High Initial Water Content Research Articles

Practical estimation of compression behaviour of dredged clays with three physical parameters

Understanding the compression behaviour of dredged clays is essential for their effective use with drainage. Measuring consolidation parameters of dredged clays at high initial water contents is a time-consuming and tough work. The research team has accumulated the database of 110 one dimensional incremental load consolidation tests for dredged clays. Based on this database, this study proposes a simple method of determining virgin compression of dredged clays using three physical parameters which can be easily measured. The compression curves of dredged clays can be divided into the pre-yield and the post-yield zones. Basic equations are suggested for describing the compression behaviour of the two zones. The associated parameters are correlated with the initial void ratio and the void ratio at liquid limit. The predicted compression curves are compared with the measured ones with the accumulated database and the independent data available from literature. The error of the void ratios predicted is found to vary within 10% compared with the measured ones. In engineering practice, the work in this study can be applied instead of the time-consuming and tough experiments to simply estimate the compression behaviour of dredged clays.

The influence of different supports on the properties of the excavation damaged zone along the FE tunnel in the Mont Terri Underground Rock Laboratory

Abstract Permeability and its spatial distribution around an underground opening in a geological formation are important for the interpretation of thermal, hydraulic and mechanical findings from an in situ demonstration experiment. Within the site characterization programme of the Full-scale Emplacement (FE) experiment, permeability measurements with nitrogen gas have been conducted from six short boreholes. Four of them were located in a section without shotcrete support and two in a section with a three-layer-shotcrete lining. As expected, the extension of the zone with an increased permeability was larger (up to 2 m) in the area without shotcrete support than that in the section with a shotcrete lining (less than 1.5 m). The water content in the sections with or without shotcrete linings also showed different behaviour over long-term monitoring. The water content in the deep borehole section in the area with a shotcrete lining stayed almost constant, while the water content in the deep borehole section in the area without shotcrete tended to continuously decrease. In general, the water content close to the tunnel is influenced by the seasonal change in the temperature and relative humidity within the tunnel, especially in the section without a shotcrete lining. Analysis of the abovementioned observations/findings was done by performing FEM (finite-element method) calculations with OpenGeoSys (OGS) software using a coupled hydromechanical model. Owing to the high stiffness of shotcrete, the displacement in the section with a shotcrete lining was smaller. This, in turn, results in a smaller extension in the excavation damaged zone (EDZ). However, shotcrete has a relatively high suction capacity and high initial water content: thus, the interface between the shotcrete and the Opalinus Clay becomes more saturated. Therefore, the excavation-induced fractures in the Opalinus Clay close to the shotcrete can be sealed by swelling. The water content decreases continuously, as a result of desaturation occurring during the operational phase and the associated change in porewater pressure.

Experimental study on settling velocity of soil particles in dredged slurry

ABSTRACTStudying sedimentation and consolidation of dredged slurry has significant implications to the design of storage yard and subsequent ground improvement. In this study, settling velocity of soil particles in dredged slurry during sedimentation and consolidation processes was investigated using an improved multilayer extraction sampling (MES) method. A series of sedimentation column tests were performed on dredged slurry with three different initial water contents. Distributions of volume of soil particles and density of dredged slurry were first obtained by the MES method, settling velocity of soil particles was then calculated by volume flux function approach. It was found that the density and velocity inflection points can be used to distinguish the settling zone and the consolidation zone. The experimental results reveal that the velocity of soil particles was quite low and monotonically decreased with sedimentation height at low initial water content throughout the whole test period, whereas it was increased at 0–1 hours and almost remained constant at 1–7 hours in the settling zone at high initial water content. The effects of initial water content on sedimentation and consolidation mode of dredged slurry and the settling velocity of soil particles were discussed. The relationship between settling velocity of soil particles and particle diameter was also studied. It is indicated that the measured velocity of soil particles was much lower than that calculated by the Stokes equation, and it was related to 0.4881–0.5906 order of particle diameter at 0–1 hours and 0.1117–0.1825 order of particle diameter at 1–7 hours for the test slurries.

