Ground Improvement: Techniques for Railway Embankments, 2003

Ground Improvement
Techniques for
Railway Embankments
V. R. Raju
Keller (M) Sdn. Bhd., Malaysia
Presented by
Keller Grundbau GmbH
Kaiserleistr. 44
D-63067 Offenbach
Tel. 069 / 80 51 - 0
Fax 069 / 80 51 - 244
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www.KellerGrundbau.com
Technical paper 10-59E
Ground Improvement Techniques
For Railway Embankments
V. R. Raju
Keller (M) Sdn Bhd, Malaysia
ABSTRACT:
Modern railway infrastructure demands a high level of performance in terms of settlements and
stability of the railway track. In areas where loose or soft cohesive deposits are found, ground
improvement is often required to ensure the required level of performance.
This paper presents some of the ground improvement techniques that are available from Keller
Group companies and being used worldwide for railway infrastructure projects. The techniques
presented are Vibro Compaction, Vibro Replacement (Stone Columns), Grouted Stone
Columns (GSC), Vibro Concrete Columns (VCC) and Deep Soil Mixing (Cement Columns).
The purpose of this paper is to provide a general introduction of the techniques to Owners,
Designers and Project Managers and to illustrate their application by describing case histories
from Europe, USA and Malaysia.
1.
INTRODUCTION
Railways are one of the oldest mode of transportation systems started some 150 years ago
under different traffic conditions as far as speed, axle loads and traffic intensity are concerned.
Increasingly, there are greater demands from modern railway organisations to increase the axle
loads and train speeds both for economic and environmental reasons. In addition to increased
axle loads and train speeds, railway lines often have to cross over existing loose or soft
cohesive deposits as a part of the alignment giving rise to the need for ground improvement.
In order to achieve a high level of performance of the rail system, attention should be focused
on post construction settlements of the subsoil and factor of safety of the structure against slip
failure. Different countries follow different sets of specifications for settlement and stability
criteria for railway systems. For example in Malaysia for a railway line designed for speeds of
160 km/h, typical requirements are as specified below:
• Maximum post construction settlement of 25mm over a period of 6 months of
commercial rail service.
• Maximum differential settlement of 10mm over a track length of 10m (1 in 1000) along
the embankment centreline.
• Minimum long-term factor of safety of 1.5 against slip failure.
Apart from the settlement and stability criteria, another important criterion is to mitigate
vibrations induced by high-speed trains in order to achieve acceptable dynamic performance of
the rail system. By improving the subsoil characteristics, it is possible to mitigate the vibrations
to the surrounding structures.
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2.
GROUND IMPROVEMENT TECHNIQUES
The presence of loose or soft soils along the alignment of railway tracks inevitably leads to
problems in terms of post construction settlements, inadequate factor of safety against slip
failure and problems associated with ground vibrations caused by high-speed trains. In order to
overcome these problems, several ground improvement techniques are available and some of
them are presented below.
2.1.
Vibro Techniques
The process of improving loose granular soils with depth vibrators started in the 1930’s and 25
years later with continuous development and modification of the equipment, additional
refinements to the technique have been implemented in order to use the technology for
treating soft cohesive soils as well. The depth vibrator as a ground improvement tool is used to
solve a wide range of static, dynamic and seismic foundation problems by densifying loose
granular soils (Vibro Compaction) and partially replacing soft cohesive soils with granular
material (Vibro Replacement or stone columns). Where lateral support from in-situ soil is
inadequate, the stone column may be grouted (Grouted Stone Columns) or concrete may be
used (Vibro Concrete Columns). The reader is referred to Moseley (1993) for further details
on vibro techniques.
2.1.1. Vibro Compaction
The basic principle behind the method is that particles of non-cohesive soil such as sand and
gravel can be rearranged by means of vibration. The vibratory action of the depth vibrator is
used to temporarily reduce the inter particular friction between the particles and rearrange
them in a denser state. The vibrator penetrates the soil by means of water jets and once at full
depth, it is gradually withdrawn leaving behind a column of well compacted soil. A schematic
showing the process of vibro compaction is depicted in Figure 1. To achieve a mass
densification, the entire area is compacted by column points in a triangle or square pattern.
This technique is well suited for the densification of relatively clean (fines content up to about
10 to 15%) granular soils such as sands and gravels. A major benefit of this method is that no
additional materials are necessary which makes it a very economical technique.
Fig. 1 Schematic showing Vibro Compaction
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2.1.2. Vibro Replacement (Stone Columns)
Vibro replacement is a technique used to improve sandy soils with high fines contents (>15%)
and cohesive soils such as silts and clays. In this method columns made up of stones are
installed in the soft ground using the depth vibrator. The vibrator is used to first create a hole
in the ground which is then filled with stone during withdrawal of the vibrator. The stone is
then laterally displaced into the soil following repenetration of the vibrator. In this manner a
column made up of well compacted stone fill with diameters typically ranging between 700mm
and 1,100mm is installed in the ground.
Two methods of installation namely the ‘wet’ and ‘dry’ methods are available for the installation
of the columns. In the wet method water jets are used to create the hole and assist in
penetration. In the dry method the hole is created by the vibratory energy and a pull down
force. Typical installation process in the case of dry method is schematically shown in Figure 2.
