Environmental Geotechnics Research Articles

Estimating the strength of soil stabilized with cement and lime at optimal compaction using ensemble-based multiple machine learning

It has been imperative to study and stabilize cohesive soils for use in the construction of pavement subgrade and compacted landfill liners considering their unconfined compressive strength (UCS). As long as natural cohesive soil falls below 200 kN/m2 in strength, there is a structural necessity to improve its mechanical property to be suitable for the intended structural purposes. Subgrades and landfills are important environmental geotechnics structures needing the attention of engineering services due to their role in protecting the environment from associated hazards. In this research project, a comparative study and suitability assessment of the best analysis has been conducted on the behavior of the unconfined compressive strength (UCS) of cohesive soil reconstituted with cement and lime and mechanically stabilized at optimal compaction using multiple ensemble-based machine learning classification and symbolic regression techniques. The ensemble-based ML classification techniques are the gradient boosting (GB), CN2, naïve bayes (NB), support vector machine (SVM), stochastic gradient descent (SGD), k-nearest neighbor (K-NN), decision tree (Tree) and random forest (RF) and the artificial neural network (ANN) and response surface methodology (RSM) to estimate the (UCS, MPa) of cohesive soil stabilized with cement and lime. The considered inputs were cement (C), lime (Li), liquid limit (LL), plasticity index (PI), optimum moisture content (OMC), and maximum dry density (MDD). A total of 190 mix entries were collected from experimental exercises and partitioned into 74–26% train-test dataset. At the end of the model exercises, it was found that both GB and K-NN models showed the same excellent accuracy of 95%, while CN2, SVM, and Tree models shared the same level of accuracy of about 90%. RF and SGD models showed fair accuracy level of about 65–80% and finally (NB) badly producing an unacceptable low accuracy of 13%. The ANN and the RSM also showed closely matched accuracy to the SVM and the Tree. Both of correlation matrix and sensitivity analysis indicated that UCS is greatly affected by MDD, then the consistency limits and cement content, and lime content comes in the third place while the impact of (OMC) is almost neglected. This outcome can be applied in the field to obtain optimal compacted for a lime reconstituted soil considering the almost negligible impact of compactive moisture.

Preface

GEOSHANGHAI 2024 INTERNATIONAL CONFERENCE Volume 6: Geoenvironmental and Energy Geotehnics Shanghai, 26-29 May, 2024 GeoShanghai 2024 International ConferenceCollege of Civil Engineering, Tongji University, 2024All Rights ReservedGeoShanghai is a series of international conferences on geotechnical engineering held in Shanghai quadrennially. The conference was inaugurated in 2006 and was successfully held in 2010, 2014 and 2018, with more than 1600 participants in total. Since the last conference, the geotechnical community has witnessed many advances both in fundamental understanding and engineering practices. To demonstrate the latest developments and promote collaborations in geotechnical engineering and related fields, we launch the 5th GeoShanghai International Conference to be held in May 2024.This volume contains three themes: Environmental Geotechnics, Energy Geotechnicsand Geosynthetics. Environmental Geotechnics is at the forefront of our efforts to rehabilitate and repurpose land, transforming landfills and contaminated soils into safe and productive environments. Energy Geotechnics addresses the critical need for Economically Valuable strategies that harness the Earth’s energy resources responsibly. Geosynthetics provide us equitable access to advanced materials that reinforce, protect, and sustain our environment. These synthetic products are pivotal in our integrative approach, offering versatility and durability in ecological applications. In our pursuit to harmonize human development with the planet’s well-being, this conference unites thought leaders and practitioners in the fields of Environmental Geotechnics, Energy Geotechnics, and Geosynthetics to explore innovative solutions for the pressing environmental issues of our time.This volume received a total of 61 papers from countries such as China, United States, Thailand, and others, totaling 58 papers accepted. All papers were reviewed and the accepted papers will be submitted to IOP Conference Series: Earth and Environmental Science indexed by Scopus.List of Tracks, Conference Steering Committee, International Advisory Committee, Technical Committee, Organizing Committee are available in this pdf.

Editorial: Physical–chemical coupling in environmental geotechnics

Editorial: Physical–chemical coupling in environmental geotechnics

Modeling the influence of lime on the unconfined compressive strength of reconstituted graded soil using advanced machine learning approaches for subgrade and liner applications.

