A case of using Sand Compaction Pile method to improve the foundation soil for expressway in Vietnam is presented. The sand compaction pile (SCP) method, which forms a composite ground by driving the pile made of compacted sands into soft ground, is one of the commonly used soil improvement techniques in Viet Nam. The SCP method used to improve the ground through the increase of bearing capacity, which is achieved by improving loose sandy soils or accelerating the consolidation of soft clay soils. Within the country where the condition of sand purchase is abundant in Viet Nam, sand compaction pile were often used for soft ground improvement to replace the Load Relief Slab and Soil-Cement Column at Hanoi-Haiphong Expressway Project recently. The procedures used for soil improvement, the instrumentation and the field monitoring data are described. A few observational methods based on settlement records are available to predict future settlement and consolidation behavior, namely the hyperbolic (Tan 1971; Chin 1975) and Asaoka (Asaoka 1978) method. The field data were from the Thai Binh Bridge approached embankment construction at Hanoi-Haiphong Expressway Project.

1. Geotechnics for Sustainable Development - Geotec Hanoi 2013, Phung (edt). Construction Publisher. ISBN 978-604-82-0013-8
1
Keywords: case history, consolidation, sand compaction pile, settlement, ground improvement
ABSTRACT: A case of using Sand Compaction Pile method to improve the foundation soil for expressway in
Vietnam is presented. The sand compaction pile (SCP) method, which forms a composite ground by driving
the pile made of compacted sands into soft ground, is one of the commonly used soil improvement techniques
in Viet Nam. The SCP method used to improve the ground through the increase of bearing capacity, which is
achieved by improving loose sandy soils or accelerating the consolidation of soft clay soils. Within the
country where the condition of sand purchase is abundant in Viet Nam, sand compaction pile were often used
for soft ground improvement to replace the Load Relief Slab and Soil-Cement Column at Hanoi-Haiphong
Expressway Project recently. The procedures used for soil improvement, the instrumentation and the field
monitoring data are described. A few observational methods based on settlement records are available to
predict future settlement and consolidation behavior, namely the hyperbolic (Tan 1971; Chin 1975) and
Asaoka (Asaoka 1978) method. The field data were from the Thai Binh Bridge approached embankment
construction at Hanoi-Haiphong Expressway Project.
1. INTRODUCTION
The sand compaction pile (SCP) method is
frequently used in construction to form compacted
sand piles by vibration, dynamic impact, or static
excitation in soft grounds. The principle of the SCP
method is based on the research papers by
Murayama and Tamimoto published in 1957 and
1960, as the hammering method developed in1957
(Ministry of construction 1957). A composite
ground consisted of rows of compacted large
diameter sand columns were driven into a soft clay
ground in coastal district of Japan, as the
foundation of a structure (Murayama 1957). The
usage of the SCP method extended to improve soft
clays since the 1960’s (Ogawa 1963, Ibaragi 1965).
The subsequent presentation of Murayama’spaper
in 1962 established the method of SCP application
to clayey soil. This method was further justified
through number of researches and construction
projects. A casing pipe with a plug of sand at its tip
was driven to the bottom of improved layer by a
vibrator method. After pouring sand or gravel
material into the casing pipe, the casing pipe was
withdrawn partly and again driven down to
compacted the sand column and enlarge its
diameter. This process is repeated as far as
compacted sand column reaches to the ground
surface. The mechanism of stabilization by the
SCP method in the case of clayey ground is
perfectly different than the sandy grounds, which is
simply to density the surrounding soil. There is
almost no effect of densification in case of clayey
soils. However, these SCPs behave as piles in soft
grounds and totally can carry more load than
without SCP. At the same time, they also work as
A case study on soft soil improvement of
Hanoi-Haiphong expressway project in
Vietnam
Hoang Tien Trung
FECON-Foundation Engng & Underground Construction, Hanoi, Vietnam. E-mail: trunght@fecon.com.vn
Jang Woo Young
GS Engineering & Construction. Seoul, Korea. E-mail: wyjang@gsconst.co.kr

