characterization of land subsidence induced by groundwater withdrawals in su xi chang area china su xi chang area is one of the typical regions in china which suffers from severe land subsidence various tools of field monitoring were integrated to study the characteristics and mechanisms of land subsidence in this region the occurrence and the development of the land subsidence in this region are strongly related to the groundwater pumping both in time and space the main consolidation layers are the soft mud layers however the compressibility of the confined sandy layers should not be ignored the second and third confined aquifers contributed more than 30 of total subsidence meanwhile irrecoverable deformations were also observed in the sandy layers different sandy layers deform diversely under different stress conditions some have the elastic feature but the soil strata including both sandy layers and clayey layers located in the center of the groundwater level depression cone exhibited obvious viscous mechanical behavior which caused the common lag phenomenon the sand composition mingled with small clay particles or interbeds and sand rheology are the two main reasons for the lag phenomena in sandy layers a series of laboratory tests for modeling the effective stress changes due to groundwater withdrawals were conducted to investigate the mechanism of the lag phenomenon based on the test results the relationship of stress strain time for saturated sands is obtained and it could be expressed as power functions the results also showed that the compression of the sandy layers was time dependent and its deformation could be remarkable when establishing land subsidence model the deformation for the similar soil formation could be elastic visco elastic and even visco elastic plastic because of the different groundwater level fluctuation experienced

a coupled one dimensional viscoelastic plastic model for aquitard consolidation caused by hydraulic head variations in aquifers accurate and practical calculation of aquitard consolidation is required for a reliable analysis of land subsidence caused by groundwater overexploitation in a multilayered aquifer system because aquitards are generally more compressible than aquifers are this study proposes a coupled one dimensional viscoelastic plastic consolidation model that considers the combined effect of changes in soil parameters and body force to simulate aquitard consolidation caused by hydraulic head variations in neighbouring aquifers the proposed model uses variable total stress and simultaneously solves hydraulic head and vertical soil displacement the constitutive relation based on the voigt model with different elastic moduli of the spring in normally consolidated and overconsolidated soils is used to describe the viscoelastic plastic deformation mechanism of aquitards in addition the proposed model considers the combined effect of variations in hydraulic conductivity elastic moduli and body force on the calculation of aquitard consolidation three hypothetical scenarios with various hydraulic head variations in aquifers are used to examine the coupled one dimensional viscoelastic plastic consolidation model the results show that neglecting plasticity and viscosity of soil causes aquitard consolidation to be respectively underestimated and overestimated in addition ignoring body force variation underestimates aquitard consolidation whereas neglecting soil parameters variation overestimates aquitard consolidation two real case scenarios are also studied to further demonstrate the applicability of the coupled one dimensional viscoelastic plastic consolidation model copyright 2015 john wiley sons ltd

model test on partial expansion in stratified subsidence during foundation pit dewatering abstract 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

numerical evaluation of land subsidence induced by groundwater pumping in shanghai to predict the future behavior of land subsidence in shanghai due to pumping of groundwater a numerical model is established in the proposed model groundwater flow in three dimensional conditions and soil deformation in one dimen sional conditions are calculated the model takes into account the multi aquifer aquitard hydrogeological condition of the soft deposit of shanghai the variation of the coefficient of compressibility and coefficient of hydraulic conductivity of the soils with the consolidation process are simulated relationships among land subsidence groundwater withdrawal volume and groundwater level are analyzed comparison between the measured value and calculated value shows that the model simulates the measured value fairly well the future of land subsidence behavior due to groundwater withdrawal is predicted and discussed via consideration of the variation of the following parameters in the future 30 years net withdrawn volume of groundwater pumping layer and pumping region resume un modele numerique est propose afin de predire le comportement futur d un affaissement de sol cause par le pompage de l eau souterraine a shanghai dans le modele propose l ecoulement de l eau souterraine en trois dimensions et la deformation du sol en une dimension sont calcules le modele considere la condition hydrogeologique multi aquifere aquitard du depot mou de shanghai les variations du coefficient de compressibilite et du coefficient de conductivite hy draulique des sols lors du processus de consolidation sont simulees les relations entre l affaissement du sol le volume de retrait de l eau souterraine et le niveau phreatique sont analysees des comparaisons entre les valeurs mesurees et calculees montrent que le modele peut simuler les valeurs mesurees relativement bien le comportement futur du sol en affaissement cause par le retrait de l eau souterraine est predit et discute en considerant les variations pour les prochains 30 ans pour les parametres suivants le volume net d eau souterraine retire la couche de pompage et la region de pompage mots cles pompage de l eau souterraine affaissement du sol ecoulement de l eau souterraine en trois dimensions consoli dation en une dimension prediction traduit par la redaction

