Energy Geotechnics Research Articles

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.

Growth, trends and prevalent topics in geotechnical engineering (1998–2022) using topic modelling

Data gathered from 65 922 articles published in 30 geotechnical engineering journals between 1998 and 2022 were used to build a topic model and study the evolution of research output in the field. Over this period, the number of journal publications has grown exponentially with the number of articles published per year doubling every 6·3 years. The average citations per article (32·7) are skewed by highly cited articles, which make up 7·8% of the articles but account for 34·5 of the total number of citations. The articles’ country of origin has become increasingly centralised, with nearly half the articles published between 2018 and 2022 coming from China (39%) and the United States (10%). The topic distribution in the field has become highly specialised, with emerging topics being fuelled by: (a) new technologies and methods (i.e. data science and sensing techniques – the fastest-growing topics), and (b) rising applications seemingly related to mitigation (e.g. offshore and energy geotechnics) and adaptation (e.g. geohazards, mass movements) to climate change. As a consequence, traditional topics (e.g. soil and rock mechanics) have reduced their share in the field, but still remain among the most cited topics in geotechnical engineering.

Thermo-hydro-mechanical behaviour of a deep plastic clay formation

Several applications which are framed in the energy geotechnics field, particularly the design of energy geo-structures, energy geo-storage, enhanced geothermal energy systems and radioactive waste disposal, require a thorough thermo-hydro-mechanical (THM) characterisation of their host soil/rock formation. The present study comes up from the need to investigate the THM behaviour of deep Ypresian clays (Ycs, 300 to 400 m below ground) since they are one of Belgium’s potential host rock formations for deep geological disposal of heat-emitting and long-lived radioactive waste.
 The impact of temperature on the hydro-mechanical response of deep clays has been extensively tackled for the last four decades. Nevertheless, to the authors’ knowledge, the study of the evolution of radial stresses during drained thermal paths under oedometer conditions has never been addressed. Such information would allow for drawing a better-defined stress state while accurately measuring volume changes. To this aim, the present study used a newly designed and fully instrumented temperature-controlled oedometer cell [3] combined with well-planned test protocols. The local instrumentation consisted of a pore pressure transducer embedded in the soil 3 mm from the bottom boundary, thermocouples at various positions and radial displacement transducers with a localised thin-wall system to estimate radial stress.
 Two well-preserved Ycs core samples retrieved at different depths at Kallo (Belgium) and belonging to distinct lithological units were tested (see Table 1). Both slightly overconsolidated samples (Yield Stress Ratios of Ycs between 1.2 and 1.8, [1, 2, 3]) presented high initial matric suctions induced on deep water-undrained sampling. Consequently, the first stage of the well-planned test protocol consisted of loading at constant water content to bring the samples to the large in situ stresses and diminish the induced matric suction. The remaining matric suction was then reduced by soaking with synthetic water equivalent to in situ. Afterwards, drained loading and unloading paths were followed to attain different vertical effective stresses at varying overconsolidation ratios (OCRs) before performing the main research goal of drained thermal paths. The heating-cooling (H-C) cycles consisted of slowly stepwise increase/decrease in temperature (steps of 10ºC) with intermediate stabilising periods of around 15 hours controlled by the embedded pore pressure transducer.
 Figure 1 depicts the vertical deformation in terms of the mean effective stress (p’) beyond in situ stress. Changes in radial stresses ruled the variations in p’ during heating-cooling cycles since the vertical effective stress was kept constant during non-isothermal paths. At a slightly overconsolidated (OC) state (Core-48), the drained ‘1st H-C’ cycle showed a quasi-reversible response in volume changes and radial stresses. At OC state (OCR=2) on Core-103 (‘2nd H-C’), the response was reversible. However, the induced volume change in normally consolidated (NC) states was not reversible with a contractive response dependent on the stress level. Therefore, the nature of the thermal-induced volume changes aligned with the behaviour observed on other plastic clays. Nevertheless, the stress dependence of the contractive response at NC state differed from the observations made by [4] on NC Boom Clay -the other poorly indurated clay considered as potential host rock in Belgium. As observed in ‘2nd H-C’ (NC conditions) on Core-48, a reduction of the radial effective stress was only recorded at temperatures higher than 70°C. In contrast, the radial effective stress systematically increased on heating at values < 70°C, tending the sample to lower deviatoric stress. This phenomenon might be
 associated with some change in the soil structure on heating that tends to a more isotropic stress state despite the oedometer condition. A clear transition between the elastic and elastoplastic domains was detected during the subsequent loading after each H-C cycle at NC states.
 Finally, the study included a thermo-mechanical elastoplastic interpretation: thermal expansion coefficients dependent on temperature and mean effective stress in the elastic domain and thermal softening function on post-yield drained heating.

