Verification of Compressibility and Consolidation Parameters of Varved Clays from Radzymin

Open Geosci. 2018; 10:911–924 Research Article Paweł Dobak, Kamil Kiełbasiński*, Tomasz Szczepański, and Piotr Zawrzykraj Verification of compressibility and consolidation parameters of varved clays from Radzymin (Central Poland) based on direct observations of settlements of road embankment https://doi.org/10.1515/geo-2018-0072 housing building etc. around the world) is necessary for Received May 18, 2018; accepted Nov 13, 2018 the safe design of foundation solutions. The selection of deformability and consolidation parameters as well as cal- Abstract: Formation of varved clays is characterized by culation methods is of a great importance. Very often, as specific compressibility and consolidation features, which a comparable experiences, the laboratory and field com- are difficult to assess. The construction of an expressway pressibility tests results must be verified with the results through the area of varved, glacilimnic sediments (Vistula of behavior monitoring of existing facilities. It allows to in- glacial period) required careful analysis of the soil reac- crease the precision of forecasts, but at the same time it tion to the increasing load caused by growing embank- must be correlated with lithological types of the substrate. ment. The settlement analyses conducted in relation to the In the latest scientific literature, the interesting ex- schedule of load increase during construction allowed to amples of back analysis application to predict corrected verify the deformability assessment of the compressible course of parameters on the basis of soft soils settlements clays. In order to quantify the compressibility and consoli- may be found. In reviewed papers the analysis was based dation parameters of clays, an iterative calculation model on the course of settlement or pore distribution observed was created. The method of the “inverse solution” was under load of embankments or buildings. Different meth- used to define optimized values of deformability param- ods of analysis based generally on exponential curve fit- eters. The observed delayed reaction of the soil to applied ting methods [1, 2] were discussed there, with the applica- load allowed to assess the nature of consolidation. Com- tion of developed consolidation theory: elasto-viscoplastic parison of the parameters obtained from the model with constitutive model [3], coupled flow and deformation in the results of laboratory and field tests allowed to evaluate unsaturated soils [4] and Burgers creep model [5]. The re- drainage characteristics during consolidation of varved sults of these analysis were expressed in different parame- clays as well as to introduce correlation coefficients for in- ters and demanded adequate initial parameters from lab- terpreting compressibility parameters on the basis of CPT oratory and field tests. tests. The values of the obtained parameters reflect the ge- Keywords: varve soils , Warsaw Ice-Dammed Lake basin, ological and engineering characteristic of the analyzed compressibility, consolidation parameters, settlement of soils. These were: estuarine, normally consolidated de- embankments, inversion solution posit from Brisbane in Australia [2], sludge and mucky soils from different province in China costal [1], alluvial soft clay in Japan [3] weathered Mud rock in China [5]. It 1 Introduction is obvious that in soft soils [6] the solution of each engineering task must be strictly correlated with its location and geological and engineering conditions. Evaluation of The accurate deformability prognosis of soft soils under proper values of compressibility and consolidation param- various objects (such as highways and railways, dikes, eters has a wider significance, for example in designing of subsoil reinforcement by preconsolidation [7]. Some investigations are dedicated to analysis of stan- *Corresponding Author: Kamil Kiełbasiński: University of War- dard conditions [8] and specific behaviour of soils which saw Warszawa, Poland; Email: [email protected] depends of their origin [9, 10]. Paweł Dobak, Tomasz Szczepański, Piotr Zawrzykraj: Faculty of Geology, University of Warsaw Warszawa, Poland Open Access. © 2018 P. Dobak et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution- NonCommercial-NoDerivatives 4.0 License 912 Ë P. Dobak et al. The case presented in this article concerns the char- ues of compressibility modulus M determined during lab- acteristics of the course of consolidation and further fore- oratory tests was determined. Such analyzes were focused casts of the soil settlement under the rapid road traffic in on the possibility of applying the results of soundings in northeastern vicinity of Warsaw (Poland). The analyzed the spatial assessment of variability