Search

Land subsidence severely threatens most of the coastal plains around the world where high productive industrial and agricultural activities and urban centers are concentrated. Coastal subsidence damages infrastructures and exacerbates the effect of the sea‐level rise at regional scale. Although it is a well‐known process, there is still much more to be improved on the monitoring, mapping and modeling of ground movements, as well as the understanding of controlling mechanisms. The International Geoscience Programme recently approved an international project (IGCP 663) aiming to bring together worldwide researchers to share expertise on subsidence processes typically occurring in coastal areas and cities, including basic research, monitoring and observation, modelling and management. In this paper, we provide the research communities and potential stakeholders with the basic information to join the participating teams in developing this project. Specifically, major advances on coastal subsidence studies and information on well‐known and new case studies of land subsidence in China, Italy, The Netherlands, Indonesia, Vietnam and Thailand are highlighted and summarized. Meanwhile, the networking, dissemination, annual meeting and field trip are briefly introduced. [ABSTRACT FROM AUTHOR]

Dynamic loads of vehicles have a considerable impact on the safety of elevated highways, but few studies have addressed the influence of dynamic loads on the safety of such linear infrastructure using Time-series SAR Interferometry (TS-InSAR). To fill this gap, we explored the displacement of elevated highways and the possible factors causing the deformation, using a long-term time-series of high resolution TerraSAR-X satellite dataset and Attribution Analysis Model (AAM) associated with dynamic loads for Shanghai, China. The results show that most deformed sections of elevated highways are located on the periphery of the network with a deformation velocity of about −5 mm year−1, as validated by ground-levelling data. Results by the proposed AAM illustrate the displacements of elevated highways correspond to the regional subsiding, dynamic loading, and construction time, as only 5% points are not identified to these factors. This study highlights TS-InSAR can be successfully applied to the safety analysis of operational linear infrastructures. [ABSTRACT FROM AUTHOR]

Large-scale reclamation projects during the past decades have been recognized as one of the driving factors behind land subsidence in coastal areas. However, the pattern of temporal evolution in reclamation settlements has rarely been analyzed. In this work, we study the spatio-temporal evolution pattern of Linggang New City (LNC) in Shanghai, China, using space-borne synthetic aperture radar interferometry (InSAR) methods. Three data stacks including 11 X-band TerraSAR-X, 20 L-band ALOS PALSAR, and 35 C-band ENVISAT ASAR images were used to retrieve time series deformation from 2007 to 2010 in the LNC. An InSAR analysis from the three data stacks displays strong agreement in mean deformation rates, with coefficients of determination of about 0.9 and standard deviations for inter-stack differences of less than 4 mm/y. Meanwhile, validations with leveling data indicate that all the three data stacks achieved millimeter-level accuracies. The spatial distribution and temporal evolution of deformation in the LNC as indicated by these InSAR analysis results relates to historical reclamation activities, geological features, and soil mechanisms. This research shows that ground deformation in the LNC after reclamation projects experienced three distinct phases: primary consolidation, a slight rebound, and plateau periods. [ABSTRACT FROM AUTHOR]

A great deal of evidence suggests that emotion enhances memory. Thus, it may be harder to forget emotional information. By means of fMRI, this question was investigated in the item-method directed forgetting paradigm. Behavioral results demonstrated that although all kinds of material could be forgotten, negative words showed reduced directed forgetting effect. At the neural level, the initial viewing of negative words elicited increased activities in inferior frontal gyrus and superior parietal lobule when contrasted with neutral words, which reflected the capture of attention by negative content. Forgetting instructions for negative and neutral words led to enhanced activations in frontal and parietal cortex, consistent with the engagement of an active inhibitory process. Surprisingly, whereas successful directed forgetting of neutral words elicited stronger activations in right middle frontal gyrus compared with incidental forgetting, no such activation was observed for negative words. The lack of activation for negative words may be due to an attentional bias in processing negative words, which may briefly interfere with the deployment of inhibitory control. The present findings are consistent with the engagement of an active forgetting mechanism that contributes to the item-method directed forgetting. However, evidence of impeded inhibitory control suggests that forgetting negative words is harder. [ABSTRACT FROM AUTHOR]

