Ground Surface Deformation Research Articles

Behavior of a Deep Excavation and Damages on Adjacent Buildings: a Case Study in Vietnam

This paper investigates the behavior of deep excavations and damages on adjacent buildings based on an excavation in a thick sand layer in Vietnam. Firstly, measured horizontal displacements of diaphragm walls were used to calibrate soil stiffness parameters for finite element analysis (FEA). Then, the behavior of diaphragm walls, groundwater, ground surface deformation, and an adjacent building was analyzed. The analysis results and damages observed in the field were used to review the validity of the criteria for evaluating the damage potential of excavation to adjacent buildings. It can be concluded from the study that the damage potential of adjacent buildings as evaluated from FEA through the strain state chart proposed by Boscardin and Cording (1989) or the damage potential index (DPI) proposed by Schuster et al. (2009) is fairly accurate with field observations.

INTEGRATION OF GIS AND ADVANCED REMOTE SENSING TECHNIQUES FOR LANDSLIDE HAZARD ASSESSMENT: A CASE STUDY OF NORTHWEST SYRIA

Abstract. Landslide susceptibility and hazard mapping has been developed providing remarkable results through the integration of geographic information system (GIS) and remote sensing. In this regard, some approaches have considered the use of Sentinel-1 data and time-series interferometric synthetic aperture radar (InSAR) techniques, such as differential InSAR (D-InSAR) and persistent scatterers interferometric (PSI), for providing precise information about total amount and velocity of ground-surface deformations and landslides within a specific area during a specific time period which is important for disaster management’s planning process.In this paper, artificial neural network (ANN) was used as a statistical analysis method for landslide susceptibility mapping in Northwest Syria using multi-layer perceptron (MLP) neural network on a training dataset of one dependent variable (landslide or non-landslide) and nine independent variables (slope, aspect, curvature, land cover, NDVI, lithology, distance from faults, distance from road, distance from stream networks). The resulting map of landslide susceptibility was validated using area under curve (AUC) analysis using a testing dataset which showed 90.28% of AUC value. Then, landslide susceptibility map was reclassified into high-moderate-low classes and integrated with intensity map of mean velocity of ground-surface deformations during the time period form (16 October 2018) until (21 March 2019) by using a landslide hazard matrix in a GIS environment in order to get landslide hazard map of the study area for that time period. The result shows that around 44.4%, 52.9% and 2.5% of total study area was classified as a high, moderate and low hazard zone of landslide, respectively.

Monitoring surface subsidence in the Binchang mining area using small baseline subset differential interferometric synthetic aperture radar with Sentinel-1A data

Surface subsidence caused by mining is difficult to monitor. Traditional field measurements are time-consuming and labor intensive. Small baseline subset (SBAS) technique is a long-term sequence method based on the principles of radar interferometry that can be used to effectively survey small ground surface deformations. This technique has been successfully applied to urban subsidence in previous studies, but it has rarely been used to study subsidence in mining areas. A total of 62 Sentinel-1A images taken from March 2017 to March 2019 were used to analyze the surface subsidence of the Binchang mining area in Shaanxi Province, China. The accuracy was evaluated using the measured field data from six ground control points for eight different months. The root-mean-square-error and correlation coefficient (r) for the data obtained using SBAS and field measurements were 2.27 cm and 0.944, respectively. We examined 12 main subsidence areas with a mean subsidence rate of −11.88 cm / year, where the maximum cumulative subsidence of a single deformation point reached 83.46 cm. The subsidence areas also had differences in spatial distribution and subsidence formation processes. The geological and groundwater conditions were the same for all areas of the study, and mining in the surrounding coal mines was the main cause of surface subsidence. We demonstrate that SBAS differential interferometric synthetic aperture radar technique can be used as an effective method for the long-term monitoring of mining deformation.