regional land subsidence simulation in su xi chang area and shanghai city china su xi chang area and shanghai city located in the south of yangtze delta china has subsided due to groundwater overpumping because of the regional scale of the groundwater exploitation cone of depression and land subsidence at present su xi chang area and shanghai city are treated as a single area for land subsidence study to avoid the uncertainty of boundary condition due to the regionalism the characteristics of aquifer system compaction are complex because of the difference in the types compositions and structures of the soils that the hydrostratigraphic units are composed of and in the histories of groundwater level change the hydrostratigraphic units have experienced considering the fact that different hydrostratigraphic units have different kinds of deformation and that an identical unit may also present different deformation characteristics such as elasticity elasto plasticity and visco elasto plasticity at different sites of the cone of depression or in different periods corresponding constitutive laws have been adopted this avoids the shortcomings of the previous research that the same constitutive law was adopted in all the hydrostratigraphic units during the entire time period a coupled flow and subsidence model which includes a three dimensional flow model with variable coefficients and a one dimensional vertical subsidence model is built according to the complicated hydrological condition in the region the simulation model is calibrated using observed data which include compression of individual strata from groups of extensometers and groundwater levels from observation wells from 1995 to 2002 the model reproduced that the primary subsidence layer in shanghai shifts from the shallow aquitard to the fourth confined aquifer because of the groundwater yield variations and the change of exploitation aquifers however the third aquitard was the primary subsidence layer in su xi chang area and the compaction deformation of the sandy aquifers was remarkable the simulation results could provide some reasonable advice about groundwater exploitation in the future

monitoring of vertical deformation response to water draining recharging conditions using bofda based distributed optical fiber sensors land subsidence is a geological disaster which has a variety of inducements this paper presents the results on the investigation of the soil deformation in land subsidence with a combination of laboratory and field experiments using the distributed fiber optics sensing dfos technology the laboratory experiment was mainly carried out to study the soil deformation in draining recharging cycles based on brillouin optical frequency domain analysis bofda in the field experiment the bofda technology and some grating sensors were applied in a borehole in the yangtze river delta region to monitor the pore pressure in certain specific strata and the change in strata parameter of the full borehole with the data that monitored 2 years the result of the laboratory experiment demonstrated that the soil structures changed in the draining recharging cycles the soil gradually tends toward elastic deformation the field experiment results show that the main deformation occurs at the aquitards adjacent to the pumping aquifer the compression amount in the vertical distribution is not uniform which is related to the distance from the pumping aquifer and the soil properties the compressive deformation of each layer is closely related to the change in groundwater level the result proposes that the bofda technology is suitable for monitoring land subsidence caused by seasonal water level fluctuations and dewatering projects it is also of great significance to investigate land subsidence mechanisms

upward recharge through groundwater depression cone in piedmont plain of north china plain summary whether a recharge was induced by groundwater depression cones is a crucial issue for water resource management in the north china plain shallow groundwater had been over pumped since 1970s and many groundwater depression cones formed the groundwater depression cone daceying machang occurred even in the piedmont plain in the area water levels of deep and shallow groundwater were observed since 2005 and field survey was conducted in the dry season 2010 the upward recharge induced by the depression cone is verified based on water level records major ions 2 h 18 o and kinds of statistical analyses since august 2006 the water level of the deep groundwater ascended by 1 9 mm d high correlations r 0 86 s 0 67 between the water level series of shallow and deep groundwater were found by two distinct correlation analyses only in the center of depression cone further the reversion of hydraulic gradient of the depression cone occurred in dry seasons since september 2008 hydro geochemical features of the shallow groundwater are consistent with deep groundwater in the center of depression cone which was demonstrated by the fuzzy c means clustering based on principal components and paired t test respectively it is concluded that the deep groundwater recharged the shallow groundwater from the center of the depression cone as a result the groundwater mixture occurred that improves the quality of the shallow groundwater seasonally changed flow of shallow groundwater enhanced the mixture the persistent overpumping of shallow groundwater and the large elevation difference around 1200 m between the recharge zone and the discharge point of deep groundwater facilitate the upward recharge

investigation of land subsidence with the combination of distributed fiber optic sensing techniques and microstructure analysis of soils abstract land subsidence is a global phenomenon caused by a variety of factors and there are still many challenges in land subsidence monitoring the results of an investigation of land subsidence using the combination of distributed fiber optic sensing dfos techniques and microstructure analysis of soil are here presented two dfos techniques brillouin optical time domain reflectometry botdr and fiber bragg grating fbg were developed in two boreholes namely gm03 and sz01 in su xi chang area china to monitor movement of strata crossed by the borehole and pore pressure in some specific strata scanning electron microscope sem and mercury intrusion porosimetry mip were employed to quantify and characterize the microstructures of undisturbed soils from the boreholes based on the botdr monitoring results the annual levels of land subsidence in gm03 and sz01 are 1 2 mm and 2 9 mm respectively and the movement history of strata were clearly tracked for both boreholes the main contributors to subsidence are two aquitards ad2 and ad3 that exist adjacent to the second aquifer af2 the results obtained by fbg based sensors indicate good agreement with botdr and it confirms that the deformation of aquifer is significantly controlled by pore pressure sem images were analyzed with pore particle and crack analysis system pcas three statistical parameters including average form factor ffavg fractal dimension df and area probability distribution index b were used to describe the geometric characteristics of pores it is found that larger average form factor larger fractal dimension and higher proportion of large pores in soil microstructures favors land subsidence mip results confirm that area probability distribution index can be used for the estimation of strata compression potential in land subsidence investigations

