Water Pressure Measurements Research Articles

LABORATORY WORK ON TOTAL SUCTION CALIBRATION CURVE FOR WHATMAN #42 FILTER PAPER

<p>Soil suction is one of main parameter in unsaturated soil mechanics as its measurement is as very important as pore water pressure measurement for effective stress concept in saturated soil mechanics.Basically, the measurement of soil suction can be classified into 2 categories; direct and indirect method. In the first method, negative pore water pressure is measured directly to obtain matric suction, whereas in indirect method, suction is obtained indirectly by using salt solution and censor. Calibration is then required to establish the relationship between concentration of salt solution and censor. Filter paper method is considered as the simplest method and relatively low cost compare to other method. The studies conducted by many investigators indicate that calibration curve from one type to another type of filter paper is quite different. This paper presents the basic concepts of laboratory work on establishing total suction calibration curve for Wahtmann #42 filter paper. The work has been conducted using NaCl and KCl solutions with different molality to generate different suction. The result indicates that the higher molality of solution, the higher suction is generated. The calibration curve from KCl exhibits a bit higher compare to the one from NaCl. The difference of both curves most probably is due to the difference of equilibration period and suction source.</p><p><strong>Keywords</strong>: Calibration curve, filter paper, suction, unsaturated soil</p>

Stability of scour protection due to earthquake-induced liquefaction: Centrifuge modelling

A key aspect of permanent offshore structures is protection against scour. This is typically in the form of a blanket of coarse gravel or cobbles surrounding the structure. These coarse particles are selected for their high resistance to being displaced by strong currents and thus protect the underlying finer sand particles from scour. However, in the event of an earthquake, the foundation sand may be susceptible to some degree of liquefaction. This research investigates the effects of seismic-induced liquefaction over a scour blanket, and if sinking is inhibited by some combination of the additional effective stress imposed by the gravel together with the interlocking resistance that develops when coarse particles are subjected to relative displacements.In order to evaluate the stability of scour protection blankets, a programme of physical modelling was carried out, involving the assessment of different configurations of stone layers over a liquefiable material, and a monopile-type foundation. Models were subjected to scaled base shaking equivalent to earthquake loading. A mass-balance of particle sinkage showed that a filter layer was critical for maintaining the integrity of the armour stones. Based on displacement and pore water pressure measurements, it was found that the presence of the scour protection blankets improved the response of the liquefiable sand under seismic loading, and even inhibited the occurrence of liquefaction. This implies that a well-designed scour protection blanket can assist in protecting against earthquake effects also.

Improving the estimation of complete field soil water characteristic curves through field monitoring data

In this work, Soil Water Characteristic Curves (SWCCs) were reconstructed through simultaneous field measurements of soil pore water pressure and water content. The objective was to evaluate whether field-based monitoring can allow for the improvement of the accuracy in SWCCs estimation with respect to the use of laboratory techniques. Moreover, field assessment of SWCCs allowed to: a) quantify the hydrological hysteresis affecting SWCCs through field data; b) analyze the effect of different temporal resolution of field measures; c) highlight the differences in SWCCs reconstructed for a particular soil during different hydrological years; d) evaluate the reliability of field reconstructed SWCCs, by the comparison between assessed and measured trends of a component of the soil water balance. These aspects were fundamental for assessing the reliability of the field reconstructed SWCCs. Field data at two Italian test-sites were measured. These test-sites were used to evaluate the goodness of field reconstructed SWCCs for soils characterized by different geomorphological, geological, physical and pedological features. Field measured or laboratory measured SWCCs data of 5 soil horizons (3 in a predominantly silty soil, 2 in a predominantly clayey one) were fitted by Van Genuchten model. Different field drying and wetting periods were identified, based on monthly meteorological conditions, in terms of rainfall and evapotranspiration amounts, of different cycles. This method allowed for a correct discrimination of the main drying and the main wetting paths from field data related and for a more reliable quantification of soil hydrological properties with respect to laboratory methodologies. Particular patterns of changes in SWCCs forms along depth could be also identified. Field SWCCs estimation is not affected by the temporal resolution of the acquisition (hours or days), as testified by similar values of Van Genuchten equation fitting parameters. Instead, hourly data may offer a clearer vision of the drying and wetting paths, due to the highest number of experimental data points. Moreover, in temperate climate situations as those of the test-sites, main drying curves and main wetting curves of a particular soil were substantially similar also for different hydrological cycles with peculiar meteorological conditions. SWCCs parameters were implemented in a numerical code (HYDRUS-1D) to simulate soil water storage for different soil horizons. Field reconstructed SWCCs allowed for simulating with a higher precision these trends, confirming the reliability of the reconstructed field curves by a quantitative point of view. Moreover, best results were obtained considering hysteresis in the modeling.

