ENGINEERING-GEOLOGICAL MAPPING OF TROPICAL SOILS FOR LAND-USE PLANNING AND GEOTECHNICAL PURPOSES - A CASE-STUDY FROM JAMAICA, WEST-INDIES

An area of a Tertiary and Cretaceous deposits, 100-310 m above sea lev el and on predominant 20-45 degrees, highly dissected, concave slopes was investigated to assess its geotechnical characteristics and land u se planning implications. Lithologies include turbidites, fluvial cong lomerates, breccias, sandstones, mudrocks, carbonates, granodiorite, a cid dykes, chloritized and epidotized volcanics, andesite and Holocene fluvial deposits. Bedrock is highly fractured and sheared, hydrotherm ally altered and highly weathered. Soils are quite variable, with a st rong geological control on soil properties. Soils are generally sandy to gravely, with local silts and clays in mudrocks, within Holocene al luvium or in hydrothermally altered and sheared granodiorites. The soi ls are composed of 0.14-80.00% gravel; 5.36-62.50% sand, 2.33-50.55% s ilt, 0.17-51.50% clay, and total fine content between 2.50 and 94.50%, with natural moisture between 4 and 44% during the dry season, plasti c limit between 6 and 35%, liquid limit between 19 and 83% and plastic ity index between 1 and 59%. Sandy soils have residual friction angles between 19 and 39 degrees, PI values less than 35% with cohesion betw een 1.00 and 5.27 KN/m(2) for cohesive samples. ASTM classification of soils include soil groups GC, GM, GW, GP, SP, SM, SC, SM, SC, ML, CL and CH. Based on the characteristics of the terrain, the geotechnical and land use planning problems include high landslide frequency and su sceptibility, soil erosion, fluvial and reservoir sedimentation, high debris flow hazard, cut slope failures, potentially expansive clays an d silts, seepage erosion and soil piping, differential settlement in i nterlayered competent and incompetent lithologies, high solution erosi on and potential subsidence over limestones, waste water disposal prob lems and groundwater pollution and seismic induced settlement and grou nd failures. These phenomena suggest that systematic site investigatio ns should be conducted prior to the utilization of these areas for con struction and development in order to minimize the deleterious effects resulting from ground failure.