Characterizing the distribution pattern and geologic and geomorphic controls on earthquake-triggered landslide occurrence during the 2017 Ms 7.0 Jiuzhaigou earthquake, Sichuan, China

This work aims to characterize the earthquake-triggered landslides (EQTLs) during the 2017 Jiuzhaigou earthquake and to describe the geological and geomorphological control of landslide hazards. The Jiuzhaigou-EQTLs were studied via field-based investigation and remote sensing techniques during few weeks immediately after the mainshock occurred. The Jiuzhaigou earthquake produced an 11.4-km2 landslide area with 5633 landslides, dominated by shallow disrupted landslides, rock falls, and rockslides/rock avalanche. Statistical analyses show that the Jiuzhaigou-EQTLs had low mobility with a modal apparent friction angle of 40–44°. The Jiuzhaigou-EQTLs mostly occurred at elevations of 2700–3500 m and below 900 m relative relief to the main riverbed, where small-scale landslides were situated at the lower to middle parts of hillslope and large-scale landslides were situated close to the ridge crests. Jiuzhaigou-EQTLs clustered on river valley-side at the upstream of Baihe River (Jiuzhai Paradise and Ganhaizi village), Rize gully, and Danzhu gully on the tectonically active region at the southwest side of seismogenic fault F2. Landslides are prone to failure on the carbonate rocks with anaclinal hillslopes, following the cataclinal and cata-plagioclinal hillslopes. Most Jiuzhaigou-EQTLs preferentially occur on the below low-level break line (L2) in V-shaped valley-side and between first-level (L2) and high-level break line (L1) in U-shaped valley-side formed from long-term paleo-glacier and river incision. We found that landslide frequency is determined by a combination of the earthquake source with ground deformation, slope distribution, and rock strength due to weathering and dissolution along the fractures. Ground surface deformation, rock type (strength), geological structures, and valley-side slope breaks dictated the Jiuzhaigou-EQTL distribution pattern and hazards. This study elucidates the roles that local conditions play in influencing the occurrence, distribution, and frequency of slope failures and provides a better understanding of EQTL phenomenon during the Jiuzhaigou earthquake.

Ground surface changes detection using interferometric synthetic aperture radar

Disasters, including earthquakes and landslides, have enormous economic and social losses besides their impact on environmental disruption. Iran, and particularly its Western part, is known as an earthquake susceptible area due to numerous strong ground motions. Studying ecological changes due to climate change can improve the public and expert sector's awareness and response to future disastrous events. Synthetic Aperture Radar (SAR) data and Interferometric Synthetic Aperture Radar (InSAR) technologies are appropriate tools for modeling and surface deformation modeling. This paper proposes an efficient approach to detect ground deformation changes using Sentinel-1A. The focal point of this research is to map the ground surface deformation modeling is presented using InSAR technology over Sarpol-e Zahab on 25th November 2018 as a study case. For surface deformation modeling and detection of the ground movement due to earthquake SARPROZ in MATLAB programming language is used and discussed. Results show that there is a general ground movement due to the Sarpol-e Zahab earthquake between -7 millimeter to +18 millimeter in the study area. This research verified previous researches on the advanced image analysis techniques employed for mapping ground movement, where InSAR provides a reliable tool for assisting engineers and the decision-maker in choosing proper policies in a time of disasters. Based on the result, 574 out of 682 damaged buildings and infrastructures due to the 2017 Sarpol-e Zahab earthquake have moved from -2 to +17 mm due to the 2018 earthquake with a magnitude of 6.3 Richter. Results show that mountainous areas have suffered land subsidence, where urban areas had land uplift.

Magnetorheological Fluid Haptic Shoes for Walking in VR.

