A study of properties of soil reinforced with coir mat with special reference to road construction in Assam

Abstract

The development of a region or a country is dependent on its infrastructure, a major part of which is its transportation network. Road network has been considered as a yardstick for civilization. Road in Assam are mainly of flexible type. These are often constructed over soft sub grade due to soft nature of the subsoil. The roads have the problems like formation of potholes, ruts, cracks and localized depression and settlement especially during rainy season. These are mainly due to insufficient bearing capacity of the subgrade in water saturated condition. According to IRC37-2001 flexible pavement are designed based on strength of subgrade soil in terms of CBR. As per this method, total thickness of pavement increases exponentially with decrease in the CBR value of subgrade soil. Thicker pavements are not only costlier but create many constructional and maintenance problem also. The minimum CBR value required of the soil to superimpose a economically viable flexible pavement are 7% (Borgohain,.2001). But the soil of Assam containing silt and clay has a CBR of 2-5 %. Table1.0 shows the CBR values of subgrade soil from a few districts of Assam In case of new connectivity since 7 % CBR being not available, geotextile material may be used for increasing the bearing capacity of subgrade. Geotextile is the famous name now universally adopted for fabrics used in geotechnical engineering for ground improvement work specially in roads and embankments. They have been placed between the aggregate layer and subgrade soil to perform several functions : Separation, Drainage, Reinforcement etc. The geotextile material selected in the present study is coir mat a coir based geotextile product. It has been observed that the use of coir mat, at interface of subgrade and WBM increases the CBR value of the subgrade and thereby reduces the pavement thickness considerably. The reasons for selecting the coir mat as geotextile material is because of its eco friendly nature and its manufacturing prospect in Assam. As a natural product,...