I am in search of a biomaterial which can be mixed with soil not only to improve its mechanical properties but also enhance the vegetation growth over the slopes where stabilization is applied.
Soils are terribly complex microbial communities. One case that may partly answer your question that is less complex than many others is desert soil crust. This is held together by bacteria, lichens, algae, and fungi. The cyanobacteria, or so-called blue-green algae, forms long microscopic filaments mixed with filaments from fungi creating a network that binds the soil together. In desert environments such as Utah, these crusts may cover ~70% of the surface of the soil with thicknesses approaching 10 centimeters. Biological desert crust protects soil from being washed or blown away while also providing a means to capture and store water. So to accomplish your aim you will want microbes that can form such networks of long filaments. By considering this process and existing types of microbes, you would want to encourage selected microbial communities by aiding the nutrients important for appropriate types of microbes.
The Utah example is very interesting, with the 10cm coverage of biological crust in desert. That might be helpful in the protection against wind errosion. I would like to treat soil biologically on slopes with a thick cover. And how can I reproduce the biological crust on sand in laboratory to elucidate the change in mechanical properties.
I believe you can collect 5 cm samples or so of the crust from different locals as test starter samples. Then I would place 1cm patches or smaller onto your lab target soil then add water as mist and provide light from bulbs that mimic sunlight. You should see growth start at the patch. You can measure how far growth extends form the patch transplant into your lab mix and the time needed for expansion.
I would suggest that you try Sugarcane Press Mud. I am working on it from the point of view of soil stabilization. It has given me positive results but not to expected levels. It is an organic waste by product from sugar industry. I haven't come across much literature regarding its use in soil stabilization though its has lot of uses as a biological soil conditioner. Have a look at the following publications...
Thank you very much for the links, those were useful.
However, the climate of the country may not allow those process to run. Rather, a biopolymer might be of a good choice. However, biopolymers are very expensive as compared to the traditional materials, such as cement.