Case studies:Frozen ground design and construction in Kotzebue,Alaska

Daniel Nichols

DOWL HKM,Anchorage,Alaska 99503,USA

1 Introduction

Alaska is the largest state in the United States of America but it is the least developed and fourth least populated.There are only 25,300 km of public roads for a total land area of 1,717,900 km2(State of Alaska,2012).Most communities in Alaska are remote — not connected to a road system outside the community,and only accessible by barge or airplane.Engineers must be able to modify standard designs to account for these limitations.For example,piping must be sized to fit within a cargo plane’s hold or construction sequencing must consider barge schedules and shortened construction seasons.

Much of Alaska has frozen soils and permafrost.Due to either climate changes or human activities and development,permafrost often thaws and becomes unstable.Unstable soils can cause damage to infrastructure by thaw settlement,frost jacking,or heaving,which increase maintenance costs,reduce functionality,and decrease the life of constructed projects.These conditions make engineering design and construction in Alaska challenging.

One place that exemplifies this is Kotzebue,Alaska.Kotzebue is a remote Inupiat village of approximately 3,200 people located 53 km above the Arctic Circle along the Chukchi Sea.The community is on a gravel spit at the end of the Baldwin Peninsula and is surrounded on three sides by the Kotzebue Sound.The gravel spit is approximately 0.9 km wide and 2 km long.The geology of the region is dominated by Quaternary glacial moraine and drift deposits (Golder Associates,2014).Locally in Kotzebue,these deposits are covered by layers of beach sands and gravels with surface organic mats or peats.The area has continuous permafrost except in areas of disturbance.Permafrost temperatures vary greatly due to localized conditions.

Kotzebue is a subarctic climate,based on the Koppen Climate Classification,although it borders on a tundra climate.Monthly daily average temperatures range from-19.7 °C in February to 12.6 °C in July.Precipitation averages 257 mm annually,with an average of 99 mm in winter.The highest recorded temperature is 29 °C and the lowest recorded temperature is-50 °C.Table 1 presents the historical,current,and future engineering climate indices for Kotzebue.It is derived from the public data available from the University of Alaska-Fairbanks Scenarios Network for Alaska and Arctic Planning (SNAP)(UAF,2014).SNAP projects are calculated using a composite of five global climate models,emission scenario A1B.

Table 1 Kotzebue Engineering Climate Indices

2 Purpose and methods

Engineering and construction conditions are extreme in Kotzebue.These provide significant challenges to engineers,which makes Kotzebue an ideal place to test existing engineering practices and try out new ones.In the past 12 years that I have been working in Kotzebue,I have observed and learned from my experiences as an engineer.It is my goal to document and share a few of the lessons learned,so this experience may be applied by others.

Three case studies are presented here:the Front Loop Water Main Extension,the Wastewater Lift Station Replacement,and the Ted Stevens Way Rehabilitation.The Front Loop Water Main Extension was chosen because it represents the accumulated knowledge in the trial-and-error process of installation of water mains and service in arctic conditions.The Wastewater Lift Station Replacement was selected because existing designs were not meeting the needs of the community and new design and construction ideas were used.And when the Ted Stevens Way road was designed in 2001,it used the best design practices of the time,yet it was rapidly deteriorating and would not meet its design life.Surveying the current conditions in 2013 uncovered failures in the design and construction,but these failures provided opportunities to improve future design.

I was the project manager for the Front Loop Water Main Extension and the Wastewater Lift Station Replacement.I was responsible for the design and management of the project from start through construction,and thus have first-hand understanding of the projects.I was able to work directly with the owner (City of Kotzebue) and the users to get their input and observations.I also had access to and reviewed the record drawings and documents of the previous projects.

I was not involved in the design or construction of Ted Stevens Way,but I was able to review and locate the record drawings and other design documents for the project.I interviewed the owner (Native Village of Kotzebue),maintenance workers,and members of the original construction crew.I then performed my own site investigation of the road.The observations and lessons learned are presented below.

3 Discussion

3.1 Case Study #1:Front Loop Water Main Extension

The City of Kotzebue (hereafter,City) operates and maintains a community water system.Kotzebue is serviced by seven circulating water loops which by 2011 were more than 30 years old.Kotzebue’s extreme temperatures require any design to incorporate extraordinary freeze protection measures.In Alaska,water mains are typically buried at 3 m,which usually provides sufficient insulation cover.The presence of permafrost and poor-strength soils in Kotzebue prevented the typical burial depths,so insulation was required to make up for the lack of cover insulation.The water loops were originally 150-mm polyvinyl chloride (PVC) pipes in insulated 300-mm aluminum corrugated metal pipe (CMP)jackets.This allowed the water loops to be buried with only about 0.7 m of cover.

