Geotechnical Problems Research Articles

Stabilized Unfitted Finite Element Method for Poroelasticity With Weak Discontinuity

AbstractPoromechanics problems in geotechnical and geological contexts often involve complex formations with numerous boundaries and material interfaces, which significantly complicate numerical analysis and simulation. The traditional finite element method (FEM) encounters substantial challenges in these scenarios because it requires the mesh to conform precisely to each boundary and interface. This requirement complicates preprocessing and necessitates meticulous manual control to achieve a high‐quality mesh. In contrast, unfitted FEMs are well‐suited for these problems as they do not require the mesh to align with the model geometry. We propose a stabilized unfitted FEM that incorporates Nitsche's method and ghost penalty stabilization techniques to address complex poroelasticity problems. This approach treats material interfaces as weak discontinuities and ensures that compatibility conditions are satisfied. The proposed method allows the mesh to be independent of both boundaries and material interfaces. Nitsche's method is used to weakly enforce both Dirichlet boundary conditions and interface compatibility conditions, resulting in a symmetric weak form. Additionally, three types of ghost penalty terms are introduced for elements intersected by boundaries or interfaces, effectively eliminating cut‐induced ill‐conditioning. The proposed methodology has been validated through benchmark and practical problems, demonstrating optimal convergence and exceptional stability. This approach significantly enhances the stability and efficiency of hydro‐mechanical analyses for complex geotechnical and geological problems.

Numerical Simulation of a Marine Landslide in Gas Hydrate-Bearing Sediments Using L-GSM

The marine gas hydrates within seabed sediments and their subsequent extraction may cause landslides. Predicting landslides in hydrate-bearing sediments is particularly challenging due to the intricate nature of the marine environment. To address this issue, we have developed a Lagrangian gradient smoothing method (L-GSM) based on gradient smoothing techniques. This approach effectively eliminates the tensile instability inherent in the original Smoothed Particle Hydrodynamics (SPH) method used for modeling solid flow. Then, we applied the L-GSM to investigate the mechanics of hydrate-bearing sediments by integrating a constitutive equation specific to these sediments, which were modeled based on the artificial methane-hydrate-bearing sediment. The robustness and precision of the L-GSM were verified through various numerical examples. Furthermore, we modeled the landslides associated with hydrate-bearing sediments under varying hydrate saturation levels. The numerical findings revealed that hydrate saturation significantly affects the dynamics of landslide movement. These satisfactory results suggest that the L-GSM has the potential to be applied to geotechnical problems associated with hydrate-bearing sediment.

The Role of Microorganisms in Bio-cement Production: An Extended Review

Bio-cement is an innovative material with the potential for replacement of conventional cement through microorganisms-influenced process. The major method uses bacterial, fungal, or algal activity to produce Microbial-Induced Calcium carbonate Precipitation (MICP). This review aims to understand the microbial aspect of bio-cement production explaining the process through MICP that is enhanced by ureolytic bacteria with a focus on <i>Sporosarcina pasteurii</i> through the provide urease. Bio-cement has many environmental advantages such as lower CO<sub>2</sub> emission in comparison with common cement and opportunities to utilization of waste products. In construction, it is used in self-healing concrete, crack repair, and soil stabilization among others to demonstrate its flexibility in the construction industry due to its available solutions to many structural and geotechnical problems. The review also includes directions for basic, applied, and translational research, targeted genetic modifications for enhanced microbial performance, bio-cement, and more effective microbial strains, and the convergence of bio-cement with 3D printing. Even though bio-cement is an environmentally friendly approach used for soil stabilization, the negative impacts that surround the environment, for further research in making the bio-cement more bio-deteriorate and energy efficient.