In this article, present RealWalk, a pair of haptic shoes for HMD-based VR, designed to create realistic sensations of ground surface deformation, and texture using Magnetorheological fluid (MR fluid). RealWalk offers a novel interaction scheme through the physical interaction between the shoes, and the ground surfaces while walking in VR. Each shoe consists of two MR fluid actuators, an insole pressure sensor, and a foot position tracker. The MR fluid actuators are designed in the form of multi-stacked disc structure with a long flow path to maximize the flow resistance. With changing the magnetic field intensity in MR fluid actuators based on the ground material in the virtual scene, the viscosity of MR fluid is changed accordingly. When a user steps on the ground with the shoes, the two MR fluid actuators are pressed down, creating a variety of ground material deformation such as snow, mud, and dry sand. We built an interactive VR application, and compared RealWalk with vibrotactile-based haptic shoes in four different VR scenes: grass, sand, mud, and snow. We report that, compared to vibrotactile-haptic shoes, RealWalk provides higher ratings in all scenes for discrimination, realism, and satisfaction. We also report qualitative user feedback for their experiences.

Localized Subsidence Zones in Gävle City Detected by Sentinel-1 PSI and Leveling Data

Among different sets of constraints and hazards that have to be considered in the management of cities and land use, land surface subsidence is one of the important issues that can lead to many problems, and its economic consequences cannot be ignored. In this study, the ground surface deformation of Gävle city in Sweden is investigated using the Persistent Scatterer Interferometry (PSI) technique as well as analyzing the historical leveling data. The PSI technique is used to map the location of hazard zones and their ongoing subsidence rate. Two ascending and descending Sentinel-1 datasets, collected between January 2015 and May 2020, covering the Gävle city, were processed and analyzed. In addition, a long record of a leveling dataset, covering the period from 1974 to 2019, was used to detect the rate of subsidence in some locations which were not reported before. Our PSI analysis reveals that the center of Gävle is relatively stable with minor deformation ranged between −2 ± 0.5 mm/yr to +2 ± 0.5 mm/yr in vertical and east–west components. However, the land surface toward the northeast of the city is relatively subsiding with a higher annual rate of up to −6 ± 0.46 mm/yr. The comparison at sparse locations shows a close agreement between the subsidence rates obtained from precise leveling and PSI results. The regional quaternary deposits map was overlaid with PSI results and it shows the subsidence areas are mostly located in zones where the subsurface layer is marked by artificial fill materials. The knowledge of the spatio-temporal extents of land surface subsidence for undergoing urban areas can help to develop and establish models to mitigate hazards associated with such land settlement.

InSAR-based detection method for mapping and monitoring slow-moving landslides in remote regions with steep and mountainous terrain: An application to Nepal

Mapping and monitoring landslides in remote areas with steep and mountainous terrain is logistically challenging, expensive, and time consuming. Yet, in order to mitigate hazards and prevent loss of life in these areas, and to better understand landslide processes, high-resolution measurements of landslide activity are necessary. Satellite-based synthetic aperture radar interferometry (InSAR) provides millimeter-scale measurements of ground surface deformation that can be used to identify and monitor landslides in remote areas where ground-based monitoring techniques are not feasible. Here we present a novel InSAR deformation detection approach, which uses double difference time-series with local and regional spatial filters and pixel clustering methods to identify and monitor slow-moving landslides without making a priori assumptions of the location of landslides. We apply our analysis to freely available Copernicus Sentinel-1 satellite data acquired between 2014 and 2017 centered on the Trishuli River drainage basin in Nepal. We found a minimum of 6 slow-moving landslides that all occur within the Ranimatta lithologic formation (phyllites, metasandstones, metabasics). These landslides have areas ranging from 0.39 to 1.66 km2 and long-term dry-season displacement rates ranging from 2.1 to 8.8 cm/yr. Due to periods of low coherence during the monsoon season (June – September) each year, and following the 25 April 2015 Mw7.8 Gorkha earthquake, our time series analysis is limited to the 2014–2015 and 2016–2017 dry seasons (September–May). We found that each of the landslides displayed slightly higher rates during the 2014 period, likely as a result of higher cumulative rainfall that fell during the 2014 monsoon season. Although we do not have high quality InSAR data to show the landslide evolution directly following the Gorkha earthquake, the similar rates of movement before (2014–2015) and after (2016–2017) Gorkha suggest the earthquake had negligible long-term impact on these landslides. Our findings highlight the potential for region-wide mapping of slow-moving landslides using freely available remote sensing data in remote areas such as Nepal and future work will benefit from expanding our methodology to other regions around the world.

