IMPROVING THE CHARACTERISTICS OF SUBGRADE CLAY SOIL USING GEOTEXTILE (A CASE STUDY ON ARBA MINCH CITY, ETHIOPIA)

Abstract

Ground improvement provides the way for the utilization of unsuitable soil for construction activities, by improving its strength and altering the other properties of the soil in a way to favor the construction needs thereby ensuring the desired use and satisfactory performance of the structure. This study aimed to determine how geotextile materials could improve the properties of subgrade clay soil. Twelve samples were collected using a shovel to dig a depth of 1.5 meters. In this thesis work, laboratory experiments were carried out to characterize the geotechnical properties of the soil, including the tests like, natural moisture content, particle size distribution, specific gravity, Atterberg limits (LL and PL), compaction (OMC and MDD), consolidation, Unconfined compressive strength, CBR, and CBR swelling. The experiments were conducted with and without the use of geotextile material. The analysis of the tests showed that natural moisture content ranges from 57.3% to 76.7%, Specific gravity 2.7 to 2.81, LL ranges from 47.63% to 72.14%, PL ranges from 19.21% to 33.72%, PI ranges from 26.87% to 43.14%, OMC ranges from 27% to 33.5% and MDD 1.27g/cm3 to 1.42g/cm3, CBR value ranges from 3.79 to 6.70 and swell values ranges from 7.99% to 12.19% , Undrained shear strength (Cu),Kpa ranges from 23.43 kPa to 57.21 kPa, coefficient compressibility Cc ranges from 0.004 to 0.0369 and Cr ranges from 0.004 to 0.0242. The soil was characterized by CL, CH and MH based on USCS classification system and A-7-6 and A-7-5 based on AASHTO soil classification system. Geotextile layer was employed and inserted inside the soil when performing CBR, Unconfined compressive strength and Consolidation tests (Oedometer tests). The CBR Value increased from 3.73 % to 7.14 % and the swelling decreased 12.19 % to 7.33 %, undrained shear strength (Cu), Kpa increased from 23.43 to 82.42 kPa and the value of coefficient compressibility Cc decreased from 0.035 to 0.0011, Cr and swelling decreased from0.004 to 0.0015, and 3.98 percent to 2.4 percent respectively, when a geotextile material inserted inside the soil. The result shows that putting geotextile at the middle layer becomes the optimum (efficient) position to enhance the strength of the soil in the present study area. And most of the untreated and all the treated soil CBR values were higher, which is acceptable for road construction projects as per ERA 2013 Standard.