Geotechnical Engineering Problems Research Articles

An Object-oriented finite element framework for modified cam clay model

In this paper, an object-oriented finite element framework is developed and modified cam clay model, which is an elasto-plastic soil constitutive model, is implemented with it. The paper briefly describes the approach of implementing the steps of finite element analysis in object-oriented programming paradigm. An implicit integration algorithm for modified cam clay model is implemented in the proposed framework, which can be used to solve boundary value problems in geotechnical engineering. The framework ensures the maintainability and extensibility of the program to implement new tasks that may be in the form of the addition of a new constitutive model with different integration algorithms, and hence it can be used for research purposes in the field of geotechnical engineering. Numerical investigations are performed to validate the stability and accuracy of the proposed framework, which also demonstrate the effectiveness of object-oriented programming in finite element analysis. Numerical examples include triaxial compression tests on normally consolidated clay (NCC) and overconsolidated clay (OCC) and bearing capacity evaluation of a flexible strip footing on a homogeneous deposit of clay. As a programming language, C++ is used.

Influence of Soil Heterogeneity on the Behavior of Frozen Soil Slope under Freeze-Thaw Cycles

Soil slope stability in seasonally frozen regions is a challenging problem for geotechnical engineers. The freeze-thaw process of soil slope caused by the temperature fluctuation increases the difficulty in predicting the slope stability because the soil property is influenced by the freeze-thaw cycle. In addition, the frozen soil, which has ice crystal, ice lens and experienced freeze-thaw process, could present stronger heterogeneity. Previous research has not investigated the combined effect of soil heterogeneity and freeze-thaw cycle. This paper studies the influence of soil heterogeneity on the stability of frozen soil slope under freeze-thaw cycles. The local average subdivision (LAS) is utilized to model the soil heterogeneity. A typical slope geometry has been chosen and analysed as an illustrative example and the strength reduction method is used to calculate the factor of safety (FOS) of slope. It has been found that when the temperature is steady, the FOS of the frozen soil slope is influenced by the spatial variability of the thermal conductivity, but the influence is not significant. When the standard deviation and the SOF of the thermal conductivity increase, the mean of the FOS is equal to the FOS of the homogeneous case and the standard deviation of the FOS also increases. After the frozen soil goes through freeze-thaw process, the FOS of the frozen soil slope decreases due to the reduction in the cohesion and the internal friction angle caused by the freeze-thaw cycles. Furthermore, the decreasing ratio of the FOS becomes more scattered after the 5th freeze-thaw cycle compared to that of the FOS after the 1st freeze-thaw cycle. The larger variability of the FOS could induce inaccuracy in the prediction of the frozen soil slope stability.

Research on rock triaxial cyclic loading and unloading characteristics based on PFC3D

Numerical methods provide a new way for solving complex geotechnical engineering problems. Firstly, we review the emergence and development of numerical methods, and introduce the basic principles of particle flow discrete element and its application in geotechnical engineering. After that, a method of servo combination of cylinder and loading plate is used, the numerical simulation of the three-dimensional rock in triaxial loading and unloading test is carried out by PFC3D software, and the loading and unloading mechanical characteristics of rock mass under the linear elastic contact constitutive model and parallel bonded contact constitutive model are studied respectively, and we obtain the triaxial loading and unloading stressstrain curves of rock under the elastic constitutive model and elastoplastic constitutive model. The residual strains and hysteresis phenomena of the rock under the two constitutive models are analysed, and the feasibility of the particle flow discrete element method in studying the mechanical characteristics of rocks is demonstrated.

Evaluation of Water seepage Along Proposed Baghdad Metro Tunnel Across Tigris River

Water seepage can cause serious problems in geotechnical engineering especially for construction under the water level. Baghdad metro tunnel is one of the leading vital projects to solve the major problem of crowding roadways in a highly population increase city like Baghdad. In this study, the seepage rate that will flow toward different selected points along the tunnel section across Tigris River was calculated during the excavation process, with the consideration of three different water levels of River at maximum, moderate, and minimum water depths. A three-dimensional model of the study has been modeled using the finite element software (PLAXIS 3D V20). The water seepage was observed for six different locations on each route of the tunnel. The study showed that the change of water depth in the river has no significant effect on the seepage – time curve shape. However, increasing the water level in River from minimum to maximum leads to increase the seepage rate about 15%.

