Search

In this paper, an anisotropic non-associative constitutive model, based on the well-established critical state soil mechanics framework, is developed for the natural and reconstituted clays subjected to monotonic and cyclic loadings. A robust non-elliptical yield surface is implemented in the model which enables it to capture a wide variety of yield stress points. In addition to a realistic soil stiffness simulation, the employed flexible plastic potential surface equips the proposed model to predict a more accurate coefficient of earth pressure at rest. The model uses a combination of conventional volumetric and comprehensive rotational hardening rules to control the evolution of the yield surface caused by plastic strain increments. The adopted rotational hardening rule uses the concept of governing plastic strain increment which not only ensures the existence of the equilibrium state of anisotropy but also takes the effect of plastic strains at different constant stress ratios into account more sensibly. The proposed model is enhanced with a novel double-image stress point bounding surface plasticity type theory to capture nonlinear behaviour inside the yield surface, and also to simulate the cyclic responses. The detailed model formulation is discussed in both triaxial stress space and the e - ln p plane, and the important features of the model are elaborately explored. The capabilities of the model are also demonstrated by an extensive sensitivity analysis. In the end, the model is used to carry out simulations of monotonic and cyclic element tests on different clays and the results are compared with the available experimental data. [ABSTRACT FROM AUTHOR]

Natural soils often exhibit an anisotropic fabric pattern as a result of soil deposition, weathering, or filling. This paper aims to investigate the effect of soil interdependent anisotropy and fabric orientation on runout motions of landslides and evaluate the most critical fabric orientation for the post-failure behavior. The shear strength properties of soil deposit (i.e., cohesion c and friction angle φ ) are modeled as negatively cross correlated bivariate random fields. The results reveal that the spatial variability and the negative cross-correlation of c and φ notably influence the post-failure behavior. In addition, the rotation of soil layer orientation significantly affects the runout motion. Based on the analyses, the deposition orientation of 30 ∘ is identified to produce the highest mean value and standard deviation of the runout distance. The findings from this study highlight the importance of considering the orientation of soil stratification, rather than only the magnitude of shear strength, in assessing the post-failure behavior of a landslide. [ABSTRACT FROM AUTHOR]

In landslide analysis, reliable prediction of landslide's influence zone is significantly difficult due to the inherent heterogeneity of soils and their spatially varying geological properties. In this paper, a probabilistic framework is proposed to evaluate the landslide hazard zoning through the prediction of their influence zone considering the effects of heterogeneous soil properties. The material point method is used to simulate the large deformations during landslide failure. The spatial variation in the shear strength parameters of soils at undrained conditions is modeled by random fields, which are discretized by the Cholesky matrix decomposition method to incorporate the effects of the soil spatial heterogeneity on the postfailure deformations. Furthermore, a practical landslide hazard zoning is conducted to quantitively evaluate the level of disaster for facilities or structures located in the vicinity of the slope by using the exceedance probability of influence distance and runout distance. Five categories based on different thresholds of exceedance probability are used to visualize the area potentially affected by the landslide. To demonstrate the capability of the stochastic assessment framework, a benchmark example of the heterogeneous clayey slope is simulated, and the associated hazard zone is predicted and discussed; it presents a practical procedure for improving the landslide influence zone prediction and provides new insights for hazard zoning. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of the soil moisture evaporation rate on the soil water retention curve (SWRC) of clays obtained using the high-capacity tensiometer (HCT) technique and following the continuous drying (dynamic) method. SWRC measurements, with and without soil moisture evaporation rate control, were carried out on reconstituted London clay specimens using 12 performance-improved HCTs recently developed at the University of Warwick. Furthermore, the HCTs' performance in terms of the maximum attainable suction (smax) and maximum measurement duration (tmax) was evaluated. Moreover, the suitability of a curve-fitting-based model, available in the literature, for attaining the entire retention curve (beyond the capacity of HCTs) was evaluated. The SWRCs for the tests with a controlled evaporation rate were found to generally exhibit higher suction at a given water content, hence inducing air-entry values that were on average 16% higher than those obtained from tests without evaporation rate control. It was also found that for suction in excess of 2 MPa, the curve-fitting-based model predictions of data obtained from tests with a controlled evaporation rate exhibited significantly lower suction at a given water content than those without evaporation rate control, suggesting that such curve fitting correlations should be used with caution. [ABSTRACT FROM AUTHOR]

