the impact of airmass boundaries on the propagation of deep convection a modeling based study in a high cape low shear environment a suite of experiments conducted using a cloud resolving model is examined to assess the role that preexistingairmassboundariescanplayinregulatingstormpropagation the27may1997centraltexastornadic event is used to guide these experiments the environment of this event was characterized by multiple preexisting airmass boundaries large cape and weak vertical shear only the experiments with preexisting airmass boundaries produce back building storm propagation storm motion in opposition to the mean wind when both the cold front and dryline are present storm maintenance occursthroughthe quasi continuousmaintenance ofa setoflong livedupdraftsandnotthrough discrete updraft redevelopment since the cold front is not required for back building it is clear that back building in this environment does not require quasi continuous updraft maintenance the back building storm simulated with both the cold front and dryline is found to be anchored to the boundary zipper the intersection of the cold front and dryline however multiplepreexisting airmass boundaries are not required for back building since experiments with only a dryline also support back building a conceptual model of back building and boundary zippering is developed that highlights the important role that preexisting boundaries can play in back building propagation

liquefaction evidence for strong earthquakes of holocene and latest pleistocene ages in the states of indiana and illinois usa abstract sand and gravel filled clastic dikes of seismic liquefaction origin occur throughout much of southern indiana and illinois nearly all of these dikes originated from prehistoric earthquakes centered in the study area in this area at least seven and probably eight strong prehistoric earthquakes have been documented as occurring during the holocene and at least one during the latest pleistocene the recognition of different earthquakes has been based mainly on timing of liquefaction in combination with the regional pattern of liquefaction effects but some have been recognized only by geotechnical testing at sites of liquefaction most paleo earthquakes presently recognized lie in indiana but equally as many may have occurred in illinois studies in illinois have not yet narrowly bracketed the age of clastic dikes at many sites which sometimes causes uncertainty in defining the causative earthquake but even in illinois the largest paleo earthquakes probably have been identified prehistoric magnitudes were probably as high as about moment magnitude m 7 5 this greatly exceeds the largest historic earthquake of m 5 5 centered in indiana or illinois the strongest paleo earthquakes struck in the vicinity of the concentration of strongest historic seismicity elsewhere paleo earthquakes on the order of m 6 7 have occurred even where there has been little or no historic seismicity both geologic and geotechnical methods of analysis have been essential for verification of seismic origin for the dikes and for back calculating prehistoric magnitudes methods developed largely as part of this study should be of great value in unraveling the paleoseismic record elsewhere

liquefaction failure and remediation king harbor redondo beach california liquefaction failure including large lateral displacements and associated settlement severely damaged marina facilities at redondo beach king harbor during the northridge earthquake of january 17 1994 although minor ground deformation apparently occurred in several areas of the harbor severe damage was restricted to the central portion of mole b one of four offshore fills constructed as a part of marina improvements in 1960 61 local ground conditions and methods used to remediate liquefaction are presented and discussed two ground modification techniques were used to mitigate the liquefaction potential of the reconstructed mole b facilities the major portion of the failure area was treated with vibroreplacement stone columns vibratory displacement and installation of the gravel columns not only densified the foundation soils but also provide additional strength and drainage capacity compaction grouting was used to densify foundation soils in the vicinity of existing improvements that were considered sensitive to construction induced ground vibrations these ground improvement techniques effectively reduced the liquefaction potential and allowed the marina improvements to be reconstructed on shallow foundations similar to the original design

numerical analysis of seismically induced liquefaction in earth embankment foundations part i benchmark model a numerical analysis has been performed for a clayey embankment founded on a liquefiable foundation soil using an effective stress based fully coupled finite element code called diana swandyne ii the results were compared with data obtained from centrifuge experiments in part i the numerical method and the analysis procedure are explained the results obtained for a series of three consecutive increasing amplitude shaking events are presented an attempt has been made to calibrate a benchmark model to be used in the application of different remedial measures which are discussed in part ii the numerical predictions compared well with the experimental data and provided further insights into the dynamic behavior of embankment foundation systems key words liquefaction numerical modeling coupled formulation centrifuge embankment earthquakes

seismic response of shallow foundation on liquefiable sand investigators conducted eight centrifuge model experiments to study the mechanism of liquefaction induced settlement of a shallow foundation as well as the effectiveness of sand densification by vibrocompaction under the footing two series of model tests were conducted with a surface circular footing placed on a medium dense saturated sand layer overlying an impervious rigid base horizontal shaking simulating an earthquake was used to excite the base of each model in flight in all cases this shaking liquefied the sand in the free field the first series of tests concentrated on the effect of the depth of soil compacted under the foundation on the footing acceleration and settlement investigators discovered that as the compaction depth increased and approached the total thickness of the soil deposit the footing acceleration during shaking increased and its settlement decreased the soil was not densified in the second series of tests this series focused on the effect of soil permeability on pore pressure buildup and footing settlement investigators learned that as the soil becomes more impervious significant negative excess pore pressures develop under the footing during shaking and the contribution of postshaking foundation settlement increases while the total foundation settlement does not change significantly building settlements observed after two earthquakes in liquefied areas of niigata japan in 1964 and dagupan philippines in 1990 are discussed comparisons are made between the field observations and the centrifuge results

