Experimental Investigation For Hydro-Mechanical Coupled Characteristics Of Laterite Soil In Rwanda

In order to study the hydro-mechanical behaviour of laterite soil,experimental investigation of the soil was conducted.The laterite soil samples from Kigali Economic Zone are taken as the research objects,and the strength characteristics of laterite soil are investigated using laboratory tests with consideration of the influence of water content and dry density.The volume change behaviour of laterite soil was obtained by consolidation test,the filter paper method was used to assess the soil water characteristics curve.Moreover,the direct shear test and triaxial test were conducted to investigate the shear strength of laterite soil.Finally,the tensile test was used to study the tensile strength of the laterite soil.The main findings,conclusions and suggestions of the research include:1)Through multiple sets of experiments,the void ratio and pressure curves and the compression modulus curves were obtained from Consolidation tests by taking into consideration different initial water contents of 19%,22%,25%,and 28%and dry densities 1.5g/cm3,1.6g/cm3 and 1.7g/cm3.The findings of the study highlighted that,both void ratio and compression modulus decrease with the increase of water content while,the increase of dry density lead to the decrease of void ratio and increase compression modulus.2)The soil-water characteristic curves of unsaturated laterite soil under water contents 20%,22%,24%,and 26%and three different dry densities 1.5g/cm3,1.6g/cm3 and 1.7g/cm3 were obtained.The results of the matric suction test were fitted using the Van Genuchten(1980)Model and experimental results show that the matric suction decreases with the increase of water content and increases with the increase of dry density.3)The results obtained from direct shear test under different initial water contents 18%,20%,22%,24%and 28%,and different dry densities 1.4g/cm3 1.5g/cm3,1.6g/cm3 and 1.7g/cm3,show that increasing water content in laterite soil resulted to the reduction of its shear strength.The cohesion and internal friction angle decrease with the increment of water content while they increase with the increment of dry density.4)The unconsolidated undrained triaxial test was used to study the characteristics of principal stress versus the strain curves of unsaturated laterite soil under different initial water contents 20%,22%,24%,26%and dry densities1.5g/cm3,1.6g/cm3 and 1.7g/cm3.The results indicate that the change of shear strength is mainly due to the influence of water content.The cohesion and internal friction angle decrease with the increase of water content and increase with the increase of dry density.5)The relationship between tensile strength,different water contents 18%,20%,22%,24%,26%and 28%and different dry densities 1.2g/cm3,1.3g/cm3 and 1.4g/cm3 was obtained by conducting the tensile tests.The results indicate that the tensile strength of unsaturated laterite increases first with the increase of water content and then decreases gradually with the increase of water content after reaching a peak point and the tensile strength of laterite soil increases with the increase of dry density.Finally,the observations from this study highlight that,water content is one of the major factors among others that highly affect the mechanical properties of the studied laterite soils.