Recent developments in graph theory have heightened the need for investigating the disruptions in the topological structure of functional brain network in major depressive disorder (MDD). In this study, we employed resting-state functional magnetic resonance imaging (fMRI) and graph theory to examine the whole-brain functional networks among 42 MDD patients and 42 healthy controls. Our results showed that compared with healthy controls, MDD patients showed higher local efficiency and modularity. Furthermore, MDD patients showed altered nodal centralities of many brain regions, including hippocampus, temporal cortex, anterior cingulate gyrus and dorsolateral prefrontal gyrus, mainly located in default mode network and cognitive control network. Together, our results suggested that MDD was associated with disruptions in the topological structure of functional brain networks, and provided new insights concerning the pathophysiological mechanisms of MDD. [ABSTRACT FROM AUTHOR]

Abstract: We report the first experimental evidence and numerical prediction of fully developed periodic oscillation in curved duct flows. The oscillation is between symmetric/asymmetric 2-cell flows and symmetric/asymmetric 4-cell flows. It appears in the range where there are no stable steady fully developed flows. We also report both experimental and numerical evidence of flow stability change along a solution branch without passing limit/bifurcation points. [Copyright &y& Elsevier]

A numerical study is made on the fully developed bifurcation structure and stability of the forced convection in a curved duct of square cross-section (Dean problem). In addition to the extension of three known solution branches to the high Dean number region, three new asymmetric solution branches are found from three symmetry-breaking bifurcation points on the isolated symmetric branch. The flows on these new branches are either an asymmetric two-cell state or an asymmetric seven-cell structure. The linear stability of multiple solutions are conclusively determined by solving the eigenvalue system for all eigenvalues. Only two-cell flows on the primary symmetric branch and on the part of isolated symmetric branch are linearly stable. The symmetric six-cell flow is also linearly unstable to asymmetric disturbances although it was ascertained to be stable to symmetric disturbances in the literature. The linear stability is observed to change along some solution branch even without passing any bifurcation or limit points. Furthermore, dynamic responses of the multiple solutions to finite random disturbances are also examined by the direct transient computation. It is found that possible physically realizable fully developed flows evolve, as the Dean number increases, from a stable steady two-cell state at lower Dean number to a temporal periodic oscillation state, another stable steady two-cell state, a temporal intermittent oscillation, and a chaotic temporal oscillation. Among them, three temporal oscillation states have not been reported in the literature. A temporal periodic oscillation between symmetric/asymmetric two-cell flows and symmetric/asymmetric four-cell flows are found in the range where there are no stable steady fully developed solutions. The symmetry-breaking point on the primary solution branch is determined to be a sub-critical Hopf point by the transient computation. [Copyright &y& Elsevier]

A numerical study is made on fully developed bifurcation structure and stability of combined free and forced convection in a rotating curved duct of square cross-section. The solution structure is determined as the variation of a parameter indicating the magnitude of buoyancy force. Steady solution structure is very complicated. Flow and temperature fields on various solution branches are identified to be symmetric/asymmetric multi-cell patterns. Dynamic responses of multiple solutions to finite random disturbances are examined by direct transient computation. Five types of physically realizable solutions are identified numerically. They are stable steady 2-cell solution, stable steady multi-cell solution, periodic oscillation, chaotic oscillation and symmetry-breaking oscillation led by sub-harmonic bifurcation (period doubling). Among them, three kinds of stable steady solutions are found to co-exist within a range of parameters. In addition, temporal periodic and chaotic oscillations can also co-exist in another range of parameters. Furthermore, sub-harmonic bifurcation is identified to be another route to chaos. Spectral analysis is used to demonstrate the presence of additional frequencies for the case of sub-harmonic bifurcations. Results show that symmetry-breaking oscillation driven by sub-harmonic bifurcations appear to be identical with the mode observed in Lipps [J. Fluid Mech. 75 (1976) 113], McLaughlin and Orszag [J. Fluid Mech. 122 (1982) 123], and Gollub and Benson [J. Fluid Mech. 100 (1980) 449] for problem of free convection between flat horizontal plates. [Copyright &y& Elsevier]

The article presents a research report conducted on the Land Subsidence with its monitoring, impact and mechanism in the coastal cities. It states that land subsidence is a geohazard which is consisted in the lower ground surface. The geohazard is a geological state which takes place because of natural and humaninduced processes occurring in the deep subsoil.