time dependent ground motion amplification characteristics at reclaimed land after the 1995 hyogoken nambu earthquake two sets of borehole array records obtained from the great hanshin earthquake as well as its fore and after shocks are investigated one of the stations is located at port island in kobe city where severe liquefaction occurred and the records from the main event include the typical phenomena of liquefaction the other station is located at rokko island in kobe city where the liquefaction phenomenon was not predominant as it was at port island the non linear ground motion amplification depending on the level of input ground motion as well as its spectral characteristics is carefully investigated two numerical techniques for seismic response ground analysis are applied for these stations one is the frequency dependent equivalent linearization technique for frequency domain analysis and the other is the effective stress based liquefaction analysis the discussion is focused on the amplification characteristics of these two reclaimed lands depending on their reclamation history the time dependent amplification ratio for peak ground motion and spectral contents is demonstrated caused by the recovery of soil rigidity due to the decrease in excess pore water pressure after the main event

the triple point on 24 may 2002 during ihop part i airborne doppler and lase analyses of the frontal boundaries and convection initiation an analysis of the initiation of deep convection near the triple point between a cold front and dryline is presented high spatial resolution doppler wind syntheses combined with vertical cross sections of mixing ratio q and aerosol scattering ratio retrieved from a lidar flying over the triple point provide an unprecedented view of the initiation process the doppler wind synthesis revealed variability along the dryline similar to the precipitation core gap structure documented for oceanic cold fronts vertical cross sections through the dryline suggest a density current like structure with the hot and dry air being forced up and over the moist air double thin lines associated with moisture gradients were also resolved the vertical profile of retrieved q approximately perpendicular to the dryline showed a pronounced jump in the depth of the moisture layer across the triple point analyses of dropsonde data show the existence of virtual potential temperature v gradients across the cold front and the dryline although the vertical velocity was strong at the triple point deep convection initiated 50 km to the east the location where convection first developed was characterized by a prominent aerosol and moisture plume reduced static stability and the largest potential instability an internal gravity wave may have provided the lift to initiate convection

research on loess flow slides induced by rainfall in july 2013 in yan an nw china the yan an area located on the loess plateau in northern shaanxi province china experienced heavy and prolonged rainfall in july 2013 which induced 8 135 slope failures loess landslides and loess flow slides destroying approximately 10 000 cave dwellings and killing 45 people field investigations have indicated that the occurrence of loess flow slides is closely related to infiltration depth slope angle slope morphology rainfall intensity and loess strength the results from this study showed that a most of the loess flow slides in yan an were small scale ranging in volume from tens of cubic meters to hundreds of cubic meters b the loess flow slides only occurred at a depth of 2 m and can effectively prevent loess flow slides

development of pervious concrete pile ground improvement alternative and behavior under vertical loading permeable granular columns are used to increase the time rate of consolidation reduce liquefaction potential improve bearing capacity and reduce settlement however their behavior depends on the confinement provided by surrounding soil which limits their use in very soft clays and silts and organic and peat soils this research effort aims to develop a new ground improvement method using pervious concrete piles pervious concrete piles provide higher stiffness and strength that are independent of surrounding soil confinement while offering permeability comparable to granular columns this proposed ground improvement method can improve the performance of different structures supported on poor soils to achieve the goal of the research project four vertical load tests were performed on one granular column and three pervious concrete piles in this paper the material properties of pervious concrete the developed installation method and the vertical load response of pervious concrete and aggregate piles are presented and the variation of soil stresses and displacement during pile installation are briefly discussed the experimental test results show that the ultimate load capacity of the pervious concrete pile was 4 4 times greater than that of an identical granular column in addition the ultimate load capacity of a pervious concrete pile installed using the developed technique was 2 6 times greater than a precast pervious concrete pile the used installation method created nonuniform lateral soil displacement and increased vertical and horizontal soil stresses

