Location
Arlington, Virginia
Date
14 Aug 2008, 2:15pm - 4:00pm
Abstract
Vacuum preloading technique incorporating prefabricated vertical drains is one of the most widely used ground improvement methods in the world for improving the engineering properties of soft clays. Although many successful on-shore cases on application of the technique have been reported, the effectiveness of applying the technique under water has not yet been investigated. Moreover, many technical and operation factors, that are playing important roles in vacuum consolidation, are also not yet fully understood. To study the feasibility of under water vacuum preloading, a large-scale field test was conducted. A 50 m by 50 m geo-membrane was laid under water in an 80 m wide by 100 m long pond. The geo-membrane was custom made with drainage outlet pipes to release the trapped air bubbles during the placement under water. Prefabricated vertical drains were installed on an equilateral triangular grid at a spacing of 1.2 m to a depth of 7 m. Internal drainage pipes were provided in the sand cushion layers to provide a passage for the prefabricated vertical drains with the external vacuum pumps. Instruments such as piezometers, vacuum sensors, inclinometers, settlement plates and extensometers were installed to monitor the performance of the system. An automatic and remote wireless monitoring system was installed for data collection because of difficult access. Vane shear tests and cone penetration tests were conducted before and after vacuum preloading to determine the effectiveness of the operation. This paper documents the constructions of the field test and reports the major observations from the monitored readings. The operation has demonstrated that under water vacuum preloading is feasible and that with proper design and construction procedure, a very tight seal can be provided by the geo-membrane separating the water and the underlying prefabricated vertical drains through out the test. The monitored results demonstrate that the stiffness and strength of the soft clay can be improved effectively.
Department(s)
Civil, Architectural and Environmental Engineering
Meeting Name
6th Conference of the International Conference on Case Histories in Geotechnical Engineering
Publisher
Missouri University of Science and Technology
Document Version
Final Version
Rights
© 2008 Missouri University of Science and Technology, All rights reserved.
Creative Commons Licensing
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.
Document Type
Article - Conference proceedings
File Type
text
Language
English
Recommended Citation
Kwong, A. K. L.; Han, X. F.; Tham, L. G.; Lee, P. K. K.; and Zhao, W. B., "A Field Test Study on under Water Vacuum Preloading Method" (2008). International Conference on Case Histories in Geotechnical Engineering. 3.
https://scholarsmine.mst.edu/icchge/6icchge/session07/3
A Field Test Study on under Water Vacuum Preloading Method
Arlington, Virginia
Vacuum preloading technique incorporating prefabricated vertical drains is one of the most widely used ground improvement methods in the world for improving the engineering properties of soft clays. Although many successful on-shore cases on application of the technique have been reported, the effectiveness of applying the technique under water has not yet been investigated. Moreover, many technical and operation factors, that are playing important roles in vacuum consolidation, are also not yet fully understood. To study the feasibility of under water vacuum preloading, a large-scale field test was conducted. A 50 m by 50 m geo-membrane was laid under water in an 80 m wide by 100 m long pond. The geo-membrane was custom made with drainage outlet pipes to release the trapped air bubbles during the placement under water. Prefabricated vertical drains were installed on an equilateral triangular grid at a spacing of 1.2 m to a depth of 7 m. Internal drainage pipes were provided in the sand cushion layers to provide a passage for the prefabricated vertical drains with the external vacuum pumps. Instruments such as piezometers, vacuum sensors, inclinometers, settlement plates and extensometers were installed to monitor the performance of the system. An automatic and remote wireless monitoring system was installed for data collection because of difficult access. Vane shear tests and cone penetration tests were conducted before and after vacuum preloading to determine the effectiveness of the operation. This paper documents the constructions of the field test and reports the major observations from the monitored readings. The operation has demonstrated that under water vacuum preloading is feasible and that with proper design and construction procedure, a very tight seal can be provided by the geo-membrane separating the water and the underlying prefabricated vertical drains through out the test. The monitored results demonstrate that the stiffness and strength of the soft clay can be improved effectively.