Background: Tibetan pigs have exhibited unique characteristics from low‐altitudes pigs and adapted well to the Qinghai‐Tibet Plateau. Objectives: The current study was undertaken to investigate the hypoxic adaptation of heart in Tibetan pigs. Methods: The hearts of Tibetan pigs and Landrace pigs raised at high or low altitudes were compared using 3D casting technology, scanning electron microscopy and real‐time quantitative PCR (qRT‐PCR). Results: We found that the ratio of the major axis to the minor axis and the density of the heart were significantly higher in Tibetan pigs than in Landrace pigs (p < 0.05). Tibetan pigs had larger diameters and higher densities of arterioles than Landrace pigs (p < 0.05), and these features have a similar variation with the expression of vascular endothelial growth factor (VEGF). The cardiac expression levels of hypoxia‐inducible factor‐1α (HIF‐1α) and endothelial nitric oxide synthase (eNOS) were significantly higher in pigs reared at high altitudes than in those reared at low altitudes (p < 0.05). In contrast, Egl nine homolog 1 (EGLN1) had the opposite trend with respect to HIF‐1α and eNOS and was related to red blood cell (RBC) counts. Notably, the expressions of erythropoietin (EPO) and endothelial PAS domain‐containing protein 1 (EPAS1) were significantly higher in Landrace pigs kept at high altitudes than in the others (p < 0.05) and were associated with haemoglobin. Conclusions: These findings show that the regulation of the heart function of Tibetan pigs in a hypoxic environment is manifested at various levels to ensure the circulation of blood under extreme environmental conditions. [ABSTRACT FROM AUTHOR]

Land subsidence can be observed with time-series of Interferometric Synthetic Aperture Radar (InSAR) data. However, existing approaches only reveal subsidence signals that are multi-scale mixed, which is not conducive to the systematic analysis of subsidence of different mechanisms. A deformation signal decomposition (DSD) method based on spectral analysis is used to decompose the deformation extracted by time-series InSAR into three classes of deformation signals. They refer to large-scale deformation related to geological settings, medium-scale deformation caused more by group excavation, and small-scale deformation along linear infrastructures. TerraSAR-X datasets for Shanghai spanning April 2013 to September 2020, and Sentinel-1A datasets spanning January 2016 to September 2020 are used in this study. The results were cross-verified between the TerraSAR-X and Sentinel-1A datasets, and validated against levelling measurements. Subsidence signals caused by different mechanisms were automatically decomposed, which facilitates a systematic analysis for targeted diagnosis of land subsidence signals. A detailed analysis was conducted jointly at three scales of surface displacement, geological conditions, major construction activities, and subsidence mechanisms. It indicated that construction activities were the leading cause of land subsidence, and suggests that local authorities that wish to mitigate surface subsidence may benefit from primarily considering this process. [ABSTRACT FROM AUTHOR]

Building change detection (BCD) plays a vital role in city planning and development, ensuring the timely detection of urban changes near metro lines. Synthetic Aperture Radar (SAR) has the advantage of providing continuous image time series with all-weather and all-time capabilities for earth observation compared with optical remote sensors. Deep learning algorithms have extensively been applied for BCD to realize the automatic detection of building changes. However, existing deep learning-based BCD methods with SAR images suffer limited accuracy due to the speckle noise effect and insufficient feature extraction. In this paper, an attention-guided dual-branch fusion network (ADF-Net) is proposed for urban BCD to address this limitation. Specifically, high-resolution SAR images collected by TerraSAR-X have been utilized to detect building changes near metro line 8 in Shanghai with the ADF-Net model. In particular, a dual-branch structure is employed in ADF-Net to extract heterogeneous features from radiometrically calibrated TerraSAR-X images and log ratio images (i.e., difference images (DIs) in dB scale). In addition, the attention-guided cross-layer addition (ACLA) blocks are used to precisely locate the features of changed areas with the transformer-based attention mechanism, and the global attention mechanism with the residual unit (GAM-RU) blocks is introduced to enhance the representation learning capabilities and solve the problems of gradient fading. The effectiveness of ADF-Net is verified using evaluation metrics. The results demonstrate that ADF-Net generates better building change maps than other methods, including U-Net, FC-EF, SNUNet-CD, A2Net, DMINet, USFFCNet, EATDer, and DRPNet. As a result, some building area changes near metro line 8 in Shanghai have been accurately detected by ADF-Net. Furthermore, the prediction results are consistent with the changes derived from high-resolution optical remote sensing images. [ABSTRACT FROM AUTHOR]

