7/29/2019 Stabilization Techniques

1/3

Stabilization Techniques: Soil, Moisture Content and Compaction

Road Bed Stabilization

Road beds are often constructed with native site soils containing a wide gradation of materials

which may include a high content of soil fines (passing 200 mesh). Px-300 assists in binding finestogether with larger materials into a dense, well-compacted material that provides a high degree ofstabilization and higher tensile strength than untreated road beds. PX300 road beds also offer ahigh resistance to moisture penetration (2.9 x 10

-8cm/sec under ASTM D 5084). Benefits include

reduced maintenance costs and utilization of on-site materials, eliminating the need to import off-site soil.

Three important determine a stabilization result::

Material GradationMoisture ContentCompactive Effort

Material Gradation

Material Gradation refers to the distribution (% by weight) of the different sizes of particles within agiven soil sample. A soil sample is well-graded if it contains a good, even distribution of particlesizes. A soil sample composed of predominantly one-sized particles is said to be poorly graded. Awell-graded soil contains smaller particles which tend to fill the empty spaces between largerparticles, leaving fewer voids after compaction.

The table below shows distribution guidelines for several different soil gradations.

Sieve Size Gradation (% passing)

inch 95%1/2 inch 85 %

No. 4 62 %

No. 16 48 %

No. 200 30 %

Two conditions prevent a successful stabilization: The presence of large rocks; and certain typesof contaminants.

Large rocks can cause structural breakdown in an otherwise successful application andcontaminants prevent the successful curing of the PX-300 solution in the treated soil. When either

or both of these conditions are present, G.M. Boston Company requires prior notice of the fact, sothat soil remediation can be done.

Moisture Content

Moisture Content, the amount of water present in a soil, is important to any road bed project. Waterlubricates the soil particles, helping them to slide into voids between larger particles and producethe greatest density. PX-300 wetting action additionally facilitates this process, along with water andenzymes. Soil fines and clay particles become "sticky" and cohesive, providing a necessary

7/29/2019 Stabilization Techniques

2/3

condition for stabilization. Engineers have determined that almost all soils have what they call anoptimum moisture content which permits optimum density from a given amount of effort. Theillustration below shows the relationship between soil dry density and moisture content.

The presence of excess moisture in site soil due to flooding or heavy rainfall will prevent an efficientcure following the PX300 application. If present site soil moisture plus the moisture accompanyinga PX300 application will result in a moisture level well above optimum, the project should be

deferred. Usually two days of dry, moderately warm weather will bring the moisture level down topoint that supports a successful PX-300 application.

If flooding or heaving rainfall will closely follow a PX-300 application, that could also impair orprevent a successful PX-300 cure by diluting and washing away the uncured PX-300. Accordingly,G.M. Boston Company strongly recommends a curing/drying period of 36-72 hours following a PX-300 application to ensure a successful project.

Without project conditions that comply with the guidelines stated above, G.M. Boston Companycannot provide assurance that a completed project will perform as expected by our customers andby us.

Compactive Effort

Compactive effort is the process of physically increasing the weight per unit volume of road bedsoil. Compaction occurs in several ways: a drum roller provides static weight or pressure, a sheepfoot roller provides a kneading action and a vibrating roller provides a shaking pressure. All areacceptable compaction methods and occasionally, are used together for optimal results. Without aproper moisture level, compaction cannot occur successfully. If too wet, the compacted soil willpush out from under the compaction equipment and, if too dry, the compacted soil will not holdtogether because it will lack the cohesive, "sticky" quality mentioned above in "Moisture Content."The moisture density curve above has particular significance here.

Building the Road

Road Bed materials using PX-300 should have a gradation mix that approaches the gradationspecification values appearing in "Material Gradation." Frequently, road beds have used materialsoutside design standards; these projects require prior sample testing to assess the likelihood ofsuccess. Where outside soil will go on top of the existing road bed site soil, it is imperative to dosample testing of the imported soil to determine that PX-300 can achieve the customer's desiredresults before commencing the project itself.

7/29/2019 Stabilization Techniques

3/3

Generally, PX-300 is not recommended by compaction of lifts greater than 6 inches. Type ofmaterial to be compacted plus the size and type of compaction equipment will determine liftthickness.

Step 1: Blade or rip the existing base to a depth of 6 inches, then windrow the loosened material. Ifthe project requires additional aggregate, the use the least-cost available material with more fines.

Check the overall gradation of the material to ensure that it conforms to the tested, pre-projectsample.

Step 2: For each acre of road base material, add 715 gallons of PX300 to the amount of waternecessary to obtain optimum moisture. Spray both the bladed surface and the windrow to reachoptimum moisture. Blend the PX-300 material using a grader blade, working the soil and aggregateback and forth to blend in the PX-300 and water. If the material is too wet, blade until it approachesoptimum moisture. If too dry, add more PX-300 solution to bring the material up to optimummoisture. After thorough mixing spread the material to grade.

Step 3: Extend and crown the road bed surface with a blade. If the material dries out on a hot day,spray again with the PX-300 moisture. Compact with a sheep foot a pneumatic roller. Use avibratory roller for the first pass only and do not use vibratory compaction thereafter; additional

vibratory compaction will cause cracking. Compact in 6 inch lifts to ensure maximum compactionand, following the final pass, do not disturb the finished surface by attempting to "dress" minorimperfections. If possible, allow the road bed to cure prior to use (and final testing). Allowing theroad base to dry (cure) will provide greater strength and decreased permeability.

If intending to apply an asphalt or chip seal wear surface, moisten the road base surface with adiluted PX-300 application before applying the new wear surface. That will ensure a better bondingof the two materials.