The Experts below are selected from a list of 252 Experts worldwide ranked by ideXlab platform
Arul Arulrajah - One of the best experts on this subject based on the ideXlab platform.
-
Piezometer measurements of prefabricated vertical drain improvement of soft soils under land reclamation fill
Engineering Geology, 2013Co-Authors: Arul Arulrajah, Melvyn Leong, Myint Win Bo, M M DisfaniAbstract:Abstract Piezometers are commonly used for monitoring the dissipation of pore water pressure and therefore the determination of degree of consolidation of soft soils after ground improvement in land reclamation projects. This paper compares the degree of consolidation obtained using pore pressure monitoring data from vibrating wire Piezometers and pneumatic Piezometers installed in a test site in the Changi East Reclamation project in Singapore. The test site consisted of a vertical drain sub-area at which prefabricated vertical drains were installed at 2.0 m × 2.0 m square spacing as well as an adjacent control sub-area where no prefabricated vertical drains were installed. Pneumatic Piezometers were installed at the same elevations as the vibrating-wire Piezometers in both sub-areas for comparison purposes. During the surcharge period of 32 months, the Piezometer monitoring data were analysed at various periods to determine the degree of consolidation of the underlying soft marine clay. The degree of consolidation values interpreted from both types of Piezometers were compared with predictions from neighbouring settlement plates to evaluate their performance. The findings of the comparison between pneumatic and electric vibrating-wire Piezometers indicate that both types of Piezometer are suitable for monitoring the consolidation behaviour of soft soil under land reclamation fills.
-
Factors Affecting Consolidation Related Prediction of Singapore Marine Clay by Observational Methods
Geotechnical and Geological Engineering, 2008Co-Authors: Arul Arulrajah, M W BoAbstract:The use of prefabricated vertical drains with preloading option is the most widely-used ground improvement method for the improvement of marine clays in land reclamation projects. The assessment of the degree of consolidation of the marine clay is of paramount importance prior to the removal of preload in such ground improvement projects. This analysis can be carried out by means of observational methods with the use of field settlement plates and Piezometer monitoring. Field settlement monitoring data can be used to ascertain the settlement of the reclaimed fill from the time of initial installation. The field settlement data can be analysed by the Asaoka method to predict the ultimate settlement of the reclaimed land under the surcharge fill. Back-analysis of the field settlement data will enable the coefficient of consolidation due to horizontal flow to be closely estimated. Piezometer monitoring data can be analysed to obtain the degree of consolidation of the improved marine clay. Back-analysis of the Piezometer data will also enable the coefficient of consolidation due to horizontal flow to be estimated. The aim of this paper is to highlight the significance and impact of the various factors that affect prediction by the Asaoka and Piezometer assessment methods. The authors findings of the Asaoka method reveal that the magnitude of ultimate settlement decreases and the degree of consolidation subsequently increases as a longer period of assessment is used in the prediction. The degree of consolidation predicted by the Piezometers is found to be in good agreement with the Asaoka method for the early period of assessment. However as the assessment period increases, the Piezometer indicates lower degree of consolidation as compared to field settlement predictions.
-
Dissipation Testing of Singapore Marine Clay by Piezocone Tests
Geotechnical and Geological Engineering, 2007Co-Authors: Arul Arulrajah, M W Bo, Hamid Nikraz, A. S. BalasubramaniamAbstract:In situ dissipation tests provide a means of evaluating the in situ coefficient of consolidation due to horizontal flow and hydraulic conductivity in horizontal direction in marine clays formation. Dissipation tests by means of piezocone were utilised in the characterisation of the coefficient of consolidation due to horizontal flow and the hydraulic conductivity in horizontal direction of Singapore marine clay at Changi. Piezocone dissipation tests were carried out prior to reclamation as well as after ground improvement with vertical drains to compare the changes in the coefficient of consolidation due to horizontal flow and hydraulic conductivity in horizontal direction prior to and after ground improvement. The quasi-static piezometric pressures from the dissipation tests were compared with piezometric pressures from Piezometers to determine their possibility of future use as an alternative to Piezometers. Post-improvement CPTU dissipation tests were carried out in the treated “Vertical Drain Area” as well as in an adjacent untreated “Control Area” for comparison purposes. This study provides support for the use of piezocone dissipation testing methods for the determination of the coefficient of consolidation due to horizontal flow and hydraulic conductivity in horizontal direction of marine clays in the region as well as an alternative to Piezometer instrumentation for monitoring of piezometric pressure during consolidation.