In this paper, an adaptive anisotropic constitutive model, namely AA1‐CLAY, is developed for clays based on the critical state framework. The model has a non‐associated flow rule, and it can also reduce to basic critical state constitutive models. A versatile yield surface (YS) is implemented in the model which can generate a broad range of shapes to improve the possibility of capturing experimental yield points of different clay types with high accuracy. In addition to the isotropic hardening rule, an innovative rotational hardening (RH) rule is also incorporated into the model to control the YS rotation rate. The proposed RH rule uses a transitional function to govern the effect of plastic strains at different constant stress ratios more realistically. Furthermore, the equilibrium state of anisotropy, which the YS tends to reach during plastic straining, is defined uniquely based on the experimental findings. The detailed model formulation is presented, and important features of the model are elaborately discussed. The capabilities of the model are also demonstrated by comparing the simulation results of several element tests on a number of different clays against the available experimental data. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of temperature variations on the creep and stress relaxation behavior of clay samples from London Bank Station. The independent and coupled effects of strain rate and temperature on one-dimensional (1D) stress–strain and stress relaxation responses were investigated based on a series of temperature-controlled constant rate of strain (CRS) compression–relaxation tests carried out at fast, intermediate, and slow displacement rates and over 20°C–55°C. The temperature effect on the creep index (Cα) was investigated based on a series of temperature-controlled multistage loading (MSL) oedometer tests. The results of the CRS compression–relaxation tests showed that with the increase in temperature, the coefficient of stress relaxation (Rα) decreases for samples that were loaded at fast and intermediate prerelaxation displacement rates (υ˙); however, it increases for samples loaded at the slow prerelaxation displacement rate. A decrease in υ˙ by a factor of 10 (i.e., from 0.010 to 0.001 mm/min) causes the Rα values to reduce by 55%–11% with the temperature increase. The increase in temperature caused an increase in Cα that were obtained from the MSL tests. The maximum value of Cα increased by 18% from 35°C to 45°C and by 37% from 45°C to 55°C. The temperature effects on other conventional parameters that included the preconsolidation pressure, and the compression and swelling indexes (Cc and Cs) were comparable with the findings reported in the literature. Comparing Cα that were obtained from the MSL tests and Rα that were obtained from the CRS tests supports the validity of Rα=Cα/Cc correlation for thermally influenced saturated reconstituted clays and that the time-dependent soil parameters could be obtained from relatively fast CRS compression–relaxation tests as an alternative to conventional time-consuming oedometer tests. [ABSTRACT FROM AUTHOR]

This paper proposes a new method of reusing uncalcined coal gangue (UCG) as a mineral admixture in magnesium ammonium phosphate cement (MAPC) blended with fly ash (FA). The effects of UCG on setting time, workability, hydration heat release, mechanical properties, hydration products, and microstructure of MAPC composites were systematically investigated. The results indicate that the addition of UCG decreased the maximum hydration temperature and extended the setting time of MAPC composites. The compressive strength of MAPC was improved by introducing an optimal amount of UCG. The XRD results showed no new crystal phase in UCG-0 (with 20% FA and 0% UCG) and some secondary hydration products, such as berlinite and lizardite, were observed in MAPC with UCG. The addition of UCG was found to inhibit the generation of dittmarite and promote the development of struvite. Results showed that differences in the crystal morphology of struvite and dittmarite influence the compressive strength of MAPC composites. [ABSTRACT FROM AUTHOR]

