rss_2.0Studia Geotechnica et Mechanica FeedSciendo RSS Feed for Studia Geotechnica et Mechanica Geotechnica et Mechanica Feed of generalized boundary conditions for homogenization of thermal and filtration properties of soils<abstract> <title style='display:none'>Abstract</title> <p>In the paper, generalized boundary conditions were used for the homogenization of coefficients of the Laplace partial differential equation in the context of Darcy flow and heat diffusion phenomena. The mesoscopic boundary value problem was defined and analyzed from the variational perspective and the finite element formulation of the homogenization problem was provided. The matrix equation for the apparent macroscopic properties, resulting from FEM discretization, was derived and utilized in two illustrative examples: homogenization of the filtration coefficient of clay amended with expanded shale and thermal conductivity of the soil with multiple fractions. It is shown, that generalized boundary conditions can provide very good homogenization results without the assumption of the periodicity of the material. For best results, the microscopic length parameter has to be properly estimated.</p> </abstract>ARTICLEtrue between Cone Penetration Test parameters, soil type, and soil liquidity index using long short-term memory neural network<abstract> <title style='display:none'>Abstract</title> <p>Accuracy and quality of recognizing soil properties are crucial for optimal building design and for ensuring safety in the construction and exploitation stages. This article proposes use of long short-term memory (LSTM) neural network to establish a correlation between Cone Penetration Test (CPTU) results, the soil type, and the soil liquidity index <italic>I<sub>L</sub></italic>. LSTM artificial neural network belongs to the class of networks requiring deep machine learning and is qualitatively different from artificial neural networks of the multilayer perceptron type, which have long been widely used to interpret the results of geotechnical experiments. The article outlines the methodology of CPTU testing and laboratory testing of the liquidity index, as well as construction and preparation of data for the network. The proposed network achieved good results when considering a database consisting of the parameters of eight CPTU soundings, soil stratifications, and laboratory test results.</p> </abstract>ARTICLEtrue effects in horizontally loaded reinforced concrete columns<abstract> <title style='display:none'>Abstract</title> <p>This paper deals with the second-order effects in horizontally loaded reinforced concrete columns. The current standard approach according to Eurocode 2 is the starting point for the considerations. Simplified methods that take into account the secondary effects, that is, the nominal stiffness method and the nominal curvature method, and their limitations are discussed. Most attention is devoted to the general method. As only general guidelines for this method can be found in the literature on the subject, the author presents his own original approach to calculations done using this method. Exemplary analyses for the corbel columns of high bay racked warehouses are made. Columns of different lengths are analyzed. The calculations show the overestimates introduced by the simplified methods and the benefits stemming from the use of the general method, especially in the case of quite slender columns.</p> </abstract>ARTICLEtrue Use of CPTU and DMT Methods to Determine Soil Deformation Moduli—Perspectives and Limitations<abstract> <title style='display:none'>Abstract</title> <p>The article presents the concept of determining constrained modulus—<italic>M<sub>0</sub></italic>, initial shear modulus—<italic>G<sub>0</sub></italic>, Young modulus—<italic>E</italic>, and rigidity index—<italic>I<sub>R</sub></italic> on the basis of parameters from static penetration tests CPTU (Piezocone Penetration Testing), SCPTU (Seismic Piezocone Penetration Testing) and dilatometer tests DMT (Flat Dilatometer Test), SDMT (Seismic Flat Dilatometer Test). The basis for constructing the empirical relationships between the mentioned modules and parameters from the CPTU and DMT studies was to determine the factors that affect these relationships. The article discusses the impact of the following factors; geological and geotechnical conditions, conditions of recording measurements in CPTU and DMT tests, factors relating to the CPTU and DMT testing methods, factors affecting reference parameters from laboratory tests, factors related to subsoil properties. The basis for obtaining the empirical relationships for determining the analyzed modules and rigidity index were extensive research of the soils of various origins, in Poland. Measurement uncertainties and factors influencing the recorded parameters in the CPTU study were documented by the studies of the Norwegian Geotechnical Institute and the former Department of Geotechnics of the Agricultural University in Poznań. In these studies, penetrometers from several reputable manufacturers were used. The article summarizes the established empirical relationships for individual modules, taking into account the effect of overconsolidation. It also comments on the interrelationship between constrained modulus <italic>M<sub>0</sub></italic> from CPTU and DMT test for soils in Poland.