DESIGN CORRELATIONS FOR KENYA RED AND RED-BROWN SOILS

IN ANTICIPATION OF AN EXTENSIVE ROAD DEVELOPMENT PROGRAM AND THE INTRODUCTION OF CEMENT AND LIME STABILIZATION, SOIL PROPERTIES WERE INVESTIGATED AND CORRELATIONSHIPS WERE SOUGHT WHICH MIGHT REDUCE THE VOLUME OF DESIGN TESTING. THE TWO KINDS OF RED SOILS FOUND IN KENYA CAN ONLY BE CLASSIFIED IN A SYSTEM BY INTRODUCING MAXIMUM DENSITY AND OPTIMUM MOISTURE CONTENT RANGES. THE REQUIRED PAVEMENT THICKNESS TO CARRY A 9,000-LB. WHEEL LOAD CAN BE CORRELATED WITH THE GROUP INDEX. CORRELATION STUDIES HAVE REVEALED THE APPARENT IMPOSSIBILITY OF DIFFERENTIATING BETWEEN THE TWO FORMS OF HALLOYSITE SOILS ON THE BASIS OF NORMAL ENGINEERING DATA. SOIL PROPERTIES OF THE KENYA RED AND RED-BROWN SOILS ARE PRESENTED. CBR VALUES, OPTIMUM MOISTURE CONTENT, AND MAXIMUM DENSITY ARE PRESENTED FOR THE SOILS TESTED. COMPACTION AT OPTIMUM MOISTURE CONTENT GIVES A CONSTRUCTION MOISTURE CONTENT TOLERANCE WITHOUT ANY LOSS IN STRENGTH. WHEN THE PLASTIC LIMIT IS APPRECIABLY BELOW THE PROCTOR OPTIMUM, THE MATERIAL IS CONSIDERED UNSUITABLE FOR USE. MINERALOGICALLY, THE TWO SOILS ARE SIMILAR IN THAT THEY WILL CONTAIN SOME CLAY MINERAL OF THE MONTMORILLONITE GROUP. HOWEVER, THEY ARE LIKELY TO DIFFER IN THE NATURE OF THEIR SURFACE CHEMISTRY BECAUSE OF THE DIFFERENCE IN THEIR ADSORBED IONS. THE KENYA BLACK COTTON SOILS ARE USUALLY ALKALINE AND IT IS BELIEVED THAT THESE SOILS GIVE ISO-CBR PATTERNS. THESE BLACK COTTON SOILS SHOULD BE COMPACTED AT A MOISTURE CONTENT BELOW PROCTOR OPTIMUM TO REDUCE THE POSSIBILITY OF THE MAXIMUM MOISTURE CONTENT REACHING VALUES IN EXCESS OF THE PLASTIC LIMIT AND CAUSING PAVEMENT DISTORTION.