Stabilization of expansive subgrade soil using Sisal fiber mixed with lime. A case of Tarcha Town, Dawro Zone, Ethiopia

Abstract

Expansive soils are one of the most abundant and problematic soils in the world, as well as in Ethiopia, which mostly causes significant damage to structures such as buildings, pavements, bridges and other civil engineering structures which constructed over it due to its considerable volume change with the existence of moisture variations. To reduce such unsuitable behavior of expansive soil, soil stabilization is required. From a number of techniques like chemical stabilization, mechanical stabilization, soil reinforcement by artificial and natural materials and others to treat this types of soil; the technique which is effective, economical and environmentally friendly be the best solution. The general objective of this research was to stabilize the expansive subgrade soil by using Sisal fiber mixed with lime. This research followed the experimental type of study and purposive sampling technique. In this study FSI, NMC, 𝐺𝑠 , Atterburg limits (LL, PL and PI), Particle size distribution, Moisture absorption rate of sisal fiber, Moisture releasing rate of sisal fiber, Decomposition rate of sisal fiber, Compaction (moisture – density relationship), CBR and CBR swell, UCS were determined. The soil sample was collected from three test pits from adequate depth (1.5m – 2m) to avoid the intrusion of organic matter. Lime and sisal fiber collected from local market. The engineering properties of the sample from all the three sources were determined and stabilization held on relatively the weakest soil sample based on the CBR values. The stabilizing agents (lime and sisal fiber) mixed to soil sample separately and then combined to determine the combined effect at a point where maximum CBR values recorded by separate testing. The varying proportion of randomly distributed sisal fiber of 0.5%, 0.8% and 1.1% by dry mass of soil sample with a varying length of sisal fiber 5cm, 8cm and 11cm were added to expansive soil. And lime added at 1.5%, 2.5%, 3.5% and 4.5% by dry mass of soil sample were added and tested separately. 3.5% of lime was added to 0.8% of sisal fiber at varying length (5cm, 8cm, and 11cm) of the fiber and mixed to soil sample to determine the combined effect. The engineering properties of untreated soil sample from laboratory tests were determined as FSI, NMC, 𝐺𝑠 , LL, PI, MDD, OMC, CBR, CBR swell and UCS were 94%, 41.77%, 2.73, 94.3%, 61.88%, 1.395g/cc, 29.7%, 1.035%, 8.45% and 149kPa respectively. Based on the test results the soil was classified as CH according to USCS and A-7-5(45) according to AASHTO soil classification system. At optimum combination of lime and SF (3.5% of lime, and 0.8% of SF at 8cm length), MDD determined as 1.387g/cc and OMC equals to 30.95%. CBR of treated sample were improved by 607.25% and CBR swell decreased from 8.45% to 0.72%. The uncured UCS of S1 was improved by 31.62% and by 83.72% and 151.62% for 7 and 21 days cured.