Ground Deformation Research Articles

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Implementing the European Space Agency’s SentiNel Application Platform’s Open-Source Python Module for Differential Synthetic Aperture Radar Interferometry Coseismic Ground Deformation from Sentinel-1 Data

Differential SAR Interferometry is a largely exploited technique to study ground deformations. A key application is the detection of the effects promoted by earthquakes, including detailed variations in ground deformations at different scales. In this work, an implemented Python script (Snap2DQuake) based on the “snappy” module by SNAP software 9.0.8 (ESA) for the processing of satellite imagery is proposed. Snap2DQuake is aimed at producing detailed coseismic deformation maps using Sentinel-1 C-band data by the DInSAR technique. With this alternative approach, the processing is simplified, and several issues that may occur using the software are solved. The proposed tool has been tested on two case studies: the Mw 6.4 Petrinja earthquake (Croatia, December 2020) and the Mw 5.7 to Mw 6.3 earthquakes, which occurred near Tyrnavós (Greece, March 2021). The earthquakes, which occurred in two different tectonic contexts, are used to test and verify the validity of Snap2DQuake. Snap2DQuake allows us to provide detailed deformation maps along the vertical and E-W directions in perfect agreement with observations reported in previous works. These maps offer new insights into the deformation pattern linked to earthquakes, demonstrating the reliability of Snap2DQuake as an alternative tool for users working on different applications, even with basic coding skills.

Satellite A-DInSAR pattern recognition for seismic vulnerability mapping at city scale: insights from the L’Aquila (Italy) case study

ABSTRACT L’Aquila downtown (Central Italy) is situated in a highly seismic region, making it susceptible to numerous historical and recent earthquakes. Among these, the earthquake of Mw 6.3 on 6 April 2009, and the one of Mw 6.7 on 2 February 1703, caused severe damage or complete destruction of the majority of buildings in the historical center. An integrated statistical analysis of A-DInSAR and seismic related building damage data is illustrated. By comparing the seismic damage maps from the 2009 and 1703 earthquakes with the A-DInSAR map produced with Cosmo-SkyMed descending orbit images (acquired between 2010 and 2021), a correlation between post-seismic deformations (in terms of average velocity) and building damage intensity has been identified. Furthermore, ground and building velocities have been separately examined, in order to evaluate the impact of building features and reconstruction efforts on ground deformations. The geostatistical analysis revealed a widespread subsidence motion (until −2 mm/year) across the whole study area. Notably, neighboring points did not exhibit consistent deformation velocities, indicating a lack of spatial correlation. Additionally, Cluster Analysis has allowed recognition of recurring subsidence/uplift trends, which, in terms of shape of curve displacement vs. time, appears independent on building damage intensity or reconstruction interventions. Our results pave the way for a novel utilization of long-term series of satellite SAR data in high-risk seismic zones, serving as a valuable tool to map the most susceptible areas and mitigate seismic risk.

A Statistical Approach for the Integration of Multi-Temporal InSAR and GNSS-PPP Ground Deformation Measurements.

Determining and monitoring ground deformations is critical for hazard management studies, especially in megacities, and these studies might help prevent future disaster conditions and save many lives. In recent years, the Golden Horn, located in the southeast of the European part of Istanbul within a UNESCO-protected region, has experienced significant changes and regional deformations linked to rapid population growth, infrastructure work, and tramway construction. In this study, we used Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS) techniques to investigate the ground deformations along the Golden Horn coastlines. The investigated periods are between 2015 and 2020 and 2017 and 2020 for InSAR and GNSS, respectively. For the InSAR analyses, we used sequences of multi-temporal synthetic aperture radar (SAR) images collected by the Sentinel-1 and ALOS-2 satellites. The ground displacement products (i.e., time series and velocity maps) were then cross-compared with those achievable using the Precise Point Positioning (PPP) technique for the GNSS solutions, which can provide precise positions with a single receiver. In the proposed analysis, we compared the ground displacement velocities obtained by both methods by computing the standard deviations of the difference between the relevant observations considering a weighted least square estimation procedure. Additionally, we identified five circle buffers with different radii ranging between 50 m and 250 m for selecting the most appropriate coherent points to conduct the cross-comparison analysis. Moreover, a vertical displacement rate map was produced. The comparison of the vertical ground velocities derived from PPP and InSAR demonstrates that the PPP technique is valuable. For the coherent stations, the vertical displacement rates vary between -4.86 mm/yr and -23.58 mm/yr and -9.50 and -27.77 mm/yr for InSAR and GNSS, respectively.

