scholarly journals Evolution of Hydraulic Conductivity of Unsaturated Compacted Na-Bentonite under Confined Condition—Including the Microstructure Effects

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 219
Author(s):  
Tian Chen ◽  
Mao Du ◽  
Qiangling Yao
Keyword(s):  
Hydraulic Conductivity ◽  
Network Evolution ◽  
Saturated Hydraulic Conductivity ◽  
Constitutive Relationship ◽  
Pore System ◽  
Compacted Bentonite ◽  
Hydraulic Behaviour ◽  
Unsaturated Hydraulic Conductivity ◽  
Microstructure Effects ◽  
Microstructure Effect

Compacted bentonite is envisaged as engineering buffer/backfill material in geological disposal for high-level radioactive waste. In particular, Na-bentonite is characterised by lower hydraulic conductivity and higher swelling competence and cation exchange capacity, compared with other clays. A solid understanding of the hydraulic behaviour of compacted bentonite remains challenging because of the microstructure expansion of the pore system over the confined wetting path. This work proposed a novel theoretical method of pore system evolution of compacted bentonite based on its stacked microstructure, including the dynamic transfer from micro to macro porosity. Furthermore, the Kozeny–Carman equation was revised to evaluate the saturated hydraulic conductivity of compacted bentonite, taking into account microstructure effects on key hydraulic parameters such as porosity, specific surface area and tortuosity. The results show that the prediction of the revised Kozeny–Carman model falls within the acceptable range of experimental saturated hydraulic conductivity. A new constitutive relationship of relative hydraulic conductivity was also developed by considering both the pore network evolution and suction. The proposed constitutive relationship well reveals that unsaturated hydraulic conductivity undergoes a decrease controlled by microstructure evolution before an increase dominated by dropping the gradient of suction during the wetting path, leading to a U-shaped relationship. The predictive outcomes of the new constitutive relationship show an excellent match with laboratory observation of unsaturated hydraulic conductivity for GMZ and MX80 bentonite over the entire wetting path, while the traditional approach overestimates the hydraulic conductivity without consideration of the microstructure effect.

scholarly journals Characterization of stony soils' hydraulic conductivity using laboratory and numerical experiments

2015 ◽  
Vol 2 (2) ◽  
pp. 1103-1133
Author(s):  
M. Pichault ◽  
E. Beckers ◽  
A. Degré ◽  
S. Garré
Keyword(s):  
Hydraulic Conductivity ◽  
Water Flow ◽  
Numerical Experiments ◽  
Saturated Hydraulic Conductivity ◽  
Rock Fragments ◽  
Hydraulic Behaviour ◽  
Unsaturated Hydraulic Conductivity ◽  
The One ◽  
The Impact

Abstract. Determining soil hydraulic properties is of major concern in various fields of study. Though stony soils are widespread across the globe, most studies deal with gravel-free soils so that the literature describing the impact of stones on soil's hydraulic conductivity is still rather scarce. Most frequently, models characterizing the saturated hydraulic conductivity of stony soils assume that the only effect of rock fragments is to reduce the volume available for water flow and therefore they predict a decrease in hydraulic conductivity with an increasing stoniness. The objective of this study is to assess the effect of rock fragments on the saturated and unsaturated hydraulic conductivity. This was done by means of laboratory and numerical experiments involving different amounts and types of coarse fragments. We compared our results with values predicted by the aforementioned models. Our study suggests that considering that stones only reduce the volume available for water flow might be ill-founded. We pointed out several drivers of the saturated hydraulic conductivity of stony soils, not considered by these models. On the one hand, the shape and the size of inclusions may substantially affect the hydraulic conductivity. On the other hand, the presence of rock fragments can counteract and even overcome the effect of a reduced volume in some cases. We attribute this to the creation of voids at the fine earth-stone interface. Nevertheless, these differences are mainly important near to saturation. However, we come up with a more nuanced view regarding the validity of the models under unsaturated conditions. Indeed, under unsaturated conditions, the models seem to represent the hydraulic behaviour of stones reasonably well.

scholarly journals Estimation of Unsaturated Hydraulic Conductivity of Granular Soils from Particle Size Parameters