Effect of rainfall infiltration on the hydraulic response and failure mechanisms of sandy slope models

This paper presents experimental results obtained from silty sand slope models subjected to an artificial rainfall. Four models were constructed to evaluate the effect of initial water content and rainfall intensity on the hydraulic behavior and failure mechanisms of the slopes. The models were instrumented with volumetric water content sensors to monitor the advance of the water front, and inclinometers to measure lateral movements of the slope. The models were subjected to rainfall intensities ranging from 25 to 50 mm/h, and durations from 19 to 152 minutes. The influence of low intensity rainfall events before a high intensity rainfall is discussed herein. The results showed that the time the slope models required to reach failure was influenced by the soil initial water content, being shorter at high initial water contents. These results are useful to understand the behavior of unsaturated natural slopes and embankments exposed to rainfall infiltration, and to complement the existing laboratory database existing in this subject.

Influence of initial dry density and water content on the soil–water characteristic curve and suction stress of a reconstituted loess soil

In the northwest of China, many loess landslides have occurred without clear triggering factors (i.e., rainfall, earthquake, human activities, etc.). To better understand and analyze the hydro-mechanical properties of these slopes and then provide evidence for their stability analysis subjected to matric suction, it is essential to clarify the soil–water characteristic curve (SWCC). In this study, we conducted a set of experimental trials to examine the influences of initial dry density, water content upon the SWCCs of a loess soil taken from a loess landslide area, by using a conventional volumetric pressure plate extractor. Two common SWCC models have been investigated to evaluate which one is better for loess soil. The suction stress characteristic curves (SSCCs) were also estimated and analyzed. We found that behaviors of SWCCs would be different when the matric suction was greater than a certain value. The two SWCC equations have approximately the same performance in describing the SWCC. The rates of desorption decrease and residual water content increases with increasing the initial dry density, while the initial dry density has little, if any, influence on the air-entry value (AEV). The specimen compacted under higher initial water content would exhibit a higher AEV value and residual water content but lower rate of desorption as compared with the lower initial water content. The magnitude of suction stress had an approximately linear relationship with matric suction before the AEV value, the SSCC shapes will be markedly varied with the initial dry density and water content.

Adjustment of mathematical models and quality of soybean grains in the drying with high temperatures

ABSTRACT The aim of this study was to evaluate the influence of the initial moisture content of soybeans and the drying air temperatures on drying kinetics and grain quality, and find the best mathematical model that fit the experimental data of drying, effective diffusivity and isosteric heat of desorption. The experimental design was completely randomized (CRD), with a factorial scheme (4 x 2), four drying temperatures (75, 90, 105 and 120 ºC) and two initial moisture contents (25 and 19% d.b.), with three replicates. The initial moisture content of the product interferes with the drying time. The model of Wang and Singh proved to be more suitable to describe the drying of soybeans to temperature ranges of the drying air of 75, 90, 105 and 120 °C and initial moisture contents of 19 and 25% (d.b.). The effective diffusivity obtained from the drying of soybeans was higher (2.5 x 10-11 m2 s-1) for a temperature of 120 °C and water content of 25% (d.b.). Drying of soybeans at higher temperatures (above 105 °C) and higher initial water content (25% d.b.) also increases the amount of energy (3894.57 kJ kg-1), i.e., the isosteric heat of desorption necessary to perform the process. Drying air temperature and different initial moisture contents affected the quality of soybean along the drying time (electrical conductivity of 540.35 µS cm-1g-1); however, not affect the final yield of the oil extracted from soybean grains (15.69%).

