scholarly journals Using inverse analysis to estimate hydraulic properties for unsaturated layered sand

2020 ◽  
Vol 4 (2) ◽  
pp. First
Author(s):  
Tô Viết Nam ◽  
Nguyễn Việt Kỳ
Keyword(s):  
Inverse Analysis ◽  
Hydraulic Properties ◽  
Numerical Study ◽  
Characteristic Curve ◽  
Soil Column ◽  
Fine Sand ◽  
Soil Suction ◽  
Medium Sand ◽  
Sand Column ◽  
Inverse Simulation

In order to better evaluate the applicability of the inverse analysis method for calculation and evaluation of hydraulic properties of unsaturated soil in more realistic conditions, a transient one – step outflow experiment for layered sands was applied in the desaturation process with the purpose to attain the profiles of suction, saturation and flow rate with time. In this study, the fine sand and medium sand were used with the same thickness of 40cm for each layer. The sand grains were mixed under water and scooped into the plexiglas column (H = 80cm, D = 28cm, wall thickness = 1cm) to prepare a fully saturated sample. For homogeneity within each sand layer, the density of two sands must be controlled during soil column construction. For numerical study, the inverse simulation and one straightforward calculation were carried out to determine the unsaturated hydraulic properties of sands. Unsaturated hydraulic parameters in the van Genuchten model were estimated using soil suction measurements at 10cm intervals and an outflow rate at the bottom of a layered sand column. To reduce the quantity of data for analysis and simulation but still keep enough typical information for the experiment, four data sets of soil suction and saturation at four locations (L2, L4, L5 and L8) were selected out of eight to compile the Soil Water Characteristic Curve. The comparison between predicted unsaturated hydraulic properties and the experimental unsaturated hydraulic properties shows good agreement in the case of the fine sand was overlaid with medium sand. The results concluded that besides the homogeneous sand, the inverse analysis based on the 1-D outflow experiment promises to be a useful method in determining the hydraulic properties for unsaturated heterogeneous sand.

An experimental study of vertical infiltration into a structurally unstable swelling soil, with particular reference to the infiltration throttle

Soil Research ◽  
1973 ◽  
Vol 11 (2) ◽  
pp. 121 ◽  
Author(s):  
BJ Bridge ◽  
N Collis-George
Keyword(s):  
Soil Column ◽  
Soil Surface ◽  
Fine Sand ◽  
Coarse Sand ◽  
Sand Layer ◽  
Wetting Front ◽  
Sand Column ◽  
Swelling Soil ◽  
Potential Gradients ◽  
Moisture Potential

The infiltration phenomena associated with a structurally unstable swelling soil are compared with those of a two-layer stable system of a fine sand layer over coarse sand, the fine sand simulating a slaked layer at the soil surface. Water content and bulk density are measured using dual source gamma ray attenuation, pore water pressures by means of individual tensiometer-transducer systems, and soil temperatures by means of individual thermistor-bridge systems. Analysis of the sand column using well-established principles shows that after the wetting front has passed the texture boundary, infiltration is controlled by Kmax of the fine sand layer and the negative moisture potential in the coarse sand at the texture boundary. After the wetting front penetrates the column, the moisture potential at the texture boundary becomes steady and is unaffected by the development of a capillary fringe and outflow at the base of the column. The negative moisture potentials at the texture boundary give rise to potential gradients up to 6.0 in the simulated slaked layer, and an infiltration rate several times that of Kmax. The low flow rates caused by the fine sand layer give rise to an unstable wetting front in the coarse sand and severe 'fingering' occurs. In the swelling soil column, with aggregates of the same size as the coarse sand, the infiltration throttle occurs immediately below the visibly slaked layer and not at the ground surface. Potential gradients through the throttle reach a maximum of 5.9 similar to that in the layered sand column, but the infiltration behaviour of swelling soil differs from the latter in other respects. Infiltration into the former does not occur under isothermal conditions, a 'hot front' 3�C above ambient occurring 2-3 mm ahead of the wetting front, and infiltration does not reach a constant rate because of changes in the hydraulic properties of the throttle with time. Moisture profiles in the swelling soil column during infiltration show the various zones described by Bodman and Colman (1944) for non-swelling soils. An enlarged apparent transition zone extend to 12 cm below the soil surface. Other properties such as density, moisture content, and total potential suggest that much of this apparent transition zone is really part of a transmission zone made up of layers of soil which have different properties because of swelling.

