Distributed optical fiber sensors (DOFS) have been attracted significant attention from geotechnical engineering communities for a few decades. Innovative development of structural design, ...encapsulation and implementation methods of optical fiber sensors leads to many new applications in geotechnical monitoring field. This paper presents a comprehensive review of Brillouin based DOFS for health monitoring of various geotechnical structures include geotextiles, soil nails, anchors, pipelines, piles, retaining walls, tunnels, and landslides. Recent application status of using two successful commercialized technologies including Brillouin Optical Time Domain Reflectometry (BOTDR) and Brillouin Optical Time Domain Analysis (BOTDA) for geotechnical health monitoring was reviewed and discussed in details. Particular emphasis was given to sensor design, encapsulation, and installation methods of DOFS in various successful geotechnical applications. Comparison analysis regarding typical advantages and limitations of different technologies (DOFS, fiber Bragg grating sensors, and conventional sensors) for geotechnical health monitoring was also presented and discussed in this paper.
Abstract
The current first generation of Eurocodes is a suite of ten European standards for the design of buildings and civil engineering works, whose implementation started in 2010. EN 1990 sets the ...basis of structural design, with the other Eurocodes dealing with different materials and specific aspects of design. Geotechnical aspects of design are covered by EN 1997 ”Geotechnical design“, usually called Eurocode 7.
The evolution of the Eurocodes started in 2012 and the main objectives of their revision were to incorporate improvements that reflect the state‐of‐the‐art in engineering design and the needs of the civil engineering market, to improve the ease‐of‐use and to harmonize practice between countries. While the original version was developed largely based on soil mechanics, the aim was that the revised version treats soil and rock on an equal basis.
The second generation of the Eurocodes is now nearly finished, and the revised EN 1997 is expected to be formally approved in 2024. This paper is the first of a set of six informative papers on the revised Eurocodes and rock engineering, prepared by members of the Rock Engineering Platform of CEN/TC250/SC7, a group of rock engineering experts that has been assisting in drafting EN 1997 from a rock‐engineering perspective. The paper presents the main changes to EN 1990 and EN 1997 as far as they affect geotechnical and rock engineering design.
Abstract
Die derzeitige erste Generation der Eurocodes ist eine Reihe von zehn europäischen Normen für die Planung von Gebäuden und Bauwerken, deren Umsetzung im Jahr 2010 begann. EN 1990 legt die Grundlagen für die Tragwerksplanung fest, die anderen Eurocodes behandeln die verschiedenen Bereiche des Bauwesens. Die Geotechnische Ingenieurbauwerke werden in EN 1997 „Geotechnische Bemessung”, üblicherweise Eurocode 7 genannt, behandelt.
Die Entwicklung der zweiten Generation des Eurocodes begann im Jahr 2012 und die Hauptziele ihrer Überarbeitung waren die Einbeziehung von Verbesserungen, die den Stand der Technik in der Planung und die Bedürfnisse des Baumarkts widerspiegeln, die Verbesserung der Benutzerfreundlichkeit und die Harmonisierung der Praktiken zwischen den Ländern. Während die erste Generation weitgehend auf das Medium Boden fokussiert war, sollten in der überarbeiteten, zweiten Generation die Medien Boden und Fels gleichberechtigt behandelt werden.
Die zweite Generation der Eurocodes ist nun fast fertiggestellt, und der überarbeitete EN 1997 wird voraussichtlich 2024 formell genehmigt. Die vorliegende Veröffentlichung ist die erste aus einer Reihe von sechs Veröffentlichungen, in denen über die Berücksichtigung des Felsbaus in der Entwicklung des Eurocodes berichtet wird. Die Veröffentlichungen wurden von Mitgliedern der „Plattform Felsbau” des CEN/TC250/SC7 erstellt, einer Gruppe von Felsbauingenieuren, die an der Ausarbeitung der EN 1997 aus Sicht des Felsbaus mitgewirkt haben. Der Beitrag stellt die wichtigsten Änderungen an EN 1990 und EN 1997 vor, soweit sie die geotechnische und felsbauliche Planung betreffen.