Water ◽  
2019 ◽  
Vol 11 (9) ◽  
pp. 1826 ◽  
Author(s):  
Ji-Peng Wang ◽  
Pei-Zhi Zhuang ◽  
Ji-Yuan Luan ◽  
Tai-Heng Liu ◽  
Yi-Ran Tan ◽  
...  
Keyword(s):  
Grain Size ◽  
Hydraulic Conductivity ◽  
Water Retention ◽  
Intrinsic Value ◽  
Estimation Method ◽  
Sandy Soils ◽  
Saturated Hydraulic Conductivity ◽  
Water Retention Curve ◽  
Porosity Variation ◽  
Unsaturated Hydraulic Conductivity

Estimation of unsaturated hydraulic conductivity could benefit many engineering or research problems such as water flow in the vadose zone, unsaturated seepage and capillary barriers for underground waste isolation. The unsaturated hydraulic conductivity of a soil is related to its saturated hydraulic conductivity value as well as its water retention behaviour. By following the first author’s previous work, the saturated hydraulic conductivity and water retention curve (WRC) of sandy soils can be estimated from their basic gradation parameters. In this paper, we further suggest the applicable range of the estimation method is for soils with d10 > 0.02mm and Cu < 20, in which d10 is the grain diameter corresponding to 10% passing and Cu is the coefficient of uniformity (Cu=d60d10). The estimation method is also modified to consider the porosity variation effect. Then the proposed method is applied to predict unsaturated hydraulic conductivity properties of different sandy soils and also compared with laboratory and field test results. The comparison shows that the newly developed estimation method, which predicts the relative permeability of unsaturated sands from basic grain size parameters and porosity, generally has a fair agreement with measured data. It also indicates that the air-entry value is mainly relative to the mean grain size and porosity value change from the intrinsic value. The rate of permeability decline with suction is mainly associated with grain size polydispersity.

scholarly journals Characterization of stony soils' hydraulic conductivity using laboratory and numerical experiments

SOIL ◽  
2016 ◽  
Vol 2 (3) ◽  
pp. 421-431 ◽  
Author(s):  
Eléonore Beckers ◽  
Mathieu Pichault ◽  
Wanwisa Pansak ◽  
Aurore Degré ◽  
Sarah Garré
Keyword(s):  
Hydraulic Conductivity ◽  
Water Flow ◽  
Predictive Models ◽  
Laboratory Experiments ◽  
Saturated Hydraulic Conductivity ◽  
Experimental Conditions ◽  
Rock Fragments ◽  
Unsaturated Hydraulic Conductivity ◽  
The One ◽  
The Impact

Abstract. Determining soil hydraulic properties is of major concern in various fields of study. Although stony soils are widespread across the globe, most studies deal with gravel-free soils, so that the literature describing the impact of stones on the hydraulic conductivity of a soil is still rather scarce. Most frequently, models characterizing the saturated hydraulic conductivity of stony soils assume that the only effect of rock fragments is to reduce the volume available for water flow, and therefore they predict a decrease in hydraulic conductivity with an increasing stoniness. The objective of this study is to assess the effect of rock fragments on the saturated and unsaturated hydraulic conductivity. This was done by means of laboratory experiments and numerical simulations involving different amounts and types of coarse fragments. We compared our results with values predicted by the aforementioned predictive models. Our study suggests that it might be ill-founded to consider that stones only reduce the volume available for water flow. We pointed out several factors of the saturated hydraulic conductivity of stony soils that are not considered by these models. On the one hand, the shape and the size of inclusions may substantially affect the hydraulic conductivity. On the other hand, laboratory experiments show that an increasing stone content can counteract and even overcome the effect of a reduced volume in some cases: we observed an increase in saturated hydraulic conductivity with volume of inclusions. These differences are mainly important near to saturation. However, comparison of results from predictive models and our experiments in unsaturated conditions shows that models and data agree on a decrease in hydraulic conductivity with stone content, even though the experimental conditions did not allow testing for stone contents higher than 20 %.

scholarly journals The impact of different tillage treatments on hydraulic conductivity of loamy soil

2012 ◽  
Vol 60 (5) ◽  
pp. 109-114 ◽  
Author(s):  
Ivana Kameníčková ◽  
L. Larišová ◽  
A. Stoklásková
Keyword(s):  
Hydraulic Conductivity ◽  
Conventional Tillage ◽  
Saturated Hydraulic Conductivity ◽  
Water Infiltration ◽  
Reduced Tillage ◽  
Loamy Soil ◽  
Double Ring ◽  
Unsaturated Hydraulic Conductivity ◽  
The Impact