2. 2
vertical drains to accelerate consolidation of clayey
grounds. In particular, for construction on
embankments over soft soil like soft clay, peaty
soil, which has very slow shear strength, the
installation of SCPs enhances the stability of the
embankment slope, helps to increase the bearing
capacity, and accelerates the consolidation rate of
the foundation soil. The automatically controlled
SCP driving system was invented in 1981
accommodating the vibration effect on soil
properties. In the Western world, the stone column
method-gravel compaction pile (GCP) method has
been used to improve soft ground since the 1970s
(Baumann and Bauer, 1974; Hughes et al., 1975).
As countermeasures for treatment of the soft
ground was applied for this project, the Sand
Compaction Pile, Sand Drain and Prefabricated
Vertical Drain are compared each other. The
displacement behaviour of SCP during installing
on site was considered, a free moving condition, in
which relative displacements occurs has been
observed. A case study on the use of the Sand
Compaction Pie method for the soil improvement for
Hanoi-Haiphong expressway project is presented in
this paper. The site conditions, the soil improvement
procedure, and the field instrumentation are
described. The field monitoring data are presented.
The achieved degree of consolidation and the effect
of soil improvement are evaluated. Several issues
concerning the practical aspects of the sand
compaction pile method are also discussed.
2. OUTLINE OF PROJECT
Hanoi-Haiphong Expressway connects Hanoi
Capital with Haiphong Port City, a route passing 4
provinces, cities: Gia Lam suburban district of
Hanoi city, Van Giang, Yen My, An Thi suburban
districts of Hung Yen province and An Lao, Kien
Thuy suburban districts of Haiphong city. Project’s
starting point is on the Ring Road III of Hanoi city,
1025 m far from north abutment of Thanh Tri
Bridge, Gia Lam suburban district of Hanoi city.
Ending point is at Dinh Vu Dam, Kien An district,
Haiphong city. Investment shall be made in
construction of Hanoi-Haiphong Expressway in
conformity to international standards, expressway
class A, design speed of 120 km/hr, six (6) traffic
lanes, total length of 105.5 km, divided into many
bidding packages. In this study, the paper presents
guideline for design and construction the Sand
Compaction Pile at Thai Binh Abutment area of
Package EX-6 from Km63+300~Km72+000.
Fig. 1 shows alignment direction (a), plan and
profile (b) of SCP treatment area at Abutment A2
with standard section at Sta.65+400.
(a)
(b)
Figure 1.Site location
Table 2. Reviewing Results and Alternatives for D/D Stage
Items
Method for soft soil
treatment
Basic
design
Design
alternative
Consolidation
Acceleration
Embank(H)<5m
Soft soil layer
thickness(D)<20
PVD
PVD
SD
Embank(H)≥5m
Soft soil layer
thickness(D)≥20
SD
PVD
SD
Sliding prevention
LRS;
SCC*
SCP;
LRS; SCC
*
LRS: Load Relief Slab; SCC: Soil-Cement Column.
This package is planned to be completed within
32 months. And a period of less than 18 months
approximately is recommended for soft soil
treatment in consideration of the following issues:
time for preparation works, time for construction of
culverts and underpass structures, time for
construction of piles and abutments, time for
construction of pavement and completion, and
reasonable reuse of surcharge and preloading
material section by section to minimize expense for
material. There are several methods to treat the soft
ground, but it is generally classified into two
categories as sliding-prevention method and
consolidation acceleration method. Soft soil
treatment proposal of Basic Design was reviewed
and, accordingly, some alternatives were primarily