a new type curve method for estimating aquitard hydraulic parameters in a multi layered aquifer system summary we propose a new type curve method for estimating the hydraulic conductivity k and the specific storage s s of an aquitard in a multi layered aquifer system theoretical type curves of rate of aquitard compaction versus time are obtained through drawdown time series in the aquitard under a condition that the drawdown history of the underlying aquifer can be approximated as piecewise linear segments pls in each of which the drawdown shows a linear increase trend with time comparing with previous analytical solutions which are limited by the assumption of a constant head in the overlying unconfined aquifer the superposition principle can be called when water levels fluctuate with time in both upper and lower aquifers adjacent to the aquitard when applying the new pls method to estimate k and s s values of an aquitard the starting point of drawdown history at adjacent aquifers should be determined at first after that the drawdown history is approximated as pls to obtain drawdown rate of change for each linear stage and turning points of drawdown history the new pls method is demonstrated at a field site in changzhou city jiangsu province of china estimated results show that k and s s are respectively 9 80 10 10 m s and 4 46 10 4 m 1 for a thick aquitard and 2 34 3 50 10 10 m s and 2 28 10 4 m 1 for a thin aquitard estimated field k values as well as s s values through the new pls method are generally in accordance with the results obtained from the geologic method by konikow and neuzil 2007 they are also in agreements with the numerically calibrated results of shi et al 2008a at the regional scale and the laboratory experimental values of in situ soil samples collected by geological survey of jiangsu province of china

contaminant transport in a small deformation aquitard affected by the delayed drainage phenomenon this paper presents a formulation accounting for the effect of delayed drainage phenomenon ddp on the breakthrough of contaminant flux in an aquitard by considering the movement of soil particles porosity variation hydraulic head variation and transient flow during the consolidation the water flow equation in an aquitard was based on the terzaghi s consolidation theory and the contaminant transport equation was derived on the basis of the mass balance law two cases were used to illustrate the effect of ddp on the contaminant transport in an aquitard of small deformation it is found that the breakthrough time of contaminant in an aquitard is very long which is mainly ascribed to the low permeability of aquitard and sorption of soil particles it is also found that the increase of depletion which is in general induced by the increase of thickness and specific storativity and the decrease of hydraulic conductivity enhance the impact of ddp on the contaminant transport in an aquitard a larger delay index 0 of ddp gives a greater delay breakthrough time dbt of solute transport in an aquitard which controls the difference of the breakthrough time of contaminant transport in aquitards with and without the occurrence of ddp for the cases where advection plays a dominant role during the process of solute transport 0 is almost linearly correlated with dbt and the ratio of dbt over the breakthrough time without consideration of ddp also approximately shows a linear relationship with the ratio of specific storativity to porosity given a fixed drawdown in the adjacent aquifer with the sorption being ignored

delimitation of ground failure zones due to land subsidence using gravity data and finite element modeling in the queretaro valley mexico abstract sedimentary basins of arid and semiarid zones are often subject to regimes of intense ground water withdrawal as it is normally the only source of water for development of communities an associated phenomenon is land subsidence which can develop to ground failures and consequently damage to infrastructure aquifer deformation can be analyzed using a stress strain or a flux force approach depending on the aquifer material compact or loose and on whether the water withdrawal forms a predominant flow direction toward a cone of depression geometry of the aquifer system also plays an important role as uneven thickness induces differential compaction and hence tensional and shear stresses on the ground mass in this work we present a stress strain approach to analyze subsidence for an unconfined aquifer of varying thickness this is done in two steps namely when the aquifer is in equilibrium and when it is totally depleted using this scheme in a region where ground failure is evident a portion of the aquifer system of the queretaro valley is analyzed the geometry of the hydrologic basement is first modeled using gravity measurements properly correlated with wells and field data then a stress analysis is implemented using the finite element method in order to identify probable zones of ground weakness which are calibrated with known ground failures the results indicate that both tensional and shear stress are present which induce ground failure in the form of surface faults

hydraulic causes for basin hydrograph skewness it has been suggested that hydrograph skewness depends on the relative dominance between hillslope and channel network transport processes where the former ones make the hydrograph positively skewed while the latter tends to make it negatively skewed more recently however the role of river hydraulics in shaping the hydrograph has been highlighted we present a set of numerical modelling experiments using a hydrodynamic model of river networks in which we investigate how channel hydraulics influence the shape of the hydrograph particularly its skewness we further investigate the influence of baseflow rainfall intensity cross section geometry and basin scale on unit hydrograph response we show that river hydraulics has a decisive role because positively skewed hydrographs may occur even when water inputs to the river network are negatively skewed and in catchments whose width function is also negatively skewed we show additional results related to the effect of the degree of non linearity in the relationship between celerity and discharge the effects of baseflow and rainfall intensity these further confirm that hydraulic factors may be decisive in determining hydrograph shape

