Land Subsidence Model Research Articles

A Joint Analytic Method for Estimating Aquitard Hydraulic Parameters.

The vertical hydraulic conductivity (Kv ), elastic (Sske ), and inelastic (Sskv ) skeletal specific storage of aquitards are three of the most critical parameters in land subsidence investigations. Two new analytic methods are proposed to estimate the three parameters. The first analytic method is based on a new concept of delay time ratio for estimating Kv and Sske of an aquitard subject to long-term stable, cyclic hydraulic head changes at boundaries. The second analytic method estimates the Sskv of the aquitard subject to linearly declining hydraulic heads at boundaries. Both methods are based on analytical solutions for flow within the aquitard, and they are jointly employed to obtain the three parameter estimates. This joint analytic method is applied to estimate the Kv , Sske , and Sskv of a 34.54-m thick aquitard for which the deformation progress has been recorded by an extensometer located in Shanghai, China. The estimated results are then calibrated by PEST (Doherty 2005), a parameter estimation code coupled with a one-dimensional aquitard-drainage model. The Kv and Sske estimated by the joint analytic method are quite close to those estimated via inverse modeling and performed much better in simulating elastic deformation than the estimates obtained from the stress-strain diagram method of Ye and Xue (2005). The newly proposed joint analytic method is an effective tool that provides reasonable initial values for calibrating land subsidence models.

Theory and methodology of critical control levels of groundwater: a case study of Tianjin, China

Groundwater is one of the most important freshwater resources worldwide. However, long-term over-abstraction of groundwater has resulted in deteriorating groundwater functions, including gradually decreasing resources function and geo-environmental function and subsequent adverse geo-environmental issues. In this study, the concept of critical control levels of groundwater including blue line levels and red line levels, which play an important role in groundwater resource management, is presented for the first time. In addition, the theory of critical control levels of groundwater is established based on the groundwater geo-environmental function and resources function. A coupled numerical model of groundwater flow field and land subsidence is then established for Tianjin based on the conceptual model and analysis of the hydrological conditions of the study area. Finally, the critical control levels of groundwater for the subarea are presented based on results obtained from a numerical model by the model space division and time discretization, hydrogeological parameters processing, model calibration and validation. The results presented herein will be useful for groundwater resource management.

A modified inverse procedure for calibrating parameters in a land subsidence model and its field application in Shanghai, China

Land-subsidence prediction depends on an appropriate subsidence model and the calibration of its parameter values. A modified inverse procedure is developed and applied to calibrate five parameters in a compacting confined aquifer system using records of field data from vertical extensometers and corresponding hydrographs. The inverse procedure of COMPAC (InvCOMPAC) has been used in the past for calibrating vertical hydraulic conductivity of the aquitards, nonrecoverable and recoverable skeletal specific storages of the aquitards, skeletal specific storage of the aquifers, and initial preconsolidation stress within the aquitards. InvCOMPAC is modified to increase robustness in this study. There are two main differences in the modified InvCOMPAC model (MInvCOMPAC). One is that field data are smoothed before diagram analysis to reduce local oscillation of data and remove abnormal data points. A robust locally weighted regression method is applied to smooth the field data. The other difference is that the Newton-Raphson method, with a variable scale factor, is used to conduct the computer-based inverse adjustment procedure. MInvCOMPAC is then applied to calibrate parameters in a land subsidence model of Shanghai, China. Five parameters of aquifers and aquitards at 15 multiple-extensometer sites are calibrated. Vertical deformation of sedimentary layers can be predicted by the one-dimensional COMPAC model with these calibrated parameters at extensometer sites. These calibrated parameters could also serve as good initial values for parameters of three-dimensional regional land subsidence models of Shanghai.

