Study to Investigate Variation of California Bearing Ratios of Soil Materials with Changes of Soaking Duration

Abstract

The study was conducted to investigate variation of CBR values with soaking duration. Four sample materials were used for laboratory tests which are cinder and natural pozzolan from Ituha borrow pit, clay soil from Mlimanyoka borrow pit in Mbeya region and then the three source materials were blended together to obtain a fourth sample materials. Characterizations of soil materials were conducted including maximum dry densities (MDD) and optimum moisture contents (OMC) were determined. The results for MDD and OMC for the four soil samples are 1680kg/m³ and 13.2% for cinder, 1543kg/m³ and 19.5% for natural pozzolan, 1524kg/m³ and 23.4% for clay and 1642kg/m³ and 15.6% for blended sample  respectively. The variation of California bearing ratios (CBR) for four soil samples were determined. The CBR values of sample materials were determined for unsoaked samples, 4 days, 8 days and 12 days soaking duration. The results of CBR values at 95%MDD for the four samples soaked for four days are 16.5% for cinder, 23% for natural pozzolan, 4.8% for clay soils and 27.4% for the blended sample. The results indicated that there are exponential decrease of CBR values with increasing soaking duration to the residual values after fully saturation of soil sample. The high CBR values of blended sample enhanced by interlocking and friction properties of the mixtures and addition of clay which act as binder to none plastic soils. It is important to determine CBR values at longer soaking duration than 4 days whenever the soil materials are to be used in areas with high water tables and frequent rainfalls. For easy estimation of CBR values for a particular soaking time, an equation has been developed, which will reduce time for laboratory works to determine CBR values at longer soaking duration.