Experimental study on sedimentation and consolidation of soil particles in dredged slurry

Sedimentation and consolidation of dredged slurry is very complex in practice. A new Multilayer Extraction Sampling (MES) method was developed in this study to better understand the underlying law of sedimentation and consolidation of soil particles in slurries. Comparing with previous methods, the advantages of this method include: (1) the equipment is easy to operate and the test procedures are simple; (2) the volume distribution and the settling velocity of soil particles can be measured and calculated by Volume Flux Function (VFF) approach at different time and heights during sedimentation and consolidation process; (3) soil formation from sedimentation of dredged slurry can be also further studied based on pore water pressure measurements in conjunction with the velocity and density distributions. The experimental results revealed that there were four different zones during sedimentation and consolidation process: water zone, hindered settling zone, consolidation zone and a new zone termed as “transition zone” where soil particles are in contact with each other but effective stress are not fully developed. It is concluded that the sedimentation and consolidation of soil particles in dredged slurry was studied successfully in a holistic manner using this new experimental method.

Numerical modelling of ultrasonic waves in a bubbly Newtonian liquid using a high-order acoustic cavitation model

To address difficulties in treating large volumes of liquid metal with ultrasound, a fundamental study of acoustic cavitation in liquid aluminium, expressed in an experimentally validated numerical model, is presented in this paper. To improve the understanding of the cavitation process, a non-linear acoustic model is validated against reference water pressure measurements from acoustic waves produced by an immersed horn. A high-order method is used to discretize the wave equation in both space and time. These discretized equations are coupled to the Rayleigh-Plesset equation using two different time scales to couple the bubble and flow scales, resulting in a stable, fast, and reasonably accurate method for the prediction of acoustic pressures in cavitating liquids. This method is then applied to the context of treatment of liquid aluminium, where it predicts that the most intense cavitation activity is localised below the vibrating horn and estimates the acoustic decay below the sonotrode with reasonable qualitative agreement with experimental data.

Investment cost analysis for electricity generation with renewable energy and measurement of water pressure from weir to water conservation of small hydropower project

Investment cost analysis for electricity generation with renewable energy and measurement of water pressure from weir to water conservation of small hydropower project

Assessment of the behavior of an active earth-slide by means of calibration between numerical analysis and field monitoring

The assessment of hazards associated with active landslides and the related risk management takes advantage nowadays of using the integration of information arising from field monitoring data, including both displacement data, at ground surface and at depth, and pore pressure measurements well distributed throughout the landslide area, along with the results of numerical models. This paper provides an example of the application of this methodological approach to a case study represented by an active sector of the large Montaguto earthslide, located in the Italian Southern Apennines, which has shown in recent years a continuous slow movement, despite the draining interventions executed in 2011 and the general stability of the other portions of the earthslide. The near real-time topographic monitoring network installed in 2010 shows the presence of different kinematic sectors within the same landslide body, characterised by different velocities and evolution trends. After the proper emergency phase occurred in 2010, a specific area has still shown in 2011 and 2012 clear signs of activity, with acceleration stages generally recorded in the Spring. In order to explore the factors that presumably control the activity of this landslide sector, a two-dimensional finite element model has been developed by using PLAXIS-2D code. Based on the available geological information, pore water pressure measurements and soil geotechnical properties, the numerical results indicate the role of geometry of the landslide mass in sector E as a factor promoting the instability of this specific area. The numerical results are in good agreement with the displacement field measured throughout the landslide channel and confirm that numerical modelling can represent a reliable support for the interpretation of the landslide failure mechanism and the corresponding evolution, when calibrated against the in situ landslide behaviour reconstructed through a monitoring system.