This technique of soil improvement can be used for nearly all types of soils.
Testing of the soil improvement, after installation of the stone columns in coarse-grained soils is
usually performed with either static or dynamic penetrometer tests (CPT or DPT). However
for stone columns constructed in fine-grained soils it is common practice to carry out load
tests directly on the columns.
Fig. 2 Schematic showing the installation of stone columns (dry method)
The Vibro Replacement technique provides an economic and flexible solution, which easily
adapts to varying ground conditions. Using Vibro Replacement, the following geotechnical
improvements are achievable:
•
•
•
•
•
•
Compaction of the subsoil and increase in density
Improvement in the stiffness of the subsoil to decrease excessive settlements
Improvement in the shear strength of the subsoil to decrease the risk of failure
Increase in the mass of the subsoil to mitigate ground vibrations
Ability to carry very high loads since columns are highly ductile
Rapid consolidation of the subsoil
2.1.3. Grouted Stone Columns (GSC)
3
A stone column depends on the lateral support offered by the in-situ soil for its stability and
load carrying capacity. In organic soils such as peat, this lateral support may not be adequate or
may diminish with time following decomposition. In such cases, columns can be constructed by
binding the gravel/stones with a cement grout suspension. This can be achieved by the addition
of cement suspension during the installation process, which combines with column material to
form a grouted body. Typical installation process of grouted stone columns is schematically
shown in Figure 3.
The design of the external bearing capacity of the grouted columns is carried out as per normal
pile design codes. The maximum vertical load per column generally ranges between 400 kN and
600 kN and is mainly influenced by the shape of the compacted toe (column base).
Fig. 3 Schematic showing the installation of grouted stone columns
2.1.4. Vibro Concrete Columns (VCC)
This is a variation of the grouted stone column technique which forms a rigid pile like
foundation element. In this technique concrete is pumped directly to the tip of bottom feed
depth vibrator to form the column. Typical installation process of vibro concrete columns is
schematically shown in Figure 4. Due to the formation of the base and its penetration into the
compacted bearing strata, the columns are generally considered as end-bearing columns and
can support high service loads. The internal load bearing capacity is dependent upon the grade
of concrete, and is determined in accordance with standard design codes as in other in-situ pile
foundation systems.
Both GSC and VCC are rigid solutions and total settlements are minimal (< 25mm). The ability
to enlarge the base of the column and also the column heads can result in a decrease in column
lengths and an increase in column spacing which results in an overall decrease in the cost of the
foundation system.
4
Fig. 4 Schematic showing the installation of vibro concrete columns
Vibro Concrete Columns are ideal for weak alluvial soils such as peats and soft clays overlying
competent founding stratum such as sands and gravels, soft rocks etc. Working loads up to 750
kN can be achieved in appropriate soils. Where the VCCs are required to support structures,
such as heavily loaded floor slabs, rafts, roads and embankment, the columns can be
constructed with an enlarged heads as shown in Figure 5. The enlarged head serves to reduce
punching shear and can either be used to give direct contact support to the slab or to provide a
uniform bearing pressure through a geogrid reinforced granular mattress as shown in the
Figure.
Fig. 5 Example of non-suspended slab on enlarged VCC heads
Quality control for all vibro techniques is essential and all construction is fully instrumented. An
in-cab computer display monitors the construction sequence in terms of material consumption,
power consumption of vibrator, all related to time and depth. A hardcopy printout provides an
immediate record of the construction of each column.
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2.2.
Dry Deep Soil Mixing
Dry deep soil mixing (DSM) technology is a development of the lime-cement column method,
which was invented by Kjeld Paus almost 30 years ago. It is a form of soil improvement
involving the introduction and mechanical mixing of in-situ soft and weak soils with a
cementitious compound such as lime, cement or a combination of both in different
proportions. The mixture is often referred to as the binder. The binder is injected into the soil
in a dry form. The moisture in the soil is utilised for the binding process, resulting in an
improved soil with higher shear strength and lower compressibility. The removal of the
moisture from the soil also results in an improvement in the soft soil surrounding the mixed
soil. The reader is referred to Broms (1999) and Holm (1999) for further details. Typical
execution process of dry deep soil mixing is schematically shown in Figure 6.
Fig. 6 Schematic showing the execution of dry deep soil mixing
Typical applications of the deep soil mixing method include foundations of embankment fill for
highway and railway, slope stabilisation, stabilisation of deep excavation and foundations for
housing development. The range of soils applicable spans over soft cohesive deposits, expansive
clays, loose-granular soils and pulverised fuel ash.
The anticipated amounts of binding agents commonly used are approximately 100 – 150 kg/m3
in silty clay and clayey silt materials. The strength develops differently over time depending on
the type of soil, amount of binder and proportion used. In most cases, the strength starts to
increase after a few hours and then continues to increase rapidly during the first week. In
normal cases, approximately 90% of the final strength is reached after about three weeks. For
the design approach of DSM and evaluation of improved deformation and shear strength
parameters, the reader is referred to Broms (1999) and the Swedish Geotechnical Society
(1997).
