Track Leveling & Alignment Stability – Options and ... · Track alignment stability is a daily...

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Track Leveling & Alignment Stability – Options and Approaches for Very Weak Subgrade Authors’ Names and Contact Information: Bryan Duevel, PE, GE McMillen Jacobs Associates 1500 SW First Avenue, Suite 750 Portland, OR 97201 503.384.2914 [email protected] Mark Pinske, PE McMillen Jacobs Associates 1109 First Ave, Suite 501 Seattle WA 98101 206.588.8188 [email protected] Carol Ravano, PE McMillen Jacobs Associates 1109 First Ave, Suite 501 Seattle WA 98101 206.588.8124 [email protected] Frank W. Pita, PE, LHG McMillen Jacobs Associates 1109 First Ave, Suite 501 Seattle WA 98101 425.785.1109 [email protected] Word Count This manuscript has 4,274 words, and 8 figures ABSTRACT Track alignment stability is a daily concern for maintenance of way crews; many leveling and alignment issues can be repaired by re-ballasting/surfacing operations. However, in some locations, the subgrade is not strong enough to support the heavy, repetitive loading of freight railroads. These areas are expensive for railroads to maintain and often have costs associated with reduced speeds. These areas are experiencing bearing capacity failure. While this phenomenon is manifested by track settlement, the mechanics of the problem are fundamentally different than soil settlement. Whereas soil settlement decreases over time as the material consolidates, bearing capacity failure may continue unabated. Recognizing the controlling soil mechanics conditions and deciding on an appropriate solution is even more complicated by the railroad’s unique constraints of limited Right-of-Way, limited access, environmental limitations, track time constraints, and limited work areas. The authors have developed an approach to select appropriate means to improve the subgrade in cases of bearing capacity failure. Generally, ground improvement can be grouped into excavate/replace, confine, and internal improvement. No system is applicable everywhere, and each has its place and restrictions. However, by knowing the controlling design and construction characteristics of each, the designer may combine the

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known site conditions, design requirements, and railroad operation considerations to select the most appropriate solution. This paper presents the underlying mechanics of bearing capacity failure, how it differs from soil settlement, and mitigation principals. Examples of mitigation alternatives are presented in four distinctly different case histories. INTRODUCTION Track alignment stability is a daily concern for maintenance of way (MOW) crews. Many leveling and alignment issues can be repaired by re-ballasting/surfacing operations. However, re-ballasting does not always solve the problem. In some locations, rail embankments have been constructed through soft, weak soils and the subgrade is not strong enough to support the heavy, repetitive loading of freight rail traffic. These areas are expensive for railroads to maintain and often have costs associated with reduced speeds. These areas are experiencing bearing capacity failure. While this phenomenon is manifested by track settlement, the mechanics of the problem are fundamentally different than soil settlement. Whereas soil settlement decreases over time as the material consolidates, bearing capacity failure may continue unabated, regardless of how much ballast is added. In some cases, adding ballast may actually make the problem worse, creating an unending and expensive maintenance problem.

Recognizing the controlling soil mechanics conditions and deciding on an appropriate solution is even more complicated by the railroad’s unique constraints of limited Right-of-Way, limited access, environmental limitations, track time constraints, and limited work areas.

There are a number of methods to mitigate bearing capacity failure that can accommodate these constraints. Generally, mitigation methods are grouped into the broad categories of buttressing, ground improvement, and structural reinforcement. No system is applicable everywhere, and each has its place, restrictions, and cost implications. However, by knowing the controlling design and construction characteristics of each, the designer may combine the known site conditions, design requirements, and railroad operation considerations to select the most appropriate solution.

This paper presents a general discussion underlying mechanics of bearing capacity failure, how it differs from soil settlement, and mitigation principals. Examples of mitigation alternatives are presented in four case histories. CAUSES OF SETTLEMENT The soil mechanisms that cause settlement can broadly be broken into two categories: soil compression (or consolidation), and soil displacement due to soil shear failure. When the soil displacement is slow, the observed settlement may be the same for both mechanisms. Both types of movement are caused by increases in load and/or the frequency of loads acting on foundation soils, but the means to control or eliminate the downward movement is distinctly different. To understand the repair options, the soil mechanics principles of each mechanism are presented in the following sections. Soil Compression Soil compression is the most common form of settlement. Soil compression occurs in all types soils (both fine and coarse grained) by the reduction of void space between particles. In very dense, tightly packed soils, there is very little void space, and therefore, very little settlement. In weak and soft soils, the void space may constitute a significant portion of the in situ soil structure which results in large settlements. Common soil compression is broken into two primary types (Das, 1990);

Elastic compression, which is settlement that occurs immediately as the soil is loaded, as open void spaces are reduced as the soil particles bend to their elastic limit.