Development of an adaptive CTM–RPIM method for modeling large deformation problems in geotechnical engineering

In this paper, a meshfree method called adaptive CTM–RPIM is developed to model geotechnical problems with large deformation. The developed adaptive CTM–RPIM is a combination of the Cartesian transformation method (CTM), the radial point interpolation method (RPIM) and the alpha shape method. To reduce the requirement for meshes, the CTM is adopted to transform domain integrals into line integrals, and the RPIM is applied to construct interpolation functions. The alpha shape method, which is capable of capturing severe boundary evolution due to large deformations, is then introduced into the CTM–RPIM to form the adaptive CTM–RPIM. The accuracy of CTM–RPIM is first verified by considering a cantilever beam under small deformation, where the influence of key parameters on the simulation results is explored. Afterward, the ability of the adaptive CTM–RPIM to handle large deformation problems is demonstrated by simulating cantilever beams with large deformations for which analytical solutions are available. Finally, the ability of the proposed method to model the geotechnical large deformations is illustrated from both quasi-static and dynamic aspects, where a slope failure problem and a footing bearing capacity problem are modeled to evaluate the stability of geotechnical structures; and a 2-D soil collapse experiment using small aluminum bars is simulated to show the method capability in describing the soil flows. These benchmark examples demonstrate that the adaptive CTM–RPIM is a numerical method with broad application prospects for modeling large deformation problems in geotechnical engineering.

Undrained cylindrical cavity expansion/contraction in stiff clays using a two‐surface plasticity model

AbstractThis paper presents a semi‐analytical solution of undrained cylindrical cavity expansion/contraction problem using a two‐surface plasticity model for natural stiff clays from the view point of poromechanics. The present solution reduces the classical boundary problem into a group of seven first‐order ordinary differential equations via an auxiliary independent variable ξ under undrained conditions. It strictly follows the premise of constant soil mass (CSM). Meanwhile, the solution for the constant soil volume (CSV) problem is used for comparison. It shows that CSM assumption is of paramount importance in developing solutions under high stress condition, while CSV induces non‐negligible errors in effective stress and pore pressure distributions. Based on the premise of CSM, extensive parametric studies on cavity expansion/contraction are undertaken to investigate the effects of the model key parameters on the stress components distribution, excess pore pressure distribution, and cavity expansion curves. The present solution could be useful while dealing with geotechnical and petroleum engineering problems involving stiff clays or soft claystones. The application in Praclay Gallery excavation in natural Boom clay well demonstrates the validity of the present solution.

Coupling of a water permeability function with a bounding surface hydromechanical model for unsaturated soils

This paper presents a water permeability function that predicts the hydraulic conductivity of deformable and unsaturated soils as the product of two interacting terms. The former term accounts for the effect of the degree of saturation, suction, particle size distribution, particle shape and soil fabric on the water permeability at a given void ratio. The latter term describes instead the influence of the void ratio on the saturated permeability. Overall, the resulting water permeability function is dependent on five model parameters: two parameters can be estimated from permeability tests on saturated soils, another parameter is dependent on the particle size distribution of the soil while the remaining two require unsaturated testing. The proposed water permeability function has then been coupled with the bounding surface hydromechanical model proposed by Bruno and Gallipoli (2019). The coupled model was then validated against three sets of experimental data published in literature. Results show the good capability of the coupled constitutive framework to capture the variation of water permeability of soils with different granularities ranging from clay to sand. Finally, the proposed coupled model can be implemented into a Finite Element code to study coupled flow-deformation problems in geotechnical and geo-environmental engineering.

Reliability Analysis of Stone Columns Bearing Capacity

Abstract Reliability analysis and stone columns techniques are widely used, with an increasing trend, in different geotechnical engineering problems. Design methods of stone columns is still based on deterministic approach, in spite some degree of uncertainties is associated with soil and stone column parameters. In the present work, reliability analysis of bearing capacity of stone columns is examined; using three methods of reliability analysis, First Order Second Moment FOSM, Point Estimate Method PEM, and Monte Carlo simulations MCs. Parametric analysis using all variables involved in stone columns design has been conducted. Distributions of random variables involved in stone columns design are considered either as normal or lognormal. The random variables correlation effect is examined. The study has allowed to evaluate parameter uncertainty effect on reliability index of stone columns, and has permitted to figure out reduced set of parameters that must be considered as random in reliability analysis of stone columns beside sensitivity analysis.