</p> </abstract>ARTICLEtrue of Clay–rubber Mixtures for the Transportation Geotechnics—the Numerical Analysis<abstract> <title style='display:none'>Abstract</title> <p>The use of waste materials (including rubber) in industry is one of the most important issues in terms of environmental protection. One of such applications is the use of soil–rubber mixtures in backfills or lower layers of embankments or road structures. The numerical analyses of the behavior of a clay–rubber mixture layer built into a road embankment are presented in this article. An elastic-perfectly plastic model with a Coulomb–Mohr yield surface was used in the finite element analysis. The parameters of soil–rubber mixtures adopted for the analysis were estimated on the basis of triaxial tests: monotonic (UU—unconsolidated undrained, and CU—consolidated undrained) and cyclic (CU) performed with low frequency (<italic>f</italic> = 0,001 Hz). The triaxial tests were carried out on mixtures of kaolin (K) and red clay (RC) with the addition of 1–5 mm rubber granulate (G) in the amount of 5–25% by weight. Numerical analyses included a static plate load test (VSS) of a layer made of a rubber–soil mixture built into the embankment and testing the stability of embankments using the <italic>c</italic>–ϕ strength reduction procedure. The results of laboratory tests confirm the necessity of testing soil–rubber mixtures each time before their use in embankments. The observed overall decrease in shear strength and stiffness of the tested material is variable and depends on the type of soil and the content of rubber waste. Satisfactory results of the analysis were obtained, both in terms of the values of layer stiffness modules and slope safety factors, which allows for the conclusion of the possibility of using soil–rubber mixtures (with the recommended granulate addition up to 30% by weight) in the layers of road embankments and (depending on the road class) in the lower layers of the pavement structure.</p> </abstract>ARTICLEtrue requirements for static liquefaction test of soil in triaxial apparatus<abstract> <title style='display:none'>Abstract</title> <p>Since in the field of research concerning liquefaction phenomenon, the largest database exists for triaxial tests, this type of apparatus was selected as the most relevant. Available data concerning laboratory research on liquefaction tests for identification of undrained response of sand indicated that the results are very sensitive to even smallest incorrectness in the testing procedure. Besides, due to a complex nature of liquefaction phenomenon, it was considered prudent to undertake some efforts directed to increase the objectivity of tests. Therefore, before commencement of the actual test program for investigation of undrained response of soil, it is necessary to carry out some preparatory experimental work consisting of application of indispensable modification necessary for enhancement of a quality of a triaxial test. The paper presents the key issues pertaining to the implementation of the experiment. Significance of these modifications for desired characteristics is emphasized. Relevance of some upgrading of the equipment for liquefaction tests is exemplified.</p> </abstract>ARTICLEtrue Resonant Column and Torsional Shearing Apparatus With Multipoint Contactless Displacement Detection System<abstract> <title style='display:none'>Abstract</title> <p>In this study, a modification of resonant column/torsional shearing (RC/TS) apparatus was proposed to perform a qualitative analysis of a noncohesive soil specimen vibration during RC tests. An additional multipoint displacement detection system was installed in the RC/TS WF8500 device. In the new measuring system, 48 mini-magnets are attached to the side surface of a cylindrical soil specimen, creating a regular grid of measuring points. Around 48 Hall sensors (Honeywell SS495A1) are used to measure changes in the magnetic field strength due to the movement of the corresponding magnets on the surface of the specimen subjected to dynamic torque. The Hall sensor generates an analog signal that is proportional to the change in the magnetic field. The measurements are collected with a newly developed data acquisition system that consists of a set of analog-to-digital converters and a set of ARM (Advanced RISC (Reduced Instruction Sets Computing) Machine) microcontrollers. The measurement system is controlled with a dedicated software, <italic>ControlRec,</italic> developed by the authors. The measurements are taken synchronically with and independently from the standard RC test procedure. The new measuring technique allows to observe displacements of the 48 points on the specimens’ surface with over 4 times higher sampling rate than in the original measuring system. As a result, additional effects related to the mechanical wave propagation through soil specimen were observed (local disturbances in distribution of vibration amplitudes or significant displacements near the bottom end of the specimen, which is assumed to be fixed in the standard RC/TS results analysis), that could not be identified using the standard equipment of the device.