Consolidation is settlement that occurs as water within void space is displaced from the soil matrix.

Consolidation is typically a problem in fine grained soils (silts and clays) and is controlled by the hydraulic conductivity (ie: rate of water flow from the area) of the soil. Consolidation may take long periods of time to complete (multiple years or longer).

Creep is a third type of settlement that occurs as soils particles reorient under constant load, however, it is not commonly encountered in rail applications so it is not discussed further herein.

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As soil units compress under loading, a settlement trough is transmitted to the surface, as shown schematically in Figure 1. This is occurring because the elastic limit of the soil was reached and also all the water feeling the added surface pressure has migrated from under the load and the entire system has reached equilibrium. Therefore, settlement caused by soil compression decreases over time for a constant load as the water migrates and equilibrium is reached.

To the Railroad’s field maintenance staff, this is the key observation; if surface settlements decrease with the use of ballast, then equilibrium is being reached but if observations showa relatively constant or increasing rate with time, then soil compression is most likely not the mechanism impacting the track and it is soil displacement.

FIGURE 1: Schematic of settlement caused by soil compression. Soil Displacement A less common settlement mechanism, but potentially more problematic, is that caused by bearing capacity or shear failure. Bearing capacity failure occurs when the imposed loads exceed the shear strength of the subgrade soils. These types of failures for rail applications are most common in weak silts and clays. Also, a high water table is typically occurring as well, but not always.

The generalized shape of the rupture surfaces that form below the load at the point of failure are shown in Figure 2 (from Terzaghi, Peck and Mesri, 1996). The failure wedges rotate below the imposed load, causing settlement at the point of load application. The outer edges of the failure surface may also form bulges at the ground surface as they displace. Typically, large settlements occur when bearing capacity failure occurs. However, they may form progressively and be masked by periodic leveling operations. In general, significant settlements will continue with very small increases in load.

If bearing capacity failure has occurred, track leveling may actually make the problem worse as ballast is generally heavier than the weak native soils; the additional load of the ballast promotes additional displacement at an increasing rate along the failure surfaces. Thus, a telltale sign that bearing capacity failure has occurred is a settlement rate that is not slowing as described above under consolidation but instead is either constant or increasing. A ‘rule of thumb’ that our staff have developed is that if an area has a steady leveling effort (such as, “one carload per month”) ethen long term elimination of downward movement will not be mitigated by this continued resurfacing in these cases.

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FIGURE 2: Schematic of settlement caused by bearing capacity failure.

MITIGATION METHODS FOR SETTLEMENT DUE TO BEARING CAPACITY FAILURE General The mitigation measures described herein apply to existing structures that are experiencing bearing capacity failure. Typically, new structures are designed with adequate factors of safety or with special construction approaches such that bearing capacity failure does not occur.

Generally, mitigation methods are grouped into the broad categories of buttressing, ground improvement, and structural reinforcement. These methods are described in the following sections, and shown schematically in Figure 3.

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FIGURE 3: Bearing capacity failure mitigation strategies.

Buttressing Buttressing involves the placement of an earthen berm on the outside edge of the embankment to widen its footprint and to add weight to resist further displacement of rotating failure wedges. This is shown conceptually in Figure 3, Option 1. The required size and location of the berm are dependent on the size of the embankment and the nature of the bearing capacity failure.

Buttressing is the simplest and potentially least expensive mitigation method as construction methods are usually straightforward and require only standard earthmoving equipment. The materials required may consist of any available borrow. Construction of buttresses is performed parallel to track, and can generally can be installed without impacts to the active track. The most significant drawback to buttressing is that it requires the expansion of the rail embankment footprint. Construction of the buttress may require the acquisition of additional ROW or easement if tight boundaries exist. In addition, the poor soils associated with bearing capacity failures are often located within wetland or shoreline environments, which often require a significant permitting effort and may require specialized equipment, such as barges, for material placement (as discussed in one of the case histories). Ground Improvement Ground improvement is a general term which refers to modification of the existing soils to improve their strength and stiffness. There are a large variety of ground improvement methods available; for mitigation