In this study, efforts were made to incorporate the influence of discontinuities and failure modes of rock into the classification of rock masses. The past tectonic activities may create ...microfractures in the rock body therefore the failure moods have been determined carefully under uniaxial compression. The results of the discontinuity analysis, conducted through kinematic study, highlighted the significant impact of wedge failure on the failure of the rock mass. In correlating the geological strength index with rock mass rating, it was observed that joint volume played a negative role, whereas compressive strength played a positive role. These correlations are particularly applicable for a certain rock type, as the compressive strength is inherently dependent on the type of rock. The analysis of failure modes under uniaxial compression reveals that the dissipation energy coefficient initially undergoes rapid increase before reaching its minimum value at the failure stage. The microstructures of the rock effect significantly the elastic and dissipation energy characteristics. Specifically, the axial splitting failure mode emerges as predominant. Given the area's past tectonic activity, these results emphasize the impact of microfractures within the rock body. Relating the failure criteria with the chemical composition of rock types reveals that rocks abundant in SiO2, such as gabbronorite, tend to exhibit brittle failure. Additionally, a dominance of Al2O3 over Fe2O3 suggests a predisposition towards brittle failure, while an increased ratio of CaO to MgO implies increased susceptibility to compression.
In this study, efforts were made to incorporate the influence of discontinuities in the classification of rock masses. Kinematic analyses were conducted to identify potential failure types along the tunnel route.
•The development of fiber optic sensors in geotechnical engineering is fully reviewed.•Three algorithms for displacement calculation were discussed by numerical simulation.•A comparison analysis of ...optical fiber sensors for geotechnical monitoring is given.
Prediction of displacement or strain is an important means and factor for evaluating the safety of geotechnical structures, such as slopes, dams, tunnels and excavation engineering. In recent years, fiber optic displacement sensors have been extensively used in civil engineering due to their obvious advantages of light weight, high precision, strong durability, wide measurement range and long-distance transmission. This paper reviews the development of two common types of fiber optic sensors (fiber Bragg grating sensors and bend loss based fiber optic sensors) for geotechnical health monitoring, and the characteristics and the state of the art research were analyzed and discussed in details. Based on the measured strains, three algorithms for transforming monitored data to required displacement were investigated. Comparison analysis regarding typical advantages and disadvantages of these fiber optic sensing technologies for geotechnical health monitoring was also presented and discussed in this paper.
An efficient nonlinear octree scaled boundary finite element method (SBFEM) is proposed to improve the ability of the SBFEM to analyse complicated structures. The polygon boundaries are directly ...solved using a pre-calculated mean-value interpolation. The nonlinearity can be considered via an internal quadratic tetrahedral integral scheme. Three simulations are performed to evaluate the accuracy, versatility, flexibility and high efficiency of the method. The difficulties of automatic modelling for both layered construction and material partitioning are eliminated using the octree meshing algorithm. The proposed method can serve as a powerful technique for the rapid design and analysis of geotechnical structures.
This paper aims to investigate the impact of copula selection on geotechnical reliability under incomplete probability information. The copula theory is introduced briefly. Thereafter, four copulas, ...namely Gaussian, Plackett, Frank, and No. 16 copulas, are selected to model the dependence structure between cohesion and friction angle. A copula-based approach is used to construct the joint probability density function of cohesion and friction angle with given marginal distributions and correlation coefficient. The reliability of an infinite slope and a retaining wall is presented to demonstrate the impact of copula selection on reliability. The results indicate that the probabilities of failure of geotechnical structures with given marginal distributions and correlation coefficient of shear strength parameters cannot be determined uniquely. The resulting probabilities of failure associated with different copulas can differ considerably. Such a difference increases with decreasing probability of failure. Significant difference in probabilities of failure could be observed for relatively small coefficients of variation of the shear strength parameters or a strong negative correlation between cohesion and friction angle. The Gaussian copula, often adopted out of expedience without proper validation, may not capture the dependence structure between cohesion and friction angle properly. Furthermore, the Gaussian copula may greatly underestimate the probability of failure for geotechnical structures.