-
Factors affecting field instrumentation assessment of marine clay treated with prefabricated vertical drains
Geotextiles and Geomembranes, 2004Co-Authors: Arul Arulrajah, Hamid Nikraz, M W BoAbstract:Abstract The use of prefabricated vertical drains with preloading option is the most widely-used ground improvement method for the improvement of soft clays in land reclamation projects. Surcharge of equivalent working load after taking into account submergence effect and settlement of the reclaimed land is placed until the required degree of consolidation of the soft clay is obtained. The assessment of the degree of consolidation of the marine clay is of paramount importance prior to the removal of preload. This analysis can be carried out by means of observational methods with the use of field settlement plates and Piezometer monitoring. Field settlement monitoring data can be used to ascertain the settlement of the reclaimed fill from the time of initial installation. The field settlement data can be analysed by the Asaoka and Hyperbolic methods to predict the ultimate settlement of the reclaimed land under the surcharge fill. Back-analysis of the field settlement data by the Asaoka method will enable the coefficient of consolidation due to horizontal flow to be closely estimated. Piezometer monitoring data can be analysed to obtain the degree of consolidation of the improved marine clay. Back-analysis of the Piezometer data will also enable the coefficient of consolidation due to horizontal flow to be estimated. The authors’ findings of the Asaoka method reveal that the magnitude of ultimate settlement decreases and the degree of consolidation subsequently increases as a longer period of assessment is used in the prediction. It is apparent that as the time interval increases, a cut-off time interval is obtained after which increasing time intervals would converge to the same magnitude of ultimate settlement. The authors’ findings of the Hyperbolic method reveal that the magnitude of ultimate settlement increases and subsequently the degree of consolidation decreases as a longer period of assessment is used in the prediction. The degree of consolidation predicted by the Piezometers is found to be in good agreement with the Asaoka and Hyperbolic methods for the early period of assessment. However as the assessment period increases, the Piezometer indicates lower degree of consolidation as compared to field settlement predictions. The aim of this paper is to highlight the significance and influence of various factors that affect predictions by the Asaoka, Hyperbolic and Piezometer assessment methods.
-
factors affecting assessment and back analysis by Piezometer monitoring
Australian Geomechanics: Journal of the Australian Geomechanics Society, 2004Co-Authors: Arul Arulrajah, Hamid NikrazAbstract:Prefabricated vertical drains with preloading optio n are the most widely-used ground improvement method for the improvement of marine clays in land reclamation projects. The assessment of the degree of consolidatio n of the marine clay is of paramount importance prior to the remova l of preload in such ground improvement projects. This analysis can be carried out by means of Piezometer monitorin g. Piezometer monitoring data can be analysed to ob tain the degree of consolidation of the improved marine clay. Back -analysis of the Piezometer data will also enable t he coefficient of consolidation due to horizontal flow to be estimate d. Factors that affect the analysis of Piezometers include period of assessment, hydrogeologic boundary condition, settl ement of Piezometer tip and reduction of initial im posed load due to submergence effect. The aim of this paper is to hig hlight the significance and impact of the various f actors that affect assessment by the Piezometer monitoring method.
Andrew Baird - One of the best experts on this subject based on the ideXlab platform.
