early stage sinkhole formation in the acque albule basin of central italy from geophysical and geochemical observations abstract sinkhole occurrence along the tyrrhenian margin of the central apennines is of great importance for applied research land management and civil protection this study reports on gps altimetry magnetic gravity geoelectric seismic and soil gas measurements of a rapidly developing sinkhole near the guidonia military airport the measurements revealed an elliptical 2 m depression elongated 220 m in the nne ssw direction with the minor axis of 110 m in the spring of 2013 two vertical cavities formed in the eastern and northeastern flanks of the depression whose depths and shapes are rapidly evolving with the formation of widespread fracturing along the same side the geophysical observations image the developing sinkhole to a depth of some 50 m the presence of the travertino lithotype around the depression down to at least 40 m and the lack of this lithotype below the lowered area the sinkhole s evolution appears to be structurally controlled by local and regional faulting these results are useful for designing further geophysical geotechnical and geochemical studies to monitor the sinkhole s evolution and to assess the hazard it presents in densely urbanized area

sharpness of upper mantle discontinuities determined from high frequency reflections an understanding of the nature of seismic discontinuities in the earth s upper mantle is important for understanding mantle processes in particular the amplitude and sharpness of these discontinuities are critical for assessing models of upper mantle phase changes and chemical layering so far seismic studies aimed at determining the thickness and lateral variability of upper mantle discontinuities have yielded equivocal results particularly for the discontinuity at 410km depth1 2 here we present short period 0 8 2 0 s recordings of upper mantle precursors to the seismic phase p p pkppkp from two south american earthquakes recorded by the 700 station short period array in california our results show that the 410 and 660 km discontinuities beneath the indian ocean are locally simple and sharp corresponding to transi tion zones of 4 km or less these observations pose problems for mineral physics models3 5 which predict a transitional thickness greater than 6 km for the peridotite to spinel phase transition in contrast to the results of long period studies6 7 we observe no short period arrivals from near 520 km depth

the origin and growth of a recently active fissure ridge travertine over a seismic fault tivoli italy abstract an enigmatic c 2 km long and 15 m high travertine ridge the colle fiorito ridge occurs in the northwestern sector of the tivoli travertine plateau central italy the main questions addressed in this paper concern the origin and mode of growth of this prominent ridge the presence of active structures beneath the studied ridge is inferred by recent and past earthquakes located at shallow depths immediately beneath colle fiorito to understand the surficial structure of the colle fiorito ridge and the travertine depositional environment we constructed a 10 m resolution dem analyzed recent and past aerial photographs and conducted field surveys and meso to micro scale sedimentological analyses to understand the ridge subsurface structure we studied a set of 32 stratigraphic well logs available from previous works and from the local decorative stone industry and realized a 2d electrical resistivity tomography ert across the ridge results show a gentle antiformal structure affected by subvertical zones of strata discontinuity the colle fiorito structure is interpreted as a previously unknown fissure ridge travertine grown at the edge of the tivoli travertine plateau perhaps when the volumetric deposition rate reached its climax in the plateau for the abundance of fluid discharge and the rise of the water table such a fluid pressure may have activated the faults and fractures beneath colle fiorito thus opening new pathways for the ascension of geothermal fluids toward the surface