Application of GMPEs to estimate the minimum magnitude and peak ground acceleration of prehistoric earthquakes at Hollywood, SC

In this study, the minimum earthquake magnitude and peak ground acceleration required to initiate liquefaction at the time of prehistoric earthquakes that date back to 11,000years before present at the Hollywood site located in the South Carolina Coastal Plain were computed. The soils at this site are estimated to be about 120,000 to 130,000years old. In-situ geotechnical data, including cone penetration data with pore water pressure measurements, were used with empirical methods that account for the age of the soil deposit to back analyse the peak ground acceleration. Results were then combined with the corresponding values obtained using Ground Motion Prediction Equations (GMPEs) to obtain a proper estimation of amax-M of the prehistoric earthquakes at the Hollywood site. When the age of the earthquake was not considered, the minimum magnitude ranged from 5.8 to 6.5 and the corresponding peak ground acceleration ranged from 0.25 to 0.32g. When the age of the earthquake was considered, the minimum magnitude was found to be 0.2 to 0.3units lower depending on earthquake age and the GMPE model. For the most recent prehistoric earthquake with the age of 546±17, the minimum magnitude ranged from 5.6 to 6.3 with corresponding acceleration ranging from 0.21 to 0.28g.

Application of Film-Like Sensors for K0and Pore Water Pressure Measurement in Clay During 1D Consolidation

In this study, the economical FlexiForce sensor, which is thin and flexible, was used to measure K0 and the excess pore water pressure during a 1D consolidation test on kaolinite clay samples. Before the sensor could be used in the measurement, a special waterproof coating was applied, after which sensor calibration was carried out. The coated FlexiForce sensor was incorporated into two types of tailor-made needle probes for the pore water pressure measurement. The experimental results demonstrate that the two types of needle probes can well capture the evolution of the induced excess pore water pressure during consolidation. Upon a loading increment, the measured excess pore water pressure at the middle of the sample continues to increase and reaches a maximum value at t = ∼4 min and subsequently start to decrease. There is a distinct change in the decreasing trend of the measured excess pore water pressure; the trend becomes mild after t = ∼480 min, indicating the end of primary consolidation. During secondary compression, the excess pore water pressure continues to decrease due to the continuous settlement. A constant K0 value, which is comparable to the prediction by Jaky's equation, is measured by the sensors in the loading path; during secondary compression, K0 increases with time.

Extending Water Retention Curves to a Quasi‐Saturated Zone Subjected to a High Water Pressure up to 1.5 Megapascals

Core Ideas A quasi‐saturated zone with trapped air was subjected to high water pressure. Saturation was measured using a dielectric soil moisture sensor. Saturation increase due to compression of air was well described by Boyle's law. The water retention curve was extended to the positive water pressure domain. We propose a mathematical model for the water retention curve in the extended domain. On closure of an underground facility, recovery of the geoenvironmental conditions is one of the essential issues for ensuring proper implementation of closure. At the Mizunami Underground Research Laboratory, Gifu, Japan, a tunnel flooding test is underway in which a section of a deep underground tunnel is filled with groundwater and the existing desaturated zone with trapped air is subjected to high water pressure. Water saturation in the unsaturated zone as a function of capillary pressure is well understood. However, the process of a saturation increase due to a further increase in water pressure is less well studied. In this study, a simplified laboratory setup using test sands with trapped air was established in a pressure chamber. The relationship between the positive water pressure up to 1.5 MPa and saturation was measured and the effect of the compression of trapped air bubbles on the change in saturation was investigated. The experimental results showed that the saturation increased further from the initial saturation of about 0.85 at zero suction. Most of the saturation increase occurred up to a water pressure of 0.5 MPa, at which the saturation reached 0.98. At 1.5 MPa, the air bubbles were compressed to a non‐detectable level so that the sands were fully saturated. A mathematical model was established based solely on Boyle's law to define the water retention curve in a broad sense for the domain where the water pressure is positive. The measured water pressure–saturation data closely followed the relationship estimated with the established model.

An investigation of pore water pressure and consolidation phenomenon in the unfrozen zone during soil freezing

Accurate modeling of soil deformation depends on the consideration of both frost heave deformation in the frozen zone and consolidation deformation in the unfrozen zone. Pore water pressure investigations are important for revealing these two deformation behaviors. Herein, we aim to reveal the consolidation process by measuring and analyzing changes in pore water pressure in the unfrozen zone. Using a custom-made pore water pressure gauge, we performed a series of real-time pore water pressure measurements in the unfrozen zone of silty clay and sandy soil samples that were exposed to closed and open freezing systems. The results show that the pore water pressure in the unfrozen zone generally increases at first and then decreases. The temperature changes in the unfrozen zone have no significant influence on the changes in pore water pressure, and the variations of the pore water pressure are mainly controlled by the stress and hydraulic boundary (changes in pore water pressure) conditions at the freezing front. Furthermore, changes in the pore water pressure are affected by several parameters, including soil type, water supply condition, initial moisture content, measured soil layer depth, and hydraulic conductivity. Soil consolidation is mainly caused by change in effective stress, which results from increase in total stress or decrease in pore pressure. Based on the observed pore water pressure variations and its numerical simulations, we propose that consolidation in the unfrozen zone during soil freezing includes compression-induced consolidation, which results from an increase in frost heaving stress, and vacuum-induced consolidation, which results from a decrease in pore water pressure. Each consolidation pattern plays an important role in the different stages of soil freezing. Compression-induced consolidation primarily occurs during the early stage of soil freezing, while vacuum-induced consolidation mainly occurs during the later stage of soil freezing.