In the field of soil mechanics, especially in transportation and environmental geotechnics, the use of machine learning (ML) techniques has emerged as a powerful tool for predicting and understanding the compressive strength behavior of soils especially graded ones. This is to overcome the sophisticated equipment, laboratory space and cost needs utilized in multiple experiments on the treatment of soils for environmental geotechnics systems. This present study explores the application of machine learning (ML) techniques, namely Genetic Programming (GP), Artificial Neural Networks (ANN), Evolutionary Polynomial Regression (EPR), and the Response Surface Methodology in predicting the unconfined compressive strength (UCS) of soil-lime mixtures. This was for purposes of subgrade and landfill liner design and construction. By utilizing input variables such as Gravel, Sand, Silt, Clay, and Lime contents (G, S, M, C, L), the models forecasted the strength values after 7 and 28 days of curing. The accuracy of the developed models was compared, revealing that both ANN and EPR achieved a similar level of accuracy for UCS after 7 days, while the GP model performed slightly lower. The complexity of the formula required for predicting UCS after 28 days resulted in decreased accuracy. The ANN and EPR models achieved accuracies of 85% and 82%, with R2 of 0.947 and 0.923, and average error of 0.15 and 0.18, respectively, while the GP model exhibited a lower accuracy of 66.0%. Conversely, the RSM produced models for the UCS with predicted R2 of more than 98% and 99%, for the 7- and 28- day curing regimes, respectively. The RSM also produced adequate precision in modelling UCS of more than 14% against the standard 7%. All input factors were found to have almost equal importance, except for the lime content (L), which had an average influence. This shows the importance of soil gradation in the design and construction of subgrade and landfill liners. This research further demonstrates the potential of ML techniques for predicting the strength of lime reconstituted G-S-M-C graded soils and provides valuable insights for engineering applications in exact and sustainable subgrade and liner designs, construction and performance monitoring and rehabilitation of the constructed civil engineering infrastructure.

Briefing: Intensive inland aquaculture ponds: challenges and research opportunities

This briefing presents an overview of inland aquaculture scenario that focuses on challenges of aquaculture farming, contaminant transport and the future of aqua farming in a broader perspective of environmental geotechnics. Un-engineered aquaculture practices are a cause of concern, and special attention is necessary in waste water management, cross-contamination with the adjacent environment, sludge–subsoil interaction, pond embankment slope failure, leachate migration into the vadose zone, geoenvironmental remediation strategies and geotechnical engineering aspects of engineered pond construction.

A computational approach to predict unsaturated soil phases

The unsaturated fractions in a porous medium such as soil are the result of the process of natural humidity changes that occur in environments where both the temperature and the relative humidity of the environment are constantly changing. These processes, important in environmental geotechnics, need to be studied to predict the resistance and permeability that the porous medium may have under various scenarios. This article allows us to establish a computational model that allows us to predict the volumes of the unsaturated fraction. The predictions of the model and its contrast with the Rojas model allow us to conclude that the model can be used on a large scale to be used in engineering applications related to water flow in soils.

Study of the rheological properties of clayey suspensions: an interest in the field of landfills

In the landfill bottom liners design process, geotechnical tests of long duration time are often conducted to ensure the presence of reactive clays and to assess their hydromechanical properties. This study aims to show the interest of the rheometry of clayey suspensions as an alternative tool for identifying clays and determining the shear strength of bottom liners. An experimental protocol, using a six-speed rotary viscometer, was first implemented on bentonite suspensions on the one hand and kaolinite suspensions on the other. The results show that to have similar shear strengths (between 1.0 and 25.4 Pa), the concentration ranges used for these two types of suspensions must be totally different: between 600 to 1200 g/L for kaolinite and 30 to 90 g/L for bentonite, confirming the usefulness of rheometry as a tool for identifying clays. Furthermore, results from rheometry tests also show an increase in the shear stress of kaolinite suspensions when there are made with leachate; such results are in agreement with geotechnical shear tests conducted on compacted samples. This study is of practical use for environmental geotechnics professionals because it offers an alternative to traditional geotechnical tests.

