Analysis of plastic zones in surrounding rocks around a circular tunnel considering the effect of intermediate principal stress and heterogeneity

Based on a modified Mohr-Coulomb criterion with a non-uniform coefficient, a calculation method of plastic zone boundary of surrounding rocks in a circular tunnel in non-uniform stress field is established. Both the effects of intermediate principal stress and heterogeneity are studied. With the increase of the intermediate principal stress, the plastic zone size of the surrounding rocks will decrease first and then increase. Lateral pressure coefficient has an effect on the shape of the plastic zone. With the increase of lateral pressure coefficient, the plastic zone gradually becomes uniform, and the failure of surrounding rock develops upward and downward from both sides. As non-uniform coefficient increases, the material is more uniform and the effect of intermediate principal stress on the plastic zone is less significant. If the effect of intermediate principal stress is not taken into account, the calculation results tend to be consistent with results calculated by the Mohr-Coulomb criterion, which are considered to be conservative

Failure Probability Model considering the Effect of Intermediate Principal Stress on Rock Strength

A failure probability model is developed to describe the effect of the intermediate principal stress on rock strength. Each shear plane in rock samples is considered as a micro-unit. The strengths of these micro-units are assumed to match Weibull distribution. The macro strength of rock sample is a synthetic consideration of all directions’ probabilities. New model reproduces the typical phenomenon of intermediate principal stress effect that occurs in some true triaxial experiments. Based on the new model, a strength criterion is proposed and it can be regarded as a modified Mohr-Coulomb criterion with a uniformity coefficient. New strength criterion can quantitatively reflect the intermediate principal stress effect on rock strength and matches previously published experimental results better than common strength criteria

Modal Spectral Element Solutions to Incompressible Flows over Particles of Complex Shape

This paper develops the virtual identity particles (VIP) model to simulate two-phase flows involving complex-shaped particles. VIP assimilates the high efficiency of the Eulerian method and the convenience of the Lagrangian approach in tracking particles. It uses one fixed Eulerian mesh to compute the fluid field and the Lagrangian description to handle constitutive properties of particles. The interaction between the fluid and complex particles is characterized with source terms in the fluid momentum equations, while the same source terms are computed iteratively from the particulate Lagrangian equations. The advantage of VIP is its economy in modeling a two-phase flow problem almost at the cost of solving only the fluid phase with added source terms. This high efficiency in computational cost makes VIP viable for simulating particulate flows with numerous particles. Owing to the spectral convergence and high resolvability of the modal spectral element method, VIP provides acceptable resolution comparable to DNS but at much reduced computational cost. Simulation results indicate that VIP is promising for investigating flows with complex-shaped particles, especially abundant complex particles

Estimation of slope safety factor based on trajectory reduction method

Currently, double reduction method (DRM) is widely used in the field of slope stability. However, one of the main challenges of the double reduction method is how to define the comprehensive safety factor based on two reduction parameters. The trajectory reduction method developed by Isakov can be used to ensure the minimum comprehensive safety factor on different conditions. However, its main shortcoming is that the method needs expensive calculation to determine the safety factor for a certain slope configuration. The paper examines the relationship between the comprehensive safety factor and cohesive and internal friction angle of soil, by using the FEM and trajectory method to calculate the minimum safety factor and corresponding reduction factor with respect to different inclinations of the slope. The initial strength effect on double reduction parameters are analyzed accordingly. The result shows for a certain slope configuration; the initial strength has little effect on the critical strength which is related to the minimum comprehensive safety factor. It means that for a slope with a certain inclination, even if the strength of soil is different, the critical strength is identical. The critical strength of soil slope is linear with the inclination of the slope, which means that every inclination corresponds to one critical cohesive and one critical internal friction angle. Consequently, a novel method to calculate the minimum safety factor is proposed in this paper. The result obtained by this method is close to the result which is from the limit equilibrium method, and compared with the original method by Isakov, this alternative method can simplify the calculation, and keep the result as accurate as the limit equilibrium method. Thus, it can be used to analyze the stability of slope