</p> </abstract>ARTICLEtrue of Numerical Model in Some Geotechnical Problems<abstract> <title style='display:none'>Abstract</title> <p>The concept of equivalence of the realistic, initial reference model and the simplified, reduced model is proposed. In reduced models, the action of the soil on the structure is replaced by the action of a layer with prescribed properties, defined by a set of parameters. The main difficulty here is to find the parameter values required by the simplified theory. The subject of this work is to find the dependence of the parameters of the reduced model on the parameters of the full model, including realistic soil behavior, in order to ensure the equivalence of both models. We show the potential of the method by presenting two examples: Winkler and Pasternak's model of a plate on the ground. We assume that both models are equivalent if they give identical results (displacements) at a finite number of observation points. An artificial neural network (ANN) is built in order to approximate and record the dependence of the parameters of the reduced model (at the network output) from the parameters of the full model (given at the network input). The complex network acts as a formula that assigns the parameters of the reduced model to a realistic description of the soil structure that is used for finite element method (FEM) modeling. The formalism we propose is quite general and can be applied to many engineering problems. The presented procedure is entirely numerical; it allows to calculate the parameters of the reduced model without resorting to symbolic calculations or additional theoretical considerations.</p> </abstract>ARTICLEtrue of Methods for Determination of Stress History Parameters in Soils<abstract> <title style='display:none'>Abstract</title> <p>Stress history acquired by any cohesive soil influences, to a large extent, three groups of fundamental properties indispensable in geotechnical design i.e. state of soil, shear strength, and stiffness characteristics. The basic stress history parameter (from which other parameters are derived) determined directly from laboratory tests is a preconsolidation stress <italic>σ′</italic><sub>p</sub>. Since the first method proposed by <xref ref-type="bibr" rid="j_sgem-2023-0017_ref_006">Casagrande in 1936</xref>, value <italic>σ′</italic><sub>p</sub> is determined in the oedometer test as a border between overconsolidated (OC) and normally consolidated (NC) zones. Approach based on division between predominantly elastic, (recoverable) strain, and plastic (irrecoverable) strain is a main principle of several methods of <italic>σ′</italic><sub>p</sub> determination, which have been proposed over the past eighty-six years.</p> <p>Accumulated experiences have revealed that any laboratory procedure based on the oedometer test does not provide realistic value of preconsolidation stress, especially in heavy preconsolidated soils. The major reason for that results from the fact that the mechanism responsible for natural overconsolidation is more complicated than mechanical preloading. Therefore, there is a necessity to reevaluate effectiveness of standard methods and look for another solution of evaluation yield stress <italic>σ′</italic><sub>Y</sub> in natural soils.</p> <p>This article presents the comparison between <italic>σ′</italic><sub>Y</sub> determined for various soils with use of standard methods based on conventional oedometer test and yield stress determined on the basis of alternative procedures. The latter are represented by various approaches as e.g. based on SHANSEP procedure or initial shear modulus and others. The most promising among these alternative methods is a new concept based on dilatancy phenomenon that takes place during shearing of a dense soil. The parameter reflecting stress history is derived from pore pressure response and is based on characteristic values of Skempton's parameter A record. Consistency of data concerning stress history parameters profile obtained for deep subsoil on the basis of various methods is shown for comparison.