Reconstructing the Velocity and Deformation of a Rapid Landslide Using Multiview Video

AbstractNoncontact measurements of spatially varied ground surface deformation during landslide motion can provide important constraints on landslide mechanics. Here, we present and test a new method for extracting measurements of rapid landslide surface displacement and velocity (accelerations of approximately 1 m/s2) using sequences of stereo images obtained from a pair of inexpensive, stationary 4K video cameras with nominal frame rates of 29.97 Hz. The method combines elements of Structure from Motion with those of optical flow to extract data on 3‐D evolution of the ground surface during slope failure. We apply the method to an experiment at the U.S. Geological Survey debris‐flow flume in which a high‐speed, liquefying landslide was triggered by gradually adding water to a 6‐m3 prism of loosely packed sediment on a 31° slope. Strip‐scanning lidar measurements made during the experiment corroborate our video‐based measurements, but the latter encompassed the entire landslide surface and were much lower in cost. Our video‐based measurements enabled computation of depth‐integrated landslide dilation/contraction rates. The range of computed rates was within the ranges inferred from independent measurements of evolving pore water pressures and reasonable estimates of the hydraulic permeability of the sediment. Dilation and contraction rates play a crucial role in landslide mechanics. The dilation and contraction we observe contradict the incompressible flow assumption used in many studies that have employed noncontact methods to infer landslide properties.

Documentation of Surface Fault Rupture and Ground-Deformation Features Produced by the 4 and 5 July 2019 Mw 6.4 and Mw 7.1 Ridgecrest Earthquake Sequence

Abstract The Mw 6.4 and Mw 7.1 Ridgecrest earthquake sequence occurred on 4 and 5 July 2019 within the eastern California shear zone of southern California. Both events produced extensive surface faulting and ground deformation within Indian Wells Valley and Searles Valley. In the weeks following the earthquakes, more than six dozen scientists from government, academia, and the private sector carefully documented the surface faulting and ground-deformation features. As of December 2019, we have compiled a total of more than 6000 ground observations; approximately 1500 of these simply note the presence or absence of fault rupture or ground failure, but the remainder include detailed descriptions and other documentation, including tens of thousands of photographs. More than 1100 of these observations also include quantitative field measurements of displacement sense and magnitude. These field observations were supplemented by mapping of fault rupture and ground-deformation features directly in the field as well as by interpreting the location and extent of surface faulting and ground deformation from optical imagery and geodetic image products. We identified greater than 68 km of fault rupture produced by both earthquakes as well as numerous sites of ground deformation resulting from liquefaction or slope failure. These observations comprise a dataset that is fundamental to understanding the processes that controlled this earthquake sequence and for improving earthquake hazard estimates in the region. This article documents the types of data collected during postearthquake field investigations, the compilation effort, and the digital data products resulting from these efforts.

Sentinel-1 InSAR measurements of deformation over discontinuous permafrost terrain, Northern Quebec, Canada