-
Evidence that Piezometers vent gas from peat soils and implications for pore‐water pressure and hydraulic conductivity measurements
Hydrological Processes, 2009Co-Authors: James M. Waddington, Maria Strack, Scott J. Ketcheson, E. Kellner, Andrew BairdAbstract:Entrapped gas bubbles in peat can alter the buoyancy, storativity, void ratio and expansion/contraction properties of the peat. Moreover, when gas bubbles block water-conducting pores they can significantly reduce saturated hydraulic conductivity and create zones of over-pressuring, perhaps leading to an alteration in the magnitude and direction of groundwater flow and solute transport. Some previous researches have demonstrated that these zones of over-pressuring are not observed by the measurements of pore-water pressures using open-pipe Piezometers in peat; rather, they are only observed with pressure transducers sealed in the peat. In has been hypothesized that open-pipe Piezometers vent entrapped CH4 to the atmosphere and thereby do not permit the natural development of zones of entrapped gas. Here we present findings of the study to investigate whether Piezometers vent subsurface CH4 to the atmosphere and whether the presence of Piezometers alters the subsurface concentration of dissolved CH4. We measured the flux of methane venting from the Piezometers and also determined changes in pore-water CH4 concentration at a rich fen in southern Ontario and a poor fen in southern Quebec, in the summer of 2004. Seasonally averaged CH4 flux from Piezometers was 1450 and 37·8-mg CH4 m −2 d −1 at the southern Ontario site and Quebec site, respectively. The flux at the Ontario site was two orders of magnitude greater than the diffusive flux at the site. CH4 pore-water concentrations were significantly lower in open Piezometers than in water taken from sealed samplers at both the Ontario and Quebec sites. The flux of CH4 from Piezometers decreased throughout the season suggesting that CH4 venting through the Piezometer exceeded the rate of methanogenesis in the peat. Consequently we conclude that Piezometers may alter the gas dynamics of some peatlands. We suggest that less-invasive techniques (e.g. buried pressure transducers, tracer experiments) are needed for the accurate measurement of porewater pressures and hydraulic conductivity in peatlands with a large entrapped gas component. Furthermore, we argue that caution must be made in interpreting results from previous peatland hydrology studies that use these traditional methods. Copyright 2009 John Wiley & Sons, Ltd.
-
Evaluating the quality of hydraulic conductivity estimates from Piezometer slug tests in peat
Hydrological Processes, 2005Co-Authors: Ben Surridge, Andrew Baird, Ann Louise HeathwaiteAbstract:Although widely used in wetland hydrological studies, hydraulic conductivity (K) estimates from Piezometer slug tests are often of questionable validity. Frequently, this is because insufficient attention is paid to the details of the test procedure. Further, in a potentially heterogeneous and anisotropic medium such as peat, the use of slug tests is prone to error. In this paper we address some of the methodological issues surrounding Piezometer slug tests in peat. We compare slug test data with laboratory determinations of vertical and horizontal K obtained using a new method. Piezometers were installed at three depths in a floodplain fen peat in Norfolk, UK. Slug tests were initiated by both slug insertion and slug withdrawal, and repeat tests were conducted to examine the robustness of our K estimates. Most of the tests displayed departures from the log-linear model of Hvorslev, the form of departure being consistent with compressible soil behaviour. The results suggest that insertion tests gave similar results to those initiated by withdrawal. Repeat testing showed that withdrawal data, in particular, gave highly reproducible normalized responses that were independent of the initial head. Values for K estimated using the slug tests were in the range 1 × 10−4 to 1·6 × 10−3 cm s−1, which is towards the upper end of the range reported for peats generally. Laboratory tests yielded similar values of K to those obtained from the slug tests. Although the laboratory tests showed that the peat was anisotropic, the K values generated by slug testing proved relatively good estimates of both vertical and horizontal K.