</p> </abstract>ARTICLEtrue Deformation During the Construction of Record Span Soil-steel Buried Structure in Ras-Al-Khaimah (UAE)<abstract> <title style='display:none'>Abstract</title> <p>The algorithm presented in this paper concerns the processing of data in the form of coordinates of measurement points located around the structure periphery, obtained from the geodetic measurements. The geometric parameter used here to study the deformation of the steel shell is the change of curvature. It is used to estimate the bending moment and hence the normal stress in the corrugated steel shell. The results given in the examples of calculations of the analyzed structure show the possibility of determining places with extreme values. For this purpose, a dense layout of measuring points and use the precision geodesy technique is necessary. Of significant importance in stress estimation is the correction of the geodetic measurement base. This is due to the fact that the points in the initial measurement do not lie on a section of the circle as a reference curve, used to determine the deformation of the shell.</p> </abstract>ARTICLEtrue Work Criterion in the Stability Analysis of an Earth Dam Subjected to Seepage<abstract> <title style='display:none'>Abstract</title> <p>Failure may take different forms: reaching the Mohr–Coulomb limit stress condition is accompanied by yielding, strain localisation may occur in shear, compaction or dilatant bands, arbitrary large strain and loss of strength may be accompanied by a field of chaotic displacements of soil particles. Failure is also related to material instability. It takes place when there is a loss of uniqueness of constitutive relationships. It has been found that instability domains exist strictly inside the Mohr–Coulomb failure surface. Material instability can be detected by local Hill's criterion, that is the second-order work at a point. Results of a coupled hydro-mechanical finite element analysis of an ‘earth dam – subgrade’ system at changing hydraulic boundary conditions have been presented in the article. Normalised values of the second-order work and factor of safety values by the shear strength reduction procedure for corresponding stages of the analysis were calculated. It has been shown that the value of the safety factor corresponds to the values of the second-order work. The analysis results show that a decrease in the value of the safety factor is accompanied by a decrease in the value of the second-order work until negative values occur at some points.</p> </abstract>ARTICLEtrue of Screw Displacement Pile-Bearing Capacity Based on Drilling Resistances<abstract> <title style='display:none'>Abstract</title> <p>This article presents an engineering, empirical method of estimating the bearing capacity and settlement characteristics <italic>Q-s</italic> of screw displacement piles and columns, based on soil resistance encountered during the drilling to form piles/columns in the ground. The method was developed on the basis of correlation analyses of the test results of 24 piles made during the “DPDT-Auger” research project (<xref ref-type="bibr" rid="j_sgem-2023-0014_ref_011">Krasiński et al., 2022a</xref>). In the proposed method, the load capacity of a screw displacement pile is estimated using two main parameters of auger screwing resistance: torque <italic>M<sub>T</sub></italic> and the number of auger rotations per depth unit <italic>n<sub>R</sub></italic>. The method applies to piles and columns made with a standard <italic>screw displacement pile</italic> (SDP) auger and with the proprietary, prototype DPDT (<italic>displacement pile drilling tool</italic>) aguer, patented in Poland (2020). Based on the estimated ultimate capacities of the pile shaft and base, an approximate method of predicting the pile settlement characteristics <italic>Q-s</italic> was also proposed, using the transfer function method. This article describes a correlation procedure of field test results together with their statistical analysis and presents a method of estimating the pile-bearing capacity based on correlation results. A calculation example is also provided. The conclusion looks at the useful practical applications that could be found for the proposed method.</p> </abstract>ARTICLEtrue of the Addition of Dispersed Reinforcement on the Resilient Modulus of Slightly Cemented Non-Cohesive Soil<abstract> <title style='display:none'>Abstract</title> <p>The aim of this article is to determine the effect of the addition of dispersed reinforcement on the resilient modulus of non-cohesive soil used as material for improved subgrade or subbase course of the pavement structure. Resilient modulus (<italic>M</italic><sub>r</sub>) is a parameter used in road construction, which characterises soil subgrade or base aggregates stiffness in flexible pavement subjected to the traffic load. This article presents laboratory test results of non-cohesive coarse material (gravelly sand – grSa – without fines) with the addition of 1.5% cement and dispersed reinforcement – polypropylene fibres in lengths of 12, 18 and 40 mm. Tests were conducted on the samples with various percentages of fibres (0, 0.2 and 0.3%) relating to the dry mass of the soil. Samples were compacted according to the standard Proctor (SP) and modified Proctor (MP) methods. Main laboratory tests were conducted in the triaxial apparatus enabling testing samples subjected to cyclic loads according to AASHTO T307 standard. Resilient modulus was determined after 7 and 28 days of curing. The results indicate the influence of fibre amount, fibre length, and curing time on the <italic>M</italic><sub>r</sub> of the soil modified with 1.5% of cement. The obtained results were also influenced by the method of compaction. The addition of polypropylene fibres decreases the resilient modulus of soil stabilised by 1.5% of cement. The best results of dispersive reinforcement were obtained for samples containing 0.3% of fibres with a length of 18 mm, compacted by the MP methods.