Three-dimensional numerical modeling of land subsidence in Shanghai, China

Shanghai, in China, has experienced two periods of rapid land subsidence mainly caused by groundwater exploitation related to economic and population growth. The first period occurred during 1956–1965 and was characterized by an average land subsidence rate of 83 mm/yr, and the second period occurred during 1990–1998 with an average subsidence rate of 16 mm/yr. Owing to the establishment of monitoring networks for groundwater levels and land subsidence, a valuable dataset has been collected since the 1960s and used to develop regional land subsidence models applied to manage groundwater resources and mitigate land subsidence. The previous geomechanical modeling approaches to simulate land subsidence were based on one-dimensional (1D) vertical stress and deformation. In this study, a numerical model of land subsidence is developed to simulate explicitly coupled three-dimensional (3D) groundwater flow and 3D aquifer-system displacements in downtown Shanghai from 30 December 1979 to 30 December 1995. The model is calibrated using piezometric, geodetic-leveling, and borehole extensometer measurements made during the 16-year simulation period. The 3D model satisfactorily reproduces the measured piezometric and deformation observations. For the first time, the capability exists to provide some preliminary estimations on the horizontal displacement field associated with the well-known land subsidence in Shanghai and for which no measurements are available. The simulated horizontal displacements peak at 11 mm, i.e. less than 10 % of the simulated maximum land subsidence, and seems too small to seriously damage infrastructure such as the subways (metro lines) in the center area of Shanghai.

Physical modeling of land subsidence due to underground cavity and its monitoring by electrical resistivity survey in geotechnical centrifuge

Physical modeling of land subsidence due to underground cavity and its monitoring by electrical resistivity survey in geotechnical centrifuge

Three dimensional numerical modeling of land subsidence in Shanghai

Abstract. Shanghai city has been suffering land subsidence caused by overly exploitation of ground water since 1921, which is a serious problem for this coastal city with altitude of 2.2–4.8 m above mean sea level. The largest cumulative land subsidence amounted to 2.6 m in the downtown area. Measures to decrease the ground water exploitation, change the pumping aquifers, and increase aquifer artificial recharge have been used to mitigate land subsidence since 1961. It is necessary to develop a proper numerical model to simulate and predict land subsidence. In this study, a decoupled three-dimensional (3-D) finite element land subsidence model including a 3-D ground water flow model and a 3-D geo-mechanical model was developed to simulate the 3-D deformation of the aquifer systems in the center area of Shanghai. The area of downtown Shanghai is 660 km2, with 10 million inhabitants, dense high buildings, and 11 metro lines. The simulation spans the period from 1979 to 1995. Two different assumptions have been tested on the side boundary, i.e., precluding the three components of the displacement, or assuming a free-displacement condition. The distribution of calculated land subsidence and horizontal displacements in different aquifers was analyzed. The computed vertical displacement fitted well with the available observations. It has been verified that the two different assumptions on the lateral boundaries in the geo-mechanical model caused different results just limited on nodes close to boundary. The developed 3-D land subsidence model is reasonable and can be used to simulate and predict 3-D movement of aquifer systems in the center area of Shanghai, which could provide scientific support to local government in controlling land subsidence and differential movements of the land surface.

Natural recharge estimation and uncertainty analysis of an adjudicated groundwater basin using a regional-scale flow and subsidence model (Antelope Valley, California, USA)

Groundwater has provided 50–90 % of the total water supply in Antelope Valley, California (USA). The associated groundwater-level declines have led the Los Angeles County Superior Court of California to recently rule that the Antelope Valley groundwater basin is in overdraft, i.e., annual pumpage exceeds annual recharge. Natural recharge consists primarily of mountain-front recharge and is an important component of the total groundwater budget in Antelope Valley. Therefore, natural recharge plays a major role in the Court’s decision. The exact quantity and distribution of natural recharge is uncertain, with total estimates from previous studies ranging from 37 to 200 gigaliters per year (GL/year). In order to better understand the uncertainty associated with natural recharge and to provide a tool for groundwater management, a numerical model of groundwater flow and land subsidence was developed. The transient model was calibrated using PEST with water-level and subsidence data; prior information was incorporated through the use of Tikhonov regularization. The calibrated estimate of natural recharge was 36 GL/year, which is appreciably less than the value used by the court (74 GL/year). The effect of parameter uncertainty on the estimation of natural recharge was addressed using the Null-Space Monte Carlo method. A Pareto trade-off method was also used to portray the reasonableness of larger natural recharge rates. The reasonableness of the 74 GL/year value and the effect of uncertain pumpage rates were also evaluated. The uncertainty analyses indicate that the total natural recharge likely ranges between 34.5 and 54.3 GL/year.

