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As the Material Point Method (MPM) uses both a mesh and a point discretisation scheme, the application of boundary conditions is difficult, currently limiting the flexibility of the method. While many boundary condition options have been used in the literature, the accuracy of Neumann boundary condition options has not yet been studied. Four options have here been evaluated for 1D and 2D benchmarks, although none of the options were found to be both accurate and generally applicable in MPM. However, for the generalised interpolation material point method (GIMP), the application of surface tractions on support domain boundaries or on a detected surface are valid options. Large differences between these two accurate options and the application of tractions at surface material points, a method regularly used in the literature, have been observed. • The consistency of four Neumann boundary condition methods is evaluated in MPM and GIMP. • Two general algorithms are presented to use (nearly) consistent Neumannn boundary condition methods in GIMP. • It is shown that the boundary conditions should be applied such that the internal and external force calculations are consistent. [ABSTRACT FROM AUTHOR]

Soil spatial variability has a significant impact on the reliability of geotechnical structures. In particular, the horizontal variability is important for linear infrastructure, which has only limited vertical height and width, but extensive length. Due to depositional and geological processes, the variability is often substantially different in the vertical and lateral directions. This variability can be characterised by a spatial correlation length, or scale of fluctuation, which is a measure of how significantly soil properties are correlated in space. An analysis of the reliability of such a measure has been undertaken using synthetic data, leading to a design chart which quantifies the statistical uncertainty in the scale of fluctuation for specific site investigation designs, which can be an important input for probabilistic analyses of the structure response. Moreover, practical guidance for site investigation design is proposed which can reduce the statistical uncertainty. The method has been applied to a real site investigation comprising a row of 29 closely spaced cone penetration tests (CPTs), within a larger site investigation of 100 CPTs, and applied to a simple design calculation for a long embankment to illustrate the impact on slope stability assessment. The site investigation data are made available to add to the limited amount of detailed data in this field. [ABSTRACT FROM AUTHOR]

Stress inaccuracies (oscillations) are one of the main problems in the material point method (MPM), especially when advanced constitutive models are used. The origins of such oscillations are a combination of poor force and stiffness integration, stress recovery inaccuracies, and cell crossing problems. These are caused mainly by the use of shape function gradients and the use of material points for integration in MPM. The most common techniques developed to reduce stress oscillations consider adapting the shape function gradients so that they are continuous at the nodes. These techniques improve MPM, but problems remain, particularly in two and three dimensional cases. In this paper, the stress inaccuracies are investigated in detail, with particular reference to an implicit time integration scheme. Three modifications to MPM are implemented, and together these are able to remove almost all of the observed oscillations. [ABSTRACT FROM AUTHOR]

The thermal cone penetration test (T-CPT) allows in situ measurement of the thermal properties of soil during a CPT – that is without withdrawing the CPT tool and introducing another tool such as a thermal needle probe. An interpretation method is presented based on one-dimensional axisymmetric analytical solutions. Numerical verification of the method is given and numerical simulations are presented to derive a calibration factor required for the interpretation model. This factor accounts for the temperature sensor location and two-dimensional geometric effects, particularly internal voids and end effects for the cone penetrometer. Finally field data are presented for the T-CPT and compared with results from in situ needle probe tests and laboratory tests on sampled material. The interpretation model is able to provide thermal conductivity values robustly. [ABSTRACT FROM AUTHOR]

Geo-energy infrastructure, such as ground source heat systems (thermo-active structures), induce thermal cycles that can result in changes of the bearing capacity of soil by changing, for example, the void ratio, soil structure, unit weight and hydraulic conductivity. The influence of repeated freeze-thaw (FT) cycles and different freezing rates on the shear strength of a frost-susceptible illite clay was investigated. Samples were subjected to between one and 20 FT cycles, and the shear strength of the thawed material was determined using undrained unconsolidated triaxial tests. After the shear strength decrease due to the first FT cycle, a transitory shear strength recovery occurred between one and three freezing cycles, followed by a shear strength decrease between three and seven FT cycles, which then approached an equilibrium value. Computed tomography scans showed ice lenses increased in size moving away from the freezing surface, and more uniform ice distribution with increasing FT cycles. Changing the freezing rate yielded differences in the formation and structure of ice lenses perpendicular to the freezing direction. The observed failure plane typically coincides with the plane of the largest ice lens due to formation of a slurry layer after thawing. [ABSTRACT FROM AUTHOR]