To adapt to the plateau environment, Tibetan pigs' lungs have developed a unique physiological mechanism during evolution. The vascular corrosion casting technique and scanning electron microscopy were used to understand arterial architecture. Blood physiological index and quantitative real-time PCR (qRT-PCR) were used for assessing whether the lung can regulate the body through anatomical, physiological and molecular mechanisms to adapt to hypoxic environments. Our study showed that the lungs of Tibetan pigs were heavier and wider and that the pulmonary arteries were thicker and branched and had a denser vascular network than those of Landrace pigs. The hemoglobin (HGB), mean corpuscular hemoglobin concentration (MCHC) values of high-altitude pigs were significantly higher than those of low-altitude pigs. The expression levels of HIF - 1 α , EPAS1 , EPO and VEGF , but not those of eNOS and EGLN1 , were significantly higher in the lungs of high-altitude pigs than in those from pigs at a lower altitude (P<0.05). These findings and a comprehensive analysis help elucidate the pulmonary mechanism of hypoxic adaptation in pigs. [ABSTRACT FROM AUTHOR]

Excessive groundwater withdrawal has caused severe land subsidence worldwide. The pore water pressure and the deformation of pumped hydrostratigraphic units are complex. A fully coupled three‐dimensional numerical simulation was carried out for different pumping plans in this paper. When groundwater is pumped from a confined aquifer, the great compaction occurs in the pumped aquifer and its upper and lower adjacent aquitard units. Land subsidence is smaller and the area affected by land subsidence is greater when groundwater is pumped from the deeper confined aquifer. The pore water pressure in the pumped confined aquifer changes immediately with pumpage. In the adjacent aquitard units, however, the pore water pressure increases in the early pumping time and decreases in the early recharging time. The decrease in the pore water pressure vertically spreads from the interface between aquitard and pumped aquifer to the other surface of the aquitard. The pumped aquifer compacts and rebounds immediately with pumping and non‐pumping or recharging actions, while the compaction and rebounding of the aquitard units clearly lag behind. The compaction of the adjacent aquitard unit first occurs near the interface between aquitard and pumped aquifer units, and the compaction zone spreads outward as the pumping goes on. The aquitards may expand vertically within some zones. Due to the inelastic deformation of soil skeleton, different pumping plans result in different land subsidence. For the same net pumpage, maximal land subsidence and horizontal displacement are the smallest for constant discharge and the greatest for recharge‐discharge cycle. Article impact statement: Analysis of pore water pressure and deformation has the value of understanding the mechanisms of pumping‐induced land subsidence. [ABSTRACT FROM AUTHOR]

Appropriate shielding methods can reduce the lightning induced voltage and current of cables. In this article, different lightning surge currents (8/20 and 5/320 μs) are coupled to the tested multi-core cable with single shielding layer and double shielding layers. The shielding effectiveness (SE) on the lightning surge current is compared for different cable shielding methods. The experimental results show that the cable induced current is effectively reduced when the shielding layer, the shielding spare core wire or the metal tube are grounded at two ends. A better shielding effect for the cable with double shielding layers is achieved by grounding both ends of the outer shielding layer and one end of the inner shielding layer, reducing the induced current to about 5% when the shielding layer is not grounded. Moreover, the SE of the spare core wire, used as the shielding wire in the multi-core cable, is better than that of the external shielding wire of the cable. The SE of the metal tube increases more and more slowly with the increase of the tube coverage percentage. Furthermore, the descending order of the SE of shielding methods involved here are grounding both ends of double shielding layers, grounding both ends of single shielding layer, spare core wire shielding and metal tube shielding. Finally, some engineering recommendations are proposed through the comparison between the shielding methods in this article and relevant works. [ABSTRACT FROM AUTHOR]

The vertical–horizontal curtain system (VH curtain) is sometimes utilized in foundation pit dewatering under complex hydrogeological conditions. However, the working mechanism of this system when the horizontal curtain is semi-permeable and cannot completely cut off the bottom aquifer remains unknown. A transparent soil physical model test was performed to reveal the water control mechanism of the VH curtain system with a semi-permeable horizontal curtain. A multi-point inert tracer with a high-speed camera was used to photograph the seepage process. The seepage mode was revealed via a model test. With the Shanghai deep tunnel project as background, a numerical simulation was performed to understand the utilization of the VH curtain. The influence of horizontal curtain position, horizontal curtain thickness, horizontal curtain hydraulic conductivity, and VH curtain combination form on the seepage path around the foundation pit and on the drawdown of water level inside and outside the pit were studied. Results provide a basis for the engineering application of the VH curtain pumping well system. [ABSTRACT FROM AUTHOR]