experimental study on the vertical deformation of sand caused by cyclic withdrawal and recharging of groundwater fast urban growth and an ever increasing frequency of extreme weather related events demand a better understanding of land subsidence and the potential measures to control it this paper presents an experimental investigation on the deformation behavior of sand undergoing cyclic withdrawal and recharging of groundwater a sand box model with dimensions 1000 mm 600 mm 892 mm was used to investigate soil deformation following lowering and rising of the water table the sand used was pingtan sand fujian china a quartzitic formation composed of elongated to slightly spherical grains three sand samples with different initial densities i e loose medium dense and dense were tested on repeated cycles the vertical deformation of the sand was measured and the corresponding strain and effective stress were calculated the observations show that initially the sand behaves as an elastic material with the subsidence caused by water withdrawal being recovered as the soil rebounds during recharging with further withdrawal recharging cycles subsidence becomes larger as plastic deformations as well as time dependent deformation occur in the soil the distinct patterns of deformation were identified to be dependent on both the initial density and the number of withdrawal recharging cycle the sand has been subjected to the different behavior of the medium dense sample compared to the loose and dense samples in particular for the first two cycles indicates that the soil response cannot be explained in respect of the initial void ratio alone and further microstructure considerations were discussed it is suggested that the orientation of the grains resulting from the sample preparation technique and the consequent induced anisotropy can be used to explain the results herein presented finally this paper provides the rationale for a micromechanical interpretation of soil deformation when subjected to changes in stress due to rising or lowering of the water table which will help in establishing measures to control land subsidence in particular to assess the efficiency of water recharging following subsidence by withdrawal

centrifuge modeling of land subsidence caused by the high rise building group in the soft soil area with the increase of the high rise buildings land subsidence induced by human activities becomes a major problem land subsidence occurs slowly but the accumulation results in the cracks in the road the damage to the pipelines and in the tilting or the cracking of the buildings with the withdrawal of groundwater controlled reasonably the engineering environmental effect of the dense high rise building group comes to be the main cause of land subsidence based on the high rise building group in the soft soil area in shanghai the mechanism of land subsidence is studied in this paper by the centrifuge model tests the central area of the building group has larger subsidence and the subsidence superimposition effect is obvious it can exceed the allowance and cause land subsidence hazard the land subsidence affected by the different building distances is also studied for smaller building distances the subsidence superimposition effect is more obvious the larger excess pore water pressure in the pile base supporting layer of the central area shows that the stress superimposition effect is larger the earth pressure under the buildings fluctuates by the disturbance of the pile tips

mathematical simulation of the subsidence of ravenna land subsidence at ravenna is the result of aquitard and reservoir compaction caused respectively by extensive groundwater withdrawals from the unconsolidated quaternary basin and gas production from a number of pre quaternary pools scattered over the area water pumpage paralleled the postwar industrial development of ravenna until the middle seventies when consumption was drastically curtailed owing to the economic crisis and the activation of a new aqueduct gas production started in 1952 the exploitation of several reservoirs is currently under way and the search for new fields is still in progress geodetic records indicate that the maximum cumulative subsidence over the period 1950 1986 including a natural geologic settlement of perhaps 2 mm yr has been 1 30 m in the industrial zone of ravenna in 1980 the municipality promoted a reconnaissance study with the primary aim of providing the information base needed to reconstruct the actual occurrence understand correctly the physical behavior and produce the essential input data to a mathematical model which realistically relates the subsidence of the city to groundwater withdrawal and gas removal with an emphasis on their respective influences the results from the three dimensional numerical simulations performed with the aid of mixed finite element finite difference and integral models show that the primary responsibility for the regional land sinking should be placed on the subsurface water overdraft which occurred until the middle 1970s gas withdrawal plays a role restricted to the area overlying each reservoir with a magnitude depending on the depth of burial thickness of mineralized rocks and overall volumetric production a major environmental impact may be expected where the gas subsidence bowl is intersected by the adriatic coastline

hydro geotechnical modelling of subsidence in the como urban area abstract the urban area of como italy is particularly susceptible to subsidence the reason is the particular structure of the subsoil combined with the anthropic modification of the lakeshore lands linked to the historical evolution of the area moreover this phenomenon exposes the lakefront areas to an increasing risk of flooding the primary purpose of this study was to develop an effective methodology for the assessment of subsidence in urban areas to be used as a support in groundwater management the development of a coupled hydrogeological geotechnical numerical model for the period 2004 2011 allowed recognizing the shoreline results as most susceptible areas to the phenomenon model results were critically evaluated through comparison with time series of psinsar and high precision levelling data available in the area the anthropic perturbations of groundwater flow linked to the construction of lake flooding defenses in 2008 2009 enhanced the subsidence phenomenon in a localized area pointing out the strong inter dependence of groundwater circulation lake level oscillations and geotechnical behavior of soils thus the model revealed the most critical zones and geotechnical units demonstrating to be a potential powerful tool to predict subsidence scenarios e g the future completion of the floods defense works in the shoreline area