3. 3
proposed for Detail Design. All the reviewing
results are summarized in following Table 2.
As countermeasures for treatment of the soft
ground among the consolidation acceleration
methods mentioned above, Prefabricated Vertical
Drain, Vertical Sand Drain are compared each
other. The PVD is the most appropriate for uniform
soft soil area and without sand seam, SD is
appropriate for sand seam and non-uniform soft
soil areas. The Load Relief Slab, Soil-Cement
Column and Sand Compaction Pile are proposed
for treatment of the soft ground among the sliding
prevention methods of this Package and compared
each other as show in Table 3.
Table 3. Comparison of sliding prevention methods for high
embankment
Items Load Relief Slab
Soil-Cement
Column
Sand Compaction
Pile
General
Aspects
- Support loads by
concrete piles
(35cmx35cm) and
0.3m concrete
slab on soft soil
layer
- Support
load by soil
cement
mixed
column
(D=1.3m)
- Support upper
load by forming
70cm diameter
compaction sand
pile in soft soil
layer
Advanta
ge
-Effective in
settlement
reduction by
transferring the
loads directly to
bearing layer
-Many
experiences in
Viet Nam
- Prevention
of sliding
and
reduction of
settlement by
using soil
cement
columns
- ffective on
sliding prevention
and consolidation
acceleration
-Sand is
abundant in Viet
Nam
Disadva
ntage
-Quality control is
required
- High
construction costs
- Difficult to
control pile
quality and
construction
procedure
- High
construction
costs
- Limited
experiences
in Viet Nam
-No construction
experiences in
Viet Nam
Time for
consolid
ation
0 month 0 month 10 months
Cost 3.0 2.3 1.0
Proposal
and Plan
SCP is the most appropriate for high embankment
and deep soft soil areas
From all above analysis, following criteria will
be recommended as principle in general for
primary selection of soft soil treatment method for
this package.
3. GROUND CONDITION
Fig. 2 shows ground condition in this package with
the results of standard penetration tests.
Soil investigation was carried out in detail design and
additional design by means of a rotary drilling. The borehole
locations are shown in Fig.2. It can be seen that the soft
ground is about 30~32m deep with fat clay and sandy lean
clay with SPT value around 4~6.
Figure 2. Reference borehole log for SCP Treatment at
Abutment A2 Thai Binh Bridge A2 Sta. 65+383~ Sta.
65+413
4. SOFT SOIL IMPROVEMENT
METHOD
4.1 Design Concept
At present, the design method of the SCP is usually
divided into two methods. One is to check the
stability of improved ground, in which a slip
surface is assumed to pass through the replacement
area composed of sand column and clay. Stability
analysis is carried out the circular arc method. A
replacement area ration and a stress concentration
ratio on the slip surface are needed for the stability
analysis. The other method is to check the
consolidation settlement of the composite ground
by considering the diameter, spacing and
arrangement of the sand compaction piles and the
stress concentration ratio of the composite ground.
a. Characteristics of composite ground
In the development of a theory for the SCP
method, many researchers have tried to simplify
the problem of analysis by neglecting the
interactions between the sand piles, and they have
come up with the basic concept of SCP ground as
shown in Fig. 3 (Murayama, 1962; Ichmoto and
Seumatsu, 1982). When the composite ground is
loaded, concentration of stress occurs in the sand

4. 4
pile accompanied by the reduction in stress which
occurs in the surrounding clayey soil as shown in
Fig. 3. This can be explained by the fact that the
vertical settlement of stress concentration in the SCP
and the surrounding soil is approximately the same,
and this causes the occurrence of stress concentration
in the sand pile which is stiffer than the surrounding
soil. The distribution of vertical stress within the unit
cell can be expressed by a stress concentration ratio,
(m) is defined as follows:
m = σs/σc (1)
where, σs = stress in the column and σc = the stress
in the surrounding cohesive soil.
The average stress, σ, over the unit cell area
corresponding to a given area replacement ratio,
as = As/(As + Ac) (2)
is expressed as:
σ = σs as + σc (1 as) (3)
where, As = the area of a SCP and Ac = the area of
the clay ground surrounding the pile.
The relationships for σs and σc in composite
ground also can be expressed using a stress
increment factor, µs, in the sand pile and stress
reduction factor, µc, in the surrounding soil and
defined by the following:
Figure 3. Basic concept of SCP ground
 
    
s s
s
m
σ σ μ σ
1 (m 1)α
(4)
 
    
c c
s
1
σ σ μ σ
1 (m 1)α
(5)
Based on eq. (1) and eq. (3), eq. (4) and (5) have a
relation of:
µsas+ µc(1+as) = 1 (6)
Therefore, eq. (2) can be rewritten as:
m = µs/µc (7)
Again, reduction of settlement due to the installation of
SCP is expressed as a settlement reduction factor, β:
β = St/S (8)
where, St = the settlement of ground without treatment and S
= the settlement of composite ground reinforced by a SCP.
Equation (2), (4), (5) and (6) are usually used as basic
parameters in design and analysis of composite ground.
b. Design theory of sand compaction pile
Replacement ratio
The volume of soft clay replaced by sand is one of
the most important factors in improving week
ground using sand compaction piles. To quantify
the amount of soil replacement, define the area
replacement ratio as as the fraction of soil tributary
to the pile replaced by the sand compaction pile.
The replacement ratio is defined by the following
expression and will be calculated for square and
triangular pattern as follow:
Figure 4. Arrangement and design concept of SCP
For a square arrangement:
 
    
 
2A A π Ds sas 2A 4 dd
(9)
For a triangular arrangement:
  
 
 
 
A 2 A π D 2s sas 2A d3 2 3d
(10)
where, d = center-to-center spacing of the SCP;
D = diameter of the completed SCP (not the
diameter of the casing).

