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Understanding the mechanism of cement grout flow in fractured rocks is essential for controlling seepage in the construction of hydraulic projects. However, simulating grouting in fractured rocks is complex due to random fracture distribution and non-Newtonian grout flow. This study proposes a numerical model for simulating cement grout flow, considering the hydro-mechanical coupled process in a three-dimensional fracture network system based on the unified pipe-network method. A pipe-network equivalence method is used to derive equivalent pipes for the process of grouting displacement, and the flow field can be solved in unified pipe networks. The hydro-mechanical coupled process is achieved by incorporating an analytical solution for the stress distribution of the center borehole model on an infinitely large plane and a constitutive model for the estimation of the fracture aperture. The time-varying property of the cement grout flow is also considered in the simulation of grouting. The reliability of the numerical model is verified by comparing with analytical solutions for grout flow in a water-saturated fracture. Grouting experiments in fracture networks are also performed to demonstrate the applicability of the proposed method. The influence of various factors on the propagation of cement grout is further investigated in three-dimensional fracture network models. [ABSTRACT FROM AUTHOR]

T he 3D Unified Pipe-Network Method (UPM) is applied to simulate the acidizing process in fractured carbonate rock. Fractures and porous media are represented by their equivalent connected fracture pipes and matrix pipes, respectively. The UPM combined with a two-scale continuum model is a numerical approach to wormhole development. Benchmark tests are attempted against commercial software and a sensitivity analysis is carried out with respect to the rock porosity heterogeneity magnitude and injection rates. The influences of the geometric properties and permeability of a fracture on wormhole propagation and the amount of reaction fluid per pore volume required to reach a breakthrough (PVBT) are analysed. [ABSTRACT FROM AUTHOR]

This paper presents a computational sand model based on the well-known pressure dependent multi-surface constitutive model to solve the necessity of employing a separate set of model parameters for each soil relative density change. The proposed model correlates the original model parameters with the soil relative density through critical-state-based soil mechanics formulations to provide a single set of model constants that adapt to different soil states. Model formulation updates are performed for the flow rules, material moduli calculations, and the computation of stress ratios at the phase transformation and failure stages. The model parameters are calibrated for Ottawa F-65 sand against cyclic soil element tests with different stress levels and various soil densities. Thereafter, numerical simulations are conducted for centrifuge experiments of gently sloped grounds to validate the proposed model. Throughout numerical simulations, the proposed model accurately replicates the sand cyclic undrained behavior as similar to laboratory-measured responses for different soil relative densities with a single calibrated set of model parameters and provides reliable numerical predictions in finite element simulations of the engaged centrifuge experiments. Overall, the proposed model robustly simulates the saturated sand seismic response, which can improve the numerical prediction accuracy of liquefaction-induced damage in different engineering applications. [ABSTRACT FROM AUTHOR]

When new metro tunnels undercrossing existing tunnels, deformation is inevitably caused in the stratum and the existing structures. However, the calculation results by conventional prediction methods often bring large errors compared to measured or simulated data because the complex influences of the stiffness of existing structures is always neglected. According to the equivalent layered method, an existing tunnel can be considered as an equivalent rock stratum instead. Based on the Peck formula, a theoretical model for predicting the deformations caused by construction of a new tunnel undercrossing an existing tunnel is established. This paper mainly picks the Metro Line 10 undercrossing the Metro Line 1 of Beijing subway as an engineering case study. The comparison shows that results by the prediction model fits the measured data well. The proposed model are widely applicable and provides a new prediction method to study the deformations of existing tunnels and strata caused by the undercrossing new constructions. [ABSTRACT FROM AUTHOR]

Soil classification plays a significant role in reutilization of excavated soils, which is produced greatly every year in China. In this work, an efficient system for identifying excavated soil type was developed at the start, transfer or end points of transportation. Firstly, soil image color patterns, cone index (CI), dielectric constant (DC), and electrical conductivity (EC) were identified as indexes for prompt characterization. Accordingly, an excavated soil information collecting system (ESICS) based on time domain reflectometry (TDR) cone penetrometer and digital camera was established at Xiecun Wharf, the largest wharf for transferring excavated soils in East China. After collection of soil information for 2 months, a multi-source soil database with 25,152 groups of soil image, CI, DC, and EC was generated. Then, based on ResNet18 convolutional neural networks, a novel classification framework with four screens (soil images, CI, DC, and EC) was proposed. Through deep learning of the database, all the excavated soils were finely classified into 12 types, which was calibrated by laboratory tests in Unified Soil Classification System and soil mineralogy. The system can realize classification with 88.7 %-accuracy within 50 s (even 97 % for the soils with simple color patterns), which leads to cost-effective management of excavated soils. [ABSTRACT FROM AUTHOR]