The insulation alone is insufficient to provide freeze protection.Extra freeze protection is provided by continuously pumping water from the water treatment plant through the loops.A water velocity of 0.6 m/s is deemed necessary to prevent freezing.The shallow depth also makes emergency repairs easier.The City reports that pipe bursting from freezing is the most common failure,which typically happens during extreme cold weather in the winter.The water treatment plant also adds heat to the loops to maintain the water mains above freezing.The heat is provided by waste heat from the electrical power plant located near the water treatment plant.No metering is done and it is unknown how much heat is added.

These design measures do a reasonable job in prevent freezing in the water mains.Most freezing occurs within the water services to individual homes,and these water services are smaller and less frequently used.The population in Kotzebue is very transient and seasonal,and many homes are left empty for long periods of time.This means that individual water services are the most vulnerable to freezing.Prior to 2012,the City had reported multiple freeze-ups of water services per year.Because the water services are installed individually and by private contractors,the quality and type of freeze-prevention measures used varies.The City has difficulty in accessing and isolating the water services because there is no uniform system.

Much of Kotzebue is built on discontinuous permafrost which tends to be classified as warm (temperature).This leaves the permafrost susceptible to thawing from environmental and man-made heat sources.When thawed,the soils tend to be unstable and subject to compression.Soil investigations have shown soils with visible ice lenses and with compressible organics and silts.Buildings,particularly houses,in Kotzebue have a variety of construction methods.Some buildings have been engineered to protect the soils from thawing further,but the majority of the buildings are private homes which have little or no such design and they vary in construction and quality.

In the late 1990s,the City of Kotzebue put together a plan for replacement of all seven water loops.The City knew that the old PVC pipes were beginning to deteriorate,and water usage was increasing faster than population growth,indicating water being lost due to leaks.The PVC pipes were becoming unstable and fragile.In the winter of 2011,a fire hydrant was run over by a truck,breaking the water main.The City maintenance crews were unable to isolate the break because the valves were nonfunctioning.Hundreds of thousands of gallons of water were lost before the entire water main loop was shut down.The water main was so fragile that a large section of pipe had to be replaced in order to find competent pipe to which to connect repairs.The maintenance was made more difficult due to frozen ground and temperatures below-34 °C.By the time the repairs were completed,several hundred homes had been without water for four days and 100,000 gallons of water were lost.

Issues like this made replacing the water loops and water services in Kotzebue a priority for the city government.In 2005,the City began to systematically replace the water loops.The final project was the replacement of the Southern Loop.The project design began in 2011 and was completed in 2012.The Southern Loop was 2,830 m long and serviced the southern section of the city.It was also the oldest portion of the community.The design abandoned the existing Southern Loop and expanded the Front Loop by 1,340 m,for a total of 4,175 m.The Front Loop had been replaced in 2009.

The design and replacement of the water main loop was fairly straightforward and incorporated standard arctic design in Alaska.The water main loop was replaced with a 200-mm HDPE circulating main inside an insulated 380-mm HDPE jacket with all joints electrofusion welded.This ensured that the water main had the strength and flexibility to withstand ground movement due to thawing and settling.The water main was protected by 90 mm of pipe insulation,circulation pumps that maintained a water velocity of 0.6 m/s,and the addition of heat at the water treatment plant.

The more difficult design issue was that of the water service piping to serve the individual buildings off the water main.The two main water service design challenges were movement due to thaw settlement at the individual buildings,and providing adequate freeze protection for the water service piping.

HDPE piping has enough flexibility and strength to withstand movement within the trench.The movement is greatest at the connection of the water service piping and a building.The water service piping and the building move independently and are two very different systems.They move at varying rates and amounts between them.Differential settlement at the piping and building interface of 75 mm or greater has been observed,and this amount can easily shear the pipe or cause joint failure.Since the project could not stabilize all of the building foundations,the interface connection at the buildings had to be designed for inevitable movement.

