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O precyzji sondowania statycznego na przykładzie badań gruntów przejściowych poletka badawczego AMU Morasko

Wierzbicki Jędrzej, Młynarek Zbigniew, Wołyński Waldemar

Przegląd Geologiczny

2020

Vol. 68, Nr 8

655--662

The Cone Penetration Test is one of the most versatile and widely used geotechnical tests over the world. Some differences in technical solutions between the equipment manufactured by different producers and the relatively quick wear of the penetrometer itself make the issue of quality and comparability of the CPTU results very actual. The tests were conducted in the testing ground of Adam Mickiewicz University in Poznań. The test site is located in the northern part of Poznań, within a marginal zone of the Poznań Phase of the Weichselian (Vistulian) glaciation. The subsoil consists of glacial till of the Riss glaciation and glacial till of the Vistulian glaciation, separated by fluvioglacial sandy sediments and covered with fine and medium sands with single gravel grains. The quality of geotechnical parameters of the tested subsoil was assessed for the initial constrained modulus and undrained shear strength. To determine these parameters, static penetrometers produced by two different manufacturers were used. The tests and the results of analysis were performed in three stages. In the first stage, each penetrometer was used to investigate homogeneity and diversity of the subsoil structure in the test sites. The subsoil structure diversity was examined by grouping statistically similar Rf coefficient values along the profile. In the second stage, the level of accuracy and precision in the assessment of the corrected cone resistance - qt, friction on the friction sleeve-fs, and pore pressure - u2 was determined for individual penetrometers. In the next stage, the differences between the constrained modulus and undrained shear strength were determined for both penetrometers. This analysis takes into account the level of precision of the corrected cone resistance.

Problem wyznaczania wytrzymałości na ścinanie gruntów przejściowych

Radaszewski R., Stefaniak K.

Przegląd Geologiczny

2017

Vol. 65, nr 10/2

864–872

The paper deals with the issue of determining intermediate soil strength parameters. Particular attention has been drawn to a selected number of issues related to the examination of this type of soils, inter alia limited possibilities of collecting a high quality sample for laboratory tests along with selecting test procedures. Particular attention has been given to discrepancies between obtained results depending on the applied test procedure. The analysis covered test results of undrained shear strength (su) of normally consolidated soils of low plasticity, according to PN-ENISO 14688 soil types: saSi and clSi,from 3 testing grounds in the Poznań region. Laboratory tests were performed on samples of intact structure (NNS) in the triaxial apparatus (TXT) and direct shear apparatus (AB-2a). In the latter case, reconstituted samples were also analysed (PR). Field research was conducted using probes: static CPTUprobe and rotating PSO probe. The results, which require further confirmation, indicate that the adopted formula of working interpretations of CPTU probing results is of significant importance in assessing shear strength; Nkt coefficient in particular. The paper proposes modification of its most often used value into a value in which there was convergence of the results obtained with the use of both types of probes: CPTU and PSO. It was noted that velocity of applying shear stress has a significant impact on the final shear strength result. A possibility of using the PSO probe as a calibration test with reference to CPTU was suggested ifperforming the more advanced TXT test was not possible. It was also indicated that the test procedure in theAB-2a apparatus needed to be verify in order to obtain a tendency of shear strength changes comparable to the field studies. The results obtained confirm the need to prepare a repetitive canon of tests (test instructions) of intermediate soils that would enable adequate interpretation of their properties.