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This paper presents an experimental study on the mechanical behavior and permeability evolution of basalt, drilled from the dam foundation of the Baihetan Hydropower Station in China. Two groups of triaxial unloading creep tests under hydro-mechanical coupling conditions were conducted. Based on the experimental results, creep deformation and failure characteristics of basalt were investigated. It was found that the relationship between the confining pressure and steady creep rate could be described satisfactorily by an exponential function. A tensile-shear failure mode was observed for basalt under the action of unloading confining pressure and hydraulic-mechanical coupling. The permeability evolution of basalt in the unloading creep process exhibited phased characteristics: permeability decreased in the initial loading phase and remained stable for a certain range of confining pressure in the steady creep phase. Exponential functions were also used to describe the evolution of permeability and confining pressure. The results of this study can provide a comprehensive understanding for the long-term stability assessment of basalt under coupled hydro-mechanical conditions.

A methodology is developed for generating floor response spectra (FRS) considering the effect of dynamic soil–structure interaction (SSI) based on the substructure technique and a recently-develope...

Purpose This paper aims to analyze the influence of rotated anisotropy on the stability of slope, the random finite element method is used in this study. Design/methodology/approach The random field is generated by the discrete cosine transform (DCT) method, which can generate random field with different rotated angles conveniently. Findings Two idealized slopes are analyzed; it is observed that the rotated angle significantly affects the slope failure risk. The two examples support the conclusion that when the orientation of the layers is nearly perpendicular to the slip surface, the slope is in a relative stable condition. The results of heterogeneous slope with two clay layers demonstrate that the rotated angle of lower layer mainly controls the failure mechanism of the slope, and the rotated angle of upper layer exhibits a significant influence on the probability of slope failure. Originality/value The method for rotated anisotropy random field generation based on the DCT has a simple expression with few parameters and is convenient for implementation and practical application. The proposed method and the results obtained are useful for analyzing the stability of the heterogeneous slopes in engineering projects.

Columnar jointed rock masses (CJRM), characterized by regular arrays of polygonal prisms or columns, are exposed in the dam foundation of the Baihetan hydropower station and pose a challenge to the stability of the project. To understand the hydro-mechanical behaviour of Baihetan CJRM, triaxial compression experiments are carried out on artificial CJRM specimens with regular arrays of hexagonal columns, which are similar to the actual CJRM. Based on the experimental results, mechanical and hydraulic behaviour of CJRM is studied. It is found that the compressive strength of CJRM varies in a typical U-shape with the joint inclination angle. Three failure modes associated with the angle of joint inclination are observed. The evolution of permeability with stress exhibits distinct phased characteristics: initial compression stage, linear elastic stage, yield stage, and strain-softening stage. The results of this study provide helpful information for the design and construction of the Baihetan project involving CJRM.

Soil-rock mixture is a widely distributed geological material in mountainous regions, where slope stability is an important issue. To investigate the influence of rock on slope stability, firstly, rocks in SRM are generated and then SRM slope models are simulated based on the finite difference method (FDM). The impact of various characteristics of rocks on slope factor of safety (FOS) is studied systematically by using the reduced strength method. The characteristic of rock considered include rock content, number of rock edges, aspect ratio, rock size and inclination of rock. The simulations indicate that increasing the rock content can prevent the development of high strain region and improve slope stability. However, the aspect ratio of rock has negligible impact on the mean value of FOS. For slopes with 45° slope angle, rocks with 45° angle of inclination result in smooth potential sliding surface, whereas rocks with 135° angle of inclination lead to more tortuous potential sliding surfaces. Statistical indices are utilized to analyze the results of numerical modelling.

The objective of this study is to provide an effective method for risk prediction and disaster control of earthquake-induced landslides. The Hongshiyan landslide induced by Ludian earthquake (Mw6.5) on August 3, 2014, in Ludian County, Yunnan Province, China, is studied. The sliding process and the mechanism of instability are investigated through numerical simulations using the particle flow codes (PFC). The characteristics of velocity and displacement and features of deposit are studied. It is found that the maximum average velocity of all particles of 23.43 m/s occurs at 7.11 s. The maximum displacement is closely related to elevation, and the sliding time of the rear edge of the sliding body is the longest. The numerical results of the landslide dam deposit morphology, with a height of 116.1 m and a length of 1001.1 m, are in good agreement with the field investigations. A series of numerical experiments on parameter sensitivity are also performed to study the influence of amplification factor and coefficient of friction on the features of the deposit.