</p> </abstract>ARTICLEtrue of Soft Soil Samples Quality on the Compressibility and Undrained Shear Strength – Seven Lessons Learned From the Vistula Marshlands<abstract> <title style='display:none'>Abstract</title> <p>This technical article presents the influence of sample quality on the compressibility parameters and undrained shear strength (<italic>c</italic><sub>u</sub>) of soft soils from the Vistula Marshlands. The analysis covers: (1) quality of soft soil according to three criteria: void ratio (Δ<italic>e</italic>/<italic>e</italic><sub>0</sub> index), volumetric strain (Δ<italic>ɛ</italic><sub>v</sub>) and <italic>C</italic><sub>r</sub>/<italic>C</italic><sub>c</sub> ratio; (2) influence of storage time on quality; (3) influence of sample quality on undrained shear strength (<italic>c</italic><sub>u</sub>), 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.</p> <p>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 <italic>c</italic><sub>u</sub> (next to the FVTs), which additionally allows in relatively easy way to establish lower and upper bounds of <italic>c</italic><sub>u</sub>.</p> </abstract>ARTICLEtrue elastoplastic constitutive model for assessing ground settlements induced by deep excavations<abstract> <title style='display:none'>Abstract</title> <p>Ground movements induced by deep excavations may cause damages on neighboring existing buildings. Finite element simulations generally give acceptable estimates of the horizontal displacements of the retaining wall, but results are less satisfactory for the vertical displacements of the ground surface behind the structure. A possible explanation is that most constitutive models describe volumetric strains in a simplified way. This paper proposes an elastoplastic constitutive model aimed at improving the prediction of vertical displacements behind retaining walls. The model comprises a single plastic mechanism with isotropic strain hardening, but has a specific flow rule that allows to generate contractive plastic strains. Identification of the parameters based on triaxial tests is explained and illustrated by an example of calibration. A numerical analysis of a well-documented sheet pile wall in sand in Hochstetten (Germany) is presented. The results given by the model are compared with the measurements and with those obtained using the Hardening Soil Model. The potential advantages of the proposed model are then discussed.</p> </abstract>ARTICLEtrue–dilatancy behaviour of remoulded Fujinomori clay<abstract> <title style='display:none'>Abstract</title> <p>The effect of the degree of consolidation and the stress path on the behaviour of remoulded Fujinomori clay for drained triaxial compression and extension was analysed using the Frictional State Concept. It is shown that the stress–dilatancy behaviour can be approximated by a linear general dilatancy equation given by the critical frictional state angle and two soil parameters. The newly formulated dilatant failure state is represented on the stress ratio plastic dilatancy plane by points lying on the friction state line defined by the friction state angle and the Friction State Concept parameters <italic>α</italic>=0 and <italic>β</italic>=1. It has been shown that the stress ratio–plastic dilatancy relationship, which is very rarely used in the interpretation of test results, is important for a complete description of the behaviour of soils during shearing.</p> </abstract>ARTICLEtrue and Tensile Strength of Nano-clay Stabilised Soil Subjected to Repeated Freeze–Thaw Cycles<abstract> <title style='display:none'>Abstract</title> <p>Improvement of the mechanical properties of clayey soils by additional elements to enhance the strength under numerous freezing and thawing cycles has been considered as a serious concern for engineering applications in cold regions. The objective of the current study is to investigate the effect of nano-clay as a stabiliser on the mechanical properties of clay. To this end, the clay specimens were prepared by adding various percentages of nano-clay ranging from 0.5% to 3% by dry weight of soil and were experimentally tested under the uniaxial compression and tensile splitting tests under different curing times (0, 7 and 28 days) after experiencing various freeze–thaw cycles ranging from 0 to 11. It can be concluded from the results that nano-clay particles may be used as a stabiliser in geotechnical applications to improve soil property. The results indicate that the optimum moisture content (OMC) of specimens increases and the maximum dry density (MDD) decreases with the increasing nano-clay content. The specimens containing about 1% nano-clay recorded maximum values of unconfined compressive strength (UCS) as well as tensile strength. For example, the addition 1% nano-clay increased the UCS and tensile values of clay specimens under the curing time of 28 days by 34% and 247%, respectively. In addition, the long-term durability of specimens against freeze–thaw cycles increases further with the addition of nano-clay content ranging from 2% to 3%.