Laboratory study of infiltration into two frozen engineered (sandy) soils recommended for bioretention

AbstractInfiltration of water into two frozen engineered soils of different gradation was studied in laboratory soil columns 1.2 m long and 0.1 m in diameter. Prior to testing, the soil moisture was adjusted to two levels, described by the gravimetric water content of 5% or 10%, and soils were compacted to about 80–90% of the maximum dry density and refrigerated to temperatures ranging from −8 to −2 °C. Water with temperatures 8–9 °C was thereafter fed on the top of columns at a constant head, and the times of water breakthrough in the column and reaching a steady percolation rate, as well as the percolation rate, were recorded. The soil water content was a critical factor affecting the thawing process; during freezing, soil moisture was converted into ice, which blocked pores, and its melting required high amounts of energy supplied by infiltrating water. Hence, the thawing of soils with higher initial water content was much slower than in lower moisture soils, and water breakthrough and the attainment of steady percolation required much longer times in higher moisture soils. Heat transfer between infiltrating water, soil ice, and frozen soil particles was well described by the energy budget equations, which constitute a parsimonious model of the observed processes. The finer grained soil and more compacted soil columns exhibited reduced porosity and required longer times for soil thawing. Practical implications of study results for design of bioretention facilities (BFs) in cold climate include the use of coarse engineered soils and fitting bioretention facilities with a drain facilitating soil drainage before the onset of freezing weather. Copyright © 2015 John Wiley & Sons, Ltd.

Modeling virgin compression of reconstituted clay at different initial water contents

The observations on compressibility of reconstituted clays show that the compression line with a higher initial water content lies above the compression line with a lower initial water content for a given clay. Hence there exists additional void ratio due to initial water contents among virgin compression lines (VCLs) of reconstituted clays. In this paper, the difference in void ratio caused by different initial water contents is investigated based on the empirical equation proposed by Liu and Carter (2000) for describing the differential void ratio at the same stress between natural and reconstituted clays. The mechanism of compressibility of reconstituted clays, when the stress level is larger than the remolded yield stress, is also discussed.

Analysis of heat transfer influences on gas production from methane hydrates using a combined method

Heat transfer affects the pressure and temperature distributions of hydrate sediments, thereby controlling hydrate dissociation. Therefore, its study is essential for planning hydrate exploitation. Previously, a two-dimensional axisymmetric model, to investigate the influence of heat transfer on hydrate exploitation from hydrate-bearing sediments, was developed and verified. Here, we extended our investigation to the influence of heat transfer on methane gas production using a combined method coupling depressurization and thermal stimulation. Our simulations showed that during decomposition by the combined method, a high specific heat capacity of the hydrate-bearing porous media or a high initial water content could inhibit gas generation. However, the initial water content had only a weak influence on the cumulative gas production and generation rate. The influence of water and methane heat convection was also weak. An increase of the thermal conductivity initially inhibited hydrate dissociation but later promoted it. The implementation of the combined method increased gas generation compared with using only thermal stimulation. However, the benefits gradually diminished with an increasing heat injection temperature.

Compression Behavior of Secondary Clay Minerals at High Initial Water Contents

This study shows the influence of initial water content on the compression behavior of secondary clay minerals: kaolin, illite, and montmorillonite. Oedometer tests were carried out on these minerals with different initial water contents which are ranging from one to two times their corresponding liquid limits. The findings show that the initial water contents can result in different compression behaviors of secondary clay minerals. The compression indices of secondary clay minerals, and , increase nonlinearly with increasing initial water contents, and compression behaviors among samples become insignificant gradually. Meanwhile, it is also noticed that the effect of initial water content on of montmorillonite is smaller than that of kaolin and illite. However, the effect of initial water contents on of secondary clay minerals is close. Due to the remolded yield stresses existing in remold soils, all the e∼logσ′ compression curves of the three secondary clay minerals present an inverse ‘S’ shape. The initial water contents have different effects on remolded yield stress of secondary clay minerals. It has most significant effect on illite, and less effect on kaolin and montmorillonite.