of the deformation pa- section of the road was built on a specific substrate - varved rameters of varved clays. clays - with distinct characteristics in relation to the soft soil discussed commonly in the literature. Compressibility and consolidation characteristic of 2 Geological and engineering varved clays is a complex issue due to structural sensitiv- ity, specific character of post-sediment structural bonds, conditions no consolidation in geological past and anisotropy of mechanical and filtration properties within thin (several 2.1 Geomorphological location mm), alternate layers. In comparison to clays of different origin, these soils show different nature of deformability, The typical area of occurrence of varved clays, so-called what has been confirmed by the results of laboratory and Warsaw Lake Basin [13] (Figure 1), was chosen for the field tests presented in a number of publications [11, 12]. study where sedimentation developed in the initial stages However, these publications do not often take into account of the Vistula glacial period [15, 16]. Later, the erosion that the compressibility depends on stress and changes in in the outer zone of the glacier removed some of the the soil consistency. deposits, leaving structurally undisturbed several-meter- For accurate predictions of settlements, it is necessary long clayey, varved sediments in the lower parts of the to analyze in details the relationship between the com- basin [16–18]. Their behaviour under loads transmitted by pressibility characteristics obtained from: the embankment as well as by later expressway operation – direct laboratory tests, was a subject of further analysis of this study. – indirect empirical correlations on the basis of The analysed research area is located within War- soundings (e.g. CPTu, DMT) saw Basin which is located on so-called Radzymin terrace – field observations of soil settlements under load. (Radzymin-Marki level), which has been created during the Vistula glaciation period [15, 16]. Its core is made of Comparison of above-mentioned three types of data varved clays which origin is connected directly with sed- allows not only to predict the settlements but also to as- imentation stagnation [14]. This terrace is now a flat and sess factors conditioning the course of strain under load extensive plain with an accumulative and erosive charac- for such a specific formation as varved clays. The typical ter. At the end of Pleistocene, it has been remodelled by area of occurrence of varved clays, so-called Warsaw Lake aeolian processes, which caused the formation of irregular Basin, was chosen for the study where sedimentation de- dunes and dune banks [16]. In the upper part or the profile, veloped in the initial stages of the Vistula glacial period. about 1-2 meters thick river sands remodelled by aeolian Later, the erosion in the outer zone of the glacier removed processes may be observed. The lower part of the profile is some of the deposits, leaving structurally undisturbed represented by clays, silty clays, clayey sands and clayey several-meter-long clayey, varved sediments in the lower silts (Figure 2). parts of the basin. Their behaviour under loads transmitted by the embankment as well as by later expressway operation was a subject of further analysis of this study. 2.2 Soil conditions - soil structure and The propose of the study was to present methodical ex- thickness of layers periments regarding the verification and forecasting consolidation behaviour of varved clays which are consid- The geological profile has been recognized down to the ered as geologically specific soil. Those analyzes were sup- depth of the impact of loads generated by the expressway. posed to refer to optional methods of determining com- It is represented by horizontally oriented, quite uniform, pressibility and consolidation parameters. In particular, non-cohesive river deposits and varved clays of glacilimnic it concerned the relationship between back analysis re- origin [14, 17]. sults and the results of laboratory tests carried out un- The first layer is represented by medium-compacted, der incremental loading (IL) and continuous loading (CL) yellow-gray fine or locally medium sand. Density index I with adaptation to changes in the load. The correlation D varies between 0.50 and 0.70. The thickness of these sed- of cone resistance obtained from CPTu tests with the val- Verification of compressibility and consolidation parameters of varved clays from Radzymin Ë 913 Figure 1: Study area location at the background of Warsaw Ice-Dammed Lake bassin. 914 Ë P. Dobak et al. Figure 2: Representative geological cross section. iments is approximately 1.0-2.0 m. These soils have good formation under the expressway embankment demands permeability

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