In this paper, the one-dimensional (1D) time-dependent behaviour of natural and reconstituted London Clay samples under saturated and unsaturated conditions is studied. For this purpose, a set of 1D consolidation tests including multi-staged loading (MSL) oedometer tests and single-staged loading (SSL) long-term oedometer creep tests were carried out on saturated and unsaturated specimens. Conventional oedometer cells were used for tests on saturated specimens, whereas a newly designed unsaturated oedometer cell, equipped with two high-capacity tensiometers (HCTs) for suction measurements, was used for unsaturated tests. The tests results revealed stress dependency and suction dependency of primary and secondary consolidation responses of the soil samples. Furthermore, counter to formerly acknowledged suggestions of independency of the slope of normal consolidation line to suction changes, it was observed that an increase in suction results in a decrease of the slope of compression curve (Cc) and the creep index (Cαe) values and an increase in yield vertical net stress (σp). Moreover, the Cαe/Cc ratio for London Clay was found to be stress- and suction-dependent, unlike the previously suggested hypotheses. [ABSTRACT FROM AUTHOR]

This paper focuses on numerical modeling of the responses of Ballina test embankment by an improved EVP-SANICLAY constitutive model with a novel rotational hardening (RH) law. The modified RH law guarantees the uniqueness of the critical state line, prevents excessive rotation of yield surface and is particularly simple that makes it very useful for practical applications. To consider strain-rate dependency of the soil behavior, Perzyna’s overstress theory is employed. Using the newly released data at Ballina test embankment site, the values of model parameters and state variables are calibrated and evaluated for Class C predictions, and their differences with the previously determined parameter values for Class A predictions are highlighted and discussed. The elasto-viscoplastic anisotropic constitutive model is implemented in PLAXIS software to carry out the simulations of the case study embankment. The numerical modeling results, in terms of time-dependent variations of deformations and pore water pressures, both during and after the embankment construction, are compared with the physical measurements at the test site. The results of Class C analyses show that the model is capable of capturing the temporal changes in surface settlement and lateral deformations with good accuracy, with the latter being particularly challenging when modeling the behavior of soft clays. Simulation of pore water pressure variations however proved more difficult. To highlight the advantages of the proposed EVP-SANICLAY model, the simulations are also compared with those using the classical Mohr-Coulomb and modified Cam-clay models, and the results are presented and discussed in detail. [ABSTRACT FROM AUTHOR]

In this paper, an anisotropic creep constitutive model, namely Creep-SCLAY1S is employed to study the installation effects of prefabricated vertical drains (PVDs) on the behavior of a full scale test embankment, namely Haarajoki embankment in Finland. The embankment was constructed on a natural soft soil with PVD installed to improve the drainage under one half of it. The Creep constitutive model used in this study, incorporates the effects of fabric anisotropy, structure and time within a critical state based framework. For comparison, the isotropic modified Cam clay (MCC) model and the rate-independent anisotropic S-CLAY1S model are also used for the analyses. The numerical predictions are compared with field measurements and the results indicate that the creep model provides an improved approximation of field settlements, and excess pore pressure build-up and dissipations. In addition, the application of two commonly used permeability matching techniques for two dimensional (2D) plane-strain analysis of the PVD problem is studied and the results are discussed highlighting their limitations and advantages. [ABSTRACT FROM AUTHOR]

This paper reports the results of a numerical investigation of the behavior of a natural soft clay deposit under the installation of a case study pile. The case study problem included installation of an instrumented close-ended displacement pile in a soft marine clay deposit, known as Bothkennar clay, in Scotland. The site has been used for a number of years as a geotechnical test bed site, and the clay has been comprehensively characterized with both in situ tests and laboratory experiments. The soft soil behavior, both after pile installation and subsequent consolidation, was reproduced by using an advanced critical-state-based constitutive model that accounts for the anisotropy of soil fabric and destructuration effects during plastic straining. Furthermore, a time-dependent extension of the model was used to study soil creep and the significance of its consideration in the overall pile-installation effects. The simulation results were compared against field measurements; furthermore, for comparison, the pile installation was also analyzed using the well-known isotropic modified Cam-clay model to highlight the importance of considering inherent features of natural soil, such as anisotropy and structure, in the simulations. A series of sensitivity analyses was also performed to evaluate the influence of initial anisotropy and bonding values on simulation results and to check the reliability of the numerical analyses. [ABSTRACT FROM AUTHOR]