Through past experience,a design was developed to provide a flexible connection to a house that allows for movement.The project design called for installation of an"arctic box," which is a simple insulated wooden box attached to the outside of a building (Figure 1).The arctic box houses and provides access to a flexible connection system.This flexible connection allows greater movement and prevents the shearing and joint failures from differential movement.The 25-mm HDPE pipes end in a 25-mm ball valve,a 90-deg elbow,and are connected into 19-mm PEX A piping with SharkBite quick-connect fittings (SharkBite USA,Atlanta,GA).PEX A piping is cross-linked polyethylene piping,and it is used because it has greater flexibility and can withstand the differential movement within the box.Only the 25-mm HDPE pipes are connected to the house.The carrier pipe and jacket stop 0.5 m below the arctic box.A rubber boot and compressible insulation are used to seal the arctic box to the carrier pipe.Thus,movement in the carrier pipe does not place stress on the arctic box or the connections.

The second challenge was providing adequate freeze protection for the water service piping up to the building.The water service piping requires both passive and active freeze protection.The passive freeze protection is necessary because the buildings are often left without power or are not used for long periods.The owners or operators of the buildings are mostly private individuals and the City of Kotzebue has no assurance that the owners will operate active freeze protection systems.This is especially true because many residents leave the community for extended periods for employment and subsistence activities.

The passive freeze prevention systems include passive water circulation and insulation.Each building is serviced by a supply pipe and a return pipe.The supply line brings the water into the building and the return line recirculates the water back into the water main.The pipes are typically 25-mm HDPE pipe.The supply line is tapped into the water main with a pitorifice,a pipe that extends into the water main with a scoop that faces into the water flow in the main (Figures 2 and 3).The return line brings water back in the main with a similar pitorifice but is turned the opposite direction of the water flow in the main.This causes a differential water pressure between the supply and the return lines,which results in the water being continually pushed or circulated through the water service.The design calls for 75-mm-long pitorifice constructed of 25-mm copper pipe,type K.The copper pipe end is bent with a radius of 57 mm with an opening of 8.6 cm2.Experience has shown that these pitorifices will keep water circulating on water service runs up to 25 m.When water services exceed those distances,the pressure differential is not sufficient to maintain circulation and prevent freezing.

Figure 1 Inside an arctic box at the connection between the water service and the building (left);outside an arctic box with a flexible boot connection to an insulated water service pipe (right)

Figure 2 Pitorifice design detail

Figure 3 Water service connection at a main using a pitorifice

The 25-mm supply and return pipes are contained in a 100-mm HDPE carrier pipe in an insulated 300-mm HDPE jacket.This provides nominal 100-mm insulation.The insulation is extruded closed-cell polyurethane foam with an initial thermal conductivity factor (U) not greater than 0.023 (K·m2)/W.As a general rule of thumb,25 mm of insulation is roughly equal to 100 mm of ground cover.The insulated pipe creates passive freeze protection equivalent to 2 m of cover.

In ideal situations these two passive systems,recirculation and insulation,should protect against the normal cold weather in Kotzebue.However,additional active systems were also added in Kotzebue because water services are a basic necessity for life and,inevitably,when these systems fail it is in the most extreme cold temperatures (-40 °C to-45 °C),which makes repairs very difficult.It is not uncommon in Alaska,when water systems freeze,to be completely shut down for weeks,leaving communities without a source of treated water.These extreme conditions require additional active freeze protection.

The City of Kotzebue also required that each building with a water service be fitted with a recirculation pump.The pumps are 1/25 HP (30 W),115 V,5 gpm (0.003 m3/s),0.75-in.(20 mm) Grundfos UP15-42 (Grundos Pumps Corp.,Olathe,KS).These pumps ensure that even in the coldest weather the water will recirculate faster than 0.6 m/s.These pumps are controlled by the owner and can be shut off during warm periods to reduce energy costs.