Climate Resilient and Sustainable Infrastructures: Geotechnical Challenges of Problematic Soils in Nigeria

Climate change adaptation and sustainable infrastructure development are important in Nigeria due to different climate zones and poor soil types like expansive clays, laterite and peat grounds. The review highlights the necessity of incorporating climate change adaptation into infrastructure development processes to minimise the potential impacts of direct climate change phenomena, including extreme rainfall, flood, and temperature. It emphasises the importance of geotechnical engineering in tackling such challenges and advancing tools and frameworks required for constructing structures that successfully counter the undesirable soil responses caused by climate change. The review used literature search methods and data synthesis to identify empirical works that explore the geotechnical problems associated with Nigeria's problematic soils and their effects on infrastructures’ durability. It organises results according to soil categories and introduces new geotechnical interventions, emphasizing chemical and mechanical stabilization methods to improve overall structural resilience. It also touches on some areas of policy and regulation that need reform in Nigeria to provide broader guidelines for geotechnical investigations and the adoption of new materials for construction. The manuscript concludes with policy implications and recommendations for implementing and developing solutions for climate-resilient infrastructure in Nigeria against climate change unpredictability concerning socio-economic activities and human life.

Exploring Topology Optimization in Geotechnical Engineering

Despite recent advancements in utilizing topology optimization in geotechnical engineering design, practical applications primarily focus on simple foundation design. In the view of this, this study aims to explore the application of topology optimization methodology to various geotechnical design problems. The optimization takes place in a finite portion of the soil, modeled via Finite Element Method (FEM) which is coupled with the rest of the semi-infinite soil, modeled via Indirect Boundary Element Method (IBEM). The optimization is carried out considering a linear bi-material interpolation through the three field Floating Point Topology Optimization (FPTO) method. Numerical results for the optimized foundations of plates, bridges and linings are presented and discussed.

A mixed total Lagrangian-updated Lagrangian Smoothed Particles Hydrodynamics method for geomechanics simulations with discontinuities

This study presents a novel approach for simulating geotechnical problems including the initiation and post-failure behavior of discontinuities. The developed method is constituted by a mixed total Lagrangian--updated Lagrangian Smoothed Particle Hydrodynamics (SPH) method, which the main characteristic is to distinguish between internal forces within a body and contact forces from interactions with other bodies as internal stress and collision stress, respectively. Internal stress effects are calculated using total Lagrangian SPH interpolations, while collision stress effects are computed with updated Lagrangian. Fractures are simulated by employing plastic deformation as a damage measure, with fully damaged particles detached from their original body and treated as a separate particulate material, interacting via collision stress. Numerical tests confirm the method's capability in accurately modeling elastic collisions, friction forces and tension and shear fractures, validated against experimental data. Finally, we show the applicability of the proposed by simulating a real-scale landslide scenario, the Selborne experiment. This final numerical test demonstrates the capability of the method to simulate a landslide detached from the main soil mass as observed in the experiment.

Insights into the mechanics of uncemented and lightly cemented compacted iron ore tailings under high confining pressures

Grading changes due to particle breakage are crucial in geotechnical engineering problems involving high pressures, such as elevated-height dry stacking facilities for compacted filtered iron ore tailings disposal. However, understanding the iron ore tailings response at high stress is still in its early stages in the Brazilian context. It is now marked by the increasing need for alternatives to tailings allocation rather than the traditional slurry disposal in impoundments. The present research, which examines the mechanical response of iron ore tailings and lightly cemented iron ore tailings over confining pressures ranging from 1.2 to 120 MPa for dry stacking purposes, provides significant insights into this area. The study relied on triaxial tests conducted on a high-pressure apparatus that employed specimens compacted at three different compaction degrees. The cement addition incurred slight differences in isotropic compression, enlarging the range of achievable states. Still, the shearing response of both uncemented and lightly cemented tailings was very similar, particularly at higher stress levels, resulting in an equivalent critical state locus. In the v- ln ṕ plane, an S-shaped function described the critical state and delineated the regions where particle breakage becomes an important source of volumetric strain. In brief, this study provides novel insights into the behaviour of uncemented and lightly cemented iron ore tailings in the context of elevated-height dry stacking facilities.