Reliable predictions of time-dependent diaphragm wall deflections in deep excavations in soft soils are crucial for managing potential damage to the surrounding environment. Bayesian updating offers a rational method for refining these predictions by using monitoring data. The inconsistency in monitoring data necessitates an examination of the impact of using different datasets on Bayesian updating. This paper presents a Bayesian updating of time-dependent deflections of diaphragm walls in deep excavations in soft soils using different datasets. The soft soil creep model is utilized to simulate the time-dependent behavior of soil. Bi-directional long-short memory neural networks are employed as surrogate models. Different updating strategies with varying numbers of data in the datasets are adopted for Bayesian updating and illustrated with the Taipei National Enterprise Center project. The results show that incorporating more monitoring data in the datasets for Bayesian updating does not guarantee better predictions unless the consistency of the monitoring data used is ensured. Additionally, the Bayesian updating process more accurately predicts short-term deflections than long-term ones, likely due to the higher consistency in short-term construction processes. It is advisable to review the construction processes to ensure the consistency of the monitoring data before selecting the appropriate dataset. [ABSTRACT FROM AUTHOR]

The hollow cylinder apparatus (HCA) is capable of achieving non-proportional stress paths and has been extensively employed to replicate stress paths with rotating principal stress in laboratory element tests. However, only macro-mechanical parameters could be observed in laboratory HCA tests and there is lack of information to understand the evolution of microscale parameters during the loading process. As a promising numerical technique, the discrete element method (DEM) allows investigation of the responses of virtual granular samples under general loading conditions and provides ideal numerical results to overcome the aforementioned limitations. In this study, a novel approach to DEM simulation of the hollow torsional shear apparatus for achieving the general loading paths was introduced. Two algorithms including the stress-controlled and the mixed-controlled loading were developed. Application cases indicated that both undrained monotonic and cyclic loading paths were successfully reproduced by using the proposed algorithms. Compared with results from the literature, DEM results demonstrated that this approach could reasonably reproduce the behaviour of granular material under general loading conditions, including aspects such as dilatancy and pore water pressure generation. [ABSTRACT FROM AUTHOR]

Multimodal fusion, a cutting-edge method aiming to integrate heterogeneous data for prediction tasks, has received limited attention in geotechnical engineering. This study focuses on classifying excavated soils with large quantities rapidly and finely. By using an excavated soil information collecting system at the largest soil transferring platform in China, 3,243 groups of multi-source heterogenous data were created, including soil images, spatial series data of cone index curves, time series data of TDR waveforms, discrete net weight data, and textual descriptions of soil morphology. After data augmentation, a big dataset containing 23,122 sets with labels based on the Unified Soil Classification System, moisture content, and mineral composition was created. Multimodal deep learning models were trained using different fusion strategies: 7 early fusion, 3 intermediate fusion, and 2 late fusion cases. Performance metrics were evaluated, including loss, accuracy, F1 Score, precision, recall, specificity, NPV, FPR, and AUROC. Results showed that intermediate fusions performed best, while late fusions performed the poorest. The two-stage intermediate fusion with five modalities achieved the best results, achieving an accuracy above 0.99 on the test set. This multimodal fusion approach effectively explores the correlation between multi-source heterogeneous data of soils, leading to scientific and engineering value in geotechnics. [ABSTRACT FROM AUTHOR]