Shanghai has the largest newly reclaimed area in China's coastal regions, and dredger fills are universally distributed in reclaimed lands there. Multi-scale geotechnical properties of dredger fills in region-scale (>1 km2), site-scale (1 m2–1 km2), mesoscale (1 cm2–1 m2), and microscale (1 µm2–1 cm2) were studied mainly through cone penetration investigation, borehole investigation, and microscopic inspections. Dredger impact craters, soil structures, and soil textures were investigated qualitatively and quantitatively to identify the dredger fills. Ultimate land subsidence since 1 July 2018 and land subsidence velocity characterized by the land subsidence from 1 July 2018 to 1 January 2019 were evaluated in Shanghai's typical reclaimed regions. Afterwards, Bayesian network including sixteen variables was proposed for land subsidence risk assessment. Surface subsidence, land subsidence velocity, and comprehensive land subsidence were the most sensitive to data point location and average initial void ratio of underlying strata. These three risk variables were also highly correlated to the thickness of the dredger fill layer and the reclamation time. This finding indicates that variances of the four independent variables (i.e., data point location, average initial void of underlying strata, land reclamation time, and thickness of dredger fill layer) significantly decide variances of the three risk levels. [ABSTRACT FROM AUTHOR]

Severe land subsidence caused by groundwater exploitation is one of the anthropogenic environmental problems. Even when groundwater exploitation has been limited or prohibited in some areas, it will continue in some water-deficient areas for a long time. Therefore, it is a challenge to reasonably exploit groundwater and not to cause severe land subsidence. A physical model test was conducted in this paper to simulate the extraction and recharge of groundwater, and to observe the soil deformation characteristics and the change of the pore water pressure. Based on the test results, the mechanism of land subsidence was investigated and different pumping modes were involved including the single-well pumping, single-well pumping and recharging, and double-well pumping and recharging tests. The tests indicated that the sand layer and clay layer had different pore water pressure change and deformation characteristics. In the sand layer, the pore water pressure decreased when pumping and increased when pumping stopped. In the clay layer, however, pore water pressure first increased rapidly and then decreased when pumping, and it decreased rapidly and then increased after pumping stopped. The variation of pore water pressure in the clay layer was consistent with the Mandel's effect and was related to the distance to the pumped layer. The further the distance was, the longer the Mandel effect lasted. The sand layer mainly exhibited elastic deformation and the clay layer almost exhibited plastic deformation. The clay layer showed clear hysteresis. The hysteresis time was increased with the distance from the pumped sand layer. In addition, the results indicated that the three pumping modes could reduce land subsidence. With regard to the pumpage and land subsidence, the double-well pumping and recharging mode was better than the other two. With pumping or pumping and recharging together, the increasing rate of vertical displacement became smaller and gradually reached a stable state. In general, these three modes were reasonable for groundwater exploitation, and could effectively control land subsidence. [ABSTRACT FROM AUTHOR]

Ground deformation is one of the most significant challenges faced by many coastal mega-cities, with major societal and economic impacts. In this context, the possibility to monitor the temporal evolution of the ground subsidence processes, which may also last for several years, is of great relevance. This goal can be obtained by applying differential SAR interferometry (DInSAR) techniques to sequences of multiple-satellite synthetic aperture radar (SAR) images. Moreover, the growing availability of large archives of SAR images collected by different SAR instruments nowadays leads to the need of developing new data merging techniques, which may take profit from the complementary information recoverable from every single set of data. In this work, a novel data merging approach for the generation of long-tem ground displacement time-series, based on the use of the modified Quantile-Quantile Adjustment (MQQA) algorithm, is proposed. Specifically, the methodology has successfully been applied to study the long-term evolution of the ground subsidence occurred in the coastal area of Shanghai from February 2007 to April 2017. A cross-comparison analysis between DInSAR and ground truth data has also been carried out, showing that the average root mean square error (RMSE) between the obtained displacement time-series and available ground truth data is of about 3 mm. This outcome confirms the validity of the novel DInSAR-based MQQA combination method. [ABSTRACT FROM AUTHOR]

