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• The main challenge of the stress measurement of geotextile is introduced. • OF based intelligent geotextile is developed by implanting OF or FBG sensor. • FRP packaged distributed OF and FBG sensors with small diameter are developed. • The developed geotextile is used to a real high-speed railway subgrade monitoring. Geotextile is one of the important reinforcement materials for high-speed railway subgrade, and its service performance is closely related to subgrade safety. In order to grasp the mechanical properties of geotextile, the OF (optical fiber) based intelligent geotextile by braiding FRP (fiber reinforced polymer) packaged OF sensor into geotextile is developed, and applied for the settlement monitoring of karst cave expansion process in one subgrade model and one high-speed railway subgrade construction. The test and field monitoring data show that the strain data measured by the optical fiber sensor is basically consistent with that measured by the settlement plate which indicates that the developed intelligent geotextile not only has good reinforcement function, but also has good sensing function. [ABSTRACT FROM AUTHOR]

• Guiyang Metro in China is located in a special karst landform. • A new special metro station construction scheme is proposed. • Design deformation monitoring technology of special terrain tunnel construction. • Analysis of tunnel deformation and mechanical behavior. • The feasibility and application achieved using this technology are discussed. The Huo-Sha Tunnel of the Guiyang Metro Line 1 in China runs from the Guiyang Railway Station to the Shachong road station, and it passes close to the railway station platform. The minimum distance between the crown and pile foundation is only 2.19 m, and the settlements of existing buildings are strictly controlled, such as pile foundations. Existing comprehensive measures, such as super pipe shed support, surrounding rock reinforcement, inverted arch grouting, and lining strengthening, are stringently adopted to prevent the influence of construction on the operation of station buildings and in-service railways, high-speed railways, and other buildings. In this study, the changing laws related to existing building subsidence, subgrade settlement, station longitudinal displacement variation, and the development trends of lining safety, stability, eccentricity, compression types, and internal force of the lining are analyzed. The following results are presented. The Huo-Sha Tunnel was gradually excavated. The roadbed settlement of the Guiyang Railway Station platform gradually increased, but it did not exceed the existing railway deformation control standards for the subsurface excavation section. The longitudinal distribution of the existing railway settlement is approximately a normal curve after the construction of the secondary lining. The outcome is consistent with the law of the surface settlement trough proposed by Peck, and the range is −50 to 50 m. The stress of the lining is primarily concentrated at the arch waist and crown, the compression types include large and small eccentricities, and the axial force value gradually increases symmetrically from the crown to the arch footing, while the maximum axial force appears at the arch footing, and all control indicators meet the corresponding control standards. The subgrade settlement of the skew section adheres to the deformation control standards of the existing railway of subsurface excavation sections after the stabilization of the secondary lining deformation. [ABSTRACT FROM AUTHOR]

• An innovative spring-shaped fiber-optic displacement sensor (SSFODS) based on OTDR for settlement monitoring is proposed. • The SSFODS shows high linearity with the R2 of 0.985, large measurement range of 90 mm, minimum displacement resolution of 0.173 mm, maximum hysteresis error of 2.81% and maximum repeatability error of 8.42%, respectively. • Several SSFODSs can be connected in series on one optical link to realize quasi-distributed sensing monitoring. In this paper an innovative spring-shaped fiber-optic displacement sensor (SSFODS) based on optical time domain reflectometer (OTDR) technology with simple construction and cheap cost was proposed for subgrade settlement monitoring. The sensor incorporated a simple spring-shaped fiber bending modulation that increased its sensitivity in bending, light source and detector. The sensing principle between the measured external displacement and bending loss of optical fiber was theoretically explained and its expression was also derived. Sensor calibration was conducted, which showed that the SSFODS was characterized by a large measurement range of 90 mm, minimum displacement resolution of 0.173 mm, maximum hysteresis error of 2.81% and maximum repeatability error of 8.42%, respectively. A soil drainage model test with the SSFODS was performed to study its performance in determining compression deformation of the soil. At last, a simple field monitoring application with two SSFODSs connected in series was conducted and the progressive compaction behavior of the fill slope was accurately captured by two SSFODSs. Additionally, it is possible to connect these SSFODSs in series on one optical link to realize quasi-distributed sensing monitoring. This capability supports a promising application of the sensor in geotechnical engineering for real-time monitoring of the stability of fill slopes, foundation pits and so on. [ABSTRACT FROM AUTHOR]