The technique is primarily used to reduce subsidence and increase shear strength and bearing
capacity of the composite soil mass. It can also be used in cases where reduction of vibrations is
required. For example vibrations caused by high-speed trains can be reduced by dry DSM
technique in order to achieve an acceptable performance of the rail system. Extensive work has
been carried out at the Swedish Geotechnical Institute and the reader is referred to Holm et.
al. (2002) for further details.
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3.
CASE HISTORIES FROM GERMANY AND AUSTRIA
Following the reunification of Germany in 1990 and the introduction of the high-speed railway
system in the country, the existing railway network leading to Berlin required up-gradation.
This called for extensive ground improvement works. Deep Vibro techniques were employed
at several locations. The map in Figure 7 shows the locations/sites where ground improvement
works were carried out. Figure 8 shows photographs from site showing 3 Vibrocats carrying
out ground improvement works for the German ICE train system and a schematic of the highspeed ICE Train with operating speeds of over 250 kmph founded on stone column. The reader
is referred to Sondermann (1996) for further details on these works.
Fig.7 Map showing sites where ground improvement was carried out for the
German railway lines leading to Berlin
Fig. 8 (Left) Photo showing 3 Vibrocats carrying out ground improvement works for the high speed ICE train system. (Right)
Schematic of the ICE Train with operating speeds of over 250 kmph founded on stone columns
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3.1.
Hamburg – Berlin High-Speed Line: Wittenberge Section
(Vibro Replacement)
The subsoil underneath a 6-km stretch in the extension works to the Hamburg – Berlin route
near Wittenberge was improved using Vibro replacement (stone columns). The improvement
was necessary for the upgrading of a normal existing line to a high-speed line on rigid pavement
(refer Sondermann 1996).
Following soil investigation works, compaction works were carried out using special equipment
and utilising the redundant ballast. A 4-row layout of stone columns were installed with a
horizontal spacing of 2m c/c and vertical spacing of 1.25m c/c on a triangular grid pattern. The
columns were installed to depths between 3m and 7m. The diameter of the columns varied
between 0.6m and 0.8m. A schematic showing the cross section and plan view of treatment
scheme is shown in Figure 9.
Fig. 9 High-speed railway embankment on rigid pavement using Vibro Replacement
During the soil improvement works, measurements were taken by geophones to record the
vibrations at depths between 2m and 3m. Evaluations of the results showed that the anticipated
soil deformation caused by the vibrations induced by high-speed trains have already occurred
during installation of the stone columns. The oscillation speed of the railway system is much
slower than that of the soil improvement works. Even during the installation next to a service
railway line (with speeds of up to 120 kmph), the vertical displacements of the rails were less
than 3mm and the horizontal displacements were negligible.
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3.2.
Hannover – Berlin High-Speed Line: Schonhausen Embankment Section
(Vibro Replacement)
A section of the Hannover – Berlin high-speed line between Hamerten and Stendal near to the
Elbe bridge is constructed on a rigid pavement system. Due to the double tracking of the highspeed line, the Schonhausen embankment at the east side of the Elbe Bridge has been widened.
The old embankment was inter-connected to the new extension backfill by stone columns on a
rectangle grid spacing of 1.85m x 2.15m c/c as shown in Figure 10.
Fig. 10 Soil improvement by stone columns at Schonhausen embankment
The soil profile at the Schonhausen embankment section is showed in Figure 11 along with the
results of pre and post cone penetration tests. Results of soil investigation indicated a sandy
layer at top 3m where tip resistance was improved significantly, this is followed by a soft clayey
silty layers up to a depth of 7m in which tip resistance was observed to be almost the same as
pre treatment values as expected.
Fig. 11 Soil profile and pre and post CPT results at Schonhausen embankment
In another section of the embankment, stone columns were installed in order to densify the
loose soil and to improve the shear strength for slope stability. In both sections, a total of
82,000 lin. m. of stone columns were installed with lengths ranging between 6m and 12m,
depending on the embankment height.
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3.3.
Hamburg – Berlin High-Speed Line: Vietznitz-Friesack Section
(Grouted Stone Columns)
The subsoil underneath the Hamburg – Berlin high-speed line at Vietznitz-Friesack section in
the area of Havellander Luchs, was found to be made of peat sandwiched between sandy layers.
Soil investigation at the site indicated a 2m thick sandy layer at the surface followed by a 2m
thick organic layer of peat followed by dense sandy layers. In order to bridge organic layers of
peat, partially grouted columns were used to transfer traffic loads to deeper strata. The soil
profile along with treatment scheme is shown in Figure 12.
Fig. 12 Soil improvement using partially grouted columns at Hamburg–Berlin high-speed line
The partially grouted columns were installed in a 0.6m diameter on a diamond grid pattern with
a side spacing of 1.41m c/c. Top and bottom of the columns were formed in sandy layers only
with stones whereas in organic layers of peat grouted columns were installed. During the
installation works the adjoining operational track was supported using a soldier pile wall as
shown in the above picture.
Extensive measurements such as vibration measurements were carried out in order to test the
long-term behaviour of the foundation system for high-speed trains. The results of such
measurements proved that, this combined method of partial grouted columns is very effective
in improving the unfavourable soil conditions.
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3.4.