In most existing trapdoor tests, the supporting structures beneath the arch feet are usually stationary, however, for embankments with flexible or floating piles in deep soft soil areas, piles supporting the arch foot usually settle under vehicle loads, significantly affecting the settlement deformation and load transfer of the embankment. Therefore, A numerical damping spring-based trapdoor model that can account for arch foot settlement is proposed to investigate the effect of arch foot settlement on the soil arching, while comprehensively considering the influence of the interaction among the pile, embankment fill, and soft soil on the evolution of soil arching in a pile-supported embankment. The results show that arch foot settlement on the soil arching differs significantly at different stages: it weakens the soil arching in the initial state and enhances the soil arching in the recovery state but little affects the soil arching in the ultimate state. Moreover, the arch foot settlement significantly reduces the height and stability of the soil arch in relatively high soft soil stiffness conditions, leading to a soil arch that is susceptible to degradation under localized loads. In addition, the arch foot settlement increases the normalized displacement needed for full mobilization of soil arching, resulting in varied levels of mobilization under the same differential settlement. [ABSTRACT FROM AUTHOR]

Horizontal wells are gradually used for dewatering at municipal solid waste (MSW) landfills in recent years. A theoretical model of leachate flow to horizontal well is required to better evaluate its dewatering performance. In this study, a dual-porosity model of the leachate flow to a horizontal well in MSW landfills is established. The proposed model divides waste into fracture and matrix domains. Leachate in these two domains flows horizontally and vertically into a horizontal well together with leachate exchange occurring between them. An analytical solution of leachate level drawdown under horizontal well draining is obtained through Laplace integral transformation and Separation of variables. The analytical solution is verified with the numerical solution obtained by finite element method in COMSOL Multiphysics software. A sensitivity analysis is performed to investigate the effect of model key parameters, including anisotropy of hydraulic conductivity k r / k z , hydraulic conductivity ratio of fracture domain to matrix domain k fr / k mr , and proportion of fracture domain in total domain w f , on leachate level drawdown. A case study of the horizontal well draining test at the Tianziling landfill indicated that the dual-porosity model performed better than the single-porosity model in leachate level drawdown estimation, especially near the horizontal well. The average value of hydraulic conductivity ratio of fracture domain to matrix domain k fr / k mr is fitted to be 419 for typical MSW with high kitchen waste content in China. [ABSTRACT FROM AUTHOR]

Deep soil mixing (DSM) grids are widely used as effective countermeasures against liquefaction hazards. A simplified two-dimensional, nonlinear, finite element model involving DSM grid-improved ground is proposed to investigate the shear stress responses of the enclosed soil. A numerical model with several approximations of longitudinal walls was carefully validated by a centrifuge model test. The waist-shaped depth distribution of the horizontal cyclic shear stress acting on the enclosed soil (i.e., the "waist effect") was revealed and well explained according to the characteristics of dynamic soil-grid interactions. Attention should be given to the increasing shear load sustained by the underlain layer, which may lead to an unexpected failure. A mathematical model for the shear stress reduction ratio was proposed based on a comprehensive numerical parametric analysis considering varying geometry and shear modulus of the DSM grid with a reasonable range. The proposed evaluation method, along with conventional liquefaction-triggering analysis, can be utilized for the seismic design of DSM grids in liquefaction mitigation. The previous design methods without considering the "waist effect" underestimate the overall horizontal cyclic shear stress acting on enclosed soil. [ABSTRACT FROM AUTHOR]

Geomembranes (GMBs) of the landfill composite liners frequently contain long defects, which will form the dominant flow path in the composite liner. The significant differences between the geosynthetic clay liner (GCL) and the compacted clay liner (CCL) lead to distinct flow patterns in the defective composite liners. For GMB/CCL composite liners, the induced flow in the CCL is two-dimensional, thus the existing solution with the assumption of one-dimensional flow significantly underestimates the leakage rate with a maximum relative error of 87% when compared to the results of a 2D finite element model. A new solution for predicting the leakage rate through GMB/CCL composite liners with a long defect is proposed with a consideration of two-dimensional flow in the CCL, with relative errors of leakage rate less than 29% for the cases investigated. The proposed solution also shows a lower relative error for the wetted distance (6–23%) compared to the existing solution (49–77%) for GMB/CCL composite liner cases. The comparisons with numerical results show that the proposed analytical solution significantly reduces the underestimation of leakage rate through the defective GMB/CCL composite liner, thus can help to improve the composite liner design for landfills. [ABSTRACT FROM AUTHOR]