Effect of temperature on the compressibility behavior of glass fiber-bentonite mixture

Effect of temperature on the compressibility behavior of glass fiber-bentonite mixture

Thermal conductivity of dried biocemented sand at higher calcification

Thermal conductivity of dried biocemented sand at higher calcification

Numerical investigation on the thermal performance of energy tunnels under groundwater flow and tunnel airflow

The integration of underground tunnels with ground heat exchangers (GHEs), also known as energy tunnels, is a promising technology that has gained attention in energy geotechnics research. This study investigates the coupled effects of groundwater and tunnel-air flows on the energy tunnel system via 3D thermo-hydraulic numerical modelling. It is found that the combination of groundwater flow parallel to the tunnel and limited airflow velocity results in reduced operational efficiency of ground source heat pump (GSHP) due to the strong thermal interference along the tunnel. The study also highlights the importance of real-scale modelling to evaluate the thermal yield of long energy tunnels, particularly when dealing with parallel groundwater flow in geothermal tunnel design.
 The use of shallow geothermal energy is a renewable solution towards net-zero carbon emissions. In recent years, a variety of conventional geotechnical structures, such as piles, retaining walls and tunnels, have been transformed into energy geostructures to also serve as GHEs to harness renewable energy for space heating and cooling purposes [7]. The thermal performance of energy tunnels is significantly affected by the presence of groundwater flow [1, 6] and the airflow in the tunnel [2, 4]. The groundwater flow and tunnel airflow can both be present in the field, however, their coupled effects on the energy tunnel system are hardly explored in the literature. This study aims to bridge this gap via real-scale numerical investigations.
 This study uses 3D thermo-hydraulic numerical modelling developed with the finite element package COMSOL Multiphysics [3]. The numerical model was successfully validated against an energy tunnel model-scale laboratory experiment [5]. Figure 1 shows the overall geometry and boundary conditions of the numerical model. A 48 m long tunnel section is thermally activated with the embedment of HDPE pipes (outer diameter of 25 mm and 2.3 mm thickness) placed in the lining segments at a spacing of 200 mm. A single tunnel ring consists of six segments with absorber pipes joined between them. Every four adjacent rings are connected in series to form a complete loop (with a single inlet and outlet), which is then connected in parallel to a flow and return header pipe(s). The entire thermally activated section comprises six loops, with identical fluid inlet temperature and flow rates, as they are fed by the same flow header pipe. The outlet fluid from each loop is mixed along the return header pipe to the GSHP. A constant 36 kW cooling thermal load is applied, and the simulation is run for ten years to allow the system to reach a steady state condition considering the minimum groundwater flow and airflow. The thermal properties of the ground are prescribed as 2 W/(m·K) and 1100 J/(kg∙K) for thermal conductivity and specific heat capacity, respectively.
 Figure 2 shows the entering water temperature (EWT, header outlet) and the coefficient of performance (COP) of the GSHP after 10 years of operation for different groundwater flow velocities and directions for tunnel air velocities = 0.05 m/s and 2 m/s.
 Results show that an increase in and leads to a decrease in EWT and an increase in COP. However, the effect of groundwater direction and velocity is more significant when airflow is limited ( = 0.05 m/s). The parallel groundwater flow leads to a higher EWT and lower COP than when the flow is inclined and perpendicular to the longitudinal tunnel axis. Consequently, the thermal performance of the system under parallel flow with a higher can be even worse than the perpendicular and inclined flow with a lower . When = 0.05 m/s, the EWT of parallel flow increases by 15% to 20% compared to the perpendicular flow, resulting in a maximum decrease of 15% in the COP. The effect of groundwater flow is much less significant when airflow is fast ( = 2 m/s): for increases from 0.05 to 2 m/d, EWT and COP change by no more than 13% and 5%, respectively, and the impact of groundwater flow direction is minor.

