Soil Mechanics Problems Research Articles

Effect of spatial variability of soil properties on slopes stability under rapid water drawdown conditions

Stability analysis of slopes is a fundamental problem of Soil Mechanics. Its main objective consists of evaluating the potential failure of the slope structure under a prescribed loading mode. A major component of the latter refers to the seepage forces induced by pore-pressure gradient, which is known to be responsible of destabilizing effects. This contribution employs a kinematic approach of limit analysis theory to obtain upper-bounds solutions to the stability problem of saturated slopes submitted to rapid water level drawdown. Random fields are used to model the uncertainty surrounding the spatial distribution of soil cohesion, friction angle, and permeability. In the context of effective stress governing the strength capacities of the soil material, it is shown that the seepage forces related to the water flow regime can be considered as external volumetric loads in the assessment of stability. The hydraulic problem governing the water filtration velocity is evaluated by resorting to an analytical variational approach, whose results are validated by comparisons with finite element solutions. The impact of hydraulic-related parameters on stability is first investigated for slopes within a deterministic framework. Subsequently, random fields are considered to take into account the variability related to the spatial distribution of the material properties, which are discretized using the Karhunen-Loève expansion with numerically computed eigenfunctions. The failure probability of slopes is assessed through Monte Carlo simulations. Several analyses have been performed to discuss the influence of the spatial variability of relevant problem parameters.

Preserving non-negative porosity values in a bi-phase elasto-plastic material under Terzaghi’s effective stress principle

Poromechanics is a well-established field of continuum mechanics which seeks to model materials with multiple phases, usually a stiff solid phase and fluid phases of liquids or gases. Applications are widespread particularly in geomechanics where Terzaghi’s effective stress is widely used to solve engineering soil mechanics problems. This approach assumes that the solid phase is incompressible, an assumption that leads to many advantages and simplifications without major loss of fidelity to the real world. Under the assumption of finite (as opposed to infinitesimal) strains, the poromechanics of two- or bi-phase materials gains complexity and while the compressible solid phase case has received attention from researchers, the incompressible case has received less. For the finite strain - incompressible solid phase case there is a fundamental issue with standard material models, in that for some loadings solid skeleton mass conservation is violated and negative Eulerian porosities are predicted. While, to the authors’ best knowledge, acknowledgement of this essential problem has been disregarded in the literature, an elegant solution is presented here, where the constraint on Eulerian porosity can be incorporated into the free energy function for a material. The formulation is explained in detail, soundly grounded in the laws of thermodynamics and validated on a number of illustrative examples.

ПРОГНОЗУВАННЯ НЕСУЧОЇ СПРОМОЖНОСТІ ПЛИТНОГО ФУНДАМЕНТА ЗА ЧИСЛОВИМ МЕТОДОМ ГРАНИЧНИХ ЕЛЕМЕНТІВ

Construction is one of the leading branches of the national economy in the historical aspect of its development. The first design task is to determine the strength of building structures. Therefore, the study of the stress-strain state and related calculations are the most important in construction. The purpose of studying soil mechanics and foundation construction techniques is the calculation and construction of structures on or in soil. The main task is the construction of structures with a sufficient degree of reliability.The selection of an adequate theoretical model remains the main problem of soil mechanics. Indeed, the deformation of the dispersed granular material of the soil takes place during the mutual sliding of the grains, the rheology of the soil is complex, as evidenced by a large amount of experimental material. Today, the path of development of soil mechanics is related to the study of problems within the framework of the elastic-plastic dilatation model and the improvement of this model based on experiments. A mathematical model of a technical object at the micro level is a system of differential equations in partial derivatives, the exact solution of which can be obtained only in a few partial cases, therefore a discrete model is built using numerical methods that use the Poisson idea that the behavior of a complex model can be represented by the behavior of its individual component elements. The intensive development and widespread use of computers significantly brought fundamental mathematical problems closer to applied ones, and strengthened their mutual influence.The emergence of a new, powerful and general method of research - a numerical experiment, more than ever before closely connected the physical content of the problem, its mathematical formulation, numerical methods of calculation and modern computers. The work uses the numerical method of boundary elements. A promising way to develop foundations and foundation structures is to use the ratios of the theory of plastic flow, and the level of development of soil mechanics significantly affects the economy and reliability of the decisions made.