Artificial neural network optimized by differential evolution for predicting diameters of jet grouted columns

A novel and effective artificial neural network (ANN) optimized using differential evolution (DE) is first introduced to provide a robust and reliable forecasting of jet grouted column diameters. The proposed computational method adopts the DE algorithm to tackle the difficulties in the training and performance of neural networks and optimize the four quintessential hyper-parameters (i.e. the epoch size, the number of neurons in a hidden layer, the number of hidden layers, and the regularization parameter) that govern the neural network efficacy. This approach is further enhanced by a stochastic gradient optimization algorithm to allow ‘expensive’ computation efforts. The ANN-DE is first trained using a prepared jet grouting dataset, then verified and compared with the prevalent machine learning tools, i.e. neural networks and support vector machine (SVM). The results show that, the ANN-DE outperforms the existing methods for predicting the diameter of jet grouting columns since it well balances training efficiency and model performance. Specifically, the ANN-DE achieved root mean square error (RMSE) values of 0.90603 and 0.92813 for the training and testing phases, respectively. The corresponding values were 0.8905 and 0.9006 for the optimized ANN, then, 0.87569 and 0.89968 for the optimized SVM, respectively. The proposed paradigm is bound to be useful for solving various geotechnical engineering problems regardless of multi-dimension and nonlinearity.

Static and dynamic characterization of fiber reinforced sand: A numerical investigation

For the characterization of fiber-reinforced soil under static loading conditions, there is a wealth of literature. However, study on the dynamic behavior of fiber-reinforced soil is very limited. Now that earthquakes are occurring frequently around the world, the dynamic soil analysis has become important for all classes of geotechnical engineering problems. Through numerical simulation of triaxial specimens, the current study explores the behaviour of fiber-reinforced cohesionless soil. The numerical model was validated using existing laboratory triaxial compression testing literature. The stress–strain response of fiber-reinforced sand has been investigated using static and cyclic triaxial testing, as well as other combinations of fiber contents. Fiber-reinforced sand is tested for bulk modulus, shear modulus, and damping values. Effects of fiber contents on static and dynamic stress–strain response of fiber-reinforced soil are highlighted. It has been observed from results that, with an increase in fiber content modulus of elasticity, bulk modulus and shear modulus values increase while damping coefficients decrease for the same. It is believed that the highlighted numerical approach will be an alternative to laboratory experiments to determine the dynamic properties of fiber-reinforced soil.

A semi‐analytical solution for displacement‐controlled elliptical cavity expansion in undrained MCC soil

AbstractConventional cavity expansion theory is a one‐dimensional problem and is not applicable for the two‐dimensional cavity expansion issue, which is also required for geotechnical problems. This paper proposes a novel semi‐analytical solution for displacement‐controlled elliptical cavity expansion (DC‐ECE) in undrained soil. The displacement and strain fields for DC‐ECE are obtained from the strain path method (SPM) with the aid of conformal mapping theory. The effective stress can be subsequently obtained by the incremental stress‐strain calculation using a suitable constitutive model such as the MCC model. Then, the computed effective stress results are substituted into the stress equilibrium equation to give the pore pressure solution. The new semi‐analytical solution reveals the non‐axisymmetric characteristics of DC‐ECE and allows the elastic‐plastic (EP) boundary, excess pore pressure, stress, and displacement to be calculated. The proposed method provides a solution to non‐axisymmetric cavity expansion issues and it can be applied to geotechnical engineering problems, including vertical drain installation, flat dilatometer tests and noncylindrical pile penetration in clay.

