Hydraulic Conductivity and Shear Strength of Dune Sand–Bentonite Mixtures

Total Page:16

File Type:pdf, Size:1020Kb

Hydraulic Conductivity and Shear Strength of Dune Sand–Bentonite Mixtures Hydraulic Conductivity and Shear Strength of Dune Sand–Bentonite Mixtures M. K. Gueddouda Department of Civil Engineering, University Amar Teledji Laghouat Algeria [email protected] [email protected] Md. Lamara Department of Civil Engineering, University Amar Teledji Laghouat Algeria [email protected] Nabil Aboubaker Department of Civil Engineering, University Aboubaker Belkaid, Tlemcen Algeria [email protected] Said Taibi Laboratoire Ondes et Milieux Complexes, CNRS FRE 3102, Univ. Le Havre, France [email protected] [email protected] ABSTRACT Compacted layers of sand-bentonite mixtures have been proposed and used in a variety of geotechnical structures as engineered barriers for the enhancement of impervious landfill liners, cores of zoned earth dams and radioactive waste repository systems. In the practice we will try to get an economical mixture that satisfies the hydraulic and mechanical requirements. The effects of the bentonite additions are reflected in lower water permeability, and acceptable shear strength. In order to get an adequate dune sand bentonite mixtures, an investigation relative to the hydraulic and mechanical behaviour is carried out in this study for different mixtures. According to the result obtained, the adequate percentage of bentonite should be between 12% and 15 %, which result in a hydraulic conductivity less than 10–6 cm/s, and good shear strength. KEYWORDS: Dune sand, Bentonite, Hydraulic conductivity, shear strength, insulation barriers INTRODUCTION Rapid technological advances and population needs lead to the generation of increasingly hazardous wastes. The society should face two fundamental issues, the environment protection and the pollution risk control. One of the actual solutions, for handling these contamination Vol. 13, Bund. H 2 problems, is by enclosing the wastes in a specific location, using insulated barriers. The efficiency of these insulated barriers depends largely on their hydraulic and mechanical behaviour along with their capacities of attenuation and retention of the contaminant. Compacted sandy soils with small additions of bentonite (bentonite- sand mixture) have been proposed and used as an adequate material for these insulation layers. In order to be efficient, theses insulation barriers should fulfil some requirements (Chapuis, 1990; Parker et al.,1993). • The typical thickness for these layers, ranges between 15 and 30 cm; • Permeability at saturated state varies between 10-6 and 10-8 cm/s (Chapuis (1990); Parker and al.1993); • Properties of exchange and adsorption should be capable to hold some preferentially pollutants; • Physical stability of the material in contact with water; • A swelling potential that ensure good contact with the host rock and permit the replenishment of existing cracks or that will develop in the future; • The sand must also possess some characteristic such grain size distribution, in order to prevent bentonite leaching from the skeleton and hence ensuring the hydraulic stability of the mixture. In Algeria, the rapid development of urban areas and the growth of oil industry in the south regions, begin to generate enormous quantities of hazardous wastes. In order to avoid groundwater pollution and environment degradation, an insulation barrier using dune sand, which is an available and economical local material, enhanced by small addition of bentonite is proposed. In searching for an adequate mixture, an investigation study is carried out on several dune sand calcium bentonite mixtures with different percentages of bentonite additions, which varies between 3% to 15%. The assessment of the hydraulic and mechanical properties for these mixtures is presented along with a comparison with a similar study on Dune sand from India enhanced with sodium bentonite (Ameta and Wayal, 2008). MATERIALS USED FOR STUDY Bentonite of Maghnia The term ‘Bentonite’ is now well established, and used to describe a clay material whose major mineralogical components are formed by the Smectite group. As a result, bentonite is a very expansive soil. The most important bentonite mines in Algeria are situated in the western region. The bentonite used in this study is extracted from Maghnia mine (Hammam Boughrara, 