Differential synthetic aperture radar interferometry (D-InSAR) has been applied in permafrost environments to detect surface deformation caused by freeze-thaw processes in the active layer and underlying permafrost. The effectiveness of Sentinel-1 InSAR in monitoring ground surface deformation over continuous permafrost terrain above the treeline has been proven. The heterogeneous landscape and developed vegetation cover increase the difficulty of applying D-InSAR in sub-Arctic discontinuous permafrost terrain. The potential of Sentinel-1 InSAR in such an environment has not been fully explored. In this study, we explore the capabilities and limitations of applying Sentinel-1 time series data for monitoring surface deformation over discontinuous permafrost terrain. The interferometric coherence time series from September 2016 to April 2018 were analyzed over typical landscapes in discontinuous permafrost environments and their thaw subsidence curves are revealed by the small-baseline subset (SBAS) InSAR technique. The seasonal thaw subsidence in the summer of 2017 was in the range of 15–80 mm in the study area. The land cover types with thaw subsidence magnitudes from low to high are exposed land, peatland, lichen–low shrub, lichen-dominated and wetland low vegetation. The difference in displacement pattern between lichen-dominated and wetland-low vegetation-dominated permafrost terrains is especially clear at the end of the thawing stage, in September and October. The differences in thaw subsidence magnitude and pattern reveal the influence of the soil water content in the active layer and permafrost properties on the thaw subsidence patterns. We also compared the Sentinel-1 retrieved cumulative displacement with the X-band TerraSAR-X and L-band ALOS PALSAR results. The difference of retrieved deformation magnitude using the three sensors is amplified when shrubs are more developed. The findings indicate that Sentinel-1 time series with a 6-day or 12-day span work well over discontinuous permafrost terrain above the tree line (i.e., tundra, tundra wetlands and less developed shrub-tundra environments) during the thawed season, but the results and accuracy are not promising over developed shrub-tundra and, especially forest-tundra environments.

Ground Surface Deformation Detection in Complex Landslide Area—Bobonaro, Timor-Leste—Using SBAS DInSAR, UAV Photogrammetry, and Field Observations

During the past 10 years, Timor-Leste has concentrated all its efforts on infrastructure development. However, it has not achieved enough due to unexpected ground deformation in mountainous areas that is seriously affecting road constructions, etc. In order to design roads and other infrastructure under such difficult conditions, it is important to know the present and future ground conditions. Continuous monitoring is a significant methods of detecting ground deformation and providing essential information to realize an effective design. The problem arises of “How can ground deformation be monitored in extensive areas, which are generally located in mountain areas that are difficult to access?” Differential Interferometry Synthetic Aperture Radar (DInSAR) has recently been applied to monitor displacement in extensive areas. In addition, Unmanned Aerial Vehicle (UAV) photogrammetry is useful for detecting the deformation in detail. Both methods are advantageous in that they do not require any sensors. Therefore, the combination of DInSAR and UAV photogrammetry is one of the solutions for monitoring the ground deformation in Timor-Leste. In this paper, DInSAR and UAV photogrammetry are applied to unstable ground in the Bobonaro region of Timor-Leste to find the recent ground deformation, since 2007, due to earthquakes and hard rainfall events. It is found that DInSAR is useful for screening usual and unusual ground behavior and that UAV photogrammetry is flexible to use and can detect displacements with cm accuracy after the DInSAR screening.

Satellite Monitoring of Mass Changes and Ground Subsidence in Sudan’s Oil Fields Using GRACE and Sentinel-1 Data