-
an assessment of the Piezometer method for measuring the hydraulic conductivity of a cladium mariscus phragmites australis root mat in a norfolk uk fen
Hydrological Processes, 2004Co-Authors: Andrew Baird, Ben Surridge, Russ P. MoneyAbstract:Despite their common global occurrence, little work has been done on characterising the hydraulic properties of root mats, particularly their hydraulic conductivity (K). A common method for estimating K in the field is the Piezometer slug test. In some root mat systems, the Piezometer slug test may be the only technique, field or laboratory, which is able to provide reliable estimates of K. We installed 17 Piezometers in a Cladium mariscus L. (Pohl) and Phragmites australis Cav. (Streud.) root mat in a UK fen. Tests were initiated by both slug insertion and slug withdrawal. Repeat tests were conducted on some Piezometers to check for test consistency. Rapid recoveries after both slug insertion and withdrawal were found, with 90% recovery reached for all tests within 1500 s and for many within 300 s. We found significant and highly reproducible differences between recovery after insertion and recovery after withdrawal, with the latter being more rapid than the former. We invoke a reversible pore blocking mechanism to explain this behaviour. Many of the Piezometers showed recoveries after withdrawal broadly consistent with the assumption of a rigid porous medium in which Darcy’s law holds. Tests on four further Piezometers were used to examine the impact of Piezometer ‘development’, different slug sizes and the use of ‘clean’ water on test behaviour. The results from these test Piezometers were difficult to interpret. Nevertheless, it appears that replacing ‘dirty’ water in the Piezometer standpipe with clean water leads to more rapid recoveries and reduces the difference between recovery after insertion and recovery after withdrawal. The K of the root mat, as estimated from withdrawal tests on 14 Piezometers and standardised to 20C, ranged between 0.00144 and 0.03022 cm s-1. This appears to be at the very top end of K values reported for fen peats and suggests that water can flow readily through this medium given sufficiently large hydraulic gradients.
-
An assessment of the Piezometer method for measuring the hydraulic conductivity of a Cladium mariscus—Phragmites australis root mat in a Norfolk (UK) fen
Hydrological Processes, 2004Co-Authors: Andrew Baird, Ben Surridge, Russ P. MoneyAbstract:Despite their common global occurrence, little work has been done on characterising the hydraulic properties of root mats, particularly their hydraulic conductivity (K). A common method for estimating K in the field is the Piezometer slug test. In some root mat systems, the Piezometer slug test may be the only technique, field or laboratory, which is able to provide reliable estimates of K. We installed 17 Piezometers in a Cladium mariscus L. (Pohl) and Phragmites australis Cav. (Streud.) root mat in a UK fen. Tests were initiated by both slug insertion and slug withdrawal. Repeat tests were conducted on some Piezometers to check for test consistency. Rapid recoveries after both slug insertion and withdrawal were found, with 90% recovery reached for all tests within 1500 s and for many within 300 s. We found significant and highly reproducible differences between recovery after insertion and recovery after withdrawal, with the latter being more rapid than the former. We invoke a reversible pore blocking mechanism to explain this behaviour. Many of the Piezometers showed recoveries after withdrawal broadly consistent with the assumption of a rigid porous medium in which Darcy’s law holds. Tests on four further Piezometers were used to examine the impact of Piezometer ‘development’, different slug sizes and the use of ‘clean’ water on test behaviour. The results from these test Piezometers were difficult to interpret. Nevertheless, it appears that replacing ‘dirty’ water in the Piezometer standpipe with clean water leads to more rapid recoveries and reduces the difference between recovery after insertion and recovery after withdrawal. The K of the root mat, as estimated from withdrawal tests on 14 Piezometers and standardised to 20C, ranged between 0.00144 and 0.03022 cm s-1. This appears to be at the very top end of K values reported for fen peats and suggests that water can flow readily through this medium given sufficiently large hydraulic gradients.
-
time lag errors associated with the use of simple standpipe Piezometers in wetland soils
Wetlands, 2001Co-Authors: Thomas Hanschke, Andrew BairdAbstract:Abstract Standpipe Piezometers are often used in wetland hydrologic studies for measuring pore-water pressures and, therefore, hydraulic heads. Here, we consider the errors associated with the use of simple standpipe Piezometers in wetland soils. The performance of two typical Piezometer designs was assessed. Rather than measure the performance of the Piezometer designs in the field, we modelled their response to computer-generated changes in pore-water pressures for three ‘model’ floodplain soils. We showed that for some Piezometer design/soil-type combinations, standpipe Piezometers can be in considerable error. Greatest errors were found where the less efficient of the two Piezometer designs (standpipe inside diameter = 5 cm, outside diameter of intake = 5.6 cm, intake length = 5 cm) was in a poorly permeable silt deposit (hydraulic conductivity = 6 cm d−1) overlain by a permeable sand (hydraulic conductivity = 210 cm d−1). If undetected, these errors could lead wetland researchers and/or consultants t...