Leaching Studies for the Assessment of Individual Immobilization Potential of Chrysopogon zizanioides Root Micro Powder from Lead, Cadmium and Chromium Contaminated Soil

ABSTRACT Contemporary issues of ground contamination, exacerbated by elevated heavy metal levels due to industrial activities and improper waste disposal, significantly impact soil properties, the biosphere, and result in various geotechnical problems. This study delves into the efficacy of Chrysopogon zizanioides (vetiver) root micro powder (VRMP) in immobilizing Lead (Pb), Cadmium (Cd), and Chromium (Cr) within contaminated soil to prevent groundwater pollution and bioavailability. Leaching experiments were conducted to evaluate the individual immobilization of heavy metals and determine the optimal VRMP dosage, testing four dosages (0%, 1%, 5%, and 10%) for their effectiveness in immobilizing Pb, Cd, and Cr in contaminated soil. The findings suggest that addition of VRMP led to an increase in pH, facilitating the enhanced immobilization of Pb, Cd, and Cr from the contaminated soil due to the reduction in mobility of these metals. Soil treated with 10% VRMP exhibited exceptional immobilization efficiency, achieving over 90% removal across all treatments. However, agglomeration caused the leaching process to take slightly longer. Consequently, a 5% VRMP dosage is considered optimal. In conclusion, vetiver root micro powder promotes a sustainable approach to immobilize Pb, Cd, and Cr in contaminated soils, underscoring the effectiveness of eco-friendly methodologies.

MAPEAMENTO DE SUSCETIBILIDADE À DESASTRES NATURAIS ATRAVÉS DO USO DA LÓGICA NEBULOSA NO MUNICÍPIO DE ALEGRE–ES

Among the various problems that Brazil currently faces, few have a social and human impact as significant as those related to natural phenomena and their negative consequences for society, especially geotechnical events and floods. In a country like Brazil, which suffers from a lack of urban planning and adequate investments in infrastructure to prevent this type of occurrence in various spheres, recurring tragedies accumulate year after year, always accompanied by the perception that they could have been avoided. On the other hand, the geosciences have been increasingly open to new geotechnologies. In this context, the present work presented new paths that offer useful resources to seek short to medium-term solutions, helping to overcome the various challenges related to this theme, both at the national, regional and municipal levels. Thus, the methodology related to geotechnologies and its various techniques was used, with emphasis on Fuzzy Logic, which was the main pillar of this study. In the end, the methodology adopted proved to be effective in pointing out the areas of greatest susceptibility to geotechnical problems and flooding, revealing great potential for future applications of greater complexity and scope.

Constitutive modelling in computational geomechanics – 61st Rankine lecture, British Geotechnical Association, 2023

Constitutive models are an essential part of computational modelling in geotechnics; they are at the heart of almost all theoretical predictions of geotechnical structures. How the stress–strain (and perhaps time) response of soil (and rock) is represented in these mathematical models is usually the key to successful prediction of the behaviour of geotechnical structures. However, the important details of these models, particularly the idealisations that are made, may be poorly or incompletely understood, or ignored, sometimes at significant cost to the unwary analyst. Indeed, the capabilities and the shortcomings of these models, especially the more advanced models, are not always easy to ascertain. In some cases, determination of the values of the input parameters is not straightforward. Consequently, it may be difficult to determine which model to select for a particular task. This paper explores some of the more important developments in the constitutive modelling of soils and addresses some of these issues of potential concern. The need for such models and the various attributes and capabilities that the commonly used models possess are reviewed. Also discussed is the issue of matching a particular model to the geotechnical problem at hand, which model attributes are required and why. The intention is to place emphasis on the physical basis of these models, rather than explore their mathematical complexity in detail. Some of the constitutive models encoded in the software packages used routinely in geotechnical practice are reviewed, and discussion is also provided on their specific limitations. Examples of practical applications, involving the solution of boundary and initial value problems, are described to illustrate both the advantages and some of the limitations of both commonly used and highly advanced constitutive models.

Spurious Accelerations in Finite Element Analysis of Geotechnical Problems: Cause and Remedy

Present study investigates the response of the two distinct geotechnical problems under earthquake loading. These two problems are: 1) nailed soil slope and 2) 1-D site response analysis. The aim of the study is to understand the cause of spurious accelerations and suggest a remedy. Two distinct interface conditions were considered in modelling the nailed soil slope. In first, the soil nail interface was considered to be perfectly bonded. In second case, the sliding at the interface was allowed. The analysis resulted into the physically acceptable deformations. However, the dumbbell shaped spurious acceleration pattern was observed in perfect bonding case. Further, the maximum acceleration was found to span from 4 g to 13 g. Such extremely high accelerations are unphysical and hence, unacceptable. In case of 1-D site response analysis, misleading acceleration spike of magnitude twice that of true acceleration was noted. The introduction of the numerical damping successfully removed the spurious accelerations and resulted in physically acceptable response for both problems. Received: 30 May 2024 | Revised: 30 August 2024 | Accepted: 20 September 2024 Conflicts of Interest The author declares that he has no conflicts of interest to this work. Data Availability Statement Data available on request from the corresponding author upon reasonable request. Author Contribution Statement Dhanaji Chavan: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Resources, Data curation, Writing - original draft, Writing - review & editing.