Multi-Scalar Oblique Photogrammetry-Supported 3D webGIS Approach to Preventive Mining-Induced Deformation Analysis

Underground coal mining will inevitably cause serious ground deformation, and therefore, preventive mining-induced deformation analysis (MIDA) is of great importance in assisting mining planning and decision-making. Current web-based Geographic Information System (webGIS)-based applications usually use 2D GIS data and lack a holistic framework. This study presents a multi-scalar oblique photogrammetry-supported unified 3D webGIS framework for MIDA applications to fill this gap. The developed web platform uses multiple open-source JavaScript libraries, and the prototype system provides user-friendly interfaces for GIS data collecting and corresponding database establishment, geo-visualization and query, dynamic prediction, and spatial overlapping analysis within the same framework. The proposed framework was tested and evaluated in the Qianyingzi mining area in eastern China. The results demonstrated that multi-scalar oblique photogrammetry balances data quality and acquisition efficiency and provides a good source of GIS datasets, and the web-based platform has a good absolute and relative spatial accuracy verified by two types of validation data. Practical application results proved the feasibility and reliability of the system. The developed web-based MIDA prototype system attains an appealing performance and can be easily extended to similar geoscience applications.

Obtaining the empirical calibration dependence for express assessment of the quality of the performance of ground structures

In this study, the authors consider sand pads, namely the production process and quality control. The main problem of using the compacting factor as a criterion for assessing the quality of sand pads is the impossibility of calculating future deformations of foundations, as well as the duration of laboratory studies to determine it. Thus, the development of a technological solution for the use of express methods for controlling the compaction of soil structures, which are based on empirical data and can reduce the economic costs of construction, is an urgent task. The direct object of the study is the sand pad under the production facility. In the process of installing a sand pad, layer-by-layer control of the degree of compaction was carried out according to the compacting factor with the determination of the maximum density according to the method of GOST 22733-2016, and the modulus of soil deformation according to selected soil samples for compression tests. For each layer, the compaction coefficient was determined at 5 points, the deformation modulus at 3 points. Additionally, tests were carried out using a dynamic density meter. The main result of the study is the construction of a calibration dependence of the constrained modulus on the dynamic modulus of elasticity of the soil based on the results of statistical processing. Based on the test results, it was found that the experimental data are equally accurate, the resulting model is adequate. The difference between the experimental data and the calibration dependence does not exceed 18 %, which is a good convergence for empirical methods. The obtained experimental dependence allows, with a sufficient degree of accuracy, to quickly control the quality of the sand pad.