Testing a new automated single ring infiltrometer for Beerkan infiltration experiments

The Beerkan method along with BEST algorithms is an alternative technique to conventional laboratory or field measurements for rapid and low-cost estimation of soil hydraulic properties. The Beerkan method is simple to conduct but requires an operator to repeatedly pour known volumes of water through a ring positioned at the soil surface. A cheap infiltrometer equipped with a data acquisition system was recently designed to automate Beerkan infiltration experiments. In this paper, the current prototype of the automated infiltrometer was tested to validate its applicability to the Beerkan infiltration experiment under several experimental circumstances. In addition, the accuracy of the estimated saturated soil hydraulic conductivity, Ks, and sorptivity, S, was assessed by applying different BEST algorithms to the data obtained with the infiltrometer. At this purpose, both analytically generated and real experimental data were used. The analytical assessment showed that the use of the infiltrometer along with BEST methods could lead to accurate estimates of the considered soil properties in most cases, which validated the design of the infiltrometer and its combination with BEST algorithms. Loamy soils and high initial water contents led to misestimating Ks and S or to failure of BEST algorithms, but advices about the infiltrometer design were developed to alleviate such problems. A comparison between the automated procedure and the original BEST procedure was made at three field sites in Sicily (Italy). Other experiments were carried out in an infiltration basin located in the pumping well field of Crépieux-Charmy (Lyon, France), in order to assess the ability of the automated infiltrometer to check clogging effects on Ks. The experiments showed that the automatic data collection increased measurement speed, allowed a more efficient data handling and analysis, and reduced sensitivity of the calculated hydraulic parameters on the applied BEST algorithm.

Testing steady-state analysis of single-ring and square pressure infiltrometer data

Testing reliability of the saturated soil hydraulic conductivity, Ks, estimated by applying the steady-state single-ring (SR) model to the quasi steady-state infiltration rates obtained with a single-ring pressure infiltrometer (PI) increases confidence in the estimated Ks values. Determining a means to estimate Ks from infiltration data collected with a square infiltrometer allows the use of sources of different shapes. Using numerically simulated infiltration rates for six homogeneous soils ranging in texture from sand to silty clay loam, this investigation suggested an overall good performance of the SR model, with estimated Ks values differing by not more than 25% from the true values for the 90% of the 96 considered runs. Larger errors were generally obtained for the silty clay loam soil. Even in this case, however, a small ring radius (0.038m), a relatively high initial soil water content (initial effective saturation=0.4) and a relatively high depth of ponding (0.10m) allowed the obtainment of accurate predictions of Ks (error=13%) with a run of practically sustainable duration (4h). The SR model was also usable to analyze quasi steady-state infiltration data collected with a square infiltrometer when infiltration was assumed to occur through a circular source having the same area of the square infiltrometer. With this assumption, the estimates of Ks differed from the true values by not more than a practically negligible 16%. The results of this investigation should help better interpret Ks values obtained with the PI and also improve the experimental methodology, depending on the soil. Moreover, a wider applicability of the infiltrometer techniques, i.e. not limited to a circular source, can be expected. Soil heterogeneity should be taken into account in the future since heterogeneity is common in the field.

Measurements of texture, sorption isotherms and drying/rehydration kinetics of dehydrofrozen-textured apple

The aim of this research work was to compare the effect of different apple processing methods on textural properties at equal water content (100% db dry basis). Pre-dried samples were treated by instant controlled pressure drop (DIC), completely frozen and thawed. In order to reach a final water content level of 100% db, the samples were post dried or rehydrated. DIC and freezing increased drying and rehydration rates. A combination of DIC and freezing showed less important effects on sorption isotherms and drying/rehydration kinetics. Freezing had significant detrimental effect on firmness for high initial water content samples. This effect disappeared and firmness kept constant regardless of the initial water content once sample initial water content is lower than 115% db. Significant initial water content effect appeared after freezing/thawing for DIC untreated samples. However, by inserting DIC prior to freezing, the textural effect of final water content became insignificant after freezing/thawing.