Water infiltration into the soil profile, surface runoff and soil erosion in arable lands depend on the conditions of the top layer. The tillage treatment of the top layer plays a key role in changes of the hydro-physical properties, mainly saturated hydraulic conductivity Ks of the surface layer. The aim of this study was to asses the impact of different tillage treatments on hydraulic conductivity in the locality Bohaté Málkovice. Field experimental works in this area were performed in 2009 and were repeted in 2011 on Haplic Chernozem, medium heavy loamy soil. The experimental area was divided into two parts; top layer of these plots was cultivated by applying conventional and reduced tillage treatment. Both these plots were sown with spring barley (Hordeum vulgare). For the field measurement of water infiltration into the soil was used double-ring infiltrometer (2009, 2011) and Minidisk infiltrometer (2011). Near the point were the infiltration was measured, the soil samples were always collected for laboratory determination of basic physical properties of soil (bulk density, porosity, initial and saturated water content, aeration of the soil) and saturated hydraulic conductivity Ks. For laboratory determination of Ks was used permeameter with constant gradient.For evaluation of saturated hydraulic conductivity Ks using the double-ring infiltration method was used Philip’s three-parameter equation and for evaluation of unsaturated hydraulic conductivity K(h) using Minidisk infiltrometer was used Zang’s method. After two years of using repeatedly applied different tillage treatments was significantly influenced saturated hydraulic conductivity Ks. The Ks value increased approximately six times for reduced tillage and more than three times for conventional tillage. Laboratory determined average values of Ks were compared with the average estimates of Ks from infiltration tests. The results were burdened by a number of errors (compaction, preferential flow). These mean values were higher for conventional and reduced tillage. Unsaturated hydraulic conductivity K(−2cm) for reduced tillage was higher, for conventional tillage decreased approximately three times.

scholarly journals Physical Properties of Sandy Soil Affected by Soil Conditioner Under Wetting and Drying cycles

1998 ◽  
Vol 3 (2) ◽  
pp. 69 ◽  
Author(s):  
M.I. Choudhary ◽  
A.M. AI-Omran ◽  
A.A. Shalaby
Keyword(s):  
Hydraulic Conductivity ◽  
Physical Properties ◽  
Bulk Density ◽  
Sandy Soil ◽  
Dry Weight ◽  
Saturated Hydraulic Conductivity ◽  
Wetting And Drying ◽  
Soil Conditioner ◽  
Wetting And Drying Cycles ◽  
Unsaturated Hydraulic Conductivity

Information on the effectiveness of soil conditioners over a prolonged period is scarce. A laboratory experiment was undertaken to evaluate the effectiveness of a polyacrylamide (Broadleaf P4) soil conditioner on the physical properties of sandy soil subjected to wetting and drying cycles. Four concentrations of Broadleaf P4 0, 0.2, 0.4, and 0.6% on dry weight basis were uniformly mixed with a calcareous sandy soil. Addition of Broadleaf P4 to sandy soil increased the water holding capacity, decreased the bulk density, and increased the porosity and void ratio at 0 and 16 wetting and drying cycles. The coefficient of linear extensibility increased considerably with increasing concentrations of the polymer. The addition of polymer at 0 and 16 cycles increased considerably the retention and availability of water in sandy soil. Saturated hydraulic conductivity decreased with increasing concentrations of Broadleaf P4 whereas unsaturated hydraulic conductivity at 0 and 16 cycles showed an increase with increasing soil moisture contents. After I6 wetting and drying cycles, the capacity of the soil to hold water was lost on average by 15.8% when compared to the 0 wetting and drying cycle. The effectiveness of the soil conditioner on bulk density, coefficient of linear extensibility, available water and saturated hydraulic conductivity was reduced on average by 14.1, 24.5, 21.l and 53.7% respectively. The significant changes in soil properties between 0 and 16 cycles suggested that the effectiveness of the conditioner decreased with the application of wetting and drying cycles. However, its effect was still considerable when compared to untreated soil under laboratory conditions.

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