An implicit material point method (MPM), a variant of the finite element method (FEM), is presented in this paper. The key feature of MPM is that the spatial discretisation uses a set of material points, which are allowed to move freely through the background mesh. All history-dependent variables are tracked on the material points and these material points are used as integration points similar to the Gaussian points. A mapping and re-mapping algorithm is employed, to allow the state variables and other information to be mapped back and forth between the material points and background mesh nodes during an analysis. In contrast to an explicit time integration scheme utilised by most researchers, an implicit time integration scheme has been utilised here. The advantages of such an approach are twofold: firstly, it addresses the limitation of the time step size inherent in explicit integration schemes, thereby potentially saving significant computational costs for certain types of problems; secondly, it enables an improved algorithm accuracy, which is important for some constitutive behaviours, such as elasto-plasticity. The main purpose of this paper is to provide a unified MPM framework, in which both quasi-static and dynamic analyses can be solved, and to demonstrate the model behaviour. The implementation closely follows standard FEM approaches, where possible, to allow easy conversion of other FEM codes. Newton’s method is used to solve the equation of motion for both cases, while the formation of the mass matrix and the required updating of the kinematic variables are unique to the dynamic analysis. Comparisons with an Updated Lagrangian FEM and an explicit MPM code are made with respect to the algorithmic accuracy and time step size in a couple of representative examples, which helps to illustrate the relative performance and advantages of the implicit MPM. A geotechnical application is then considered, illustrating the capabilities of the proposed method when applied in the geotechnical field. [ABSTRACT FROM AUTHOR]

An investigation of the three-dimensional coupled thermohydromechanical behaviour of a prototype repository in fractured granitic rock is presented. The pre-placement behaviour of the repository is first considered, making use of a full three-dimensional simulation of the problem. An effective continuum approach, augmented with discrete features with a high hydraulic conductivity, is employed. The method adopted is found to be able to simulate accurately the highly anisotropic flow regime observed at the pre-placement phase. The major features of the full repository experiment under applied heating conditions were then successfully simulated. The range of buffer hydration rates, the thermal response of the repository, and the associated mechanical response were successfully simulated. Approaches to capture both the transient microstructural behaviour of the compacted bentonite (MX-80 type) and a MX-80 pellet material are incorporated. The repository behaviour was shown to be strongly influenced by complex coupled processes, including interactions between the system components. The adoption of a three-dimensional modelling approach proved to be essential to realistically simulate the behaviour of a repository incorporating anisotropic flow behaviour. Finally, potential impacts of the processes considered on performance of the barrier system and in safety assessment are considered. [ABSTRACT FROM AUTHOR]

This paper presents a new Modified Cam Clay (MCC) type yield function, that is designed for robust and efficient use with implicit stress integration algorithms. The proposed yield function attains non-elliptical (e.g. tear and bullet) shapes, as well as the typical elliptical shape of the MCC model. Like that of MCC, and unlike most other yield functions with non-elliptical shapes available in literature, it is non-singular and unique throughout stress space. The experimental yielding stresses of a wide range of geomaterials have been accurately simulated using the yield surface. The yield function can be used in constitutive models based on classical elasto-plasticity theory. • A new flexible yield function for geomaterials is proposed. • The yield surface is unique and non-singular in meridian stress space. • The yield surface is robust for implicit stress integration schemes. • The yield surface is derived thermodynamically but can be used in all models. • Proposed yield surface matches experimentally observed yield loci of geomaterials. [ABSTRACT FROM AUTHOR]