The second active freeze prevention system was the addition of two electric heat trace lines,one in the water service and one in the arctic box.The design called for 1.5 W/m,self-limiting RAYCHEM type 5XL1-CT heat traces (Pentair USA,Houston,TX).In the City’s experience,a 1.5 W/m heat trace provides the right amount of heat for the least amount of energy.Each heat trace line is connected to its own digital thermostat (DigiTrace EC-TS-10;Pentair USA,Houston,TX).Two heat trace lines are used to save energy costs.Most freezing occurs in the arctic box with the pipes at the interface with the building.In these areas,the pipes are above ground and are regularly subjected to colder temperatures than the pipes in the ground.If only one heat line were used,the entire heat trace line would be turned on whenever the arctic box temperature dropped below freezing.With two separate heat trace lines,only the short line within the arctic box turns on regularly,saving power.The heat trace line in the water service pipe is usually only used as a backup heat source.It is only turned on when the recirculation pump fails or in extreme weather.The heat trace line in the water service pipe is placed within a 25-mm Schedule 40 "orange" HDPE pipe.This pipe has a higher heat rating than the regular 25-mm HDPE pipe used for the supply and return lines.The heat trace pipe protects the return and supply lines from heating up too much,and it is sealed to keep the heat trace dry in case the carrier pipe becomes filled with water.This has been a common reason for failures in the heat trace lines.

The construction was completed in fall 2012.The winter of 2012-2013 was unusually cold,and in February 2013 the mean daily temperature was-22.4 °C,which is 4.2 °C lower than the normal temperature.The only failures of frozen lines reported along the entire project were determined to be operational or construction errors.In one building,the heat trace had not been turned on,and in another the recirculation pump was installed backwards,pushing against the pitorifice flows.Once those problems were fixed,none of the repaired lines froze again.

3.2 Case Study #2:Wastewater Lift Station Replacement

The City of Kotzebue operates and maintains a wastewater collection system.The system includes a combination of gravity sewer mains,lift stations,and force sewer mains.The system has been constructed in pieces over time since the 1960s as the city has expanded and grown.Most of the system is more than 30 years old and is past its useful design life.This is most obvious at the lift stations.Many of the 12 lift stations in Kotzebue were built in the early 1980s,when the standard lift station design included a prefabricated canister-style wet well with a submersible pump.These lift stations were not enclosed in a building and were exposed to the extreme weather of Kotzebue.These prefabricated lift stations made shipping and installation simpler,but exposure to the elements decreased their design life.By the late 1990s the City reported regular failures in these canister lift stations.

Lift Station #5 was one of these typical prefabricated,submersible pump lift stations;it was constructed in the early 1980s.It collected approximately half the sewer flow in Kotzebue,including the Northwest Arctic Borough K-12 School,the largest single user in the community.By the late 2000s,the pumps were regularly operating at or over capacity at 0.009 m3/s.Clothing or other debris would often get wrapped around the pumps,overloading them.This caused significant strain on the pumps,which would cause multiple failures each winter.Repairs typically involved a three-man crew.The wet well would have to be isolated and by-pass pumps installed.The pumps were attached on rails which were used to guide the pumps as they were raised and lowered.The rails were corroded and would ice up.All the work was done outside,often during the winter time with temperatures below-18 °C or colder.Repairing or cleaning the pumps was hazardous work that would often take 24 man-hours to complete.

By 2012,the city had secured funding to replace Lift Station #5.The city did not have a record of the original design,but in 2009 the city had replaced Lift Station #2,which incorporated a similar submersible pump system but within a building structure.Enclosing the lift station was a huge benefit and improved the maintenance and operation of the pumps.But the new submersible pumps had the same problems as the old lift station:The hoist system would break,requiring the maintenance crews to go "fishing" for the pumps,and the rail system often jammed,causing difficulties with raising and lowering.When this happened,the whole lift station would have to be shut down and by-passed.The pump wet well would then be pumped dry to allow maintenance personnel to climb down into the wet well to manually raise the pump.

The City was not pleased with this system.In conjunction with DOWL HKM,an engineering firm based in Anchorage,Alaska,the City reviewed other options.It was decided that the new lift station would include surface end-suction pumps.This allowed the pumps and motors to be on the surface,out of the sewer waste.The suction ends were designed to minimize clogging from clothing and other debris.If the end did become clogged,a water connection was installed and the suction pipe could be back-flushed clean.This new system took one person 10 min to accomplish what a three-man crew did in 8 h on the submersible pumps.The one downside to the surface pumps was the increased building size.A typical submersible lift station is approximately 20 m2whereas a surface lift station is 33 m2.

