MINISTRY OF
EDUCATION AND
TRAINING
MINISTRY OF AGRICULTURE
AND RURAL DEVELOPMENT
THUYLOI UNIVERSITY

PHAM QUANG DONG
RESEARCH ON THE VACUUM CONSOLIDATION METHOD
FOR SOFTSOIL IMPROVEMENT IN WORKS
CONSTRUCTION
Major : GEOTECHNICAL ENGINEERING
Code : 62-58-60-01
SUMMARY OF DOCTORAL DISSERTATION
HANOI – 2015
The thesis is completed at:
THUYLOI UNIVERSITY

Promotors: 1. PROF. DR. TRINH MINH THU
2. PROF. DR. NGUYEN CHIEN
Reviewer 1:
Reviewer 2:
Reviewer 3:
The thesis was defended successfully at the Doctoral graduation
committee at
ThuyLoi University – 175 Tay Son – Dong Da – Hanoi
at …..hour…..date…..moth…..year…..
The thesis could be found at: National Library
Or Water Resources University Library - 175 Tay Son – Dong Da –
Hanoi
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PREFACE
1. Background of the topic
The vacuum consolidation method has been applied successfully all over
the world, and now it is chosen to improve the softsoil in Vietnam because this
method has advantages as: shorten construction time, save loading materials,
easily remove loading material after improvement, no environment pollution
in construction, especially appropriate for ground improvement in a large
and/or long area.
Vietnam has applied this method to improve the ground for some works,
with technology and equipment managed by foreign partners. However, the
knowledge and mastering of technology and equipment, and building of
relationship among parameters of soft soil layer during vacuum consolidation
process for soft soil in Vietnam are topical and essential. Therefore, the topic
“Research on the vacuum consolidation method for soft soil improvement
in works construction” has large scientific and practical significance.
2. Purposes of the topic
- To define the variation pore water pressure and deformation (settlement)
of soft soil layer during vacuum consolidation.
- To establish the relationship between Plasticity Index (PI), degree of
consolidation (U), thickness of improved soft soil layer (H), and consolidation
time (t) when improving the soft soil by vacuum consolidation method.
3. Object and Scope of research
- The softsoil in different projects at Dinh Vu – Hai Phong, Duyen Hai –
Tra Vinh, Nhon Trach – Dong Nai, Thai Binh Thermal Power Plant – Thai
Binh.
- The softsoil in some another areas which have similar physical and
mechanical behaviors.
4. Contents of research
(1) Literature reviews the vacuum consolidation solutions for improving
soft soil foundation all over the world and in Vietnam. Evaluate the existing
problems in technics and point out the matters that the thesis is focusing on
solving. (2) Apply the background theory to figure out parameters of vacuum
consolidation process and compare with physical model test in laboratory and
with the field treatment. (3) Study the installation and the operation procedures
to be well controlled the vacuum consolidation technology. (4) Studying the
variation pore water pressure and the deformation of soft soil layer in vacuum
consolidation process by physical model. The study results are compared with
calculated results from numerical model to see the conformity of digital
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calculation model. (5) Determining the rationality of the numerical model to
calculate and formulate the relationship between plastic index, consolidation,
depth of softsoil improvement and consolidation time when apply the vacuum
consolidation method.
5. Research Method
(1) Theory calculation and analysis method: research the vacuum consolidation
problem, study the contents related to solving the vacuum consolidation problem.
(2) Practical method: physical model experiment to determine the variation
process of pore water pressure and deformation at interested locations and depths
during the application of vacuum consolidation. (3) Statistics method: Processing
the experimental and statistic data to establish and build the relationship between
the parameters of vacuum consolidation process. (5) Expert method: organize
workshops, scientific reports to collect comments from experts and scientists in
the researched field.
6. Scientific and practical meanings
a) Scientific meaning
There are few studies on factors that affect the vacuum consolidation process
in Vietnam, therefore the results of this thesis on the variation pore water
pressure and settlement in the softsoil of Vietnam can be used to predict the
behaviors of softsoil when improving by vacuum consolidation.
Currently, there is no software applied for the vacuum consolidation
problems, therefore, the selection of the appropriate finite element software
has great scientific meaning.
To have basis for giving initial forecast on the consolidation process when
improving the soft soil layer using vacuum consolidation method, the ability of
building a relationship between consolidation parameters, consolidation time,
plasticity index and the depth of soft soil layer for improvement is essential.
b) Practical meaning
The research results will determine the variation law of soft soil layer, and
establish its relationship when improving the softsoil by vacuum
consolidation, give a tool for geo-technician to give initial forecast on
consolidation process when improving the softsoil by this method.
7. Contributions of the thesis
(1) Establish a large scale physical model which is the first model which
applies the vacuum consolidation method to improve the soft coastal underlying
soil has been performed at the Geotechnical Laboratory, ThuyLoi University to
study the variation process of pore water pressure and the deformation of
softsoil at different interested locations and depths.
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(2) Select appropriate software to calculate the vacuum consolidation
together with loading for the problem in the laboratory and at site.
(3) Compute the relationship between plasticity index, degree of
consolidation, thickness of soil layer for improvement and consolidation time
when improving the soft soil by the vacuum consolidation method.
8. Layout of the Thesis
Preface
Chapter 1: Overview on the vacuum consolidation method for improving
the softsoil and literature review
Chapter 2: Experimental study on the vacuum consolidation method for
softsoil improvement in the laboratory
Chapter 3: Calculation model for vacuum consolidation problems
Chapter 4: Establishment of a relationship between parameters of vacuum
consolidation problems
Conclusion and recommends
List of publications
References
Chapter 1
OVERVIEW OF VACUUM CONSOLIDATION METHOD FOR
SOFTSOIL IMPROVEMENT AND THEORY OF THE METHOD
1.1. Softsoil
There have been many different definitions about softsoil, but it could be
summarized that softsoil is the soil not suitable for works construction. The
building in softsoil requires very careful improvement to ensure the structrures
will be safe during the construction and operation time.
1.2. Overview of research and application of vacuum consolidation
method
1.2.1. The application of vacuum consolidation method for improving
softsoil in the world
The vacuum consolidation method for improving softsoil was introduced
for the first time in 1952 by W. Kjellman, in 1980, the vacuum consolidation
was improved by a combination of loading and prefabricated vertical drain. In
1989, Menard Construction Company (from France) applied this
improvement, since then, the method has been widely applied in many
countries. Since 1997, Cofra Construction Company of Netherland had an
improvement is to remove the protective membrane which made the
construction difficult and vulnerable, however, a loading layer must be used to
compensate the removed atmosphere pressure difference. Basically, the