hydraulic response of highly compressible aquitards during consolidation the transient hydraulic behavior of highly compressible aquitards is investigated through numerical analysis and field studies variations in the hydraulic parameters of an aquitard during consolidation are accounted for by incorporating empirical relationships derived from standard consolidation tests into the one dimensional flow equation the resulting equation is highly nonlinear the hydraulic response of an aquitard with physical properties typical of the compressible clays of mexico city is evaluated with both standard linear analysis and with a nonlinear approach where the hydraulic parameters are stress dependent the results indicate that decreases in the hydraulic diffusivity of the aquitard due to consolidation lead to diminished leakage flux slower groundwater velocities and solute transport rates longer transient response periods and less land subsidence than would be predicted by classical linear theory evaluation of field data from a site near mexico city indicates that significant interpretive errors may arise if the stress dependence of the hydraulic parameters is ignored in these types of systems

distribution and generative mechanisms of ground fissures in china abstract in this study 5002 ground fissures in more than 1500 localities across 22 provinces in china are investigated and mapped to reveal their spatial distribution the distribution of these ground fissures in china exhibits six regular patterns assemblages in north china syngenesis in extensional basins clustering along fault zones distributing along geomorphic boundaries developed on the edge of subsidence areas and clustering in large and medium sized cities combined with regional gps numerical simulations physical model test and in sar monitoring the generative processes of ground fissures are analyzed and discussed in relationship to four mechanisms 1 deep dynamic tectonism controls on the location of ground fissures 2 intracontinental dynamic tectonism resulting in ground fissure assemblages 3 fault stress inducing formation of ground fissures and 4 groundwater overmining resulting in the reactivation and expansion of ground fissures the geological environment is thus responsible for the establishment and appearance of ground fissure more importantly ground fissure propagation in china is the result of the synergistic effects of internal geological dynamic including in deep tectonism intracontinental tectoniim and fault movement coupled with anthropomorphic stress this genetic model can be summarized as one that is tectonically controlled stress driven and affected by regional hydrodynamic

land subsidence by groundwater over exploitation from aquifers in tectonic valleys of central mexico a review abstract structurally controlled differential subsidence scds is the gradual sinking of the ground characterized by the development of a damage band terrain discontinuities and collapses aligned according to the strike of a controlling geological structure scds has been reported since the 1980s in several cities settled on tectonic valleys in central mexico although groundwater abstraction is the main trigger recent research efforts also point out a tectonic component as a driving force the monitoring and quantification of scds has been done through a variety of techniques such as extensometry gps and insar furthermore the associated hazards endangering the population are floods aquifer pollution cracking and housing collapse this paper presents a comprehensive review of the current state of scds allowing for the first time the standardization of its definition mechanisms and triggering factors additionally this helps to avoid misinterpretation in the cases of sinking produced by the mexico city subsidence type mcst and thus provides the elements for proper methodological study of scds finally the review includes future research directions that need to be improved in order to reduce the impact of the phenomenon

the effects of artificial recharge of groundwater on controlling land subsidence and its influence on groundwater quality and aquifer energy storage in shanghai china long term groundwater overpumping in shanghai has caused serious land subsidence to restore the declined piezometric groundwater levels and to decrease the land subsidence rate artificial recharge ar of groundwater into confined aquifers through injected wells has been proposed as an important measurement since the beginning of the 1960s in the case of shanghai recharge source is tap water whose chemical constituents and temperature are different from groundwater consequently the issues of groundwater quality change and thermal energy are worthy of discussion in this paper we discussed the influences of ar for controlling land subsidence on 1 groundwater level and land subsidence rate 2 groundwater quality 3 aquifer thermal energy storage the results based on the collected long term historical data in the study area show that ar not only is beneficial to groundwater level rising and land rebound but also provides cheap energy sources for industrial production the groundwater quality presented the trend of desalination and a general increase in sulfate iron and manganese contents organic and nitrogenous compounds after the tap water injection however the ar s influence on groundwater quality was limited with the radius 100 m for single well recharge and 1000 m for well groups recharge to control the development of the land subsidence within a safe limit in the study area the injected confined aquifers and the distribution of the ar wells need to be further adjusted due to the limitation of current ar

evaluation of the effectiveness of an alternative to control groundwater inflow during a deep excavation into confined aquifers this paper presents a case study of groundwater control for a deep excavation into confined aquifers in fuzhou china field pumping tests were first carried out prior to the excavation to investigate the groundwater conditions at the site and as well as to evaluate the feasibility of previous designed dewatering systems 34 m diaphragm walls together with pumping wells the results showed that under the condition of previous dewatering systems it would have been extremely difficult to safely lower the water level inside the excavation a co working scenario of partially penetrating curtains and horizontal waterproof curtain with jet grouting was then proposed to control groundwater inflows additional water tightness assessment tests wat were then performed that allowed to confirm the efficiency of the proposed method from the feedbacks of wat this proposed scenario not only successfully lowered the water lever inside the excavation below the excavation bottom maximum drawdown up to 14 9 m but also it minimized the drawdown outside the excavation less than 0 2 m furthermore an approach was proposed to approximately estimate the hydraulic conductivity of the jet grouting at the real site from the result of wat the hydraulic conductivity of jet grouted soil is three orders of magnitude lower than that of the original sediments

