Control of deformation of buildings affected by subsidence using persistent scatterer interferometry

PLEASE SCROLL DOWN FOR ARTICLE

This article was downloaded by: [Bru, Guadalupe]On: 22 September 2010Access details: Access Details: [subscription number 927193369]Publisher Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Structure and Infrastructure EngineeringPublication details, including instructions for authors and subscription information:http://www.informaworld.com/smpp/title~content=t713683556

Control of deformation of buildings affected by subsidence using persistentscatterer interferometryG. Brua; G. Herreraa; R. Tomásb; J. Duroc; R. De la Vegad; J. Mulasa

a Área de Peligrosidad y Riesgos Geológicos, Departamento de Investigación y ProspectivaGeocientífica, Instituto Geológico y Minero de España (IGME), Ministerio de Ciencia y Tecnología,Madrid, Spain b Departamento de Ingeniería de la Construcción, Obras Públicas e InfraestructuraUrbana, Escuela Politécnica Superior, Alicante, Spain c Altamira Information, c/ Còrsega, 381-387,Barcelona, Spain d Departamento de Explotación Recursos Minerales y Obras Subterránea, ETS Ing.Minas Universidad Politécnica c/ Ríos Rosas 21, Madrid, Spain

First published on: 22 September 2010

To cite this Article Bru, G. , Herrera, G. , Tomás, R. , Duro, J. , De la Vega, R. and Mulas, J.(2010) 'Control of deformationof buildings affected by subsidence using persistent scatterer interferometry', Structure and Infrastructure Engineering,,First published on: 22 September 2010 (iFirst)To link to this Article: DOI: 10.1080/15732479.2010.519710URL: http://dx.doi.org/10.1080/15732479.2010.519710

Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf

This article may be used for research, teaching and private study purposes. Any substantial orsystematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply ordistribution in any form to anyone is expressly forbidden.

The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae and drug dosesshould be independently verified with primary sources. The publisher shall not be liable for any loss,actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directlyor indirectly in connection with or arising out of the use of this material.

http://www.informaworld.com/smpp/title~content=t713683556

http://dx.doi.org/10.1080/15732479.2010.519710

http://www.informaworld.com/terms-and-conditions-of-access.pdf

Control of deformation of buildings affected by subsidence using persistent scatterer

interferometry

G. Brua, G. Herreraa*, R. Tomasb, J. Duroc, R. De la Vegad and J. Mulasa

aArea de Peligrosidad y Riesgos Geologicos, Departamento de Investigacion y Prospectiva Geocientıfica, Instituto Geologico yMinero de Espana (IGME), Ministerio de Ciencia y Tecnologıa, c/ Rıos Rosas 23, E-28003, Madrid, Spain; bDepartamento deIngenierıa de la Construccion, Obras Publicas e Infraestructura Urbana, Escuela Politecnica Superior, Universidad de Alicante P.O.Box 99, E-03080 Alicante, Spain; cAltamira Information, c/ Corsega, 381–387, 2n 3a – E-08037, Barcelona, Spain; dDepartamentode Explotacion Recursos Minerales y Obras Subterranea, ETS Ing. Minas Universidad Politecnica c/ Rıos Rosas 21, 28003, Madrid,

Spain

(Received 19 January 2010; final version received 24 August 2010; accepted 25 August 2010)

In this article, satellite radar data are analysed to control the deformation of the buildings of Murcia City (SE Spain)affected by subsidence. This phenomenon has occurred as a result of groundwater overexploitation in drought periods,and special attention is paid to the most recent drought which occurred between 2005 and 2008. In the first part of thiswork, the study area is presented followed by a description of the characteristics and effects of subsidence on thebuildings of the urban area. Persistent scatterer interferometry is used to process a satellite base radar dataset measuringthe temporal and the spatial evolution of subsidence. These results are analysed with respect to several factors thatcontrol subsidence mechanisms: water table decrease, thickness of the compressible layer and the type of foundation ofthe buildings. To validate these results, a detailed structural damage analysis of several buildings is presented. Accordingto the results presented in this work, it may be concluded that damage of buildings is triggered by soil consolidation dueto groundwater overexploitation, demonstrating that the inclusion of this technique can be particularly interesting instructural monitoring framework of civil infrastructures, as a complementary tool to control subsidence damage.

Keywords: subsidence; crack map; building damage; differential settlements; DInSAR; deformation

1. Introduction

Ground subsidence due to aquifer system consolida-tion triggered by ground water overexploitationinvolves the settlement of ground surface affectingwide areas. Human structures built on these aredamaged when their foundations cannot accommodatedifferential settlements. It is estimated that there areover 150 cities in the world with serious problems ofsubsidence due to excessive groundwater withdrawal(Hu et al. 2004). For instance, well-known examples ofsubsidence include the Po Valley (Italy), Mexico DC,Antelope, Santa Clara and San Joaquin Valleys(USA), Bangkok (Thailand) and many other areas inthe world. Subsidence has occurred in the metropolitanarea of Murcia City (SE Spain) as a result of excessivepumping of groundwater.