Energy Geotechnics and Geostructures

Continuous global economic and population growth has driven the ever-increasing demand for energy [...]

Rock Mechanics for GeoEnergy Applications

The discipline of rock mechanics, which emerged in the 1960s and 1970s as a distinct scientific subject, is undergoing rapid development, including a significant shift within the traditional civil, transportation, and petroleum fields. This shift leans toward using Earth resources to mitigate adverse climate change and to boost sustainable and renewable energy production. Energy geotechnics, or “GeoEnergy,” focuses on novel geomechanics and geotechnical engineering strategies to meet emerging sustainability market demands. GeoEnergy applications that employ rock mechanics and engineering include geothermal systems, geologic carbon sequestration, underground hydrogen storage, compressed air energy storage, and nuclear waste repositories.

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.

Energy geostructures: A review of analysis approaches, in situ testing and model scale experiments

This position paper was developed by members of the task force on “Energy Geostructures” of the International Society of Soil Mechanics and Geotechnical Engineering (ISSMGE) Technical Committee TC308 on ‘Energy Geotechnics’. The article includes a summary and review of some of the most recent analysis approaches, in situ testing, full scale testing and model scale experiments with a focus on energy piles and other energy geostructures. The geotechnics literature in these topics has increased rapidly in the last five years suggesting a surge in this emerging research area. Here complementary lines of research can be distinguished, one focusing on thermal analysis and another focusing on thermo-geomechanical analysis. Limitations, shortcomings and knowledge gaps are identified and needs for further research and development within the geotechnical community are highlighted.

Preface to the Proceedings for the 2nd International Conference on Energy Geotechnics (ICEGT2020)

With ever increasing energy demand and related climate change implications, the development of sustainable energy systems based on integrated schemes of energy production, transport, transfer, and storage is an important challenge to society. The broad and emerging area of Energy Geotechnics has the potential to address this challenge from multiple perspectives by integrating concepts from geotechnical engineering and geomechanics with cross-disciplinary concepts from geology, hydrology, geophysics, geochemistry, petroleum engineering, and energy policy. The 2nd International Conference on Energy Geotechnics is organized by the members of the International Society of Soil Mechanics and Geotechnical Engineering (ISSMGE) Technical Committee 308 on Energy Geotechnics, and is the main international venue for interaction, communication, and technology transfer for academic and non-academic parties, including researchers and practitioners, in the broad areas within Energy Geotechnics

Phase-field modeling of geologic fracture incorporating pressure-dependence and frictional contact

Geologic fractures such as joints and faults are central to many problems in energy geotechnics. Notable examples include hydraulic fracturing, injection-induced earthquakes, and geologic carbon storage. Nevertheless, our current capabilities for simulating the development and evolution of geologic fractures in these problems are still insufficient in terms of efficiency and accuracy. Recently, phase-field modeling has emerged as an efficient numerical method for fracture simulation which does not require any algorithm for tracking the geometry of fracture. However, existing phase-field models of fracture neglected two distinct characteristics of geologic fractures, namely, the pressure-dependence and frictional contact. To overcome these limitations, new phase-field models have been developed and described in this paper. The new phase-field models are demonstrably capable of simulating pressure-dependent, frictional fractures propagating in arbitrary directions, which is a notoriously challenging task.