Artificial Neural Network-Based Model for Prediction of Frost Heave Behavior of Silty Soil Specimen

Frost heave action is a major issue in permafrost regions that can give rise to various geotechnical engineering problems. To analyze and predict this phenomenon at a specimen scale, this study conducted a fully coupled thermal-hydro-mechanical analysis and evaluated the frost heave behavior of frozen soil considering geotechnical parameters. Furthermore, a parametric study was performed to quantitatively analyze the effects of major geotechnical properties on frost heave behavior. According to the results of the parametric study, the amount of heave tended to decrease as the particle thermal conductivity increased, whereas the frost heave ratio tended to increase as the initial hydraulic conductivity increased. After evaluating the sensitivity of each parameter to frost heave behavior through statistical analyses, an artificial neural network model was developed to practically predict frost heave behavior. According to the verification results of the neural network model, the trained network model demonstrated a reliable accuracy (R2 = 0.893) in predicting frost heave ratio, even when the model used test datasets that were not part of the training datasets.

Application of Harmony Search Algorithm to Slope Stability Analysis

Slope stability analysis is undoubtedly one of the most complex problems in geotechnical engineering and its study plays a paramount role in mitigating the risk associated with the occurrence of a landslide. This problem is commonly tackled by using limit equilibrium methods or advanced numerical techniques to assess the slope safety factor or, sometimes, even the displacement field of the slope. In this study, as an alternative approach, an attempt to assess the stability condition of homogeneous slopes was made using a machine learning (ML) technique. Specifically, a meta-heuristic algorithm (Harmony Search (HS) algorithm) and K-means algorithm were employed to perform a clustering analysis by considering two different classes, depending on whether a slope was unstable or stable. To achieve the purpose of this study, a database made up of 19 case studies with 6 model inputs including unit weight, intercept cohesion, angle of shearing resistance, slope angle, slope height and pore pressure ratio and one output (i.e., the slope safety factor) was established. Referring to this database, 17 out of 19 slopes were categorized correctly. Moreover, the obtained results showed that, referring to the considered database, the intercept cohesion was the most significant parameter in defining the class of each slope, whereas the unit weight had the smallest influence. Finally, the obtained results showed that the Harmony Search algorithm is an efficient approach for training K-means algorithms.

Assessing the accuracy and efficiency of different order implicit and explicit integration schemes

A first order accurate fully implicit integration scheme and four different order explicit substepping integration schemes with automatic error control are used in this paper to integrate the constitutive relations of a critical state model for saturated soils. Their respective computational performance in terms of accuracy and efficiency is assessed in order to provide practical guidance for deciding which of the five is most suitable for solving numerical problems in geotechnical engineering involving critical state models. Even though existing literature of integration schemes applied to geotechnical problems has traditionally been focussed on the first order accurate implicit backward Euler and on the second order accurate explicit modified Euler with substepping almost exclusively, the findings of this paper suggest that the little extra work required in the implementation of an explicit third order Runge-Kutta substepping scheme is worth the effort, especially in terms of computational cost.

Behavior of Residual Soil with High Silt Content Under Low Frequency Cyclic Loading Using Modified Direct Simple Shear Apparatus

This paper presents the experimental work on typical Malaysian silty residual soils in order to evaluate fundamental soil properties in particular its stiffness under low frequency cyclic loading. There has been very little information on local silty residual soils which is very important for local geotechnical design purposes. Lack of such information contributes to the dependency of foreign soil data which might not be representative of local silty residual soils. This study departs from the basis of there have been verified evidences that we are not spared from seismic activity in Malaysia. Hence, it would be misleading if we were to exclude soil properties under cyclic loading for design purposes in Malaysia. This research revolves around the development of simplified device to evaluate the stress-strain behaviour of soils under simple shear strain conditions. The cyclic loading test results on Malaysian sedimentary residual soil sample exhibit increase of drained shear stiffness, GSTIF and gained strength after 30 cycles indicating cyclic hardening behaviour. It is evident that magnitudes of cyclic load and cyclic displacement influences the rate of soil volume change. Nevertheless, the densification of soil samples due to increment of cycles caused reduction in volume change. It is foreseen that the obtained parameters could assist in the practical geotechnical engineering problems related to cyclic conditions.

Numerical modelling of large deformation problems in geotechnical engineering: A state-of-the-art review

Many problems in geotechnical engineering involve large movements or rotations, examples include natural processes such as landslides, and man-made processes such as earthmoving and pile penetration. While the use of numerical modelling, primarily the finite element method (FEM), is now routine in geotechnical design and analysis, the limitations of conventional FEMs soon become apparent when attempting to model large deformation problems. For this reason, the search for alternatives remains a key goal of many geotechnical researchers, both to find accurate methods but also to develop efficient ones. In this review paper, prompted by Technical Committee 103 of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE), we survey the current state-of-the-art in numerical modelling techniques aimed at large deformation problems in geotechnics. The review covers continuum and discontinuum methods and provides a clear picture of what is and is not currently possible, which will be of use to both practitioners seeking suitable methods and researchers developing existing or new methods.

