STABILIZATION OF EXPANSIVE SOIL BY USING COFFEE HUSK ASH

Abstract

Expansive soils have high potential for swelling and shrinking as a result of change in moisture content and they are one of the major soil deposits in Ethiopia. Road constructed on an expansive soil needs special attention during the design and construction stages. This study investigates the feasibility of using coffee husk ash as an expansive soil stabilizer. Coffee husk is a byproduct of coffee beans: when coffee husk is burnt under controlled condition (muffle furnace) at 550 oC for 4 hour the resulting ash is coffee husk ash (CHA). To investigate the effect of adding CHA to an expansive soil, laboratory experiments such as atterberg limit tests, free swell index tests, Proctor density, CBR test and unconfined compressive strength (UCS) tests were performed for different percentages of coffee husk ash (CHA). Standard Procter testes were conduct to evaluate the compaction behavior and unconfined compressive tests were performed on samples of 3.6 cm diameter and 7.8 cm height for uncured, 7 and 14 days of curing. The soil was stabilized with CHA in stepped concentration of 5%, 10%, 15% up to 30% by dry weight of the soil for different laboratory tests. Also the effect of curing period was evaluated over a period of 7 to 14 days for UCS and CBR tests. Analysis of the results shows improvement on the geotechnical properties of CHA stabilized soil. CHA reduces plasticity index by 68% up to 25% of CHA content, swelling ratio by 76% up to 20% CHA content and OMC decreased from 47% to 30% at 15% CHA content with an increase in MDD from 1.22 g/cm3 to 1.384 g/cm3. The UCS is also increased from 35.73kPa to314kPa and the un soaked and soaked CBR values increased from 16.2% to 21.5% and from 1.62 to 5.1% respectively after 14 day of curing and with the addition of 15% CHA content. After the addition of the optimum amount of the CHA the value of the laboratory tests are changed. From this investigation CHA is an alternative expansive soil stabilizing material sa it has changed and for further investigation use another stabilizing agent in addition to CHA to change the soil property from medium plastic to low plastic.