Austrian Railway line near Hollenegg
(Vibro Replacement under operational railway line)
The railway line Graz - Wies - Eibiswald is one of the oldest railway lines in Austria. It was built
in the second half of the 19th century. The subgrade material used at that time was locally
available and in some parts poor quality fill. This lead to problems of serviceability and repeated
maintenance during the operation of the track. Geotechnical investigations revealed that the
upper meters directly below the tracks were made up of loose soils which required
densification.
The Keller Vibro Replacement technique was chosen as an economical solution which allowed
continued operation of the railway line during ground improvement works. There was no
necessity for removal of the rails and the ballast. The works were carried out during the line
block periods at night. For this purpose, a specially modified Keller Vibrocat including all
necessary auxillary equipment was mounted on top of a railway wagon (see Figure 13).
Columns were installed between the sleepers as shown in the drawing below. The stone was
transported by rail to the working areas. This allowed a complete demobilization of plant and
materials at the end of the working shift.
Fig. 13 Vibro Replacement equipment mounted on a railway wagon for ground improvement works underneath an
operational railway line
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4.
CASE HISTORIES FROM SCANDINAVIA
Over the years more than 80 ground improvement works for railway-projects have been
executed in Scandinavia by the dry deep soil mixing method (lime-cement column method).
Works have involved stabilisation of soft soils and columns have in later years also been
installed to reduce vibrations. The latter has become necessary due to the increasingly more
common high-speed trains in Scandinavia, with operating speeds around 200 km/h. The map of
Scandinavia is shown in Figure 14, the dots in the map indicate locations where ground
improvement was carried out for railway tracks during the period 2000-2002.
Fig. 14 Map of Scandinavia
(Dots indicate the locations where ground improvement using dry DSM was carried out during 2000-2002)
Over 12 million linear meters of columns have been installed during the last two decades by
LCM Markteknik (a subsidiary of Keller and Peab) in Scandinavia. Over 35% of this work has
been for railways. Following is a case history from one of the projects.
4.1
Lekarekulle-Frillesås Line
(Lime-Cement Column Method)
The Swedish Railway Authorities have been expanding the single railway tracks to double tracks
for the West Coast Line (Vastkustsbanan). The client concluded that the subsoil underneath a
1.5 km section of the existing railway in Frillesas, Sweden needed to be stabilised. The new
double track would be positioned 0-3m below the surrounding ground level. The most
desirable option for stabilisation was chosen to be the lime-cement column method.
The ground investigation report showed a top layer of organic soil or filling and underneath a
layer of sand and dry crust. The layer of sand was about 1m and the dry crust was about 1-3m
thick. Beneath this layer was a sandy-silty-clay, which rested upon a layer of friction-soil on
rock. The depth down to firm soil was about 12m. The clay was found to be of middle range
12
sensitive and the density increased over depth. The dry crust had a water content of 20-45%,
while the clay had a water content around 30-65%. The clay was weakly over-consolidated with
about 20kPa. The shear strength of the clay varied between 10-90 kPa.
Following the soil investigation works and lime-cement column mixing tests, it was concluded
that 3,260 lime-cement (50/50) columns, with a diameter of 600mm, spaced 1.5m in a
rectangular grid pattern, and a total of 33,950 linear meters would have to be installed. The
columns were designed to reach firm ground. Typical picture showing the execution works is
shown in Figure 15.
Fig. 15 Installation of lime-cement columns for soil stabilisation adjoining a railway track
Tests were made on 20 columns by the FOPS-method. A probe is mounted underneath the
mixing tool and the drag-wire is pushed up into the Kelly-pile for reverse column testing as
shown in Figure 16. Monitoring results showed that the vertical displacement of the existing
track was negligible.
Fig. 16 Typical picture showing details of FOPS testing method
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5.
CASE HISTORIES FROM U.S.A.
Railroad infrastructure development has a long history in the United States of America.
Throughout this history, engineers have been confronted with the difficulty and expense
involved in the maintenance of existing rail traffic through difficult and complex geological
settings. Railroad upgrades are often required to handle increased freight and commuter traffic,
double stack cars or high speed trains. In addition to this, there are problems relating to
landslides or washouts of hillside rail, sinkhole activity and stabilisation of compressible and
liquefaction prone soils. All of this is expensive and often requires disruption of existing traffic.
A number of in-situ site improvement and remedial techniques which are proven, cost effective
and which can be implemented quickly with minimal disruption to rail schedules are offered by
Hayward Baker (a Keller Group company) in the United States. The following Table lists
applications of various ground improvement techniques implemented at site locations in the
United States. The reader is referred to Pengelly (2000) for further details. Some of the details
of these case histories are presented in the following sections.
Table 1 Selected list of ground improvement and foundation techniques applied
in the U.S.A. for railway projects
Technique Site Location
Vibro
LACTC Flyover, Los Angeles
Replacement SFM Rail yard, San Francisco
Purpose
Densification of loose silty sands
Mitigation of liquefaction potential
Deep Soil
Mixing
Alameda Corridor, Los Angeles
Stabilisation of in-situ soils
Lime/Flyash
Injection
Santa Fe Railroad, St. Joseph, MO
Subgrade stabilisation
Compaction
Grouting
Union Pacific (UP) Railroad, Kansas
CSX Railroad, Georgia
Union Pacific Embankment Tunnel,
Longview, Texas
Filling of voids in the shale
Avoidance of sinkhole formations
Densification of soil mass
Jet Grouting
Tilford Tunnel, Atlanta, Georgia
Charles Street Bridge, , Rhode Island
Union Pacific Storm Drain Tunnel, Ft.