the colli albani mafic caldera roma italy stratigraphy structure and petrology new results for the colli albani volcano roma italy surveyed for the geological map of italy at 1 50 000 scale carg project integrated with previous data provide insights on caldera evolution the colli albani a quiescent volcano became active at 600 ka eruptive compositions are consistently mafic 50 km 3 deposits forming the villa senni eruption unit ignimbrites at ca 355 ka two edifices were built within the caldera 1 the horseshoe shaped tuscolano artemisio ta composite edifice or lithosome consists of coalescing peri caldera fissure related scoriae cones interbedded with lava flows the fissure system forms two segments controlled by regional fractures 2 the steep sided faete stratovolcano 949 m a s l filled the caldera the ta and faete lithosomes partly interfinger and were emplaced at 350 260 ka their products indicate reduced eruption rates relative to the vl period and a change to effusive and mildly explosive eruptions the most recent and still active phase of phreatomagmatic activity formed overlapping maars and tuff cones along the western and northern slopes of the volcano collectively named via dei laghi composite lithosome the colli albani caldera is poly phase 1 a piecemeal caldera is associated with large volume ignimbrites of the vl edifice the present shape of the caldera is related to the villa senni eruption 2 the ta composite edifice erupted from peripheral caldera fissures is unrelated to explosive phases of caldera collapse the ta final products cover a morphologically stable caldera wall the peripheral fractures feeding the ta composite edifice are interpreted as volcano tectonic structures activated during the late stage downsag of the caldera reduced eruption rates during the ta and the faete stages 10 1 km 3 1 ka respect to 10 0 km 3 1 ka for the vl edifice suggest a reduced recharge of the magma chamber that may have induced prolonged deflation and downsagging of the caldera floor and the opening of outward dipping peripheral fractures by this interpretation the ta edifice represents the surface expression of ring dykes at depth the absence of similar fissure structures along the western caldera rim may relate to the deep geometry of the ring faults dipping inward in those areas and therefore not favourably oriented for magma intrusion during a period of general subsidence by contrast the following and still active phreatomagmatic phase that has emplaced the via dei laghi composite edifice is located right on the western side of the caldera and may therefore relate to resurgent conditions classical petrological and pers pearce elements ratios analyses indicate that lavas are co genetic and show a differentiation trend up through stratigraphy driven by

sinkholes in italy first results on the inventory and analysis the italian geological survey apat carried out field surveys and analysis of collapse phenomena sinkholes in italy the main goal of the project is to collect geological geomorphological geochemical and hydrogeological data about the sinkhole prone areas in italy in order to develop a spatial database of the characteristics of each phenomenon the preliminary results of this study provide information on the distribution geological setting and monitoring and remediation actions associated with these natural collapses in italy many italian regions are affected by these natural disasters some of them are caused by karst collapses or anthropic activity however some occur in areas characterized by buried carbonate bedrock up to 190 m as well as by peculiar geological structural and geochemical scenarios in these areas it is not reasonable to ascribe the formation mechanism to karst activity instead these types of cavities quickly develop in terrains with a variable granulometry often in connection with upwelling fluids in this work some natural specific cases have been studied in order to define the relationships between the geology regional tectonic elements mineral spring waters and strong gas vents and the genesis of the sinkholes a first attempt of sinkhole classification is also presented

the influence of loess cave development upon landslides and geomorphologic evolution a case study from the northwest loess plateau china abstract loess caves landslides collapses bank erosion and soil erosion which are independently and interactively shaping the modern loess landscape are widely distributed across the chinese loess plateau the study area is located in a small watershed in huining county gansu province which is one of the areas with the strongest development of loess caves across the loess plateau this area is an ideal site for studying geological hazards and geomorphic evolution on the loess plateau seventeen landslides and 176 loess caves with a density of 887 units km2 were investigated with a uav unmanned aerial vehicle and mapped by gis geographic information system using high resolution uav images and topographic data we carried out an interpretation of loess caves bank erosion and landslides studied the spatial distribution and developmental patterns of loess caves landform morphology and the relationship between loess caves and landslides based on gis spatial analysis mathematical statistics and field surveys and analyzed the influence of loess microtopography on slope landforms finally six typical evolutionary models of soil erosion loess cave development landslide occurrence barrier dam formation are preliminarily proposed the primary slope stage early cave stage accelerated cave stage cave connecting stage landslide creeping stage and landslide dam forming stage this study is a useful exploration and an attempt to reveal the influence of loess cave development on slope stability and disaster chain effects