5. 5
Design approach:
To develop a practical design method, assume the
total volume tributary to a sand compaction pile
remains constant during the site improvement
work. Also, neglect any increase in relative density
caused by vibration as the casing is driven, and
assume the loose sand is only displaced laterally
away from the sand pile during construction.
Referring to Fig. 4, let the change in volume of the
in situ sand equal the volume of sand compaction
pile per unit length, l=1m, Vscp giving:
Vscp = V0 –V1 =
 
 
 
 
o 1e e
Vv eo
(11)
Figure 5. Volume block diagram of in situ sand before
and after SCP construction
The area replacement ratio, which is defined by
equation (2) giving:
as=



scp o 1
o
V e e
A 1 e
(12)
where, eo = initial void ratio of loose sand before
improvement; e1= final void ratio of loose sand
after improvement.
The equation (12) can be changed to a more
useful form for design by considering a unit length
of SCP construction. For a unit length l=1, solving
for sand compaction pile spacing d gives for a
square arrangement:
d =
 
 
 
2
o o
o scp
o 1 o 1
1 e 1 e D
V .V .
e e e e 4

(13)
and for a triangular arrangement
d =


2
o
o 1
1 e D
.
e e 2 3

(14)
 Shear strength
Soft ground after being treated by SCP will be
considered a composite ground comprising of SCP
and surrounding soft soil. Shear strength of the
composite ground τsc is calculated as follow:
    
 
u
sc s o o c c z
2
s s s z s
C
τ (1 a )(C (P P μ .σ )U
p
a (γ .Z μ .σ )tan .(cosθ)
(15)
    
 
u
sc s o o c c z
2
m z s s s
C
(1 a )(C ( P P . )U
p
(γ .Z σ ).μ .a .tan .(cosθ)
  

(16)
where, Cu/p = ratio of strength increase; '
s = sub
water unit weight of sand; Z = depth to the failure
surface; s = friction angle of sand;  = Angle
between acting surface and horizontal surface;
z = increased stress at failure surface due to
embankment loading; '
m = Average sub water unit
weight of composite soil.
Friction angle of sand (of SCP) and ratio of
stress division depending on replacement ratio is
shown in Table 1 below:
Table 1. Friction angle and Ratio of stress division
depending on replacement ratio
Replacement
Ratio, as
Friction Angle
of sand, s
Ratio of stress
division, m
0.0 ÷ 0.4 30 3
0.4 ÷ 0.7 30 2
0.7 ÷ 1.0 30 ÷ 35 1
Cohesion and internal friction angle of the
composite soil being used for slope stability
analysis are evaluated from following equation
(13) and (14) respectively, which is derived from
equation (11).


1
tan (n.tan )s  (17)
UP.
c
μ
c
P
o
(P
p
u
C
o
)(C
s
a(C ).1  (18)
where, n = as.µs ; Po = effective overburden
pressure; Pc= pre-consolidation pressure
 Settlement
Settlement of the composite ground is less than
non-treated ground because SCP shares load acting
upon the ground and, accordingly, SCP reduces
stress acting upon soil. Following equation is used
to get settlement of the composite ground.
For normal consolidation



 
 
 
C P μ .ΔPc o cS H.log
1 e Po o
(19)

6. 6
For over consolidation and Pc > Po+ΔP



 
 
 
C P μ .ΔPs o cS H.log
1 e Po o
(20)
For over consolidation and Pc< Po+ΔP

 
 
   
   
   
C CP P μ .ΔPs cc o cS H.log H.log
1 e 1 eP Po oo c
(21)
In the sand layer, the following formula can be
used for immediately settlement (De beer method)


 
 
 
P P ΔPo oS 0.4. .H.logi N Po
(22)
where, Po = overburden pressure; ΔP = pressure
caused by embankment; Cc = compression index;
Cs = swell index; Pc = pre-consolidation pressure;
H = soil thickness; N = standard penetration
test value.
 Coarse Sand Blanket Thickness
The thickness of CSB is estimated based on the
water head level caused by embankment loading,
which is calculated from the following equation:

2L .S
Δh
K.h
(19)
where, Δh = water head level; h = thickness of
CSB; K = permeability of CSB; L = horizontal
drain length; S = settlement velocity.
In order to ensure the drainage capacity, the
thickness of CSB shall not be less than the above
Δh value and 50cm
4.2 Design soil parameters
Detail of the soil condition and soil properties was
got in the Soil Investigation Report for Package
EX-6 prepared by Transport Engineering Design
Int. The following paragraphs will only be of
analysis of soil values for soft soil treatment. The
unit weight with depth of soil 2 is plotted in Fig.
6a, according to testing data. Initial undrain shear
strength of soft soil (Co) will be evaluated from the
following basis Field vane shear test (FVST) and
Triaxial test UU-diagram (UU Test). Moreover, for
a reliable Co value for design, the analyzing Co
value will be referred to the following basic Cone
penetration test (CPT) with Co=(qc-po)/Nk where, qc
Cone resistance value, po overburdened effective
pressure, Nk empirical cone factor, (Nk=15) and
Standard penetration test (SPT) with Co=N*100/16
(KPa). The values of Co of soil 2 are plotted in
following Fig. 6b.
(a)Unit weight (b) Co
Figure 6. Profile of unit weight & Initial undrain shear
strength Co of soft soil
Undrain shear strength of soft soil will be
increase due to consolidation with a factor called
“Factor of Increase of undrain shear strength” – m,
which is evaluated from Triaxial test, CU scheme –
CU test and, as instructed in the Standard
22TCN262-2000, m equals to tan(φcu). All m-value
from CU testing data are plotted in following Fig.
7a. Fig. 7b plots all values of pre-consolidation
pressure of the EX-6 deposit in comparison with
overburden pressure of the soil.
(a) (b) (c)
Figure 7. Profile of UU test (a), Pc with depth and in
comparing with overburden pressure (b) and Cc with
depth (c)
Fig. 7b clearly indicates that the soil is over
consolidation from about 8m upward with Pc in
order of 7t/m2
, and from this level downward the
soil is normal consolidation. The following figure
7c plotting values of compression index Cc of soil
2a versus depth also quite clearly marks this
boundary. According to Fig.7c, the following Cc
value will be recommended for design:
 Soil 2: <8m, Cc= 0.25
8-28m, Cc= 0.48
>28m, Cc= 0.36

7. 7
Table 4. Summary of soil parameters recommen-ded for soft
soil treatment design
Soil
properties
Unit
Soil
L2-1
Soil 2
<8m 8m-28m >28m
γ t/m3
1.87 1.74 1.67 1.74
Co t/m3
0 1.8 0.07z+1.24
φo
- 24 - - -
m - - 0.3 0.25
e -
-
Fig.
4-1
Fig.
4-2
Fig.
4-3
Cv.10-3
cm2
/sec
Kv.10-7
cm/sec
Cc - - 0.25 0.48 0.36
Cs - - 0.03 0.05 0.04
Pc t/m2
- 7.00 - -
OCR - - 2.40 1 1
N - 7
Embankment material
γ(t/m3
) C(t/m2
) φo
1.85 0 30
Figure 8a. Testing curves and typical one for soil 2
above 8m in depth
Figure 8b. Testing curves and typical one for soil 2 from
8m to 28m
Figure 8c. Testing curves and typical one for soil 2
below 28m in depth.
The physical properties of the soil strata are
summarized in Table 4.
Consolidation testing data comprising of
consolidation compression curves, consolidation
coefficient and permeability and typical values of
these parameters are plotted in following Fig. 8a,
8b and 8c for soil 2.
5. MONITORING RESULTS
5.1 Monitoring systems
Monitoring system was carried out install and
control during construction work in order to
confirm whether to cause a slip failure and to
generate a settlement as calculated and predicting
by design or not. This paper presents monitoring
works for approach of Thai Binh Bridge, Abutment
A2 Sta. 65+383 ~ Sta. 65+413. As for the
monitoring equipments, settlement plate,
Alignment stakes, Observation well, Piezometer
and Inclinometer were installed at section Sta.
65+400 as shown in Fig. 6.
Figure 9. Arrangement of Monitoring Equipments
Procedure and method for installation of
monitoring equipment at the site was shown in Fig.
9. SSP shall be installed on the separation
geotextile, in such a way that the top of the base
plate rests horizontally (a). Alignment stakes

