Constrained modulus of fine-grained soils from in situ-based correlations and comparison with laboratory tests

¹ In Situ Site Investigation, St. Leonards on Sea, UK
² Geolabs Limited, Watford, UK

^* Corresponding author: jpowell@geolabs.co.uk

Abstract

The Constrained Modulus of soil is an important parameter to quantify compressibility of soils and calculate consolidation settlements, especially for clays. It is often expressed in terms of 1D constrained modulus, M or its inverse coefficient of volume change, m_v. One method that has been suggested to assess M is from Cone Penetration Testing (CPTU) measurements through various correlations. Although, this is sometimes difficult, because of uncertainties regarding the appropriate stress, σ’_v0, which are highly affected by the groundwater and bulk density γ, of soils. The usual method to measure M (or m_v) is from oedometer tests in laboratory. Correlating in situ tests with laboratory tests results is crucial to increase the quality of soils strengths and stiffness information for design. However, most of the times it is a challenging process, which involves many uncertainties from different soils’ tests. This paper will look at comparison of CPTU derived M to oedometer tests taking into consideration various types of soils mostly from well-documented testbed sites where high quality in situ (CPTU for all sites and SDMT where available) and oedometer tests are carried out. The importance of CPTU measurements and site-specific correlations with laboratory tests to establish unique soil type coefficients for use in equations to derive CPTU-based M will be highlighted.