In-Situ Plate Load Test Measurements of Stress Distribution Properties for Coarse Unbound Granular Materials

A field test was conducted to study in-situ stress distribution of coarse crushed rock (CR) materials. The existing literature on CR materials with upper sieve size > 90 mm is very limited, and there is a need to characterize these materials and validate the application of existing theory and models for unbound granular materials. The objective of this paper is to compare plate loading test (PLT) measurements on two CR subbase materials, and to analyze and compare computed and measured vertical stresses below subbase layers of these materials: open-graded CR 22/125 mm and dense-graded CR 0/125 mm. Earth pressure cells (EPCs) were installed to measure vertical stress at 0.6 m depth, σ 0.6 , during static PLTs with 300 mm plate diameter. The ratio of σ 0.6 to the average stress at the surface, σ 0 , was compared with outputs from Boussinesq’s theory and multilayer nonlinear analyses in KENPAVE. The average σ 0.6 for all loading levels during the second cycle of PLT was 41% higher for CR 22/125 as compared to CR 0/125. The average ratio Δσ 0.6 /Δσ 0 for EPC measurements were 12.4% and 9.7% for CR 22/125 and CR 0/125, respectively. Based on Boussinesq’s theory, Δσ 0.6 /Δσ 0 was 8.7%. Computed with KENPAVE, the average Δσ 0.6 /Δσ 0 was 5.4% for both sections. The EPC measurements indicate better load distribution properties for dense-graded as compared to open-graded CR. These findings could be applied for empiric design systems by differentiating the load distribution parameters of such materials. Furthermore, the results indicate a need to validate the application of analytical or mechanistic-empirical pavement design tools for pavement structures comprising coarse CR materials.