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of bearing capacity failures, the most applicable are compaction and permeation grouting. These methods involve injecting pressurized grout columns or zones in a pattern to systematically reinforce the soil. The grout is injected through a small diameter (<6 inch) casing that can be installed at any orientation by either drilling or pushing into place. The grout columns can provide a structural barrier through the failure zone and increase the density and stiffness of the soil by displacement as the grout is injected. Grout columns may also provide a bridge between the surface loads to stronger soils below the weak zone. The ground improvement methods described are installed immediately below the track and embankment, and thus fall within the existing ROW and out of the wetland limits. This eliminates cost and schedule delays related to these issues. Ground improvement can be installed with small equipment that can be easily adapted to a hi-rail configuration (typical equipment consists of a hopper truck and a small drill rig) that may be moved off track to allow rail traffic to pass. If access is available parallel to track, grouted columns can be advanced at an angle below the track without occupying it. The cost of ground improvement is greater than buttressing (but less than structural reinforcement in most cases). Ground improvement is also a specialized construction technique, and specialty contractors are required to perform the work. Structural Reinforcement Structural reinforcement involves the installation of structural measures to intercept the failure zone beneath the track section or embankment. The structure transfers load deeper into the ground into more competent strata, and/or provides passive resistance to additional displacement. The most effective structural system is a sheet pile wall, which provides continuous reinforcement through the failed zone. Discrete vertical elements such as H-Piles, micropiles, or recycled rail may also be used to provide reinforcement. The depth and spacing of any structural system will vary by the size of the embankment and the depth of the failure zone; but generally the minimum length of these elements is about 25 feet. Structural reinforcement of this type has a very small footprint (equal to the width of the structural element). Typically, they may be installed within the existing ROW. These elements also may be installed from hi rail cranes or excavators. If site access allows, construction equipment may be positioned off the tracks. The primary drawback of structural reinforcement is its high cost. Of the alternatives outlined in this paper, this method is the most expensive, and directly related to the cost of the reinforcement elements. Method Selection Each of the mitigation methods described above can be effective eliminating soil displacement caused by bearing capacity failure. The “best” method for a particular project must consider the geotechnical mechanics of the problem (width, depth of failure), physical site constraints, ROW limits, wetland impacts, track time restrictions, permitting, and costs.

Frequently, the capital construction costs associated with the mitigation measures described greatly exceed the cost of track re-leveling when considering a small window of time (< 5 years). However, when projecting the continued maintenance costs beyond this window, the relative costs begin to approach one another. Construction costs also do not capture the cost of lost revenue and delays caused by reduced speeds and maintenance outages. CASE HISTORIES In the following sections, 4 case histories are presented that describe bearing capacity failure problems and the successful measures employed to mitigate the problems.

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Centralia Steam Plant Spur Background The Centralia Steam Plant spur is located in Centralia, Washington and is approximately 5,900-feet in length. The spur provides a link between a coal-fired power plant mainline track. The power plant is located adjacent to a coal mine that originally supplied its fuel. The rail is supported on a relatively low height embankment that ranges in height from 2 to 12 feet that was placed directly upon the local soils.. Historically, rail traffic along the spur consisted of a few trains per year, primarily associated with equipment deliveries to the plant. When the power plant switched to importing coal, train traffic increased to 11 to 13 heavily loaded unit trains per week. As the result of the increased loading and frequency, the embankment settlement and lateral movements of the track became problematic, requiring re-ballasting of the track on a biweekly basis. Evidence of lateral bulging of the toe of the embankment was visible as well.

The rail spur travels over generally flat terrain across its length, with low areas supporting seasonal wetlands. The subsurface materials consist of a thin cap of medium dense sandy fill material overlying very weak fine grained fill, as well as, interbedded silty sands and sandy silts and clays. Shear strength of the fine grained soils was estimated to be between 250 and 750 pounds per square foot (psf). Groundwater is seasonally at the ground surface (at the base of the embankment).

FIGURE 4: Completed sheet pile embankment reinforcement.

Geotechnical Mechanics Based on the observed surface and subsurface conditions, the settlement was determined to be caused by a progressive bearing capacity failure of the native soils underlying the embankment. The bulging observed at the toe of the embankment was a manifestation of rotational failure wedges below. The cap

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of denser soils immediately below the embankment was strong enough to support the track when rail traffic was light. However, when the train frequency increased, the cap was weakened by the repetitive loading and finally failed. As the subgrade was in a state of near failure, the addition of ballast simply displaced the failure wedges further rather than arresting the movements. Solution Three mitigation alternatives were developed to stabilize the embankment: placement of stabilization berms outside the limits of the existing embankment; installation of sheet piles driven parallel to the tracks within the embankment; and ground improvement by grouting or stone columns. Ultimately, the Owner selected the sheet pile stabilization method.