The primary objective of this article is to present a case study of valley deformation in high arch dam and its relationship with water level fluctuations. Data of displacement versus reservoir lev...

The mechanism of toppling deformation and failure is important in the stability analysis of anti-dip layered rock slopes, especially in a complex hydrogeological environment. In this paper, the fle...

During the reservoir filling of many high arch dams, it was observed that the valley slopes on both sides deformed towards the river. The measured value of valley narrowing lateral deformation (VNL...

To enrich understanding of how fluid flows through the natural filled jointed rock, the permeability experiments of the natural filled jointed dacite rock under repeated loading and unloading condi...

Purpose The purpose of this paper is to investigate the mechanical behavior and propagation of cracks of numerical granite samples through the Brazilian split test and to provide a reference for predicting the behavior of real granite samples. Design/methodology/approach The numerical models of granite containing two fissures are established using the parallel bond model (PBM) and the smooth joint model (SJM) in PFC2D. The peak stresses, number of cracks and anisotropic ratios are obtained to study the influence of the mineral composition and the angle of inclination of rock bridge on the strength, failure mode and deformation characteristics. Findings The numerical results obtained show that the mineral composition has a marginal influence on the peak stress. When the angle of inclination of rock bridge β increases, the peak stress drops to its minimum value at β = 90° and then gradually increases to a relatively low level. The behavior of cracks falls into three categories based on the distribution of cracks. By analyzing the stress–strain curve and the process of crack propagation for sample No. 4 with β = 60°, it is found that the process of failure can be divided into four stages and tensile cracks dominate. The anisotropic ratios of peak stress and a number of cracks obtained show that the peak stress is low anisotropic and the number of cracks is medium anisotropic. Originality/value This paper presents a numerical simulation method to analyze mechanical behavior and propagation of cracks under different conditions. The proposed method and the results obtained are useful for predicting the behavior of real granite samples in laboratory and engineering projects.

The velocity and the displacement time history obtained by directly integrating the acceleration time history will drift unrealistically because of the over-determinacy of the integration constants. Applying baseline corrections to resolve drift disturbs the frequency content and renders the corrected processes mutually inconsistent. In this study, eigenfunctions of sixth-order eigenvalue problem are introduced as basis functions for decomposing recorded ground motion time history. Taking advantage of the eigenfunctions and their first two order of differentiations are drift-free and consistent, the decomposed and reconstructed acceleration, velocity, and displacement time histories can be drift-free and mutually consistent without direct integration and baseline correction. Two earthquake ground motions are presented as examples, which show that the decomposed acceleration, velocity, and displacement time histories are drift-free, mutually consistent, and almost the same as the seed motion. The new approach can replace integral in the generation of velocity and displacement time histories.

This study presents a new approach for obtaining a set of tri-directional time histories compatible with target design spectra by modifying real recorded earthquake ground motions. The influence matrix method (IMM) based on eigenfunction expansion is improved for typical design response spectra with different shapes and employed in order to achieve accurate matching with the target design spectra. By applying the Gram–Schmidt orthogonalization in each iteration of the IMM procedure, the correlation coefficient between any two components can be guaranteed to be strictly zero. Hence, the generated three components in the orthogonal directions are statistically independent. The generated time histories satisfy the requirements of current codes and standards. Two examples are presented to illustrate the procedure and the superiority of the proposed method, with the maximum relative error between the generated time histories and target design spectra being less than 0.2% in [0.6, 100] Hz, and the code requirements being satisfied strictly.