8. 8
consists of 5 wood stakes per side, each 1.5m long,
penetrating to a depth of 1.0 m and placed at 4.0m
intervals on each side of the embankment (b).
Alignment nails shall be placed on the top surfaced
of the stakes, exactly on an alignment
perpendicular to the roadway alignment. The
depths of the inclinometers shall be installed at
least 2m into the underlying hard stratum (c).
Electric Piezometer shall be saturate 24 hours (d)
to removal of air bubble in the cell before
installation, and then taking the zero-reading. It is
measured exactly again before installation in the
field (e). Take readings directly after installation
and continue periodically as the water pressure
decreases after installation. We installed
Observation well below original ground around
0.5m and filling coarse sand around the PVC Pipe
to the designed elevation (f).
(a) (b)
(c) (d)
(e) (f)
Figure 10. Installed monitoring equipment at the site
Typical monitoring frequency was proposed at
daily basic for the first week, and then increased to
few days or weekly basic during filling operation as
shown in Table 5. Each instrument or observation
point shall be read immediately before and after
each change in loading, daily during filling
operations, then at twice weekly intervals during the
first month. Thereafter, until the end of the
settlement period, each instrument or observation
point shall be read at intervals not greater than once
a week. Monthly readings shall then be made
through the end of the construction period.
Table 5. Frequency of reading
Items
During
embankment
or structural
fill
After embankment
~1month
~until the
end of the
settlement
~Until the
end of the
contract
period
-AWS,
SSP,
Piz.,
Inc.,
OW
1 time/day
-Before and
after change
in loading
-During
filling
operations
2 times/
week
1 time/
week
1 time/
month
5.2 Measurement control method and feed-back
analysis
A graphical approach to estimate final consolidation
settlement and settlement rates from settlement data
obtained during a certain time period was proposed
by Asaoka (1978) and Hyperbolic method (1971).
For the stability analysis, Tominaga-Hashimoto
method and Matsuo-Kawamura method are used,
which may be able to manage the stability of the
landfill quantitatively.
5.3 Monitoring Results
This paper presents the geotechnical analysis of
monitoring data to evaluate current status of soft
soil treatment and to propose starting next step for
a case study Abutment A2 Thai Binh Bridge in
Viet Nam using SCP method. Table 8 below
presents detail construction processing in different
with detail design.
Fig. 11 shows the chart of time-settlement curve
during a construction period of 1st
stage (from 6
Otober 2012 to 21 June 2013) based on the
monitored data obtain from settlement plate and re-
calculated the settlement follow actual construction
time by theory in. The settlement amount reached
about 64.6 cm in compared with calculation is
127.46 cm.

9. 9
Table 6. Settlement prediction method
Classification Hyperbolic Asaoka method
Concept
Equation  

f 0
1
s s
a t
 f 0
1
s s

 f 0
1
s s



0
f
1
s
1


Reliability
Prediction values and measured values are close.
When degree of consolidation is over 70%
prediction can be possible within 10% of error
range
Predictedsettlement is less than measured
settlement and predicted value is getting close to
measured value with time.
When degree of consolidation is over 80%,
prediction can be possible within 10% of error
range
Table 7. Stability control method
Classification Tominaga-Hashimoto Matsuo & Kawamura
Concept
Control standard
Embankment will failure if α2 ≥ 0.7 or α2 ≥α1
+0.5
Embankment will be in danger if Pi/Pf>0.8
Pi: Embankment Load
Pf: Embankment load on failure
Reliability
In case lateral movement (δ) exceeds vertical
settlement (S), it indicates unstable due to shear
deformation. So regression line is inclined toward
I-II area.
The data of S and δ/S obtained from monitoring
data are plotted in the chart. In case the plotted data
is proceeding toward the failure line, it indicates
unstable.
Table 9. Actual excess pore pressure results
dU
Max(t/m2
)
Install EL
Initial
GWL
Initial GWL
Monitoring
U0 (t/m2)
Ut
(t/m2
)
dU
(t/m2
)
U (%)
5m 11.5 -5.4
0.94 0.94
4.46 5.62 1.16 89.60
15m 9.85 -15.4 23.48 25.62 2.14 78.27
25m 8.56 -25.4 39.75 41.43 1.68 80.37