The increase in building size was not just an issue of increased construction costs.The soils under Lift Station#5 were a mixture of frozen gravel and sands.The temperature of the permafrost in the area was approximately 0 °C.The City’s funding sources would not allow money to be spent on passive refrigerated foundations,such as refrigerated piles or thermosyphons.The permafrost within Kotzebue is unstable and is only likely to become more unstable over time.Without a passive refrigerated foundation there is no way to prevent the permafrost from thawing over time.As the permafrost slowly melts,there will be creep settlement.The only option is to retard the thawing and minimize the differential settlement.

The new Lift Station #5 incorporated several designs to minimize differential settlement.A significant amount of differential movement comes from seasonal frost heaving.The first design change was to excavate down 0.6 m past the bottom of the foundation.This removed all frost-susceptible soils and organics.Insulation board 100 mm thick was placed at the bottom of the excavation and extended to 3 m outside the building footprint.The excavation was backfilled with non-frost-susceptible (NFS)gravels.The NFS gravels reduce the amount of fines below 3%,which allows for ice expansion within the gravel and minimizes seasonal frost heaving.The insulation plays two roles.The first is to decrease the depth of seasonal thaw so less of the soil column under the building is susceptible to frost heaving.The second is to draw the permafrost up and protect the permafrost from thawing due to the addition of gravel and a building.The building is also kept unheated except when occupied for extended periods during maintenance operations.This minimizes the heat transferred from the building into the ground.

The building has a floating concrete slab on-grade.The slab reinforcement is not tied into the foundation wall,as is typically done.Instead,a large expansion joint was placed around the entire wall.This allows the slab to move independent of the building and its foundation.If settlement occurs under the slab,only the slab would move and the building foundation would not be damaged.

The sewer wet well was another area of concern for settlement and movement.The new wet well was 5.2 m deep with the bottom of excavation 6 m deep,and operated at 1.0-1.5 m of standing water.This creates a large heat sink surrounded by permafrost.In order to minimize permafrost thawing and settlement,the wet well was over-excavated by 1 m.Six-tenths of a meter of NFS gravel was compacted in 300-mm lifts to 95% of maximum dry density.Insulation board 150 mm thick was placed directly underneath the wet well base.The new wet well was constructed of a 1.8-m-diameter concrete manhole with 150-mm walls.The wet well was coated with 150 mm of spray foam with elastomeric coating.The elastomeric coating sealed the insulation,preventing water damage and provided a smoother surface to inhibit heaving from seasonal frost.

The new wet well was made of precast concrete sections.The barrel sections were fitted together with a groove joint filled with Ram-Nek mastic sealant (Henry Company,El Segundo,CA).Two galvanized joint straps were added at each barrel joint to minimize movement between the barrel sections.The pipe penetrations in the well and the lid included cast-in-place Kor-N-Seal rubber boots (Trelleborg Pipe Seals Milford,Inc.,Milford,NH).These allow 25-50 mm of differential movement between the pipes and the wet well without causing damage.The wet well was constructed completely separate from the building.The wet well penetrates the on-grade concrete slab without any reinforcement between the two.An expansion joint or gap was included around the entire wet well,allowing for differential movement without damage.

Another difficulty in construction of the lift stations was the excavation depth.Six-meter or greater excavations are required to install the wet wells.United States Occupational Safety and Health Administration’s (OSHA)regulations require that all excavations 6 m or greater must have engineered trench protection.Typically,a sheet pile retaining wall is used for deep excavations,but Kotzebue’s remote location makes shipping sheet piles and pile-driving equipment very expensive.Therefore,in Kotzebue,past projects have had to cut back trench slopes to maintain safe working conditions.Typically,the loose sands and gravels in Kotzebue require a 30-m diameter hole for a 6-m-deep excavation.This would have caused difficulties at Lift Station #5 because it is located within 9 m of a road and an apartment building.In addition,excavation activities usually begin in June or July due to contractors waiting for warmer weather or barge shipping schedules.This increases the risk of permanently thawing permafrost around the excavation.Thawed soils in Kotzebue are often unstable and running sands are common,increasing excavation sizes and risks.The contractor for the Lift Station #5 developed a novel solution to this problem.The contractor began excavation work in April when the weather was warmer but still below freezing.The contractor used a 450-mm auger to drill vertical holes in a 4.6-m circle centered around the proposed wet well (Figure 4).This created a perforation or perimeter guide for excavation.The contractor used an excavator with a specialty multi-ripper bucket (Figure 5).The bucket had offset,serrated teeth for rock-ripping operations.With this excavator the contractor was quickly able to rip the permafrost out of the excavation site vertically with minimal trench protection because of the stable,frozen soils.