characteristics of aquifer system deformation in the southern yangtse delta china excessive groundwater pumpage has caused regional cones of depression and severe land subsidence in the southern yangtse delta china the characteristics of aquifer system compaction are complex because of the difference in the types compositions and structures of the soils that the hydrostratigraphic units are composed of and in the histories of groundwater level change the hydrostratigraphic units have experienced based on the data measured from extensometer groups and observation wells the characteristics of deformation for individual hydrostratigraphic units are analyzed the results show that different hydrostratigraphic units have different kinds of deformation and that an identical unit may also present different deformation characteristics such as elasticity elasto plasticity and visco elasto plasticity at different sites of the cone of depression or in different periods if the groundwater level rises continuously and remains constant later the aquifers and the aquitard units that consist of hard clay primarily exhibit elastic behaviour but the aquitard units that consist of soft clay deform plastically and by creep and exhibit visco elasto plastic behaviour if the groundwater level falls but is much higher than the previous lowest value aquifers and aquitards consisting of hard clay exhibit elasto plastic behaviour if the groundwater level falls below the previous lowest value aquifers and aquitards consisting of hard clay deform plastically and by creep and exhibit visco elasto plastic behaviour

processes governing natural land subsidence in the shallow coastal aquifer of the ravenna coast italy abstract we identified the processes governing natural land subsidence in a shallow coastal aquifer near ravenna north eastern italy by analysing the relationships among different data set time series water table level rainfall drainage sea level etc and establishing the correlations with vertical ground motion observed at a high resolution settlement gauge for the first time we establish the relationships between water table fluctuations and vertical displacement in a real field dataset as well as demonstrate the important contribution of primary consolidation and aquifer stratigraphy to natural land subsidence our study highlights the presence of three deformation components related to different processes controlling land subsidence elastic delayed elastic and irreversible plastic components the elastic and delayed elastic components are closely related to water table fluctuations that change the effective stress in two portions of the coastal aquifer at a daily in the sandy unconfined portion and seasonal time scales in the finely layered clay rich semiconfined prodelta portion respectively the irreversible component represents the trend in the land subsidence time series and is due to primary consolidation pore water pressure dissipation of the fine grained prodelta levels above where the settlement gauge is located the amplitudes of the elastic component can be up to 0 2 0 3 mm whereas the amplitude of the delayed elastic component reaches 0 89 mm the primary consolidation rate of deformation is 0 9 mm year and constrains the likely age of prodelta sediments deposition to 1300 2800 years before present the average degree of consolidation for the prodelta sediments varies from 0 8 to 0 99 according to consolidation coefficients varying from 1 58 to 3 15 m2 year which are accepted values in the literature our analysis point out that primary consolidation in the shallow fine grained sediments of the shallow coastal aquifer is still ongoing the delayed elastic land subsidence rate has similar magnitude to that due to primary consolidation and is likely connected to poroelastic effects in the prodelta sequence following seasonal variations in water table our findings are important for planning land subsidence management and monitoring strategies especially where the surface aquifer structure is heterogeneous due to different depositional settings

a numerical model to calculate land subsidence applied at hangu in china abstract the deep unconsolidated sedimentary aquifers of eastern china are heavily over exploited and this causes aquifer compaction 1 which results in land subsidence the geological formation contains significant thicknesses of clay which introduces time delays between the extraction of the groundwater and the resulting subsidence a new computer code called the interbed drainage package has been developed for the popular modflow model to address this behaviour it has been applied in a simulation of the port of hangu and the results are being used to manage the land subsidence problem

identifying poromechanism and spatially varying parameters of aquifer compaction in choushui river alluvial fan taiwan abstract subsidence occurs in many alluvial depositional environments causing substantial socio economic losses thick aquifers with interbedding or lens structured clay can contribute significantly to compaction the poromechanism of aquifer compaction is usually complicated and its spatial variation is poorly understood inhibiting our ability to fully explain the region wide nature of groundwater exploitation induced land subsidence in this study we explore the poromechanism of aquifer deformation in the choushui river alluvial fan taiwan groundwater level and multi layer compaction data were collected for analyses elastic plastic and viscous characteristics all appear in the deformation data to various extents a visco elasto plastic vep model composed of a visco elastic set and a visco plastic set in series which are associated with different viscous dampers is proposed to model the deformation compared with existing models the proposed model is superior in terms of simulating compaction as well as its applicability and versatility the proposed vep model is applied to observation wells in the proximal middle and distal fans of the choushui river alluvial fan to explore the spatial variation in the poromechanical properties the results show that the young s modulus of the elastic spring increases with depth and with the distance from the distal fan to the proximal fan the young s modulus of the plastic element decreases with depth the system response factor of the visco plastic set decreases with depth and with the distance from the distal fan to the proximal fan aquifer recovery incapability increases with depth both the trend and dynamic fluctuations in compaction for the choushui river alluvial fan are well captured by the proposed vep model which is essential for assessing long term land and water resource management and evaluating potential short term threats to infrastructure caused by seasonal subsidence