Simulation of fully coupled finite element analysis of nonlinear hydraulic properties in land subsidence due to groundwater pumping

A fully coupled mathematical model of land subsidence caused by groundwater pumping was established based on the mechanics of porous seepage and the theory of fluid–solid interaction. The mathematical model employing the Galerkin finite element method was proposed to simulate the deformation dependencies of hydraulic properties due to the water pressure decrease in aquifers. This model has been verified by comparing with the known analytical solutions in the confined aquifer. Results show that the simulated drawdown and displacements match well with those of analytical solutions. To evaluate the nonlinear effects of hydraulic properties in the seepage and consolidation coupling phenomena, the numerical model is applied to an ideal three layers numerical experiment. The results show that the subsidence rate is faster than conventional groundwater theory when the nonlinear hydraulic properties (NHP) are considered in the coupled model. The reason is that the water level decline due to groundwater withdrawal induces the soil compression and the porosity and permeability decrease. Decrease of permeability in regions adjacent to the pumping well produces hydraulic gradient and seepage forces that may result in accelerated subsidence. Therefore, the effect of the NHP is an interaction process of pore water pressure and soil consolidation deformation and should not be ignored. Further studies of various hydrogeology problems are recommended to consider the heterogeneity concerning different stratigraphic condition in the field.

Development and application of a regional land subsidence model for the plain of Tianjin

In this paper, a coupled numerical groundwater and land subsidence model was developed for the Tianjin Plain. The model was employed to investigate the groundwater resources and their changes over the last decade, and to further predict the changing patterns of the groundwater level and associated land subsidence in future. First, according to the regional hydrogeology, the simulation area was defined with an area of 10.6×103 km2, which was divided into six aquifer units. A coupled groundwater and land subsidence numerical model was built by using Modflow2005 and the land subsidence simulation module SUB (subsidence and aquifer-system compaction), in which the groundwater flow was modeled as three-dimensional unsteady flow and the land subsidence simulation was based on one-dimensional consolidation theory. The model was then calibrated by using the groundwater level contour lines, hydrographs, and land subsidence hydrographs over the period of 1998–2008. In addition, groundwater balance analysis of the simulation period indicated that under multi-year groundwater withdrawal condition the cross-flow recharge, compression release, and lateral boundary inflow contributed 44.43%, 32.14%, and 21.88% to the deep aquifer recharge, respectively. Finally, the model was applied to predict the changing patterns of the groundwater levels and the associated variations in land subsidence under the control of groundwater exploitation after implementation of the south-to-north water diversion project. The simulation results demonstrated that the groundwater level may gradually increase year by year with an decrease in the groundwater withdrawal; and the land in dominated land subsidence regions including the urban area, Dagang, Hangu, Jinghai, Wuqing, and Jinnan, may rebound at an average rate of 2–3 mm/a, and the land subsidence rate in the other regions may decrease.

Interpretation of increased deformation rate in aquifer IV due to groundwater pumping in Shanghai

Shanghai is a typical example of a region in China suffering from severe land subsidence. Previous investigations have shown that land subsidence is strongly related to groundwater pumping in both the temporal and spatial domains. A series of field investigations shows that the deformation rate of aquifer IV (AqIV) has increased, contributing significantly to the total subsidence in Shanghai. To predict the deformation behavior of AqIV in Shanghai due to groundwater pumping, four different models have been applied in this study: (i) a model based on groundwater flow theory, (ii) an elastic model based on Cauchy mechanics, (iii) a creep model incorporated into Cauchy mechanics, and (iv) a recently proposed land subsidence model by Budhu based on Cosserat mechanics. Based on a number of assumptions, Budhu’s concept was extended to consider the time-dependent behavior of groundwater potential in aquifers and the consolidation behavior of overburdened aquitards. The calculated results of AqIV’s deformation were compared with the field-measured data. The results show that when using groundwater flow theory and Cauchy mechanics, it is difficult to predict the increased deformation rate of the sandy layers in aquifers even when the creep behavior is incorporated into the calculation. However, Budhu’s method based on Cosserat mechanics can predict this increased deformation rate well. The predicted result indicates that increased deformation of aquifer IV is due to volumetric contraction caused by shear stress rather than the creep of aquifer sand. The phenomenon of deformation delay in aquifers can also be interpreted with the proposed model.