The focus of this article is on generating spectrum‐compatible acceleration, velocity, and displacement time histories for seismic analysis and design of engineering structures. If a generated acceleration time history is integrated to obtain the corresponding velocity and displacement time histories, it has been found that there are usually drifts in the resulting processes. Such drifts are due to overdeterminacy in the constants of integration. Baseline correction, although widely used, is not a suitable remedial measure to remove drift because it distorts the frequency content and renders the corrected processes no longer mutually consistent.The objective of this article is to develop an efficient and accurate method for generating drift‐free, consistent, and spectrum‐compatible time histories, which are essential properties for these time histories to be used as seismic input in time history analysis. To ensure drift‐free and consistent behavior, the eigenfunction method is applied to expand the time histories in eigenfunctions of a sixth‐order ordinary differential eigenvalue problem. The influence matrix method considering the influence of one frequency component on all others is capable of achieving perfect spectrum compatibility which has never been accomplished.

Located in reservoir area of Dahuaqiao Hydropower Station in Lancang River, the Dahua ancient deposit landslide exhibits high possibility of reactivation due to reservoir impoundment. In this study, physical model tests are conducted to investigate the variations of groundwater, deformation, and failure process of the landslide under different fluctuation speeds of reservoir water level. Influence of groundwater on landslide stability when reservoir water level fluctuating is analyzed then. Results indicate that the seepage pressure caused by water level difference can increase landslide displacement. During the dropping process of reservoir water level, the relationship between landslide displacement and water level difference can be described by a power function model. Groundwater has negative effects on stability of landslides, and the damage is characterized by traction landslide. More attentions should be paid on the displacement of the front edge of the landslide during the first rise and drop of reservoir water level. The study provides indispensable information for scheduling reservoir water level in the Dahuaqiao and others similar reservoir areas, thus having vital importance.

This paper studies consensus problems of multi-agent systems. A novel hybrid consensus protocol with dynamically changing interaction topologies is designed to take the time-delay into account in both the continuous-time communication among agents and the instant information exchange at discrete-time moments. By using a new Halanay-type inequality and an auxiliary function, sufficient conditions are established to guarantee that the proposed consensus protocols lead to average-consensus. Our consensus criteria show that the networked multi-agent system with time-delay can achieve average-consensus with appropriate network topologies, suitably designed impulsive instants, and admissible time delays. Numerical simulations are provided to demonstrate the effectiveness of the theoretical results.

Pavement infrastructure is experiencing unanticipated climate conditions due to global warming. Extreme weather events, such as excessive precipitations, are increasing in intensity and frequency u...

This study presents an application of the innovative fragility method proposed in companion paper (Part I) to a horizontal heat exchanger in Darlington nuclear generating station. To illustrate the advantages of the proposed method, seismic fragility curves and High Confidence of Low Probability of Failure seismic capacity of the heat exchanger are calculated by the conventional and proposed fragility methods. The results show that, by using two ground motion parameters, the median seismic capacity of the heat exchanger has remarkable 53.9% increase, and the High Confidence of Low Probability of Failure seismic capacity is increased by 25.0%. These increases come from the reduction of conservatism of the median seismic demand by incorporating the correlation between two ground motion parameters. Although applications of components mounted on supporting structures are not presented, seismic capacities of components are expected to increase as long as the effect of structural dominant modes on seismic responses are captured by employing the proposed method. For critical structures, systems, and components that limit the plant seismic capacity, the proposed fragility method should be implemented to evaluate their seismic capacities.

Pavement infrastructure is experiencing unanticipated climate conditions caused by global warming. Extreme weather events, such as extreme precipitations, are increasing in intensity and frequency, creating rising concern in pavement vulnerability and resilience analysis. Previous design approaches based on historical climate data may no longer be adequate for addressing future conditions. To promote pavement resilience under climate change, assessing pavement risk for extreme events is essential for prioritizing vulnerable infrastructure and developing adaptation strategies. The objective of this study is to develop a quantitative evaluation methodology for assessing pavement risk from extreme precipitations under climate change. Hazard analysis, fragility modeling, and cost estimation are the three major components for risk evaluation. An ensemble of 24 global climate models is used for predicting future extreme precipitations under various climate-forcing scenarios. The Mechanistic-Empirical Pavement Design Guide is employed to simulate performance change for performing fragility modeling. Risk assessment models considering a full range of hazards were used to quantify risk of asset value loss over specified analysis periods. Results indicate that future extreme precipitation events are expected to cause an increased medium risk of asset value loss. However, high uncertainties are involved in the estimation owing to variations in predicted climates. Major pavement damages do not necessarily equate with highest risk because the probability of occurrence of major damage is relatively lower. The proposed approach provides a practical tool for analyzing the interaction among extreme precipitation levels, pavement designs, damage states, occurrence probability, and asset value at risk.