Prediction of UCS and CBR of a stabilized Black-cotton soil using artificial intelligence approach: ANN

The mechanics of soil deal with soil types whose behavior in the real world can be erratic, including expansive soil, particularly black cotton soil, for which a variety of laboratory tests are required to establish its physical properties. Modelling the behavioral patterns of expansive-soil is difficult and often away from the capabilities of most traditional physical-based engineering measures. In comparison with conventional approaches, artificial intelligence-based approaches provide better predictions of the complex soil properties. The bearing capacity of soil is considerably very important for geo-techniques and engineering geology, since it is a significant parameter for the foundation and pavement's design. To improve granule connections and reduce soil expansibility and contractility, the expansive black cotton soil(BCS) is chemically Processed with a variety of supplements such as fly ash, lime, and cement in this study. By estimating the effects of stabilizers on CBR and UCS, this study tests the suitability of stabilizing black cotton soil in road construction. The second goal is to create an ANN-based model for predicting CBR and UCS while taking other soil properties as inputs. The research clearly illustrates that ANN Pattern is well suited to dealing with expansive soil stabilization, as evidenced by a high R2 and low RMSE, MAE and RRMSE. As a result of this paper, practicing engineers will be able to find the best modelling techniques and generate the necessary data to resolve soil mechanics problems using ANN.

Contact tensions under the sole of rigid deep laying foundations and ground anchors

Purpose. To solve the problem of the allocation of contact vertical normal tensions along the sole of a rigid round stamp, located in an elastic isotropic half-space at a certain depth h  0. To compare the obtained solution with the well-known classical result for h = 0, to check the obtained results for adequacy. Methodology. Based on the analysis of the decision on the stress-strain state of the base, inside which there is a vertical arbitrary load distributed over the area of the circle, the necessary formulas are obtained to solve the problem. An algorithm for constructing an approximate solution has been developed, the essence of which is to use a combination of the boundary element method and the iteration process by S.N.Klepikov. For a number of depths, approximate solutions of the considered problem are obtained. Findings. The proposed algorithm for the approximate solution of the problem of indenting a round rigid stamp into the upper boundary of an elastic isotropic half-space has good agreement with the exact solution and can be used to solve contact problems. The outlines of the contact stress diagrams depend on the depth at which they are determined – the greater the depth, the flatter the outlines of the diagrams are, while starting from a certain depth, the diagrams of contact stresses practically coincide. The greater the depth is at which the stamp is located, the more force must be applied to obtain equal displacements of the stamp. Originality. The obtained research results significantly expand the possibilities of solving various problems of soil mechanics and foundation engineering, make it possible to obtain absolutely new results. In particular, a clear dependence of the contact stresses along the sole of a rigid round stamp on the depth at which it is located was identified. In addition, the presented data allow us to designate an absolutely new direction in the calculation of the foundations of ground anchors, namely, the calculation of their deformations. Practical value. For engineering practice, it is important that the greater the value of Poisson’s ratio of the base is, the greater the contact stresses are, other things being equal.

МАТЕМАТИЧНЕ МОДЕЛЮВАННЯ ЗА МГЕ ПРОЦЕСУ ПІДСИЛЕННЯ ФУНДАМЕНТІВ

Taking into account the presence of weak soils on the territory of Ukraine, additional vertical deformations occur in soil foundations, associated with a violation of their structure. Water saturation of such soilsleads to a change in VAT and affects the conditions for the reliable operation of construction objects. In this regard, it becomes necessary to strengthen the foundations of these building objects, to improve the bearing capacity of these foundations. Therefore, in practice, the search for new ways to strengthen the foundations, improve their bearing capacity is constantly being carried out. In difficult engineering and geological conditions, the deterioration of the physical and mechanical properties leads to a rise in deformations and a decrease in the bearing capacity of the foundations. Reinforcement of foundations is also necessary when constructing superstructures. In the robot, using the numerical method of boundary elements, the behavior under load of a shallow foundation on a natural basis reinforced with cross piles is predicted. Reinforcement of foundation structures requires determination of their bearing capacity and stress-strain state (SSS) after reconstruction. Normative design of foundations, based on subsidence and rolls, which are borderline permissible from the point of view of the operational suitability and reliability of structures, puts forward increased requirements for the accuracy of calculating the displacements of foundations. Thecomplexity of the properties of soils and the many factors that influence their mechanical behavior have long been a barrier before which the mathematical methods of continuum mechanics were de-strengthened. The emergence of modern ECM allowed algebraicizing the mathematical formulation of most problems in soil mechanics, which require taking into account a large number of nonlinear determining factors and the transition to elastic-plastic models. The use of a numerical eexperiment, as never before, closely linked the physical meaning of the problem, its mathematical formulation, numerical methods of calculation and the ECM. In the robot, to obtain a forecast of the bearing capacity of a reinforced foundation, anelastic-plastic model of a discrete soil medium and a numerical MGE are used

