Amtrak’s Oakington RoadCase Study: Constraints, Analysis ... · This case study exemplifies...

Amtrak’s Oakington Road Case Study: Constraints, Analysis and Solution

Authors

James HyslipHyGround Engineering Williamsburg, Massachusetts, USA

Michael TrosinoAmtrak Philadelphia, Pennsylvania, USA

William PaganoAmtrak Philadelphia, Pennsylvania, USA

ABSTRACT

This paper presents a case study of the correction of a long-term chronic substructure problem at

a particularly challenging location on Amtrak’s Northeast Corridor known as Oakington Road. Problems

at Oakington Road began in the 1990s when the high-speed track was modified to provide improved

clearance for freight traffic within the tight confines of a limited right-of-way with an overhead bridge

structure and with soft underlying soil.

This case study exemplifies Amtrak’s operational constraints as well as its embrace of new

technologies to solve problems. The approach taken to solve the problem included extensive site

characterization, ground penetrating radar, detailed aerial lidar surveying, CPT and DCP testing, field

instrumentation, and soil sampling and testing. Analytical procedures were adopted to determine the

stress and deformational characteristics of the ballast section considering both reinforced and un-

reinforced conditions. The remedial design focused on right-of-way drainage and the use of geosynthetic

reinforcement of the track substructure, consisting of geogrid, geocell and geotextile materials.

Keywords: ballast, track maintenance, drainage, subgrade

© AREMA 2016® 925

1.0 BACKGROUND

The condition of Amtrak’s fixed infrastructure has a direct influence on its ride quality, service

performance, and revenue generation. Amtrak experiences many challenges in maintaining its fixed

infrastructure, not the least of which is its need to handle joint-use operations of both high-speed

passenger trains and heavy axle-load freight traffic. Amtrak’s joint-use operation puts an acute emphasis

on track substructure (ballast, subgrade, drainage), which needs to provide support for high loads and

also provide for tight track-geometry tolerances.

The Oakington Road site has been a chronic substructure problem since the mid-1990s when the

middle track of a three-track high-speed corridor was lowered to provide improved clearance for freight

traffic. The Oakington Road site is a 125 mph section of Amtrak’s joint-use Northeast Corridor located at

Milepost 63.7 between Havre De Grace and Aberdeen, Maryland. The average total traffic for each track is

approximately 12 MGT per year. The site area is within the tight confines of a limited right-of-way with an

overhead bridge structure and with soft underlying soil. The narrow cut section has poor external surface

drainage along the tracks and also poor internal drainage within the tracks. The natural subgrade at the site

is primarily a poorly-consolidated clay that is prone to water softening. Figure 1 shows a historic photo

(1998) and a more recent photo (2015) of the Oakington Road site. Note the lower elevation and mud of

the middle track (Track 3).

Figure 1: Looking north at the Oakington Road site in 1998 (left) and in 2015 (right). (Tracks are numbered 2, 3 and 4 from right to left in the photos.)

The middle track (Track 3) at the Oakington Road site has been a chronic problem since the

1990s; however, since this track is a slower speed freight track, the poor track performance was tolerable.

Due to increases in traffic, Amtrak train operations in this area have been increasingly requiring running

passenger traffic on Track 3. In addition, there has been a need to increase track flexibility to allow for

high load freight traffic on all three tracks. As part of this project, there was a desire to increase the track

centers (presently 12 foot track centers) as much as possible in order to reduce the interference due to

926 © AREMA 2016®

passing wide load traffic on adjacent tracks. The improved clearances will enable Amtrak to run “high

and wide” traffic on any of the three tracks without limiting operations on the adjacent tracks.

In 2015, funding became available to remedy both the poorly-performing center track and the vertical

and horizontal clearances for all tracks. The primary task for improving Track 3 performance was to provide

adequate drainage from Track 3, through Track 2, to a longitudinal ditch or drain. In order to provide

improved clearance under the bridge, the high-speed Track 2 needed to be shifted horizontally away from

Track 3 approximately 2 feet, and lowered approximately 1.5 feet. The lowering and shifting of Track 2

required complete removal of the original roadbed under Track 2 and re-establishing the shifted track on the

relatively soft clay subgrade. All of the work required being performed while at least two of the three tracks

remained in service. The two key aspects of design were providing enough strength within the track

foundation to preclude overstressing or deformation of the clay subgrade and to provide long-term drainage

improvement.

2.0 INVESTIGATION & PLANNING

Amtrak employed many technologies to determine the appropriate course of action.

Technologies included high accuracy topographic and asset mapping, ground penetrating radar (GPR),

track geometry signature analysis, geotechnical testing and instrumentation. In addition, the site required

extensive field reconnaissance.