On account of the numerous discontinuities and multiple physics involved, the numerical evaluation of pollution propagation is computationally sophisticated and time-consuming. This paper proposes a new approach based on the unified pipe-network method to simulate nuclide migration in highly fractured rock masses. This method explicitly represents fracture networks with interconnected nodes and pipes in a spatial domain and applies a set of universal constitutive models to both fractures and rock matrices. Whether fractures or rock matrix are the dominators of mass transport depends on the connectivity of fracture networks. Minor changes in connectivity may trigger significant percolation threshold effects. [ABSTRACT FROM AUTHOR]

Abstract A mesh mapping method is proposed to incorporate stress effect into the hydraulic analysis for highly fractured rock masses. Mechanical and hydraulic mesh are introduced for the hydraulic and mechanical simulations, respectively. The mechanical mesh contains strong discontinuities for capturing the fracture opening, closure and shearing, while the hydraulic mesh only consists of merged triangles on fractures. Using finite element method and unified pipe network method, stress effects on the equivalent permeability of complex discrete fracture networks (DFNs) are studied. The numerical result demonstrates that the mesh mapping method is effective to the stress-dependent analysis of 3D complicated DFNs. [ABSTRACT FROM AUTHOR]

Based on binocular stereo photography measurement technology, the actual distribution information of joints and fractures in the tunnel face were obtained via image processing and feature extraction, and the preliminary evaluation of surrounding rock stability of Laohushan tunnel was conducted according to surrounding rock classification method. Since all available surrounding rock classification approaches didn’t consider the influences of the size effect of tunnel excavation span and unfavorable geologic bodies such as weak-fracture zones, an improved discontinuous deformation analysis (DDARF) method was adopted to conduct a numerical simulation of the deformation and fracture processes of the surrounding rock. Using the traveling wave method, triangle DDA blocks were automatically generated in the calculation zone, and the block boundaries were divided into real joints and virtual joints. Based on the real joint information obtained via aforementioned photographic measurement, the real joints in the tunnel face were dynamically modified, in order to achieve the simulation of joint distribution. The results revealed that the fracture evolution regularity, deformation failure mechanism, and block dropping phenomenon that the DDARF joint simulation model calculated are in good agreement with actual conditions, while those obtained based on conventional models present differences from field situation. Additionally, focusing on the localised rockfall phenomenon of Laohushan tunnel, the crack extension rate was introduced to conduct a quantitative comparison of the rock crack evolution process with or without anchor supporting. The research results offer practical guidance for field construction and anchorage support scheme optimization. [ABSTRACT FROM AUTHOR]

Full-face excavation can be difficult when tunnels are constructed in composite soil containing oversized cobbles. To mitigate construction risks, a section of the mine-by experimental tunnel was excavated as part of the Kokhav Hayerden Pumping Storage Project in Israel. The response on the face was monitored by using the Modular Reverse-Head Extensometer technique and the extrusion mechanism was studied via FLAC3D software. To successfully model randomly-distributed granules mixed in the host clay matrix, a heterogeneous method was developed to nominate individual mesh zones by assigning rigid material properties through a random Numpy list. The behaviour of the response of the face was closely depicted by the proposed model, as compared to in-situ monitoring data. For stability analysis, a strength reduction method was used and demonstrated similar factors of safety to semi-analytical solutions, which suggested the anchor design at the mine-by section may be optimized for subsequent tunnel chainages. Despite the cobble granules limiting face extrusion in the mixed strata, it brought additional concern when granules constantly spall from the working face. This could be attributed to the loss of shear strength in the host material caused by a combination of excessive shear strain and stress relaxation during tunnel excavation. [ABSTRACT FROM AUTHOR]

This paper presents failure probability assessment and parameter sensitivity analysis of a contaminant’s transit time through a compacted clay liner. Monte Carlo simulation (MCS) was used to assess failure probability, and the failure samples generated in the MCS were used to investigate the sensitivity of various uncertain parameters to the failure probability. To facilitate the MCS, a database on various transport parameters was developed by collecting and analyzing measurement data reported in literature. Failure probability assessment and parameter sensitivity analysis showed that the uncertainties in adsorption parameters, longitudinal dispersivity, and hydraulic conductivity have the most significant effects on failure probability. [ABSTRACT FROM AUTHOR]