Worth, Texas
To replace the existing support
To increase the slope stability
To stabilise the soil mass
Chemical
Grouting
West River Bridge, New Have,
Connecticut Claremont Detention
Basin, Albuquerque, New Mexico
Stabilisation of granular soils
Solidification of sandy soils
Mini Piles
Canton Viaduct, Canton, Massachusetts
Straight Creek Bridge, Tazewell,
Tennessee
Embankment slide, Green Bottom,
West Virginia
To form load bearing elements
To form a deep foundation system
Anchors
14
To form
system
an
earth
retention
5.1.
LACTC Flyover: Los Angeles, California
(Vibro Replacement)
As part of an up-gradation of the San Bernardino Commuter railway line, the Los Angeles
County Transportation Commission (LACTC) needed to add flyovers along existing right-ofway of the Southern Pacific Railroad. Soil investigations performed in these areas revealed two
sections with loose sands. N values indicated that these sands had low blow counts that
averaged to 6 up to depth of 15 feet. The new flyovers would be constructed of pre-cast
concrete panels, the loads of which would induce excessive settlements on the soils in their
present condition. Due to the proximity of the flyovers to existing active rail lines and the
congested nature of the area, the conventional method of removing and replacing the soil was
not an attractive option. Vibro replacement was selected to install stone columns, which would
reinforce the soil mass as well as densify the soil between the columns.
Stone columns were installed on 9-foot centres to depths of 15 feet. Due to the sensitive
nature of the active rail line and other adjacent structures, vibration monitoring was performed.
Typical pictures showing the installation and monitoring works are shown in Figure 17. The
peak particle velocity was maintained below 2 inches/sec at distances greater than 5 feet
beyond the vibrator. After installation of stone columns, electric cone penetrometer testing
was performed to verify improvement of the soils. Required relative densities of 80% were
achieved in all of the areas where stone columns were installed.
Fig. 17 Installation and monitoring works at the site
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5.2.
New Rancocas Creek Railroad Bridge: New Jersey
(Vibro Concrete Columns)
The new Rancocas Creek railroad bridge is one of the major structures for a new light-rail line
that extends from Camden to Trenton, via New Jersey along the east shore of the Delaware
River. As part of this project, an embankment with retaining wall system needs to be
constructed replacing the old earth embankment at the southern approach to the Rancocas
Bridge. Based on an evaluation of several retaining wall systems, the T-WALL retaining wall
system was selected.
Subsoil investigation at the site revealed that the soil profile consists of silty sands up to a depth
of 8 feet followed by peat and organic silts up to a depth of 25 feet, followed by silty sands up
to a depth of 40 feet. The result of settlement analysis of the proposed approach using the
characteristics of the unimproved ground indicated a maximum settlement of 24 inches. It was
expected that the duration of settlement would last for many years due to the continued
compression of the peat soils, which necessitated improvement of the existing subsoil.
Among the several ground improvement techniques, Vibro Concrete Columns (VCC) were
selected due to the advantages of rapid construction schedule and greater element stiffness.
The VCCs were installed with a spacing of 7 to 9 feet on a triangular grid pattern, to a total no.
of 625 columns in less than 3 weeks time. The construction technique provided for longer
vibrating times at the bottom and top of the columns to expand the base and top to as much as
30 inches. A 3-foot thick geosynthetic reinforced load transfer platform was placed over the
VCCs to transfer the vertical load from the retaining wall system to the VCC. The typical cross
section showing the treatment scheme, load transfer platform and T-WALL retaining system is
shown in the Figure 18. The measured settlement in a single column load test under 150% of
design load was about 0.46 inches, which indicates the VCC satisfied the criteria for a design
compression capacity of 200 kips.
Fig. 18 Typical cross section showing the treatment scheme and T-WALL retaining system
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5.3.
Santa Fe Railroad
(Lime/Fly-ash Injection)
The Santa Fe Railroad suffered severely from recurring track misalignment. The reason for
these problems was the settlement of the roadbed near St. Joseph, Missouri. Soil investigations
using electric cone penetrometer testing revealed very weak soils to depths of 18 to 20 ft with
deep water saturated ballast pockets.
Lime/Fly-ash slurry injection was selected as a longterm solution to fill the cracks, weakness planes,
voids and ballast pockets. The cone pentrometer
testing enabled the engineers to accurately locate the
distressed zones and to deliver the proper amount
of slurry to precise locations. Based on the test
findings, an injection program was designed to
penetrate 20 ft deep and to stabilise every crib. A
typical picture showing the execution of Lime/Fly-ash
slurry injection is shown in Figure 19. Works were
carried out without removing the track and the
ballast. The results of pre and post cone penetration
tests are plotted as shown in Figure 20. Typical
photos showing the alignment of the track before
and after treatment is shown in Figure 21.