INVESTIGATIONS ON INSAR DATA PROCESSING STANDARD FOR VOLCANO ISLAND MONITORING IN INDONESIA

Abstract. In critical situations such as disaster and humanitarian relief, the reliable geospatial data will present an appropriate decision on a timely manner. As fundamental datasets, large-scale topographic maps are are mandatory in order to perform geospatial analysis for many societal challenges. Indeed, Large Scale Topographic Mapping in Indonesia shall be accelerated in an innovative and productive way to consider the production efficiency, especially for the geospatial data acquisition as its primary source. Interferometric Synthetic Aperture Radar (InSAR) data acquisition presents some advantages, especially in conjunction with the security clearance and global weather as some main constraints for the geospatial data acquisition. In terms of disaster preparedness and emergency response, radar interferometry techniques can play an important role by generating a Digital Elevation Model (DEM) as an input to Decision Support Systems (DSS). In addition, the techniques of differential Interferometric Synthetic Aperture Radar (D-InSAR) can provide the earth surface deformation from time series Radar Datasets. A set of standards related to the InSAR data acquisition are essential, especially with regards to the improved sensors, and processing methods implemented by the worldwide space agencies nowadays. Hence, the precise definition of a standard is fundamental in order to prepare the InSAR data as one potential source of geospatial data and information, especially for LSTM data production. Generated time series of Digital Elevation Model (DEM) can identify the potential cause of 2018’s Sunda Strait tsunami (Tampubolon, 2019). It was related with the increasing eruption activity of Anak Krakatau (Child of Krakatoa). From DEM analysis, the Volcanic mudflow material avalanche has been detected before the tsunami hit the coastal surrounding area. In this paper, more advanced techniques was investigated by the combination between Time Series DEM Analysis and Ground Displacement detection. The focus on the integration between reliable TanDEM-X and up-to-date Sentinel 1A/B was proposed on another volcano island of Gamalama in Ternate. As TanDEM-X uses X-band as its medium wave, it can produce more reliable DEM as a reference data. On the other hand, Sentinel 1 uses C-band that can contribute to detect the ground deformation over the aforementioned volcano island. TanDEM-X uses a more robust and consistent approach to scan the earth surface by single data acquisition scheme, which is generally more accurate and reliable for the DEM generation. However, many factors influence the selection of a platform that can be best suited for radar interferometry. Initially, the German TanDEM-X Coregistered Singlelook Slant-range Complex (CoSSC) using bi-static InSAR approach has been implemented in order to generate DEMs comply with the LSTM specification in Indonesia. The basic principle is performing a simultaneous measurement of the same scene and identical doppler spectrum by using 2 sensors, thereby avoiding temporal decorrelation (DLR, 2012). Subsequently, the differential InSAR techniques by using Sentinel 1A/B has been performed in order to detect the ground deformation. Finally, tt can be shown that the reliable TanDEM-X data has increased the ground deformation resolution and accuracy in order to provide potential solution for disaster preparedness.

LAND SUBSIDENCE IN WUHAN REVEALED USING A MULTI-SENSOR INSAR TIME SERIES FUSION APPROACH

Abstract. Satellite Interferometric Synthetic Aperture Radar (InSAR) is widely utilized for topographic, geological, and natural resource investigations. However, many existing InSAR studies on ground deformation are limited to relatively short observation periods and single sensors. This paper introduces a novel method for fusing multi-sensor InSAR time series data, specifically designed to address scenarios involving partial overlaps and temporal gaps. The method employs a new Power Exponential Knothe Model (PEKM) to fit and fuse overlaps in the deformation curves, while a Long Short-Term Memory (LSTM) neural network predicts and fuses data during temporal gaps in the series. In this study, the city of Wuhan in China was selected as the experimental area. SAR datasets from COSMO-SkyMed (2011–2015), TerraSAR-X (2015–2019), and Sentinel-1 (2019–2021) were fused to map long-term surface deformation over the past decade. An independent InSAR time series analysis from 2011 to 2020, based on 230 COSMO-SkyMed scenes, was used as a reference for comparison. The correlation coefficient between the fusion algorithm’s results and the reference data is 0.87 in the time overlapping region and 0.97 in the time-interval dataset. The overall correlation coefficient of 0.78 demonstrates that the proposed algorithm achieves a similar trend as the reference deformation curve. Based on the long time series settlement results obtained through fusion, a detailed analysis of the causes of settlement was conducted for several subsidence zones. The subsidence in the Houhu area is primarily attributed to the consolidation and compression of soft soil. Soil mechanics were employed to estimate the expected completion time of subsidence and calculate the degree of consolidation for each year. The COSMO-SkyMed PSInSAR results indicate that the area has entered the late stage of consolidation and compression, gradually stabilizing over time. Furthermore, the subsidence curve observed in the area around Xinrong reveals that the construction of an underground section of subway Line 21 has caused significant settlement in that particular region. The high temporal granularity of the PSInSAR time series also enables precise detection of a rebound phase following a major flooding event in 2016. The experimental results demonstrate the accuracy of the proposed fusion method in providing robust time series for analyzing long-term land subsidence mechanisms. Additionally, these findings unveil previously unknown characteristics of land subsidence in Wuhan, thus clarifying the relationship with urban causative factors.