Monitoring environmental hazards, owing to natural and anthropogenic causes, is an important issue, which requires proper data, models, and cross-validation of the results. The geodetic satellite missions, for example, the Gravity Recovery and Climate Experiment (GRACE) and Sentinel-1, are very useful in this respect. GRACE missions are dedicated to modeling the temporal variations of the Earth’s gravity field and mass transportation in the Earth’s surface, whereas Sentinel-1 collects synthetic aperture radar (SAR) data, which enables us to measure the ground movements accurately. Extraction of large volumes of water and oil decreases the reservoir pressure and form compaction and, consequently, land subsidence occurs, which can be analyzed by both GRACE and Sentinel-1 data. In this paper, large-scale groundwater storage (GWS) changes are studied using the GRACE monthly gravity field models together with different hydrological models over the major oil reservoirs in Sudan, that is, Heglig, Bamboo, Neem, Diffra, and Unity-area oil fields. Then, we correlate the results with the available oil wells production data for the period of 2003–2012. In addition, using the only freely available Sentinel-1 data, collected between November 2015 and April 2019, the ground surface deformation associated with this oil and water depletion is studied. Owing to the lack of terrestrial geodetic monitoring data in Sudan, the use of GRACE and Sentinel-1 satellite data is very valuable to monitor water and oil storage changes and their associated land subsidence over our region of interest. Our results show that there is a significant correlation between the GRACE-based GWS anomalies (ΔGWS) and extracted oil and water volumes. The trend of ΔGWS changes due to water and oil depletion ranged from –18.5 ± 6.3 to –6.2 ± 1.3 mm/year using the CSR GRACE monthly solutions and the best tested hydrological model in this study. Moreover, our Sentinel-1 SAR data analysis using the persistent scatterer interferometry (PSI) method shows a high rate of subsidence, that is, –24.5 ± 0.85, –23.8 ± 0.96, –14.2 ± 0.85, and –6 ± 0.88 mm/year over Heglig, Neem, Diffra, and Unity-area oil fields, respectively. The results of this study can help us to control the integrity and safety of operations and infrastructure in that region, as well as to study the groundwater/oil storage behavior.

Stability of the excavation face on a shield tunnel crossing beneath an existing tunnel

When a shield tunnel crosses the route of an existing tunnel, the new tunnel will have great influence on the inner structure and the upper surface of the existing tunnel. The support force of the excavation face is an important factor in controlling the ground surface deformation. In the construction of shield tunnelling, the damage caused by insufficient supporting force at the excavation face is much greater than the damage caused by excessive supporting force. In this paper, Abaqus software is used to simulate the instability of the excavation face caused by the small support pressure of the excavation face when the tunnelling machine crosses the route of the existing tunnel at close range. The variation of the ultimate supporting force of the excavation face and the influence of the support force of the excavation face on the existing tunnel and the ground surface settlement are analysed for different horizontal distances between the excavation face and the existing tunnel. The results show that the existence of the existing tunnel has a significant impact on the ground settlement caused by the excavation of the new tunnel. Moreover, when the shield is pushed to the same position, different supporting pressures will produce different vertical deformation increments for the new tunnel segments.

Calculating vertical deformation using a single InSAR pair based on singular value decomposition in mining areas

Vertical deformation estimation can be a significant tool in preventing geological hazards and managing environment impacts of underground mining. Common ground surface vertical deformation calculations are challenged by difficult data collection and dependence on prior knowledge. SVD (singular value decomposition) method was applied to estimate ground surface vertical deformation from single pair SAR (synthetic aperture radar) data in a mining region. During the study, LOS (line of sight) and azimuth displacement was obtained using two pass D-InSAR (differential interferometry synthetic aperture radar) and MAI (multi-aperture radar interferometry) technology, respectively. Two adjustment equations were composed using the imaging geometry of D-InSAR and MAI. The singular value decomposition theorem was used to acquire M-P (Moore-Penrose) generalized inverse of the rank deficiency coefficient matrix. From this, the optimal approximation solution of unknown parameters was calculated using weighted least squares. A working panel in the Datong mining area, Shanxi province, China, was selected to verify the SVD approach using the two ascending Sentinel-1A data. The accuracy of vertical deformation estimated by SVD approach is reliable. The RMSE (root mean square error) of vertical deformation is 2.64 mm (along upright profile) and 4.95 mm (along horizontal profile). These results suggest that the SVD approach will complement widely used vertical ground surface deformation calculations. Further study is needed to validate the method from other deformation scenarios from landslides, groundwater loss, earthquakes, underground mining, and glacier movement.

