Experimental Studies on Treated Sub-base Soil with Fly Ash and Cement for Sustainable Design Recommendations
Engineers in Malaysia often faced with problem of constructing roadbeds on problematic soils. These soils do not possess enough strength to support the wheel loads upon them either in construction or during the service life of the pavement. Thus, soil treatment must be conducted to provide a stable sub-base or a working platform for construction of pavement. One of the strategies to achieve this is soil stabilization. The soil stabilization includes both physical and chemical stabilization. Chemical stabilization involves mixing binding agents with natural soils to remove moisture and improve strength properties of the soil. Generally the role of stabilizing agent in the treatment process is either reinforcing of the bounds between the particles or filling of the pore spaces. There are two types of chemical stabilization depending to the depth of the problematic soil and the type of geotechnical application: surface or deep stabilization. The traditional surface stabilization begins by excavating and breaking up the clods of the soil followed by the addition of stabilizing agents. The known amount of water is mixed with the soil and additives and compacted. Approximately 150 to 250mm depth of soil can be strengthened by this surface method. Moreover, by using heavy equipment with appropriate modification, the depth of stabilized zone can be increased to 1m. These methods are used extensively to stabilized bases and sub-bases of highways and airfield pavements (3). The pavement soil qualities will be improved by thoroughly mixing and compacting with additives include portland cement, fly ash, bitumen, and combinations of any of the additives (4). The type of the additive and the amount required are dependent upon the soil classification and the degree of improvement desired (5). The pavement structure consists of a relatively thin wearing surface constructed over a base course and a sub-base course that rests upon a sub-grade course. Asphalt/concrete is primarily used for the wearing surface. The properties of all the pavement layers are considered in the design of the flexible pavement system (6). They suggested that construction of long-lasting, economical flexible pavement requires materials that exhibit good engineering properties. The sub-base should possess desirable properties to extend the service life of the roadway section and reduce thickness of the flexible pavement structure. Strength, drainage, and permanency of strength are the few desirable properties. The fly ash classified 'F' exhibits low self-cementing properties and however, with a addition of an activator such as lime the fly ash Class 'F' produces cementitious product (7). Even for very expansive clayey soil, unconfined compressive strength increased by 106% when fly ash content was increased from 0 to 25% (8).
Assessment of Soaked California Bearing Ratio Value Using Geotechnical Properties of Soils
California Bearing Ratio value is used for the evaluation of subgrade strengths during design of flexible pavements. To simulate worst moisture condition of the field, soaked California Bearing Ratio value is used in the design of pavements. But this test is an expansive and time consuming method. In this study, a detailed survey was carried out within a 5 km radius of Sirsa and 10 locations were identified for soil sampling. The soil samples were collected at 50 cm depth from ground surface and analysed for different geotechnical properties like specific gravity, particle size, liquid limit, plastic limit, plasticity index, maximum dry density, optimum moisture content and soaked California Bearing Ratio. With the help of particle size distribution curves, coefficient of uniformity and coefficient of curvature were evaluated to find out the gradation of particles. Influence of the geotechnical properties on soaked California Bearing Ratio was studied. Stepwise regression procedure was carried out for the selection of most influencing variables. Incorporating selected variables, multiple regression model was developed for the prediction of soaked California Bearing Ratio. The performance of the multiple regression model was assessed in terms of correlation coefficient, F-statistics and residuals pattern. Using the developed model, soaked California Bearing Ratio can be computed for the study area.
LAND DEGRADATION IN THE DEVELOPING WORLD: ISSUES AND POLICY OPTIONS FOR 2020
Land degradation takes a number of forms, including depletion of soil nutrients, salinization, agrochemical pollution, soil erosion, vegetative degradation as a result of overgrazing, and the cutting of forests for farmland. All of these types of degradation cause a decline in the productive capacity of the land, reducing potential yields. Farmers may need to use more inputs such as fertilizer or manure in order to maintain yields, or they may temporarily or permanently abandon some plots. Degradation may also induce farmers to convert land to lower-value uses. For example, farmers may plant cassava, which demands few nutrients, instead of maize, or convert cropland to grazing land.