Abstract: The method of preloading associated with prefabricated vertical drains was used to accelerate the consolidation process and anticipate the long-term settlements of the foundation soil of two cylindrical oil tanks founded on an alluvial deposit mainly consisting of silty clays. In-situ investigations, including boreholes and cone penetration tests (CPTs), and laboratory tests were carried out to define the geotechnical profile of the construction site and the soil mechanical properties. Dissipation tests were also carried out during the CPTs and allowed evaluating the horizontal consolidation and permeability coefficients through several procedures. An extensive field monitoring of the site was carried out during the embankment construction, the preloading period and, after the embankment removal, during the hydraulic leakage test of the tanks. Differential settlements and angular distortions of the tank foundation evaluated from the measured settlement profiles were compared with expected profile shapes for tanks overlying homogeneous compressible soil layers and with available empirical relationships. A general fair agreement was observed even if the heterogeneity of the alluvial soil deposit affects the tank response. Observed absolute and differential settlements and distortions are consistent with the allowable limits provided by the literature and with the design prescriptions, thus confirming the effectiveness of the preloading and drainage technique adopted in the project and envisaging a satisfactory performance of the tank under service conditions. [Copyright &y& Elsevier]

• Mechanism of the temperature-induced error is revealed by theoretical analysis. • The value of the temperature-induced error is determined by theoretical derivation. • A correction method for the temperature-induced error is proposed for HLSs. • The temperature-induced error can be eliminated effectively by this method. In an HLS, the error come from many factors, among which temperature may be one of the most important factors. If the ambient temperature changes, the liquid level in the liquid storage tank and the water level at all the points for placement of sensors will change. However, due to the complex interconnection structure of HLS, the change of the liquid level at the reference measurement point and that at the other monitoring points are not the same, resulting in ambient temperature induced error, which can be calculated according to the theoretical formula. This error can be eliminated effectively by using the correction method for ambient temperature induced error in hydrostatic leveling systems. When this part of error is eliminated, the error of the monitoring points is reduced. At last, the method was used in the Gongchangling open-pit iron mine to reveal the variation characteristic of surface settlement above goaf. [ABSTRACT FROM AUTHOR]

Since 2015, Uganda has welcomed over 700,000 refugees from South Sudan, Democratic Republic of the Congo, Burundi, and other East African nations, and currently hosts over 1.4 million refugees with 92% of that population living in UNHCR-managed settlements. Despite refugee settlements being essential spaces for physical protection and humanitarian aid distribution and reception, the sheer rate of refugee influx and settlement growth has introduced uncertainties around site planning, aid delivery, food security, and landscape change. For example, there is little publicly available information on settlement establishment, growth, or changes in land use/land cover for the vast majority of UNHCR-managed settlements in Uganda and around the world. To address this shortcoming, this research characterizes the spatial and temporal patterns of refugee settlement landscape dynamics using the case study of the Pagirinya Refugee Settlement in Northern Uganda, Landsat and Sentinel-2 satellite image time series, and BFAST, an automated land cover disturbance detection algorithm. To delineate the extent of the settlement and surrounding disturbance, a refugee settlement boundary was generated using a 2018 Landsat NDVI composite, which included land disturbed by settlement establishment and subsequent growth. Landsat time series data were sampled within this boundary to parametrize a BFAST model to detect settlement disturbance, which was deployed over 351 Landsat images from 2005 to 2018. This approach yielded sub-monthly land cover disturbances from 2016 to 2017 with an accuracy of 87.5% resulting from the rapid (within one month) settlement establishment, road construction, the spread of dwellings and other built-up infrastructure throughout the settlement, as well as the conversion of natural grassland to small-scale agriculture within the first six months after refugee settlement began. These results were generated using open-access data and open-source algorithms to pave the way for developing a near real-time satellite image-based settlement monitoring framework, which would aid refugee response and evaluation efforts that are central to Uganda's refugee hosting and settlement plans, as well as implementation of the Global Compact on Refugees. • BFAST analysis of Landsat time series at Pagirinya Refugee Settlement detected establishment and growth with 85.7% accuracy • Classification of Landsat NDVI composite provided a more effective functional boundary than UNHCR settlement boundary data • Research moves towards a near real-time approach for refugee settlement monitoring, evaluation, and planning [ABSTRACT FROM AUTHOR]