600 km west of the capital Algiers). Dune Sand Dune sand is a material which available in large quantities within the Algerian south, it is known as desert sand. The dune sand used is a local material from Laghouat region. Characterization Tests Vol. 13, Bund. H 3 • Mineralogical and chemical analysis X-ray diffraction is one of the most widely used methods for identification of clay minerals and studying their crystal structure within the soils. Diffraction test carried out on bentonite, showed that the predominant clay mineral is the montmorillonite group as shown by the spectre in the Figure 1, beside it reveals also the presence of quartz, calcite and traces of kaolinite and illite. Results of chemical analysis showed that Maghnia bentonite is composed mostly of silicate with 17 % of aluminates (Table 1). The ratio of SiO2/Al2O3 around 3.77, which is in agreement with reported values for bentonite between 2 and 5.5. For dune sand and according to the chemical analysis (Table 2), the major component is silicate SiO2 (95%). M: Montmorillonite: MgO.AlO3.5SiO2.H2O I: Illite: K(Al Fe)2.AlSi3O10(OH)2 H2O K: Kaolinite: Al2Si2O5(OH)4 Figure 1: X-ray diffraction analysis of bentonite of Maghnia Table 1: Chemical composition of Maghnia bentonite (comma “,” is decimal point) SiO2 % Al2O3% Na2O % CaO % K2O % MgO % Fe2O3 % P.F% 65,2 17,25 3 5 1,7 3,1 2,1 2,65 Table 2: Chemical composition of the dune sand (comma “,” is decimal point) SiO2 % SO3% Cl % CaCO3% M.O % Organic Matter 95,87 0,91 0,36 2,5 ------ • Scanning electronic microscope (SEM) The image obtained by SEM with 5000 times magnification (Figure 2.a), has been realised on fine powdered bentonite. It shows that Maghnia bentonite is composed by white sheet like agglomerates enclosing between them large void space. As visualized by SEM at large scale, the dune sand is formed by rounded shapes grains with a slightly angularities, (figure 2.b). Vol. 13, Bund. H 4 a. Bentonite of Maghnia b. Dune sand Figure 2: S.E.M of the bentonite of Maghnia and the dune sand of Laghouat • Identification Tests Bentonite The grain size distribution of the bentonite is shown in Figure 3. It is very fine clay; about 60% of particles have a diameter less than 2 µm (table 3). The value of the Plasticity Index indicates that the bentonite of Maghnia is highly plastic; this is confirmed by large specific surface (Sp) of 462 m2/g. According to the Skempton et al. classification (1953), based on the activity, the bentonite of Maghnia presents a high percentage of calcite Montmorillonite (Ca+2). (NF P94-068). In addition, for Maghnia bentonite, the corrected activity parameter (Seed and al. 1962) determined using equation (1) exceeds 1,75 which indicates the bentonite is a very active clay. PI Ac = ..........................(1) C 2 − n C2: Percentage of grains less than 2 µm; n = 5 for natural soils; n =10 for reconstituted soil Vol. 13, Bund. H 5 100 80 60 Dune Sand Bentonite 40 Passing proportions weight (%) by 20 0 100 10 1 0,1 0,01 1E-3 1E-4 Particle size (mm) Figure 3: Grain size distribution of bentonite and dune sand Dune Sand The grain size distribution of dune sand is plotted in Figure 3. Values corresponding to uniformity and curvature coefficients are Cu = 1,67 and Cc=1,1, respectively. Thus, the dune sand is classified as poorly graded fine sand according to the Unified Soil Classification System (USCS). The physical characteristics of bentonite and dune sand are summarized in table 3. Table 3: Tests of identification of bentonite and dune sand (comma “,” is decimal point) 2 C2 < 2 µm Φ ≤ 80µm LL PL PI Ac SP (m /g) Cu Cc ES (%) % % % % % B 60 85 140,6 47,5 93,5 1,86 462 --- --- --- S --- 2 --- --- --- --- 1,4 1,67 1,1 86,17 PROPERTIES OF DUNE SAND - BENTONITE MIXTURES Dune sand – bentonite mixtures used in this study are: 3% B + 97% S, 5% B + 95% S, 10% B + 90% S, 12% B + 88% S, 15% B + 85% S (B: Bentonite, S: dune sand). • Atterberg Limits In soil mechanics, the fine materials are classified on the basis on Atterberg limits which can provide information for macroscopic behaviour (Mitchell, 1993). Atterberg limits obtained for different mixture are presented in Figure (4); mixtures with less than 10% are non plastic soils, Vol. 13, Bund. H 6 for percentage of bentonite additions between 10% and 12%, the soils become as little plastic clayey soils, while with percentage of 15% the soil appears to be a plastic. Evolution of consistence limits according to percentage of bentonite additions follows a parabolic law (figure.4). The plastic index ranges from 5,9 to 12,5 for bentonite content varies between 10% and 15%. 