The Calculation Method for the Horizontal Bearing Capacity of Squeezed Branch Piles Considering the Plate–Soil Nonlinear Interaction

The m-method is a commonly used method to calculate the internal force and deformation of pile foundations under lateral loads. However, for squeezed branch piles, the increase in the load-bearing plate leads to changes in the pile section and the generation of a resistance bending moment under loading, which means the load–displacement relationship at the load-bearing plate will no longer satisfy the linear relationship. In this paper, a hyperbolic load transfer model is established to describe the nonlinear relationship between the soil resistance and lateral displacement at the branch of the pile, and the m-method is used for the straight section of the pile. Laboratory model tests are used to verify the correlation between theory and experimentation. The results show that the theory is consistent with the measured curve. On the basis of the theoretical calculation, the influence of the bearing plate and pile body parameters on the force of the squeezed branch pile is analyzed. The research shows that that the bearing capacity of the squeezed branch pile is improved by increasing the plate’s diameter, placing the plate closer to the ground, and ensuring that the pile top is embedded. The theoretical calculation method established in this paper can correctly and accurately reflect the bearing capacity characteristics of squeezed branch piles under horizontal loads, and it is more safe than performing measurements. Additionally, it can be applied to squeezed branch piles with different plate diameters, plate positions, plate section forms, and plate quantities as well as for piles with different boundary conditions and soil conditions. Moreover, it can also be applied to other pile shapes. This method is of significance for the analysis of the bearing characteristics of piles with variable sections under lateral loads.

SYNERGY OF ADVANCED PROCESSING TECHNIQUES USING COPERNICUS SAR AND OPTICAL SATELLITE IMAGERY TO DETECT GROUND DISPLACEMENTS: THE CASE STUDIES OF PYRGOS AND PAREKKLISIA VILLAGES IN CYPRUS

Abstract. Cyprus has a long history of destructive tectonic activity and related geohazards. This is mainly due to its location on the Mediterranean fault zone and the interaction of the Eurasian and African plates. To study the occurrence of land displacements on a national scale, various space-based monitoring techniques exploiting the Copernicus program’s datasets were studied using Sentinel-1 and Sentinel-2 satellite images for the period of 2016–2021. More specifically, differential spectral indices were calculated by subtracting the reference 2016 Sentinel-2 image from an image for every year until 2021, and a parallelised version of Persistent Scatterer Interferometry (PSI) was conducted using a time series of Sentinel-1 data over the same period, to identify ground displacements over time. The PSI analysis in the area around Pyrgos and Parekklisia villages, detected Line-of-Sight (LoS) uplift phenomena of a maximum rate of 8 mm/y, in ascending and descending Sentinel-1 satellite passes. Similarly, deformation was identified from optical image processing. The integration of both techniques provided qualitative and quantitative information about ground deformation events in both areas, showcasing a complementarity of results obtained, with PSI detecting displacements in urban/built-up areas, and multispectral change detection in rural environment. In terms of correlation, the two techniques showed a fit of 31.34% in ascending and 26% in descending pass, providing additional information on the size of affected areas. This synergistic approach facilitates the systematic monitoring of areas of interest, providing significant and timely information to decision-makers, to take actions and adopt protective measures when and where it is required.

InSAR Monitoring Using Persistent Scatterer Interferometry (PSI) and Small Baseline Subset (SBAS) Techniques for Ground Deformation Measurement in Metropolitan Area of Concepción, Chile

InSAR capabilities allow us to understand ground deformations in large metropolitan areas, this is key to assessing site conditions in areas in an inherently expanding context. The multi-temporal interferometry of SAR data records ground surface displacement velocities over large metropolitan areas, identifying anomalous and potential geological hazards. The metropolitan city of Concepción, Chile, is an alluvial basin in one of the world’s most seismically active subduction zones, where many subduction earthquakes have occurred throughout history. In this study, we monitored the deformations of the ground surface in the metropolitan area of Concepción using two interferometric techniques, the first being Persistent Scatterer Interferometry (PSI) and the second, the Small Baseline Subset (SBAS) technique. To do this, we have used the same Sentinel-1 dataset, obtaining ground movement rates between 2019 and 2021. The velocities were aligned with the GNSS station available in the area. Ground deformation patterns show local deformations depending on factors such as soil type and heterogeneity, and regional deformations due to geographical location in the subduction area. Our results highlight the similarity of the deformation rates obtained with different processing techniques and have also allowed us to identify areas of deformation and compare them to site conditions. These results are essential to evaluate ground conditions and contribute to urban planning and risk management in highly seismic areas.