upper mantle s velocity structure of central and western south america we have used broadband seismograms recorded at portable and permanent seismic stations in south america to image the three dimensional s velocity structure beneath central and western south america we have interactively fitted the waveforms of s and surface wave trains in 500 seismograms from 90 earthquakes and 60 different stations the constraints on upper mantle s velocity structure provided by the waveform fits have been combined with independent estimates of depth to the mohorovicic discontinuity yielding model sa99 the s velocity structure of sa99 reveals a highly heterogeneous upper mantle with a maximum peak to peak difference of 1 km s above 100 km the heterogeneity seems to be correlated with tectonic and geologic domains sa99 shows high lithospheric s velocities for the precambrian cratons the amazon basin is also underlain by high s velocities while three other intraplatform basins are underlain by low s velocities at various depths sa99 shows extremely low velocities in the mantle wedge beneath the volcanically active andes we explain these low s velocities as originating from realistic amounts of volatiles released by the subducting nazca crust and resulting amounts of partial melt within the peridotitic mantle wedge without requiring elevated temperatures while sa99 could be consistent with diffuse influx for corner flow in the mantle wedge it does not support models that require influx of subcontinental upper mantle into the mantle wedge through a laterally uniform low viscosity channel

a response function approach for rapid far field tsunami forecasting predicting tsunami impacts at remote coasts largely relies on tsunami en route measurements in an open ocean in this work these measurements are used to generate instant tsunami predictions in deep water and near the coast the predictions are generated as a response or a combination of responses to one or more tsunameters with each response obtained as a convolution of real time tsunameter measurements and a pre computed pulse response function prf practical implementation of this method requires tables of prfs in a 3d parameter space earthquake location tsunameter forecasted site examples of hindcasting the 2010 chilean and the 2011 tohoku oki tsunamis along the us west coast and beyond demonstrated high accuracy of the suggested technology in application to trans pacific seismically generated tsunamis

410 km discontinuity sharpness and the form of the olivine α β phase diagram resolution of apparent seismic contradictions summary estimates of the thickness of the 410 km seismic discontinuity believed to be due to the olivine modified spinel transformation in olivine are as low as 4 km based on discontinuity reflectivity the seismically estimated thickness is however biased to values narrower than the true transformation interval if linear interpolation of properties is used for modelling a 5 km linear velocity gradient yields an average reflection coefficient identical to that of a 10 km transition interval based on olivine phase diagram features moreover alternative forms of the phase diagram equally consistent with experimentally determined iron magnesium partitioning can yield true transition intervals as narrow as 4 km this reconciles a discrepancy between phase equilibrium and seismic measures of discontinuity thickness in two ways 1 seismic thickness estimates are too narrow and 2 narrow transition intervals are permissible given existing phase equilibrium constraints incorporating recent results on the influence of h2o on discontinuity properties it appears that 410 km discontinuity reflectivity is much more sensitive to varying h2o concentration than to temperature suggesting that discontinuity reflectivity variations reflect changes in mantle chemistry

integrated geophysical survey in a sinkhole prone area microgravity electrical resistivity tomographies and seismic noise measurements to delimit its extension abstract detection forecasting early warning and effective monitoring are key aspects for the delimitation of sinkhole prone areas and for susceptibility assessment and risk mitigation to attain these goals direct and indirect techniques can be employed and the integration of different indirect non invasive geophysical methods including 2d and 3d electrical resistivity tomography microgravity and single station seismic noise measures was carried out at il piano elba island italy where at least nine sinkholes occurred between 2008 and 2014 the most likely origin for these sinkholes had been considered related to net erosion of sediment from the alluvium caused by downward water circulation between the aquifer hosted in the upper layer quaternary alluvial deposits and that in the lower triassic brecciated dolomitic limestone and cretaceous slate the integrated geophysical survey therefore was carried out a to differentiate shallower from deeper geological layers b to detect possible cavities that could evolve into sinkholes c to suggest possible triggers and d to delimit the sinkhole prone area the results of the integrated geophysical surveys suggest that the study area is mainly characterised by paleochannels and that the sinkhole prone area boundaries correspond to these paleochannels