10. 10
Table 8. Status of construction
Items
Sta. 65+383 – Sta. 65+413
Detail
Design
Actual
Condition
Method
Method
treatment
SCP
Treatment
Depth (m)
30.0
Spacing (m) 1.5
Filling time (days) 70 234
Waiting time (days) 120 24
Total (days) 190 258
Figure 11. Settlement-time Curve
Figure 12. Lateral Displacement with Depth by
Inclinometer
(a) Asaoka method
(b) Hyperbolic method
Figure 13. Estimated final settlement by Asaoka &
Hyperbolic
Inclinometers were installed at both side of
embankment. Figure 12 shows the chart of lateral
displacement with depth monitored by
inclinometer installed at 3 points as shown in
Figure 9. The maximum displacement amount
reached about 80 mm at 12m depth from top of
ground.
From consolidation settlement results, collected
in both Asaoka and Hyperbolic methods. Fig. 13
shows final estimated settlement from by analysis
result, an average final consolidation settlement
Su of 70.27 cm and degree of conssolidation
Cu =92.1% was obtained.
Three electrical piezometers were installed
under the center embankment with different depth.
The excess pore water pressure at 5m, 15m and
25mm was shown in table 9 and Figure 14.

11. 11
(a)
(b)
Figure 14. Monitoring data of Piezometer&
Prediction of ΔP for each depth
Figure 15. Settlement & consolidation after Feedback
analysis
5.4 Feedback analysis by measurement results
The purpose of feedback analysis is adjusted
design parameter using actual observation data in
order to predicted settlement tendency in actual
condition. This estimation will help to predicted
exactly final settlement and consolidation time can
be calculated through feedback analysis. Also,
slope stability can be assessed based on this
analysis. The procedure of feedback analysis
concludes: Obtaining the settlement curve with
original design parameter and actual site
construction speed and period. Obtaining the
settlement curve with measured data and settlement
analysis based on Hyperbolic & Asaoka method.
Finally, designed parameter such as Cs and Cc
would be adjusted to obtain new designed
settlement curve the same with actual observation.
Figure 15 show the recalculated settlement is
larger than the settlement observation based on actual
construction time after ending the stage 1. The
designed parameter carried out adjusting as shown in
Table 10.
The Figure 15 shows the settlement result after
feedback analysis. The settlement St amount
reached about 64.68 cm (a) and consolidation is
96.68% (b)
Table 10. Adjusted design parameter
Items Sta. 65+400
Soil Parameter
Detail
design
Feedback
Cc
Layer 2-1 0.25 0.152
Layer 2-2 0.48 0.293
Layer 2-4 0.36 0.219
Cs
Layer 2-1
1 1Layer 2-2
Layer 2-4
Sta. 65+400: about 39.05% reduction compared to
designed value (Cc)
6. CONCLUSION
The paper summarizes successful ground impro-
vement techniques (Sand Compaction Piles) used in
Hanoi-Haiphong Expressway Project, Viet Nam.
1) The advantage of SCP method is sliding preven-
tation for higher embankment and deep soft soil
areas, beside the sand is abundant in Viet Nam.
2) The SCP method can be applied widely to
reduce the settlement & consolidation at bridge
approachment to replace the Load Relief Slab
Method and Soil-Cement Column Method at
Hanoi-Haiphong Expressway Project.