Analysis of Land subsidencein coastal and urban areas by using various techniques– Literature Review

Over the past several decades, subsidence has emerged as a significant issue affecting urban, coastal, and mining areas worldwide. This phenomenon has been exacerbated by a decrease in groundwater resources, which has become a major problem on a global scale. Insufficient availability of surface water has led to excessive exploitation of the earth's groundwater system through unplanned processes. As a result, serious problems have arisen, including economic challenges, hazardous activities, and damage to the Earth's surface. One of the most significant and impactful consequences of excessive groundwater extraction is land subsidence. During a comprehensive literature review focusing on land displacement, 40 research papers were analyzed and discussed. These studies explored various techniques employed to monitor subsidence, such as synthetic aperture radar (SAR), interferometry synthetic aperture radar (InSAR), persistent scatterer interferometry synthetic aperture radar (PS-InSAR), and differential synthetic aperture radar (D-InSAR). Researchers have consistently found a strong correlation between the over extraction of underground fluids, such as water, oil, and gas, and land subsidence. One prominent cause of land subsidence identified by researchers is the over extraction of underground fluids. When excessive amounts of water, oil, or gas are extracted from underground reservoirs, the resulting voids and reduced pressure cause the overlying land to sink and compact. This process can have severe consequences for human settlements, infrastructure, and ecosystems in affected areas. The depletion of groundwater reserves, in particular, has become a pressing concern because of its vital role in supporting agricultural, industrial, and domestic water needs.Furthermore, the underground construction of tunnels has also been identified as a significant contributor to land subsidence. The excavation of tunnels creates voids and alters the natural balance of underground structures, leading to ground settlement and subsidence. This issue is particularly relevant in urban areas where extensive tunneling projects are undertaken to facilitate transportation, utilities, and infrastructure development. To monitor and assess land subsidence, various methods and processes are employed. SAR, InSAR, PS-InSAR, and D-InSAR techniques are valuable tools in this regard. SAR uses satellite-based radar systems to capture high-resolution images of the Earth's surface, enabling the detection of subtle changes over time. In contrast, InSAR employs two or more radar images to measure ground deformation by analyzing interference patterns. PS-InSAR focuses on persistent scatterers, which are specific targets that exhibit stable radar reflections over time, providing precise measurements of subsidence. D-InSAR combines two radar images acquired at different times to accurately calculate differential ground movements. By using advanced monitoring methods, scientists can assess the extent of subsidence and develop strategies to mitigate its negative impacts. It is crucial to adopt sustainable practices and ensure careful management of groundwater resources to effectively address this pressing issue.

Gas buffering of magma chamber contraction during persistent explosive activity at Mt. Etna volcano

A sequence of more than 20 short-lasting explosive eruptions took place at Mt. Etna volcano, during a 2-month period in 2021. Here we perform a joint analysis of the gravity decrease and ground deflation that accompanied the sequence of eruptions. Results from this joint analysis are cross-checked against the output of a numerical code providing independent geochemical insight on how the density of the magmatic liquid/gas mixture in the source reservoir varies as a function of the pressure. This cross-analysis provides a framework to explain why (i) the bulk volume reduction sensed by the ground deformation data is much lower than the volume of the erupted products and (ii) the observed gravity changes point to a strong mass decrease, incompatible with a pure mechanism of magma withdrawal. We conclude that pressure-driven gas exsolution and expansion compensated the withdrawal of magma, thus buffering the contraction of the source reservoir and leading to the inferred mass decrease.

Behavior of an anchored sheet pile quay in soft clay reinforced by various structural types of cemented soil

In this research, the potential benefits of using various structural types of cemented soil, including block-type, column-type, and wall-type, to reinforce the active zone behind a quay wall were investigated by experimental and numerical methods. The response of the quay wall and ground was analysed from aspects of soil movement, quay wall displacement, lateral earth pressure, and bending moment, and a close agreement between the experimental and numerical results was observed. Experimental and numerical results showed that the cemented soil effectively prevented potential deep soil sliding, and then lateral displacement of the quay wall and ground deformation was reduced. Among various structural patterns, the case with the block-type cemented soil exhibited smaller lateral earth pressure on the quay wall, while the case with the wall-type cemented soil more effectively reduced the bending moments and lateral displacements of the quay wall; therefore, wall-type cemented soil seems to be more favourable considering their improved performance under the same load intensities and excavation depth. This research provides a hint and guideline for the preliminary design of cemented soil-stabilised sheet pile quay structures in soft clay based on the lateral load-reduction effect of the varying structural types of the cemented soil.