Drilling wells in unconsolidated formations is commonly undertaken to extract drinking water and other applications, such as aquifer thermal energy storage (ATES). To increase the efficiency of an ATES system, the drilling campaigns are targeting greater depths and enlarging the wellbore diameter in the production section to enhance the flow rates. In these cases, wells are more susceptible to collapse. Drilling fluids for shallow formations often have little strengthening properties and, due to single‐string well design, come into contact with both the aquifer and the overburden. Drilling fluids and additives are experimentally investigated to be used to improve wellbore stability in conditions simulating field conditions in unconsolidated aquifers with a hydraulic conductivity of around 10 m/d. The impact on wellbore stability is evaluated using a new experimental setup in which the filtration rate is measured, followed by the use of a fall cone penetrometer augmented with an accelerometer to directly test the wellbore strengthening, and imaging with a scanning electron microscope (SEM) to investigate the (micro)structure of the filter cakes produced. Twelve drilling fluids are investigated with different concentrations of bentonite, polyanionic cellulose (PAC), Xanthan Gum, calcium carbonate (CaCO3), and aluminum chloride hexahydrate ([Al(H2O)6]Cl3). The filtration results indicate that calcium carbonate, average dp <20 μm, provides pore throat bridging and filter cake formation after approximately 2 min, compared to almost instantaneous discharge when using conventional drilling fluids. The drilling fluid containing 2% [Al(H2O)6]Cl3 forms a thick (4 mm) yet permeable filter cake, resulting in high filtration losses. The fall cone results show a decrease of cone penetration depth up to 20.78%, and a 40.27% increase in deceleration time while penetrating the sample with CaCO3 compared with conventional drilling fluid containing bentonite and PAC, indicating a significant strengthening effect. The drilling fluids that contain CaCO3, therefore, show high promise for field implementation. [ABSTRACT FROM AUTHOR]

A recursive ensemble Kalman filter (EnKF) is used as the data assimilation scheme to estimate strength and stiffness parameters simultaneously for a fully coupled hydro-mechanical slope stability analysis. Two different constitutive models are used in the hydro-mechanical model: the Mohr-Coulomb (MC) model and the Hardening Soil (HS) model. The data assimilation framework allows the investigation of the effect of constitutive behaviour on its ability to estimate the factor of safety using measurements of horizontal nodal displacement at the sloping face. In a synthetic study, close-to-failure and far-from-failure cases of prior property estimations illustrate the effect of initial material property distribution with different material models. The results show that both models provide a reliable factor of safety when the distribution of prior parameters is selected close-to-failure. However, the HS model results in the improved estimation of factor of safety for the far-from-failure case while this is not the case for the MC model. In addition, for the same level of accuracy the computational effort required for the HS model is comparatively less than for the MC model. [ABSTRACT FROM AUTHOR]

Due to a lack of large deformation dyke assessment models, primary failure mechanisms, such as inner slope failure, are often used as a proxy to assess the probability of failure of a dyke. However, a dyke continues to fulfil its main function unless, or until, flooding occurs. The Random Material Point Method (RMPM) is used here to investigate residual dyke resistance, which is the resistance against flooding after initial failure. RMPM combines random fields with MPM in a Monte Carlo simulation and has been extended here to include the effects of an external hydrostatic pressure on a dyke's outer slope. The residual resistance of an idealised dyke (computed using RMPM) is shown to reduce the probability of flooding by 25% with respect to the initial failure. A lower degree of anisotropy of the spatial variability increases the residual dyke resistance. RMPM simulates, as expected, a lower residual dyke resistance for larger initial failures and/or a higher water level. A 'safe' remaining geometry has not been found, since even small initial failures can result in an unacceptable probability of flooding, highlighting the importance of modelling the entire failure process. [ABSTRACT FROM AUTHOR]

An implicit contact algorithm for the material point method (MPM) has been developed to simulate contact. This allows recently developed implicit MPM codes to simulate large-scale deformations and interaction with external bodies. The performance of the method has been investigated and compared to an existing explicit method using benchmark and geotechnical examples. In particular, the proposed formulation has been shown to conserve energy in a similar way to the explicit formulation and reach similar results. The method typically converges to the analytical solution when an adequate time step and mesh size are used, with the time step generally being around ten times larger than the explicit method, although during the contact phase this does not always result in faster computation due to the iterative solution procedure. [ABSTRACT FROM AUTHOR]

The stability of a dike is influenced strongly by its water content, via both changing its weight and strength. While safety calculations using both analytical and numerical methods are well studied, the impact of surface boundaries exposed to natural conditions is rarely considered, nor is the fact that this surface is covered in vegetation and is susceptible to cracking. This paper presents a numerical study of stability of dikes covered with grass, subject to meteorological forcing and crack formation due to drying conditions. Building on a previous study and adding the impact of cracking, a crop model and a Finite Element Method (FEM) model are integrated together using an optimisation method to ensure mass balance and consistency. The crop model, used to simulate vegetation growth and infiltration/evaporation in response to meteorological forcing, is modified to consider preferential flow due to cracking. The FEM model, used to simulate the dike stability and hydro-mechanical behaviour, has the material properties modified to simulate the impact of cracks. Results simulating a ten-year period indicate a strong impact of cracking on the factor of safety. The vegetation was found to be responsive to both crack presence and an increase in the amount of cracks, which suggests that monitoring vegetation could be a useful tool to identify cracked (vulnerable to cracking) locations along dikes. [ABSTRACT FROM AUTHOR]

