.edu.vn Received August 23 2018 Revised October 17 2018 Accepted May 21 2019 ABSTRACT Ground improvement technique by prefabricated vertical drain PVD in combination with vacuum preloading is widely used to facilitate consolidation process and reduce residual settlement. However this technique seem hardly be estimated by both analytical method and numerical method because it has complex boundary conditions such as vacuum pressure changing with time . Moreover lateral displacements caused by this technique are also significant problem. Numerical modelling may be an effective design tool to estimate behavior of soft soil treated by this method however it needs to have a proper calibration of input parameters. This paper introduces a matching scheme for selection of soil drain properties in analytical solution and numerical modelling axisymmetric and plane strain conditions of a ground improvement project by using Prefabricated Vertical Drains PVD in combination with vacuum and surcharge preloading. In-situ monitoring data from a case history of a road construction project in Vietnam was adopted in the back-analysis. Analytical solution and axisymmetric analysis can approximate well the field data meanwhile the horizontal permeability need to be adjusted in plane strain scenario to achieve good agreement. In addition the influence zone of the ground treatment was examined. The residual settlement was investigated to justify the long-term settlement in compliance with the design code. Moreover the degree of consolidation of non-PVD sub-layers was also studied by means of two different approaches. Keywords Ground improvement Prefacricated vertical drain Soft clay Stability Vacuum consolidation. 1. Introduction 1.1. Site Due to the .