Murcia City occupies part of the Segura Riverflood plain covering a surface of 20 km2. Duringdrought periods, groundwater extraction increasesproducing the depletion of the water table (Aragonet al. 2004). In fact, a piezometric level loweringbetween 5 and 15 m was measured during recentdrought periods: 1980–1983, 1992–1995 and 2005–

2008. After the second drought ground, subsidencewas triggered causing damage in buildings and otherstructures that were documented by Martınez et al.(2004) with an estimated cost of 50 million euros,generating a significant social impact. In order tomeasure and record ground deformations, an extens-ometer network has been monitoring since 2001 anddifferent persistent scatterer interferometry (PSI) tech-niques have been applied in previous works (Mulaset al. 2004, Tomas et al. 2005, Herrera et al. 2009a,b).

In this article, we describe and analyse the effects ofsubsidence phenomenon on the buildings of MurciaCity, focusing our attention on the most recentdrought period 2005–2008. For this purpose, weevaluate the relationship between ground deformationand the most important factors that control subsidencephenomenon, as well as its effects on the buildings. Thespatial and temporal evolution of surface deformationhas been calculated with a PSI technique, the StablePoint Network (SPN). Then, deformation results havebeen evaluated with respect to water table decrease, thethickness of the compressible layer and the type offoundation of the buildings. In order to validate these

*Corresponding author. Email: [email protected]

Structure and Infrastructure Engineering

2010, 1–13, iFirst article

ISSN 1573-2479 print/ISSN 1744-8980 online

� 2010 Taylor & Francis

DOI: 10.1080/15732479.2010.519710

http://www.informaworld.com

Downloaded By: [Bru, Guadalupe] At: 16:13 22 September 2010

results, a detailed structural damage analysis of severalbuildings is made to demonstrate the usefulness ofadvanced radar technology to support urban forensicanalysis associated to subsidence phenomenon.

2. Description of the study area: Murcia City

2.1. Description of subsidence phenomenon

The study area is part of Segura River valley located inthe oriental sector of the Betic Cordillera (Figure 1A).

Permian and Triassic deformed materials make up thebasement and correspond to the Internal Zones of theBetic Cordillera. The basin filling comprises UpperMiocene to Quaternary sediment fluvial deposits(Figure 1B). These recent sediments are very compres-sible and the most problematic from a geotechnicalpoint of view (Mulas et al. 2003). They constitute the‘Guadalentın – Segura Quaternary aquifer System N8470 (IGME 1986), which is divided in two units (Ceronand Pulido 1996, Aragon et al. 2004). The superficial

Figure 1. (A) Situation and (B) geology of the Vega media of the Segura River.

2 G. Bru et al.


aquifer reaches 30 m below the surface, and it isformed by recent clay, silt and sands facies. Accordingto Aragon et al. (2004), vertical and horizontalhydraulic conductivities vary between 0.03 and0.1 m/day and 0.01 and 5 m/day, respectively. Thedeep aquifer, located below, is composed of a sequenceof gravels and sands alternating with silt and claylayers. In this case, horizontal and vertical hydraulicconductivities vary typically between 10 and 100 m/day and 1 and 50 m/day.

The subsidence phenomenon in the city ofMurcia is related to excessive water pumping ofthe topmost layer of the deep aquifer. Our sub-sidence model suggests that when water is pumpedfrom the upper gravels of the deep aquifer, agradient is created resulting in the lowering of thewater table. Consequently, pore pressure in thesuperficial aquifer declines and the aquifer undergoesa consolidation process (Mulas et al. 2003). Ingeneral, piezometric level is closely related withannual precipitation because rain infiltration andirrigation are the most important sources of rechargeof the aquifer. During the drought periods, waterextractions in authorised and illegal wells from deepaquifer increase and infiltration decreases. Hence,piezometric level decline has been observed duringthe historical droughts during 1980–1983, 1992–1995and 2005–2008. The drought in the 1980s derived inpiezometric falls is higher than 5 m during 1983 inthe Segura Valley. However, there is no informationabout ground subsidence during this period. The1992–1995 drought caused a generalised lowering of8 m (Mulas et al. 2000), with maximum valueshigher than 15 m. The 2005–2008 drought periodscaused a water table lowering in the range between 6and 13 m.

During the 1992–1995 periods, consolidation pro-cess produced land subsidence in large areas of MurciaCity and moderate to severe damage in buildings andother structures, such as sidewalks, roads, walls, etc.Since no instrumental data were available, Martınezet al. (2004) estimated a 4 cm superficial settlement fora 10 m decline of water table using a finite elementnumerical model. In 2001, the extensometric networkwas installed in four suburban areas of in the Southand East of the city, measuring up to 2.8 cm of verticaldisplacement from 2001 to 2005. During themost recent drought period, started in 2005, the watertable depletion coincides with an acceleration ofground subsidence. In this period, the displacementvelocity has doubled with respect to the formerreaching 4.9 cm in 2008. Additionally, during 2004–2008, ground movements were monitored through theanalysis of radar satellite SAR images using the SPNtechnique.

