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Techniques for locations without proper materials

Although granular materials (clean well graded sand and gravel) are the road embankment materials of choice, there are many sites in the north in which they are not available. In many cases the nearest source for desirable materials is too far away to be economically feasible to use. In such circumstances, in -situ or locally available materials must be utilized. When frost susceptible materials must be utilized in a road or airport embankment, it is imperative to provide the best drainage possible.

Barriers to restrict capillary moisture flow into the embankment from below may also be considered. These may be layers of coarse grained material or geotextile layers. The purpose is to break the capillary action of fine grained soil in the embankment so that moisture cannot "wick" to the freezing front from a shallow water table or high moisture content soil below. This will help to prevent the formation of ice lenses in the embankment and reduce the amount of excess


moisture during the following spring thaw. When layers of coarse-grained material are used for this purpose, they must be protected from infiltration of fines that would destroy their function. Filter fabrics separating the layers of coarse-grained material from silty soil above are under study for this purpose.

Freezing just the moisture normally in the embankment does not cause large amounts of heaving. A soil with 20% moisture by volume will expand 9% of the 20% or only 1.8%.

Finnish, Swedish, and Russian road designers often use a lightweight expanded clay aggregate (LECA) or "lightweight gravel" when natural gravel is not readily available, or when they want the specific properties that this material provides. The Finnish call their product "Kevytsora" which translates into "lightweight gravel"; the Russians call their product "ceramsite." The Russian material is reportedly heavier (380 to 650 kg/m3) and less uniform in size than the Finnish product (280 to 500 kg/m3).

The lightweight gravel is formed by firing plastic clay materials until they sinter into hard but very porous nodules. Their porosity makes the nodules very lightweight yet they are strong enough to be used in place of gravel without crushing. The material is available in several grades with different densities and size gradations. Crushing strength is reported to be between 180 and 700 kPa (25 and 100 psi) depending on the density of the material. The allowable load in Finland, however, is 200 kPa (28 psi). The friction angle of compacted LECA is 37°. Uncompacted, its friction angle is 33°.

The price of the Finnish product is between 140 and 180 mk/m3 (27 and 35 US$/yd3 in 1990 dollars). The Russian product is reported to be 100 mk/m3 (19 US$/yd3 in 1990 dollars) in rail cars at the Russian border (Eerola 1990).

The low density of the material makes it less expensive to transport, keeping it competitive with natural gravel materials if they must also be shipped in from considerable distance. The low density of the material gives it good insulating properties so that it restricts the flow of heat more than conventional


coarse grained materials. It is used extensively in high-way construction and for

frost heave, abatement design. Its light weight also makes it attractive when

embankment weight needs to be minimized to reduce settlement over poor

subgrade materials, such as over permafrost or muskeg. It is also used as an

aggregate to make light weight concrete structures such as sidewalks, utility

poles etc.

Feasible Осуществимый



To prevent Предохранить

Coarse-grained Крупногравийный

Volume Объем

To expand Увеличиваться

Lightweight Легкий

Porosity Пористость

Friction angle Угол трения

Concrete Бетон

Sidewalk Тротуар

Plastic grid reinforcing

Some sites have an abundance of clean sand that by itself is not a very attractive embankment material. However, if the sand can be confined into small cells, it can be an acceptable material. Investigations into the enhancement of the load carrying capability of grid confined sand have been carried out at the United States Army Waterways Experiment Station (WES) in Vicksburg, Mississippi. Confinement of the unbound sand was achieved with a honeycomb-like grid material. Initial materials for the grid were paper, aluminum and plastic. In Alaska, Coetzee experimented with a high density polyethylene plastic grid confinement material manufactured by Presto Products Ltd. This grid can be shipped collapsed and deployed into a honeycomb-like grid at the site. The honeycomb is then filled with sand to form the grid confined layer. Results from


tests of the load carrying capability of the confined layers by both WES and Coetzee were encouraging and indicated that the confinement grids could give substantially improved performance when sand or other unbound aggregates are the only available local materials.

Coetzee used layered theory to evaluate a grid-confined sand layer. He reports that the results show that an 8 in. deep layer of grid-confined sand was better able to support applied wheel load than a 6 in. layer of gravel. Table 3. lists properties of the Presto GEOWEB® grid (Coetzee 1987).