40 LL PL 30 20 10 Liquid Limit (LL), Plastic Limit (PL) (%) (PL) Limit Plastic (LL), Limit Liquid 0 0 5 10 15 20 Bentonite content B (%) Figure 4: Relationship between Atterberg Limits and Bentonite content. • Swelling test Swelling tests are carried out using a classical œdometer. Dimensions of samples are 50 mm in diameter and 20 mm in height. The test is realised according to the free swelling method (Serratrice & Soyez, (1996)). The dune sand – bentonite mixture samples are prepared by a static compaction (velocity of 1 mm/min) for water contents and dry densities corresponding to the optimum Proctor conditions. The total free swelling (G %) is computed using the following relationship: ∆H G(%) = × 100..........................(2) H ∆H = Hf - H0 H0: initial height (before swelling). Hf: final height (after swelling). Results of free swelling are grouped in table 4. Swelling evolution of S/B mixtures over time is shown in figure 5.
Recommended publications
  • Hydraulic Conductivity of Composite Soils
    This is a repository copy of Hydraulic conductivity of composite soils. White Rose Research Online URL for this paper: http://eprints.whiterose.ac.uk/119981/ Version: Accepted Version Proceedings Paper: Al-Moadhen, M orcid.org/0000-0003-2404-5724, Clarke, BG orcid.org/0000-0001-9493-9200 and Chen, X orcid.org/0000-0002-2053-2448 (2017) Hydraulic conductivity of composite soils. In: Proceedings of the 2nd Symposium on Coupled Phenomena in Environmental Geotechnics (CPEG2). 2nd Symposium on Coupled Phenomena in Environmental Geotechnics (CPEG2), 06-07 Sep 2017, Leeds, UK. This is an author produced version of a paper presented at the 2nd Symposium on Coupled Phenomena in Environmental Geotechnics (CPEG2), Leeds, UK 2017. Reuse Items deposited in White Rose Research Online are protected by copyright, with all rights reserved unless indicated otherwise. They may be downloaded and/or printed for private study, or other acts as permitted by national copyright laws. The publisher or other rights holders may allow further reproduction and re-use of the full text version. This is indicated by the licence information on the White Rose Research Online record for the item. Takedown If you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing [email protected] including the URL of the record and the reason for the withdrawal request. [email protected] https://eprints.whiterose.ac.uk/ Proceedings of the 2nd Symposium on Coupled Phenomena in Environmental Geotechnics (CPEG2), Leeds, UK 2017 Hydraulic conductivity of composite soils Muataz Al-Moadhen, Barry G.
    [Show full text]
  • Vertical Hydraulic Conductivity of Soil and Potentiometric Surface of The
    Vertical Hydraulic Conductivity of Soil and Potentiometric Surface of the Missouri River Alluvial Aquifer at Kansas City, Missouri and Kansas August 1992 and January 1993 By Brian P. Kelly and Dale W. Blevins__________ U.S. GEOLOGICAL SURVEY Open-File Report 95-322 Prepared in cooperation with the MID-AMERICA REGIONAL COUNCIL Rolla, Missouri 1995 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Gordon P. Eaton, Director For additional information Copies of this report may be write to: purchased from: U.S. Geological Survey District Chief Earth Science Information Center U.S. Geological Survey Open-File Reports Section 1400 Independence Road Box 25286, MS 517 Mail Stop 200 Denver Federal Center Rolla, Missouri 65401 Denver, Colorado 80225 II Geohydrologic Characteristics of the Missouri River Alluvial Aquifer at Kansas City, Missouri and Kansas CONTENTS Glossary................................................................................................................~^ V Abstract.................................................................................................................................................................................. 1 Introduction ................................................................................................................................................................^ 1 Study Area..................................................................................................................................................................