Impact of Calcium Chloride on the Microstructure of a Collapsible ‎Soil

The study of the collapse of soils under the effect of flooding is a major problem in soil ‎mechanics. Most of the work done on the treatment of these soils has been devoted to ‎the use of binders of hydraulic or organic types. However, little work has been devoted to the use of salt calcium chloride in ‎collapsible soil treatments.‎ The purpose of this study is to evaluate the effect salt calcium chloride on a reconstituted collapsible soil in the laboratory, at ‎different levels of water content, compaction energy and concentration of the saline solution. The ‎results obtained showed a significant reduction in the potential for soil deformation ‎and an illustration and a noticeable interaction between the soil particles ‎and the saline solution resulting in a denser material.

Effect of soil saturation and grain size on coupled hydrothermal flow in fine sands based on X-ray [formula omitted]CT imaging

Coupled hydrothermal flow can occur in soils, for example in applications such as ground heat storage and nuclear waste disposal. Therefore, approaches to quantitative analysis of water transfer in response to imposed thermal gradients are required, especially in unsaturated conditions. Analysis methods also require validation by laboratory and field data, which can be hard to obtain. This paper explores the possibility of using X-ray μCT techniques to observe and quantify water content changes in soils under thermal gradients. Specimens of a fine sand and a silty fine sand were prepared at degrees of saturation between 20% and 50%, before being subjected to heating from their base. Repeated scans, set up to balance image quality and scan duration, were carried out during the heating process, and Gaussian decomposition techniques were used to determine the changing soil phase proportions throughout the experiments. Based on these results and the accompanying numerical simulation of the experiments, it is shown that rapid vapour diffusion plays a more significant role than liquid flow in all cases. The rate of water content and hence degree of saturation change was more rapid in the less saturated specimens, especially for the fine sand. In practical terms, these moisture changes would result in reduction in thermal conductivity, especially in the soils of lower saturation. As well as providing insight into the dominant water transfer processes, the experiments show the feasibility of applying X-ray μCT techniques to thermal problems in soil mechanics.

An unconditionally stable explicit finite element algorithm for coupled hydromechanical problems of soil mechanics in pseudo‐static conditions

AbstractIn this article, we present a novel explicit time‐integration algorithm for the coupled hydromechanical soil mechanics problems in a pseudo‐static regime. After introducing the finite element discretization, the semidiscrete ordinary system of equations is integrated explicitly in time with the Runge–Kutta method. It is noted that this formulation is conditionally stable in time. By introducing a stabilization technique, the Polynomial Pressure Projection, and selecting appropriately the stabilization parameter, the formulation becomes unconditionally stable. To illustrate the performance of the method several numerical analysis are reported, considering both elastic and elasto‐plastic soil behavior.