M W Bo - One of the best experts on this subject based on the ideXlab platform.
-
Factors Affecting Consolidation Related Prediction of Singapore Marine Clay by Observational Methods
Geotechnical and Geological Engineering, 2008Co-Authors: Arul Arulrajah, M W BoAbstract:The use of prefabricated vertical drains with preloading option is the most widely-used ground improvement method for the improvement of marine clays in land reclamation projects. The assessment of the degree of consolidation of the marine clay is of paramount importance prior to the removal of preload in such ground improvement projects. This analysis can be carried out by means of observational methods with the use of field settlement plates and Piezometer monitoring. Field settlement monitoring data can be used to ascertain the settlement of the reclaimed fill from the time of initial installation. The field settlement data can be analysed by the Asaoka method to predict the ultimate settlement of the reclaimed land under the surcharge fill. Back-analysis of the field settlement data will enable the coefficient of consolidation due to horizontal flow to be closely estimated. Piezometer monitoring data can be analysed to obtain the degree of consolidation of the improved marine clay. Back-analysis of the Piezometer data will also enable the coefficient of consolidation due to horizontal flow to be estimated. The aim of this paper is to highlight the significance and impact of the various factors that affect prediction by the Asaoka and Piezometer assessment methods. The authors findings of the Asaoka method reveal that the magnitude of ultimate settlement decreases and the degree of consolidation subsequently increases as a longer period of assessment is used in the prediction. The degree of consolidation predicted by the Piezometers is found to be in good agreement with the Asaoka method for the early period of assessment. However as the assessment period increases, the Piezometer indicates lower degree of consolidation as compared to field settlement predictions.
-
Dissipation Testing of Singapore Marine Clay by Piezocone Tests
Geotechnical and Geological Engineering, 2007Co-Authors: Arul Arulrajah, M W Bo, Hamid Nikraz, A. S. BalasubramaniamAbstract:In situ dissipation tests provide a means of evaluating the in situ coefficient of consolidation due to horizontal flow and hydraulic conductivity in horizontal direction in marine clays formation. Dissipation tests by means of piezocone were utilised in the characterisation of the coefficient of consolidation due to horizontal flow and the hydraulic conductivity in horizontal direction of Singapore marine clay at Changi. Piezocone dissipation tests were carried out prior to reclamation as well as after ground improvement with vertical drains to compare the changes in the coefficient of consolidation due to horizontal flow and hydraulic conductivity in horizontal direction prior to and after ground improvement. The quasi-static piezometric pressures from the dissipation tests were compared with piezometric pressures from Piezometers to determine their possibility of future use as an alternative to Piezometers. Post-improvement CPTU dissipation tests were carried out in the treated “Vertical Drain Area” as well as in an adjacent untreated “Control Area” for comparison purposes. This study provides support for the use of piezocone dissipation testing methods for the determination of the coefficient of consolidation due to horizontal flow and hydraulic conductivity in horizontal direction of marine clays in the region as well as an alternative to Piezometer instrumentation for monitoring of piezometric pressure during consolidation.