2.2. Effects of subsidence

Subsidence occurred in the 1992–1995 drought causedmoderate to severe damage in more than 150 buildingsand other structures, such as sidewalks, roads, walls,etc. A forensic analysis was made on 35 buildings(IGME 2000), which included general building infor-mation (foundation, structure, date of construction,etc.) and a description of the pathologies observed inthe external and internal facades. In the most recentdrought (2005–2008), subsidence has caused newdamage to buildings and infrastructures that havebeen documented in several field surveys.

The subsidence of the compressible deposits due toground water depletion causes different types ofdamage. The most common pathologies that affectedthe buildings of Murcia City during the 1992–1995drought were (De Justo et al. 2002, Vazquez and DeJusto 2002, IGME 2000):

. Negative skin friction on concrete piles founda-tions. It consists of a relative movement betweenthe pile and the soil that produces shear stressalong the interface.

. The putrefaction of old wood piles of buildingsdue to the water level decline.

. Differential settlements of shallow foundations(SF) due to soil consolidation and the subsequentangular distortions on the buildings structure.

These pathologies are usually manifested as cracksthat are formed when the structure is not capable toabsorb the tensions caused by the movements sufferedby the building, appearing first in those elements thatare more rigid (walls and facades) or weaker (joints).The appearance of cracks is also related with otherfactors, such as the type of foundation (deep orsuperficial), the rigidity of the structure, the quality ofthe materials and the presence of other pathologies.

Figures 2a–f show several examples of damage onbuildings of the City of Murcia. In Figure 2a, thehorizontal cracks are due to vertical displacement ofthe sidewalk with respect to building, which indicatesthe existence of negative skin friction on foundationpiles. Note that the concrete reinforcement between theground and the building is dated on the 23rd March2007, which means that there has been movement afterthat date. Figure 2b shows diagonal 458-dip anglecracks on a facades caused by differential settlementsof the structure. Notice the opening of the dilatationjoint with the adjacent building, caused by thesettlement of the zone located at the right side of thebuilding. This joint has been covered with a metalsheet. A similar problem is observed in Figure 2d.Another common damage consists on the aperture of

Structure and Infrastructure Engineering 3


the dilatation joints between buildings. This pathologyoccurs due to the monolithic tilt of one building inrelation to the adjacent (Figures 2e and f) due to adifferential settlement.

3. The stable point network technique

3.1. Introduction to differential interferometry

Advanced remote sensing techniques based on satelliteradar data have become a powerful method to detectand monitor slow ground surface deformations at alow cost. Synthetic aperture radar (SAR) images

acquired by ERS-1, ERS-2 and ENVISAT C-bandsatellites of the European Space Agency (ESA),provide a wide coverage of 100 by 100 km, a high-spatial resolution of 20 by 4 m and the availability of awide historical archive of SAR images acquired since1991. The information contained in each pixel of aSAR image consists of a complex number that can berepresented by the amplitude and the phase compo-nents of the measured signal. The phase containsinformation related to the distance between thesatellite sensor and the ground surface. It is usedto estimate displacements through differential

Figure 2. Observed damages of the buildings of Murcia City (the buildings are labelled in Figure 4a with the same label).Therefore: (a) Building a. (b) Building b. (c) Building c. (d) Building d. (e) Building e. (f) Building f.

4 G. Bru et al.


interferometry. The standard differential interferome-try (DInSAR) methods compare two SAR imagesacquired at two different times over the same area,which enables to detect the ground surface deforma-tions that have occurred between the two acquisitiontimes. Several authors have applied standard DInSARto subsidence (Galloway et al. 1998, Amelung et al.1999, Crosetto et al. 2003, Hoffman et al. 2003) butstrong limitations can be appreciated related totemporal and geometric decorrelation.

These limitations have been partially resolved bythe advanced DInSAR methods, the so-called PSItechniques. They make use of large sets of SAR imagesacquired in different times over the same area,permitting to observe the temporal evolution of thedisplacement of every detected ground target with ahigh precision and spatial resolution. The first PSItechnique, namely the permanent scatterers technique(PSInSARTM), was developed by Ferretti et al. (2001).Later, other authors developed similar methods(Arnaud et al. 2003, Mora et al. 2003, Werner et al.2003, Hooper et al. 2005). To date, most of the PSIapplications have focused on subsidence analysis(Ferretti et al. 2004, Tomas et al. 2005, Cascini et al.2006, Zerbini et al. 2007, Bell et al. 2008, Herrera et al.2009a,b)

3.2. The SPN technique

For the present work, ground subsidence measure-ments were obtained with a PSI technique called theSPN. This technique is the result of several years ofresearch projects within the differential interferometrydata analysis field for CNES (French Space Agency),ESA and Altamira Information SL. This techniqueuses the DIAPASON interferometric chain developedby the French Space Agency (CNES) for all SAR datahandling, e.g. co-registration work and interferogramgeneration.