Castanea sativa Mill. plantations as a low-carbon landslide hazard mitigation measure

In the last twenty years, several rainfall-induced landslides occurred in areas surrounding Mount Vesuvius (Campania, Italy). Landslides usually involve the shallow pyroclastic soil layers (2-3 m thick) covering the steep slopes of the Lattari Mountains. The cultivation of trees for fruit production on the pyroclastic cover is a common practice by local farmers. Woody vegetation contributes to slope stability through the mechanical reinforcement of soil by roots. We investigated the use of Sweet chestnut (Castanea sativa Mill.) trees as a low-carbon landslide mitigation measure to be applied in large areas where conventional geotechnical engineering solutions would be costly and extremely invasive, in order to respond to the demand in energy and environmental geotechnics for eco-friendly approaches. The root distribution of C. sativa in terms of root volume ratio was determined from soil cores. The mechanical reinforcement of soil by tree roots was quantified based on root-soil interaction models. Slope stability was analysed by means of limit equilibrium analyses performed on an infinite slope. The safety factor calculated for a cultivated slope was higher than for a fallow slope due to the mechanical reinforcement provided by roots. Therefore, the cultivation of C. sativa is a useful mitigation measure against shallow landslides.

Numerical investigation on water exchange of shale samples

Interest in the hydraulic and mechanical characterization of shales has grown in recent years, because of their application in the context of energy geotechnics. In the frame of nuclear waste disposal shales are considered as host formations for the placements of nuclear waste at high depths. In the frame of hydrocarbon production they are considered as unconventional reservoirs, from which extracting natural gas. Understanding how fluids flow through shales is then a key aspect for both fields of application. This paper focuses on the analysis of the transport of water vapour through laboratory samples. After reviewing the balance and flow laws that govern the transport of fluid in unsaturated porous media, a simplified model is put forward. The model was implemented in a commercial finite element code, and it was used to reproduce the results of a literature study on wetting and drying of Opalinus Clay shale samples, imposed through the vapour equilibrium technique. Back analysis of the water content and volume strains of these specimens suggests that existing models underestimate the actual flow rate of water vapour which takes place at low suctions. The current interpretation also seems to be consistent with microstructural investigations on the interconnection between large pores of this material.

An immersed phase field fracture model in fluid-infiltrating porous media with evolving Beavers-Joseph-Saffman condition

This study presents a phase field model for brittle fracture in fluid-infiltrating vuggy porous media. While the state-of-the-art in hydraulic phase field fracture considers Darcian fracture flow with enhanced permeability along the crack, in this study, the phase field not only acts as a damage variable that provides diffuse representation of cracks or cavities, but also acts as an indicator function that separates the domain into two regions where fluid flows are governed by Stokes and Darcy equations, respectively. Since the phase field and its gradient can be respectively regarded as smooth approximations of the Heaviside function and Dirac delta function, our new approach is capable of imposing interfacial transmissibility conditions without explicit interface parametrizations. In addition, the interaction between solid and fluid constituents is modeled by adopting the concept of mixture theory, where the fluid velocities in Stokes and Darcy regions are considered as relative measures compared to the solid motion. This model is particularly attractive for coupled flow analysis in geological materials with complex microstructures undergoing brittle fracture often encountered in energy geotechnics problems, since it completely eliminates the needs to generate specific enrichment function, integration scheme, or meshing algorithm tailored for complex geological features.