A Real-Time Structural Damage Detection method for High-Pile Wharf Foundations

As one of the most common structural forms in port engineering, the operation environment of high-pile wharf is quite harsh and complex, and its pile foundation often produces structural damage of different degrees. Until now, there is a lack of efficient, safe and economic damage detection methods. A novel and precise real-time structural damage detection (SDD) method using both finite element modelling (FEM) and 1D convolutional neural networks (CNNs) is established in this study. The results indicate that the proposed method could accurately identify the presence and location of damage in real time. The results also demonstrated that the proposed 1D CNNs based model are more sensitive to the longitudinal and lateral displacement responses of the high-pile wharf structure

Wind driven natural ventilation through multiple gridirons of a pile-supported wharf to prevent atmospheric corrosion in the marine environment

Salt fog originating from the offshore zone can easily accumulate in the semi-enclosed space (called the gridiron space) formed by the beams and slabs of a pile-supported wharf. Such accumulation can lead to the premature failure of the durability of the wharf’s substructure. Previous works have mainly focused on material-level measures to eliminate the adverse effects of salt fog accumulation, such as the use of anti-corrosion concrete and anti-corrosion coatings, which could result in increased construction costs. In fact, salt fog can be extracted from a gridiron by natural ventilation in some cases, so it is important to examine the flow characteristics of the gridiron space. In this work, a numerical simulation was conducted with natural ventilation and auxiliary ventilation groups. The critical value of the shield ratio (defined as the height ratio of edge stringer to air inlet) that led to the weakest turbulence of airflow inside the gridiron was studied in the natural ventilation group. In addition, the effect of various configurations of vents was discussed; in accordance with the results, design recommendations were proposed to enhance the durability of a pile-supported wharf.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Analysis of plastic zones in surrounding rocks around a circular tunnel considering the effect of intermediate principal stress and heterogeneity

Based on a modified Mohr-Coulomb criterion with a non-uniform coefficient, a calculation method of plastic zone boundary of surrounding rocks in a circular tunnel in non-uniform stress field is established. Both the effects of intermediate principal stress and heterogeneity are studied. With the increase of the intermediate principal stress, the plastic zone size of the surrounding rocks will decrease first and then increase. Lateral pressure coefficient has an effect on the shape of the plastic zone. With the increase of lateral pressure coefficient, the plastic zone gradually becomes uniform, and the failure of surrounding rock develops upward and downward from both sides. As non-uniform coefficient increases, the material is more uniform and the effect of intermediate principal stress on the plastic zone is less significant. If the effect of intermediate principal stress is not taken into account, the calculation results tend to be consistent with results calculated by the Mohr-Coulomb criterion, which are considered to be conservative

A hybrid methodology for structural damage detection uniting FEM and 1D-CNNs: Demonstration on typical high-pile wharf: Demonstration on typical high-pile wharf

Vibration-based structural damage detection (SDD) has been a subject of intense research in structural health monitoring (SHM) for large civil engineering structures over the decades. The performance of the conventional SDD approaches predominantly relies on the rational choices of the damage feature and classifier. Hand-crafted features or fixed classifiers would not be the optimal choice for all structural damaged scenarios. This paper proposes a novel, quick and precise real-time SDD framework for high-pile wharf foundations using a combination of finite element modeling and 1D convolutional neural networks (CNNs). The distinct advantage of this method lies in extracting the damage-related features from the raw displacement response directly and automatically, and the computational complexity of the compact 1D CNNs is significantly lower because the data processing involves only simple 1D operations. The results show that the presented 1D CNNs have a superior ability to accurately identify the occurrence and location of damage in real time. In addition, the comprehensive performance of the CNNs trained by the displacement response dataset in component form is significantly better than that based on the dataset in absolute value form. The results also demonstrated that although the proposed CNNs are more sensitive to the longitudinal and lateral displacement responses of the high-pile wharf structure, the vertical component still has a positive effect on the improvement of the generalization and robustness of the CNNs.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Applied Mechanic