A method of determining nonlinear large strain consolidation parameters of dredged clays

A method of obtaining the large strain consolidation parameters of dredged clays considering the influence of the initial water content is investigated in this study. According to the test results of remolded clays with high initial water contents reported by Hong et al. (2010), a relationship between the void ratio (e) and effective stress (σ') is established. Furthermore, based on the available permeability data from the literature, a new relationship between the permeability coefficient (k) and the ratio (e/eL) of the void ratio to the void ratio at the liquid limit (eL) is proposed. The new proposed expression considering the initial water content improves the e−k equation established by Nagaraj et al. (1994). Finally, the influence of the initial void ratio and effective stress on the large strain consolidation coefficient g(e) defined by Gibson et al. (1981) and k/(1+e) in large strain analysis is discussed. The results show that, under a constant effective stress, the value of k/(1+e) increases with the initial void ratio. The large strain consolidation coefficient shows the law of segmentation change, which decreases with the increase of the effective stress when the effective stress is less than the remolded yield stress, but increases rapidly with the effective stress when the effective stress is larger than the remolded yield stress.

Importance of sedimentation process for formation of microfabric in clay deposit

When a clay sample is reconstituted from a slurry state to a normally consolidated state, a higher initial water content generally derives a higher void ratio in e–logp relationship. However, in undisturbed Holocene clay samples collected from a soil layer under the seabed, void ratio is much higher than that for the reconstituted, even though the reconstituted sample was consolidated from a sample slurry state with a very high initial water content. Therefore, the higher void ratio for undisturbed Holocene clay cannot be explained by the initial water content. There must be another key factor to explain the higher void ratio for undisturbed Holocene clay. In this study, the difference between the microfabric of deposited clay from suspension state and reconstituted clay from a slurry state is investigated to clarify the key factors contributing to the higher void ratio. The clay in this study is Osaka Bay Holocene clay sampled from GL −15 to −19m below the seabed. Sedimentation tests from the suspension state were carried out in various conditions of initial water content, salt concentration, and pH. A series of sedimentation tests was carried out with two types of hollow cylinders: an observation glass cylinder with an inner diameter of 60mm and a height of 400mm (specimen height of 350mm), and a cylindrical acrylic container with an inner diameter of 100mm and a height of 1800mm (specimen height of 1500mm). In the 100-mm diameter cylinder, the deposited sample was consolidated by a pressure of 19.6kPa, then mounted in an oedometer ring with an inner diameter of 60mm and a height of 20mm. An incremental loading oedometer test was then carried out up to 39.2kPa. The microfabric of the consolidated specimen was observed by scanning electron microscope (SEM) and quantitatively investigated by mercury intrusion porosimeter (MIP). It was shown that the high void ratio of natural clay deposit is not only due to the high initial water content but also to the sedimentation process with flocculation. This plays an important role in the formation of the microfabric of natural clay deposits characterized by a significantly higher void ratio than reconstituted samples.

Laboratory investigation of the effect of cyclic wetting and drying on the behaviour of an expansive soil

The behaviour of an expansive soil was studied through a number of experiments involving cycles of wetting and drying. Laboratory tests were conducted on compacted samples of an expansive soil (a mixture of bentonite and kaolin, CH) in a modified oedometer under different constant surcharge pressures. The void ratio and water content of samples were determined at different stages. The results show that the swelling–shrinkage was reversible after the soil reached the equilibrium condition where the deformations were the same and the wetting and drying paths (in the water content–void ratio space) converged to an S-shaped curve. The hysteresis phenomenon was studied through the variation of the void ratio with suction, and the results showed that it diminished gradually with the increase in cycles of wetting and drying. The effect of fabric on the behaviour of soil samples was studied during cycles of wetting and drying. The results show that the samples with lower initial water content (on the dry side of optimum) have more swelling potential than samples with a higher initial water content (on the wet side of optimum).