Evaluation of Vacuum Preloading with Vertical Drains as a Soft Soil Improvement Measure

Site condition and construction technology are described in detail, as well as the solutions to common problems encountered during the construction phase of such a project. A numerical model is established based on the case study and validated by the actual field measurements. The differences between modeled results and field measurements were 2.4-49.4%, which validate the accuracy of the numerical model. Settlement at the surface of soft soils was found to increase when the length and permeability coefficient of prefabricated vertical drains were increased, and decreased as the spacing increased. The estimated degree of consolidation at the final stage of vacuum preloading was 93.4% based on the degree of settlement, and 88.3% based on pore water pressure measurements. Thus, vacuum preloading with vertical drains was found to be an effective method by which to improve the strength of soft soils prior to construction on them.

Effect of Ambient Temperature Variation on Triaxial Shear Testing of Sands

Abstract Triaxial shear tests are often carried out in a temperature controlled laboratory environment, and a few degrees change in ambient temperature are often neglected or considered to have negligible effect on the experiment. In this study, the effect of the ambient temperature fluctuation on volume and pore water pressure measurements is investigated for triaxial testing of sand samples. The experimental results show that even few degrees (±2°C) variation in temperature can produce relatively large pore water pressures in a saturated soil specimen in triaxial testing. These changes can particularly impact triaxial shear testing results of sands. An analytical procedure is also introduced that reasonably captures temperature-induced volume and pore pressure changes in a triaxial sample. The analytical method is then used for a parametric study of the mechanisms involved in temperature-induced effects.

Optoacoustic effect is responsible for laser-induced cochlear responses

Optical stimulation of the cochlea with laser light has been suggested as an alternative to conventional treatment of sensorineural hearing loss with cochlear implants. The underlying mechanisms are controversially discussed: The stimulation can either be based on a direct excitation of neurons, or it is a result of an optoacoustic pressure wave acting on the basilar membrane. Animal studies comparing the intra-cochlear optical stimulation of hearing and deafened guinea pigs have indicated that the stimulation requires intact hair cells. Therefore, optoacoustic stimulation seems to be the underlying mechanism. The present study investigates optoacoustic characteristics using pulsed laser stimulation for in vivo experiments on hearing guinea pigs and pressure measurements in water. As a result, in vivo as well as pressure measurements showed corresponding signal shapes. The amplitude of the signal for both measurements depended on the absorption coefficient and on the maximum of the first time-derivative of laser pulse power (velocity of heat deposition). In conclusion, the pressure measurements directly demonstrated that laser light generates acoustic waves, with amplitudes suitable for stimulating the (partially) intact cochlea. These findings corroborate optoacoustic as the basic mechanism of optical intra-cochlear stimulation.

A Water–Urea–Ammonium Sulfamate system: Experimental investigation and thermodynamic modelling

The Water–Urea–Ammonium Sulfamate ternary system was investigated by means of experimental methods and thermodynamic modelling. Experimental part of the work includes (i) DSC measurements of liquidus and solidus of the Urea–Ammonium Sulfamate, the Water–Ammonium Sulfamate subsystems with the estimation of eutectic point position and a set of experiments on the phase boundaries in the ternary system; (ii) vapor pressure measurements in the binary Water–Ammonium Sulfamate and ternary Water–Ammonium Sulfamate–Urea systems at 298.15 K in a wide concentration range. Excess Gibbs energies of the Water–Ammonium Sulfamate–Urea system and its binary subsystems were described by the Pitzer-Simonson-Clegg model which is reduced to polynomial formalism in case of nonelectrolyte systems. Results of the Water–Urea subsystem reassessment are given.