Sensitivity of granular pile dimension parameters to deformation response of soft ground under building load

Granular pile is one of the proven soil improvement mechanisms applied especially for reinforcement of compressible soils supporting light structures. The improvement performance of granular piles is influenced by various factors including the dimension parameters (length, spacing and diameter of the piles). The influence of these three dimension parameters on deformation response of reinforced weak soil has widely been reported. However, the most influential parameter affecting deformation of the weak soil has not been clearly identified. Apparently, these dimension parameters do not equally influence the performance of stone columns in lessening soil deformation. Hence, comparative analysis was carried out in the current study to find out the dimension parameter to which deformation of stone column reinforced weak ground is most sensitive. Finite element based parametric numerical analysis was conducted to simulate the weak ground reinforced with a group of granular piles supporting light weight building. For the parametric study, five dimensions for each parameter (diameter, spacing and length) were considered. The dimensions were purposely varied by uniform percentage increase. Field settlement monitoring data was used to track deformation response of the site and validate the finite element results. The numerical analysis reveals that the simulation results have good agreement with the field settlement monitoring data. From sensitivity view point, column spacing was found to be the most controlling and influential parameter affecting deformation of the reinforced weak soil. Similarly, column length is the dimension parameter to which ground deformation is least sensitive.

Numerical Study on the Responses of Suction Pile Foundations under Horizontal Cyclic Loading Considering the Soil Stiffness Degradation

This paper analyzes the deformation responses of single-cylinder and four-cylinder suction pile foundations in soft clay under horizontal cyclic loading. Based on the existing stiffness degradation model of soft clay, a more suitable model for marine soft clay is proposed by carrying out dynamic triaxial experiments under different stress levels. The stiffness degradation and cumulative displacement of soil under cyclic loading are implemented in ABAQUS by compiling a USDFLD subroutine. The rationality is verified by comparison with the displacement response of the pile measured by the centrifugal model test and the scaled model test reported in the literature. With the aid of the current model, the stress state and deformation of suction pile foundations under horizontal cyclic load are further analyzed. The numerical results reveal the path of soil stiffness degradation and the deformation response of foundations during horizontal cycling. The cumulative displacement generated by the cyclic load is quantitatively displayed. It is proved that this model has the capability to reflect the cumulative displacement under cyclic loading and shows promise in analyzing the long-term deformation response of offshore foundations.

Impact assessment of unsustainable airport development in the Himalayas using remote sensing: A case study of Pakyong Airport, Sikkim, India

Ground deformation is a widespread phenomenon that accelerates due to anthropogenic land development. Thus reclaimed/created land is more vulnerable to deformation and subsidence, especially in mountain areas. Advanced Differential Synthetic Aperture Radar Interferometry (A-DInSAR) can be used to monitor such projects. The Pakyong Airport is an engineering feat, constructed by cutting a mountain and converting it into a tabletop in a landslide-prone zone and seismically active region of the Sikkim Himalayas. The cutting of hill slopes for airport construction and other anthropogenic activities has increased slope instability in the region. This paper studies the slow-moving landslides in the airport neighbourhood using A-DInSAR on Sentinel-1 time series data consisting of 64 images of ascending track and 82 images of the descending track. The time period of monitoring was from October 2014 to April 2018 (43 months). The images have been connected using the Minimum Spanning Tree graph for interferogram generation for estimating deformation. The atmospheric noise was removed, and the results enabled the identification of deformation (in line-of-sight) on the airstrip as well as in the neighbouring area, both the upslope and downslope of the airport. The deformation rates estimated were up to ±90 mm/year in Pakyong from both tracks. We could successfully capture such land movement associated with the Pakyong Airport construction and help assess the impacts of infrastructure construction on the slope stability of the area. The controlling factors such as precipitation, seismicity, geology and others were analysed with respect to the deformation obtained. This study helps in assessing the land deformation after construction (cutting and filling of the slope) in the area. The deformation detected in this study needs to be addressed for the safety of the residents as well as for the infrastructure present in the area.