Data-enhanced design charts for efficient reliability-based design of geotechnical systems

This paper proposes a new design chart approach for reliability assessment, which enables clear visualization of the representative soil shear strength parameters under various reliability levels and effective stress levels. Utilizing the design charts, reliability assessment or reliability-based design can be performed with significantly reduced numbers of evaluations of the geotechnical system response. The design charts are established solely based on the probability distributions of soil parameters, and are applicable to a variety of geotechnical problems involving the same soil type. For practical illustration of the proposed approach, design charts are produced from the shear strength databases of saprolitic soils and colluvial soils in Hong Kong, and then applied to the reliability-based design of a slope with soil nail reinforcements. The ensuing design solutions require much fewer soil nails compared to the conventional design practice, while also achieving a better system reliability. The same charts are then applied to the reliability-based design of a retaining wall, where a series of design options are identified with equivalent reliability index against overturning failure and pullout failure. Through the proposed approach, the use of design charts promotes efficient reliability-based design of geotechnical systems with rational incorporation of reliability concepts.

Artificial Neural Network Model to Predict the Factor of Safety in Earth Dams Subjected to Rapid Drawdown

Rapid drawdown has been identified as one of the most frequent causes of slope failures due to the effects associated with drought and operational changes when incorporating hydroelectric plants, which influence the filling level of earth dams. The main goal of this research is to obtain predictive models based on Artificial Neural Networks that return the factor of safety of the upstream slope in homogeneous earth dams in the face of the effect of rapid drawdown. Three geometries and 40 soils were defined to form the embankment, from which hybrid numerical models of transient water flow with unsaturated soils were built, considering three discharge speeds. From these results, a database was built to develop the predictive models, by means of the KNIME program and an algorithm based on Artificial Neural Networks. The behavior of the factor of safety as a function of time is also analyzed to establish its recovery intervals. Main results show that the minimum factor of safety is obtained between 52 % and 88 % of the total drawdown time. Regarding the predictive models, the adjusted R2 determination coefficients were greater than 95 % in all cases and the errors remained below 10 %. This demonstrates a high effectiveness of this algorithm and the validity of its application to geotechnical problems.

Potential of Limestone Calcined Clay Cement (LC3) in soil stabilization for application in roads and pavements construction

Clay soil is associated with geotechnical problems of swelling and shrinkage, which causes deformations on structures. Ordinary Portland Cement (OPC) which is the most common stabilizing agent for clay soils, remains unaffordable in most developing countries, and its production also contributes about 8 % of global anthropogenic CO2 emissions. The present study aimed to investigate the effect of Limestone Calcined Clay Cement (LC3) on the stabilization of clay soils for applications in road construction. Clay soil was mixed with quarry dust to reduce the clay content and save cement. The mixture was stabilized using LC3 and OPC separately in proportions of 1 %, 3 % and 5 %. The effect of stabilizer dosage on the performance of clay soil was studied by monitoring the changes in Atterberg limits, Proctor test and soaked California Bearing Ratio (CBR). The mineralogical and microstructural investigation was carried out using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Thermogravimetric Analysis (TGA). Plasticity index (PI), linear shrinkage (LS), and optimal moisture content (OMC) of stabilized soil was found to decrease with increase in the dosage of LC3 and OPC. The Maximum Dry Density (MDD) and soaked CBR increased with addition of both LC3 and OPC. Formation of calcium silicate hydrate (C-S-H) in both LC3 and OPC stabilized clay soil, as well as formation of Hemi-carboaluminate in LC3 stabilized clay soil was responsible for improved properties of the stabilized soil. The performance of LC3 was found to be comparable to that of OPC, at optimum cement ratio of 5 %.