The evaluation of the hydraulic properties evolution of granular sandstones in relation with groundwater inrush within faults is an important issue for mining engineering applications. This paper presents the results of an experimental investigation of small particle migration from granular sandstone samples under different original porosities, particle size compositions and water flow pressures. A new rock testing system has been setup to carry out the tests. Based on the results, it is observed that the overall permeability evolution during the tests can be divided into four different phases, including i) re-arrangement of large rock fragments, ii) water inrush with substantial particle migration, iii) continued moderate particles seepage, and iv) steady state water flow. The crushing of edges and corners of large rock fragments, and the evolution of the fracture network has mainly been observed in the first two phases of the tests. The results indicate that the migration of small particles has an essential effect on permeability and porosity increase during water inrush through fractured sandstone. The samples with higher original porosity, higher percentage of fine particles in their formation and under higher water flow pressures, achieve higher permeability and porosity values when the test is complete. Furthermore, using the measured data, the performances of a number of empirical models, for permeability evolution in fractured porous media, have been studied. The prediction results indicate that not all of the fractures in a sample domain contribute in small particle migration. There are parts of the fracture network that are not effective in particle flow, a sample with less original porosity, more fine particles and under lower water pressure shows less ineffective fractures. Therefore, using the concept of the effective porosity (fracture) is sufficient enough for the flow calculation. [ABSTRACT FROM AUTHOR]

This paper focuses on constitutive and numerical modeling of strain-rate dependency in natural clays while also accounting for anisotropy and destructuration. For this purpose the SANICLAY model that accounts for the fabric anisotropy with the additional destructuration feature that accounts for sensitivity of natural clays, is considered as the reference model. An associated flow rule is adopted for simplicity. The model formulation is refined to also account for the important feature of strain-rate dependency using the Perzyna’s overstress theory. The model is then implicitly integrated in finite element program PLAXIS. Performance of the developed and implemented model is explored by comparing the simulation results of several element tests and a boundary value problem to the available experimental data. The element tests include the constant strain-rate under one-dimensional and triaxial conditions on different clays. The boundary value problem includes a test embankment, namely embankment D constructed at Saint Alban, Quebec. For comparison, the test embankment is also analyzed using the Modified Cam-Clay (MCC) model, the SANICLAY model, and the viscoplastic model but without destructuration. Results demonstrate the success of the developed and implemented viscoplastic SANICLAY in reproducing the strain-rate dependent behavior of natural soft soils. [ABSTRACT FROM AUTHOR]

This paper investigates the computational performance of S-CLAY1S constitutive model by varying its yield function equation. S-CLAY1S is an advanced anisotropic elasto-plastic model that has been developed based on the extension of conventional critical state theory. In addition to modified Cam-Clay׳s hardening law, S-CLAY1S also accounts for inherent and evolving plastic anisotropy, interparticle bonding and degradation of bonds during plastic straining. A modified Newton–Raphson stress update algorithm has been adopted for the implementation of the model and it was found that the algorithm׳s convergence performance is sensitive to the expression of the yield function. It is shown that for an elasto-plastic model which is developed based on the critical state theory, it is possible to improve the performance of the numerical implementation by changing the form of the yield function. The results of this work can provide a new perspective for computationally cost-effective implementation of complex constitutive models in finite element analysis that can yield in more efficient boundary value level simulations. [ABSTRACT FROM AUTHOR]