Seismic Response Comparisons of Prefabricated and Cast In Situ Subway Station Structures in Liquefiable Site

Based on the engineering practice of the first prefabricated subway station (Shuangfeng Station) in Changchun, China, the applicability of prefabricated subway station structures (PSSSs) in liquefiable sites in seismically defended areas is investigated. In this paper, the finite difference software FLAC3D 5.0 is used to carry out the seismic response analysis of the PSSS in liquefiable ground, and the calculation results of the PSSS are compared with those of the same type of cast-in-place subway station condition. The results show that the trend of foundation excess pore pressure ratio (EPPR) in the PSSS condition is similar to that of the cast-in-place condition. For different ground vibration inputs, there is not much difference between the PSSS and the cast-in-place structure on the pore pressure (PP) of the surrounding liquefiable soil. The acceleration response of the PSSS is slightly smaller than that of the cast-in-place structure, and it has a better ability to adapt to ground deformation. The deformation of the upper part of the PSSS is slightly larger than that of the lower part, which is an important part of its deformation control, and the middle part is the key part of its strength control due to the presence of the center plate, which results in a significant increase in stiffness and stress. The flexible connection of the PSSS is easier to adapt to a larger vertical deformation than rigid connection, and its ability to resist overturning is better. Under the premise of ensuring static waterproofing, the PSSS can be constructed in liquefiable sites in earthquake-proof areas.

Ground-motion effects on liquefaction response

This article evaluates the influence of ground-motion characteristics on the liquefaction response of free-field level-ground deposits. Ground motions imposed on liquefiable soils have historically been characterized by the peak ground acceleration (PGA). In simplified procedures for liquefaction evaluation, the use of the ground surface PGA can be justified by the fact that it is closely related to the peak shear stresses developing in the critical zone for liquefaction manifestation, at shallow depths. In nonlinear dynamic analysis (NDA), however, such simplified characterization of the input motion using the bedrock-level PGA can result in large record-to-record variability in the computed response. Record-to-record variability can be substantially reduced by employing more appropriate ground-motion intensity measures (IMs) for specific aspects of the liquefaction response observed in NDA. Among 25 IMs examined in this study, the Modified Acceleration Spectrum Intensity (MASI), defined as the integral of the acceleration spectrum over periods 0.1–1.5 s, is found to be the most efficient IM for the prediction of the pore-pressure response of liquefiable deposits, whereas Velocity Spectrum Intensity (VSI) ranks among the best-performing IMs for response parameters related to ground deformations. Importantly, such “multiple-period spectrum IMs” are shown to perform consistently better than several highly-regarded time-integrated IMs (e.g. Arias intensity, CAV). Conclusions and recommendations are drawn on the basis of a comprehensive series of NDAs involving 180 input motions and 13 deposit models based on characteristic soil profiles from Christchurch.

Transient ground bulge derived from a dense broadband seismic array during an aquifer step-drawdown pumping test

We deployed nine broadband seismometers within 32 m of a well where a four-hour step-drawdown pumping test was conducted at a site near Shuangxi, Taiwan in August 2018. The whole seismic array simultaneously recorded hour-long seismic signals that we interpret as ground tilt evolution during and after the pumping. Here we document data from the six seismic stations within 10 m of the boreholes to show the ground deformation closest to the pump site. Instead of ground subsidence due to groundwater over-draw as documented in many long-term and even short-term GPS and tiltmeter studies, four out of the six seismometers show ground bulge at the pumping site with radial directional tilts up to 1.0 × 10-5 rad for a drawdown of 10 m. We interpret the bulge as the dominant transient crustal response to the unloading of discharged groundwater, outpacing the minor subsidence due to reduced effective stress from reduced pore fluid head. After the pumping stopped, the ground tilt signals started to level back, though not simultaneously: some signals recorded delays up to an hour, possibly related to replenishment of groundwater from far-field or different aquifers and shallow depth hydrological heterogeneity including minor faults and fractures. We conducted seismic reflection surveys and found mostly layered structures without large fault offsets. Using an analytical solution that calculates the ground tilt due to surface load changes, we calculated the effects of unloading on ground deformation. The predicted tilt signals are in the range of 10-5 rad, the same order as the seismically derived tilts from this study. For 10 m of drawdown we estimate 10-5 to10-4 m of vertical ground uplift for this particular site. Our study demonstrates that dense broadband seismic arrays may offer a relatively less expensive and non-invasive tool to study temporal and spatial evolution of ground motions, and thus the ground water flow patterns, during pumping tests.