The basis of the SPN technique is the separation ofthe different components from the interferometricphase, FINTERF, the topographic component, FTOPO,the movement component, FMOV, the atmosphericcontribution, FAPS and the noise component, FNOISE;

FINTERF ¼ FTOPO þ FMOV þ FAPS þ FNOISE ð1Þ

The topographic component can be extracted from anexternal digital elevation model (DEM). Consequently,assuming that FNOISE and FAPS are known we candeterminate the phase contribution due to grounddeformation FMOV.

Figure 3 gives an overview of the SPN processingchain: the SPN procedure generates three mainproducts starting from a set of SLC SAR images:

the subsidence rate that can be derived using adataset of at least six images; a map of height error;and finally, the displacement time series, whichrequires at least 20 images depending on the velocityof displacement with respect to the temporal separa-tion of image acquisitions. Nevertheless, an increasein the number of SAR images improves the qualityof the measurements providing an error of 1 mm/year for subsidence rates and 2 m for height errors.To date, the performance of the SPN method hasbeen validated for subsidence analysis by Herreraet al. (2009a,b).

3.3. The SPN processing and results

The SPN technique has been used to analyse SARimages acquired by ERS-2 and Envisat satellites fromthe ESA covering the period January 2004–December2008. A crop of about 5 6 5 km2 was selected fromthe 100 6 100 km2 acquired SAR images, correspond-ing to Murcia City. For the elaboration of theinterferometric pairs threshold values of the perpendi-cular spatial baseline, the temporal baseline and therelative Doppler centroid difference have been selected(Table 1). The DEM of the shuttle radar topographymission (SRTM) has been used to cancel the

Figure 3. SPN processing chain main flow chart.



topographic component of the interferometric phase.The pixel selection for the estimation of displacementswas based on a combination of several qualityparameters including low amplitude standard devia-tion and high model coherence.

The main result of the SPN processing has been thedisplacement rate map presented in Figure 4a, whichhas been geocoded and superimposed on an aerialimage, showing nine colours that represent intervals ofline of sight (LOS) displacement, which is the linedefined by the satellite incidence angle and the groundsurface reflector. The number of measurements, i.e. thenumber of detected pixels or persistent scatterers (PSs),the measurement spatial density and the averagesubsidence rate can be consulted in Table 1. Notethat 84% of the PSs show displacement rates largerthan 3 mm/year, whereas only 31% show rates greaterthan 6 mm/year. Concerning the spatial distribution ofthe PSs, two different trends can be distinguished: the

Northeast and the suburbs South from Segura Rivershow displacement rates larger than 6 mm/year, whilethe North-Western part of the city exhibits subsidencerates close to 3 mm/year.

Figure 4b shows a cumulative displacement map ofthe building blocks of Murcia City. For this purpose,we have calculated the average subsidence rate of allthe PSs included within the area defined by every blockof buildings. The polygon that defines each block ofbuildings has been extracted from a 1:5000 topo-graphic map. In order to illustrate the subsidence ratevalues, the same colour scale to that presented inFigure 4a has been used. This procedure has shownthat one or more PSs have been detected within 1297blocks of buildings, which represent *19% of thetotal. Note that from these amount 90% of thebuilding blocks show displacement rates greater than3 mm/year, whereas 40% show rates greater than6 mm/year.

Table 1. SPN processing details and radar deformation results.

Processing details Deformation results

Perpendicular baseline 800 m N8. measurements 4129 PSsTemporal baseline 3 years Measurements density 206 PSs/km2

Doppler centroid difference 400 Hz Average subsidence rate 5.5 mm/yearDetected blocks of buildings 1297Blocks of buildings with a subsidence rate greater than 6 mm/year 40%

Figure 4. Deformation maps for the period January 2004–December 2008. (a) Cumulative displacement map of Murcia Cityprojected along LOS, obtained by SPN technique. (b) City blocks’ cumulative displacement map projected along LOS.

6 G. Bru et al.


4. Analysis of the structural damage of the buildings

of Murcia City

4.1. Analysis of subsidence factors and buildingsettlement

Murcia City is settled on Quaternary floodplaindeposits and abandoned fluvial channels that conformthe compressible upper aquifer (Figure 5a). As it has

been commented before, in this case subsidencephenomenon is primarily controlled by ground watertable variation and the stratigraphy of the soil. Thestratigraphic column is formed of landfills, silt andclays and layers of sand and gravel. The compressiblethickness has been calculated by subtracting sand andgravel beds and varies from *1.5 to over 36 m. Themap of Figure 5b shows the distribution of the

Figure 5. (a) Quaternary sedimentary deposits. (b) Compressible thickness distribution. (c) Water table decrease distributionfor the 2005–2008 drought period. (d) City blocks classes, based on the relative proportion found between shallow (SF) and deep(DF) foundations.



compressible thickness in more than 450 borehole testsavailable in the city, (IGME 1994, 2000, 2001, 2005,Tomas 2009). Note that nearly 30% of the boreholetests do not reach the gravel aquifer, so the realthickness can be even greater. In the Northwest part ofthe city, compressible deposit layer exceeds 30 m, andit gradually decreases towards the city centre down to6–18 m. The thickness reaches again high values, up to24 m, in the Northeast of Murcia City and towards theSouth below Segura River. Available piezometers(Figure 5c) reveal that water table decrease for the2004–2008 period has been greater in the Eastern andSouthern part of the city than in the North.