Groundwater Exploitation Management Under Land Subsidence Constraint: Empirical Evidence from the Hangzhou–Jiaxing–Huzhou Plain, China

Land subsidence caused by extensive groundwater pumping has become a factor which cannot be ignored in the sustainable exploitation of groundwater resources. The Hangzhou-Jiaxing-Huzhou Plain is one of the locations with China's most severe land subsidence problems; the region has experienced dramatic land subsidence since the 1960s. Historical records of groundwater extraction, hydraulic head, and land subsidence show the latter to be the result of continual and excessive extraction of groundwater from deep confined aquifers. This study reconstructs land subsidence using an integrated regional groundwater flow and land subsidence model. The model is calibrated using land subsidence and groundwater level measurements from 1996 to 2007. Simulation results reproduce the cones of depression for groundwater heads and nadirs of land subsidence reasonably well. The calibrated model is used to evaluate the efficacy of land subsidence prevention plans from 2008 to 2010, and to predict future land subsidence over the next decade considering several groundwater exploitation scenarios. The results show the main cause of land subsidence to be inelastic compaction of the aquifer system resulting from continuously declining water levels. The model reveals that while the area of land subsidence will continue to extend, the rate of this extension may be significantly decreased by reduction of groundwater extraction. If the current land subsidence prevention and reclamation plans are continued and surface water diversion projects implemented, though land subsidence cannot be halted, the rate at which it is occurring can be effectively reduced.

Research on Prediction Model of Support Vector Machine Based Land Subsidence Caused by Foundation Pit Dewatering

Foundation Pit Dewatering always arouses surrounding land subsidence that has significant influence on the neighboring environment and even leads to serious natural disasters. So an accurate prediction of the settlement is the precondition of forecasting and evaluating the Foundation Pit Dewatering environment influence. Using the distance from settlement points to Foundation Pit, Equivalent compression modulus, the drawdown, Supporting structure stiffness and equivalent permeability coefficient as the independent variables, adopting the 38 groups of Engineering practical monitoring datas as the samples to establish the prediction model of Land Subsidence caused by Foundation Pit Dewatering based on Support Vector Machine theory. The project trial result shows that compared with traditional empirical method, the model possesses bigger forecast precision.

Modeling of Land Subsidence in the South Pars Gas Field (Iran)

The objective of this study is to predict the subsidence of the South Pars gas field at the end of production period. With respect to the notable reservoir thickness, significant pressure drop due to extraction and high areal extent of the South Pars gas field there is a high subsidence potential in this field. In order to determinate the maximum land subsidence and subsidence profile of the South Pars gas field, at first, the reservoir compaction was estimated based on the thickness of the reservoir, the pressure drop in the reservoir and the uniaxial compaction coefficient of the reservoir rock, and then the effect of the reservoir compaction on the field surface was modeled with the use of analytical and semi-numerical methods. The compaction of the reservoir at the end of production period was estimated to be about 0.48 m. Both of the subsidence modeling methods show similar results and predict that the maximum subsidence will reach about 0.6 m at the end of production period.

Coupled Numerical Simulation Research on Dewatering and Land Subsidence in Deep Foundation Pit

With the construction of deep and large foundation pit, land subsidence disasters caused by dewatering in deep foundation pit become very serious. Using the coupled model of foundation pit dewatering and land subsidence and putting it into foundation pit dewatering construction, analyzes and summarizes the effect of land subsidence in space and time, which will provide references for the design and construction of foundation pit dewatering.

Calculation of Land Subsidence Induced by Dewatering of Pit Based on Comprehensive Template Model

Based on the hierarchical summation method of elasticity theory, the comprehensive template model of land subsidence induced by dewatering of pit is put forward. According to the soils experience range of conversion relationship β (between deformation modulus E0 and compression modulus Es ), we can calculate upper and lower limits of Es. When the compression modulus Es is respectively taken upper and lower limit, the curve between falling groundwater values and sedimentation values can be taken in conditions of unit thickness different soils of different pore ratio. So the comprehensive template model is built. The example shows that the comprehensive template model can be effectively calculated land subsidence induced by dewatering of pit.

System Analysis and Numerical Simulation of Land Subsidence in Shanghai

Land subsidence has become a major geological hazard in Shanghai . Based on the view of system theory, The paper sets a numerical model of land subsidence, the results of model simulation are as follows: 1) the speed of land subsidence will be 8.81mm/a in Shanghai in the next 10 years if it can maintain present trends of load increase and groundwater mining; 2) Since 1998, we adjust the ratio of groundwater extraction and filling to 1:1, the accumulated quantity of land subsidence will rebound to 30mm in 2017, from 2018, it will continue to drop. However, the overall future land subsidence will keep the trend of slow growth; 3) Double the exploitation capacity in1998, the speed of land subsidence will be 41mm/a in 2020, the accumulative quantity of land subsidence will be close to 1m. According to the average high tide level (5.15m) in the Huangpu River in 2000-2008, the actual average high tide level of the Huangpu River will reach about 6m and exceed the orange warning response against flood and typhoon in Shanghai. If superimposing sea level rise and strong typhoon disasters, it will face with more serious flood risk.