a petrological and organic geochemical study of permian coal seams east of maracaja south santa catarina parana basin brazil abstract coal samples from the permian rio bonito formation collected from borehole mml 09 east of maracaja south santa catarina parana basin brazil were characterized by petrological vitrinite reflectance measurements maceral analyses and geochemical rock eval total organic carbon toc and gc ms methods the mean vitrinite reflectance values range from 0 73 to 0 87 rrandom indicating a rank level of high volatile b a bituminous the maceral composition showed predominance of vitrinite 49 4 to 61 2 vol and inertinite 9 to 24 5 vol the rock eval analysis presented the following values s1 and s2 ranging from 0 74 to 2 51 mg hc g coal and 34 1 to 108 87 mg hc g coal respectively hydrogen indices between 158 and 240 mg hc g toc and tmax c between 440 and 448 c the toc contents of the coal samples present values ranging from 18 85 to 45 31 wt vitrinite reflectance and rock eval tmax values indicate that the coals are in the beginning of the oil generation window the potential for the formation of liquid hydrocarbons is rather low due to the nature of the humic coal whereas the rank level indicates that generation of gas from the coal has occurred the biomarker analysis using gc ms and gc ms ms allowed the interpretation of the depositional environment and provided another way of determining the degree of maturity of the coals besides vitrinite reflectance and tmax the pristane phytane pr ph ratio is 1 mainly controlled by organic matter type implied suboxic conditions during sedimentation the vitrinite reflectance measurements tmax values and 20s 20s 20r and ratios for c29 regular steranes revealed the marginally mature stage of the organic matter although the distribution of hopanes indicated a mature stage of the organic matter due to the absence of hopanes and predominance of the 22s epimer over the 22r epimer for the hopanes from c 31 to c 35

parameter estimation of an overconsolidated aquitard subjected to periodic hydraulic head variations within adjacent aquifers abstract extensometers provide long term records of deformation over a depth interval of interest an overconsolidated aquitard usually undergoes elastic deformation if the hydraulic head within adjacent aquifers remains higher than the preconsolidation head within the aquitard the vertical hydraulic conductivity k v and elastic skeletal specific storage s ske are two critical parameters that control the deformation behavior of an overconsolidated aquitard and they could be interpreted from valuable extensometer data an analytical solution for the elastic aquitard deformation caused by periodic hydraulic head variations phhv within adjacent aquifers is derived using the separation of variables method based on euler s formula the phase difference in phhv between adjacent aquifers is found to reduce the amplitude of periodic aquitard deformation meanwhile the phase difference is found to cause no influence on the growth pattern of the phase shift which is between the periodic aquitard deformation and phhv versus the period a new parameter estimation method is further proposed to interpret aquitard k v and s ske from periodic aquitard deformation data this new method yields robust k v and s ske estimates of a moderately thick aquitard whose deformation history has been recorded by an extensometer located in shanghai china the field study confirms that the phase difference in phhv between the aquifers adjacent to the overconsolidated aquitard of interest cannot be ignored

kinematic shock sensitivity analysis a series of numerical experiments is performed to determine the flow and channel characteristics that are most conducive to kinematic wave steepening and associated kinematic shock phenomena relevant flow and channel characteristics are identified at the outset and a program of 80 computer runs is completed varying the inflow hydrograph peak froude number time to peak and base to peak flow ratio and the channel cross sectional shape it is found that all have a definite effect on kinematic shock development the size of the wave is perhaps mostly responsible for the occurrence or nonoccurrence of the shock

a novel approach to model earth fissure caused by extensive aquifer exploitation and its application to the wuxi case china initially observed in the semi arid basins of southwestern usa earth fissures due to aquifer over exploitation are presently threatening a large number of subsiding basins in various countries worldwide different mechanics have been proposed to explain this process such as differential compaction horizontal movements and fault reactivation numerical modeling and prediction of this major geo hazard caused by overuse of groundwater resources are challenging because of two main requirements shifting from the classical continuous to discontinuous geomechanics and incorporating 2 dimensional features the earth fissures into large 3 dimensional 3d modeling domain the subsiding basin in this work we proposed a novel modeling approach to simulate earth fissure generation and propagation in 3d complex geological settings a nested two scale approach associated with an original non linear elasto plastic finite element interface element simulator allows modeling the mechanics of earth discontinuities in terms of both sliding and opening the model is applied on a case study in wuxi china where groundwater pumping between 1985 and 2004 has caused land subsidence larger than 2 m the model outcomes highlight that the presence of a shallow 80 m deep bedrock ridge crossing the yangtze river delta is the key factor triggering the earth fissure development in this area bending of the alluvial deposits around the ridge tip and shear stress due to the uneven piezometric change and asymmetrical shape of the bedrock have caused the earth fissure to onset at the land surface and propagate downward to a maximum depth of about 20 30 m maximum sliding and opening are computed in the range of 10 to 40 cm in agreement with the order of magnitude estimated in the field