The selected design involved installation of sheet piles extending 30 feet below ground surface on both sides of the track, mid-slope within the embankment in the most problematic areas. The Owner selected this approach for the following reasons:

The mitigation could be installed using hi-rail equipment and therefore did not require access across wetland areas.

There was virtually no earthwork required, which minimized site disturbance. Further, the mitigation did not extend beyond the limits of the existing embankment.

The construction was simple, and could be completed in small segments between trains. The Owner had the equipment and materials on hand; the work was completed by the Owner’s

in-house forces. Ultimately, the mitigation stabilized the embankments and they are still performing well, seven years later. Algoma Double Track Background The Algoma Double Track project is located in northern Idaho, and is approximately three miles in length. The alignment parallels the shoreline of a large, glacial lake. The project involved building a second parallel track on the land side of the heavily-used existing track. During the project design, the local Roadmaster informed the design team that steady settlement was occurring along a 300-foot-long segment of the original main line track, requiring an estimated carload of ballast every month. The rail embankment was about 35 feet high at this location, and about 50 feet above the lake level.

Subsurface investigations were completed in the area and identified that the settling area was underlain by a layer of very soft, highly plastic clay up to 35 feet thick. This material typically had Standard Penetration Test (SPT) blow counts of zero (N=0). The soft clay was underlain by very dense glacial till soils consisting of silty gravely sand. Geotechnical Mechanics Analysis of the area identified that the embankment was undergoing general shear failure and soil displacement laterally towards the lake. The failure was manifesting in settlement at the crest of the embankment. In this particular case, the added ballast was negatively impacting the embankment stability as the ballast was heavier than the displaced native soils. Thus movement would continue and even potentially accelerate as more ballast was added. Solution A number of solutions were considered to mitigate the problem area but ultimately compaction grouting was selected. This method involves the injection of small diameter, low-mobility grout columns within a selected depth range. In this case, the columns were extended through the embankment and soft soils below, terminating within the dense underlying soils. The columns transfer loads to the stronger bearing soils as well as densify the soft soils by displacement as the grout is injected.

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FIGURE 5: Typical section through mitigation area.

This solution was favorable for a number of reasons:the construction equipment and staging had

a very small footprint, the treatment area was relatively small, and this solution could be installed without impacting rail traffic on the existing mainline. As shown in Figure 5, the mixing and pumping equipment was placed where the new embankment is shown and only ‘hand’ held equipment and hoses where moved to the side of the embankment. As a result, traffic was not disrupted since the hoses could be passed under the tracks. The compaction grouting successfully mitigated the problem, and the area has been in use for more than 15 years since installation. Ocala Siding Background The Ocala siding is located about 20 miles southwest of Lovelock, Nevada. An approximately 15,500 foot section of this embankment was experiencing settlement and lateral spreading due to embankment side slope failure and internal erosion (piping). The topographically low area is known as the Humboldt Sink, a large temporary lakebed. The embankment was originally constructed over a century ago with “side borrow” material, which is whatever soil that was encountered immediately adjacent to the track. In this region, “side borrow” material is loose or soft, fine, poorly graded sand to a silt originally deposited in a shallow playa lake.

Original embankment heights ranged from 5 to 20 feet along this section built with the lake deposits. The embankment distress was first reported by track maintenance personnel who noted the repeated necessity to raise and/or realign the track over this same section of line. A portion of the embankment east of the distressed embankment was built from coarse sand gravel excavated from a prominent ridge that forms the eastern border of the Humboldt Sink. This sandy gravel ridge, greater than 40 feet in height, has been stable with no history of settlements or lateral spreading.

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Geotechnical Mechanics Inspection of the embankment discovered significant open cracks (> 3” in width) paralleling the track on both slopes as well as numerous “snake holes” produced by internal erosion of the fine sand and silt embankment n areas noted for lateral track movement and settlement,. Both of these phenomena are caused by, or aggravated by, the buildup of water in the ballast section. Increased pore pressure in high embankments causes failure (longitudinal cracking) of the side slopes or piping erosion of lower embankments. Years of re-ballasting created a ballast depression known generally as a “bathtub” in areas of on-going embankment distress that collected rainwater, thus aggravating the problem.

