By: Monica Acosta Soil Stabilization
Overview • What is Soil Stabilization? • History • Types of Stabilizers • Lime • Portland Cement • Placement • Conclusion
What is Soil Stabilization? Improving the engineering properties of soils used for pavement base courses, subbase courses, and subgrades by the use of additives which are mixed into the soil to effect the desired improvement.
History Although this process of improving the engineering properties of soils has been practiced for centuries, soil stabilization did not gain significant acceptance for highway construction in the United States until after World War II.
Types • Lime Cement-Fly Ash (LCF) • Lime-Fly Ash (LF) • Portland Cement • Bitumen • Lime
Lime According to The National Lime Association. Lime can be used to treat soils in order to improve their workability and load-bearing characteristics in a number of situations. Quicklime is frequently used to dry wet soils at construction sites and elsewhere, reducing downtime and providing an improved working surface. An even more significant use of lime is in the modification and stabilization of soil beneath road and similar construction projects. Use of lime can substantially increase the stability, impermeability, and load-bearing capacity of the subgrade.
Example • According The National Lime Association: • In the short-term, considering the structural contribution of lime-stabilized layers in pavement design can create more cost-effective design alternatives. A recent interstate project in Pennsylvania, for example, began with a $29.3 million traditional design approach. An alternate design using lime stabilization, consistent with AASHTO mechanistic-empirical designs, cost only $21.6 million—more than 25 percent savings. The savings came from: • treating the existing subgrade material with lime, rather than removing the material and replacing it with granular material; and • thinner layers of flexible pavement for the lime stabilized alternate due to the increased strength of the lime stabilized subbase. • In the longer term, lime stabilization provides performance benefits that reduce maintenance costs.
Portland Cement • A cement-modified soil (CMS) is a soil material that has been treated with a relatively small proportion of Portland cement. The objective of the treatment is to amend undesirable properties of problem soils or substandard materials so that they are suitable for use in construction. Preparing soil using Portland Cement for the new 380 Airbus at Chicago airport
Cement-modified silt-clay soils are soils that contain more than 35% silt and clay (defined as material passing a No. 200 (75 µm) sieve in accordance with ASTM D4318). The general objective is to improve soils that are otherwise unsuitable for use in subgrades or subbase layers. Specific objectives may be to decrease plasticity and volume change characteristics, to increase the bearing strength, or to provide a stable working platform on which pavement layers may be constructed. Types of Cement-Modified Soils
Cement-Modified Soils Cont. • Cement-modified granular soils are soils that contain less than 35% silt and clay (defined as material passing a No. 200 (75 µm) sieve in accordance with ASTM D4318). The usual objective is to alter substandard materials so that they will meet requirements specified for pavement base or subbase layers.
Results of Using Portland Cement: • Reduction in plasticity characteristics as measured by Plasticity Index (PI) • Reduction in the amount of silt and clay size particles • Increase in the California Bearing Ratio (CBR) • Increase in shearing strength • Decrease in volume-change properties
In-place mixing of lime with existing base and paving material on city street.
Civil and Environmental Engineering Professor Craig Benson and graduate student Burak Tanyu install a lysimeter to test the effect of fly ash on ground water. (Photo: Courtesy College of Engineering)
Pull-type spreader stabilizing a base for a future mall. Highway Reconstruction
Conclusion The benefits of using chemical or bitumen additives are to: • improve the soils' strength • workability • durability and gradation • reduce plasticity • reduce pavement thickness • for dust control during construction and • for soil waterproofing to preserve the soils' natural strength by retarding ingress of surface water.
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