As California's development and infrastructure continues to grow, it will become increasingly difficult to find sites with suitable soil properties that support this growth without the need for additional engineering enhancements. The conditions at many sites must be improved by some method of soil enhancement such as: static or dynamic loading, reinforcement, drainage or chemical stabilization of the existing site conditions. Thus, it has become important for the design and engineering community to know the different soil improvement methods, the degree to which soil properties may be improved, and the costs and environmental benefits involved. In this way, the designer or engineer knows the options and has the knowledge to advise clients on the best engineering approach to save cost, reduce the environmental impact, and obtain the maximum performance benefit for the specific project.
When considering the chemical stabilization option, the first criteria is to establish the relative engineering equivalency between treating a substandard material to improve its engineering properties or importing a qualified material.
The term Value Engineering is defined as the ratio of function to cost. Either improving the function or reducing the cost can therefore increase value. It is a primary tenet of Value Engineering that quality not be reduced as a consequence of pursuing value improvements.
In the design and construction industry, chemical stabilization provides not only added value to engineering performance but reduces project cost and improves California's long-term environment sustainability.
Two examples of design engineers making chemical stabilization the right choice for their performance requirements are in the design/construction of building and pavement foundations.
Structures: Previously, for projects requiring non-expansive fill to reduce potential for shrink/swell under building structures, this has historically been achieved by removing and off-hauling expansive clays and importing non-expansive structural material (PI
Today this process is implemented by chemically modifying the existing expansive soils with small amounts of quicklime. The added engineering value of this modification is a non-expansive structural fill section with reduced permeability and higher compressive strength than an unbound aggregate import. This value engineering is coupled with significant cost reduction by utilizing native material more effectively and eliminating the cost of exporting importing practices.
Pavements: The value engineering chemical stabilization provides in pavement design has long been demonstrated.
The notion of hauling heavy loads of unsustainable quarry rock products across urban areas to meet a design criterion that could otherwise be met, and even improved upon, by other means is an unsustainable notion. Unfortunately, this scenario (considered conventional) is still taking place throughout California, even though it is well documented that the state has and will continue to experience aggregate shortages.
Today's empirical method of pavement design, developed in the 1940's, is essentially a design-to-failure approach. Pavements are designed to handle X number of loads before they will need to be replaced. This method is based on preventing permanent deformation of each pavement layer, with the total pavement thickness based on traffic and tensile properties, as well as shear strength characteristics of the paving materials.
This empirical design method uses general assumptions that the relationships developed between sections will apply under all conditions in which they will be used. If the site characteristics indicate that the native subgrade soils will have a low bearing capacity, the empirical design method would require significant section thickness in the base and surfacing material to overcome these conditions.
In pavement design, the use of chemical stabilization is quickly being understood as a method to reduce cost while improving the engineering life-cycle properties of the pavement structure. Pavement design engineers have realized that the need for a stable working platform (foundation) is essential to the idea of precluding distresses that originate deep in the pavement structure.
These designers understand that most pavement distress does not occur from traffic loading, unless under designed for conditions, but rather from unstable subgrade soils and unbound aggregates that become weak under saturated conditions.
The foundation is crucial in the construction and performance of pavements and is required to fulfill the concept of developing a perpetual pavement structure. The need for a high-strength, low-permeable consistent foundation are required for a perpetual pavement design not to exceed a critical fatigue level and only require surface maintenance or treatments over its extended life-cycle.
As one of the main benefits of a stabilized section is the retained strength when fully saturated, the use of chemical stabilization is adding value to water resource projects as high strength - low permeable liners, facing armor to replace riprap for slope protection, and core structures for levees and abutments.
In biosolid processing of compost and sludge, the stabilized section has proved its worth. These facilities require heavy loading under all weather conditions as well as maintaining grades to avoid contamination of processed materials. The stabilization option has improved the life-cycle duration of these facilities while reducing the maintenance requirement.
Today, this process continues to be applied in new ways as more designers realize the engineering benefits of chemical stabilization. HSI's goal is to ensure that the process is optimized so the full benefit is realized.