TABLE 2. Average Thermophysical Properties of Selected MaterialsThermal Conductivity Density Specific Heat

BTU/hr ft F Ibm/ft3) BTU/lbra F

Material (W/mK) (kg/m) (J/kgK)

 

LECA (expanded clay)      
Grade 1 0.09(0.15) 12(280)
Grade 5 0.13(0.22) 31(500)
EPS (extruded polystyrene) 0.02(0.03) 3.0(55) 0.29(1210)
Foamglass 0.03 (0.06) 9.0(145) 0.24(1000)
Gravel      
2% moisture 0.90(1.6) 130(2080) 0.38(1591)
Concrete 0.81(1.4) 144(2300) 0.21(880)
Snow (aged but undisturbed) 0.06(0.10) 15.6(250)
TABLE 3. Presto Geoweb Grid Information  

Material High-density polyethylene (HDPE)

Young's modulus Approximately 100.000 psi (6.9 X 105 kN/m2)

Ultimate strength and associated strain

in the direction of extrusion 3650 psi 455%

Normal to direction of extrusion 3065 psi 238%

Folded panel size 13 ft X 1 ft X 8 in.

Expanded panel size 8 ft X 20 ft X 8 in.

Sheets of HOPE per panel 60

Number of cells per panel 561


Approximate cell area (expanded) 027ft2
Panel area 154ft2
Thickness of HDPE sheet 0. 055 in
Shipping weight per panel 122 lbm
Coetzee(1987)  
Words and expressions:  
Reinforcing Укрепление, усиление
Abundance Избыток, множество
Load carrying capability Грузоперевозочная возможность
To fill with sand Наполнять песком
To encourage Ободрять, поддерживать
To evaluate Определить
Conductivity Проводимость
Extrusion Вытеснение, выталкивание
Approximately Приблизительно
Weight Вес

Chemical stabilizers

The frost susceptibility of soils is always of concern in any construction project in the cold regions whether it is in Minnesota, Alberta, the Yukon Territory, or Alaska. Wherever the temperature of the region falls below freezing for a long enough period to cause significant frost penetration of the soil, the problems associated with frost heaving and jacking are of concern. We typically dismiss the problems by specifying "non-frost-susceptible soil" in the design. However, many areas of the north, particularly the far north simply do not have a source of non-frost-susceptible material available. Such materials must be imported from other areas often at great expense. This is a particularly acute problem in remote areas of northern Canada and Alaska where shipping is by barge, and the barge can operate only in the summer. In such areas local materials must often be used to make the project economically feasible. Higher


maintenance costs must be expected of course, but there simply is no alternative.

Modification of local materials to eliminate or reduce their degree of frost susceptibility is an area of research with large potential for cost savings. Danyluk (1986) tested eight possible stabilizing additives. The purpose was to determine if they could be used to alter the soil sufficiently to increase the unconfined compressive strength, permeability, and after-thaw California Bearing Ratio (CBR). Table 4. shows the results of Danyluk's stabilizer experiments.

Although 10% calcium acrylate additive gave the overall best performance, it is considered too expensive to be used on a large scale. Twenty percent Type I Portland cement with 2% calcium chloride provided the best results in the range of materials that could be considered economically feasible on a moderate scale. Cost analysis indicated that it would cost

TABLE 4. Results of Stabilizers in Fine -Grained Soil

 

  Unconfined      
  Compressive Frost-Heave After
Stabilizer Strength Permeability Ratio Thaw
(% by Weight) Ob/in (cm 590-X 1Q-5) Treated/Untreated CBR
Untreated 13.4 4.5 1.0 0.4
20% Cement 39.2 2.9 1.12 3.1
20% Cement. 2%        
calcium chloride 64.0 0.7 0.91 7.2
20% Cement. 2%        
sodium sulfate 55.1 0.8 0.85 2.3
20% Cement. 20%        
Hydrogen peroxide 31.8 1.4 1.05 4.3
20% Lime 8.5 1.11
8% Asphalt emulsion 51.6 0.28 0.85 3.7
10% Calcium acrylate 0.09 0.35 21.2
l%Tetrasodium        
Pyrophosphate 0 12 0.28

Danyluk (1986).


California bearing ratio between $18 and $39 per cubic yard FOB Anchorage, Alaska. These prices still make the additive prohibitive for all but limited applications, but may be attractive for smaller scale projects such as around foundations of small structures, driveways and access ramps or where surface conditions are more critical such as airstrips and runways.

More recently work in Alaska has centered on the use of fly ash from coal burning power plants as a stabilizing additive. The lime content of Alaskan coal is high, and although lime is not the most effective additive in Danyluk' s study, it is locally available in Alaska and therefore becomes economically attractive.

Chemical additives for soil modification is clearly a research area that needs more work to find effective and economically feasible materials.

Words and expressions:

Frost susceptibility Морозоустойчивость

Acute problem Острая проблема

Barge Баржа .,

Degree Степень

Additive Добавка

Ratio Соотношение

Lime Известь

Price Цена

Airstrip Взлетно-посадочная площадка

Runway Взлетно-посадочная полоса



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