A study of infiltration on three sand capillary barriers

2004 ◽  
Vol 41 (4) ◽  
pp. 629-643 ◽  
Author(s):  
Hong Yang ◽  
H Rahardjo ◽  
E C Leong ◽  
D G Fredlund
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soil Column ◽  
Fine Sand ◽  
Water Entry ◽  
Barrier Effect ◽  
Capillary Barrier ◽  
Soil Columns ◽  
Medium Sand

The capillary barrier effect was investigated by conducting infiltration tests on three soil columns of fine sand over medium sand, medium sand over gravelly sand, and fine sand over gravelly sand. The barrier effect was verified in the underlying layer of coarser material, and the water-entry values of the coarser layers were confirmed to be nearly equal to the residual matric suctions of the soils. The coarser layer of gravelly sand, which had a lower water-entry value, was more effective in forming a barrier than the coarser layer of medium sand, which had a higher water-entry value. When the capillary barrier was comprised of a coarser layer of gravelly sand, there was more water stored in the finer layer at the end of the drying stage than when the capillary barrier was comprised of a coarser layer of medium sand. Non-equilibrium static conditions of pore-water pressure profiles were observed in the three soil columns, and a generalized ultimate pore-water pressure profile of a capillary barrier system was proposed. In addition, the final volumetric water contents versus matric suctions of the soils as measured from the soil columns were reasonably consistent with the soil-water characteristic curves (SWCCs) of the soils, suggesting that the drying SWCC of a soil could also be obtained from the drying process in a soil column (or a capillary open tube). The drying SWCC could be established from measurements in the soil column up to a height corresponding to two times the residual matric suction head of the soil.Key words: capillary barrier, soil column, soil-water characteristic curve, pore-water pressure, water content, matric suction.

A numerical study of coupled consolidation in unsaturated soils

1998 ◽  
Vol 35 (6) ◽  
pp. 926-937 ◽  
Author(s):  
Tai T Wong ◽  
Delwyn G Fredlund ◽  
John Krahn
Keyword(s):  
Soil Water ◽  
Pore Water ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Numerical Study ◽  
Water Pressure ◽  
Characteristic Curve ◽  
Soil Column ◽  
Pressure Response ◽  
Soil Water Characteristic Curve

This paper first describes the numerical implementation of the coupled formulation for the theory of consolidation of unsaturated soils. The developed computer code is verified using the Mandel-Cryer problem and then is applied to the solution of coupled multidimensional consolidation problems. Using a parametric study, it is demonstrated that, in unsaturated soils, the Mandel-Cryer effect is suppressed and the consolidation process in unsaturated soils is affected significantly by the shape of the soil-water characteristic curve. Finally, the developed model is used to analyze the consolidation of an unsaturated-saturated soil column. Analysis results indicate that the classical "undrained" pore-water pressure response to an externally applied load only occurs in the saturated zone while the pore-water pressure response is subdued in the unsaturated zone. This paper also shows a method of deriving one of the two additional material parameters required for the analysis of unsaturated soils from laboratory test results.Key words: coupled consolidation, unsaturated soils, Mandel-Cryer effect, soil-water characteristic curve.

Measurement of Soil Suction and Soil-Water Characteristics of Bentonite-Sand Mixtures

2010 ◽  
Author(s):  
Pan Hu ◽  
Qing Yang ◽  
Maotian Luan
Keyword(s):  
Soil Water ◽  
Vapor Phase ◽  
Unsaturated Soils ◽  
Characteristic Curve ◽  
Phase Method ◽  
Soil Suction ◽  
Compacted Bentonite ◽  
Water Characteristics ◽  
Wide Range ◽  
High Level

The soil-water characteristic curve (SWCC) is a widely used experimental means for assessing fundamental properties of unsaturated soils for a wide range of soil suction values. The study of SWCC is helpful because some properties of unsaturated soils can be predicted from it. Nowadays, much attention has been paid to the behaviours of highly compacted bentonite-sand mixtures used in engineering barriers for high level radioactive nuclear waste disposal. It is very important to study the various performances of bentonite-sand mixtures in order to insure the safety of high-level radioactive waste (HLW) repository. After an introduction to vapor phase method and osmotic technique, a laboratory study has been carried out on compacted bentonite-sand mixtures. The SWCC of bentonite-sand mixtures has been obtained and analyzed. The results show that the vapor phase method and osmotic technique is suitable to the unsaturated soils with high and low suction.

scholarly journals Compositional and industrial assessment of Isua-Akoko, Akure, Ayadi and Lafe (Ode Aye) clay deposits of Ondo state, Nigeria

1970 ◽  
Vol 21 (1) ◽  
pp. 41-49
Author(s):  
O Adegbuyi ◽  
GP Ojo ◽  
AJ Adeola ◽  
MT Alebiosu
Keyword(s):  
Chemical Properties ◽  
Fine Sand ◽  
Coarse Sand ◽  
Grain Size Analysis ◽  
Size Analysis ◽  
Medium Sand ◽  
Southwestern Nigeria ◽  
Firing Test ◽  
Clay Deposits ◽  
Ondo State