The biologically active soils covered by plants are widely applied in landfill final covers for controlling the emission of methane from municipal solid waste. The current study focuses on developing alternative formulations of steady-state analytical modeling for coupled methane transport and oxidation in vegetated landfill cover systems considering the effect of mass exchange via plants' roots. The proposed analytical frameworks are validated by a set of experimental data. The varied examples of coupled methane transport and oxidation are evaluated by the proposed solution to discuss the effects of the properties of roots and soils on the overall performance of vegetated landfill covers. It was shown that the increment of the root depth or root density can effectively contribute to the reduction of CH 4 emission from landfill cover systems while coupled effects of advection/diffusion and oxidation rate may influence the overall performance of CH 4 transport. For example, increasing root density from 100 m/m3 to 3 × 103 m/m3 can lead to a reduction of CH 4 emission rate by a factor of 1.3. This is mainly attributed to the increase of aerobic zone with the root density growing. It is found that the methane removal efficiency is more sensitive to variations of the saturation outside the root zone (S 2) than that in the root zone (S 1) as gases inlet fluxes are largely reduced and the role of the plant is weakened for a larger S 2. The present analytical models may provide an easy-to-use tool for performance evaluation of cover systems, benchmark studies, parameter identification and sensitivity analysis. [ABSTRACT FROM AUTHOR]

Identifying the location of a leakage is the very first basic step for preventing the escape of landfill gas and leachate from defects. A two-dimensional semi-analytical model is presented for the transport of tracer gas injection in landfills. Tracer gas transport in the landfill cover, liner and waste body is considered. Constant concentration and flux boundary conditions for the injection well are adopted. The proposed approach can be used for leakage detection of the barrier systems in landfills. It is shown that the air-filled porosities of the waste body and the upper cover have a great influence on the tracer gas emission flux on the cover system while the effect of air-filled porosity of the bottom liner can be neglected. The transport mechanism of the tracer gas in the waste body can have a significant impact on the behaviour of the tracer gas in the upper cover and the bottom liner. SF 6 emission flux increases with decreasing of the thickness of the upper cover and increasing thickness of the waste body. It is proposed that a constant flux injection boundary should be adopted in the field for leakage detection. The analytical model presented here is a relatively simplified model, which can be used for the validation and guidance of field tracer test. [ABSTRACT FROM AUTHOR]

An analytical solution to non-isothermal diffusion of chemicals in finite porous medium with different combinations of boundary and initial conditions is presented. The average degree of diffusion was proposed to assess the contaminant removal efficiency from polluted soil with different initial contaminant concentration distribution conditions considering chemical and thermal diffusion. The dimensionless time factor for the average degree of diffusion U = 90% can be decreased by a factor of 8.4 in the case with rectangular initial solute concentration distribution considering thermal diffusion. An application of the model to study the effects of initial solute concentration distribution and adsorption on the average degree of diffusion show that both the adsorption performance of clayey soil to the contaminant and the initial solute concentration distribution have a significant effect on the average degree of diffusion. In the cases with rectangular and inverse triangular initial solute concentration distributions, when U = 50%, the times increase by factors of 2.2 and 5.3, respectively, compared to the case with triangular initial solute concentration distribution. An application of the model to study the effects of temperature on the average degree of diffusion of contaminant in polluted soil show that the temperature difference has a significant effect to promote the contaminant transport in clayey soil by increasing both of the thermal diffusion and chemical diffusion effect. It may be an effective method to remove contaminant from polluted soil by thermal diffusion. [ABSTRACT FROM AUTHOR]

Typical applications of rockbolts in slope engineering are mainly used to prevent movements of blocks or wedges of rock on discontinuities dipping out of the face as the rockbolts can modify the normal and shear forces acting on the sliding planes. In this paper, the numerical model of the NPR-cable was developed and integrated with 2-dimensional discontinuous deformation analysis (2D-DDA). The load transfer at the NPR-cable was simulated by mechanically locking nodes. Verifications of the NPR-cable model were carried out based on the application of limit equilibrium analysis to calculate the required cable forces for possible sliding or toppling of blocks. It showed a good agreement had been made between the numerical and the analytical results. Furthermore, the NPR-cable model was further applied in the simulation of physical modeling of slope under slide-toe-toppling failure. The role of existing discontinuities on the slide-toe-toppling failure was presented. The interactions between the model-scale NPR-cable and the blocks were also presented. It showed the advantages of NPR-bolt in preventing slide-toe-toppling failure. [ABSTRACT FROM AUTHOR]