Centrifuge experiments for shallow tunnels at active reverse fault intersection

Tunnels extend in large stretches with continuous lengths of up to hundreds of kilometers which are vulnerable to faulting in earthquake-prone areas. Assessing the interaction of soil and tunnel at an intersection with an active fault during an earthquake can be a beneficial guideline for tunnel design engineers. Here, a series of 4 centrifuge tests are planned and tested on continuous tunnels. Dip-slip surface faulting in reverse mechanism of 60-degree is modeled by a fault simulator box in a quasi-static manner. Failure mechanism, progression and locations of damages to the tunnels are assessed through a gradual increase in Permanent Ground Displacement (PGD). The ground surface deformations and strains, fault surface trace, fault scarp and the sinkhole caused by fault movement are observed here. These ground surface deformations are major threats to stability, safety and serviceability of the structures. According to the observations, the modeled tunnels are vulnerable to reverse fault rupture and but the functionality loss is not abrupt, and the tunnel will be able to tolerate some fault displacements. By monitoring the progress of damage states by increasing PGD, the fragility curves corresponding to each damage state were plotted and interpreted in related figures.

Bayesian Inversion of Wrapped Satellite Interferometric Phase to Estimate Fault and Volcano Surface Ground Deformation Models

AbstractBayesian inference and an improved downsampling method is used to determine earthquake and volcano source parameters using a popular geodetic observation method, satellite radar interferometry. The main novelty of the proposed approach is that the interferometric wrapped phase can be directly inverted, circumventing the ill‐posed phase unwrapping processing step. Phase unwrapping errors severely affect the estimation of earthquake and volcano source parameters using interferometric observations. Therefore, it is desirable to avoid phase unwrapping completely. To overcome the need for phase unwrapping, we propose a downsampling algorithm and a method to estimate the covariance function of the wrapped phase and establish an appropriate misfit function between the observed and simulated wrapped phase. Uncertainties in source parameters are assessed with a Bayesian approach, and finally, the robustness of the inversion methodology is tested in multiple simulations including variable decorrelation and atmospheric noise simulations. The method is shown to be robust in challenging noise scenarios. It features an improvement in performance with the Bayesian approach, compared to similar previous methods, avoiding any influence of seed starting models and escaping local minima. The impact of a small percentage of incorrectly unwrapped phase observations in current state‐of‐the‐art methods is shown to strongly affect the estimation process. We conclude that in the cases where phase unwrapping is difficult or even impossible, the proposed inversion methodology with wrapped phase will provide an alternative approach to assess earthquake and volcano source model parameters.

Geomechanical monitoring of ground surface and pit wall deformations

Geomechanical monitoring of ground surface and pit wall deformations

Land subsidence and uplift related to groundwater extraction in Wuxi, China

Wuxi City is located in the Yangtze River Delta region, China and is underlain by a multi-layered aquifer system in porous Quaternary deposits. Groundwater extraction, mainly from the second confined aquifer, has led to severe regional land subsidence. The ground surface started to recover after the restriction and, ultimately, the banning of groundwater pumping. This paper reports the results of long-term surveys, groundwater piezometric head (GPH) measurements and the monitoring of ground surface deformation by levelling and borehole extensometers. The subsidence is attributed to the compression of both the aquifer and aquitards in the porous strata. The spatial characteristics of subsidence are related not only to the distribution of the GPH, but also to the thickness and compressibility of different strata, the distance from the pumped aquifer and the distribution of pumping. There was a temporal lag in subsidence relative to groundwater drawdown. The uplift is related to a period of recovery following the peak pumping period and groundwater recovery subsequent to the restriction and/or banning of groundwater pumping. The uplift was <10 mm under these two conditions, although the GPH recovered to >40% of the previous maximum at the Qianzhou borehole extensometer station.

Ground Distortion in the Sredneamurskaya Lowland Caused by Seasonal Freezing

We undertook a field survey of ground surface deformation under the influence of the frost heave process. The study has been conducted on the testing sites located in the different areas of the Sredneamurskaya lowland terrain (South of the Far East). It has been established that there is the most advanced alteration of the surface in the flood plains and broad water course valley bottoms, and there is a minimal alteration aslope and at the nearby water-dividing flat areas. Ground surface deformation is more active in the areas where the earthworks had been executed in comparison with the natural areas.