Abstract: Prediction of liquefaction and the resulting lateral displacement is a complex engineering problem due to heterogeneous nature of soils and participation of a large number of factors involved. In this paper new models are developed, based on evolutionary polynomial regression (EPR), for assessment of liquefaction potential and lateral spreading. The models developed for liquefaction and lateral spreading are compared to those obtained from neural network and linear regression based techniques. It is shown that the developed models are able to learn the complex relationship between either of these problems and their contributing factors in the form of a function with high level of accuracy (mostly in excess of 90%). The results of the EPR model developed for the liquefaction determination are used to find a novel 3-D boundary surface that discriminates between the cases of occurrence and non-occurrence of liquefaction. The developed boundary surface is employed to calculate the factor of safety against liquefaction occurrence. [ABSTRACT FROM AUTHOR]

Abstract: In this paper a new approach is presented, based on evolutionary polynomial regression (EPR), for determination of liquefaction potential of sands. EPR models are developed and validated using a database of 170 liquefaction and non-liquefaction field case histories for sandy soils based on CPT results. Three models are presented to relate liquefaction potential to soil geometric and geotechnical parameters as well as earthquake characteristics. It is shown that the EPR model is able to learn, with a very high accuracy, the complex relationship between liquefaction and its contributing factors in the form of a function. The attained function can then be used to generalize the learning to predict liquefaction potential for new cases not used in the construction of the model. The results of the developed EPR models are compared with a conventional model as well as a number of neural network-based models. It is shown that the proposed EPR model provides more accurate results than the conventional model and the accuracy of the EPR results is better than or at least comparable to that of the neural network-based models proposed in the literature. The advantages of the proposed EPR model over the conventional and neural network-based models are highlighted. [Copyright &y& Elsevier]

In this paper, a multi-surface anisotropic constitutive model is proposed for clayey soils, based on bounding surface theory and a classical anisotropic critical state-based model. In the proposed model, in addition to the volumetric hardening law, a rotational hardening rule is also incorporated into the bounding surface formulation with a non-associated flow rule. The model uses the bounding surface plasticity theory to produce a more realistic representation of the nonlinear behavior of clays with high overconsolidation ratios. Detailed model formulation is presented including an innovative approach to find image stress points on the bounding surface which offers an original conception of changing the projection center, even at the absence of plastic loading. A modified procedure is also discussed to improve the performance of the proposed model for simulating the response of highly overconsolidated clays. The proposed modifications, together with the novel mapping rule, form a new framework that can be used to improve the simulation capabilities of different constitutive models that have elliptical yield/bounding surfaces. The efficiency of the framework is demonstrated by comparing the simulation results against element test data from a number of different clays at lightly to highly overconsolidated conditions. The new model shows promising capabilities in capturing the important aspects of natural clays response during straining, in particular for the combined effects of small strain nonlinearity with fabric orientation. [ABSTRACT FROM AUTHOR]

In this paper, a new genetic programming (GP) approach for predicting settlement of shallow foundations is presented. The GP model is developed and verified using a large database of standard penetration test (SPT) based case histories that involve measured settlements of shallow foundations. The results of the developed GP model are compared with those of a number of commonly used traditional methods and artificial neural network (ANN) based models. It is shown that the GP model is able to learn, with a very high accuracy, the complex relationship between foundation settlement and its contributing factors, and render this knowledge in the form of a function. The attained function can be used to generalize the learning and apply it to predict settlement of foundations for new cases not used in the development of the model. The advantages of the proposed GP model over the conventional and ANN based models are highlighted. [ABSTRACT FROM AUTHOR]

Abstract: Determination of liquefaction induced lateral displacements during earthquake is a complex geotechnical engineering problem due to the complex and heterogeneous nature of the soils and the participation of a large number of factors involved. In this paper, a new approach is presented, based on genetic programming (GP), for determination of liquefaction induced lateral spreading. The GP models are trained and validated using a database of SPT-based case histories. Separate models are presented to estimate lateral displacements for free face and for gently sloping ground conditions. It is shown that the GP models are able to learn, with a very high accuracy, the complex relationship between lateral spreading and its contributing factors in the form of a function. The attained function can then be used to generalize the learning to predict liquefaction induced lateral spreading for new cases not used in the construction of the model. The results of the developed GP models are compared with those of a commonly used multi linear regression (MLR) model and the advantages of the proposed GP model over the conventional method are highlighted. [Copyright &y& Elsevier]