    [Show full text]
  • Transmissivity, Hydraulic Conductivity, and Storativity of the Carrizo-Wilcox Aquifer in Texas
    Technical Report Transmissivity, Hydraulic Conductivity, and Storativity of the Carrizo-Wilcox Aquifer in Texas by Robert E. Mace Rebecca C. Smyth Liying Xu Jinhuo Liang Robert E. Mace Principal Investigator prepared for Texas Water Development Board under TWDB Contract No. 99-483-279, Part 1 Bureau of Economic Geology Scott W. Tinker, Director The University of Texas at Austin Austin, Texas 78713-8924 March 2000 Contents Abstract ................................................................................................................................. 1 Introduction ...................................................................................................................... 2 Study Area ......................................................................................................................... 5 HYDROGEOLOGY....................................................................................................................... 5 Methods .............................................................................................................................. 13 LITERATURE REVIEW ................................................................................................... 14 DATA COMPILATION ...................................................................................................... 14 EVALUATION OF HYDRAULIC PROPERTIES FROM THE TEST DATA ................. 19 Estimating Transmissivity from Specific Capacity Data.......................................... 19 STATISTICAL DESCRIPTION ........................................................................................
    [Show full text]
  • Method 9100: Saturated Hydraulic Conductivity, Saturated Leachate
    METHOD 9100 SATURATED HYDRAULIC CONDUCTIVITY, SATURATED LEACHATE CONDUCTIVITY, AND INTRINSIC PERMEABILITY 1.0 INTRODUCTION 1.1 Scope and Application: This section presents methods available to hydrogeologists and and geotechnical engineers for determining the saturated hydraulic conductivity of earth materials and conductivity of soil liners to leachate, as outlined by the Part 264 permitting rules for hazardous-waste disposal facilities. In addition, a general technique to determine intrinsic permeability is provided. A cross reference between the applicable part of the RCRA Guidance Documents and associated Part 264 Standards and these test methods is provided by Table A. 1.1.1 Part 264 Subpart F establishes standards for ground water quality monitoring and environmental performance. To demonstrate compliance with these standards, a permit applicant must have knowledge of certain aspects of the hydrogeology at the disposal facility, such as hydraulic conductivity, in order to determine the compliance point and monitoring well locations and in order to develop remedial action plans when necessary. 1.1.2 In this report, the laboratory and field methods that are considered the most appropriate to meeting the requirements of Part 264 are given in sufficient detail to provide an experienced hydrogeologist or geotechnical engineer with the methodology required to conduct the tests. Additional laboratory and field methods that may be applicable under certain conditions are included by providing references to standard texts and scientific journals. 1.1.3 Included in this report are descriptions of field methods considered appropriate for estimating saturated hydraulic conductivity by single well or borehole tests. The determination of hydraulic conductivity by pumping or injection tests is not included because the latter are considered appropriate for well field design purposes but may not be appropriate for economically evaluating hydraulic conductivity for the purposes set forth in Part 264 Subpart F.
