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• Proposing a network theory for geotechnical structure deformations in 2D condition. • Accumulated errors of three relative nodes are less than 6% in calibration tests. • Recommending the rubber gasket as the point connection in practical applications. The Brillouin optical time domain analysis (BOTDA) technology is gaining immense popularity and increasingly being utilised to measure strains in geotechnical structures. The deformations are usually determined by recording strains of selected points, from which the precaution and early warning of instability can be obtained. The errors of the measured strains using BOTDA are related to uncertainties in different connection methods and accumulated errors of the network in the monitoring zone. In this study, a network theory was derived first to measure the deformations of a geotechnical structure in two-dimensional (2D) condition. Next, two physical models (one with four nodes and the other with eight nodes) were established. The performance of the calculated deformations using the network theory based on the measured strains from BOTDA was examined and analysed by comparing the preset displacements from micrometres. From the test results, it is found that the stress concentration at the connection, which has a direct impact on the measured data, can be effectively reduced when using the rubber gasket. There is a good agreement between the calculated deformations and the preset displacements. The accumulated errors are less than 6% for three groups of relative stable nodes, which demonstrates that the proposed network theory can be well utilised in various fields and practical applications that require high precision. [ABSTRACT FROM AUTHOR]

Highlights • Proposing a slope stability analysis method based on displacement measurement. • Fabrication process of FBG-made inclinometer and PIV setup is presented. • Comparatively studying the performance of difference displacement algorithms. • Optimization model of searching slope slip surface is established. Abstract This paper proposes an effective and convenient method to analyze slope stability in real time, which is based on fiber Bragg grating (FBG) sensors. First, a new type of FBG inclinometer is designed to capture the internal slope displacement variation considering temperature compensation, and an optimum displacement algorithm is selected by an experiment. Once the monitoring work is prepared, the potential slope slip surface is determined by monitored displacement in an optimization model based on the maximum displacement increment of the objective function. Finally, integral processing is used with the Bishop method to simplify the calculation, and a safety factor is estimated by the integral method. An experimental model test of homogeneous soil is conducted to verify the feasibility and reliability of the proposed analytical method and the FBG monitoring technique. [ABSTRACT FROM AUTHOR]

Highlights • Propose an FBG-based method on measuring early-age shrinkage of GO modified MKPC. • Temperature of cement paste was monitored and the setting time was determined. • GO can affect the shrinkage behavior of cement by affecting the hydration degree. • 0.06 wt% GO is an optimum content obtained by measured results. Abstract In this paper, a novel early-age shrinkage measurement method was used to investigate the influence of graphene oxide (GO) additive on the magnesium potassium phosphate cement (MKPC) mortar. Temperature and shrinkage strain of the MKPC mortar were simultaneously measured by using fiber Bragg grating sensors during the hydration process. The early age setting time of cement samples was determined by temperature records, which showed with the increasing content of GO the early age setting time is decreased. Through the measurement approach, conclusions also can be drawn that with an increase in the amount of GO, the early-age shrinkage strain of the MKPC paste decreases initially and subsequently increases. The MKPC mixture containing 0.06 wt% of GO possessed minimum shrinkage strain variation on the whole hydration reaction. The reasons for this phenomenon were fully discussed in the paper. Scanning electron microscopy and energy dispersive spectrometer were used in another test to prove the inference. [ABSTRACT FROM AUTHOR]

Highlights • Discussing the limitations of Werkmeister's criteria and the simplification adopted in European Standard. • Defining a "representative cycle number" to distinguish the post-compaction and second cyclic compression periods. • Proposing more reasonable and versatile new criteria to characterize the shakedown ranges of granular materials. Abstract The Werkmeister's criteria are widely utilized for characterizing the permanent axial strain behaviour of granular materials. These criteria are based on shakedown theory and are adopted in the European Standards. In this paper, the limitations of Werkmeister's criteria and the simplification adopted in European Standard are discussed. To overcome these shortcomings, new criteria on characterizing the shakedown ranges of granular materials are proposed. The mathematical expression and physical meanings of the proposed criteria are presented and discussed in detail. It is noteworthy mentioning that, based on the new criteria, the characterizing of shakedown range only assesses the whole development trend of permanent axial strain occurred during the secondary cyclic compression period. Firstly, the performances of the new criteria and Werkmeister's criteria are compared using the test data from existing literature. It can be concluded that the new criteria are capable of giving quite satisfactory prediction. Furthermore, in this study, several cyclic triaxial tests with step-wisely increasing cyclic deviatoric stress were conducted to verify the new criteria. The test results show a transitional range, which indicates the onset of the disruption of external loading to the original stable structure of granular materials. [ABSTRACT FROM AUTHOR]

Geotechnical monitoring and instrumentation play a key role to assess the safety and performance of the geotechnical structures. Conventionally used electrical instruments possess several inherent limitations while monitoring geotechnical health. In recent years, much attention has been paid towards optical fibre sensing technology for geotechnical health monitoring. This paper highlighted different types of optical fibre with a special focus on the calibration methodology and advantages of Fibre Bragg Grating (FBG) sensors over other conventionally used sensors. A comprehensive review of recent research and development activities in geotechnical health monitoring using FBG-based sensors including ground, slope, pile and pullout, moisture, mining activities and design and development of FBG-based sensing instruments is analyzed and discussed. Furthermore, the paper highlights emerging trends in FBG sensing technology for geotechnical health monitoring, including the integration of machine learning algorithms and the development of novel sensor designs. [ABSTRACT FROM AUTHOR]

• Development of a radial strain measurement system for triaxial specimen. • Long-term performance of the system under varying pressure and temperature is presented. • Proof test results on rubber and geomaterials under static and cyclic loadings are presented. • The new system can measure radial strain at the order of 0.0001%. • The new system can capture the cyclic radial strain from the ranges of ±0.002% to ±0.025%. The importance of local strain measurement on triaxial specimens has been widely recognized. The design of the radial strain measurement system has been relatively less advanced as compared to the axial strain measurement system. In this study, a new linear variable differential transformers (LVDTs)-based radial strain measurement system is developed. Firstly, the setup and methodology of the new radial strain measurement system along with the advantages are described in detail. The detailed calibration process of the measuring system is introduced, together with the error analysis. Also, the long-term performance of this new system under different levels of cell pressure and the varying temperature is examined. The paper also presents the radial strain measurement results of triaxial tests performed on natural rubber, quartz sand specimen, and cement-stabilized marine deposit column. In particular, the performance of the new measurement system under cyclic loading condition is evaluated, which is rarely reported in the existing literature. The calibration and test results confirm that the new measurement system can provide reliable and accurate radial strain results and minimize any associated measurement bias as the specimens are subjected to both static and cyclic loadings. [ABSTRACT FROM AUTHOR]