Shear strength of municipal solid waste rejected from material recovery facilities in the city of São Paulo, Brazil

The mechanical behavior of municipal solid waste (MSW) is a critical issue in environmental geotechnics, given the pollution and public health risks associated with slope failures. In Brazil, waste composition is expected to change due to the hierarchy of sustainable practices established by the National Solid Waste Policy, which aims to improve the recovery of organic and recyclable materials. Not much progress has been made since the implementation of this law; thus, its effects on the design and operation of landfills are not fully clear. This study presents and discusses compaction and shear strength parameters of dry MSW after mechanical sorting of medium and large recyclable items and shredding. The maximum dry unit weight for the standard Proctor compaction test ranged from 6.6 to 10.0 kN/m3 and the optimum moisture content ranged from 20% to 42%. Stress-displacement curves of direct shear tests showed strain hardening and shear strength parameters of Mohr-Coulomb envelopes were displacement-dependent. The friction angle ranged from 3.2° to 42.9° and the cohesion intercept ranged from 1.3 to 31.3 kPa, at a displacement of 9 mm (15% of the specimen length). These results are in line with the literature, since a high content of waste materials that proved to affect geotechnical properties, such as plastic, paper, cardboard, textile, and glass, remained after pre-treatment.

Geoenvironmental approaches in an old municipal waste landfill reclamation process: Expectations vs reality

Nowadays, environmental geotechnics and engineering are facing several challenges to be addressed during landfill reclamation works. The purpose of the technical paper is to present examples of reclamation works designed to reduce the soil–water environment impact of an old municipal solid waste landfill and to ensure geotechnical safety. The authors tried to prove that even though the initially designed reclamation works could be difficult to implement and execute, they could bring the desired effect in real conditions. Several technical solutions to re-engineer shape the landfill body and reinforce the slope stability are discussed in the article. Commonly known pollution-reducing methods were also presented and discussed. For many years of operation, a landfill study area was located in difficult hydrogeological conditions, with no systems in place to prevent contamination. Using monitoring and numerical modelling, it has been shown that reclamation works increase the quality of groundwater and improve the conditions for landfill slope stability over time. The study also showed that both vertical barriers and leachate drainage systems can improve the condition of plant communities in landfill surroundings. Accordingly, reclamation works do not fundamentally change the function of a landfill but do limit its negative impacts on the environment, such as reducing the spread of pollutants into soil and water, protecting the slopes from erosion, reducing dust, allowing establishing of new vegetation cover, and improving the visual quality of the landscape. The research proved that expected reclamation results could only be reached if complex approaches and constant monitoring are provided when executing the reclamation works.

Foreword for the special issue on the 14th JGS Symposium on Environmental Geotechnics

Foreword for the special issue on the 14th JGS Symposium on Environmental Geotechnics

Assessing temperature dependence of soil water adsorption strength by molecular simulation

Soil water adsorption strength represents the changing rate of adsorptive water content with regard to soil suction or water potential changes, dictating the magnitude of the soil water-retention curve at the dry end. Non-isothermal conditions are frequently encountered in energy and environmental geotechnics, posing the requirement to assess temperature effects on soil water adsorption strength. Yet, it remains challenging in assessing the temperature effects at the high suction range due to limitations in available experimental techniques. Here, the grand canonical Monte Carlo (GCMC) simulation was explored as a method to address this challenge. A series of GCMC simulations has been performed to assess the temperature effect on the external surface adsorption of three representative soil minerals – that is, K-muscovite, Na-montmorillonite and α-quartz. Molecular simulation results preliminarily reveal that the water adsorption strength of the external surface of these soil minerals only demonstrates marginal dependence on temperature. This observation is consistent with experimental results, substantiating the feasibility of the proposed method.

Hydro-mechanical behavior of two clayey soils in presence of household waste leachates

BACKGROUND AND OBJECTIVESIn landfills, containment is provided by natural or artificial clayey materials known for their low permeability and for their pollutant retention capacity. However, the properties of these media are modified by leachates, whose migration they are supposed to limit. This study aims to reconsider the criteria for choosing suitable materials to make a bottom liner through both their long term hydraulic and mechanical performances.METHODSTwo fine materials sampled in Burkina Faso (West Africa) have been characterized in order to compare their hydro-mechanical behavior in the presence of household waste leachates. The first material is classified as an inorganic clay of low to medium plasticity according to Casagrande plasticity diagram, it is mainly kaolinitic with some traces amounts of smectites. The second one is classified clayey sand of low to medium plasticity, the predominant mineral clay being kaolinite. Hydro-mechanical tests were performed on both sampled materials to judge the sealing properties of these materials, as well as the characteristics of deformation and rupture which have an important effect to ensure the durability of a bottom liner. All these tests were performed first with distilled water then with leachates as interstitial fluids in order to understand the modification of the hydro-mechanical properties of the clayey soils.FINDINGSLeachate contamination always alters hydraulic properties of the materials. However, between the two soils, the most clayey and the most impervious (soils from Nouna) undergo the deeper weathering. Indeed, hydraulic conductivity of these soils in contact with a synthetic leachate increases from 1.71x10-10 to 1.51x10-9 m/s. In contrast to soils from Boudry, these soils also undergo very significant settlements over the long term with compressibility indexes varying from 0.164 to 0.225. For both soils, the shear strength increases showing that, from this point view, the leachate work in the sense of of the bottom liner stability. For soils from Nouna, the effective cohesion increases from 3 to 21 kPa with a slight decrease of friction angle; for soils from Boudry a slight increase of cohesion is noticed while friction angle increases from 34 to 37°.CONCLUSIONThis comparative study is of practical use to environmental geotechnics professionals because it shows that the choice in designing a bottom liner must be a compromise between long term hydraulic and mechanical behaviors of soils. It is also important to know the nature of the flows to contain in order to ensure the durability of the structure.

