Evaluating The Effects of Non-Woven Geo-textiles and Geo-membranes Reinforcement on Performance Improvement and Drainage Barrier Efficiency on Expansive Subgrade Soil.

Abstract

Subgrade is a very important components of pavement structures in which the ultimate wheel loads rests on it. The strength of subgrade materials could sometimes fall under doubt due to the presence of moisture problem, highly plastic soil and high clay mineral contents. This doubt leads to extreme deterioration and distress which in turns consumes much of budget for maintenance work. One mechanism of minimizing doubt of strength and/or performance and drainage problem is stabilization of weak expansive subgrade soil with geo-synthetic materials. These particular studies used non-woven geo-textiles and geo-membrane for strength and drainage problems respectively. Purposive sampling was used to get samples for laboratory tests which were about 230 Kg by weight. Generally, the study is designed to evaluate the effects of non-woven geo textiles and geo-membranes reinforcement on performance improvement and drainage barrier efficiency on expansive subgrade soil. Reinforcement was made at middle of the mould and at the middle and at one-third of the mould for single and double layer reinforcement respectively. The depth of reinforcements was selected by reviewing the previous investigations with which good effectiveness have shown. The study has examined Natural Moisture Content, Unconfined Compression Strength Test, Particle Size Distribution, Atterberg’s Limit, Specific Gravity, Free Swell Index, Compaction and California Bearing Ratio tests for natural soil whereas Compaction and California Bearing Ratio test for reinforced soil by using ASTM manuals for all the tests. After analyzing laboratories results the soils under investigations were classified as A-7-6(21) as per AASHTO and CH as per USCS respectively which was fat clay soil with montmorillonite clay mineral contents, high swell potential and highly plastic clay soil in which its specific gravity and group index (GI) was 2.72 and 21 respectively showing that the soil is poor subgrade soil in its natural state. The mineral contents, swelling potential and plasticity of the soil were determined from the combined results of free swell ratio and Atterberg’s limit test. For single layer and double layer reinforcements OMC and MDD was slightly decreased and increased respectively for each layers. The CBR value of the natural soil was 2.38. After Reinforcement, single reinforcement has shown good performances with CBR value of 12.24%. The percentage of performance improvement in terms of CBR value for single reinforcement was 414.3%. Double layer reinforcement with expansive subgrade soil was showed CBR value of 6.82% and the percentage of performance improvement in terms of CBR value was 186.5%. The CBR swell of natural soil was 6.25 which is above minimum requirements as per ERA manual (2%).As a result of reinforcements CBR swell was reduced to 1.59% and 0.88% for single and double layer reinforcement respectively. The percentage of swelling decreases was about 74.56% and 85.92% for each layer respectively. The aim of controlling moisture migration within expansive subgrade soil was achieved with double reinforcement.