Permeability characteristics of dredged soil stabilzed with fly ash based geopolymer for road embankment

The drainage capacity of road embankments is essential, given the Philippines is usually hit by numerous typhoons every year resulting in the devastating flood and ponding areas. In most cases, engineers opt to put much more of their attention on the strength and stability improvement of the soil, while neglecting the drainage capacity of the soil. The strengthening of the soil may come at a cost since it could also negatively alter the drainage capacity of the soil. When water is not immediately drained during rainfall, it exerts pressure on the porous materials and percolates, resulting in the failure and deterioration of the infrastructure. The paper aimed to assess the fly ash based geopolymer for soil stabilization on dredged soil for road embankment. Geotechnical properties such as permeability coefficient and strength were analyzed. The fly ash used in the study was obtained from the thermal power plant located in Mindanao whereas the soil was obtained in a river bank near the power plant. In this study, different percentage replacements by mass, specifically 10%, 20%, and 30%, were investigated to identify their drainage characteristics. The soil samples were maintained in a humid condition for twenty-eight days for the testing. Both vertical and horizontal permeability were conducted based on falling head permeability test and constant head permeability test associated with confined aquafier, respectively. For the vertical permeability, the researchers based the set-up of the permeameter on ASTM D-5856. Unfortunately, until now, there is still no apparatus and standard way of measuring the horizontal permeability. This led the researchers to improvise a new permeameter set-up based from a well-concept incorporating Darcy\u27s law. Unconfined compressive strength test was conducted to attain the strength property of the geoplymer-soil mix. After getting the results of the tests for the strength and permeability various comparison were made. Also, SEM analysis was conducted to visually see the porous structure of the geopolymer-soil mix. The results showed the relationship between the strength and permeability to be inversely related with respect to the addition of the polymer. The pure soil having a degree of x10⁻⁰² cm/s was said to have good permeability, however, the 10% replacement having a degree of x10⁻⁴ cm/s was classified to have a poor permeability. Nevertheless, both the 20% and 30% having a degree of x10⁻⁶ and x10⁻⁷ cm/s, respectively, was classified to be practically impervious. A comparison was made between the vertical and horizontal permeability. As for the overall conclusion, proper surface drainage design is needed if geopolymer mix were to be used for road embankments since improving the strength of the soil sacrifices its permeability