12. 12
Table 11 Summary Table of Embankment Construction Monitoring Status
Item Description Unit
EX6-A2 Bridge B05 : Km65+383~65+413
D D EX6-A2-B05 EX6-A2-B05
Sta. 65+383 Sta. 65+400 Sta. 65+400
General
Information
Treatment method - depth SCP @ 1.5~30.0 SCP @ 1.5~30.0 SCP @ 1.5~30.0
Elevation of VDs tip EL.m - -29.00 -29.00
Number of stages 2 2 2
Finish Grade (Elevation)=FG (DD) EL.m +8.71 +8.71
Initial ground level(DD) EL.m +1.09 +1.09
Initial ground Water level (DD) EL.m
Ground level after BHC stage EL.m +0.99 +0.99
Geotextile level EL.m +1.00 +1.00
Embankment height (DD m 7.50 7.62 7.62
Estimated Settlement (DD) cm 160.4 160.4 160.4
Proposed embankment thickness
(Embankment height + settlement)
m 9.10 9.22 9.22
VD installation date date -
SSP installation date date - 6-Oct-12 6-Oct-12
Construction
Stage
Starting date of embankment date 6-Oct-12 6-Oct-12
Completion date of First Stage Filling date 28-May-13 28-May-13
Analysis date date 21-Jun-13 21-Jun-13
Emb. Elevation at end of stage filling EL.m +6.596 +6.596
Emb. Elevation at analysis date EL.m +6.514 +6.514
Emb. Thickness m 7.000 6.170 6.170
Emb. filling time day 70 234 234
Waiting time day 120 24 24
Monitored settlement (end of stage
filling)
cm 110.96cm 56.40cm 56.40cm
Monitored Settlement after waiting cm 127.46cm 64.60cm 64.60cm
Re-calculate settlement after waiting
(St)
cm
-
103.40cm 103.40cm
Feed back settlement after waiting (St) cm 64.68cm 64.68cm
Estimated settlement Re-calculate
or Feedback (Sf)
cm 66.90cm 66.90cm
Estimated Settlement Asaoka cm 67.49cm 67.49cm
Estimated Settlement Hyperbolic cm 73.04cm 73.04cm
Degree of consolidation - Asaoka % 95.71% 95.71%
Degree of consolidation - Hyperbolic % 88.44% 88.44%
Design requirements of this project satisfy satisfy
Conclusion Next stage could be started
3) The goal of this study is present a principle
theory Sand Compaction Pie method for the soil
improvement and behavior of composite ground
with a case study in Vietnam.
4) The geotechnical analysis of monitoring data
are presented to evaluated current status of soft
soil treatment and control the construction
procedure as well as to present new experiences
in monitoring work.
5) This paper will be a basic reference for soft soil
treatment engineer in Vietnam. The continous
development of this paper will attend to control
the quality of SCP after construction with many
field testing was carried out to estimate
7. REFERENCES
Adjusted Soft Soil Treatment Calculation Report
for Package EX-6, Hanoi-Haiphong Expressway
Project. Submitted by: Yooshin-KPT J.V. Detail
Design Consulting Servies (2010).
Aboshi, Hisao, Yasuo Mizuno, and Mashahiko
Kuwabara. "Present state of sand compaction pile
in Japan." Deep Foundation Improvements:
Design, Construction, and Testing, ASTM Special
Technical Publication 1089 (1991): 32-46.
Bang W.Shin; Eun C.Shin (1992). Sand Compaction
Piles: Theory and Practice for offshore
development. Proceedings of the Second
International Offshore and Polar Engineering
Conference. ISBN 1-880653-01-X, Vol 1.
Barksdale, R. D (1981). "Site improvement in
Japan using sand compaction piles."Georgia
Institute of Technology, Atlanta: 48-75.
Chow, Y. K (1996). "Settlement analysis of sand
compaction pile." Soils and foundations 36.1:
111-113.

13. 13
Moh, Z. C., Ou, C. D., Woo, S. M., & Yu, K. (1981).
Compaction sand piles for soil improvement.
In Proc. X Int. Conf. on Soil Mechanics and
Foundation Eng., Stockholm, Vol. 3, pp. 749-752.
Sung-Min Cho; Byoung-Ill Kim; Young-Uk Kim;
Seung-Hyun Lee (2005). Effect of Soil
Compaction Piles on Settlement Reduction in
Soft Ground. International Journal of Offshore
and Polar Engineering (ISSN 1053 – 5381).
Vol. 15, No. 3, September 2005, pp. 235-240.
Juneja, A., B. Mir, and A. Parihar. "Effects of sand
compaction pile installation in model clay
beds." International Journal of Geotechnical
Engineering 5, no. 2 (2011): 199-209.
Tonimoto, K (1973). Introduction to the Sand
Compaction Pile Method as Applied to
Stabilization of Soft Foundation Grounds. No.
Tech. Rpt. 1973.
Terashi, Masaaki, Masaki Kitazume, and Shogo
Minagawa (1990). "Bearing Capacity of
Improved Ground by Sand Compaction
Piles." Deep foundation improvements: design,
construction, and testing: 47-61.
Yoon, M. J., et al (2004). "A study on the shear
strength of sand compaction pile with composite
soil and mixed soil." The KSCE Annual
Conference and Civil Expo 2004.