-
Factors affecting field instrumentation assessment of marine clay treated with prefabricated vertical drains
Geotextiles and Geomembranes, 2004Co-Authors: Arul Arulrajah, Hamid Nikraz, M W BoAbstract:Abstract The use of prefabricated vertical drains with preloading option is the most widely-used ground improvement method for the improvement of soft clays in land reclamation projects. Surcharge of equivalent working load after taking into account submergence effect and settlement of the reclaimed land is placed until the required degree of consolidation of the soft clay is obtained. The assessment of the degree of consolidation of the marine clay is of paramount importance prior to the removal of preload. This analysis can be carried out by means of observational methods with the use of field settlement plates and Piezometer monitoring. Field settlement monitoring data can be used to ascertain the settlement of the reclaimed fill from the time of initial installation. The field settlement data can be analysed by the Asaoka and Hyperbolic methods to predict the ultimate settlement of the reclaimed land under the surcharge fill. Back-analysis of the field settlement data by the Asaoka method will enable the coefficient of consolidation due to horizontal flow to be closely estimated. Piezometer monitoring data can be analysed to obtain the degree of consolidation of the improved marine clay. Back-analysis of the Piezometer data will also enable the coefficient of consolidation due to horizontal flow to be estimated. The authors’ findings of the Asaoka method reveal that the magnitude of ultimate settlement decreases and the degree of consolidation subsequently increases as a longer period of assessment is used in the prediction. It is apparent that as the time interval increases, a cut-off time interval is obtained after which increasing time intervals would converge to the same magnitude of ultimate settlement. The authors’ findings of the Hyperbolic method reveal that the magnitude of ultimate settlement increases and subsequently the degree of consolidation decreases as a longer period of assessment is used in the prediction. The degree of consolidation predicted by the Piezometers is found to be in good agreement with the Asaoka and Hyperbolic methods for the early period of assessment. However as the assessment period increases, the Piezometer indicates lower degree of consolidation as compared to field settlement predictions. The aim of this paper is to highlight the significance and influence of various factors that affect predictions by the Asaoka, Hyperbolic and Piezometer assessment methods.
Lucia Simeoni - One of the best experts on this subject based on the ideXlab platform.
-
laboratory tests for measuring the time lag of fully grouted Piezometers
Journal of Hydrology, 2012Co-Authors: Lucia SimeoniAbstract:Summary Time-lag is the most important parameter describing the conformance of a Piezometer because it represents the time that it takes for the instrument to reach equilibrium when there is a pore water pressure change in the soil. The use of fully grouted Piezometers would make the installation easier and faster than the conventional one, since it prevents the failure risks during the placement of the sand pack and the overlying bentonite seal. This paper describes a number of laboratory tests performed to evaluate the time-lag of fully grouted Piezometers. A pore water pressure change was applied at the bottom of cylindrical samples of grout and the pressure equalization was measured at the top. The samples were made of a cement–bentonite mixture and were 2 cm, 4 cm or 8 cm in height. Time-lags resulted in no longer than 6 min, that is a time generally acceptable in geotechnical projects. It was also found that the time-lag relies on the pore water pressure value. For a given draining path length, the higher the pore water pressure the shorter the response time. This behavior has been explained by assuming that the time-lag depends on both the hydraulic and compressible characteristics of the grout mixture and that these characteristics vary with the pore water pressure because the grout is in a quasi saturated state.
A. S. Balasubramaniam - One of the best experts on this subject based on the ideXlab platform.
-
Dissipation Testing of Singapore Marine Clay by Piezocone Tests
Geotechnical and Geological Engineering, 2007Co-Authors: Arul Arulrajah, M W Bo, Hamid Nikraz, A. S. BalasubramaniamAbstract:In situ dissipation tests provide a means of evaluating the in situ coefficient of consolidation due to horizontal flow and hydraulic conductivity in horizontal direction in marine clays formation. Dissipation tests by means of piezocone were utilised in the characterisation of the coefficient of consolidation due to horizontal flow and the hydraulic conductivity in horizontal direction of Singapore marine clay at Changi. Piezocone dissipation tests were carried out prior to reclamation as well as after ground improvement with vertical drains to compare the changes in the coefficient of consolidation due to horizontal flow and hydraulic conductivity in horizontal direction prior to and after ground improvement. The quasi-static piezometric pressures from the dissipation tests were compared with piezometric pressures from Piezometers to determine their possibility of future use as an alternative to Piezometers. Post-improvement CPTU dissipation tests were carried out in the treated “Vertical Drain Area” as well as in an adjacent untreated “Control Area” for comparison purposes. This study provides support for the use of piezocone dissipation testing methods for the determination of the coefficient of consolidation due to horizontal flow and hydraulic conductivity in horizontal direction of marine clays in the region as well as an alternative to Piezometer instrumentation for monitoring of piezometric pressure during consolidation.