Fig. 19 Typical picture showing the
execution of Lime/Fly-ash slurry injection
Fig. 20 Results of pre and post
cone penetration tests
Fig. 21 Photos of the track
before (above) and after (below) treatment
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5.4.
CSX Railroad, Georgia
(Compaction Grouting)
A 1500 ft length of mainline railroad in North Georgia is located in a sinkhole prone (karst)
geologic setting. In the mid to late 1980’s, the frequency of sinkhole activity increased
dramatically, attributed to a combination of drought conditions, groundwater draw-down from
a nearby quarry, and the natural sinkhole activity usually associated with karst topography. The
frequency and severity of the sinkhole activity resulted in a slow order in train speeds (from 60
mph down to 10 mph) and round-the-clock visual monitoring. Although the frequency of new
sinkhole activity decreased after the quarry ceased operation, remnant sinkholes, initially
formed when groundwater levels were depressed, continued to appear. To reduce the risk of
drop-outs that could impact railroad traffic, the owners selected compaction grouting as the
most economical, technically feasible preventative measure. An added advantage was that the
track could remain operational during the work.
The grouting program was designed to fill any voids in the upper rock surface, form a grout
barrier along the rock/soil interface and densify the loosened overburden soils. Grouting was
performed along an 850 linear foot treatment area. The grout holes were drilled at an angle
from the eastern edge of the track to intercept the surface of the limestone directly beneath
the centreline of the track as shown in Figure 22. Casing was advanced to penetrate at least five
feet into the upper bedrock surface. Drilling was monitored and logged to identify soft/loose
soil zones or void areas. Grout locations were injected on a primary/secondary grid sequence,
with tertiary locations identified and grouted where secondary holes did not encounter tight
conditions. Primary holes were drilled at 20 foot centres and Secondary holes were drilled at
10 foot offsets to the primaries. If no pressure was observed, the grout was pumped to 3 cubic
yard per foot of casing for the first three feet above the rock.
As a result of the grouting program, the sinkhole activity was arrested which enabled the slow
order in train speeds and full-time monitoring to be discontinued. To date, the track has
continued to perform satisfactorily (Brill and Hussin (1992)).
Fig. 22 Application of compaction grouting for a railway embankment
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6.
CASE HISTORIES FROM MALAYSIA
The development of railway infrastructure in Malaysia dates back to the early 20th century.
Recent development of industrial complexes has necessitated the construction of additional
railway lines to transport raw materials and finished products. Fig. 23 shows a map of Malaysia
with locations were ground improvement has been carried out by Keller (M) Sdn. Bhd. Details
of these works are described in the following case histories.
Fig. 23 Map of Malaysia showing locations where ground improvement has been carried out
6.1.
KTM Track: Sungei Besi, Kuala Lumpur (1992)
(Vibro Replacement, Cut Off Trench Wall)
The presence of large variations in ground water levels arising from deep tin mining activities
near Sungei Besi, between Salak South and Serdang in Kuala Lumpur, Malaysia, resulted in
erosion and possible migration of soil material below an existing KTM track. This resulted in
the gradual subsidence of the track resulting in reduced train speeds and the requirement for
constant maintenance. Soils at the site were made up of alternating layers of loose silty sands
and soft clayey silts arising mostly from tin mining activities to depths of about 12m. This was
underlain by dense layers or limestone. Ground improvement works in the form of a cut off
trench wall adjoining the track to arrest the flow of water across the track and the stabilisation
of the soil underlying the track using vibro replacement was carried out. Figure 24 shows a
cross section of the treatment scheme. A total of 3900 nrs. of minimum 0.85m diameter stone
columns were installed to a maximum depth of 12m. Columns were installed on a triangular
grid with a spacing of 2.1m.
Fig. 24. Cross section showing cut-off trench wall and stone columns beneath track
19
6.2.
Petronas Kedah Fertilizer Plant Line at Gurun (1997)
(Vibro Replacement)
The building of the Petronas Kedah fertilizer plant in 1997 near Gurun in northern Malaysia was
accompanied by the construction of a special railway line connecting the KTM main railway line
to the fertilizer plant. The long profile of the railway line required the construction of
embankments with heights ranging between 2m and 8m. The proximity of the existing KTM line
did not allow the use of earth slopes and a reinforced earth wall was used (see Figure 25). The
presence of very soft clayey silts (SPT N = 0 to 2) to depths down to 9.0m posed problems of
wall stability and excessive settlements.
Fig 25: Cross section showing the reinforced earth wall, the adjoining existing KTM line and the ground
improvement scheme
Vibro Replacement using the dry bottom feed technique was used to treat the soft soils. In
total 18,000 lin.m. of 1.0m diameter stone columns were installed using two Keller Vibrocats.
Figure 26 shows the two Vibrocats at work with the KTM train in the fore ground.
Fig.26 Vibro Replacement works along the KTM railway line at Gurun for the Petronas Kedah Fertiliser Plant
20
6.3.
Kertih to Kuantan Railway Line (2000 - 2001)
(Vibro Compaction and Vibro Replacement)
The development of Petrochemical facilities on the east coast of Malaysia necessitated the
construction of a dedicated railway line between Kertih and Kuantan by Petronas.
Soils along the alignment ranged between loose sands along coastal areas to sensitive fine
grained soils (silts and clays) and also highly organic soils in inland forest and swampy areas.