Partial expansion was observed in stratified subsidence during foundation pit dewatering. However, the phenomenon was suspected to be an error because the compression of layers is known to occur when subsidence occurs. A slice of the subsidence cone induced by drawdown was selected as the prototype. Model tests were performed to investigate the phenomenon. The underlying confined aquifer was generated as a movable rigid plate with a hinge at one end. The overlying layers were simulated with remolded materials collected from a construction site. Model tests performed under the conceptual model indicated that partial expansion occurred in stratified settlements under coordination deformation and consolidation conditions. During foundation pit dewatering, rapid drawdown resulted in rapid subsidence in the dewatered confined aquifer. The rapidly subsiding confined aquifer top was the bottom deformation boundary of the overlying layers. Non-coordination deformation was observed at the top and bottom of the subsiding overlying layers. The subsidence of overlying layers was larger at the bottom than at the top. The layers expanded and became thicker. The phenomenon was verified using numerical simulation method based on finite difference method. Compared with numerical simulation results, the boundary effect of the physical tests was obvious in the observation point close to the movable endpoint. The tensile stress of the overlying soil layers induced by the underlying settlement of dewatered confined aquifer contributed to the expansion phenomenon. The partial expansion of overlying soil layers was defined as inversed rebound. The inversed rebound was induced by inversed coordination deformation. Compression was induced by the consolidation in the overlying soil layers because of drainage. Partial expansion occurred when the expansion exceeded the compression. Considering the inversed rebound, traditional layer-wise summation method for calculating subsidence should be revised and improved. [ABSTRACT FROM AUTHOR]

In this paper, a method is derived for evaluating the thermo-economic performance of solar aided power generation (SAPG) hybrid systems. These systems can achieve emissions reduction and energy savings compared to conventional coal-fired power generation systems. In the discussed model of SAPG hybrid system, various stages of heating feed-water in a conventional coal-fired power plant steam Rankine system are replaced by steam injected from solar direct steam generation (DSG). In order to determine the thermo-economic viability of SAPG compared to conventional power generation, convenient methods are required for evaluating the performance of SAPG systems. Therefore, an analysis method is developed which involves defining a generalized steam–water distribution matrix equation. This matrix approach simplifies the traditional thermal calculation and has a one-to-one correspondence with the system structure. As a case study, the proposed method is successfully used to solve the case of a 600 MW power generation system with the integration of DSG. A comparison of the case study system with (SAPG) and without (non-SAPG) the integration of the solar DSG shows thermo-economic benefits to the hybridised system. If the state parameters are taken as variables, this method can be used to study the effects of changes in system, equipment, operation, and load on the thermal economy of the integrated system. [ABSTRACT FROM AUTHOR]

Summary: Shanghai is one of the cities suffering from land subsidence in China. Land subsidence has caused serious financial losses. Thus, artificial recharge measures have been adopted to compensate the drawdown in shallow, confined aquifers and thereby control land subsidence. In this study, a multi-cycle recharge–recovery field experiment was performed to investigate the response of a shallow, confined aquifer to artificial recharge through a well. In the experiment, a series of recharge–recovery cycles with different recharge volumes and durations, with and without artificial pressure, were performed. The water levels monitored in the recharge and observation wells indicated the response of the aquifer to the multi-cycle recharge–recovery process. Meanwhile, a finite-difference method (FDM) numerical model was established, and its parameters were obtained via a reversed numerical analysis on the experimental data. The responses of the shallow, confined aquifer to the multi-cycle recharge–recovery process were simulated in detail using the model. The calculation results showed that the water level dropped significantly when the recharge ended. Moreover, the efficiency of a multi-cycle recharge was found to be higher than that of a concentrated one under the same recharge volume and time. The relationship between recharge frequency and efficiency, expressed as H =0.29498 f 0.40163 and R 2 =0.97264, respectively, was obtained through the FDM numerical simulation. In the recharge intervals, the optimal recharge efficiency was achieved when the water level rose to 40% of the peak. [ABSTRACT FROM AUTHOR]