Centrifuge evaluation of the influential factors in the uplift capacity of suction foundations in clay

ABSTRACTThe passive suction of suction foundations plays a significant role in pull-out resistance. The factors influencing the uplift capacity include stress state, embedment ratio, and loading rate. This article investigates the effect of embedment ratio and loading rate on the bearing behavior of suction foundations using centrifuge testing. A series of uplift tests on a suction foundation in clay were performed using a beam centrifuge. During the tests, uplift displacement, suction, and loading rate were monitored. The suction was obtained by measurement of water pressure. To compare the influence of different factors on uplift capacity due to passive suction, two types of uplift tests were conducted; the first was on the closed caisson and the second was on the vented caisson. The results show that the pull-out resistance increased with an increase of the uplift loading rate, which was induced by the suction. The maximum resistance occurred when the upward displacements reached 14%D under a ratio of skirt length (L) to diameter (D) (L/D) of 0.5 and 17%D under an L/D ratio of 2. These findings provide a way for suction caissons to resist pull-out load or for structures to be removed from the seabed.

Measured basal water pressure variability of the western Greenland Ice Sheet: Implications for hydraulic potential

The gradient of the hydraulic potential field at the ice-bedrock interface beneath the Greenland Ice Sheet (GrIS) dictates the routing and energetics of subglacial water, thereby influencing drainage system characteristics and sliding dynamics. In the ablation zone of the GrIS, variable water pressure due to an active subglacial drainage system and basal topography with high relief potentially interact to drive unknown spatial patterns and temporal changes in the hydraulic potential field. Here we present a suite of water pressure measurements collected in 13 boreholes along a 46 km transect on the western GrIS to investigate the role of spatial and temporal basal water pressure adjustments in hydraulic potential gradient dynamics. All borehole sites show pressures with similar seasonality, having relatively steady and high values during winter, variable and irregular behavior during spring and fall, and diurnal cycles that can persist for multiple weeks during the peak melt season. Despite much higher variability during the melt season, the median pressure of the summer period is nearly the same as the median pressure of the winter period. However, time variability of water pressure due to basal drainage processes can force changes in the magnitude and orientation of the hydraulic potential field over diurnal periods. We find that the basal water pressure across the transect generally mimics the ice thickness field but with superimposed large pressure gradients that develop at shorter scales within the basal drainage system. This leads to a complex hydraulic potential field across regions of similar ice thickness.

Closure to “Settlement of the Kansai International Airport Islands” by G. Mesri and J. R. Funk

Closure to “Settlement of the Kansai International Airport Islands” by G. Mesri and J. R. Funk

Hydraulic Modeling of a Water Distribution Network in a Tourism Area with Highly Varying Characteristics

Hydraulic models are efficient decision support tools for effective management of water distribution networks (WDNs). This study presents an EPANET hydraulic model application at Old Town DMA (District Metered Area), a well-known tourism area in Antalya City, Turkey. Old Town DMA has highly variable WDN characteristics and it contains about 1400 active and inactive water subscribers, mostly related to tourism facilities. Daily and hourly water consumption profiles and water consumption rates by different subscribers in the DMA exhibit wide variations. The temporal and spatial variations of water consumptions and highly varying topographic levels of the DMA are taken into account to allocate nodal water demand in hydraulic modeling. Water pressure and flow rates are continuously monitored online at the SCADA station located at the entrance of the DMA. Additionally, continuous water pressure measurements are performed via portable pressure loggers at 4 different points located at different elevations of the DMA. The monthly water consumption of each water subscriber is recorded. Moreover, the daily and hourly water consumption rates of 13 different water subscribers were monitored for 5 days. The obtained data sets were used to prepare water consumption patterns for different water subscribers and to estimate nodal demands. The hydraulic model was calibrated for Hazen - Williams pipe roughness coefficient and the predicted pressure values were in good agreement with field measurements.

Laboratory determination of coefficient of consolidation from pore water pressure measurement

In the recent past, many studies have been carried out on the determination of coefficient of consolidation (cv) from the time (t)–deformation (d) data obtained from conventional consolidation tests. Several researchers have also proposed different curve fitting procedures for determining cv from the t–d data. It is anticipated that the cv values obtained from the t–d data may be influenced by initial and secondary compressions. Nevertheless, the pore water pressure data measured during the consolidation process will be independent of initial and secondary compressions. In this study, the conventional Asaoka (1978) method is extended to evaluate cv and end-of-primary (EOP) consolidation from the pore water pressure data measured from laboratory experiments. Laboratory experiments were carried out on the modified one-dimensional consolidation apparatus on different remoulded clay samples measuring pore water pressure during the consolidation process. The cv and EOP computed from the proposed approach have been compared with the results of the t–d data and found to be in good agreement.