Geotechnical Characteristics for a Proposed Power Plant Foundation in Coastal Plain Sand, within Calabar Metropolis, Cross River State Nigeria

  • Benneth Awusa
  • Abidemi Awodeyi
  • Felix Edet
Keywords: foundation, coastal sands, settlement, bearing capacity


Construction of safe civil structure requires sufficient geotechnical data in order to determine the safe bearing capacity of the soil and rock materials, with the aim of recommending suitable foundation. In this study, geotechnical characteristics of coastal plain sand for design and construction of power plant foundation in a coastal plain sand, Calabar, has been carried out. Soil samples were collected from different locations within the study site. These samples were subjected to physical and geotechnical tests. Atterberg limits results revealed that the materials are of relatively low compressibility, with the liquid limit (LL) ranging from 26-32%. The plastic limit (PL) ranged between 15% and 21%, while the plasticity index (PI) ranged between 9% and 11%. The natural moisture content had a mean value of 23%, while the unit weight ranged from 16kN/m3 to 21kN/m3 and specific gravity (SG) values from 2.69-2.71. The samples had coefficient of uniformity (CU) and coefficient of curvature (CC) values ranging from 2.5 to 4.0 and 0.840 to 1.157 respectively, indicating that the sands are poorly graded. Secondary CPT penetrometer sounding record has mean ultimate and allowable bearing capacity values of 213.3kN/m2 and 85.3kN/m2. The soil samples underlying the study area have a medium shear strength with a mean value of 49kN/m2. The maximum dry density of the soil in the area averaged 17.8Mg/m3, which indicated a soil of low compressibility which is suitable as sub-base material. The subsurface log revealed a soil of medium dense to dense with two different soil strata/layers with ultimate and allowable bearing capacity of the soil averaging 561kN/m2 and 224kN/m2. Thus, with an allowable bearing pressure average 224kN/m2, a shallow foundation of raft/mat type will constitute low settlement, provided the maximum allowable bearing pressure is not exceeded.