РОБОТА БУРОНАБИВНИХ ПАЛЬ З РОЗШИРЕНОЮ ПЯТОЮ В НАБУХАЮЧИХ ГРУНТАХ ЗА ЧИСЛОВИМ МЕТОДОМ ГРАНИЧНИХ ЕЛЕМЕНТІВ

The topic is devoted to the topical problem of foundation construction and soil mechanics - elastic-plastic modeling of joint work of the system "soil base - brown pile" in order to determine the bearing capacity of the foundation to ensure stability and low subsidence of the structure, thus avoiding its possible uneven subsidence or destruction. To do this, it is necessary to provide forecasting and numerical implementation of calculations of the pile foundation structure.
 From the standpoint of the mechanics of a dispersed elastic-plastic medium, the idea of the peculiarities of the behavior under the load of a brown pile with an extended heel in clay swellable soils is presented.
 The calculations take into account the main content of the theory of elastic-plastic processes - the dependence of the stress- deformed state on the load history.
 The main computational equation of the soil model is the integral equation received K. Brebbia [1].
 Depending on the properties of the soil and the applied stresses, the sediment of the building is carried out as a result of compaction or extrusion of the soil from under the foundation.
 In both cases, the phenomenon of subsidence is due to soil flow, so it is natural that to the forefront of solving static problems of foundation construction is a condition or equation that determines the boundary between solid and fluid state of the soil depending on stresses.
 The application of numerical MGE to the solution of the nonlinear problem of geomechanics is substantiated by theoretical calculations, supported and illustrated by data of numerical calculation

A Review on the Failure Modes of Rock and Soil Mass under Compression and the Exploration about Constitutive Equations of Rock and Soil Mass

The constitutive equation of rock and soil has always been the core problem in rock and soil mechanics. Up to now, the nature of nonlinear shear strength of rock and soil has not been revealed. In many engineering practices, it is still considered that the failure mode of rock and soil is always shear failure, and Coulomb linear constitutive equation is adopted, or Mohr envelope is fitted by data. However, the constitutive equation of rock mass is nonlinear, and its failure mode is not only shear failure. A large number of single triaxial tests show that there is not only shear stress, but also tensile stress in the failure process of rock and soil. Theoretical and experimental research on failure mode of rock mass under pressure are one of the important means to improve and develop soil mechanics. It is important to understand the nonlinear nature of rock and soil constitutive equation to explore the energy variation and the distribution of tensile stress and shear stress in different failure modes of rock and soil.

Introduction of Plastic Block Method in the Upper Bound Limit Analysis of Soil Stability Problems

In this paper, a new method, called the Plastic Block method, was introduced to improve the current rigid block solutions in framework of rigorous limit analysis method. It is a combination of rigid block limit analysis and finite-element limit analysis methods used in the upper bound limit analysis solutions of stability problems in soil mechanics. The method is similar to the first one in terms of speed of solution process and consideration of a collapse mechanism as a priority, and also is similar to the second one in terms of capability of considering plastic deformability of the blocks in calculation of internal dissipation of energy (besides that of velocity discontinuities between them). Comparison of the results obtained by the proposed method, using a few number of blocks (in case of the classical bearing capacity problem of shallow foundations selected to illustrate capability of the method), showed the better (smaller) upper bound not only in comparison with the well-known rigid block solutions, but also in comparison with some cases of finite-element limit analysis solutions obtained by the models including a large number of elements.

Geotechnical Characteristics of Regolith Derived from Nanka Formation, Southeast Nigeria

Regolith derived from Nanka Formation; Southeast Nigeria was evaluated for their geotechnical characteristics. The methods of investigations include Fieldwork experiment and laboratory analysis of water and soil samples. The result of hydraulic parameters of the soil at 1meter, 2 meters depth and drilled cuttings from boreholes revealed permeability average values of 1.29E-05(cm/s) and 9.15E-6(cm/s), hydraulic conductivity average value of 1.27E-04(cm/s) and 8.93E-05(cm/s). Drilled cuttings from three boreholes revealed permeability average value of 8.15E-06(m/s), 2.68E-06(m/s) and 6.20E-06, hydraulic conductivity average values of 8.90E-03(m/s), 2.92E-03(m/s) and 6.75E-3(m/s).These values indicate permeable soil with high hydraulic conductivity typical of silty-clay and sand. The permeability/hydraulic conductivity accounts for the high infiltration/percolation of water into the soil. Infiltration of water through the soil initiates geochemical reactions and dissolution mineral which leaves the soil loose and unconsolidated. Geotechnical characteristics show low to medium plasticity and a liquid limit average of 42.36 and 35.45, indicating the capacity of the soil to absorb moisture and expand, bulk density average value of 1.90 mg/m3and compaction test of maximum dry density average value of 1.80 g/cm3 at an optimum water content average of 12.89% indicate low density. Shear strength components of cohesion values range from 0 to 55KN/m2 with average value of 25 KN/m2 and friction angle values range from 7° to 25° suggesting low cohesion and angle of internal friction. This is attributed to the low clay content and the cohesive force is not enough to sustain the soil. Field experiments of cone penetration test of in-situ results indicate a weak and incompetent soil material that is unstable and vulnerable to erosion. The finding would be relevant in soil mechanics problems.