Figure 4 Contractor drilling perimeter guide holes with a 450-mm auger

This innovative method for excavation of frozen soils had great benefits to the project.This technique reduced the excavation diameter from 30 m to 4.5 m.Keeping the excavation frozen eliminated the need for dewatering and the risk of running sands.The excavation was completed in two weeks instead of the estimated four weeks.It also allowed the contractor to start work two months ahead of construction schedule.Decreasing construction time was essential to the project because of the short shipping and construction season.

Lift Station #5 construction was completed in September 2013.As of this writing,the building and wet well have almost completed an entire winter cycle.The City reported a warmer winter with multiple freeze-and-thaw cycles,which were particularly harsh and could cause severe frost jacking and movement.The City reports that the building and wet well are stable without any observed movement or damage.The Lift Station #5 design was able to overcome difficult site and weather conditions by using multiple design innovations to minimize permafrost thaw and settlement.The design was able to save construction schedule and budget by finding alternatives to the traditional refrigerated foundation systems.

Figure 5 Contractor using a multi-ripper bucket to excavate frozen ground in a stable excavation

3.3 Case Study #3:Ted Stevens Way Rehabilitation

Kotzebue is located on a narrow gravel spit in the Kotzebue Sound.The spit is less than a 1.5 km wide.The airport at the southern end of the spit effectively cuts off the City of Kotzebue from the mainland.In 2001,a bridge and gravel road was constructed from the north end of Kotzebue to the mainland.The road,which is called Ted Stevens Way,loops around and connects back to the southern end of the spit below the airport.The road is considered a critical link for the community.It provides the only access to vital utilities,including the two community water sources,a wind farm,and a solid waste landfill.It also provides valuable access to subsistence areas.The community members hunt caribou,water fowl,ptarmigan,and rabbits along the road and in the fall they pick blueberries,salmon berries,and lingonberries.

The original road terrain is mostly flat with some gentle hills,and was constructed directly over virgin wet tundra that had several small stream crossings.There was limited soils investigation done prior to the design.Only eight test borings were drilled along the route,all of which were taken in low-lying areas.The soil columns were remarkably uniform,consisting of a 0.5-to 2.5-m layer of peat over a layer of silt down to the bottom hole.The deepest test borings were more than 30 m deep.The silts consisted of 94% to 97% fines passing a #200 sieve screen.The soils were classified by the Unified Soil Classification System (ASTM,2011),and were frozen for the entire depth.Most of the soil contained ice visible to the unaided eye;most of the soils were classified as Vr or Vs,which have notable ice formation and segregation throughout the soil.Some of the test borings had small layers of non-visible,bonded ice in excess to the soil(Nbe).The soil ice classifications were adapted from the U.S.Army Cold Regions Research Engineering Laboratory classifications (Kaplar and Linell,1966).One boring had a 3-m ice lens at 6-m depth,and another had two ice lenses totaling 1.5 m thick at 3.5 m depth.These silts are stable only when frozen.With that much visible ice in the silt,if thawed there could be 20% or greater settlement.

The road has a total length of 6,270 m.The travel way is 5.6 m wide with a 0.6-m shoulder on either side.The design called for construction directly on top of the tundra,so a separation geotextile was placed directly on top of the tundra.No excavation was done for the road and the tundra mat was left in place as insulation.The typical cross section consisted of 1.5 m of non-frost susceptible (NFS) gravel fill.The first 1,055 m had one layer of 50-mm insulation board,and most of the rest of the road had two layers of 50-mm insulation board;all of the insulation board was placed 450 mm below the finish grade.The side slopes were designed for 3 horizontal to 1(3:1) vertical drop except where the natural grade was too steep;in those places the side slopes were 2 horizontal to 1 vertical (2:1) drop.

The road crosses two major streams.Crossings were made with structural plate arch pipes,one 4,700mm×3,000mm and one 6,300mm×4,000mm.Thirty corrugated metal pipe (CMP) culverts,450 mm and 900 mm in diameter,were installed in drainage areas.One of the culverts was located in a larger drainage and was 1,100 mm in diameter.The design called for excavating to set the culvert half depth below existing grade,bedding rock,and 100 mm of insulation under each pipe.

