Premature failures in chemically stabilized expansive soils cost millions of dollars in maintenance and repair. One reason for these failures is the inability of existing stabilization design guidelines to take into account the complex interactions between the clay minerals and the stabilizers. It is vital to understand these complex interactions, as they are responsible for the improved strength and reduction of swelling/shrinking in these soils, which in turn affects the overall health of the infrastructure. This research study examined the longevity of chemically stabilized expansive soils subjected to wetting/drying conditions, with a major focus on clay mineralogy. Eight different natural soils with varying clay mineralogy were subjected to wetting/drying durability studies after they were stabilized with chemical additives including quicklime and cement. Performance indicators such as volumetric strain and unconfined compressive strength trends were monitored at regular intervals during the wetting/drying process. It was observed that clayey soils dominant in the mineral montmorillonite were susceptible to premature failures. It was also noted that soils dominant in other clay minerals exhibited early failures at lower additive contents. For the first time, an attempt was made to address the field implications of the laboratory studies by developing a correlation that predicts service life in the field based on clay mineralogy and stabilizer dosage.

The use of synthetic fibres as reinforcement to stabilise expansive soils is gaining momentum. As a contribution towards this growing field of research two different types of synthetic fibres, Fiber Mesh® and Fiber Cast®, were evaluated as a stabilisation alternative for expansive soils in the presence of lime. California bearing ratio (CBR) is chosen as a performance indicator as it is a good pointer towards pavement effectiveness. Variables such as length and amount of the fibres as well as curing period were studied. Both deterministic and probabilistic (or reliability) analyses is presented in this paper. While the deterministic analysis helps in understanding the measured experimental data, the probabilistic approach accounts for the stochastic nature of the experimental data and provides a better rationale for the design methods. The deterministic approach showed that the improvement in CBR increased with higher fibre contents and longer lengths and the effect was prominent when lime was used as a stabiliser. There were some exceptions to this behaviour, which were noted in the paper. The probabilistic analysis showed that the amount and lengths of fibres were important factors in CBR strength. It was also determined that the variation in the target CBR value had a considerable effect on optimising the length and amount of the fibres.

Clayey soils with medium to high plasticity are prevalent in several parts of the world, causing billions of dollars in damage annually to various civil infrastructures. Several ground-improvement techniques can be employed to counteract this issue. However, these methods are impractical in certain situations and unsustainable in others due to their economic and environmental impacts. Microbial-induced calcite precipitation (MICP) could provide a more sustainable alternative. Researchers have successfully used MICP to alter specific geotechnical properties of sands and silts. This research investigates the applicability of MICP via biostimulation to treat clayey soils with low to high plasticity. The goal is to determine the viability of this technique to alter the engineering behavior of clayey soils, especially given the low permeability of these soils. For this purpose, four soils were selected from four different locations in Idaho and Montana. The soils were selected such that their plasticity varied from low to high to study the effect of plasticity index on the effectiveness of MICP treatments. In addition to the four soils, three additional artificial mixes were studied to study the effect of clay content on MICP effectiveness. Both macroscale and microscale studies were conducted on untreated and biostimulated soils to observe strength gain, swelling reduction, and calcium carbonate precipitation. The results show that MICP via biostimulation would be a promising method to treat problematic clayey soils.

Stabilization design guidelines based on soil plasticity properties have certain limitations. Soils of similar plasticity properties can contain different dominant clay minerals, and hence, their engineering behavior can be different when stabilized with the same chemical additive and dosage. It is essential to modify stabilizer design guidelines by including clay mineralogy of the soil and its interactions with chemical additives used. Chemical properties of a soil including cation exchange capacity (CEC), specific surface area (SSA) and total potassium (TP) are dependent on clay mineral constituents, and an attempt is made in this study to develop a rational and practical methodology to determine both clay mineralogy distribution and dominant clay mineral in a soil by using three measured chemical soil properties and their analyses. This approach has been evaluated by determining and evaluating clay minerals present in artificial and natural clayey soils of known and unknown clay mineralogy. A total of ...