Globally, coal mining wastes (CMWs) are associated with significant environmental and economic costs. Processing CMW into an ingredient of foam concrete is a promising solution but the behaviour of this particular construction material has not been sufficiently evaluated, especially during the initial period of cement hydration. The purpose of this paper is to present novel laboratory set-up and experimental procedures designed to investigate the early age behaviour of hydrating foam concrete samples made with a CMW from Poland. Two types of tests were devised to simulate air-curing conditions and water-curing conditions, respectively. These tests were carried out in custom-built unsaturated oedometer cells, and the matric suction in the test samples was monitored for approximately 14 days, using Warwick high capacity tensiometers. Experimental results show that in both curing conditions, a higher matric suction during cement hydration corresponds to a denser sample at the end of the monitoring period. A comparison of water-cured and air-cured samples also reveals different responses to CMW inclusion in their mix designs. The responses can be convincingly explained based on complementary test data and idealised capillary tube models adapted for the hydrating foam concrete samples. • A novel laboratory set-up, incorporating high capacity tensiometers (HCTs) into purpose-built unsaturated oedometer cells, is proposed to investigate the curing behaviour of foam concrete during early age hydration. The incorporation of the HCTs made it possible to directly monitor the matric suction evolution of the mix and the corresponding interplays depending on the foam concrete samples' (water- or air-) curing conditions. • The influence of natural sand replacement by coal mining waste (CMW) in the foam concrete mix has been studies, together with the corresponding effects on the evolutions of matric suction and porosity during the early age hydration. • Two different types of tests were devised for measuring the impacts of different curing environments on foam concrete properties. The first type was adapted for a water-curing condition and is akin to a chemical shrinkage test. The second type was adapted for an air-curing condition where water inflow was not permitted into the hydrating foam concrete sample over the monitoring period. In both cases. The evolution and interplays of matric suction were studied in correspondence with formation/stabilisation of the pore networks. • Simplified capillary models are proposed that meaningfully describe the rather complex kinetics of foam concrete hydration associated to the matric suction variations. [ABSTRACT FROM AUTHOR]

Damage process in engineering systems is strongly affected by spatial heterogeneity and local discontinuities in the materials, which are significantly influencing the reliability and integrity of the systems. In this paper, we present a new stochastic approach as a tool for performing uncertainty quantification in simulating damage evolution in heterogeneous brittle materials. One of the advantages of the proposed method is its ability to capture the influence of uncertainty in the mechanical properties of whole simulation domain, not just the properties of the immediate neighbourhood around the crack tip, on direction of crack propagation. In fact, through this approach the direction of crack propagation at a specified point of localised damage can be probabilistically determined based on nonlocal mechanics theory, in which the influence of local discontinuities and weak points located at further distances from the crack tip, in addition to those located at the immediate neighbourhood of the local damage, are incorporated into the model. The reliability and performance of the methodology are examined through simulation of numerical examples and comparison with analytical results and experimental data. The case studies show how the crack initiation angle can be reasonably estimated with this methodology and how this approach provides realistic values of fracture toughness K IC and fracture energy G f . [ABSTRACT FROM AUTHOR]