This paper investigates the implementation of a nonlocal regularisation of the material point method to mitigate mesh-dependency issues for the simulation of large deformation problems in brittle soils. The adopted constitutive description corresponds to a simple elastoplastic model with nonlinear strain softening. A number of benchmark simulations, assuming static and dynamic conditions, were performed to show the importance of regularisation, as well as to assess the performance and robustness of the implemented nonlocal approach. The relevance of addressing stress oscillation issues, due to material points crossing element boundaries, is also demonstrated. The obtained results provide relevant insights into brittle materials undergoing large deformations within the MPM framework. • As FEM, MPM suffers from numerical pathologies when dealing with brittle soils. • Nonlocal formulations provide a simple and efficient approach for regularisation. • Nonlocal models can yield objective results in large deformation simulations. • MPM, as FEM, can benefit from a nonlocal formulation without added complexity. • Nonlocal formulation in MPM stabilises outcomes across mesh sizes. [ABSTRACT FROM AUTHOR]

Climatic conditions and vegetation cover influence the water flux in a dike body, which affect the effective stress and self-weight, hence its stability. The vegetation is the intermediate layer between the atmosphere and the soil, and therefore this layer influences the boundary water flux by transpiration and leaf interception, so considering vegetation in numerical analysis of slope stability provides insight into changing stability. This study investigates Soil-Vegetation-Atmosphere (SVA) interaction impact on macro stability of grass covered dikes. Two numerical models have been used in the current study: (i) a crop model for simulating the water balance in the root zone (unsaturated zone); (ii) a Finite Element Method (FEM) coupled to the crop model for hydro-mechanical and safety analysis to calculate the Factor of Safety (FoS). Results of idealised analysis show that the Leaf Area Index (LAI) is coupled to the moisture in the root zone with a time lag, therefore, it is likely that it could be used as an indicator of safety. This proof-of-concept study enables dike managers to use the mentioned parameters as a proxy to identify vulnerable locations along a dike even in an early stage due to the lag correlation. This offers the opportunity to use remote sensing rather than physical inspection or installing sensors, along with history matching, to initially identify vulnerable locations along dikes. [ABSTRACT FROM AUTHOR]

• Combined impact of conduction, dispersion and buoyancy-driven flow on thermal losses of ATES is assessed. • Conduction always occurs and dominates dispersion effects, buoyancy-driven flow effects depend on conditions. • Storage geometry (A/V and L/R th) influences the recovery efficiency for all storage temperatures. • For conduction dominated conditions, the geometry is improved by decreasing A/V (smallest at L/R th =2). • For conditions with high potential for buoyancy-driven flow, increasingly smaller L/R th (<1) decreases thermal losses. The technical and economic success of an Aquifer Thermal Energy Storage (ATES) system depends strongly on its thermal recovery efficiency, i.e. the ratio of the amount of energy that is recovered to the energy that was injected. Typically, conduction most strongly determines the thermal recovery efficiency of ATES systems at low storage temperatures (<25 °C), while the impact of buoyancy-driven flow can lead to high additional heat losses at high storage temperatures (>50 °C). To date, however, it is unclear how the relative contribution of these processes and mechanical dispersion to heat losses across a broad temperature range is affected by their interaction for the wide range of storage conditions that can be encountered in practice. Since such process-based insights are important to predict ATES performance and support the design phase, numerical thermo-hydraulic ATES simulations were conducted for a wide range of realistic operational storage conditions ([15–90 °C], [50,000–1,000,000 m3/year]) and hydrogeological conditions (aquifer thickness, horizontal hydraulic conductivity, anisotropy). The simulated heat loss fractions of all scenarios were evaluated with respect to analytical solutions to assess the contribution of the individual heat loss processes. Results show that the wide range of heat losses (10–80 % in the 5th year) is the result of varying contributions of conduction, dispersion and buoyancy-driven flow, which are largely determined by the geometry of the storage volume (ratio of screen length / thermal radius, L/R th) and the potential for buoyancy-driven flow (q 0) as affected by the storage temperature and hydraulic conductivity of the aquifer. For ATES systems where conduction dominates the heat losses, a L/R th ratio of 2 minimizes the thermal area over volume ratio (A/V) and resulting heat losses for a given storage volume. In contrast however, the impact of dispersion decreases with L/R th and particularly for ATES systems with a high potential for buoyancy-driven flow (q 0 > 0.05 m/d), increasingly smaller L/R th ratios (<1) strongly reduce the heat losses due to tilting. Overall, the results of this study support the assessment of thermal recovery efficiencies for particular aquifer and storage conditions, thereby aiding the optimization of initial ATES designs. [Display omitted] [ABSTRACT FROM AUTHOR]