Amtrak used aerial lidar surveying data from both fixed-wing lidar data available from the State of

Maryland, as well as from the helicopter-based FliMap corridor mapping system. The digital terrain model

derived from the lidar data provided key information for drainage improvement designs. On-site

structures such as bridge abutment foundations, catpole foundations, drainage inlets and culverts, and

old trolley crossings were investigated by site visits and Amtrak archival research. Figure 2 shows the

lidar-derived elevation and topography maps for the project area.

© AREMA 2016® 927

Figure 2: Oakington Road site mapping. Lidar point map (top) and contour map (bottom).

Preexisting soils and groundwater information from the 1990s was available from previous cross-

trench (test pits), Cone Penetrometer Tests (CPTs), stiffness measurements and piezometer installations.

Recent testing in 2015 was performed by Dynamic Cone Penetrometer (DCP) and hand augers with

supplemental laboratory soils testing at the University of Massachusetts Amherst geotechnical

engineering laboratory. Undisturbed samples were used for measuring the shear strength of the soil and

“disturbed” samples were used for soil classification and geotechnical indices. The lab tests were

consisted of Unconfined Compression tests, Fall Cone tests, Atterberg Limits, water content and

hydrometer tests. Geologic research of published geologic papers was done by the Amtrak geotechnical

engineer.

The subgrade was determined to be low plasticity clay (USCS: CL) with a natural moisture

content above the plastic limit. Shear strength was determined from field and laboratory testing to range

from a low of 1.2 ksf to as high as 2.7 ksf, which is in the consistency range from medium stiff to stiff.

The configuration (layering) of the top few feet of material below the tie was determined from

GPR data and verified by cross-trenches, CPT and DCP results, as well as drainpipe excavation. The

GPR information also provided the moisture condition of the track substructure, and the location of water

at different levels was used to infer where likely hardpan or deformed soil layers existed and which way

the subsurface water was flowing. On-site utilities were also investigated by “soft dig” methods by a

contractor who located the fiber optic cable duct bank that runs parallel to Track 2, just outside the

catpole line.

3.0 ANALYSIS & DESIGN

It was evident to Amtrak that the best solution to stabilizing the tracks involved not only providing

sufficient strength in the substructure below the tracks, but also providing proper internal and external

drainage. The design was also influenced by the staging needs and constructability of the trackwork, which

required safety and efficiency at all times.

928 © AREMA 2016®

Granular layer thickness (GLT) design methodology (Ref. 1 & 2) was used to develop the required

track foundation design to support the current and anticipated future traffic. The GLT design considered the

water softening tendencies of the subgrade. The GLT design approach is based on limiting the traffic-

induced, long-term, cyclic stress so as to avoid subgrade deformation in the form of excessive plastic

deformation (ballast pocket) and progressive shear failure (subgrade squeeze). Excessive plastic

deformation is the result of greater load-induced settlement of the subgrade surface directly under individual

rails or under the entire track. Progressive shear failure, or subgrade squeeze, occurs in predominantly

fine-grained subgrade due to repeated overstressing and gradual shear failure and remolding of the

subgrade soil near the surface. Both of these phenomena result in depressions under the track that can

result in water holding depressions, which can subsequently lead to further softening and deformation of the

subgrade.

The conventional GLT design approach provides the required thickness of the granular layer, which

is the combined thickness of the subballast layer and the ballast layer. Based on the anticipated traffic and

dynamic loads, a 50 year design life, as well as the condition of the track subgrade, the GLT design

approach indicated the need for well over 54 inches of combined ballast and subballast thickness.

However, rebuilding the track with this thickness of granular layer was impractical and expensive. To solve

this problem, reinforcing the granular layer was a practical option. Stress reduction to the subgrade can be

achieved by reinforcing the granular layer through the use of tensile reinforcement, such as geogrid or

geocell. The geogrid/geocell reinforcement provides tensile strength and confinement to the granular

layers, thereby increasing the stiffness of the granular layer which results in lower vertical stresses

transmitted below the reinforced layer. The influence of geocell reinforcement on the GLT design approach

was based on experimental tests that were conducted in the 1990s at the AAR’s Facility for Accelerated

Service Testing (FAST) site (Ref. 3). Based on this work, the geocell was incorporated into the GLT design

methodology by considering an increase the subgrade strength of 32%.

The GLT design methodology considers the anticipated accumulated tonnage (traffic in MGT)

and axle loads. The 12 MGT of traffic used for design has an approximate distribution of 5 MGT of

passenger traffic with 17 ton axle loads, 5 MGT mixed-freight traffic with average 24 ton axle loads, and 2

MGT of heavy-axle load traffic with 36 ton axle loads. Based on this mix of loading conditions, the

equivalent axle load used in the design was 23 tons.

