An Investigation of some factors influencing the use of colliery discards as a fill material for reinforced earth construction

Abstract

This thesis is concerned with an investigation of some factors influencing the use of coarse colliery discards as a fill material for reinforced earth construction. The work carried out in this study is primarily a laboratory study, investigating the properties of the fill materials, reinforcements and the soil-reinforcement interaction coefficients. Test were carried out on Cardown colliery discards to establish the geotecnical properties and to establish weather the discards satisfied the criteria set out by BE3/78(revised) and the DTp specification for Highway works(1986). Instruments ranging fro free field strain coils were used to measure strains in the soils. All methods utilised are reported. But, the success of the methods considered varied due to the nature of the fill materials.A through investigation was carried out to establish the shear strength envelope. The shear strength envelopes were established, they are as follows: i0 Particle sizes pertaining to the whole grading curve; ii)Specific particles size ranges; These tests indicate that the envelope can e segregated into two sections, one for the low stress region and another for the high stress region. The results of the former indicate tht the shear strength is stress dependent and can be accurately fitted by curvilinear regression analyses. The interaction tests carried out in this study and the data reviewed fro the other sources when represented non-dimentionally indicates that the RMS strips and the Tenser SR2 grinds yield the highest alpha values and hence the coefficients of friction. The result of shales tested with RMS strips yeild the highest coefficients of interaction. Envelopes have been formulated, subsequent to the collection of data for all the materials considered in this study. The results indicates that the alpha values as presented in BE3/78(re viced) are conservative, in the case of the RMS strips. The pull-out tests carried out in this study indicates that the RMS strips are the most efficient of all the conventional strips. The grid tests yielded the highest pull-out forces and they were most efficient of all the reinforcements tested. The field pull-out test data as reported by we indicated that the friction coefficients were lower with respect to the laboratory Data. This can be attributed to the difference in compaction. Comparison of the coefficient of friction indicates that the skin friction tests as measured in the shearbox are lower with respect to the pull-out test data. An equation was formulated using the results of the established Mohr envelopes with respect to particle size, skin friction tests and the spacing of the ribs in a RMS strip. The predicted values are accurate to within 10% of the measured values. The assessments of the cost benefits of using collier discards as the fill materials indicate that the benefit of colliery discard utilization is dependent on the cost of the fill and the haulage costs. With the benefits being over 30% with respect to conventional structures. The results of this study indicate that colliery discards when carefully selected and tested can be used as a fill material in reinforced earth constructions.