Geotechnical Characteristics of Regolith Derived from Nanka Formation, Southeast Nigeria

Regolith derived from Nanka Formation; Southeast Nigeria was evaluated for their geotechnical characteristics. The methods of investigations include Fieldwork experiment and laboratory analysis of water and soil samples. The result of hydraulic parameters of the soil at 1meter, 2 meters depth and drilled cuttings from boreholes revealed permeability average values of 1.29E-05(cm/s) and 9.15E-6(cm/s), hydraulic conductivity average value of 1.27E-04(cm/s) and 8.93E-05(cm/s). Drilled cuttings from three boreholes revealed permeability average value of 8.15E-06(m/s), 2.68E-06(m/s) and 6.20E-06, hydraulic conductivity average values of 8.90E-03(m/s), 2.92E-03(m/s) and 6.75E-3(m/s).These values indicate permeable soil with high hydraulic conductivity typical of silty-clay and sand. The permeability/hydraulic conductivity accounts for the high infiltration/percolation of water into the soil. Infiltration of water through the soil initiates geochemical reactions and dissolution mineral which leaves the soil loose and unconsolidated. Geotechnical characteristics show low to medium plasticity and a liquid limit average of 42.36 and 35.45, indicating the capacity of the soil to absorb moisture and expand, bulk density average value of 1.90 mg/m3and compaction test of maximum dry density average value of 1.80 g/cm3 at an optimum water content average of 12.89% indicate low density. Shear strength components of cohesion values range from 0 to 55KN/m2 with average value of 25 KN/m2 and friction angle values range from 7° to 25° suggesting low cohesion and angle of internal friction. This is attributed to the low clay content and the cohesive force is not enough to sustain the soil. Field experiments of cone penetration test of in-situ results indicate a weak and incompetent soil material that is unstable and vulnerable to erosion. The finding would be relevant in soil mechanics problems.

Vibration creep of loess soils

Taking into account the rheological properties (creep) of clay soils when solving problems of soil mechanics is important, because many inaccuracies in forecasts related to soils arise from an under-accounting of these properties, which are characteristic of clay soils. The report deals with the issues of vibration creep of moisten loess soils, related to the precipitation of structures and the permissible load on the soil. The method of experimental research and the results of experiments on the dependence of the coefficient of soil vibration creep on the acceleration of vibrations are presented. The factors influencing the vibration creeping deformations of the forest, including the role of soil adhesion and the duration of shaking, are established. Research results are of great importance in the practice of constructing unique engineering structures in seismic areas.

Relation between the Friction Angle of Sand at Triaxial Compression and Triaxial Extension and Plane Strain Conditions

The strength of sand is usually characterized by the maximum value of the secant friction angle. The friction angle is a function of deformation mode, density, and stress level and is strongly correlated with dilatancy at failure. Most often, the friction angle is evaluated from results of conventional compression tests, and correlation between the friction angle of sand at triaxial compression and triaxial extension and plane strain conditions is a vital problem of soil mechanics. These correlations can be obtained from laboratory test results. The failure criteria for sand presented in literature also give the possibility of finding correlations between friction angles for different deformation modes. The general stress-dilatancy relationship obtained from the frictional state concept, with some additional assumptions, gives the possibility of finding theoretical relationships between the friction angle of sand at triaxial compression and triaxial extension and plane strain conditions. The theoretically obtained relationships presented in the paper are fully consistent with theoretical and experimental findings of soil mechanics.

