Determination of the designed deformation properties of soils under radial stresses inside the borehole

The paper presents a method for determining the deformation modulus of soils using a sand pleximeter installed inside a borehole. Radial stresses generated by the compressed sand core produce measurable wall displacements, which form the basis for evaluating the deformation modulus. The limitations of the classical Lamé solution-particularly its overestimation of radial stress decay due to the negligible tensile capacity of soils-are highlighted. To address this, new coordinate functions are proposed and calibrated with laboratory data, showing significantly better agreement with measured stress attenuation. The study also analyzes the corresponding radial displacement fields and outlines practical applications of the obtained modulus in geotechnical design.