adaptive explicit implicit quasi three dimensional finite element model of flow and subsidence in multiaquifer systems a quasi three dimensional finite element model is presented for the analysis of groundwater flow and land subsidence due to pumpage in multiaquifer systems in the model aquifers are simulated with the aid of two dimensional horizontal finite element grids each aquifer is connected to its neighbors above and below by one dimensional vertical finite element strings which allow leakage to take place across aquitards and aquicludes land subsidence is modeled by varying the void ratio of each vertical element according to a nonlinear version of terzaghi s one dimensional consolidation theory a major feature of the new method is its ability to solve the finite element equations explicitly in one part of the mesh and implicitly in another part depending on the ratio between the stability limit of each node and any given time step size since the hydraulic diffusivity of aquitards is usually very small compared to that of aquifers it is often possible to solve the finite element equations explicitly for most and sometimes all aquitard nodes this leads to a virtual decoupling of the aquifer equations during a given time step which results in a significant saving of computer time and storage

a typical earth fissure resulting from loess collapse on the loess plateau in the weihe basin china abstract earth fissures are major geological hazards that frequently occur in the weihe basin in northwestern china and can cause severe damage to infrastructure this paper reports a case study of earth fissures resulting from loess collapse in the village of xibai in the weihe basin a series of geological investigations consisting of a site investigation trench excavation geological drilling exploratory well drilling and geotechnical testing were conducted to determine and analyze the characteristics of the xibai village earth fissures as well as the physical characteristics of the loess in the earth fissure development area the earth fissures were parallel to the village sewage pit and had a total length of 800 m with a maximum depth of 8 5 m the xibai village earth fissures were nearly vertical comparing the results of self weight collapsibility coefficient and three parameters void ratio dry density and water content of loess at different distances from the sewage pit the collapsibility of malan loess in this area and the effects of leakage from the sewage pit were determined the results revealed that a tilted seepage line was generated and the loess below this seepage line underwent varying degrees of self weight collapse deformation the nonuniform collapse settlement and rotation deformation of loess above the seepage line were thus generated while tensile stress was created in the upper part of the loess this rotation of loess similar to the deformation of the cantilever beam caused the formation of the earth fissures at the site with higher tensile stress based on the rotation mechanism this study explained the development process of collapse earth fissures and predicted that the xibai village earth fissures would continue to develop outward in the future

modeling visco elastic plastic deformation of soil with modified merchant model eighty four to ninety eight percent of land subsidence in shanghai city is caused by the visco elastic plastic deformation of sediments numerical experiments are done on the sediments with visco elastic plastic deformation in shanghai to verify the modified merchant model mm model and land subsidence model based on the modified merchant ls mm model there are two advantages of the mm model and the ls mm model one is that only a few parameters are involved there are three parameters in the mm model and four parameters in the ls mm model the other one is that both models can describe elastic elastic plastic and visco elastic deformation in addition to visco elastic plastic deformation the corresponding models are developed by setting proper values of the three parameters of 1 and 2 the two advantages make the ls mm model flexible and applicable to the simulation of the large regional land subsidence with visco elastic plastic deformation and other different kinds of deformation the results can be improved by variable parameters especially specific storage

land subsidence due to groundwater withdrawal in the northern beijing plain china abstract beijing is an international metropolis where over exploration of water resource makes land subsidence becoming more and more serious the related problems cannot be avoided in the coming years because of the giant increase of population the aims of this study are to quantify land subsidence over the period 2003 to 2010 grasp the evolution of the process and investigate the relation with the triggering factors in the northern area of the beijing plain various data including deep compaction from vertical multiple borehole extensometers land subsidence from persistent scatterer interferometry and leveling surveys groundwater levels hydrogeological setting from wellbores and landsat tm image were collected and effectively used to detect the spatial and temporal features of land subsidence and its possible relation with groundwater level changes compressible layer thickness and urban development results show that land subsidence is unevenly distributed and continuously increased from 2003 to 2010 the average loss of elevation over the monitoring period amounted to 92 5 mm with rates up to 52 mm y the distribution of the subsidence bowl is only partially consistent with that of the groundwater depression cone because of the variable thickness of the most compressible fine deposits in fact extensometers reveal that silty clay layers account for the larger contribution to land subsidence with the 15 m thick silty clay layer between 102 and 117 m depth accounting for about 25 of the total subsidence finally no clear correlation has been observed between the subsidence rates and the increase of the load on the land surface connected to the impressive urban development this study represents a first step toward the development of a physically based model of the subsidence occurrence to be used for planning remediation strategies in the northern beijing plain

time series analysis of subsidence associated with rapid urbanization in shanghai china measured with sbas insar method river delta plains deltas are susceptible to subsidence producing undesirable environmental impact and affecting dense population the city of shanghai located in the easternmost of yangtze delta in china is one of the most developed regions in china that experiences the greatest land subsidence excessive groundwater withdrawal is thought to be the primary cause of the land subsidence but rapid urbanization and economic development mass construction of skyscrapers metro lines and highways are also contributing factors in this paper a spatial temporal analysis of the land subsidence in shanghai was performed with the help of the small baseline subset interferometric synthetic aperture radar twenty l band alos palsar images acquired during 2007 2010 were used to produce a linear deformation rate map and to derive time series of ground deformation the results show homogeneous subsidence within the research area but exceptionally rapid subsidence around skyscrapers along metro lines elevated roads and highways was also observed because groundwater exploitation and rapid urbanization responsible for much of the subsidence in the shanghai region are expected to continue future subsidence monitoring is warranted