Effects of sampling disturbance in geotechnical design

This paper describes an experimental study of the effects of sampling disturbance in an Australian natural soft clay and the consequences of different sample quality on the representativeness of soil parameters used in geotechnical designs. The paper is divided into three sections. Laboratory test results obtained from specimens retrieved using three different tube samplers as well as the Sherbrooke (block) sampler are first described. Then, the sample quality assessment, using available indices proposed for soft soils, is presented. It is shown that sample quality varies with the stress paths and boundary conditions applied in laboratory tests. Finally, mechanical soil properties derived from specimens retrieved using the different samplers are used in the prediction of two classical problems in soil mechanics: the settlement and excess pore pressure response underneath an embankment as well as the settlement and bearing capacity of a shallow footing. These two examples are used here to highlight the consequences of poor sampling in practice.

Treatment of Collapsible Soils by Additions of Granulated Slag and Natural Pozzolan

The study of collapsible soils, due to flooding, is a major problem in soil mechanics. The majority of researches carried out regarding this type of soil have been devoted to their identification, collapse mechanisms and treatments using salts, hydraulic binders and glass fibers. However, little research has been reported on their improvements using industrial waste (e.g., slag) or natural materials (e.g., pozzolan) in order to meet environmental and socio-economic challenges. In this work, a series of tests were conducted to examine the effect of adding granulated slag and natural pozzolan, at different contents, on the suction and the collapse potential (Cp) of a soil reconstituted in the laboratory, and having a behavior similar to natural and undisturbed soils. The obtained results showed clearly that treated collapsible soils with granulated slag and natural pozzolan, lead to a significant reduction in the collapse potential (Cp) followed by a decrease of suction. Furthermore, SEM/EDAX analysis conducted on the same samples revealed that the soil pores were filled with these two materials particles and as a result a significant improvement of the physical and mechanical characteristics of the soil was noted.

Оптимізація плитного фундаменту висотної будівлі за методом граничних елементів

The theme is devoted to the actual problem of engineering and soil mechanics - elastic-plastic modeling of the joint operation of the ground — slab foundation system in order to determine the bearing capacity of the and the choice of its optimal thickness. The development of the construction industry is associated with the introduction in the building practice of new technologies of predictive calculation. Significant increase in the weight of modern structures, which is transferred to the basis, necessitates the development of non-linear methods for calculating drill piles, which in these conditions are the most effective types of structures. Construction of buildings is a labor-intensive process that requires well-balanced, well-calculated steps and solving complex mathematical problems. This is especially true for the installation of a part of the building, which perceives the load and transfers them to the — the foundation. It is extremely important to provide stability and low occupancy of the structure, thus avoiding its possible uneven subsidence or destruction. To do this, ensure prediction and numerical implementation of calculations of structures. Therefore, the model of the equation of equilibrium of the immersed in the soil medium, which satisfies the Laplace differential equation, is developed. The main calculation equation of the soil model is the integral equation obtained by K. Brebbia. The attachment of numerical MGE to the solution of the nonlinear problem of geomechanics is substantiated by theoretical calculations, supported and illustrated by numerical calculations. Nonlinear task of the process of deformation of bases is solved using step method of O. A. Iliushin The soil was modeled by theory of V. M. Nikolaievskyi and I. P. Boiko. Full deformations were determined, which consisted of increments of elastic and plastic deformations. The layout of the calculation matrix of the influence of the MGE was performed on the basis of the decisions of R. Mindlin. The results of the forecast for the IHE are given on the plot of the loading-settling of the base plate. The fidelity of the choice of the settlement dilatation model is confirmed by the correspondence of numerical studies with experimental research.

Adaptive mesh-free lower bound limit analysis using non-linear programming

An adaptive mesh-free approach is developed to compute the lower bounds of limit loads in plane strain soil mechanics problems. There is no pre-defined connectivity between nodes in the mesh-free techniques and this property facilitates the implementation of h-adaptivity. Nodes may be added, moved or discarded without complex changes in the data structures involved. In this regard, the Shepard mesh-free method is used in conjunction with the nodal stress rate smoothing technique and the lower bound limit analysis theory to establish a non-linear optimization problem. This problem is solved by second order cone programming technique and the result is a stress field that satisfied the lower bound requirements in non-rigorous manner. The lack of rigorousness arises from relaxation during nodal stress rate smoothing process. An error estimator is introduced by the application of Taylor series expansion and, by controlling the local error via a user-defined tolerance, the adaptive refinement strategy has been established. To demonstrate the effectiveness of proposed method, the procedure is applied to the examples of purely cohesive and cohesive-frictional soils.