a review of cold fronts with prefrontal troughs and wind shifts the conceptual model of a classical surface based cold front consists of a sharp temperature decrease coincident with a pressure trough and a distinct wind shift at the surface many cold fronts however do not conform to this model time series at a single surface station may possess a pressure trough and wind shift in the warm air preceding the cold front hereafter called a prefrontal trough and prefrontal wind shift respectively although many authors have recognized these prefrontal features previously a review of the responsible mechanisms has not been performed to date this paper presents such a review ten disparate mechanisms with different frontal structures have been identified from the previous literature these mechanisms include those external to the front i e those not directly associated with the cold front itself synoptic scale forcing interaction with lee troughs drylines interaction with fronts in the mid and upper troposphere and frontogenesis associated with inhomogeneities in the prefrontal air mechanisms internal to the front i e those directly associated with the structure and dynamics of the front include the following surface friction frontogenesis acting on alongfront temperature gradients moist processes descent of air ascent of air at the front and generation of prefrontal bores gravity waves given the gaps in our knowledge of the structure evolution and dynamics of surface cold fronts this paper closes with an admonition for improving the links between theory observations and modeling to advance understanding and develop better conceptual models of cold fronts with the goal of improving both scientific understanding and operational forecasting

modeling the stone column behavior in soft ground with special emphasis on lateral deformation abstractamong various ground improvement techniques soft soil reinforcement by stone columns is one of the most common and convenient methods with numerous benefits including increased bearing cap

mitigation of liquefaction induced lateral deformation in a sloping stratum three dimensional numerical simulation finite element fe simulations are increasingly providing a versatile environment for conducting lateral ground deformation studies in this environment mitigation strategies may be assessed in order to achieve economical and effective solutions on the basis of a systematic parametric study three dimensional fe simulations are conducted to evaluate mitigation by the stone column sc and the pile pinning approaches mildly sloping saturated cohesionless strata are investigated under the action of an applied earthquake excitation for that purpose the open source computational platform opensees is employed through a robust user interface that simplifies the effort intensive pre and postprocessing phases the extent of deployed remediation and effect of the installed sc permeability are investigated the influence of mesh resolution is also addressed generally sc remediation was found to be effective in reducing the sand stratum lateral deformation for a similar stratum with permeability in the silt range sc remediation was highly ineffective in contrast pile pinning appeared to be equally effective for the sand and silt strata permeability scenarios overall the conducted study highlights the potential of computations for providing insights toward the process of defining a reliable remediation solution

instability and liquefaction of granular soils under undrained and partially drained states an experimental investigation of the initiation of instability liquefaction in saturated sand under partially drained conditions is presented the domain of stress space in which this instability develops is identified under various degrees of drainage and its relationship to the zone of instability observed under undrained shear is explored it is shown that partially drained conditions may render sand unstable that would otherwise be stable in a completely undrained state extremely small void ratio increases that cannot be regarded as physical loosening of sand if sand is partially drained contribute to instability implications of the findings are discussed in practical problems of liquefaction key words sand liquefaction undrained partially drained instability triaxial test

a dryline in southeast wyoming part ii airborne in situ and raman lidar observations part i of this study describes the mesoscale structure of a dryline over southeastern wyoming this dryline formed just east of the western rim of the high plains on 22 june 2010 and became more defined as it progressedeastwardduringtheafternoon partialsodescribesthenumericallysimulatedstructureandevolution of this dryline and the observed initiation of deep convection in the vicinity of the dryline an instrumented aircraft the university of wyoming king air repeatedly flew across this dryline mostly low enough to penetrate the moist air wedge east of the dryline flight level in situ data along these low level penetrations indicate relatively high values of convective available potential energy cape 1500jkg 21 yet low convective inhibition within a few kilometers of the dryline water vapor transects obtained from a compact nadir pointing raman lidar aboard the aircraft reveal an extremely sharp humidity gradient below flight level along the dryline coinciding with the fineline seen in operational weather radar base reflectivity imagery theyalsorevealseveralplumesofhigher specifichumiditywithinthedryelevatedmixedlayerabovethemoistair wedge possibly precursors of cumulus clouds the vertical structure of the dryline revealed by raman lidar and the flight level data correspond well to that in the high resolution numerical simulation

performance of embankments on liquefiable soils improved with dense granular columns observations from case histories and centrifuge experiments abstractdense granular columns dgcs are generally known to mitigate the liquefaction hazard through a combination of 1 installation induced ground densification 2 enhanced drainage and 3

kinematic and moisture characteristics of a nonprecipitating cold front observed during ihop part i across front structures abstract a wide array of ground based and airborne instrumentation is used to examine the kinematic and moisture characteristics of a nonprecipitating cold front observed in west central kansas on 10 june 2002 during the international h2o project ihop this study the first of two parts is focused on describing structures in the across front dimension coarsely resolved observations from the operational network and dropsondes deployed over a 200 km distance centered on the front are combined with higher resolution observations from in situ sensors doppler radars a microwave radiometer and a differential absorption lidar that were collected across a 40 km swath that straddled a 100 km segment of the front the northeast southwest oriented cold front moved toward the southeast at 8 10 m s 1 during the morning hours but its motion slowed to less than 1 m s 1 in the afternoon in the early afternoon the cold front separated cool air with a northerly component flow of 2 4 m s 1 from a 10 km wide ban