Constitutive equations for inelastic behavior of anisotropic materials have been a challenge for decades. Presented is a new spherocylindrical microplane constitutive model that meets this challenge ...for the inelastic fracturing behavior of orthotropic materials, and particularly the shale, which is transversely isotropic and is important for hydraulic fracturing (aka fracking) as well as many geotechnical structures. The basic idea is to couple a cylindrical microplane system to the classical spherical microplane system. Each system is subjected to the same strain tensor while their stress tensors are superposed. The spherical phase is similar to the previous microplane models for concrete and isotropic rock. The integration of stresses over spherical microplanes of all spatial orientations relies on the previously developed optimal Gaussian integration over a spherical surface. The cylindrical phase, which is what creates the transverse isotropy, involves only microplanes that are normal to plane of isotropy, or the bedding layers, and enhance the stiffness and strength in that plane. Unlike all the microplane models except the spectral one, the present one can reproduce all the five independent elastic constants of transversely isotropic shales. Vice versa, from these constants, one can easily calculate all the microplane elastic moduli, which are all positive if the elastic in-to-out-of plane moduli ratio is not too big (usually less than 3.75, which applies to all shales). Oriented micro-crack openings, frictional micro-slips and bedding plane behavior can be modeled more intuitively than with the spectral approach. Data fitting shows that the microplane resistance depends on the angle with the bedding layers non-monotonically, and compressive resistance reaches a minimum at 60°. A robust algorithm for explicit step-by-step structural analysis is formulated. Like all microplane models, there are many material parameters, but they can be identified sequentially. Finally, comparisons with extensive test data for shale validate the model.
In order to determine the pile internal forces of wharf under simultaneous seismic excitation in orthogonal horizontal directions with ease, the total internal forces can be obtained by multiplying ...the pile forces of two‐dimensional model under transverse earthquake loading with a magnification factor. The factors were computed from the seismic response of wharves having various aspect ratios (length to width) and eccentricity ratios when subjected to 30 pairs of bi‐directional earthquake records. Mean magnification factors and their corresponding dispersion are presented for all ground motion ensembles. The influence of aspect ratio and eccentricity ratio is evaluated and discussed. It is concluded that the magnification factor can be expressed as the function of aspect ratio and eccentricity ratio, and follows lognormal distribution. The proposed equation of magnification factor can be an alternative for internal force analysis of wharves under bi‐directional ground motion.
The total internal forces of pile under bi‐directional horizontal motions can be determined by multiplying the pile forces under transverse earthquake loading with a magnification factor based on two‐dimension analysis. The magnification factor can be expressed as the function of aspect ratio and eccentricity ratio of wharf. The magnification factor follows lognormal distribution, which enables designers to compute factor with certain reliability.
The objective of this paper is to investigate the effect of copulas for constructing the bivariate distribution of shear strength parameters on system reliability of geotechnical structures. First, ...the bivariate distribution of shear strength parameters is constructed using copulas. Second, the implementation procedure of system reliability analysis using direct Monte Carlo simulation (MCS) is developed. Finally, the system reliability of a retaining wall and a rock wedge slope is presented to explore the effect of copula selection on geotechnical system reliability. The results indicate that the system reliability of geotechnical structures under incomplete probability information could not be determined uniquely because the bivariate distribution of cohesion and friction angle with given marginal distributions and correlation coefficient could not be determined uniquely. The copulas for modeling dependence structure between cohesion and friction angle have a significant influence on the system reliability of geotechnical structures. Such an influence includes two phases separately. The first phase is that the dependence structure between shear strength parameters characterized by copulas affects the reliability of single failure mode, depending on the marginal distributions, dependence structure between shear strength parameters, and reliability level of each failure mode. The second phase is that the reliability of each failure mode influences on system reliability, only depending on reliability level of each failure mode and correlations among various failure modes. It is important to distinguish between the effect of copula selection on reliability of each failure mode and that on geotechnical system reliability.
The primary factors responsible for inducing landslide disasters are earthquakes and rainfall. Using the strength reduction method within the finite element analysis software Abaqus, a study was ...conducted to analyze the stability of coastal geotechnical slopes. This investigation considered the combined influence of rainfall and earthquakes, taking into account the geological conditions and characteristics specific to these coastal areas. The results indicate that, under the same seismic acceleration amplitude, the shear strength of the slope soil gradually decreases as the water content increases, resulting in a decrease in the stability coefficient. Similarly, with a constant water content in the slope, an increase in seismic acceleration amplitude leads to heightened soil shear stress, consequently decreasing the stability coefficient. Maintaining constant water content while increasing seismic acceleration results in elevated soil shear stress, reduced shear strength, and a subsequent decrease in the stability coefficient. The simultaneous occurrence of intense rainfall and a strong earthquake pushes the slope to its most precarious state, causing the most significant reduction in the stability coefficient. Incorporating anti-slip piles substantially enhances the slope’s stability coefficient, and an optimal arrangement of anti-slip piles for the most unfavorable conditions is proposed.
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