FIGURE 6: Out-of-level track and shell buttress construction (note sandy gravel ridge in

background). Solution The mitigation solution chosen by the owner was to construct a compacted sandy gravel buttress shell and install gravel-filled synthetic strip drains on both slopes of the embankment. Construction of these sandy gravel shells and strip drains was done at two separate times – the first project was a 2,400 foot length section of embankment that was constructed in 2002, while the second project was a 13,200 foot length section of embankment that was constructed in 2012-13.

The sandy gravel shells were constructed using excavated material from the prominent ridge that forms the eastern border of the Humboldt Sink and shown in the background of Figure 6. This borrow pit was chosen due to the good performance of the embankment nearby that had been constructed from this material. The compacted shells ranged in height from 5 to 20 feet and were constructed at a 1.5:1 slope and an 18-foot flat bench at the top. The sandy gravel fill was hauled by 40-ton articulated haul trucks and spread in 12-inch loose lifts with a bulldozer. Compaction of the fill was obtained by the weight of the articulated haul trucks constantly driving over the embankment in the process of being constructed.. For the 2012 embankment construction, approximately 90,400 cubic yards of sandy gravel shells were

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constructed on the north embankment and approximately 103,800 cubic yards of sandy gravel shells were constructed on the south embankment. To date, the report from the local maintenance staff is that surfacing this area is no longer problematic and train speeds are at their maximum. Great Salt Lake Causeway

Background

The Great Salt Lake (GSL) Causeway spans the Great Salt Lake, between Ogden and Lucin, Utah. Construction of the dumped fill embankment began in 1902 as a short cut to the original transcontinental railroad line. Approximately 28 miles of embankment were completed by 1904, but the center 12.5 miles could not be completed as designed; workers were unable to place adequate quantities of fill material on the soft sediments to bring the embankment above the water level. Therefore a timber trestle was constructed in the center section.

In the 1950s, the timber trestle was replaced with an engineered fill embankment. The foundation soils were very soft, organic silty clays, underlain by Glauber’s salt, a non-homogeneous salt formation material, ranging in thickness from 2 feet on the west end and 30 feet on the east end. Geotechnical Mechanics Since its completion in 1960, the center 12.5 mile section of the Causeway has continued to consolidate following the principles described in this paper earlier and the rate is slowing. It has taken a long time simply because the fill thickness and therefore weight is large and the soft soils beneath are very thick. However, in some portions toward the eastern end, the salt layer is supporting the new embankment and it is distributing the load over a larger area of underlying soft sediments, which results in less total settlement.

However, in early 1999, a 1000 foot long section around MP748, which was originally placed on a thick salt layer, began settling at approximately nine inches per month and was being leveled, nearly continuously, by the local surfacing crew. In August 2000, this 1000-foot long section of the embankment at MP748 dropped 10 feet overnight. The same maintenance crews wereable to raise the track level four feet in one day to keep it above the water level, but during the night, the track dropped down to water level again.

Based on the observed surface and subsurface conditions, the failure at MP748 was identified quickly as a bearing capacity/lateral spreading failure of the salt layer and the soils underlying this portion of the Causeway. Mudwaves, as shown in Figure 7, could be seen off of both sides of the Causeway, indicating rotational failure.

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FIGURE 7: Rail embankment and ground bulge (in lake).

Solution

In the short-term, the embankment was widened, not raised, which slowed the rapid settlement of the track area. The long-term solution was to construct two massive, rock-filled berms, one north and one south of the failure area on top of the ground bulges known as mudwaves, to act as counterweights and prevent additional movement. The fill to construct the berms was delivered by side dump car work trains. Draglines, located on barges on each side of the causeway, spread the material out over the soft bottom sediments and excavators placed the armor rock on the outer edge of the berms for wave protection. Figure 8 is a photo of the final berm configuration.

Subsequent to the repair, three borings were drilled in the area to ascertain the cause of the failure. Based on the results of the borings, it appeared that the salt layer, which was identified in the original design drawings of 1956 and in the borings from the early 1980’s, was no longer present. It is suspected that the salt layer partially dissolved, which weakened its shear strength. The salt broke into pieces and could no longer support the weight of the fill.