</p> </abstract>ARTICLEtrue monitoring of structures in the light of the Polish and international requirements<abstract> <title style='display:none'>Abstract</title> <p>The paper concerns the wide range of strategies used to protect structures against man-made dynamic excitation. The most popular approaches applied worldwide are compared, and the main differences and similarities are summarized. The literature studies are supported by the results of the measurements performed on different types of real structures, which are sensitive and insensitive to the dynamic load. To make the conclusions more general, various types of excitation forces are examined (long-term and short-term excitations, traffic load, and loads resulting from geotechnical works). The main issue raised in the paper is the problem of unequivocal and accurate assessment of the potential structure damage, based on the different legislations. It can be seen that the application of different codes can even result in opposite conclusions about the safety of the structure.</p> </abstract>ARTICLEtrue Novel Method for Optimizing Parameters influencing the Bearing Capacity of Geosynthetic Reinforced Sand Using RSM, ANN, and Multi-objective Genetic Algorithm<abstract> <title style='display:none'>Abstract</title> <p>In this study, a novel method is proposed to optimize the reinforced parameters influencing the bearing capacity of a shallow square foundation resting on sandy soil reinforced with geosynthetic. The parameters to be optimized are reinforcement length (L), the number of reinforcement layers (<italic>N</italic>), the depth of the topmost layer of geosynthetic (U), and the vertical distance between two reinforcement layers (X). To achieve this objective, 25 laboratory small-scale model tests were conducted on reinforced sand. This laboratory-scale model has used two geosynthetics as reinforcement materials and one sandy soil. Firstly, the effect of reinforcement parameters on the bearing load was investigated using the analysis of variance (ANOVA). Both response surface methodology (RSM) and artificial neural networks (ANN) tools were applied and compared to model bearing capacity. Finally, the multiobjective genetic algorithm (MOGA) coupled with RSM and ANN models was used to solve multi objective optimization problems. The design of bearing capacity is considered a multi-objective optimization problem. In this regard, the two conflicting objectives are the need to maximize bearing capacity and minimize the cost. According to the obtained results, an informed decision regarding the design of the bearing capacity of reinforced sand is reached.</p> </abstract>ARTICLEtrue Temperature Field Effect on Dynamic Stability Response of Three-layered Annular Plates for Different Ratios of Imperfection<abstract> <title style='display:none'>Abstract</title> <p>The paper presents the temperature field effect on the dynamic stability problem of plates with imperfection. The main objective is to conduct numerical investigations which show the relations between the imperfection ratio and plate dynamic response in a thermal environment. The plate is composed of three layers: thin facings and a thicker core. The plate can be loaded mechanically and thermally or only thermally. The facings are mechanically compressed with the forces acting in a plane. The temperature field model is defined by the temperature difference, which occurs between the plate edges. Two plate models are examined as follows: built using the approximation methods – orthogonalization and finite differences – and composed of finite elements. The analytical and numerical solution procedure is the main one, which is the proposal to perform the problem analysis. The plate reaction is described by the obtained values of the critical temperature differences for plates loaded only thermally and by the critical mechanical loads and the corresponding temperature differences for plates loaded mechanically and subjected to the uncoupled temperature field. The effect of the plate imperfection ratio under time-dependent loads is shown by numerous observations and results, which are shown graphically. The importance of the imperfection ratio on the plate's dynamic stability response in complex loading conditions is studied.</p> </abstract>ARTICLEtrue