The effect of temperature on the monotonic and cyclic shearing response of a soil–structure interface is of critical importance for the application of thermal-active geo-structures. To investigate this, soils and soil–concrete interfaces were comprehensively tested with a temperature-controlled direct shear device under both fixed temperatures and thermal/mechanical cycles within the range of 2–38 °C. Monotonic and cyclic shearing with various boundary conditions, including constant normal load (CNL), constant normal stiffness (CNS) and constant volume (CV), were conducted to resemble the conditions that thermal-active-geo-structures may experience. The strength properties of the sand, clay, and sand–concrete and clay–concrete interfaces were partially influenced by heating and cooling under all boundary conditions. However, several effects were observed which could affect the performance of thermo-active structures. Heating cycles caused the clay–concrete interface to be overconsolidated, implying a lower excess pore pressure would be generated during shearing. The cyclic CNS tests suggested that the interface strength could degrade due to (thermally induced) cyclic shear displacements, with this effect strongly related to the state of the soil rather than the temperature directly. In these tests, the medium-dense sand–concrete interface degraded to almost zero shear strength after 5 cycles, whereas the clay–concrete interface asymptotically degraded to around 60% of its strength after 10 cycles. [ABSTRACT FROM AUTHOR]

Heating and Cooling constitute a major part of society's final energy use and a significant contributor to greenhouse gas emissions. The world society ought to mitigate climate change through decarbonisation, which must include the transition to low-temperature, sustainable and renewable heating and cooling technologies. Shallow Geothermal Energy is one of the most energy efficient and least greenhouse gas emitting available alternatives to provide space heating and cooling. The decarbonisation of the heating and cooling sector may have to comprise both individual systems and shared electrified heating and cooling systems from renewable sources of energy, where economies of scale and synergies between different types of consumers can be exploited. To this end, the focus of this paper is on the integration of shallow geothermal energy technologies into district heating and cooling systems. A key contribution of this work is the illustration of a number of practical case studies, highlighting the potential of existing shallow geothermal systems for DHC networks, which, as front runners in adopting such technologies, serve as paradigms for future development. Follows a discussion providing an outlook over the next 25 years. All in all, the future of utilizing shallow geothermal energy for district heating and cooling seems to be promising to play a pivotal role in sustainable urban development and decarbonizing the heating and cooling sector. [ABSTRACT FROM AUTHOR]

Geological Disposal Facilities (GDF) for radioactive waste will generally rely on clay-rich materials as a host geological formation and/or engineered barrier. Gas will be produced within the GDF, which can build up significant gas pressure and will activate the migration of gas through the clay materials via different transport mechanisms. These transport mechanisms are usually investigated in laboratory tests on small clay samples of a few centimetres. In this paper, a new Pneumo-Hydro-Mechanical (PHM) Finite Element model to simulate gas migration in saturated clay samples of this scale is presented. In the proposed modelling approach, continuum elements are used to represent the mechanical and flow processes in the bulk clay material, while zero-thickness interface elements are used to represent existing or induced discontinuities (cracks). A new triple-node PHM interface element is presented to achieve this. The performance of model is illustrated with synthetic benchmark examples which show the ability of the model to reproduce observed PHM mechanisms leading to propagation of cracks due to the gas pressure (gas fracturing). [ABSTRACT FROM AUTHOR]

This paper presents the development of a numerical model for reactive transport of multicomponent chemicals in unsaturated soils. The model has been developed based on a coupled thermal, hydraulic, chemical, and mechanical (THCM) formulation, and extended by the inclusion of geochemical processes under mixed equilibrium and kinetically controlled reactions in-between the solid, aqueous, and gas phases in soil. This has been achieved by coupling the transport model, COMPASS, with the geochemical model, PHREEQC. Key coupling between the geochemical modelling and the flow of chemicals has been established via the inclusion of porosity modification from mineral precipitation-dissolution reactions and the consequential effects on flow processes. Verification of the developed model is addressed via a series of benchmark simulations with a focus on testing the coupling between the transport model and geochemical model. Good results have been achieved for the verification of the theoretical and numerical implementation of the new developments in the model. A simulation is presented to demonstrate the effects of mineral reactions on porosity evolution and chemical diffusion in a low porosity soil. The model developed is an advanced tool for studying the hydrogeochemical processes in unsaturated soils under variable THCM conditions. [ABSTRACT FROM AUTHOR]