It was determined that the required GLT, considering the geocell reinforced subballast, was 29inches. Starting from the bottom of the design section, the “granular layers” included a 5” thick layer of

PennDOT 2A aggregate as a subbase. This aggregate gradation was selected based on filter separation

control to prevent infiltration of the subgrade from below or from the clean stone above. The subbase

material was placed above a biaxial geogrid (Tensar BX1200), which was used to provide stability on the

subgrade during construction. This geogrid layer was also extended beyond the geocell section to

provide a transition to the undisturbed track on both the north and south sides.

© AREMA 2016® 929

The geocell used was “PRS 330 Neoloy 150 48PGR-D” manufactured by PRS-Neoweb based in

Israel was used in the design section. The PRS-Neoweb material consists of novel polymeric alloy (NPA)

that was proven through research and published papers to sustain large hoop stresses with relatively

small strains. The geocell was backfilled with AASHTO No. 57 coarse aggregate, which is a clean, free-

draining gradation of primarily ¾ inch size stone. The PRS-Neoweb has perforated webbing, which when

combined with the free-drainage aggregate infill, provides a highly-permeable layer in the track. The

design called for the stone to be filled within the geocell and up to 3 inches above the top of the 6” deep

geocell. The design required a minimum of 15” of AREMA No. 3 ballast under the tie. Figure 3 shows

the design foundation cross-section for Track 2 at the Oakington Road site.

Figure 3: The Granular Layer Thickness (GLT) design for Oakington Road site.

The drainage design criteria required maximizing the internal drainability of Track 2 and Track 3,

as well as providing effective removal of water from the track right-of-way. Good external track drainage

requires that an unobstructed and downwardly sloping path exists from the ballast shoulder to the ditch,

and then from the ditch to the right-of-way egress point, so that water is effectively and rapidly removed

from the track vicinity.

Determining the optimum ditch profile typically means minimizing the required excavations by

considering the outlet points, grade of the track, and minimum elevation requirements. Figure 4 illustrates

930 © AREMA 2016®

the external drainage design developed for the Oakington Road site. The frame of reference provided by

the top of rail indicates the grade of the track. The lowest elevation of the subgrade surface, as revealed

by GPR, shows the depth to which any lateral drains (if needed) must be excavated under the track. The

invert of the drain, shown in Figure 4 by the two straight lines terminating at the outlet, must be excavated

to an elevation low enough to compliment the track’s internal drainage. Note that the slope of the ditch

can be similar to that of the top of rail as shown on the right of Figure 4, but sometimes the drainage

design requires that it slope in the opposite direction of the track grade, as shown on the left.

Figure 4: External drainage profile for Oakington Road site.

The design included a plan for a French drain enclosed in filter fabric to be installed to drain

subsurface water below the design section to both to the north side of the site and to the south side of the

site with the crown of the drain located north of the bridge. The drain was to cross the fiber optic line at

two distinct and predetermined locations, one at the north end of the site and one at the south end of the

site that were located by soft digs.

The external drainage design is also shown in plan view in Figure 5. This figure was used to

convey specifics of the drainage design to field construction forces. The locations of features along the

right-of-way are shown and the depth to the drain invert from top-of-rail is shown to provide field quality

control.

© AREMA 2016® 931

Figure 5: Plan view of drainage design for Oakington Road site.

4.0 CONSTRUCTION

The most important aspect of the renewal work was safety during construction. All site activities

needed to be done in the safest manner possible, with the least impact on Amtrak trains, and in a timely

and efficient manner. Therefore, a wall was needed to provide the assurance of stability of the active

Track 3 under normal train operation, and also act as a barrier for the construction personnel from the

active track. In addition, installation of the geocell section needed to advance in one direction and heavy

vehicles needed to have the ability to stay off the active geocell installation area while operating in a safe

manner with plenty of room to maneuver and pass other vehicles. Thus, an access road was needed

along the top of the cut area and a wall was needed to provide stability to the adjacent slope.

Figures 6 through 8 show three photos of the site during construction. Track 2 was removed and

the retaining walls were constructed. The drain was installed on the prepared subgrade (Figure 6). Once

the subbase layer of well-graded aggregate (PennDOT 2A) was established as a stable working platform,

the geocell material was placed (Figure 7), and then filled with clean stone aggregate (AASHTO No. 57).

Ballast was then placed (Figure 8).

932 © AREMA 2016®

Figure 6: Looking south at the installation of the 24” diameter subdrain.

Figure 7: Looking north at the installation of the geocell within the limits of the retaining walls.

© AREMA 2016® 933

Figure 8: Looking north at the installation of the south end of the geocell.