On the role of rock fragments and initial soil water content in the potential subsurface runoff formation

Abstract Stony soils are composed of fractions (rock fragments and fine soil) with different hydrophysical characteristics. Although they are abundant in many catchments, their properties are still not well understood. This article presents basic characteristics (texture, stoniness, saturated hydraulic conductivity, and soil water retention) of stony soils from a mountain catchment located in the highest part of the Carpathian Mountains and summarizes results of water flow modeling through a hypothetical stony soil profile. Numerical simulations indicate the highest vertical outflow from the bottom of the profile in soils without rock fragments under ponding infiltration condition. Simulation of a more realistic case in a mountain catchment, i.e. infiltration of intensive rainfall, shows that when rainfall intensity is lower than the saturated hydraulic conductivity of the stony soil, the highest outflow is predicted in a soil with the highest stoniness and high initial water content of soil matrix. Relatively low available retention capacity in a stony soil profile and consequently higher unsaturated hydraulic conductivity leads to faster movement of the infiltration front during rainfall.

Influence of cookies composition on temperature profiles and qualitative parameters during baking

Summary During baking of bakery products temperature of baking, temperature profiles, moisture content, volume and colour changes are strongly coupled. The objective of this paper was to study the influence of the cookies composition on temperature profiles and quality parameters (width and thickness, colour formation and textural properties: hardness, fracturability and work of breaking force) during baking process. Composition of cookies differs due to flour type and initial moisture content. Cookies were baked at 205 °C and temperature was measured in the centre of samples which were 7 mm thick with a 60 mm diameter. The results of temperature profiles of the cookies during baking have shown the same trend for all of the 18 samples. Samples with the higher initial water content have lower values of total colour difference and also significantly affect textural properties.

Poroelastic Theory of Consolidation in Unsaturated Soils

The theory of poroelastic behavior in a deformable porous medium containing two immiscible, viscous, compressible fluids was applied to the three‐dimensional consolidation of unsaturated soils. Three coupled partial differential equations were developed that feature the displacement vector of the solid phase and the excess pore water and air pressures as dependent variables. These equations generalize the classic Biot consolidation model, which applies to saturated soils, with effective stress emerging naturally from a pure compliance formulation of the relation between stress and strain. Under uniaxial strain and constant total compaction stress, the equations simplify to two coupled diffusion equations for the excess pore water and air pressures. Analytical solutions describing the response to instantaneous compression under both permeable and semipermeable boundary drainage conditions were obtained using the Laplace transform. Numerical calculations of pore water pressure, effective stress, and total settlement were made for a soil with clay texture as a representative example. The results show that excess pore water pressure dissipates faster at higher initial water content, leading to higher effective stress. The loading efficiency also was found to be highly sensitive to initial water saturation.

Managing crop stubble during fallow period for soil water conservation: field experiment and modelling

In the arid and semi-arid environments where the rainfall is limited and variable, fallow period soil moisture conservation using stubble is one of the ways of increasing the soil moisture required for crop sowing and development. However, the effectiveness of moisture conservation using stubble depends on the paddock management, soil water content, and rainfall characteristics. To assess the effect of stubble rate and amount of rainfall on the soil moisture conservation, a two-season field experiment was conducted using four stubble rates (0, 2, 4, 6 t/ha) and two water supply amounts. The soil water dynamics was also analysed using a validated Agricultural Production System Simulator (APSIM). In the relatively wet summer season with a high initial soil water content, the amount of water stored in the 2, 4, and 6 t/ha stubble rate treatment plots was higher than that of the bare plots by 10.4, 15.9, and 17.8 mm, respectively. However, in the summer season with a relatively high amount of in-season water input and low initial soil water content, the soil water storage was increased by 29.4, 35.6, and 43.0 mm, respectively. Comparing the results of the two seasons, the highest increase was observed for the 2 t/ha stubble rate. The amount of conserved soil moisture was found to be the highest when the soil profile water content at the start of the summer-fallow period is low and the amount of rain during the summer season is high. The good agreement between the measured and APSIM-simulated soil water contents (R 2 = 0.812), indicates that the model can be used to assess the soil water dynamics under a fallow condition. The APSIM-simulated soil water balance using the weather data of the past 100 years indicated that in a year with low start-of-fallow period soil water content, a 6 t/ha stubble rate can increase the end-of-fallow period soil moisture by up to 60 %.