If we compare Figures 4a, 5b and 5c it is observedthat the maximum subsidence is measured at theSouthern part of the city, coinciding with thickcompressible deposits (greater than 18 m) and max-imum piezometric decrease. Besides, the Northernpart, also characterised by thick compressible depositsbut low ground water level decrease, exhibits thelowest ground deformation measurements. Moderateto high subsidence rate values have been measured inthe Northeast of the city (Figure 4), where thethickness of the compressible thickness varies between15 and 25 m (Figure 5b) and the water table fall is thehighest (Figure 5c). In Table 2, it can be appreciatedthis same relationship for the buildings studied in thiswork (Figures 2, 7 and labels in Figure 4a).

The occurrence of ground subsidence in Murciaproduces settlement and damage on buildings, whichare directly related to their foundation and structure.The buildings of Murcia were classified by IGME(1994) in two types of foundation:

. Deep foundations (DF): wood/concrete shaftresistance piles built in the compressible deposits

or concrete piles working by toe resistance on theuppermost gravel substrate.

. SF: concrete strip footings, beams and slabs.

In order to analyse the spatial distribution of thefoundation of the buildings in Murcia City, a map waselaborated based on the relative proportion of eachfoundation type (deep or superficial) present in everybuilding block (Figure 5d). Attending to the percen-tage of deep or superficial foundation of the buildingsfound within every block, a total of 10 classes ofbuilding blocks were distinguished (bars in Figure 6).Over half of the metropolitan area surface is con-stituted by one class that embodies large areas of theSouth of the city and the suburbs, in which 95% of thebuildings bear on SF while only the 5% does it on piles(Figure 6a). Generally, the height of the buildingsbelonging to this class does not exceed two floors.Moving towards the city Centre, deep foundationproportion increases and most of buildings have morethan five floors, reaching up to 14.

The relation between ground surface deformationmeasured by the SPN technique and the type offoundation has been studied. For this purpose, PSsdeformation rates have been classified in three inter-vals: from 3 to 73 mm/year (low rate), from 77 to725 mm/year (high rate) and from 73 to 77.5 mm/year (medium rate). The plot in Figure 6b representsthe amount of PSs of each deformation intervallocated within the area that corresponds to each classof building blocks. It is observed that the percentage ofPSs measuring high deformation rates is greater whereSF are dominant, whereas the inverse occurs wheremainly DF are present. One can conclude that thehigher the proportion of buildings is laid on superficialfoundations, the higher the deformation rate is.

Table 2. Maximum water table decrease and compressible thickness obtained in the closest borehole and piezometersrespectively of all the buildings studied in this article (see buildings location in Figure 4a).

BuildingCompressiblethickness (m)

Distance toborehole (m)

Maximum watertable decrease (m)

Distance topiezometer (m)

Average subsidencerate (mm/year)

a 22.0 77 10.0 155 78.3b 20.8 26 8.9 266 77.7c 17.0 35 10.0 220 77.4d 9.6 114 9.3 564 77.2f 6.1 111 4.9 105 74.2g 18.5 90 6.6 38 75.9h 14.0 70 6.7 407 74.7i 18.5 116 6.7 3.95 75.3e (B1/P1) 7.5 89 6.6 415 76.1e (B2/P2) 16.0 98 8.8 529 76.1e (B3/P3) 22.0 155 8.9 683 76.1

In building ‘e’ different boreholes (B1, B2 and B3) and piezometers (P1, P2 and P3) are shown because they will be used in the following section4.2.

8 G. Bru et al.


However, it has to be taken into account that this isnot the only factor that controls subsidence phenom-enon, which also depends on the water table decreaseand the thickness of compressible layer. Moreover,punctual settlements can be due to constructivedefaults or local soil defects. Note that low deforma-tion rates are found at the Northern suburbs and highdeformation rates are present at the city centre belowRiver Segura.

