Strength and permeability characteristics of expansive soil with gypsum and rice husk ash used for roadway construction

• Main Author: Edora, Angelo B.
• Format: text
• Language: English
• Published: Animo Repository 2021
• Subjects: Swelling soils—Testing; Swelling soils—Permeability; Soil stabilization; Civil Engineering; Structural Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/6353; https://animorepository.dlsu.edu.ph/context/etd_masteral/article/13410/viewcontent/EDORA_ANGELO_11771992_STRENGTH_AND_PERMEABILITY_CHARACTERISTICS_OF_EXPANSIVE_SOIL_WITH_GYPSUM_AND_RICE_HUSK_ASH_USED_FOR_ROADWAY_CONSTRUCTION_2_Redacted.pdf
• Institution: De La Salle University

Expansive soils pose threats not only for built residential houses and superstructures but also for roadway construction. The shrink-swell behavior of expansive soils creates a continuous strain on the pavements which can results to cracking and settlements. Usually, mechanical soil stabilization techniques were done to improve the geotechnical properties of these soils. However, these techniques are costly. This study aims to establish a more economic and more environmental-friendly way of stabilizing expansive soils for roadway construction application. Varying combinations of recycled gypsum and rice husk ash (RHA) were used in soil stabilization. Optimum mix proportions from the study of Tan & Adajar (2020) were adapted. A constant amount of 10% RHA was used as a complementary additive of gypsum. A maximum increase of 1.923 kN/m3 in maximum dry density and a corresponding maximum reduction of about 26.27% in optimum moisture content were attained by proctor compaction tests. Therefore, the additives used were effective in improving the compaction characteristics of the soil based on ASTM D4609. Gypsum alone was able to reduce the void ratio of the soil to 1.399 but the addition of RHA greatly increases the void ratio of the specimens. Bearing capacity of the soil slightly increase with the addition of 15% gypsum. While, the addition of the 10% RHA dramatically increase the soaked CBR index of the soil. A peak average value of 21.11% was recorded for 15% Gypsum+10% RHA soil specimen. Falling head permeability tests show that as the amount of gypsum in gypsum+10% RHA soil specimen increases, the permeability of the soil also increases. A direct relationship is then formed between the strength and permeability. This unusual relationship between these two parameters may be caused by clumping of soil particles into bigger particles which increases the void spaces in the soil. Additionally, the introduction of RHA, which has bigger particles than the soil, created more void spaces and reduces the amount of fine particles in the mix proportion. Empirical models to predict soaked CBR index and coefficient of permeability in terms of varying amount of gypsum in gypsum+10% RHA mix proportions were formulated.