The Material Point Method (MPM) has been gaining increasing popularity as an appropriate approach to the solution of coupled hydro-mechanical problems involving large deformations. This study extends the implicit GIMP-patch method for coupled poroelastic problems recently proposed by Zheng et al. (2021b) to tackle large-deformation problems in (nearly) isochoric elastoplastic geomaterials, particularly by remedying the numerical inaccuracies caused by volumetric locking, such as spurious stress oscillations and an excessively stiff overall response of the system at hand. To overcome these difficulties in two-phase coupled analyses, the B ¯ approach of Hughes (1980) is incorporated into an existing version of the implicit GIMP-patch method. Details regarding the formulation and implementation of the proposed method are provided, while several benchmark problems are numerically analysed to evaluate its performance in the presence of elastoplastic behaviour. Particular emphasis is placed on (i) mitigating effective stress oscillations and (ii) solving several two-phase, coupled, large deformation geotechnical problems. The numerical results confirm the suitability of the implicit B ¯ GIMP-patch method for the solution of geotechnical problems spanning weak to strong hydro-mechanical coupling and small to large deformations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A reliability-based analysis framework, accounting for uncertainty arising from the spatial variability of soil properties, has been validated for the controlled, well-instrumented slope failure of an historic dyke in the Netherlands. Using soil property statistics derived from the results of laboratory and cone penetration test (CPT) data for the different soil layers at the site, the dyke was analysed for the initial (i.e. operating) conditions, as well as for the later stage of the test leading up to failure. The computed probabilities of failure and back-figured factors of safety were consistent with the point at which failure occurred in the test, as was the range of possible failure mechanisms. The uncertainty in the stability assessment was reduced by considering the spatial nature of the soil variability, and by conditioning analyses to CPT measurement data. It is shown that the reliability-based approach enables more informed stability assessments that could make the difference between a dyke being assessed as safe or requiring costly improvement. [ABSTRACT FROM AUTHOR]

Ground source heat pumps (GSHP) coupled to shallow borehole heat exchangers (BHE) represent a low emission technology to provide space heating and cooling. However, ongoing long-term heating or cooling of the ground caused by unbalanced loads leads to a performance decline and in the worst case to a system shutdown. Enhanced regeneration can increase the system efficiency, reduce the necessary borehole length or compensate unbalanced loads. In this study, a literature review about the regeneration of shallow BHE fields to counteract ground thermal imbalance is conducted to give an overview about the state-of-the-art and identify research gaps. The most common heat sources for artificial regeneration in heating-dominated applications are space cooling and solar thermal flat-plate collectors, while the most common heat sinks in cooling-dominated applications are space heating and cooling towers. In heating-dominated applications, mostly single buildings are studied. There is a lack of studies on district heating and cooling applications, which are especially needed as the benefit of regeneration increases with system size. There is also a lack of long-term, large system size experimental work to validate theoretical studies. • Regeneration is necessary for a sustainable operation of large borehole heat exchanger fields. • Regeneration methods can be divided into artificial and enhanced natural regeneration. • In heating-dominated applications, typical heat sources are space cooling and solar thermal heat. • In cooling-dominated applications, typical heat sinks are space heating and cooling towers. • There is a lack of long-term experiments on regenerating large borehole heat exchanger fields. [ABSTRACT FROM AUTHOR]

This paper presents a single-point Material Point Method (MPM) for large deformation problems in two-phase porous media such as soils. Many MPM formulations are known to produce numerical oscillations and inaccuracies in the simulated results, largely due to numerical integration and stress recovery performed at non-ideal locations, cell crossing errors, and mass moving from one background grid cell to another. The same drawbacks lead to even worse consequences in the presence of an interstitial fluid phase, especially when undrained/incompressible conditions are approached. In this study, an explicit stabilised MPM, based on the Generalised Interpolation Material Point (GIMP) method with Selective Reduced Integration (SRI), is proposed to mitigate typical numerical oscillations in (nearly) incompressible coupled problems. It includes two additional features to improve stress and pore pressure recovery, namely (i) patch recovery of pore pressure increments based on a Moving Least Squares Approximation, and (ii) two-phase extension of the Composite Material Point Method for effective stress recovery. The combination of components leads to a new method named GC-SRI-patch. After a detailed description of the approach, its effectiveness is verified through analysing various consolidation problems, with emphasis on the representation of pore pressures in time and space. [ABSTRACT FROM AUTHOR]

