The article presents test results on the use of the flat dilatometer test (DMT) to evaluate changes in undrained shear strength su in soils of various origins. Reference values for the undrained shear strength calculated with Marchetti’s original formula were su values obtained from the piezocone penetration tests. The tests were conducted at eight investigation sites in Poland, where five groups of soils were separated: loess-deluvial, loess-deluvial cemented, young till, aged till, and Pliocene clay. The soils exhibited varied overconsolidation effects. The study results revealed that the factors influencing the relationship between undrained shear strength and the KD coefficient from DMT test were various because of the origin, grain size distribution of the soils and cementation. In order to include the influence of overconsolidation and grain size distribution in calibration of su from DMT, a modified KD1 coefficient was introduced into the formula describing this relationship. The final solution was obtained with multiple linear regression. A relatively high statistical evaluation of this relationship was determined for aged till and deluvial and uncemented loess.

The paper contains the analysis of the influence of overconsolidation effect on the values of constrained moduli, assumed by means of two most popular in situ advanced tests. The tested soils included two geological formations: normally consolidated tills of the Pomeranian phase and overconsolidated tills of the Posnanian phase. The overconsolidation ratio (OCR) was derived from CPTU, DMT and oedometric tests. The tests revealed that for the assessment of changes in constrained modulus in the subsoil with CPTU and DMT, the formulas determining the relationship between cone resistance, DMT results and constrained moduli requires empirical coefficient different for soils of varied genesis.

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This paper shows an example of the grouping of piezocone penetration test (CPTU) characteristics using functional data analysis, together with the results of clustering, in the form of a subsoil rigidity model. The subsoil rigidity model was constructed based on layer separation using the proposed method, as well as the k-means method. In the construction of the subsoil rigidity model, the constrained modulus M was applied. These moduli were determined from empirical relationships for overconsolidated and normally consolidated soils from Poland based on cone tip resistance.