4.2. Structural damage analysis

In this section, measured ground deformation fromradar satellite data is compared with several damagedbuildings. The comparison of the forensic analysismade in 1999 (IGME 2000) with respect to observeddamage in 2009 has permitted to validate measuredground deformations from radar data. As a conse-quence of the last 2005–2008 drought period, it isobserved that recently damaged buildings are concen-trated in the Eastern and the Southern areas of the city,where subsidence rates are greater than 4.5 mm/year(Figure 4b). In order to separate recent from olddamage on buildings (related to the 1992–1995 droughtperiod), the same buildings reported on 1999 have beenstudied. Additionally, in other non-reported buildings,new cracks have appeared over pre-existing ones thatwere repaired and controlled with cluster cramps.Figure 7 shows two pictures taken in 1999 and 2009 ofthree buildings named ‘g’, ‘h’ and ‘i’ (see location in

Figure 4a). According to the forensic report of 1999,the type of foundation of building ‘g’ is superficial andthe damage caused by the first drought period involvedcracks in the structure, internal facades and cellar’s, aswell as the breakage of the manholes and flagstones,and cracking of the union joint of the building with thesidewalk. At present, the union joint crack has beenrepaired and new horizontal and 458-dip angle crackswere identified on the union joint with the sidewalk.On building ‘h’, recent ground subsidence causeddamage not only in its facades, but also on theadjacent sidewalk. The picture taken in 1999 shows acrack and titling of the dividing joint. At present, thiscrack is still opening, causing the breakage of theconcrete within the joint and the plaster cramps (which

Figure 7. Pictures of buildings g, h and i (labelled in Figure4a with the same label), taken in 1999 (left) and 2009 (right).

Figure 6. (a) Aerial extension occupied by each city blockclass expressed in percentage. The colours used for the barscorrespond to the ones in Figure 4d. (b) PSs deformation rateintervals found in each city block class.



were placed to control the movement and are dated on2007). Vertical cracks are also identified on the showwindow wall, where cracks angle direction on plastercramps indicate that the sidewalk is descending inrelation to the building, probably caused by negativefriction. The University Hospital pictures (building ‘i’in Figure 7) show that the cracks on the facade and onthe back door stairs are open again, following the samepath of the originals. This damage is caused bynegative friction of foundation piles, which havealso generated a continuous horizontal crack in theunion joint with the sidewalk along the buildingperimeter.

In Table 2, it is shown the average subsidence ratemeasured by all the PSs included within a distance of100 m from each building. Additionally, it is shown foreach of them, the maximum water table decreasemeasured in the closest piezometer as well as thethickness of the compressible layer. In the case ofbuilding ‘e’, it has been necessary to show the values ofthree borehole tests and three piezometers because it isobject of further analysis.

The case study of building ‘e’, located in the 27th ofCartagena Street (Figures 2e and 8), has been analysedseparately because it is a good example of thedifferential settlement intensifying effect, which occurswhen different type of foundations are joined.

In this area in 1995, the piezometric level declinereached 9 m producing ground settlement and sub-sequent structural damage in several buildings ofCartagena Street. Very similar piezometric variationswere observed on the second drought period (Figure9a) and new damage appeared on buildings. Anotherfactor that has to be taken in account is thecompressible thickness heterogeneity which aggravatesthe effects of the differential settlement, as the soil willnot subside in an homogeneous way. The stratigraphiccolumns from the closest boreholes (Figure 9b) showthat the compressible thickness varies from 7.5 to 22 m(Table 2). On the other hand, building ‘e’ is formed bytwo blocks of different heights; being 10 and 6 floors,respectively. The adjacent buildings, 25th and 29th ofCartagena Street, were also affected by differentialsettlement in the first drought period. A behaviourmodel has been elaborated to explain the location ofcracks and their shape (Figure 9c). Soil stratificationhas been depicted taking into account the results of thenearest boreholes tests (Figure 9b): the compressiblelayer is formed by landfills, silts and clays; the sandbeds above gravels have not been represented becausethey not always present; finally the deepness of gravelshas been estimated by interpolation.

The pillars of the cellar of building 25th presentedlongitudinal cracks caused by the combined action of

Figure 8. Measured deformation rate in the buildings of Cartagena Street. (a)The location of the three closets piezometers (P1,P2 and P3) and borehole tests (B1, B2 and B3). (b) Zoom to the 27th of Cartagena Street (white square in ‘a’).

10 G. Bru et al.


the lack of concrete compactness and the differentialsettlement with respect to building 27th. The reason forthe pillars not to settle as the rest of the structure wasbecause they are joined with the foundation of building27th, which is constituted by piles that are less affectedby subsidence. In fact building 27th, submitted 458-dipangle cracks on its facades, indicating that the borderpiles had been pulled down by the settlement of theadjacent buildings. Finally, the huge separation of theunion joint with building 29th (Figure 2e) is caused bythe greatest settlement of this building, which is inagreement with the highest deformation rates mea-sured in the area and the greater thickness of thecompressible layer. Indeed, this zone is characterised

by the existence of greater cracks along the union ofthe pavement with the buildings. Overall, the forensicanalysis of these buildings shows that even though thecracks and union joints were repaired and sealed afterthe first drought period, new damage has appeared dueto the most recent drought. This analysis demonstratesthe high susceptibility of the area to subsidence due toground water extraction and the vulnerability of thebuildings of Cartagena Street.