The work was completed in September and October of 2015. The reinforced substructure of

geogrid and geocell was installed below Track 2 within an approximately 844-foot long section that was

more or less centered about the Oakington Road overpass. Key aspects of the construction were:

A minimal number of personnel were allowed to enter the active work area at any one

time.

A temporary 844 foot long steel guiderail retaining wall was installed between Track 2

and Track 3. This 844 foot long wall served to provide additional stability for the adjacent

Track 3, to protect workers on the site from entering the active right of way and to provide

guidance on final material levels of the design section of the geocell

The installation of the geocell section advanced in one direction, from north to south.

Excessive traffic and heavy vehicles were able to stay off the subgrade of the proposed

geocell installation area while operating in a safe manner with plenty of room outside of

the geocell installation area.

The installation of the subsurface drainage by means of a 24” diameter perforated pipe

enclosed with a geosynthetic sleeve was installed from north to south within the area of

the geocell installation (between the two guiderail retaining walls) prior to the installation

of the geocell.

Soil pressure cells were installed below the geocell layer, and in a control section without

geocell reinforcement, in order to provide information on the effectiveness of the geocell

to reduce stress to the subgrade. The instrumentation and monitoring is being performed

934 © AREMA 2016®

as part of an FRA-sponsored project being performed by a team of researchers from

Harsco Rail, the University of Delaware and Columbia University.

5.0 CONCLUSION

The Track 2 renewal and clearance improvement project at the Oakington Road site was

completed successfully in October 2015. During construction, normal Amtrak operations continued on

the remaining two tracks. Monitoring of track geometry is on-going on a continual basis in order to

measure the effectiveness of the reinforced GLT. In addition, geotechnical instruments are embedded in

the track foundation, and these devices will be monitored until sometime in 2017.

ACKNOWLEDGEMENTS

The success of this project was due to the outstanding Amtrak field forces, led by John Pielli.

Other Amtrak Engineering staff involved with the project included Al Cloutier, Cecilia Kopp, Jim Paladino

and Derek Joslin. Special acknowledgment is given to Steve Chrismer (now with LTK, formerly Amtrak

and formerly AAR) for his focus on this project and his good work in the 1990s in CPT investigations and

geocell testing. Hamed Kashani and Aaron Judge of HyGround performed most fo the design analysis.

The authors would also like to acknowledge Joe Palese of Harsco Rail, and his team from the University

of Delaware and Columbia University. Thanks goes to Itay Asoolin PRS for providing the geocell material

and installation guidance.

REFERENCES

(1) Li, D., Sussmann, T. and Selig, E. (1996). “Procedure for Railway Track Granular Layer Thickness

Determination.” Report R-898, Association of American Railroads, Transportation Technology

Center, Pueblo, Colorado, October.

(2) Li, D., Hyslip, J., Sussmann, T., and Chrismer, S. (2016). Railway Geotechnics. CRC Press, Taylor

& Francis Group, LLC, Boca Raton, FL.

(3) Chrismer, S. (1997). “Test of Geoweb to Improve Track Stability Over Soft Subgrade.” Technology

Digest TD 97-045, Association of American Railroads, Transportation Technology Center, Pueblo,

Colorado, December.

© AREMA 2016® 935

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936 © AREMA 2016®

AREMA 2016 Annual Conference & Exposition

Amtrak’s Northeast Corridor

Philadelphia

Boston

New York

Washington Oakington Road Site


Investigation


Aerial Lidar

Oakington Road Site


Aerial Lidar & Terrain Model


1998

2015

Oakington Road Site


Cross-Trenches (1990s)

from: Ebersöhn & Selig, 1995

© AREMA 2016® 937


Cone Penetrometer Testing (1990s)


Geotechnical Sampling & Testing


Ground Penetrating Radar


Cross-Section – Lidar & GPR


Analysis & Design


Top of Tie Top of Subgrade (centerline)

Oakington Road OHBR

Swan Creek UGBR

Invert Elevation of Northside Ditch/Drain (Track 4 side)

Crossdrains from Track 3 to Ditchline (through Track 4)

Drainage Profile

938 © AREMA 2016®


Drainage Profile


Drainage Plan View


Granular Layer Thickness Design

Progressive Shear Failure (Subgrade Squeeze)

Excessive Plastic Deformation


GLT Design Charts

l C f & E iti


Geocell Testing at TTCI (Chrismer, 1997)


Design

© AREMA 2016® 939


Acknowledgments

Steve Chrismer

John Pielli, Al Cloutier

Cecilia Kopp, Jim Paladino, Derek Joslin

Hamed Kashani, Aaron Judge

Joe Palese, Itay Asoolin


© AREMA 2016® 941

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