New Numerical Technique for the Inbuilt Modified Cam Clay Constitutive Model in FLAC3D

Fast Lagrangian Analysis of Continua (FLAC) is a powerful numerical platform for simulating the deformation and stability of geotechnical structures. Presently, it is documented that the embedded Modified Cam Clay constitutive model in the FLAC platform is deficient in solving geotechnical problems. This paper outlines the new calibration approach by determining the isotropic preconsolidation pressure multiplier based on the relationship between the total stress in the geotechnical problem and the reference pressure. The multiplier was used to establish the nominated maximum isotopic preconsolidation pressure and maximum referential consolidation ratio at the bottom of the soil layer. Subsequently, the maximum isotopic preconsolidation pressure was used to determine the bulk maximum. In addition, the developed approach was used to investigate the lateral displacement of the large grid wall foundation by deep mixing under the adjacent surcharge loading. The feasibility was validated using the centrifuge results. The coefficient of determination between lateral displacement from numerical and centrifuge modelling R2 was 0.95. The proposed numerical technique and calibration approach demonstrated that the embedded Modified Cam Clay model can be used to solve practical geotechnical problems.

Experimental and finite element assessment of stabilizing configurations for underground heritage sites

Heritage sites in Alexandria, Egypt, are some of the UNESCO world heritage sites at high risk from geo-environmental hazards, in particular caused by sea level rise and heavy rain due to the climate change. Recently, safeguarding UNESCO world subterranean and built heritage draws more attention. After recent environmental catastrophies in Alexandria, sustainable conservation materials and stabilizing configurations of underground monumental structures has also become urgent and highly demanded. Based on typical damage due to the heavy weathering caused by the ground water table and salt, this paper offers a guide for engineers and conservators, where rock structures consolidation and stabilizing configurations to protect these structures in the static state and against strong seismic events is presented. In this paper, typical geotechnical problems and damage to the Catacombs of of Kom El-Shoqafa are presented first, followed by an experimental evaluation methodology that includes spectroscopic and morphological characterization in addition to the mechanical testing of untreated and treated rock samples with synthetic organosilicone and acrylic compounds. The effectiveness of the new silica-based consolidants was evaluated in terms of the amount of solid adsorbed, mechanical properties (e.g., surface hardness, ultrasonic velocity, modulus of elasticity and modulus of compressive strength), and resistance to salt crystallization. The treated groups showed better mechanical strength than the control group. The ability of the treated samples to resist climate change negative impact was also greatly improved. According to laboratory tests, new silica-based hardeners and hydrophobic materials have great potential for strengthening weathered Calcarenitic rock structures. It was observed that the rock samples containing the modified binder (MTMOS + Wacher BS 15) reach higher mechanical strength parameters. After the experimental study (testing procedures), FEM analysis was performed using PLAXIS 2D code to validate the silica-based consolidants and verify their efficiency in improving the response of rock structures in static and seismic states against strong earthquake events. The results of this work confirm the high potential of low-cost injection techniques and stabilizing configurations (pre- stressed anchors and concrete friction piles) technology, confirming the possibility of achieving significant improvement in the geotechnical properties of Calcarenitic rock structures and enhancing the seismic performance of underground archaeological structures using low-cost injection technology that is easy to manufacture.

Influence of adding gypsum on the properties of lime-stabilized expansive soil

Abstract Expansive soils present major structural and geotechnical engineering problems. Expansive soil undergoes considerable changes in volume because of variations in water content. These variations in volume can occur as either swelling or shrinking and are commonly referred to as swell-shrink soils. Considering key aspects, such as the characteristics of the soil, is essential when dealing with swelling soils. There are expansive soils in both humid areas, where they pose problems with a high plasticity index, and in semi-arid or arid areas, where even moderately swelling soils can cause considerable damage. In order to solve problems related to expansive soil, it is important to stabilize it using various additives like gypsum, lime, and so on. The effects of adding three percentages of gypsum (2%, 4%, and 8%) to 6% lime-stabilized expansive soil to improve its engineering properties are investigated through several tests. The results of tests displayed that adding gypsum has improved properties of prepared soil with 6% lime. The optimum mixture for (gypsum-lime) that gets the highest improvement in soil properties is (6% lime + 4% gypsum). This mixture shows reducing in the free swell, swelling pressure, and plasticity index (from 8.51% to 2.81%, from 715.68 Kpa to 89.18 Kpa, from 33% to 29% respectively). Also, this mixture shows increasing in CBR (from 13.69% to 16.17%) and unconfined compressive strength (UCS) for the curing time of 0, 7, and 14 days (from 264.318 Kpa to 492.131 Kpa, from 380.584 Kpa to 736.318 Kpa, and from 480.192 Kpa to 828.590 Kpa respectively). The maximum dry density (MDD) and optimum moisture content (OMC) increase with increasing gypsum content, While the specific gravity decreases.