Loose/soft soil depths ranged between 3m and 14m. A total of 253 Nrs. of pre CPT tests were
carried out (at the rate of 1 CPT per 1000 sq.m. of treatment area) to obtain a clear picture of
the soil conditions over a 10km length of railway track alignment.
Where soils were relatively clean sands, Vibro Compaction was carried out to densify the loose
soils. Compaction results were verified using post compaction CPT tests and plate load tests.
Figure 27a shows a typical setup of crane and depth vibrator to carry out vibro compaction. In
most cases, compaction was carried out to depths of only 3m (Surface Vibro Compaction) as
required by design.
Figure 27b shows a typical pre and post compaction CPT test result in sandy soil strata. The
vibro compaction technique was able to effectively compact granular soils even for shallow
depths of 3m and tip resistances of over 10 MPa were observed. In total about 3,500m of track
was treated using Vibro Compaction.
Reduced Level (m)
5
4
3
PRE
2
POST
1
0
-1
0
(a)
2
4
6
8
10 12 14
Tip Resistance, Qc (Mpa)
16
18
20
(b)
Fig 27a. Typical setup for Vibro Compaction along railway alignment
Fig 27b. Typical pre and post compaction CPT test result
Where soft cohesive and organic silts and clays were found (SPT N = 0, CPT Qc = 200 to 300
kPA) to depths of 8m to 14m, Vibro Replacement using the wet top feed method was used.
The alignment often passed through thick jungles with swampy soil conditions (the night
watchman had to also watch out for tigers!). The top 0.5m of the soil was basically
decomposed vegetation. The trees, shrubs and decomposed materials were first cleared and an
access road was built adjoining the railway alignment (see photo in Fig 28). A 1m thick sand
21
blanket was placed to form a stable working platform. In swampy locations where the top soil
was very soft, the sand platform had to be thicker.
Fig 28: Railway alignment through a jungle after site clearing and construction
of access road at CH 34,000.
Up to 8 wet stone column installation rigs were used for a period of 18 months to treat a total
of 3,800 m of railway track using Vibro Replacement. The works were carried out at 12
different sites and logistics of plant and material transport through jungle and at times hilly
terrain was a major concern.
85 Nrs. of plate load tests were carried out to test both Vibro Compaction and Replacement
results. Where test loads were 50 tons or less, reaction was provided by the crawler cranes
available on site (see Figure 29).
Fig. 29 Plate load test using crawler crane as reaction for tests to 50 tons
22
6.4.
Ipoh – Rawang Double Track Project (2001 - 2003)
(Vibro Replacement)
Malaysia is to play a key role in the planning and coordination of the Trans-Asia Railway line
between Kunming in China and Singapore. The line covering a total distance of approx. 5,500
km is expected to link and promote the economic development of countries such as China,
Vietnam, Laos, Burma, Combodia, Thailand, Malaysia and Singapore. The Ipoh to Rawang
Double Track project which is under construction will form a part of the Trans-Asia Railway
line and covers a distance of approx. 150 km .
The alignment of the new double track line follows closely the existing single track line and in
many locations one of the lines is shared. However, more stringent gradient requirements of
the new line has resulted in an increase in embankment heights.
The Ipoh to Rawang stretch has seen extensive tin mining activity in the past and the soil
conditions encountered on site have been largely influenced by these activities. Over 200 Nrs.
of CPT tests were carried out to investigate the ground conditions. Soils are highly variable
mixtures of loose sands and very soft silts and clays to depths ranging between 6m and and in
certain extreme cases as deep as 24m. Fig 30 shows a typical CPT test result from the region
showing a 1.5m thick sandy layer followed by very soft clayey silt (Qc = approx 150 to 250 kPa)
to 6.5m depth. This is followed by alternating layers of sands and silts.
Tip Resistance Qc [MPa]
Depth [M]
0
1
2
3
4
Friction Ratio
5
0% 1% 2%
0
0
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
10
10
11
11
12
12
13
13
14
14
15
15
3% 4% 5%
Fig. 30: Typical CPT test result from a location where vibro replacement was carried out.
Vibro Replacement was chosen as a technically sound, flexible and economically viable solution
to treat these soils to meet specifications as listed in section 1 of this paper. The following
section briefly describes the works that were carried out.
23
Mainline treatment
Treatment was been carried out adjoining the existing track to support the new track. A 1.0m
thick sand platform was placed from which stone columns were installed to the required depths
(ranging between 8m and 18m). Embankment heights ranged between 2m and 11m.
Vibro Replacement was also used for locations where excavation and replacement of unsuitable
soils to depths of 3 to 4m was the original design option. Vibro Replacement eliminated the
necessity for deep excavations adjoining operational tracks and the risks associated with such
excavations. It was also found to be more economical when the cost of excavation support was
included in the calculation. Figure 31 shows a schematic of the half width treatment. Where
necessary, the soil under the rehab track will be treated later, once the train has been shifted
to the newly built track.
Fig 31: Schematic showing half width treatment adjoining existing railway line
Where the new alignment was separated from the existing line, full width treatment was
carried out in one go. Figure 32 shows a schematic for full width treatment. The photo in figure
shows vibro replacement works alongside the existing track.