geotechnical site characterization in the greater memphis area using cone penetration tests abstract the determination of seismic ground hazards in memphis and shelby county tennessee is facilitated by the use of electronic cone penetration tests that can provide up to four independent readings with depth from a single sounding one series of soundings is being performed for site specific mapping to determine the presence and extent of potentially liquefiable sediments in situ soil resistance to liquefaction and initial soil stiffness for ground motion amplification studies another series of soundings is being conducted in conjunction with field paleoliquefaction mapping in the new madrid seismic zone to better define the intensity magnitude and geographic extent of ground failures caused by large past earthquake events as well as information about the source sands in this paper an overview is given on the types of multi channeled penetrometer data that are being collected including vertical profiles of cone tip stress qt sleeve friction fs penetration porewater pressure u1 or u2 downhole shear wave velocity vs and or electrical conductivity ke representative soundings are presented from select sites to illustrate repeatability data post processing methods and that derived downhole vs profiles are generally in good agreement with non invasive surface techniques at two memphis test sites cyclic stress based procedures for liquefaction are discussed with relation to data from a paleoliquefaction site in germantown tennessee and estimates of the minimum magnitude of the historic event are discussed while estimates of the earthquake magnitude are preliminary pending additional study on attenuation relationships and site response in the deep soils of the mississippi embayment it is inferred from evaluation of in situ test data using cyclic stress based techniques that the december 1811 new madrid earthquake was likely larger than a mw 7 5 event

mitigation of liquefaction and associated ground deformations by stone columns soil liquefaction and associated ground failures have been a major source of damage during the past earthquakes the risk of liquefaction and associated ground deformation can be reduced by various ground improvement methods including the stone column gravel drain technique this paper presents the current state of the stone column technologies as a liquefaction countermeasure a comprehensive review is provided aiming to a identify key considerations for the general use of stone columns as a liquefaction countermeasure b provide insights for design and construction c compile the latest research developments and d identify sources of useful information case histories of field applications and observed field performance are cited to portray different stone column applications and observed effectiveness the paper identifies areas where more research is needed and includes recommendations for future research and development

centrifuge modeling of prefabricated vertical drains for liquefaction remediation drainage methods for liquefaction remediation have been in use since the 1970s and have traditionally included stone columns gravel drains and more recently prefabricated vertical drains this paper presents the results from a dynamic centrifuge test designed to evaluate the performance of a liquefiable site treated with prefabricated vertical drains the centrifuge model consisted of gently sloping untreated and treated liquefiable soil deposits overlain by a clay crust the model was subjected to multiple shaking events that included both recorded earthquake acceleration time histories and sinusoidal input motions comparisons of deformations and excess pore water pressures in the untreated and treated areas showed that drains were effective in expediting the dissipation of excess pore water pressures and reducing deformations however depending on the characteristics of the input ground motion the peak excess pore pressures in the treated area were not always substantially smaller than in the untr

a depth consistent spt based empirical equation for evaluating sand liquefaction abstract focusing on the deficiencies of the current liquefaction evaluation methods typically on deep sandy layers of 10 m to 20 m a new liquefaction evaluation formula which is based on the 156 spt data from liquefaction investigation in china mainland is proposed the formula is plausible for wide depth range up to 20 m the formula which takes a hyperbolic function form fits the liquefaction data at shallow depth and predicts satisfactorily deep liquefaction the liquefaction dataset available from china earthquakes and foreign earthquakes i e kobe earthquake and chichi earthquake are statistically summarized the deficiencies of prevailing liquefaction evaluation methods and the csr method by seed are pinpointed to validate the proposed formula a liquefaction dataset consist of 312 liquefaction data from china mainland and foreign countries is used for re evaluation the results indicate that the new formula is quite feasible for wide sandy layer buried depth different seismic intensities and varying groundwater tables comparing with the current chinese code methods and the csr method the new formula which approaches to an asymptote eliminates the abnormality of the csr method that decreases inversely when the depth exceeds a certain value the new formulae solve the deficiency of chinese codified liquefaction evaluation methods that are conservative for intensity vii at shallow depth

numerical and centrifuge modeling of seismic soil foundation structure interaction on liquefiable ground abstractthe effective mitigation of the liquefaction hazard requires an improved understanding of the consequences of liquefaction in terms of ground shaking permanent displacement and building performance in this paper results from centrifuge experiments of a shallow founded structure on liquefiable sand are used to evaluate the predictive capabilities of a state of the art numerical tool solid fluid fully coupled 3d nonlinear numerical simulations were performed using the pdmy02 soil model implemented in a software modeling domain the numerical model captured excess pore pressures and accelerations well in the free field but largely underestimated volumetric settlements due to loss of water during shaking this was associated with the drastic increase in soil hydraulic conductivity when approaching liquefaction which was not taken into account numerically as well as the underestimation of soil volumetric compressibility the contribution of volumetric strains to total building settlement was