Parametric study to implement a water-weakening process in UDEC

Despite the prevalence and validity of the universal distinct element code (UDEC) in simulations in geotechnics domain, water-weakening process of rock models remains elusive. Prior research has made positive contributions to a presupposed link between modelling parameters and saturation degree, Sr. Nevertheless, this effort presents inaccurate results and limited implications owing to the misleading interpretation, that is, devoid of the basic logic in UDEC that modelling parameters should be calibrated by tested macroscopic properties in contrast to a presupposed relation with Sr. To fill this gap, a new methodology is proposed by coupling a computationally efficient parametric study with the simulation of water-weakening mechanisms. More specifically, tested macroscopic properties with different Sr values are input into parametric relations to acquire initial modelling parameters that are sequentially calibrated and modulated until simulations are in line with geomechanical tests. Illustrative example reveals that numerical water-weakening effects on macroscopic properties, mechanical behaviours, and failure configurations are highly consistent with tested ones with noticeable computational expediency, implying the feasibility and simplicity of this methodology. Furthermore, with compatibility across various numerical models, the proposed methodology substantially extends the applicability of UDEC in simulating water-weakening geotechnical problems.

Future-proofing geotechnics workflows: accelerating problem-solving with large language models

ABSTRACT The integration of Large Language Models (LLMs), such as ChatGPT, into the workflows of geotechnical engineering has a high potential to transform how the discipline approaches problem-solving and decision-making. This paper investigates the practical uses of LLMs in addressing geotechnical challenges based on opinions from a diverse group, including students, researchers, and professionals from academia, industry, and government sectors gathered from a workshop dedicated to this study. After introducing the key concepts of LLMs, we present preliminary LLM solutions for four distinct practical geotechnical problems as illustrative examples. In addition to the basic text generation ability, each problem is designed to cover different extended functionalities of LLMs that cannot be achieved by conventional machine learning tools, including multimodal modelling under a unified framework, programming ability, knowledge extraction, and text embedding. We also address the potentials and challenges in implementing LLMs, particularly in achieving high precision and accuracy in specialised tasks, and underscore the need for expert oversight. The findings demonstrate the effectiveness of LLMs in enhancing efficiency, data processing, and decision-making in geotechnical engineering, suggesting a paradigm shift towards more integrated, data-driven approaches in this field.

Modeling, reinforcement, and assessment of the landslide in Ben Djerrah (Guelma, Algeria) using the finite element method

Landslides are detected in many places in Algeria, posing a danger to people and property. This is a significant geotechnical problem. To address this issue, a set of solutions is available. However, it is crucial first to understand the causes of soil slippage. This can be achieved through laboratory experiments and on-site investigations in the threatened areas where slippage occurs. In this paper, we study the landslide of Ben Djerrah using the finite element method by the Plaxis software. This slope stability of Ben Djerrah is cited in Guelma (Algeria). The numerical analysis used by the strength reduction method (SRM) with the Mohr-Coulomb criteria gave us the most important results for this slide. The smaller factor of safety (0.974) and the critical slope surface location and shape (rotational) indicate that Ben Djerrah is unstable. To stabilize the slope, we reinforced it using a propped solution with piles. The numerical analysis used it to model the slope of Ben Djerrah by pile to stop the movement of soil from sliding. The results show that the slope of Ben Djerrah is stable after being reinforced by a pile, and the shape of the failure surface has become less than the previous area that resulted from soil sliding without a pile.