An improved quantification method for characterisation of clay microstructure using SEM

Clay is a material widely used in environmental geotechnics. Quantification of clay microstructure properties using scanning electron microscopy (SEM) images is intuitively the simplest way, but the challenges remain in extracting more credible quantified micro-parameters that can represent the holistic macroscopic properties of clay from SEM images and with higher efficiency. In this paper, an improved quantification method is proposed to deal with this issue. The influence of different milling and drying methods on quantification results was analysed to improve reliability and efficiency. The A–K threshold determination method (A–K method) was proposed to calculate the optimal threshold in image processing. Also, the interval estimation method was introduced to obtain the optimal magnification and number of images. Then, this quantification method was applied to Hangzhou clay. The results show that anisotropy in the clay microstructure should be considered when choosing the observed surface. Moreover, there is no significant difference in micro-parameters between liquid nitrogen frozen-vacuum drying and critical point drying. A comparison among the A–K method, artificial method and theoretical methods that can determine thresholds shows that the proposed A–K method combines the advantages of all methods. The optimal magnification and number of images can be determined by mathematical theory, which also improves reliability and efficiency.

Sustainable environmental geotechnics practices for a green economy

The revitalisation of the global economy after the Covid-19 era presents environmental geotechnics with the opportunity to reinforce the need for a change in paradigm towards a green, circular economy and to promote aggressively the use and development of sustainable technologies and management practices. This paper aims to assist in this effort by concentrating on several thematic areas where sustainability solutions and future improvements are sought. These include the re-entry of construction and demolition of wastes, excavated materials, industrial wastes and marine sediments into the production cycle and the reuse of existing foundations. Despite the recent trend in advanced countries towards recycling and waste-to-energy thermal treatment, landfills still constitute the most common municipal solid waste management practice, especially in low-and-middle-income countries, and technological solutions to improve their environmental footprint are hereby presented. At the same time, remediation solutions are required to address the multitude of contaminated sites worldwide. Advanced developments that incorporate environmental, economic and social dimensions are expounded by the authors, together with sustainable ground improvement solutions for infrastructure projects conducted in soft and weak soils. The topic of thermo-active geostructures concludes this paper, where, apart from their infrastructure utility, these structures have the potential to contribute to the renewable energy source.

Environmental Geotechnics: Referees 2021

Environmental Geotechnics: Referees 2021

One-dimensional compression creep change under temperature and suction effects

ABSTRACT The impact of temperature and unsaturation on the creep behaviour of bentonite is an important topic for environmental geotechnics as in the case of waste storage and energy geostructures. This paper presents an experimental study on the one-dimensional creep of Maghnia bentonite (MB), using two high-pressure oedometer cells, allowing to impose temperature and suction conditions for an unsaturated medium . The characteristics of these two cells and the protocol developed in the framework of this experimental study are briefly presented. The findings highlight a new perspective on the hypothesis (A) which distinguishes between primary and secondary consolidation, and hypothesis (B), which is governed by structural viscosity. The results indicated that the creep behaviour followed the principle of hypothesis (A) under temperature effect, while it followed hypothesis (B) principle under the suction effect. The void ratio variability under secondary compression depends not only on the vertical stress, but also on the temperature and the first load level . Moreover, as soil suction descreases, the normalized void ratio become higher. The creep coefficient (Cαe) increased as temperature and vertical stress increased, while they decreased as the suction increased.