The Native Village of Kotzebue (NVK),the local Inupiat tribal government,is responsible for operation and maintenance of the Ted Stevens Way.In 2013,NVK was interested in repairing and improving the road in preparation for the construction of a 30-km road to a new deep-water port.Ted Stevens Way would need improvements if it was to handle the new traffic demands of that port.

In July 2013,I joined an observation trip with NVK personnel to assist them in evaluating the existing condition of Ted Stevens Way.The NVK personnel who were involved with the original construction reported that construction funding was limited and the schedule was rushed.Several chronic issues were discovered during the observation trip,including culvert heaving,culvert settlement,and major side-slope subsidence.

The majority of the culverts showed signs of heaving in the middle with large stagnant ponds at each end (Figure 6).Because water was no longer flowing through the culverts,it was traveling under and around the culverts and into the road base.The extra water under the road was freezing in winter,causing the road to heave under the culverts.Each year the heaving would jack up the middle of the culverts.NVK personnel reported,and I confirmed by observation,that during construction the culverts were not set to design grades,but were installed directly on the ground.The culverts never functioned as designed and never fully drained water under the road.As a result,water ponded up at the upstream end.The ponded water acted as a heat sink,thawing the permafrost below and causing the ground upstream to settle.Each year the culverts would heave more and the ends would settle more,and the culverts were being crushed by the heaving action.Several of the culverts no longer had sufficient road cover over them and they were being damaged by traffic loads.

A 900-mm and a 1,100-mm culvert had the exact opposite type of failure.The culvert ends were sticking above the ground and the center of the culverts were settling in the middle (Figure 7).Both culverts were in low-lying areas relative to the surrounding road.At first it was unclear what was causing the settlement when all the other culverts were heaving.Then NVK personnel reported that during construction of those particular culverts,the project had fallen behind schedule and,to save time,no insulation was installed under the culverts.This resulted in the culverts causing thaw settlement under the road.The settlement was greater in the middle,causing the culvert ends to rise up above the ground.Afterwards,water would no longer flow through the pipes,and this caused more water to flow into the road base.The settlement created low points in the silt soils,causing water to pond in the middle of the road and accelerating the thaw of the permafrost.The culvert ends were approximately 0.5 to 1.0 m above original grade.The culverts were damaged to the point that no daylight could be seen through them.

The most severe damage along the road was side-slope failure.All along the road,large sections of side slopes were shearing off (Figure 8).Lateral cracks 100 mm wide and 0.3 m deep ran approximately 0.8 m from the road shoulder.Guardrails were shifted 1 m down the fill slope and many of the guardrails had completely failed due to shear failure of the side slopes (Figure 9).Insulation boards had been damaged and exposed along the edges.In one area,the insulation layers had been pulled so far apart that sink holes had formed in the road large enough to see the insulation.In some areas the traveled road width had been functionally decreased from 7 m to 5 m.

The shear failure of the side slopes was caused by the thaw settlement at the side slope toes.No lateral drainage system was installed along the road and there were no drainage ditches (the only drainage structures were the culverts at drainages crossing under the road).This resulted in small ponds forming along the toes of the slopes.The standing water acted as heat sinks,which were accelerating permafrost thawing and causing the settlement.The greatest slope failures were observed where the fill was the greatest:some of the road sections had as much as 4 m of fill.Insulation was installed only 450 mm below finished road grade.This was done because gravel absorbs heat and insulation placed higher up in the gravel reduces the transfer of heat into the underlying permafrost;in effect,this reduces the size of the heat sink.The problem arose on thicker gravel cross sections:insulation placed at the top was 7 m wide from edge of shoulder to edge of shoulder.[A 4-m-thick road section with a 2:1 slope means the base is three times wider (21 m) than the top where the insulation is placed.] Thus,two-thirds of the gravel area on Ted Stevens Way had no insulation.This caused the gravel on the side slopes to retain more heat than the road surface,allowing thaws to go deeper and thaw settlement to occur along the side slopes.The thaw settlement was causing more water collection,and the increase in water accelerated the thawing.Over time,the settlement under the slope became too great and shear failure occurred.In some areas the shear failure was so great it created gaps between the insulation boards,which resulted in a loss of gravel surface (Figure 10).

The two main issues were improper drainage with standing water,and thaw settlement along the side slopes.These were caused by a combination of design deficiencies and faulty construction.There were several recommendations made to the NVK on how Ted Stevens Way could be rehabilitated.