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

the sirente crater field italy revisited 1 a scientific debate has developed in the last few years as to whether a 130 m diameter sag pond surrounded by a saddle shaped rim and neighboring smaller sags from the sirente plain abruzzi italy represent the only known italian meteoritic crater field a mud volcano or an anthropogenic feature to decipher the nature of the sirente landforms we carried out geophysical and geochemical investigations geoelectric profiles document two karstified shelf carbonate ridges lying at 10 40 m depth below calcareous lacustrine silts and deeper more conductive sediments likely soils tephra filling the plain the smaller sags lie just above the ridges implying a karstic origin whereas the main sag also resting above a carbonate ridge shows no roots in excess of 10 20 m depth in contrast to the crater interpretation high resolution magnetic surveys reveal negative positive anomaly stripes in correspondence with the buried ridges valleys respectively the smaller sags as well as the main crater are located in the domain of negative residuals the positive long wavelength magnetic signature is likely due to the strongly susceptive soils tephra filling the buried valleys magnetic modeling shows that the field observed over the crater is incompatible with the field generated by a buried meteorite with realistic characteristics the smaller sags are characterized by small magnetic anomaly couplets perfectly reproducible considering the susceptibility contrast between the fill in soil and the surrounding silts our data show that the sirente crater and the minor depressions are simply the results of human activity and karstic processes respectively

identification and quantitative analysis of sinkhole contributing factors in florida s karst abstract sinkholes are one of the major geohazards in karst areas causing loss of life and significant economic loss as well sinkhole forming mechanism varies depending on the geological environment and florida s sinkholes are formed through the process of interaction between groundwater flow and cover soils the significance of this paper is 1 to identify key sinkhole contributing factors and 2 to quantify the impact of those factors on sinkhole formation particularly this study accounted for geomechanical factors that contribute to sinkhole raveling due to erosion and mechanical stability of overburden soils identification of key sinkhole contributing factors will allow developing a probabilistic sinkhole prediction model the study area was focused on east central florida where cover collapse sinkholes often occur uniform distribution transformation was employed for the quantitative analysis on each factor and then case studies with specific examples are then presented to validate the results of the quantitative analysis in conclusion the identified key factors are hydraulic head difference soil permeability thicknesses of aquifer systems and proximity to karst features e g existing sinkhole the critical permeability kcrit showing a rapid increase of sinkhole occurrence is about 20 cm h thickness and characteristics of cover soils seem a controlling factor of sinkhole types and the overburden thickness around 40 to 45 m tends to form the collapse type a multivariate regression analysis indicates that the thickness of the surficial aquifer system is the most significant factor and then the head difference and the proximity to karst features follow in order

a genetic classification of sinkholes illustrated from evaporite paleokarst exposures in spain this contribution analyses the processes involved in the generation of sinkholes from the study of paleokarst features exposed in four spanish tertiary basins bedrock strata are subhorizontal evaporites and in three of the basins they include halite and glauberite in the subsurface our studies suggest that formation of dolines in these areas results from a wider range of subsidence processes than those included in the most recently published sinkhole classifications a new genetic classification of sinkholes applicable to both carbonate and evaporite karst areas is thus proposed with the exception of solution dolines it defines the main sinkhole types by use of two terms that refer to the material affected by downward gravitational movements cover bedrock or caprock and the main type of process involved collapse suffosion or sagging sinkholes that result from the combination of several subsidence processes and affect more than one type of material are described by combinations of the different terms with the dominant material or process followed by the secondary one e g bedrock sagging and collapse sinkhole the mechanism of collapse includes any brittle gravitational deformation of cover and bedrock material such as upward stoping of cavities by roof failure development of well defined failure planes and rock brecciation suffosion is the downward migration of cover deposits through dissolutional conduits accompanied with ductile settling sagging is the ductile flexure of sediments caused by differential corrosional lowering of the rockhead or interstratal karstification of the soluble bedrock the paleokarsts we analysed suggest that the sagging mechanism not included in previous genetic classifications plays an important role in the generation of sinkholes in evaporites moreover collapse processes are more significant in extent and rate in areas underlain by evaporites than in carbonate karst primarily due to the greater solubility of the evaporites and the lower mechanical strength and ductile rheology of gypsum and salt rocks