14th BSGC2020 - Future Challenges for Geotechnical Engineering Preface

The Baltic Sea Region Geotechnical Conference (BSGC) series dates back to 1968, making it one of the oldest regional geotechnical conferences. The 14th Baltic Sea Region Geotechnical Conference, originally scheduled to take place in Helsinki in May 2020, had to be postponed due to COVID19 pandemic. It finally took place as virtual conference on 18th-19th January 2021, arranged in parallel with the 18th Nordic Geotechnical Meeting (NGM). The conference attracted total of 271 participants from 32 countries, successfully allowing to share insights and discuss ideas related to Future Challenges for Geotechnical Engineering, the main topic of the meeting.This 14th BSGC proceedings contain 31 technical papers presented during the conference alongside 14 interesting industry presentations. In the proceedings, the papers are divided into sections related to:• Soil and rock investigations• Digital applications in geotechnics• Environmental Geotechnics and recycling• Modelling• Design experiences and theoretical solutions• Ports and foundation engineering• Case studies and geotechnical artFurthermore, three keynote speakers presented during the 14th BSGC. The signature keynote entitled Signatures and impacts of climate change in coastal environments of the Baltic Sea and affiliations was given by Professor Tarmo Soomere, the President of Estonian Academy of Sciences. The other two keynotes were awarded jointly with 18th NGM.List of Organizing Committee, Scientific Committee are available in the pdf.

Microplastics in soils: an environmental geotechnics perspective

Microplastics (MPs) are emerging persistent contaminants in the terrestrial subsurface, and evidence has emerged for significant effects of MPs on the biological and ecosystem functions of soils. Main MP sources include land spreading of sewage sludge and biowaste composts, plastic mulching film used in horticultural fields, waste water irrigation and leachate from the landfills, among others. This updated state-of-the-art review paper describes recent experimental and numerical research and developments in understanding the accumulation and fate and effects of MPs in the soil environment (focusing on their storage, degradation, transportation, leaching to groundwater etc.), followed by mitigation and bioremediation measures, including MP-eating soil bacteria and fungi and the best management practices for reducing MP pollution of soil. Other areas covered are the combined effects of MPs and various other environmental contaminants (heavy metals, organic pollutants and antibiotics) in soil ecosystems and the standardisation of methods for detection, quantification and characterisation of MPs in soils, which is critical for MP research. The paper concludes by identifying knowledge gaps and presents recommendations on prioritised research needs.

COMPARISON OF MEASURED AND ESTIMATED PERMEABILITY FOR ARTIFICIALLY PREPARED COARSE-GRAINED SOIL SAMPLES

Knowledge about soil permeability is important in various scientific fields: hydrology and hydrogeology, geotechnics, environmental geotechnics, and others. Depending on the different goals that need to be achieved by a particular engineering project, the conditions in which the permeability coefficient is determined in terms of applied hydraulic gradients, applied stresses, type of test fluid, etc. are adjusted, as well as the required precision of its determination. In addition, the permeability coefficient is a soil property with the largest range of possible values. It can be determined through various laboratory and field methods, and by applying established empirical correlations using data on the grain-size distribution and empirical coefficients that depend on some factors, such as hydraulic radius (specific surface), curvature, porosity, etc. This paper presents the results of laboratory testing of the permeability coefficient by the constant head test and the use of a permeameter. The results were compared with the permeability coefficient obtained by applying a number of empirical correlations. Artificial samples were prepared in the laboratory by mixing different previously prepared soil fractions in order to determine the influence of particle size and soil gradation on the estimated soil permeability coefficient.

Suggestions for Improving Geotechnical and Infrastructure Courses Teaching on Higher Education

The purpose of this paper is to prepare questionnaire-based research proposals by undergraduate students for the Soil Mechanics course of the Dept. Civil Infrastructure Engineering, as well as postgraduate students for the course of Environmental Geotechnics of the Postgraduate Programme "Advanced Environmental Management Technologies in Engineering Works" of the General Department of Larissa of the University of Thessaly, with the ultimate goal being the upgrade of the classes. It is noted that the lecturers of the course participated in the evaluation of the Environmental Geotechnics course through a relevant questionnaire. The research strategy concerns the design of the questionnaire in conjunction with the objectives of the course. According to the curriculum, geotechnical courses aim to enable students to apply the methodologies for calculating the physical characteristics and mechanical properties of the soil, which functions either as a superstructure load recipient or as a structural material for the construction of geotechnical works. The questionnaires took into account the content of each lesson, students' preferences in the learning process, the ability to self-evaluate, evaluate and develop collaborations, the desired number of teaching hours available to cover the subject and the adequacy of the knowledge acquired in each module of the course. Finally, the students' responses were evaluated, and useful conclusions were drawn which could contribute positively to the qualitative improvement of the teaching of the above courses