the mesoscale structure of a nocturnal dryline and of a frontal dryline merger abstract a horizontal gradient in moisture termed the dryline is often detected at the surface over the southern great plains of the united states during the spring and early summer the dryline exhibits distinct diurnal variations in both its movement and structure recent research has focused on dryline structure during the afternoon and evening particularly showing how strong 1 5 m s 1 ascent frequently creates an environment favorable to the initiation of convection quite close within 10 km to the dryline interface to date however there have been very few detailed analyses of the dryline interface at night so that the nocturnal behavior of the interface predicted by theory and numerical studies is relatively poorly evaluated in this study special observations taken by a doppler lidar serial rawinsonde ascents and a dual channel microwave radiometer are utilized to describe the behavior of a nocturnal dryline observed on 12 13 may 1985 the analysis presented here reveals that the mes

mechanisms of seismically induced settlement of buildings with shallow foundations on liquefiable soil seismically induced settlement of buildings with shallow foundations on liquefiable soils has resulted in significant damage in recent earthquakes engineers still largely estimate seismic building settlement using procedures developed to calculate postliquefaction reconsolidation settlement in the free field a series of centrifuge experiments involving buildings situated atop a layered soil deposit have been performed to identify the mechanisms involved in liquefaction induced building settlement previous studies of this problem have identified important factors including shaking intensity the liquefiable soil s relative density and thickness and the building s weight and width centrifuge test results indicate that building settlement is not proportional to the thickness of the liquefiable layer and that most of this settlement occurs during earthquake strong shaking building induced shear deformations combined with localized volumetric strains during partially drained cyclic loading are the dominant mechanisms the development of high excess pore pressures localized drainage in response to the high transient hydraulic gradients and earthquake induced ratcheting of the buildings into the softened soil are important effects that should be captured in design procedures that estimate liquefaction induced building settlement

dynamic centrifuge tests to evaluate reinforcing mechanisms of soil cement columns in liquefiable sand abstractfour centrifuge tests were performed to investigate the reinforcing mechanisms of soil cement columns in liquefiable sand two unimproved baseline models and two models improved with soil cement columns were subjected to sine sweep and earthquake base motions of varying intensities to observe acceleration pore pressure lateral displacement and settlement responses the dynamic records were processed to derive the effective natural frequency of the profiles and to obtain the dynamic stress strain responses for unimproved and improved soil it was found that the shear reinforcement mechanisms of columns was not effective in reducing cyclic stress ratios in the treated soil liquefaction triggering occurred nearly at same time for both unimproved and improved soil cases and the magnitude of the resulting soil settlement was not significantly reduced when the bases of the columns were free to rotate the columns rocked within the soil and produced negligible shear stiffening of the soil profile w

empirical methodology to estimate seismically induced settlement of partially saturated sand abstractsettlement of soil layers during and after earthquake shaking is a major cause of damage to buildings and geotechnical structures the available empirical design methods to consider seismically induced settlement focus on sands in dry or water saturated conditions and there is currently a gap in the basic understanding of the mechanisms of seismically induced settlements of partially saturated sands an effective stress based empirical methodology is proposed to estimate the seismically induced settlement of a free field layer of sand in partially saturated conditions this approach estimates the settlement by separately considering the volumetric strains caused by compression of void space during strong shaking seismic compression and dissipation of excess pore water pressures generated during earthquake shaking postcyclic reconsolidation a parametric evaluation of the methodology indicates that the small strain shear modulus the parameters of the modulus reduction curve the approach to e

water film in liquefied sand and its effect on lateral spread a one dimensional 1d saturated sand layer of 2 m in thickness in which a silt seam is sandwiched is liquefied by an instant shock it is found that a water film is easily formed beneath the silt seam with a thickness as thin as a few millimeters just after liquefaction in loose sand and that the film lasts longer than the postliquefaction settlement the effect of the water film on pore pressure distribution and sand settlement is intensively studied one gram shake table tests are then carried out for 2d models with or without seams of silt within a saturated sand layer in the former case water films formed beneath silt seams just after liquefaction enable the soil mass above them to glide because of an unbalanced force along the water films not only during but also after shaking in the latter case the soil deforms continuously mostly during shaking and stops afterward thus a significnat effect of water films formed beneath thin low permeability sublayers in a liquefied loose sand on the failure mode and timing in lateral spread is clearly demonstrated by these simple model tests