5. Conclusions

In this article, subsidence due to ground waterextraction and its effects on the buildings of Murcia

Figure 9. (a) Piezometric level measured near Cartagena’s Street (see location in Figure 8a). (b) Stratigraphic columns of thethree nearest boreholes (see location in Figure 8b). (c) Settlement model of the buildings 25th, 27th and 29th of Cartagena Street.



City (SE Spain) is presented. In the past decades, twomajor drought periods occurred in 1992–1995 and2005–2008 causing moderate to severe damage inbuildings and other structures, such as sidewalks,roads, walls, etc. The most common types of pathol-ogies observed on the buildings of Murcia City are:negative skin friction on concrete piles foundations;old buildings wood piles putrefaction due to the waterlevel decline; differential settlements of SF due to soilconsolidation and the subsequent angular distortionson the buildings structure.

The SPN technique has been used to analyse asatellite-based radar dataset measuring groundsurface deformation in Murcia City in the period2004–2008. This technique has permitted to measuredeformation in more than 200 points per squarekilometre, identifying the Southern and Eastern areasas the most affected by subsidence due to groundwater extraction. As a matter of fact most of thebuilding blocks that show deformation ratesgreater than 6 mm/year are located in these zones ofthe city.

Measured ground surface deformation has beencorrelated with the compressible thickness, the max-imum piezometric decline and the type of foundationof the buildings in Murcia City. In this sense, it hasbeen observed that the higher the proportion ofbuildings bare on superficial foundations, the higherthe deformation rate is. Nevertheless, it has to be takeninto account that this is not the only factor thatcontrols building settlement, as ground subsidencephenomenon depends on the water table decrease andthe thickness of compressible layer.

The structural damage analysis of several buildingshas been possible by comparing forensic analysisavailable from 1999 with data gathered in 2009,proving that new damage have appeared on severalbuildings that were also damaged after the firstdrought period. Measured ground surface deformationfrom radar satellite on these buildings has permitted toidentify the subsidence triggered by the 2005–2008drought as the main cause of the observed structuraldamage.

Therefore, according to the results presented hereinit may be concluded that there is a high susceptibilityto subsidence due to ground water extraction in theSouthern and Eastern areas of Murcia City, as well asa high vulnerability of several buildings includedwithin these zones. Even though it is necessary tocarry out an exhaustive structural analysis of damageconstructions in the future, it has been demonstratedthat the inclusion of this technique can be particularlyinteresting in structural monitoring framework of civilinfrastructures, as a complementary tool to controlsubsidence damage.

Acknowledgements

The European Space Agency (ESA) Terrafirma project hasfunded all the SAR data processing with the SPN techniqueas well as the subsidence interpretation and modelling workpresented above. Additionally, this work has been partiallyfinanced by the Spanish Geological and Mining Institute withthe collaboration of the Regional Government of Murcia andthe universities of Alicante (Projects VIGROB-157 andVIGROB-184). The Cartographical Service of Murcia(CARTOMUR) has provided DEM data and aerial photo-graphs used in this work.

References

Amelung, F., et al., 1999. Sensing the ups and downs of LasVegas: InSAR reveals structural control of land sub-sidence and aquifer-system deformation. Geology, 27,483–486.

Aragon, R., et al., 2004. Impacto de la explotacion intensivade aguas subterraneas en la ciudad de Murcia (Espana),analisis hidrogeologico. In: Proceedings of 23th interna-tional congress of IAH-ALHSUD, 11–14 October,Zacatecas, Mexico, 2622–2624 (on CDROM) [InSpanish].

Arnaud, A., et al., 2003. ASAR ERS interferometric phasecontinuity. In: Proceedings of IEEE internationalgeoscience and remote sensing symposium (IGARSS-03),21–25 July, Toulouse, France, Vol. 2, 1133–1135.

Bell, J.W., et al., 2008. Permanent scatterer InSAR revealsseasonal and long-term aquifer-system response togroundwater pumping and artificial recharge. WaterResources Research, 44, 1–18.

Cascini, L., et al., 2006. Subsidence monitoring in Sarnourban area via multi-temporal DInSAR technique.International Journal of Remote Sensing, 27, 1709–1716.

Ceron, J.C. and Pulido, A., 1996. Groundwater problemsresulting from CO2 pollution and overexploitation inAlto Guadalentın aquifer (Murcia, Spain). EnvironmentalGeology, 28, 223–228.

Crosetto, M., Castillo, M., and Arbiol, R., 2003. Urbansubsidence monitoring using radar interferometry: algo-rithms and validation. Photogramming Engineering andRemote Sensing, 69, 775–670. 783.

De Justo, J.L., Vazquez, N.J., and De Justo, E., 2002.Rozamiento negativo en pilotes producidos por lasubsidencia en Murcia. Ingenierıa Civil, 125, 95–103 [InSpanish].