    [Show full text]
  • Comparison of Hydraulic Conductivities for a Sand and Gravel Aquifer in Southeastern Massachusetts, Estimated by Three Methods by LINDA P
    Comparison of Hydraulic Conductivities for a Sand and Gravel Aquifer in Southeastern Massachusetts, Estimated by Three Methods By LINDA P. WARREN, PETER E. CHURCH, and MICHAEL TURTORA U.S. Geological Survey Water-Resources Investigations Report 95-4160 Prepared in cooperation with the MASSACHUSETTS HIGHWAY DEPARTMENT, RESEARCH AND MATERIALS DIVISION Marlborough, Massachusetts 1996 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Gordon P. Eaton, Director For additional information write to: Copies of this report can be purchased from: Chief, Massachusetts-Rhode Island District U.S. Geological Survey U.S. Geological Survey Earth Science Information Center Water Resources Division Open-File Reports Section 28 Lord Road, Suite 280 Box 25286, MS 517 Marlborough, MA 01752 Denver Federal Center Denver, CO 80225 CONTENTS Abstract.......................................................................................................................^ 1 Introduction ..............................................................................................................................................................^ 1 Hydraulic Conductivities Estimated by Three Methods.................................................................................................... 3 PenneameterTest.............................................................^ 3 Grain-Size Analysis with the Hazen Approximation............................................................................................. 8 SlugTest...................................................^
    [Show full text]
  • The Influence of Horizontal Variability of Hydraulic Conductivity on Slope
    water Article The Influence of Horizontal Variability of Hydraulic Conductivity on Slope Stability under Heavy Rainfall Tongchun Han 1,2,* , Liqiao Liu 1 and Gen Li 1 1 Research Center of Costal and Urban Geotechnical Engineering, Zhejiang University, Hangzhou 310058, China; [email protected] (L.L.); [email protected] (G.L.) 2 Key Laboratory of Soft Soils and Geoenvironmental Engineering, Ministry of Education, Zhejiang University, Hangzhou 310058, China * Correspondence: [email protected] Received: 5 August 2020; Accepted: 10 September 2020; Published: 15 September 2020 Abstract: Due to the natural variability of the soil, hydraulic conductivity has significant spatial variability. In the paper, the variability of the hydraulic conductivity is described by assuming that it follows a lognormal distribution. Based on the improved Green–Ampt (GA) model of rainwater infiltration, the analytical expressions of rainwater infiltration into soil with depth and time under heavy rainfall conditions is obtained. The theoretical derivation of rainfall infiltration is verified by numerical simulation, and is used to quantitatively analyze the effect of horizontal variability of the hydraulic conductivity on slope stability. The results show that the variability of the hydraulic conductivity has a significant impact on rainwater infiltration and slope stability. The smaller the coefficient of variation, the more concentrated is the rainwater infiltration at the beginning of rainfall. Accordingly, the wetting front is more obvious, and the safety factor is smaller. At the same time, the higher coefficient of variation has a negative impact on the cumulative infiltration of rainwater. The larger the coefficient of variation, the lower the cumulative rainwater infiltration.
    [Show full text]
  • Negative Correlation Between Porosity and Hydraulic Conductivity in Sand-And-Gravel Aquifers at Cape Cod, Massachusetts, USA
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by DigitalCommons@University of Nebraska University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln USGS Staff -- Published Research US Geological Survey 2005 Negative correlation between porosity and hydraulic conductivity in sand-and-gravel aquifers at Cape Cod, Massachusetts, USA Roger H. Morin Denver Federal Center, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/usgsstaffpub Part of the Earth Sciences Commons Morin, Roger H., "Negative correlation between porosity and hydraulic conductivity in sand-and-gravel aquifers at Cape Cod, Massachusetts, USA" (2005). USGS Staff -- Published Research. 358. https://digitalcommons.unl.edu/usgsstaffpub/358 This Article is brought to you for free and open access by the US Geological Survey at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in USGS Staff -- Published Research by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Journal of Hydrology 316 (2006) 43–52 www.elsevier.com/locate/jhydrol Negative correlation between porosity and hydraulic conductivity in sand-and-gravel aquifers at Cape Cod, Massachusetts, USA Roger H. Morin* United States Geological Survey, Denver, CO 80225, USA Received 3 March 2004; revised 8 April 2005; accepted 14 April 2005 Abstract Although it may be intuitive to think of the hydraulic conductivity K of unconsolidated, coarse-grained sediments as increasing monotonically with increasing porosity F, studies have documented a negative correlation between these two parameters under certain grain-size distributions and packing arrangements. This is confirmed at two sites on Cape Cod, Massachusetts, USA, where groundwater investigations were conducted in sand-and-gravel aquifers specifically to examine the interdependency of several aquifer properties using measurements from four geophysical well logs.