development and evolution of loess vertical joints on the chinese loess plateau at different spatiotemporal scales abstract the vertical joints of aeolian loess are ubiquitous on the chinese loess plateau clp the distribution variability of which mainly depends on the differences in structural characteristics of loess water drivers e g rainfall or irrigation loess strata e g sedimentary depth and microtopography this study conducted extensive field investigation and experiments to enhance the understanding of morphologies cross scale transformation mechanism and structural bases of loess vertical joints lvjs moreover the development and evolution processes of lvjs were refined by considering loess sedimentary dynamics results show that 1 lvjs are the product of diagenesis in loess strata during loess historical sedimentary process 2 the pore concentration zones and vertical tubular channels in loess are the structural bases of forming original vertical joints ovjs at the micro mesoscale which is supported by the results from the three dimensional computing tomography ct scanning and scanning electron microscopy sem tests and 3 the morphologies of lvjs vary with the microtopography at different spatiotemporal scales and is characterized by the cross scale transformation mechanism i e that they could transform up i e an expansion behavior or down i e a degradation behavior at the micro meso and sub macro scales under the influences of dry wet cycles loess pile thickening and exogenic forces besides we also propose the development and evolution mechanism of ovjs in loess from the viewpoint of unsaturated loess which would help understand the loess anisotropic genesis structural evolution preferential flow and the occurrence of geohazards such as landslides and soil erosion

numerical study of shear stress distribution for discrete columns in liquefiable soils abstractdiscrete columns such as stone and soil cement columns are often used to improve the liquefaction resistance of loose sandy ground potentially subjected to strong shaking the shear stress reduction in the loose ground resulting from the reinforcing effect of these stiffer discrete columns is often considered as a contributing mechanism for liquefaction mitigation current design practice often assumes that discrete columns and soil deform equally in pure shear i e shear strain compatible deformation in addition because the discrete column is stiffer than the soil it is assumed to attract higher shear stress thereby reducing the shear stress in the surrounding soil in this paper shear stress reduction in liquefiable soils and shear strain distribution between liquefiable soil and discrete columns along with the potential of development of tensile cracks is investigated using three dimensional linear elastic finite element analysis parametric analyses are performed for a range of geom

influence of prefabricated vertical drains on the seismic performance of similar neighbouring structures founded on liquefiable deposits increasing the resilience of structures to seismically induced soil liquefaction is a major objective for the earthquake engineering community increasingly soil drains are being used to mitigate

the cold front of 15 april 1994 over the central united states part i observations abstract detailed observations of the interactions of a cold front and a dryline over the central united states that led to dramatic undulations in the boundary layer including an undular bore are investigated using high resolution water vapor mixing ratio profiles measured by raman lidars the lidar derived water vapor mixing ratio profiles revealed the complex interaction between a dryline and a cold frontal system an elevated well mixed and deep midtropospheric layer as well as a sharp transition between 5 and 6 km altitude to a drier region aloft was observed the moisture oscillations due to the undular bore and the mixing of the prefrontal air mass with the cold air at the frontal surface are all well depicted the enhanced precipitable water vapor and roll clouds the undulations associated with the bore the strong vertical circulation and mixing that led to the increase in the depth of the low level moist layer and the subsequent lifting of this moist layer by the cold frontal surface

evaluation of simulation models of lateral spread sites treated with prefabricated vertical drains abstractfinite element analyses are performed of centrifuge tests consisting of untreated and drain treated lateral spread sites with the goal of evaluating the ability of numerical simulations to predict the response of sites improved with prefabricated vertical drains finite element models of varying complexity are analyzed a two dimensional model of the full centrifuge test a three dimensional unit cell model around a single drain and a two dimensional unit cell model all the finite element models predict pore pressures consistent with the centrifuge tests the deformation responses of the finite element models show that unit cell analyses produce significantly larger deformations than those observed in the centrifuge this result is caused by the fact that the centrifuge test geometry is not well represented by the infinite slope condition assumed in a unit cell the full two dimensional model predicts deformations that are more consistent with those of the centrifuge because it can capture the

dynamic analyses of two buildings founded on liquefiable soils during the canterbury earthquake sequence abstracta series of major earthquakes near christchurch new zealand produced different levels of liquefaction induced ground failure and damage to multistory buildings in the city s central busin

equivalent linear computation of response spectra for liquefiable sites the spectral envelope method abstracta simplified methodology is proposed for the computation of elastic response spectra at liquefiable sites based on the widely used equivalent linear frequency domain site response analysis method the actual response spectrum is obtained as the upper bound envelope of the thus calculated response spectra corresponding to the preliquefaction and the postliquefaction segments of the seismic excitation the former computed for the natural soil properties and the latter for the properties of the liquefied soil the time of liquefaction onset which separates the two seismic excitation segments is defined in terms of the minimum factor of safety against liquefaction within the liquefiable layer additional guidelines are provided for the estimation of the excess pore pressure buildup and the associated soil softening during the preliquefaction segment of the seismic excitation as well as for the definition of the liquefied soil stiffness and the hysteretic damping ratio the proposed methodology h