Figure 6 Culvert failure due to frost heaving under Ted Stevens Way

Figure 7 Culvert failure due to thaw settlement under Ted Stevens Way

Figure 8 Side slope and insulation board damage due to shear failure caused by thaw settlement

Figure 9 Guard rail damaged by side slope failure and thaw settlement (left);side slope and guard rail damage due to shear failure and thaw settlement (right)

Figure 10 Loss of gravel surface due to separation of insulation board layers caused by side slope shear failure

The first would be to remove and reinstall all of the 450-,950-,and 1,100-mm culvert crossings.The culvert areas should be excavated to remove thawed soils,and this could be done in spring when the frost depth is the shallowest.NFS gravels should be used to fill in over excavations,especially at the culvert inlets and outlets.Insulation board (150-mm) should be installed under the culverts and the culvert inlets should be buried so the pipe spring line matches natural grade.The culvert outlet should be set with the bottom of the pipes on existing grade.All-weather wood splash guards should be placed at the outlets to protect them from erosion (wood should be used because it is a better insulator than gravel).Interceptor ditches should be installed lateral to the side-slope toes to direct water away from the road.

The second rehabilitation effort would be to reconstruct the failed slopes.This would involve excavation of the side slopes and removing thawed soils.Separation geotextile should be placed between the permafrost and the gravel,and NFS gravel should be used to prevent heaving and allow drainage through the road base.Insulation board must be installed along the side slopes;on side slopes with slopes less than 3:1 the insulation can be placed parallel to the slope with 450 mm of cover material,and on side slopes with slopes greater than 2:1 the insulation must be placed horizontally in overlapping tiers.Most insulation comes in 2.4m×1.2m boards,so the boards should be placed lengthwise (2.4 m) into the slope on each 0.3 m soil lift,each board with a 0.6-m overlap on the board underneath it.Side slope insulation should be a minimum of 100 mm thick in order to provide the side slopes with the thaw protection to reduce settlement and shear failures along the slope.

4 Conclusions

Permafrost,unstable soils,and remote conditions are obstacles to design and construction in cold regions of the world.Kotzebue,Alaska is a perfect testing ground for frozen ground design and construction techniques,having unstable permafrost,expanding infrastructure,remote location,and a history of what works and what does not work.

This case study of Kotzebue’s Front Loop Water Main Extension project shows that the main issues facing utilities in the Arctic are freezing and differential movement,especially at building interfaces.Freeze protection can be designed by using a combination of passive and active methods.Passive methods include non-pump circulation and insulation techniques.Active methods include heat trace lines and circulation pumps.Buildings and pipes move at different rates,causing a stress on pipes and joints.These interfaces must have sufficient flexibility and strength to withstand such stresses.

The Wastewater Lift Station Replacement project has much to teach about protecting infrastructure from permafrost thawing caused by changing climate or human activities.Often it is not feasible to use refrigerated foundation systems in cold regions,so foundation systems must incorporate insulation to retard thawing.Because frozen ground thaw is inevitable without refrigerated foundations,buildings and their foundations must be able to move independently.

The Ted Stevens Way Rehabilitation project shows how even the best design practices of previous times are sometimes not adequate.Engineers must constantly re-evaluate design and construction techniques,and this is especially important in an ever-changing environment.

The issues raised in these projects are not unique to Kotzebue.I hope the lessons learned from these projects can be used in other arctic regions to improve engineered designs and projects.

I would like to thank the City of Kotzebue Public Works Department for their assistance.I appreciate the support and encouragement from DOWL HKM.I could not have done my work and completed this report without the support and editing of my wife,Rebecca Nichols.

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Golder Associates,2014.Geotechnical Services Report,March 4,2014,Kotzebue Youth Center,Kotzebue,Alaska.Golder Associates,Anchorage,AK.

Kaplar CW,Linell KA,1966.Description and Classifications of Frozen Soils.Technical Report 150,U.S.Army Materiel Command,Cold Regions Research &Engineering Laboratory,Hanover,NH.

State of Alaska,2012.Certified Public Road Mileage in Centerline Miles.http://www.dot.alaska.gov/stwdplng/transdata/pub/2012cprmFinal.p df (retrieved December 31,2012).

University of Alaska-Fairbanks (UAF),2014.Scenarios Network for Alaska &Arctic Planning.http://www.snap.uaf.edu/charts.php (retrieved March 28,2014).