In January 2020, a scientific borehole planning workshop sponsored by the International Continental Scientific Drilling Program was convened at Cornell University in the northeastern United States. Cornell is planning to drill test wells to evaluate the potential to use geothermal heat from depths in the range of 2700–4500 m and rock temperatures of about 60 to 120 ∘ C to heat its campus buildings. Cornell encourages the Earth sciences community to envision how these boreholes can also be used to advance high-priority subsurface research questions. Because nearly all scientific boreholes on the continents are targeted to examine iconic situations, there are large gaps in understanding of the "average" intraplate continental crust. Hence, there is uncommon and widely applicable value to boring and investigating a "boring" location. The workshop focused on designing projects to investigate the coupled thermal–chemical–hydrological–mechanical workings of continental crust. Connecting the practical and scientific goals of the boreholes are a set of currently unanswered questions that have a common root: the complex relationships among pore pressure, stress, and strain in a heterogeneous and discontinuous rock mass across conditions spanning from natural to human perturbations and short to long timescales. The need for data and subsurface characterization vital for decision-making around the prospective Cornell geothermal system provides opportunities for experimentation, measurement, and sampling that might lead to major advances in the understanding of hydrogeology, intraplate seismicity, and fluid/chemical cycling. Subsurface samples could also enable regional geological studies and geobiology research. Following the workshop, the U.S. Department of Energy awarded funds for a first exploratory borehole, whose proposed design and research plan rely extensively on the ICDP workshop recommendations. [ABSTRACT FROM AUTHOR]

A hybrid material point/finite volume method for the numerical simulation of shallow water waves caused by large dynamic deformations in the bathymetry is presented. The proposed model consists of coupling the nonlinear shallow water equations for the water flow and a dynamic elastoplastic system for the seabed deformation. As a constitutive law, we consider a linear elastic-non-associative plastic model with the Drucker-Prager yield criterion allowing for large deformations under undrained cases. The transfer conditions between these models are achieved by using forces sampled from the hydraulic pressure and the friction terms along the interface between the seabed soil and shallow water. A detailed description regarding the coupled algorithm for the hybrid material point/finite volume method is presented. Several numerical examples are investigated to demonstrate the performance of the finite volume method for simulations of shallow water flow and the material point method for capturing the large deformation process of the solid phase. We also present numerical simulations of an undrained clay column collapse that induced shallow water waves and a dam-break problem to demonstrate the excellent performance of the proposed hybrid material point/finite volume method. [ABSTRACT FROM AUTHOR]

• Survey conducted to understand factors favouring/limiting earthen construction in India. • Low societal image of earth as building material is a key barrier towards its acceptance. • Image of earth is strongly linked to poverty and intensive maintenance requirement. • Compressed earthen technique (CSEB) has potential to improve image and acceptance for housing. • Successful demonstration in diverse location needed to promote earthen construction. There is an enormous demand for rural housing in India that needs to be catered for within a short span of time. Building with earth (mud) is proposed as an economical and environmental friendly alternative due to the rising costs of conventional building materials. However, the construction of earthen houses has significantly declined in India and thus it is necessary to evaluate if they can make a valuable contribution to contemporary housing shortage. Therefore, an informal survey was conducted in India to understand factors favouring or limiting the construction and daily use of earthen houses. The outcome of the survey suggests that 'Image' is the key barrier against a wide acceptance of traditional earthen houses which are linked to poverty. While modern earthen construction is desired, it is expensive for low-income households. The role of earth in addressing the contemporary housing shortage is analysed and suggestions are given for the implementation of modern earthen technologies for low-cost affordable rural housing. Initiatives by middle-high income households, entrepreneurs and government can trigger a widespread interest in earthen construction. Successful demonstration of durable earthen structures at diverse locations and contexts can act as catalysts for change of the image of earth and make it a desirable material for low-cost housing in rural India. [ABSTRACT FROM AUTHOR]