To prevent a similar-type failure as that which occurred at MP748, the railroad has a settlement monitoring program. Monuments were established on the Causeway, and surveyors have measured elevation changes two to three times per year since 2002. This data is reduced, and the daily settlement rate is calculated and plotted against historical settlement rates to distinguish between zones of potential bearing capacity failure versus normal consolidation.

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FIGURE 8: Nearly completed buttress construction (note the work train).

CONCLUSIONS Track alignment and settlement is not always a problem that can be solved by reballasting/surfacing. In areas of weak subgrade soils, bearing capacity or shear failure may be the cause of settlement. In these cases, resurfacing will not solve the problem; in fact, it may increase the settlement over time. MOW personnel should identify problem areas that routinely need one or more carloads of ballast per month to maintain track alignment and investigate if bearing capacity failure is the cause. Mitigation measures are available for this problem that will eliminate settlement issues through these areas. The “best” method for a particular project must consider the geotechnical mechanics of the problem (width, depth of failure), physical site constraints, ROW limits, wetland impacts, track time restrictions, permitting, and costs. While the costs of implementing bearing capacity failure mitigation measures is high relative to incremental leveling costs, over the long term costs are less than continued maintenance, and improve the efficiency of freight movement. REFERENCES

1. Das, B.M., 1990. Principles of Foundation Engineering, Second Edition, PWS Publishing Company, Boston.

2. Terzaghi, K., Peck, R.B., and Mesri, G., 1996. Soil Mechanics in Engineering Practice, Third Edition, John Wiley & Sons, Inc., New York.

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Table Titles and Figure Captions FIGURE 1: Schematic of settlement caused by soil compression. FIGURE 2: Schematic of settlement caused by bearing capacity failure. FIGURE 3: Bearing capacity mitigation strategies. FIGURE 4: Completed sheet pile embankment reinforcement. FIGURE 5: Typical section through mitigation area. FIGURE 6: Out-of-level track and shell buttress construction (note sandy gravel ridge in background). FIGURE 7: Rail embankment and ground bulge (in lake). FIGURE 8: Nearly completed buttress construction (note the work train).

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A R E M A 2 0 1 5 A N N U A L C O N F E R E N C E

Minneapolis, MN | October 4-7, 2015

INTRODUCTION• LEVEL TRACK INTEGRAL

TO RAIL PERFORMANCE• RESURFACING IS COMMON

TASK FOR MOW CREWS• $$$ FOR BALLAST AND

REDUCED TRACK SPEED• MORE BALLAST IS NOT

ALWAYS THE SOLUTION



INTRODUCTION• SUBGRADE MAY BE TOO

WEAK TO SUPPORT TRACK

• BEARING CAPACITY PROBLEM FUNDAMENTALLY DIFFERENT THAN SETTLEMENT



CAUSES OF SETTLEMENT• SOIL COMPRESSION

– ELASTIC COMPRESSION (IMMEDIATE)

– CONSOLIDATION (LONG-TERM)

• SOIL DISPLACEMENT– BEARING CAPACITY

FAILURE



SOIL COMPRESSION

EMBANKMENT

SURFACE SETTLEMENT

SOFT SOIL UNITCOMPRESSION



SOIL DISPLACEMENT

EMBANKMENT

BULGING GROUND

FAILURE SURFACE

SURFACE SETTLEMENT



SOIL DISPLACEMENT

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SOIL DISPLACEMENT

• IF SETTLEMENT DOES NOT DECREASE OVER TIME, BALLASTING MAY MAKE PROBLEM WORSE

CAR1



MITIGATION MEASURES

BUTTRESSING– SIMPLEST

– LEAST EXPENSIVE

– REQUIRES ROW

EMBANKMENTFILL BUTTRESS

FAILURE SURFACE

CAR1



MITIGATION MEASURES

GROUND IMPROVEMENT– IMPROVES SOIL MASS

STRENGTH/STIFFNESS

– SMALL FOOTPRINT

– MORE EXPENSIVEFAILURE SURFACE

EMBANKMENT

GROUT COLUMNS



MITIGATION MEASURES

STRUCTURAL REINFORCEMENT

– SMALLEST FOOTPRINT

– AVOIDS ROW / OHWCONFLICTS

– MOST EXPENSIVE FAILURE SURFACE

EMBANKMENT

SHEET PILES



CASE HISTORIES• CENTRALIA SPUR

• ALGOMA SIDING

• OCALA SIDING

• GREAT SALT LAKE CAUSEWAY



CENTRALIA SPUR• SITE LOCATED IN WESTERN WASHINGTON;

