Improved correlation of soil modulus with SPT N values

Abstract

Determining soil “E” (modulus of deformation) value has been a persistent challenge in geotechnical engineering. Existing correlations between “E” and SPT (standard penetration test) “N” values for granular soils yield a notably broad spectrum of “E” values, leading to uncertainty and subjectivity in design. A comprehensive review of these correlations reveals significant limitations, such as limited data, small-scale or indirect tests, and other constraints. The present study highlights the deficiencies inherent in existing correlations and proposes a reliable correlation for granular soils. The present study utilizes the results of numerous large-scale load tests conducted on RCC (reinforced cement concrete) foundations resting on granular soils, at various locations in India and at a refinery site in Nigeria. These tests totalling 85 in number serve as a basis for developing an improved and reliable E–N correlation for granular soils. Soil “E” values (secant) were back-calculated for each footing load test result and correlated with SPT “N” values. The correlation presented in this article is based on a sound large database and yields higher “E” values than those predicted by most available correlations. This advancement will lead to substantial cost savings and enhanced reliability in the design of foundations and substructures.

Keywords

• modulus (e)
• spt
• n values
• design of foundations
• large-scale footing
• e–n correlation