Coseismic landslides are common secondary earthquake geohazards in meizoseismal areas. Newmark sliding block permanent displacement method has been widely adopted to develop regional coseismic landslide hazard maps. However, uncertainties from the slope parameters (e.g., cohesion, pore water pressure, and block thickness) are not commonly considered in the ground displacement predictions. This study proposes a novel framework that consists of two uncertainty assessment methods of Monte Carlo and logic tree simulations (MCS and LTS) with seven different displacement regression functions to predict the regional coseismic landslides' permanent displacement. Compared with the existing methods, the proposed framework is argument-driven, avoiding huge number of repetitive simulations. The Jiuzhaigou earthquake, in China, is considered as an illustrative example to compare the performance of the framework with considered regression functions. The corresponding results show that using LTS, with a certain regression function, leads to better predictions compared to using MCS. It is demonstrated that the proposed framework can provide a meaningful measure for making informed decisions to diminish the potential risk of earthquake induced landslides, and/or generating emergency strategies to mitigate post-earthquake consequences. It should be noted that the application of the proposed method for deposits where the soil strength parameter values do not fit the normal distribution may be limited as only normal distribution for soil strengths is considered in this study. [ABSTRACT FROM AUTHOR]

Accurate assessment of slope failures and their large deformations is critical for effective landslide mitigation. This study introduces the new Cooperative Stochastic Material Point Method (CSMPM), addressing challenges in probabilistic characterization of slope large deformations considering three-dimensional (3D) soil heterogeneities. The method employs an enhanced Karhunen-Loève (KL) expansion to model 3D soil spatial variability efficiently. By using rough and refined grids, derived through the enhanced KL expansion, the study achieves computational efficiency without compromising accuracy. By combining the computational advantages of the rough grid with the precision of the refined grid, the CSMPM enables efficient probabilistic analysis of 3D heterogeneous slopes. The results demonstrate its capability to identify slope large deformation failure modes and quantify the associated failure probability. Notably, the shallow failure mode exhibits fan-shaped horizontal diffusion, introducing uncertainty, while the compound failure mode presents challenges in landslide prevention. The progressive failure mode poses the highest hazard. Horizontal heterogeneities significantly influence both large deformation likelihood and failure modes, emphasizing the importance of 3D soil spatial variability in geotechnical reliability assessments. The CSMPM, with its innovative approach, proves to be a practical tool for enhancing our understanding of geohazards and associated uncertainties, as well as large deformations. It provides valuable insights for improving risk assessment of slope hazards. [ABSTRACT FROM AUTHOR]

Purpose – In this paper, the peak kinetic energy density (KED) of soil particles during earthquake excitation is used as an intensity measure for the evaluation of liquefaction potential under field conditions. The paper seeks to discuss this measure. Design/methodology/approach – Using centrifuge tests data, it is shown that seismic pore water pressure buildup is proportional to cumulative KED at a particular soil depth. Linear relationships are found between cumulative kinetic energy and corresponding cumulative strain energy. To consider the effect of soil amplification, several equivalent linear ground response analyses are performed and the results are used to derive an equation for depth reduction factor of peak kinetic energy density. Two separate databases of liquefaction case histories are used in order to validate the proposed model. The performance of the proposed model is compared with a number of commonly used shear stress-based liquefaction assessment methods. Finally, the logistic regression method is employed to obtain probabilistic boundary curves based on the present model. Parametric study of the proposed probabilistic model is carried out to verify its agreement with the previous methods. Findings – It has been shown that the kinetic energy model works satisfactorily in classifying liquefied and non-liquefied cases compared with the existing recommendations of shear stress-based criterion. The results of the probabilistic kinetic energy model are in good agreement with those of previous studies and show a reasonable trend with respect to the variations of fines content and effective overburden pressure. The proposed model can be as used an alternative approach for assessment of liquefaction potential. Originality/value – These findings make a sound basis for the development of a kinetic energy-based method for assessment of liquefaction potential. [ABSTRACT FROM AUTHOR]