1 MILE LENGTH

• EMBANKMENT HEIGHTS 2-12 FT

• PROBLEM:– DRAMATIC INCREASE IN SETTLEMENT ONCE

TRAFFIC INCREASED FROM 1/MO TO 10/WK

– RE-BALLASTING BI-WEEKLY

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CENTRALIA SPUR

• THIN “CRUST” OVER WEAK SUBGRADE

• WETLANDS AT TOE OF EMBANKMENT



CENTRALIA SPUR

• SETTLEMENT UNDER VERY LOW EMBANKMENT



CENTRALIA SPURSOLUTION:

– SHEET PILE WALL



ALGOMA DOUBLE TRACK

• SITE IN NORTH IDAHO; APPROXIMATELY 300 FT IN LENGTH

• EMBANKMENT HEIGHT ~ 35 FT

• PROBLEM:

– STEADY SETTLEMENT REQUIRING

RE-BALLASTING MONTHLY



ALGOMA DOUBLE TRACK

• ADJACENT TO LAKE• 35 FT OF VERY SOFT CLAY

ABOVE DENSE GLACIAL TILL• SUBGRADE SHEAR

FAILURE; DISPLACING TOWARDS LAKE

• SOLUTION:- COMPACTION GROUTING DENSE GLACIAL TILL

GROUT COLUMNS

EXISTING RAIL EMBANKMENT

NEW RAIL EMBANKMENT

LAKE SOFT CLAY



ALGOMA DOUBLE TRACK

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OCALA SIDING

• NE OF RENO, NEVADA; ~ 3 MILE LENGTH

• TYPICAL EMBANKMENT HEIGHTS: 5-20 FT

• PROBLEM:

– ON-GOING TRACK RAISING AND REALIGNMENT OVER A NUMBER OF YEARS



OCALA SIDING• EMBANKMENT

CONSISTS OF FINE SAND AND SILT

• INTERNAL EMBANKMENT EROSION / DISPLACEMENT

• BALLAST “BATHTUB EFFECT”



OCALA SIDING• SOLUTION:

– 18 FT GRANULAR STABILIZATION BERMS

– STRIP DRAINS



OCALA SIDING EMBANKMENT CONSTRUCTION



OCALA SIDINGCOMPLETED EMBANKMENT



GREAT SALT LAKE CAUSEWAY

• CROSSES GREAT SALT LAKE BETWEEN OGDEN AND LUCIN, UTAH

• CENTER 12.5 MILES CONSTRUCTED OVER VERY SOFT SEDIMENTS

• PROBLEM:

– 10 FEET OF SETTLEMENT OVERNIGHT ALONG 1,000 FEET OF TRACK

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GREAT SALT LAKE CAUSEWAY



GREAT SALT LAKE CAUSEWAYSUBSURFACE CONDITIONS – EARLY 1950’S

WEST SIDE MID-LAKE (thin to thick salt)

MID-LAKE(deep salt)

EAST SIDE

100 to 150 feet of NC Clay above 100s of feet of OC Clay



GREAT SALT LAKE CAUSEWAY CONSTRUCTION – LATE 1950’S

• 60-FOOT WIDE CREST

• 70 FEET HIGH• 175 TO 600

FEET WIDE BASE OF BERMS

• 46 MILLION YD3 OF FILL



10’

GREAT SALT LAKE CAUSEWAYMP 748 FAILURE IN 2000






• FAILURE THE RESULT OF CONSOLIDATION LEADING TO BEARING CAPACITY FAILURE

GREAT SALT LAKE CAUSEWAY SETTLEMENT AND FAILURE

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GREAT SALT LAKE CAUSEWAY• SOLUTION:

– CONSTRUCT TWO LARGE BERMS TO COUNTERACT BEARING CAPACITY FAILURE



FIRST TRAIN AFTER 7 DAYS OF REPAIRS




CONCLUSIONS• TRACK SETTLEMENT CANNOT ALWAYS BE

SOLVED BY RE-BALLASTING• IF MORE THAN MONTHLY RE-BALLASTING,

LIKELY BEARING CAPACITY FAILURE AND RE-BALLASTING WON’T IMPROVE CONDITION.

• MITIGATION MEASURES ARE AVAILABLE• MITIGATION COSTS HIGH INITIALLY, BUT

LOWER THAN FUTURE MAINTENANCE



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