Comparison of Safe Bearing Capacity Based on Laboratory and Field Tests

Abstract

AbstractSoil is considered by the engineer as a complex material produced by weathering of the solid rock. Soil is the most important material, which is used for construction of civil engineering structures. Among all parameters, the bearing capacity of soil to support the load coming over its unit area is very important. There are various methods for calculation of bearing capacity of soil put forth by scientists like Prandtl, Terzaghi, Meyerhoff, Hansen, Vesic, and others. Principal factors that influence ultimate bearing capacities are type of soil, width of foundation, soil weight in shear zone, and surcharge. Structural rigidity and the contact stress distribution do not greatly influence bearing capacity. Bearing capacity analysis assumes a uniform contact pressure between the foundation and underlying soil. With other factors unchanged, the type of failure of soil, depth of foundation, and effect of water table also govern the bearing capacity of soil. Field tests are very important in knowing the actual performance of soil after loading. Commonly used field tests are plate load test and standard penetration test. In the present study, standard penetration tests are conducted at site. Pit was excavated for different depths, i.e., 1.5, 2.0, 2.5, and 3.0 m, and the soil samples from these depths were collected for determination of its geotechnical properties. Based on these properties, safe bearing capacities were determined by IS code method. At each depth, standard penetration tests were conducted to know the number of blow count “N.” Based on the blow count “N,” safe bearing capacities were determined by empirical equation. The values of safe bearing capacities obtained at different depths by both methods are compared. They show the fairly good agreement at lesser depth of foundation, but as depth of foundation increases, the safe bearing capacity based on blow count “N” is found to be higher.KeywordsStandard penetration testDepthMoisture contentDensityCohesion