    [Show full text]
  • Empirical Excess Pore Pressure Dissipation Model for Liquefiable Sands
    6th International Conference on Earthquake Geotechnical Engineering 1-4 November 2015 Christchurch, New Zealand Empirical Excess Pore Pressure Dissipation Model for Liquefiable Sands S.C. Chian1 ABSTRACT In the early phase of excess pore pressure dissipation, the excess pore pressure in a liquefied homogeneous soil stratum reduces most significantly at the base, leading to a curvature at the lower part of the initial isochrone while the upper half remains fairly unchanged. In the later phase, the curvature leaves the initial isochrone completely and progresses until excess pore pressure is fully dissipated. In this paper, a simplified exponential equation is introduced to capture the excess pore pressure dissipation over time. This equation is applied to several dynamic centrifuge tests and shown to depict a suitable fit to the dissipation time history over a wide range of hydraulic conductivity of sands. Introduction Soil liquefaction has been studied extensively over the past several decades since its field observation following the 1964 Niigata Earthquake. However, it still poses serious threats to infrastructure in earthquake prone areas to date, where liquefiable soil layers are present. This is evident in recent earthquakes such as the Christchurch Earthquake and the Great East Japan Earthquake in 2011. Numerous researchers have taken notice of the loss of shear strength due to generation of excess pore pressure during earthquake shaking, however not many have investigated the impact of dissipation of excess pore pressure as thoroughly. Severe ground displacement/settlement can occur during the dissipation of excess pore water pressure. This can lead to tilting of buildings, sliding/lowering of dam crest, lateral spreading of bridge abutment wall, etc.
    [Show full text]
  • Performance-Based Hydraulic Conductivity Models for Unbound Granular Materials
    Performance-Based Hydraulic Conductivity Models for Unbound Granular Materials Haithem Soliman, Ph.D. Assistant Professor Department of Civil & Geological Engineering University of Saskatchewan Email: [email protected] Ahmed Shalaby, P.Eng. Professor and Head Department of Civil Engineering University of Manitoba E-mail: [email protected] Paper prepared for presentation at the “Advanced Testing and Modeling of Road and Embankment Materials” Session of the 2016 Annual Conference of the Transportation Association of Canada Toronto, Ontario. 1 Abstract Specifications for unbound granular materials (UGM) must be based on the function of the unbound layer (drainable layer, high stiffness, or both). Using performance-based specifications that are based on laboratory performance of UGM (resilient modulus, permanent deformation, and permeability) provides durable and longer lasting unbound layers. This paper investigates the effect of fines content variation on the permeability (hydraulic conductivity) of two types of UGM, gravel and 100% crushed limestone. Hydraulic conductivity tests were conducted on compacted gravel UGM with 4.0% fines, 9.0% fines, and 14.5% fines. For 100% crushed limestone, hydraulic conductivity tests were conducted on compacted samples with 4.5% fines, 10.5% fines, and 16.0% fines. For gravel, the hydraulic conductivity decreased by 84% due to increasing fines content from 4.0% to 14.5%. For Limestone, the hydraulic conductivity decreased by 81% due to increasing fines content from 4.5% to 16.0%. For gradations with comparable fines content, limestone material showed higher hydraulic conductivity than that for gravel. The laboratory measured hydraulic conductivity was compared to Level 2 design inputs in the Mechanistic-Empirical Pavement Design Guide (Pavement ME).
    [Show full text]
  • Forecasting of Landslides Using Rainfall Severity and Soil Wetness: a Probabilistic Approach for Darjeeling Himalayas
    water Article Forecasting of Landslides Using Rainfall Severity and Soil Wetness: A Probabilistic Approach for Darjeeling Himalayas Minu Treesa Abraham 1 , Neelima Satyam 1 , Biswajeet Pradhan 1,2,3,* and Abdullah M. Alamri 4 1 Discipline of Civil Engineering, Indian Institute of Technology Indore, Madhya Pradesh 452020, India; [email protected] (M.T.A.); [email protected] (N.S.) 2 Centre for Advanced Modelling and Geospatial Information Systems (CAMGIS), Faculty of Engineering and Information Technology, University of Technology Sydney, Broadway, Sydney P.O. Box 123, Australia 3 Department of Energy and Mineral Resources Engineering, Sejong University, Choongmu-gwan, 209 Neungdong-ro, Gwangjin-gu, Seoul 05006, Korea 4 Department of Geology & Geophysics, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia; [email protected] * Correspondence: [email protected] Received: 18 February 2020; Accepted: 9 March 2020; Published: 13 March 2020 Abstract: Rainfall induced landslides are creating havoc in hilly areas and have become an important concern for the stakeholders and public. Many approaches have been proposed to derive rainfall thresholds to identify the critical conditions that can initiate landslides. Most of the empirical methods are defined in such a way that it does not depend upon any of the in situ conditions. Soil moisture plays a key role in the initiation of landslides as the pore pressure increase and loss in shear strength of soil result in sliding of soil mass, which in turn are termed as landslides. Hence this study focuses on a Bayesian analysis, to calculate the probability of occurrence of landslides, based on different combinations of severity of rainfall and antecedent soil moisture content.