Reliable prediction of fracture process in shale-gas rocks remains one of the most significant challenges for establishing sustained economic oil and gas production. This paper presents a modeling framework for simulation of crack propagation in heterogeneous shale rocks. The framework is on the basis of a variational approach, consistent with Griffith’s theory. The modeling framework is used to reproduce the fracture propagation process in shale rock samples under standard Brazilian disk test conditions. Data collected from the experiments are employed to determine the testing specimens’ tensile strength and fracture toughness. To incorporate the effects of shale formation heterogeneity in the simulation of crack paths, fracture properties of the specimens are defined as spatially random fields. A computational strategy on the basis of stochastic finite element theory is developed that allows to incorporate the effects of heterogeneity of shale rocks on the fracture evolution. A parametric study has been carried out to better understand how anisotropy and heterogeneity of the mechanical properties affect both direction of cracks and rock strength. [ABSTRACT FROM AUTHOR]

Gas release from the crushed coal formation during coal mining poses a threat to the normal storage and gas transport within coal seam. This sort of release is largely related with the evolution of gas seepage properties of crushed coal, namely, the evolution of gas seepage properties plays an important role in the gas extraction and the outburst prevention of coal seam. Meanwhile, the evolution is directly related to the volume and geometry of fractures within the crushed coal and strongly influenced by particle size and porosity (axial displacement). In order to investigate the effect, a gas flow apparatus connecting with the MTS815.02 system was designed. The gas seepage properties of crushed coal specimens with five particle sizes of a (2.5–5 mm), b (5–10 mm), c (10–15 mm), d (15–20 mm) and e (mixed sizes) under the variable axial displacement of 10, 15, 20, 25, 30, 35, and 40 mm, respectively are measured by the revised MTS815.02 system. The results of test show that: The porosity decreases with the increase of axial displacement and the weight loss of larger particle size, respectively. Particle crushing during compaction is a main reason to increase small-size and emerge size 0–2.5 mm. Gas flow seepage properties of crushed coal are found to be strongly influenced by particle size and axial displacement. The permeability decreases and non–Darcy coefficient increases with the increase of axial displacement (decreases of porosity) and the decrease of larger particle size, respectively. The permeability and non-Darcy coefficient are controlled by the fracture among the coal particles. The seepage properties of crushed coal are not only related to particle size, loading levels (axial displacement), but also the compound mode. Based on the regression analysis, the relationship between the permeability and non-Darcy coefficient and porosity shows that the exponential function can fit the experimental data well. [ABSTRACT FROM AUTHOR]

Historically coal mining wastes have been viewed as heterogenous and hazard-prone geomaterials. Given that failures of colliery tips and tailing dams are reported on a regular basis, reclamation of coal mining wastes from storage facilities is increasingly being considered. There is a resistance to the use of coal mining waste in construction industry despite scattered but growing reports of successful applications. As the construction industry around the globe seeks to reduce its carbon emissions by looking for supplements for cement, the voluminous amount of coal mining wastes currently stored in spoil heaps and impoundment facilities present a potential source of raw materials. This article reviews the literature on the geochemical, geotechnical and structural engineering properties of coal mining waste geomaterials to assess their suitability as replacement for both aggregates and binders in concrete and cementitious composites (as opposed to reviewing the properties of those products themselves). It is found that coal mining wastes are indeed good candidates (as raw materials) for the uptake and process into higher level construction purposes. Geochemically, the key to a successful upcycling operation is the knowledge of their mineral contents (which is typically diverse and varies from one mine to another) and the processes they undergo while being transformed into constituents of new materials. The few studies on concretes made with coal mining wastes indicate that the mineralogical and mechanical characterization of the wastes to obtain a mix featuring strength and durability performance that meets specification is important to a successful utilization. In the geotechnical literature, coal mining wastes are known to be highly heterogeneous and may host expandable minerals with potential durability problems. However, this review also found that simple geotechnical index tests can be conducted to yield useful information for the initial screening of coal mining wastes into a construction product. The state-dependent properties of coal mining wastes (e.g., water retention, hydraulic conductivity, shear strength) are found to be governed by complex factors such as coal content, particle size and shape, pore size and shape, and the presence and interaction of pore air and pore water in the void space, some of these are well-studied but much of these are to be further researched. [ABSTRACT FROM AUTHOR]