Ferretti, A., Prati, C., and Rocca, F., 2001. Permanentscatterers in SAR interferometry. IEEE Transactions onGeoscience Remote Sensing, 39, 8–20.

Ferretti, A., et al., 2004. InSAR permanent scatterer analysisreveals ups and downs in San Francisco Bay area. EOS,85 (34), 317–324.

Galloway, D.L., et al., 1998. Detection of aquifer systemcompaction and land subsidence using interferometricsynthetic aperture radar, Antelope Valley,Mojave Desert,California.Water Resource Research, 34, 2573–2585.

Herrera, G., et al., 2009a. Validation and comparison ofadvanced differential interferometry techniques: Murciametropolitan area case study. ISPRS Journal of Photo-grammetry and Remote Sensing, 64, 501–512.

Herrera, G., et al., 2009b. Advanced interpretation ofsubsidence in Murcia (SE Spain) using A-DInSARdata – modelling and validation. Natural Hazards andEarth System Science, 9, 647–661.

12 G. Bru et al.


Hoffmann, J., Galloway, D.L., and Zebker, H.A., 2003.Inverse modeling of interbed storage parameters usingland subsidence observations, Antelope Valley, Califor-nia. Water-Resources Research, 39, SBH 5–1–5–10.

Hooper, A., et al., 2005. A new method for measuringdeformation on volcanoes and other natural terrainsusing InSAR persistent scatterers. Geophysics ResearchLetters, doi:10.1029/2004 GL021737.21.

Hu, R.L., et al., 2004. Review on current status andchallenging issues of land subsidence in China. Engineer-ing Geology, 76, 65–77.

IGME, 1986. Calidad de las aguas subterraneas en la CuencaBaja del Segura y costeras de Alicante. Madrid: InstitutoGeologico y Minero de Espana.

IGME, 2000. Estudio Geotecnico del subsuelo del AreaMetropolitana de Murcia. Instituto Geologico y Minerode Espana, 200 pp. [In Spanish].

IGME, 2001. Seguimiento y control instrumental de lasubsidencia del terreno en Murcia: Fase I. InstitutoGeologico y Minero de Espana, 120 pp. [In Spanish].

IGME, 2005. Seguimiento y control instrumental de lasubsidencia del terreno en Murcia: Fase II. InstitutoGeologico y Minero de Espana, 150 pp. [In Spanish].

Martınez, M., et al., 2004. Efectos de una subsidenciamoderada por extraccion de agua subterranea en Murcia,Espana. In: Proceedings of 23th Congress of IAH-ALHSUD, 11–14 October, Zacatecas, Mexico, 249–252(on CD-ROM) [In Spanish].

Mora, O., Mallorquı, J.J., and Broquetas, A., 2003. Linearand nonlinear terrain deformation maps from a reducedset of interferometric SAR images. IEEE Transactions onGeoscience and Remote Sensing, 41, 2243–2253.

Mulas, J., et al., 2000. Estudio Geotecnico del subsuelo delArea Metropolitana de Murcia. Instituto Geologico yMinero de Espana, 220 pp. [In Spanish].

Mulas, J., et al., 2003. Geotechnical and hy-drologicalanalysis of land subsidence in Murcia (Spain). In:Proceedings of 1st international conference on groundwaterin geological engineering, 22–26 September, Bled, Slove-nia, Vol. 50, 249–252.

Mulas, J., et al., 2004. Estimacion de la subsidencia del AreaMetropolitana de Murcia mediante Interferometrıa Radar.Instituto Geologico y Minero de Espana, Madrid, 38 pp.[In Spanish].

Tomas, R., 2009. Estudio de la subsidencia de la ciudad deMurcia mediante interferometrıa SAR diferencial avanza-da. Thesis (PhD). Universidad de Alicante. [In Spanish].

Tomas, R., et al., 2005. Mapping ground subsidence inducedby aquifer overexploitation using advanced differentialSAR interferometry: Vega media of the Segura River (SESpain) case study. Remote Sensing of the Environment, 98,269–283.

Vazquez, J.N. and De Justo, J.L., 2002. In: COPOT, Murcia,ed. La subsidencia en Murcia. Implicaciones y consecuen-cias en la edificacion. Ed. COPOT, Murcia. 262 pp. [InSpanish].

Werner, C., et al., 2003. Interferometric point target analysisfor deformation mapping. In: Proceedings of IEEEinternational geoscience and remote sensing symposium(IGARSS-03), 21–25 July, Toulouse, France, Vol. 7,4362–4364.

Zerbini, S., et al., 2007. A combination of space andterrestrial geodetic techniques to monitor land subsi-dence: case study, the Southeastern Po Plain, Italy.Journal of Geophysics Research, 112, B05401;doi:10.1029/2006JB004338.



Date post:	04-Dec-2023
Category:	Documents
Upload:	upm-es
View:	0 times
Download:	0 times

Control of deformation of buildings affected by subsidence using persistent scatterer interferometry

Documents