centrifuge tests of adjacent mat supported buildings affected by liquefaction abstractgeotechnical centrifuge tests can provide valuable insights into the mechanisms governing the performance of buildings affected by liquefaction an area particularly lacking knowledge is the effect of liquefaction on adjacent structures which is a common possibility in urban areas two well instrumented centrifuge tests were performed to investigate the response of isolated and adjacent structures founded on ground that underwent varying degrees of liquefaction three types of single degree of freedom model structures were used in the experiments acceleration pore water pressure and settlement measurements illustrated that liquefaction induced settlement of structures depends on a complex interaction of ground motion soil and structural characteristics for the cases examined in this study adjacent structures experienced moderately lower foundation accelerations than isolated structures of the same type adjacent structures tended to tilt away from one another and settled less than isolated

static and cyclic liquefaction potential of fraser delta sand in simple shear and triaxial tests the potential for static and cyclic liquefaction of the sand that underlies the highly seismic fraser delta is assessed under simple shear test conditions typical of an earthquake shaking a comparison of liquefaction potential is also made between simple shear and conventional triaxial stress conditions it is shown that the liquefaction potential of sand is profoundly influenced by the stress path the reduction factors currently applied to the cyclic triaxial resistance for representing simple shear response may involve a large degree of conservatism in design a direct measurement of soil behaviour under stress conditions typical of earthquake loading may thus have large economic benefits key words sand liquefaction static cyclic triaxial simple shear

dryline bulge evolution in a two dimensional mixed layer model abstract this study examines the diurnal response of a mixed layer model of the dryline system to localized anomalies of surface heat flux topography mixed layer depth and inversion strength the two dimensional mixed layer model is used to simulate the dynamics of a cool moist layer east of the dryline capped by an inversion under synoptically quiescent conditions the modeled domain simulates the sloping topography of the u s great plains the importance of this study can be related to dryline bulges that are areas with enhanced convergence that may trigger convection in suitable environmental conditions all anomalies are represented by a gaussian function in the horizontal whose amplitude size and orientation can be altered a positive surface heat flux anomaly produces increased mixing that creates a bulge toward the east while a negative anomaly produces a westward bulge anomalies in topography show a similar trend in bulge direction with a peak giving an eastward bulge and a valley givi

a mixed layer model of the diurnal dryline abstract this study examines the diurnal behavior of the dryline system using a mixed layer model to represent the cool moist air capped by an inversion to the east of the line this inversion is referred to as the dry front and the intersection of this dry front with the terrain is the dryline the results indicate that boundary layer heating is sufficient to drive the dryline and explain its diurnal variation the daytime eastward propagation of the model dryline of 200 km agrees well with other numerical studies and is in approximate agreement with dryline observations the present model results also indicate a nearly vertical inversion slope up to a height of 2 km in the early afternoon model simulations with sloping terrain consistently yield a nocturnal low level jet between 0000 local time lt and 0100 lt with a speed of 20 25 m s 1 located below the inversion the effect of each mixed layer process such as entrainment surface heat flux and nighttime cooling is examined entrainment tends

numerical simulation of building response on liquefiable sand abstractthe effective design of earthquake resistant structures and liquefaction mitigation techniques requires an improved understanding of the development and consequences of liquefaction in this paper the results from centrifuge experiments of structures with shallow foundations on liquefiable sand were used to evaluate the predictive capabilities of a state of the practice numerical tool fully coupled numerical simulations with the ubcsand model implemented in flac 2d captured building settlements measured in these experiments reasonably well for one scaled input motion mostly within factors of 0 7 and 1 8 the soil model captured the overall contribution of deviatoric displacement mechanisms and localized volumetric strains during partially drained cyclic loading the primary limitation of the model became evident for slower rates of earthquake energy buildup when the extent of soil softening and building displacement was overestimated by up to a factor of 4 the observations from recent case hi

analysis of pv drains for mitigation of seismically induced ground deformations in sand slopes abstractprefabricated vertical pv drain arrays have been proposed as a minimally intrusive technique for mitigating seismically induced ground deformations in sandy liquefiable slopes this paper

insight into the seismic liquefaction performance of shallow foundations the mechanisms that control the seismic liquefaction performance of shallow foundations are identified for the special still com mon case of a clay crust separating the foundation from the liquefied ground for that purpose foundation response is first analyzed with the nonlinear dynamic finite difference method and consequently evaluated in connection with published field and experimental evidence insight is given into the excess pore pressure buildup under the foundation the seismic settlement accumulation the static bearing capacity degrada tion and the inertia induced interaction with the superstructure it is thus shown that a naturally or artificially created nonliquefiable soil crust may effectively mitigate the detrimental effects of liquefaction and allow for a performance based design of surface foundations without