definition of sinkhole triggers and susceptibility based on hydrogeomorphological analyses sinkholes represent a geological risk that is often underrated mainly due to its very localized nature in fact sinkholes occur only under particular circumstances and typically affect relatively small areas despite these characteristics the difficulty in forecasting the precise location and timing of their sudden collapse creates serious problems for civil protection authorities and urban planners in this framework identifying the mechanism and thus the triggering factor of sinkholes is strategically pivotal in developing management plans the present paper addresses the sinkhole prone area of il piano elba island central italy the integration of hydrogeological surveys coupled with a thorough study of historical maps and aerial photographs suggests that the main triggering factor in this area may not be related to water pumping from the karst aquifer as initially hypothesized instead sinkholes appear to be caused by ravelling and erosive processes occurring entirely in the sedimentary cover when heavy rainfall induces water overpressure within the superficial aquifer

international geomagnetic reference field the eleventh generation the eleventh generation of the international geomagnetic reference field igrf was adopted in december 2009 by the international association of geomagnetism and aeronomy working group v mod it updates the previous igrf generation with a definitive main field model for epoch 2005 0 a main field model for epoch 2010 0 and a linear predictive secular variation model for 2010 0 2015 0 in this note the equations defining the igrf model are provided along with the spherical harmonic coefficients for the eleventh generation maps of the magnetic declination inclination and total intensity for epoch 2010 0 and their predicted rates of change for 2010 0 2015 0 are presented the recent evolution of the south atlantic anomaly and magnetic pole positions are also examined

resistivity imaging of controlled source audiofrequency magnetotelluric data the controlled source audiofrequency magnetotelluric csamt method is an electromagnetic em method where a transmitter a grounded electric bipole or a current loop is placed far away from the receiver sites if the transmitter is located at distances greater than 3 5 skin depths the plane wave approximation is valid and the techniques used for natural source mt interpretation can be applied goldstein and strangway 1975 sandberg and hohmann 1982 the csamt method can be employed in a detailed survey by closely spacing a number of receiver sites along a traverse the borehole csamt technique is proposed in west and ward 1988 to enhance the ability of the surface csamt method to detect subsurface inhomogeneities in these cases two dimensional 2 d smooth model inversion rodi et al 1984 sasaki 1989 degroot hedlin and constable 1990 would be particularly useful for deriving a resistivity model from the far field data and for presenting the survey results in the form of an image

complex resistivity survey for the evaluation of ground reinforcement in a karst area abstract a complex resistivity cr survey was used to evaluate ground reinforcement following the injection of mortar which is rich in clay minerals known to show strong induced polarization effects cr surveys were used to determine the distribution of injected mortar along six survey lines parallel to a road in a karst area in yongweol ri muan gun korea which had suffered from ground subsidence and had been reinforced cr data were collected at 0 125 hz along each survey line and inverted to find two phase anomalies we show that the phase anomalies indicate the accumulation of injected mortar this interpretation was confirmed according to the amount of mortar injected at each borehole and the time lapse tl direct current data obtained during the reinforcement process furthermore the cr data were three dimensionally inverted with the results compared to those of a two dimensional 2 d inversion to demonstrate that 3 d inversion can provide more detailed information than 2 d analysis a cr survey is an effective tool to determine the distribution of injected mortar

seismic evidence for water deep in earth s upper mantle water in the deep upper mantle can influence the properties of seismic discontinuities in the mantle transition zone observations of converted seismic waves provide evidence of a 20 to 35 kilometer thick discontinuity near a depth of 410 kilometers most likely explained by as much as 700 parts per million of water by weight