Bearing capacity of single pile and in-flight T-bar penetration for centrifuge modeling of land subsidence caused by the interaction of high-rise buildings

With an increasing number of high-rise buildings in major cities worldwide, land subsidence induced by the interaction between closely-spaced buildings in soft soil areas has become a major challenge for many researchers. The paper considers the interaction of high-rise buildings by determining the bearing capacity of a single pile in the centrifuge model test. The T-bar penetration test was conducted in flight to measure the shear strength of the soft soil, together with vane shear tests when the model had slowed down. By analyzing the relationship curves between land subsidence and the centrifuge acceleration, the allowable bearing capacity of a single pile for the high-rise building was obtained. It is considered that such analysis is a more appropriate method of determining the pile requirements for groups of adjacent high-rise buildings in soft soil areas.

Cusp Catastrophe Intelligence Combinatorial Prediction of Land Subsidence

Seeking for a scientific and reasonable predict model is the key point to ensure accurate and reliable prediction results for the land subsidence. In this paper, the research of subsidence area pointed out by picks the process of land subsidence which causes by the water reservoir that conforms to the characteristic of nonlinear dynamics, thus, a new model is established to solve the combinatorial weighted coefficients by using the predict precision, and a simple method is introduced to solve the grey model and neural network combination forecast model. Based on many examples, the new cusp catastrophe land subsidence model is proved to be very effective and much more accurate.

MODELLING OF LAND SUBSIDENCE ALONG TANAH MAS -PELABUHAN SECTION SEMARANG CITY USING FINITE ELEMENT METHOD

Land subsidence has been an apparent problem in the northern part of Semarang city, Central Java, which has caused enormous physical and economical impacts. This area is underlain by alluvium sediments of clay, silt, sand and gravel. The nature of the alluvium soil is soft and highly compressible which induces natural consolidation to occur. The lowering of groundwater table due to exploitation and loads of building and earth fill accelerate the rate of consolidation settlement. A study of land subsidence modeling was carried out in the northern part of Semarang city. Collection and analysis of data on the geology, hydrology, soil properties and monitored settlements were conducted. Modeling of land subsidence involved stress deformation analysis using finite element method. The settlements computed for selected section of the city of Semarang were compared with measurements of settlement in the city area. The simulation results appear to be in reasonably good agreement with the measurement results. Simulation results at selected section indicated that the contribution of lowering groundwater table factor accounts for less than 50% of total monitored subsidence. Meanwhile simulation results using application of external loading and lowering of groundwater table showed better agreement with the monitored subsidence. Information of magnitude and factors causing land subsidence is important particularly for city planning purposes.

Spatial-temporal characteristics of land subsidence corresponding to dynamic groundwater funnel in Beijing Municipality, China

Due to long-term over-exploitation of groundwater in Beijing Municipality, regional groundwater funnels have formed and land subsidence has been induced. By combining a groundwater monitoring network, GPS monitoring network data, radar satellite SAR data, GIS and other new technologies, a coupled process model based on the dynamic variation of groundwater and the deformation response of land subsidence has been established. The dynamic variation of groundwater funnels and the land subsidence response process were analyzed systematically in Beijing. Study results indicate that current groundwater funnel areas are distributed mainly in the southwest of Shunyi District, the northeast of Chaoyang District and the northwest of Tongzhou District, with an average decline rate of groundwater level of 2.66 m/yr and a maximum of 3.82 m/yr in the center of the funnels. Seasonal and interannual differences exist in the response model of land subsidence to groundwater funnels with uneven spatial and temporal distribution, where the maximum land subsidence rate was about −41.08 mm/yr and the area with a subsidence rate greater than 30 mm/yr was about 1637.29 km2. Although a consistency was revealed to exist between a groundwater funnel and the spatial distribution characteristics of the corresponding land subsidence funnel, this consistency was not perfect. The results showed that the response model of land subsidence to the dynamic variation of groundwater was more revealing when combining conventional technologies with InSAR, GIS, GPS, providing a new strategy for environmental and hydrogeological research and a scientific basis for regional land subsidence control.