effect of fabric anisotropy on liquefaction of sand abstractliquefaction of sand is the main cause of failure for earth structures during earthquakes some past research showed that the fabric anisotropy of soils in the ground can cause different responses to both static and dynamic loading the inherent fabric anisotropy of sand due to the deposition history and pattern may also affect the liquefaction potential of the ground in this study a group of earthquake centrifuge tests was performed on models of a level ground to investigate its seismic response with the soil deposited by different angles a special rigid container was designed and used to prepare the models it was found that the fabric anisotropy greatly influenced the response of the ground in displacement acceleration and excess pore pressure the models with larger deposition angles had higher liquefaction potential the results show that liquefaction evaluation of a sand layer should take into account the influence of fabric anisotropy caused by its deposition history and pattern

the bhuj india earthquake lessons learned for earthquake safety of dams on alluvium abstract the bhuj india earthquake of 26 january 2001 m s 7 9 caused dams built on alluvium to sustain damage ranging from cosmetic to severe major damage was caused almost entirely by soil liquefaction in the alluvium the critical factor was the level of earthquake ground motion the bhuj earthquake showed that peak horizontal accelerations phas 0 2 g were generally safe phas 0 2 g were hazardous when unconsolidated granular foundation soils were water saturated n values of 0 2 g must be evaluated over the full area beneath a new dam and all soils deemed susceptible to liquefaction must be either removed or treated for remediating an old dam reliable options are removal and replacement of liquefiable alluvium beneath upstream and downstream portions of the dam combined with building berms designed to provide stability for the dam should there be a strength loss in soils beneath the dam

seismically induced settlement of ground experiencing undrained shaking and laterally constrained compression a method is proposed for estimating seismically induced settlement of saturated sands experiencing undrained shaking and laterally constrained compression an empirical relationship is developed between the seismic coefficient of vertical compression mvs and standard penetration test blow count n60 as a function of factor of safety against liquefaction fl based on data interpreted from 18 sets of laboratory cyclic direct simple shear tests and 23 cases of field observations of seismic liquefaction the proposed method is compared with seismic settlement observed at 78 sites subjected to 7 1 8 0 magnitude earthquakes and with predictions by the previous well known methods of settlement analysis for undrained shaking for silty clayey sands the significant effect of the plasticity of fines on seismic settlement is illustrated the use of pre or post earthquake penetration resistance for back analyses of field seismic settlement observations is examined a tentative correction factor is suggested fo

a study of convection initiation in a mesoscale model using high resolution land surface initial conditions abstract a coupled convection resolving mesoscale atmosphere land surface model lsm is used to investigate land surface planetary boundary layer pbl interactions responsible for the initiation of deep moist convection over the southern great plains of the united states on 19 june 1998 a high resolution land data assimilation system provides initial conditions to the lsm facilitating examination of soil moisture effects on forecasts of deep convection during the late morning and early afternoon the southwestern portion of a simulated southwest northeast sw ne oriented surface water vapor gradient zone evolves into an intense dryline unlike the northeastern portion which remains relatively weak despite these regional differences midafternoon convection initiation occurs within a 100 km wide region of enhanced pbl depth along much of the sw ne extent of the water vapor gradient zone the afternoon pbl depth maximum results from a midmorning to early afternoon surface sensible heat flux maximu

influence of bearing pressure on liquefaction induced settlement of shallow foundations earthquake induced soil liquefaction continues to pose problems for structures on shallow foundations one particular problem is the excessive settlement that such structures undergo as a consequence of earthquake shaking for design and insurance purposes it is therefore necessary to be able to estimate the magnitude of these settlements current procedures relate the potential settlement to foundation size and liquefiable depth however the influence of foundation bearing pressure is also a significant factor in particular experimental results have indicated that large bearing pressures may inhibit liquefaction underneath a shallow foundation resulting in lower induced settlement by collecting new data from 23 buildings that suffered settlement and tilting as a consequence of soil liquefaction during the 27 february 2010 maule earthquake in chile the existing method of estimating liquefaction induced settlement is reassessed and shown to require bearing pressure information based on both the new

impact of a front dryline merger on convection initiation near a mountain ridge in beijing abstracta case study is presented of convection initiation ci resulting from the merger of a cold front with a dryline in southwestern beijing china on the afternoon of 11 june 2011 this process is analyzed with s band doppler radar data surface automatic weather station data and mesoscale numerical simulation results the formation of this dryline is analogous to that on the great plains of the united states and it is conducive to ci with mesoscale updrafts generated from the baroclinic frontogenesis and with favorable instability immediately on the moist side prior to the front dryline merger as the cold front approached the observed boundary layer convergence line or the simulated meso scale secondary dryline ci occurred ahead of the cold front with little contribution from frontogenetic baroclinity of the dryline the cold front then merged with the dryline and the baroclinity of the dryline was enhanced by the associated convergence to a degree comparable to that caused by frontogene