hidden sinkholes and karst cavities in the travertine plateau of a highly populated geothermal seismic territory tivoli central italy abstract sinkholes and other karst structures in settled carbonate lands can be a significant source of hazard for humans and human works acque albule the study area of this work is a plio pleistocene basin near rome central italy superficially filled by a large and thick deposit of late pleistocene thermogene travertine human activities blanket large portions of the flat territory covering most evidence from geological surface processes and potentially inducing scientists and public officials to underestimate some natural hazards including those connected with sinkholes to contribute to the proper assessment of these hazards a geomorphologic study of the basin was performed using digital elevation models dems recent aerial photographs and field surveys historical material such as old aerial photographs and past geomorphologic studies both pre dating the most part of quarrying and village building was also used together with memories of the elderly population this preliminary study pointed out the presence of numerous potentially active sinkholes that are at present largely masked by either quarrying or overbuilding where this first study pointed out the apparent absence of sinkholes in areas characterized by high density of buildings a detailed subsurface study was performed using properly calibrated electrical resistivity tomography ert and dynamic penetration measurements dpsh together with some borehole logs made available from the local municipality this second study highlighted the presence of sinkholes and caves that are this time substantially hidden to the resolution of standard methods and materials such as aerial photographs dems and field surveys active sinkhole subsidence in the acque albule basin may explain at least in part the frequent damages that affect numerous buildings in the area the main conclusion from this study is that the mitigation of sinkhole hazard in highly populated areas has to pass through a thorough search of hidden sinkholes that can be masked by the anthropocenic molding and blanketing of the territory for these purposes data from historical pre anthropocene documents as well as where possible subsurface investigations are fundamental

variability of p660s phases as a consequence of topography of the 660 km discontinuity abstract records from the broad band nars nl array deployed in the netherlands western germany and belgium have been analyzed for p to s converted phases from the 660 km discontinuity p660s no individual seismogram from this array shows a clear p660s phase stacks of up to 113 crosscorrelograms show p660s energy that is weak in comparison with similar stacks elsewhere very high amplitude observations of p660s in single seismograms from the same region have been made in a previous study paulssen 1985 geophys res lett 12 709 712 paulssen 1988 j geophys res 93 10489 10500 such variations may be due to relief on the 660 km discontinuity in this paper we quantify the effects of different topographies on the time delays amplitudes and waveforms of the direct p wave as well as on the p660s converted wave synthetic p and p660s waveforms are calculated by applying a kirchhoff helmholtz integration over the wave fields at the 660 km discontinuity interface for topography on scales of a few hundreds of kilometers the effects on the p wave are very small compared with those on the p660s phases time delays focused and defocused amplitudes and waveform distortion of p660s phases influenced by such topography diminish the coherence of p660s in synthetic stacks our results show that topography of the 660 km discontinuity with dominant scale lengths of a few hundreds of kilometers and variations in depth of 15 km to 25 km is consistent with the pattern of p660s observations in single seismograms and stacks

soil gas distribution in the main coseismic surface rupture zone of the 1980 ms 6 9 irpinia earthquake southern italy soil gas measurements of different gas species with different geochemical behaviors were performed in the area of the pecore plain a 200 m 300 m sized fault bounded extensional basin located in the northern mount marzano massif in the axial belt of the southern apennine chain the pecore plain area was affected by coseismic surface faulting during the ms 6 9 1980 irpinia earthquake the strongest and most destructive seismic event of the last 30 years in southern italy the collected data and their geostatistical analysis provide new insights into the control exerted by active fault segments on deep seated gas migration toward the surface the results define anomalies that are aligned with the nw se trending coseismic rupture of the 1980 earthquake along the western border of the plain as well as along the southern border of the plain where a hidden e w striking fault is inferred geospatial analysis highlights an anisotropic spatial behavior of 222rn along the main nw se trend and of co2 along the e w trend this feature suggests a correlation between the shape and orientation of the anomalies and the barrier conduit behavior of fault zones in the area furthermore our results show that gas migration through brittle deformation zones occurs by advective processes as suggested by the relatively high migration rate needed to obtain anomalies of short lived 222rn in the soil pores

sudden deep gas eruption nearby rome s airport of fiumicino 1 on 24 august 2013 a sudden gas eruption from the ground occurred in the tiber river delta nearby rome s international airport of fiumicino we assessed that this gas analogous to other minor vents in the area is dominantly composed of deep partially mantle derived co2 as in the geothermal gas of the surrounding roman comagmatic province increased amounts of thermogenic ch4 are likely sourced from meso cenozoic petroleum systems overlying the deep magmatic fluids we hypothesize that the intersection of ne sw and n s fault systems which at regional scale controls the location of the roman volcanic edifices favors gas uprising through the impermeable pliocene and deltaic holocene covers pressurized gas may temporarily be stored below these covers or within shallower sandy permeable layers the eruption regardless the triggering cause natural or man made reveals the potential hazard of gas charged sediments in the delta even at distances far from the volcanic edifices