Land reclamation has been increasingly employed in many coastal cities to resolve issues associated with land scarcity and natural hazards. Especially, land subsidence is a non-negligible environmental geological problem in reclamation areas, which is essentially caused by soil consolidation. However, spatial-scale evaluation on the average degree of consolidation (ADC) of soil layers and the effects of soil consolidation on land subsidence have rarely been reported. This study aims to carry out the integrated analysis on soil consolidation and subsidence mechanism in Chongming East Shoal (CES) reclamation area, Shanghai, at spatial-, macro-, and micro-scale so that appropriate guides can be provided to resist the potential environmental hazards. The interferometric synthetic aperture radar (InSAR) technique was utilized to retrieve the settlement curves of the selected onshore (Ra) and offshore (Rb) areas. Then, the hyperbolic (HP) model and three-point modified exponential (TME) model were combined applied to predict the ultimate settlement and to determine the range of ADC rather than a single pattern. With two boreholes Ba and Bb set within Ra and Rb, conventional tests, MIP test, and SEM test were conducted on the collected undisturbed soil to clarify the geological features of exposed soil layers and the micro-scale pore and structure characteristics of representative compression layer. The preliminary results showed that the ADC in Rb (93.1–94.1%) was considerably higher than that in Ra (60.8–78.7%); the clay layer was distinguished as the representative compression layer; on micro-scale, the poor permeability conditions contributed to the low consolidation efficiency and slight subsidence in Rb, although there was more compression space. During urbanization, the offshore area may suffer from potential subsidence when it is subjected to an increasing ground load, which requires special attention. [ABSTRACT FROM AUTHOR]

• CT was applied to various types of soil that were collected in a reclamation area. • The coefficient of variation-based results showed the soil heterogeneity. • The averaged Hu was correlated with the physical properties and compressibility. • The averaged Hu values reflected the relative amount of soil particles and water. Nowadays, land reclamation by dredged soil has become an effective solution to the growing demand for land resources in coastal areas. However, the widespread dredger fill (artificial deposits in reclamation area) can compress the underlying soil layers, causing different degrees of land subsidence and posing a threat to infrastructure in relation to agriculture. Therefore, it is necessary to facilitate an understanding of the physical properties and compressibility of soil in the reclamation area. X-ray computed tomography (CT), as a non-destructive method, can provide insight into the structure of soil. In this paper, 44 undisturbed soil samples comprised of dredger fill, sandy silt, muddy clay, clay, and silty clay, were collected from ten 55 m deep boreholes in Chongming East Shoal reclamation area in Shanghai. CT and conventional tests were conducted on all soils. The coefficient of variation of the scanning-slice-related standard deviation was used to evaluate the soil heterogeneity, which reflects the spatial variability of the arrangement of soil particles. The results indicated that the slice-related coefficient of variation had a reliable capacity to evaluate the soil heterogeneity; the averaged Hounsfield (AHu) values of the soil sample had a significant statistical correlation with the conventional-test-derived physical properties (wet bulk density, dry bulk density, gravimetric water content, and porosity). The AHu values essentially reflected the relative amounts of soil particles and water in saturated soil. The granulometric compositions that can lead to denser arrangements of soil particles tended to have higher Hu values. A linear relationship was also found between AHu values and the compression index, which may help to predict the compressibility of the soil. As a rule, these findings open new avenues for research into the physical properties and compressibility evaluation of varied types of soil. [ABSTRACT FROM AUTHOR]

With the development of the economy, land reclamation, as a result of dredged soil, has become an effective measure to alleviate land scarcity in many coastal cities around the world. Chongming East Shoal (CES), a typical reclamation area in Shanghai that is formed by multi-phase reclamation projects, was selected as the study area. The small baseline subset–interferometry synthetic aperture radar (SBAS-InSAR) method was applied to derive the map of velocity distribution and accumulated deformation with 70 Sentinel-1 synthetic aperture radar (SAR) images collected from 22 March 2015 to 2 December 2019. In addition, 25 undisturbed soil samples, including dredger fill and underlying soil layers, were collected from five boreholes (maximum depth 55 m) through a field investigation. Laboratory tests were then performed on all soil samples in order to facilitate an understanding of geological features, including the measurement of basic physical properties, cation exchange capacity, compressibility, microscale structure, and pores. The present results show that the whole CES was undergoing differential ground deformation, with a velocity ranging from −47.5 to 34.6 mm/y. Fast (−3.4 mm/y) to slow (−0.3 mm/y) mean subsidence velocities were detected in multi-phase reclamation areas from inland areas to the coastline, and were controlled by building load and geological features of soil layers. Urbanization is the main factor that triggers accelerated subsidence and should receive special attention for reclamation areas that have been finished for a long time (over 20 years in this study). The geological features indicated that poor drainage conditions in offshore soil layers resulted in slow subsidence. The field investigation and laboratory test can be powerful explanatory tools to monitor the results from a mechanical perspective. [ABSTRACT FROM AUTHOR]