Experimental and Numerical Investigation of Thermo-Mechanical Properties for Nano-Geocomposite

Heat transfer in dry granular material is dominated by conduction among the grains. The quality and quantity of the contact dictate the preferred heat path. Owing to the high thermal conductivity and considerable mechanical strength, nanomaterials are suitable to improve the contact by filling inter- and intra-granular pores. A thermo-mechanical study with 0–5 weight percentage of 63 nm and 125 nm silicon carbide (SiC)/sand mixtures has been conducted. A numerical model based on a modified effective-medium approximation considering the effective mean free path is implemented in the lattice element method with gas theory to predict the ETC of the mixtures. The numerical modeling and experimental results showed satisfactory agreement to a large extent. To test the mechanical stability of the developed mix, direct shear test and consolidation tests have been performed on the nano-geomixture to observe changes in the mechanical strength due to a powder-like appearance of SiC. No significant reduction in strength and settlement behavior of the mixture has been reported. The developed nanocomposite could be used in energy geotechnics application.

Salient comments from an expert panel on energy geotechnics

This paper presents the main discussions and comments associated with the Panel 1-C on ‘Geo-engineering for Energy’. This discussion panel was organised by the International Society for Soil Mechanics and Geotechnical Engineering’s Technical Committee on Energy Geotechnics (TC308) in the context of the XV Pan-American Conference on Soil Mechanics and Geotechnical Engineering, which was held in Buenos Aires, Argentina, between 15 and 18 November 2015. Three experts in the area of energy geotechnics were invited to express their views on four questions prepared by the panel organisers. This contribution also presents a brief description of the TC308 activities, the questions suggested to the invited panellists, the associated replies and some closing comments from the organisers of the panel.

Editorial: XV Pan-American Conference: Selected papers on energy geotechnics

Editorial: XV Pan-American Conference: Selected papers on energy geotechnics

Introduction to the Special Issue of Geotechnical and Geological Engineering Entitled: “Thermo-Hydro-Mechanical Behavior of Soils and Energy Geostructures”

This special issue of Geotechnical and Geological Engineering highlights state-of-the-art research on the thermo-hydro-mechanical behavior of soils, rocks and energy geostructures. Although the impetus of the special issue was to collect journal papers on subjects related to an NSF-funded international workshop on ‘‘Thermally Active Geotechnical Systems for Near Surface Geothermal Energy’’ held in March 2013 at Ecole Polytechnique Federale de Lausanne in Switzerland, the special issue expanded to collect a broader set of papers from the field of Energy Geotechnics that involve thermal soil behavior. A total of 15 journal papers were selected to be published as part of the special issue, and went through the standard peer review process for the journal. Two papers focused on the thermal properties of unsaturated soils. Likos (2014) presented a pore-scale model for predicting the thermal conductivity of unsaturated sands using basic soil properties. Dong et al. (2014) presented an evaluation of various approaches to predict the thermal conductivity of unsaturated soils, and compared them with experimental data for sand, silt and clay. One paper was presented on the thermal volume change of unsaturated soils, and the impact of these volume changes on the response of a heated shallow foundation (Houston et al. 2014). Three papers were published on different aspects of geothermal heat exchangers in conventional applications (boreholes and horizontal trenches). Wu et al. (2014) studied relationships between the thermal conductivity dryout curve for unsaturated soils and the performance of geothermal heat exchangers in horizontal trenches, Ozudogru et al. (2014a) compared the performance of different numerical simulations to evaluate the response of geothermal heat exchangers in vertical boreholes, and Walker et al. (2014) studied the impact of different stratigraphic units on the overall thermal response of a geothermal heat exchanger in a vertical borehole. Seven papers were focused on the thermal and thermo-mechanical response of energy piles. Loveridge et al. (2014) analyzed the response of different types of auger cast piles that were converted into energy piles. Yu et al. (2015) used numerical modeling to evaluate the thermal conductivity of different soil layers from the analysis of a thermal response test on an energy pile. Kramer et al. (2014) evaluated the thermal response of an energy pile in sand constructed within a laboratory container. Murphy and McCartney (2014) studied the J. S. McCartney (&) Department of Structural Engineering, University of California San Diego, 9500 Gilman Dr, La Jolla, CA 92093-0085, USA e-mail: mccartney@ucsd.edu