Evaluation of the relative density based on flat dilatometer test

Overseeing the relative density of soils in all types of earth structures during both construction and operation is crucial to ensure that these structures attain the necessary density and strength. Especially in linear structures that extend over significant lengths, geotechnical investigations should include planning tests that allow for determining the maximum number of geotechnical parameters, such as cone penetration tests (CPTU) or Marchetti dilatometer tests (DMT). The article presents the in situ tests aimed at assessing the relative density of sandy soils. Empirical formulas available in the literature for determining the relative density D_r from DMT gave inconsistent results compared to those obtained from dynamic soundings, especially in the near-surface zone, where high K_D readings significantly overestimate relative density values. Assuming the results of DPL probe tests as reference values, a formula for the compaction index based on DMT soundings has been proposed. In contrast to the formulas commonly used in the literature, the proposed formula for the relative density depends not only on the horizontal stress index K_D, but also on the dilatometer modulus E_D.