Multi frequency Ground-Penetrating Radar method for mapping underground pipes and man-made objects

Mapping of subsurface infrastructure such as pipelines, pipe ducts as well as man-made objects located below the earth surface is a difficult task in geotechnical engineering due to the need to direct contact to the object. Ground-Penetrating Radar (GPR) method as one of geophysical methods is an appropriate technique to solve such problems due to its capability to effectively provide the existence, the location and the depth of buried shallow objects. Despite many advantages, the application of GPR method is limited by achieved depth and resolution range that is frequency dependent. To overcome such problems, the so-called multi-frequency compositing method with Optimal Spectral Whitening (OSW) technique is studied and applied on real data acquired in the Muarakarang Combined Cycle Power Plant area located in the Northern part of Jakarta, the Capitol of Indonesia. Datasets from GPR measurement with 100 MHz and 250 MHz was used. Each radargram from the same path was processed individually and then joined to become multiple composite radargram. The resulted composite radargram from a GPR line we studied has shown clearer image for interpretation rather than individual interpretation. The applicability of this multi-frequency compositing recommend further study to solve some facing problems in geotechnical engineering.

ASS-GPR: Adaptive Sequential Sampling Method Based on Gaussian Process Regression for Reliability Analysis of Complex Geotechnical Engineering

Reliability analysis of complex geotechnical engineering is time-consuming since its performance function is highly nonlinear and implicit. In this paper, an adaptive sequential sampling metamodeling-based method is proposed to deal with such problems. Gaussian process regression (GPR), utilized to approximate the real performance function, is constructed by the initial design of experiments (DOEs). Based on the geometric meaning of the most probable point (MPP) in the first-order reliability method (FORM), the potential MPP, which is a point infinitely close to the limit-state surface and with the minimum distance to the origin while considering a distance constraint, is searched and added to the DOE to refine the GPR. Then, the Monte Carlo simulation (MCS) is adopted to evaluate the failure probability by the refined GPR. The above two procedures are repeated until the stopping criterion is reached. Three examples, including one mathematical example and two geotechnical engineering problems, are analyzed. The results show the proposed method requires fewer performance function calls and is an efficient, accurate, and robust reliability analysis method.

A stable node-based smoothed PFEM for solving geotechnical large deformation 2D problems

The strain smoothed nodal integration particle finite element method (NS-PFEM) has a high level of computational efficiency. However, it suffers from the ‘overly soft’ problem. This study presents the development of a stable nodal integration PFEM for solving geotechnical large deformation problems. A node-based strain smoothing (SNS) PFEM is developed by combining a 3-node triangular element-based PFEM and a stable nodal integration method with strain gradient in the smooth domain for single solid phase. Its performance is examined by simulating two benchmark tests on elastic material (i.e., cantilever beam and infinite plate with a circular hole) and three cases on elastoplastic material (i.e., cavity expansion, penetration of a rigid footing in soft soil and progressive failure of slope). Results show that the integration of stabilisation term gives the SNS-PFEM ‘close to exact’ stiffness, thereby resolving the ‘overly soft’ and temporal instability issues seen with the NS-PFEM. The proposed method is powerful and easily extensible for analysing large deformation problems in geotechnical engineering.

An improved node-based smoothed point interpolation method for coupled hydro-mechanical problems in geomechanics

An improved version of the node-based smoothed point interpolation methods (NSPIMs) is proposed for coupled hydro-mechanical problems of geotechnical engineering. In the improved NSPIMs (I-NSPIMs), the polygonal nodal smoothing domains are estimated with area-equivalent circular domains. The smoothed strains over the circular nodal smoothing domains are then assumed to be linear, in contrast to the constant smoothed strain adopted in the original NSPIMs. The efficiency of the proposed method is investigated through five practical examples, all showing clear superiority of I-NSPIMs over the original formulation of NSPIMs in small deformation problems of geomechanics.