The physical and chemical properties of clay deposits around Isua-Akoko, Akure, Lafe and Ayadi in Ondo State southwestern Nigeria have been examined. The results have shown that Isua-Akoko, Akure and Lafe Clays are plastic fire clays while Ayadi clay is kaolinite. Grain size analysis reveals that Isua Akoko Clay contains 45% of clay, 18% silt, 12% fine sand,14% medium sand and 11% coarse sand and no gravel; Akure clay contains 42% clay, 14% silt, 13% fine sand, 20% medium sand and 8% coarse sand with 1% gravel. Lafe Clay contains 21% clay, 8% silt, 25% fine sand, 37% medium sand and 8% coarse sand with 1% gravel while Ayadi clay contains 83% clay and 17% silt. The liquid limits of these clay samples range from 41% to 73%% and plastic limits range from 18% to 26% respectively. The chemical analysis reveals that the most abundant mineral is silica (60.97%) and aluminum was next in abundance (23.69%) while other oxides are low. The results show that Isua-Akoko and Akure are residual while Lafe and Ayadi are sedimentary and transported Clays. The firing test, PH, and bleaching tests of the clays are also discussed. The chemical and physical characteristics of the clay deposits are strongly indicative of their industrial importance in the production of ceramics, refractories, paving bricks, paint and pharmaceutical products.KEYWORDS: Kaolinite, fire clay, gravel, ceramics and alumina.

scholarly journals Laboratory Plate Loading Test on Calcareous Sands from a Hydraulic fill Reef Island

2021 ◽  
Author(s):  
Xing Wang ◽  
YANG WU ◽  
Jie Cui ◽  
Chang-qi Zhu ◽  
Xin-zhi Wang
Keyword(s):  
Bearing Capacity ◽  
Deformation Modulus ◽  
Fine Sand ◽  
Medium Sand ◽  
Calcareous Sand ◽  
Loading Test ◽  
Moisture Condition ◽  
Hydraulic Fill ◽  
Deformation Properties ◽  
Plate Loading

Abstract The landforms and vertical strata distribution characteristics of Yongxing Island show that the reclaimed reef island is characterized by soft upper strata (calcareous sand) and hard lower strata (reef limestone). In this study, a series of plate loading tests was conducted to examine the influences of particle gradation, compactness, and moisture condition on the bearing mechanism and deformation properties of the calcareous sand foundation. When the foundation is shallowly buried, the relative density range corresponding to a calcareous sand foundation exhibiting local shear failure is narrower than that of a terrigenous sand foundation. For the same compactness, dry calcareous medium sand has a much larger bearing capacity and deformation modulus than dry calcareous fine sand. The effect of water on the bearing capacity of the calcareous medium sand is greater than the effect on calcareous fine sand. Its weak cementation and low permeability make the initial deformation of saturated calcareous fine sand slightly smaller than that under dry conditions. The stress dispersion angle of the calcareous medium sand foundation is 52°, which is larger than that of terrigenous sand. A larger stress dispersion angle leads to a higher bearing capacity and deformation modulus than those of terrigenous sand.

Method for Quick Prediction of Hydraulic Conductivity and Soil-Water Retention of Unsaturated Soils

2018 ◽  
Vol 2672 (52) ◽  
pp. 108-117 ◽  
Author(s):  
Shaoyang Dong ◽  
Yuan Guo ◽  
Xiong (Bill) Yu
Keyword(s):  
Finite Element ◽  
Hydraulic Conductivity ◽  
Soil Properties ◽  
Soil Water ◽  
Unsaturated Soil ◽  
Unsaturated Soils ◽  
Hydraulic Properties ◽  
Water Retention ◽  
Characteristic Curve ◽  
Soil Water Retention

Hydraulic conductivity and soil-water retention are two critical soil properties describing the fluid flow in unsaturated soils. Existing experimental procedures tend to be time consuming and labor intensive. This paper describes a heuristic approach that combines a limited number of experimental measurements with a computational model with random finite element to significantly accelerate the process. A microstructure-based model is established to describe unsaturated soils with distribution of phases based on their respective volumetric contents. The model is converted into a finite element model, in which the intrinsic hydraulic properties of each phase (soil particle, water, and air) are applied based on the microscopic structures. The bulk hydraulic properties are then determined based on discharge rate using Darcy’s law. The intrinsic permeability of each phase of soil is first calibrated from soil measured under dry and saturated conditions, which is then used to predict the hydraulic conductivities at different extents of saturation. The results match the experimental data closely. Mualem’s equation is applied to fit the pore size parameter based on the hydraulic conductivity. From these, the soil-water characteristic curve is predicted from van Genuchten’s equation. The simulation results are compared with the experimental results from documented studies, and excellent agreements were observed. Overall, this study provides a new modeling-based approach to predict the hydraulic conductivity function and soil-water characteristic curve of unsaturated soils based on measurement at complete dry or completely saturated conditions. An efficient way to measure these critical unsaturated soil properties will be of benefit in introducing unsaturated soil mechanics into engineering practice.

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