Fig 32: Schematic showing full width treatment adjoining existing railway line
24
Fig 33: Photograph showing a Keller vibrocat and a crane hung rig carrying out vibro replacement works
adjoining the existing track
In total, vibro replacement works were executed at 23 separate locations covering a track
length of 6.76 km. Works were often carried out very close to the existing track (approx. 2m
away) without any disturbance to normal train operations.
Road Over Rail Embankments
The double tracking of the existing line necessitated the increase in the bridge spans which
implied that in most cases, new bridges had to be built adjoining the existing ones. Approach
embankments for the bridges reached a maximum height of 12m and were often supported by
reinforced soil walls. Figure 32 shows the treatment scheme for the new embankment adjoining
the existing one. Vibro Replacement was carried out at 4 bridge locations covering a treatment
area of 48,000 sq.m.
Fig 32: Schematic showing treatment for road over rail embankments
25
6.5.
Ipoh – Rawang Double Track Project
(Dry Deep Soil Mixing)
As part of the construction of Ipoh – Rawang Electrified Double Track Project a stretch of
800m length of soft soils were treated using Dry Deep Soil Mixing (Dry DSM) method. The
treatment area was located between CH 341,650 and CH 342,450 near the town of Serendah.
At this area embankment heights varied between 1.5m and 3m and embankment width ranged
between 20m and 25m.
The results of soil investigations showed that the top 5m was made up of a soft clayey silt with
a tip resistance of about 200 kPa implying a shear strength in the order of 10 kPa to 15 kPa.
This was followed by an approx. 1.5m thick silty sand layer with a tip resistance of about 3 MPa.
This was followed by alternating layers made up of soft clayey silts and loose silty sands to a
depth of 11m followed by dense sand layers. Ground water was found at a depth of approx.
1.0m below ground level.
Cement columns of diameter 0.6m were installed to achieve a design undrained shear strength
of 250 kPa underneath the rails and 150 kPa in the remaining area. Typically the spacing of the
column grids (square/rectangle) varied between 1m to 1.3m c/c under the rails and 1.4m to
1.5m c/c in the remaining area underneath the embankment. Columns were installed from toe
to toe of embankment and were installed down to the dense sand layers resulting in lengths
ranging between 7m and 14m. Schematic showing typical cross section of embankment and
treatment scheme is shown in Figure 33.
After completion of the treatment, 4-column plate load tests have been carried out. Test
results showed settlement within 10mm for 150% of design load. During the construction of
embankment over the treated ground, settlements and lateral movements of the embankment
were monitored using rod settlement gauges and inclinometers, which showed settlements to
date to be less than 15mm and lateral movements less than 20mm indicating acceptable
performance of the cement columns.
Fig. 33 Schematic of treatment scheme
26
7.
CONCLUSIONS
Experience in several countries has shown that ground improvement is often required for
founding embankments for modern high speed railway infrastructure. Deep vibro techniques
and deep soil mixing methods have found extensive application worldwide and have proven to
be flexible in the ability to treat a wide range of soils and site constraints/conditions and
efficient in terms of time required to complete the treatment works and for consolidation. The
fact that they have been widely used is a confirmation that the techniques are technically sound
and at the same time economical.
ACKNOWLEDGEMENTS
This paper is a compilation of ground improvement techniques developed and applied to
railway projects by several companies and organisations of the Keller Group. The author
wishes to acknowledge the contributions of Project Managers and Engineers from Keller
Grundbau GmbH from Germany and Austria, LCM Markteknik from Sweden, Hayward Baker
from U.S.A and Keller Malaysia in the preparation of this paper.
REFERENCES
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Embankment in a Karst Environment”, Proceedings of the Twenty-Third Ohio River Valley Soils
Seminar, Louisville, Kentucky, October, 1992.
BROMS, B.B. (1999) “Design of lime, lime/cement and cement columns”, Proceedings of the
International Conference on Dry Mix Methods for Deep Soil Stabilisation, Stockholm, Sweden, pp.
125-153.
Holm, G. (1999) “Applications of Dry Mix Methods for deep soil stabilisation”, Proceedings of the
International Conference on Dry Mix Methods for Deep Soil Stabilisation, Stockholm, Sweden, pp. 3–
13.
Holm, G. et al (2002), "Mitigation of Track and Ground Vibrations Induced by High Speed
Trains at Ledsgard, Sweden", Swedish Geotechnical Institute, SD Report 10, Sweden, pp 1-44.
Moseley, M.P. and Priebe, H.J. (1993) “Vibro techniques”, Ground Improvement, Edited by M.P.
Moseley, Blackie Academic & Profession, pp. 1 – 19.
Pengelly, A.D. (2000) “Ground Modification Techniques for Railroad Subgrade Improvement”.
Hayward Baker Report, Maryland, USA.
Sondermann, W. (1996) “Soil Improvement by Vibro Replacement for Rigid Pavement
Construction to the High Speed Railway System”, 3rd Geotechnique-Colloquium, Darmstadt,
Germany, Technical paper 10-53 E.
Swedish Geotechnical Society (1997) “Lime and Lime Cement Columns”, SGF Report 4:95E,
Linkoping.
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