This study presents a framework to perform Probabilistic Seismic Hazard Analysis (PSHA) for soil sites, which yields accurate soil UHS and associated seismic hazard curves. The variabilities of soil parameters, the nonlinear responses of soils, and the vector-valued site responses analysis comprehensively integrate into the PSHA for soil sites. In this framework, site amplification is used to modify the Ground Motion Prediction Equations (GMPEs) to make them suitable for a soil site. Based on the modified GMPEs with updated uncertainties, PSHA for soil sites are performed accurately; thus, acceptable soil UHS and associated seismic hazard curves considering site-specific uncertainties could be achieved. Using an example soil site, influences of soil parameter variabilities and soil nonlinearity on UHS and associated seismic hazard curves are discussed in this study.

Efficient and accurate determination of Floor Response Spectra (FRS) is critical in seismic risk analysis and design. Scaling methods, which allow the generation of FRS corresponding to new Ground Response Spectra (GRS) by multiplying existing FRS with appropriate scaling factors rather than by performing re-analyses of the structure, are efficient and economical approaches. However, in many practical situations, it is challenging to generate FRS not only by scaling but also by analyzing structural responses due to the lack of structural model information. A recent breakthrough in generating FRS using a direct spectra-to-spectra method prompted the development of the scaling method presented in this paper. The analytical formulation of the direct method provides a strong physical insight into the essential characteristics of FRS, which allows the identification of dynamical information of significant equivalent modes of the underlying structure from the available FRS and GRS. Scaling factors are then determined in terms of the dynamical information (modal frequencies, modal damping ratios, and modal contribution factors) and input GRS. Numerical examples of a typical service building in nuclear power plants show that the FRS obtained by this scaling method agree very well with the results obtained from a large number of time history analyses. It is also demonstrated that this method provides accurate FRS for various damping ratios when the interpolation methods recommended in the current standards are not applicable. The proposed method, which is efficient, accurate, and convenient to implement, allows engineers to use as much of the available results of previous analyses as possible without performing a complete dynamic analysis, which is time consuming and introduces extra costs.

This paper studies the consensus problem of multi-agent systems with both fixed and switching topologies. A hybrid consensus protocol is proposed to take into consideration of continuous-time communications among agents and delayed instant information exchanges on a sequence of discrete times. Based on the proposed algorithms, the multi-agent systems with the hybrid consensus protocols are described in the form of impulsive systems or impulsive switching systems. By employing results from matrix theory and algebraic graph theory, some sufficient conditions for the consensus of multi-agent systems with fixed and switching topologies are established, respectively. Our results show that, for small impulse delays, the hybrid consensus protocols can solve the consensus problem if the union of continuous-time and impulsive-time interaction digraphs contains a spanning tree frequently enough. Simulations are provided to demonstrate the effectiveness of the proposed consensus protocols.

Representative volume element (RVE) is an important parameter in numerical tests of mechanical properties of heterogeneous geomaterials. For this study, a digital image processing (DIP) technology was proposed for estimating the RVE of heterogeneous geomaterials. A color image of soil and rock mixture (SRM) with size of 400 &times, 400 mm2 taken from a large landslide was used to illustrate the determination procedure of the SRM. Six sample sizes ranging from 40 &times, 40 mm2 to 240 &times, 240 mm2 were investigated, and twelve random samples were taken from the binarized image for each sample size. A connected-component labeling algorithm was introduced to identify the microstructure. After establishing the numerical finite difference models of the samples, a set of numerical triaxial tests under different confining pressures were carried out. Results show that the size of SRM sample affects the estimation of the mechanical properties, including compressive strength, cohesion, and internal friction angle. The larger the size of the samples, the less variability of the estimated mechanical properties. The coefficient of variation (CV) was applied to measure the variability of mechanical properties, and the RVE of the SRM was determined easily with a predefined acceptance threshold of the CV. The results show that a DIP-based modeling method is an effective method got the RVE determination of heterogeneous geomaterials.