Estimation of four-day soaked CBR using index properties

California Bearing Ratio (CBR) is an important parameter used to evaluate the strength of subgrade and sub-base soils for design of flexible pavements and hence it plays a significant role in road and highway constructions. Obtaining CBR is heavily time consuming and it is difficult to acquire a representative CBR value. Therefore, many correlations have been developed by various researchers worldwide to predict the CBR. Due to differences in soil formations in the tropi­cal environment, these existing global correlations found to be not satisfactory with local soils in Sri Lanka. Hence, this study was carried out to develop empirical correlations between CBR and index properties those best suit for local soils, using the data obtained from Atterberg limits and sieve analysis tests together with compaction tests. The new correla­tions were established using the method of regression analysis in the form of empirical equations representing the role of index properties. Robust regression by the method of least absolute residuals using MATLAB was considered in the analysis to reduce the impact of outliers along with traditional multiple regression using Microsoft Excel. As a final ver­ification, several laboratory tests were conducted to compare the results with proposed regression equations

Use of flyash to improve soil properties of drinking water treatment sludge

Abstract Improvement of soft soil using cementitious additives is a widely practiced technique in the construction industry. However, cement mixing is considered to be an expensive technique and this research has attempted to study the use of an industrial waste; flyash to improve a drinking water treatment sludge. Flyash is a fine, glass powder recovered from the gases of burning coal during the production of electricity at Norochchole, thermal power plant in Sri Lanka. The larger amount of drinking water treatment sludge which is a very soft clayey soil, is disposed into the environment without acquiring any benefit. Use of flyash in improving soft soils such as sludge with a low maximum dry density and low CBR will solve few burning issues such as dumping of flyash and sludge, health issues due to disposal of flyash and sludge, difficulties to find soils with better properties for road constructions and other construction related applications. Identifying the characteristics of the sludge, studying the variation of maximum dry density and optimum moisture content with flyash content, strength gain with time, and the applicability of the improved soil in the industry are the key findings and observations of this study. It was observed that the optimum proportion of the flyash to be added to the sludge to achieve a remarkable gain in its properties is around 30% of its dry weight. Acceptable CBR value was achieved after 7 days curing followed by standard 4 days soaking period