Improvement of Engineering Properties of Weak Subgrade Soil by Ensete Ventricosum Fiber Reinforcement. (A case in Jimma Town)

Abstract

Weak and unsuitable soil conditions have always caused problems for civil engineers during the construction of structures. To avoid problems in a cost- effective manner, proper and reliable solutions need to be developed. Therefore, development of effective stabilization techniques for these environmentally sensitive lands and soils has been called for. In Jimma town most of roads are deteriorated. For this deterioration one of the reasons behind is weakness of subgrade soil. Therefore modification or improvement of such soil is required to get stable subgrade soil. Over centuries the Ensete ventricosum fibers have been extracted from the stems as major material for the weaving, ropes and cord production, as well as for baskets production. To use this material as a fiber for soil reinforcement, this study investigated properties and strength on reinforced soil. The objective of this study was to use ensete ventricosum fiber in improvement of weak subgrade soil by examining its effect on engineering properties. The disturbed samples were collected at desired amount from dippo and koshe at adequate depth. And ensete ventricosum fiber sample were collected based on desired content from local market of Jimma zone Shebe. From sieve analysis tests, percentage of passing through sieve No. 200 (0.075mm sieve size) of koshe and dippo is 93.16% and 95.07 % respectively. While from the Atterberg’s limit test results, natural soil sample contains a liquid limit of 82.9and 80.53%, a plastic limit of 36.11% and 35.1%, and plasticity index of 46.8% and 45.43%, koshe and dippo samples respectively. This result shows that both samples are clay soil. Both natural sample soils were classified as A-7-5 according to AASHTO soil classification system and CH according to USCS. As observed from CBR test result, when fiber content increases, CBR value also increases until 0.75% fiber content is added and then decreases for both samples. So this 0.75% fiber content can be taken as optimum content to produce best mix of soil and reinforcement fiber which improve weak subgrade soil. From compaction test, it is observed that fiber content increases, MDD decreases and OMC increases for both samples. MDD decreases from 1.35 g/cm 3 of natural sample to 1.28 g/cm 3 of 1% fiber reinforced sample and from 1.47g/cm 3 of natural sample to 1.39g/cm 3 of 1% fiber reinforced sample for koshe and dippo samples respectively. Again OMC increases from 30.16% of natural sample to 36.65% of 1%fiber reinforced sample for koshe sample and from 20.21 of natural sample to 27.05% of 1%fiber reinforced sample for dippo sample. UCS value increased by 91.7% at 25mm ,121.97% at 50mm, 229.9% at 75mm length from natural soil for dippo sample and 57.1% at 25mm,80.5% at 50mm,176.8% at 75mm for koshe sample for constant content of 0.75% of fiber is added . It is observed that the UCS value of fiber reinforced soil increases with increase in fiber length