    [Show full text]
  • Determining the Unsaturated Hydraulic Conductivity of a Compacted Sand-Bentonite Mixture Under Constant Volume and Free-Swell Conditions
    Determining the unsaturated hydraulic conductivity of a compacted sand-bentonite mixture under constant volume and free-swell conditions Y.J. Cui, A.M. Tang, C. Loiseau, P. Delage Université Paris Est, Ecole des ponts, I. Navier Corresponding author Prof. Yu-Jun Cui ENPC/CERMES 6 et 8 avenue Blaise Pascal, Cité Descartes, Champs-sur-Marne, 77455 MARNE-LA-VALLEE CEDEX 2, France. Tel: 33 1 64 15 35 50 Fax: 33 1 64 15 35 62 E-mail: [email protected] 1 Abstract Highly compacted sand-bentonite mixtures are often considered as possible engineered barriers in deep high-level radioactive waste disposals. In-situ, the saturation of these barriers from their initially unsaturated state is a complex hydro-mechanical coupled process in which temperature effects also play a role. The key parameter of this process is the unsaturated hydraulic conductivity of the barrier. In this paper, isothermal infiltration experiments were conducted to determine the unsaturated hydraulic conductivity according to the instantaneous profile method. To do so, total suction changes were monitored at different locations along the soil specimen by using resistivity relative humidity probes. Three constant volume infiltration tests were conducted showing, unexpectedly, a decrease of the hydraulic conductivity during infiltration. One test performed under free-swell conditions showed the opposite and standard trend. These observations were interpreted in terms of microstructure changes during wetting, both under constant volume and free swell conditions. Key-Words: Compacted sand/bentonite mixture, infiltration, instantaneous profile method, relative humidity, constant volume, free-swell, unsaturated hydraulic conductivity 2 Introduction In radioactive waste disposal at great depth, compacted expansive soils are sometimes considered as possible engineered barrier to be placed between the radioactive waste and the host rock.
    [Show full text]
  • Hydraulic Conductivity and Porosity Heterogeneity Controls on Environmental Performance Metrics: Implications in Probabilistic Risk Analysis
    Advances in Water Resources 127 (2019) 1–12 Contents lists available at ScienceDirect Advances in Water Resources journal homepage: www.elsevier.com/locate/advwatres Hydraulic conductivity and porosity heterogeneity controls on environmental performance metrics: Implications in probabilistic risk analysis Arianna Libera a,∗, Christopher V. Henri b, Felipe P.J. de Barros a a Sonny Astani Dept. of Civil and Environmental Engineering, University of Southern California, Los Angeles, CA, USA b Dept. of Land, Air and Water Resources, University of California, Davis, CA, USA a b s t r a c t Heterogeneities in natural porous formations, mainly manifested through the hydraulic conductivity ( K ) and, to a lesser degree, the porosity ( ), largely control subsurface flow and solute transport. The influence of the heterogeneous structure of K on transport processes has been widely studied, whereas less attention is dedicated to the joint heterogeneity of conductivity and porosity fields. Our study employs Monte Carlo simulations to investigate the coupled effect of − spatial variability on the transport behavior (and uncertainty) of conservative and reactive plumes within a 3D aquifer domain. We explore multiple scenarios, characterized by different levels of heterogeneity of the geological properties, and compare the computational results from the joint − heterogeneous system with the results originating from generally adopted constant conditions. In our study, the spatially variable − fields are positively correlated. We statistically analyze key Environmental Performance Metrics: first arrival times and peak mass fluxes for non-reactive species and increased lifetime cancer risk for reactive chlorinated solvents. The conservative transport simulations show that considering coupled − fields decreases the plume dispersion, increases both the first arrival times of solutes and the peak mass fluxes at the observation planes.
    [Show full text]