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Influence of Soft Soil Samples Quality on the Compressibility and Undrained Shear Strength – Seven Lessons Learned From the Vistula Marshlands

Konkol Jakub

Studia Geotechnica et Mechanica

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2023

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Vol. 45, nr s1

262--281

EN

This technical article presents the influence of sample quality on the compressibility parameters and undrained shear strength (cu) of soft soils from the Vistula Marshlands. The analysis covers: (1) quality of soft soil according to three criteria: void ratio (Δe/e0 index), volumetric strain (Δɛv) and Cr/Cc ratio; (2) influence of storage time on quality; (3) influence of sample quality on undrained shear strength (cu), and (4) reliability of compression and undrained shear strength parameters estimation. The sample quality of three different soft soils (peat, organic clays, and organic silts) was investigated using dataset of geotechnical investigations from the Vistula Marshlands. The reliability of oedometer tests and compressibility parameters determination was shown. Different undrained shear strength estimates (from lab and field tests) were juxtaposed with sample quality. In situ estimates of undrained shear strength were compared with results of triaxial tests and direct simple shear test on reconstituted samples as well as SHANSEP estimates. The results of research are grouped in seven lessons. The most important outcomes are: (1) the quality of samples is at best moderate or poor and there is no significant influence of storage time on sample quality, (2) regardless of testing method, the undrained shear strength natural variability of the Vistula Marshlands soft soils is between 20% and 50% depending on deposit depth and soil type, (3) the most accurate estimation of undrained shear strength can be obtained from field vane test (FVT) while unconsolidated, undrained compression (UUC) triaxial tests should be avoided, (4) SHANSEP approach can be considered as a valuable estimate of cu (next to the FVTs), which additionally allows in relatively easy way to establish lower and upper bounds of cu.

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Analysis of using the empirical model of organic soil consolidation to predict settlement

Meyer Zygmunt, Olszewska Magdalena A.

Architecture Civil Engineering Environment

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2023

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Vol. 16, no. 2

111--117

EN

The paper describes two models for determining the constrained elasticity modulus of organic soils based on the settlement of an overloading embankment. In these methods, based on the settlement of the embankment of the load exerted on the subsoil, using the inverse problem, it is possible to determine the constrained modulus. A parameter determined in this way can also be determined during consolidation. Changes in the settlement at successive stages of consolidation can be used to determine the constrained modulus of the organic soil at a given point in time. Assuming a “temporarily stable” (quasi-stationary) state at each analysed stage of consolidation. The constrained elasticity modulus was determined for the settling at a given moment. constrained modulus tests of organic soils were carried out for two embankments previously described in the literature. In this case, the modulus was also analysed during consolidation. These embankments are founded on peat and peat-gyttja substrates. In both cases, the layer of organic soil was 4 m. The presented methods with the assumption of a one-dimensional state of deformation, despite the state of spatial stress, can be used during construction using the “design and build” technology. The constrained modulus determined from the embankment overload will represent the actual deformations – volumetric deformations (including other deformations that actually occurred) during the consolidation period. The paper was concluded with several conclusions.

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Interpretation of CPT and SDMT tests for Lublin loess soils on the example of Cyprysowa research site

Nepelski Krzysztof

Budownictwo i Architektura

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2019

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Vol. 18, nr 3

63--72

EN

This paper presents an example of interpretation of in situ tests, CPT static sounding and seismic Marchetti dilatometer tests (SDMT). The studies were carried out on loess soils in Lublin. Four CPT tests and four SDMT seismic tests were performed. The method of deriving geotechnical parameters from in situ testing was described. In particular, the formulas for calculating the constrained modulus based on the cone resistance qc were analysed. Some of the parameters were interpreted with the use of proposed formulas. Values of deformation parameters determined with various methods for different strain ranges were compared.