the impact of groundwater drawdown and vacuum pressure on sinkhole development physical laboratory models abstract a considerable proportion of the damaging sinkholes worldwide correspond to human induced subsidence events related to groundwater withdrawal and the associated water table decline e g aquifer overexploitation dewatering for mining buoyancy loss in pre existing cavity roofs is generally claimed to be the main underlying physical mechanism it has been also postulated that rapid water table drawdowns may create a vacuum effect in the subsurface and contribute to enhance sinkhole activity in karstic terrains with a low effective porosity cover our laboratory physical model explores the role played by vacuum pressure induced water table drops with different magnitudes and rates on sinkhole development simulating an invariable mantled karst comprising cavernous bedrock and a low permeability cover the multiple tests performed include real time monitoring of the water level drawdown magnitude duration rate the negative air pressures in the bedrock cavity and the cover and several features of the subsidence phenomena deformation style size magnitude rate the main findings derived from the test results include 1 vacuum pressure may trigger the development of cover collapse sinkholes in areas with low permeability covers 2 different water table decline patterns magnitude duration rate may result in different subsidence styles or rheological behaviours sagging versus collapse 3 ground fissuring frequently related to extension at the margin of sagging depressions may cancel or significantly diminish the vacuum effect 4 an overall direct relationship between the water table decline rate and the subsidence rate some possible strategies are proposed to ameliorate the adverse effect of the negative air pressure on sinkhole hazard which most probably has a local impact restricted by the concurrence of rapid water drawdowns and low permeability covers

foundation evaluation of underground metro rail station using geophysical and geotechnical investigations abstract excavations for underground space developments in a thickly populated urban area are sometimes hindered by unexpected formidable consequences like formation of sinkholes or uneven settlement of foundations such troublesome incidences occasionally damage structures in the vicinity of excavations although adequate design guidelines and codes of practices are adopted the disturbance of subsurface regime due to excavation or construction activities often leads to undesired stability issues with resultant appearance of weak zones the reinforcement of weak zones by grouting is one of the common remedies without demarcating the weak or the affected zones becomes counter productive excavation at a location in chennai mega city for metro rail was severely affected by soil piping with development of sinkholes and weakening of the surrounding strata subsequently development of cracks in the adjacent buildings and caused tilting of the nearby taller structures the mandated the geophysical and geotechnical investigations were carried out to demarcate the affected area to avoid further deterioration of the site cross hole seismic p and s wave velocities were estimated between10 pairs of boreholes up to 20 m depth on both the sides of the excavation two electrical resistivity tomography ert profiles each of 141 m in length were carried out in the same location cross hole s wave velocity profiles and resistivity tomograms clearly indicate the presence of weak zones and possible sinkhole locations site specific empirical relationship was established between s wave velocity and standard penetration test spt n value this relationship was further used for determination of spt n values from the measured vs values to compare the subsurface conditions identified under pre and post excavations the results confirmed the presence of weak zones which are responsible for the weakening of the surrounding strata in the foundation geophysical and geotechnical investigations similar to present investigation can be useful for designing metro rail projects in a subsurface environment comprising alluvium sand clay mixed with silt pebbles and boulders lying near a region of ground water pocket in a thickly populated urban area

a preliminary sinkhole raveling chart abstract sinkholes are a major geohazard in karst areas where soluble carbonate bedrock exists downward seepage resulting from the groundwater recharge continuously erode cover soils into cavities within the underlying bedrock resulting in raveling of cover soils identifying these raveled soils or zones is critial in preventing and mitigating the sinkhole collapse in this study a proof of concept was performed to demonstrate the concept of a sinkhole raveling chart that can quantify the severity levels of raveling the raveling chart is constructed based on cone penetration test cpt data collected through multiple sinkhole active sites in central florida a preliminary analysis e g data preparation grouping and zoning was carried out to construct the prototype sinkhole raveling chart this prototype raveling chart as a function of tip resistance qc and sleeve friction fs could delineate not only the raveled and non raveled zones but also the areas that correspond to different levels of raveling severity