| 1. |
- Loukil, Mohamed Sahbi, 1984-
(författare)
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Experimental and numerical studies of intralaminar cracking in high performance composites
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The macroscopic failure of composite laminates subjected to tensile increasing load is preceded by initiation and evolution of several microdamage modes. The most common damage mode and the one examined in this thesis is intralaminar cracking in layers. Due to this kind of microdamage the laminate undergoes stiffness reduction when loaded in tension. For example, the elastic modulus in the loading direction and the corresponding Poisson’s ratio will decrease.The degradation of the elastic properties of these materials is caused by reduced stress in the damaged layer which is mainly due to two parameters: crack opening displacement (COD) and crack sliding displacement (CSD). At fixed applied load these parameters depend on the properties of the damaged and surrounding layers, on layer orientation and on thickness. When the number of cracks per unit length is high (high crack density in the layer) the COD and CSD are reduced because of to crack interaction.The main objective of the first paper is to investigate the effect of crack interaction on COD using FEM and to describe the identified dependence on crack density in a simple and accurate form by introducing an interaction function dependent on crack density. This interaction function together with COD of non-interactive crack gives accurate predictions of the damaged laminate properties. The application of this function to more complex laminate lay-ups is demonstrated. All these calculations are performed assuming that cracks are equidistant.However, the crack distribution in the damaged layer is very non-uniform, especially in the initial stage of multiple cracking. In the second paper, the earlier developed model for general symmetric laminates is generalized to account for non-uniform crack distribution. This model is used to calculate the axial modulus of cross-ply laminates with cracks in internal and surface layers. In parametric analysis the COD and CSD are calculated using FEM, considering the smallest versus the average crack spacing ratio as non-uniformity parameter. It is shown that assuming uniform distribution we obtain lower bond to elastic modulus. A “double-periodic” approach presented to calculate the COD of a crack in a non-uniform case as the average of two solutions for periodic crack systems is very accurate for cracks in internal layers, whereas for high crack density in surface layers it underestimates the modulus reduction.In the third paper, the thermo-elastic constants were calculated using shear lag models and variational models in a general calculation approach (GLOB-LOC) for symmetric laminates with transverse cracks in 90° layer. The comparison of these two models with FEM was presented for cross-ply and quasi-isotropic laminates.Using FEM, we assume linear elastic material with ideal crack geometry. Fiber bridging over the crack surface is possible which can affect COD and CSD. The only correct way to validate these assumptions is through experiments.The main objective of the fourth and the fifth paper is to measure these parameters for different laminate lay-ups in this way providing models with valuable information for validation of used assumptions and for defining limits of their application. In particular, the displacement field on the edge of a [90/0]s and [903/0]s carbon fiber/epoxy laminates specimens with multiple intralaminar cracks in the surface layer is studied. The specimen full-field displacement measurement is carried out using ESPI (Electronic Speckle Pattern Interferometry).
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| 2. |
- Broberg, Patrik, 1983-
(författare)
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Imaging and analysis methods for automated weld inspection
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- All welding processes can give rise to defects, which weakens the joint and can eventually lead to the failure of the welded structure. In order to inspect welds for detects, without affecting the usability of the product, non-destructive testing (NDT) is needed. NDT includes a wide range of different techniques, based on different physical principles, each with its advantages and disadvantages. The testing is often performed manually by a skilled operator and in many cases only as spot-checks. Today the trend in industry is to move towards thinner material, in order to save weight for cost and for environmental reasons. The need for inspection of a larger portion of welds therefore increases and there is an increasing demand for fully automated inspection, including both the mechanised testing and the automatic analysis of the result. Compared to manual inspection, an automated solution has advantages when it comes to speed, cost and reliability. A comparison of several NDT methods was therefore first performed in order to determine which methods have most potential for automated weld inspection. Automated analysis of NDT data poses several difficulties compared to manual data evaluation. It is often possible for an operator to detect defects even in noisy data, through experience and knowledge about the part being tested. Automatic analysis algorithms on the other hand suffer greatly from both random noise as well as indications that originate from geometrical variations. The solution to this problem is not always obvious. Some NDT techniques might not be suitable for automated inspection and will have to be replaced by other, better adapted methods. One such method that has been developed during this work is thermography for the detection of surface cracks. This technique offers several advantages, in terms of automation, compared to existing methods. Some techniques on the other hand cannot be easily replaced. Here the focus is instead to prepare the data for automated analysis, using various pre-processing algorithms, in order to reduce noise and remove indications from sources other than defects. One such method is ultrasonic testing, which has a good ability for detecting internal defects but suffers from noisy signals with low spatial resolution. Work was here done in order to separate indications from corners from other indications. This can also help to improve positioning of the data and thereby classification of defects. The problem of low resolution was handled by using a deconvolution algorithm in order to reduce the effect of the spread of the beam.The next step in an automated analysis system is to go beyond just detection and start characterising defects. Using knowledge of the physical principles behind the NDT method in question and how the properties of a defect affect the measurement, it is sometimes possible to develop methods for determining properties such as the size and shape of a defect. This kind of characterisation of a defect is often difficult to do in the raw data, and is therefore an area where automated analysis can go beyond what is possible for an operator during manual inspection. This was shown for flash thermography, where an analysis method was developed that could determine the size, shape and depth of a defect. Similarly for laser ultrasound, a method was developed for determining the size of a defect.
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| 3. |
- Holmquist, Mats, 1954-
(författare)
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Lärande nätverk : En social oas i utvecklingsprocessen
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Intresset för nätverk mellan organisationer växer i arbetslivet. Fler och fler chefer, ledare och ansvariga går med i nätverk för att få stöd i sitt utvecklingsarbete. Varför? Vad är det för speciellt med lärande i nätverk? Vad får individen och organisationen ut? Mina egna och kollegors erfarenheter från tio års praktiskt arbete i fem nätverk i Halland, har gett mig en unik tillgång till data för att söka svar på frågorna.Med hjälp av flervetenskaplig teori och tidigare empirisk forskning har jag skapat en modell över nätverk som stöd i utvecklingsprocessen. Modellen har jag använt till att analysera mina data för att förstå lärprocessen i nätverk, vilka förutsättningar och organiseringsformer som är viktiga för att stimulera det kollektiva lärande som uppstår i samverkan mellan olika individer och organisationer. Jag har även undersökt vad deltagandet ger i utbyte och vad som stödjer respektive hindrar en transformering till organisatorisk nytta och förändring.Resultaten visar att nätverk fungerar som en social oas för chefer och ledare, som kan vara ganska ensamma och osäkra i sitt arbete. De uppskattar en plats där de kan möta andra i en liknande situation, för att under tillitsfulla former utbyta erfarenheter och reflektera över sina handlingsalternativ. Deltagarnas olikheter tillför variationer som stimulerar ett kreativt lärande och genererar innovativa idéer.I stort sett alla deltagare är mycket positiva till nätverkformen. Utbytet är huvudsakligen personliga insikter och kunskaper i form av ökat självförtroende, reducerad osäkerhet och stärkt förändringskompetens. Deltagandet ger även inspiration, idéer och organisatoriska förändringsförslag. När dessa sedan ska föras över från nätverket till organisationen möter dock deltagarna ofta svårigheter och hinder.Organisationernas förmåga att absorbera nätverksresultaten brister. De har många gånger svårt att ta tillvara nya kunskaper och idéer, att integrera nätverkslärande med organisatoriskt lärande och därmed svårt att utnyttja den utvecklingspotential som nätverk rymmer. Viktiga hinder är strategi- och förankringsbrist på ledningsnivån.Nätverkets styrka som en stödjande social oas för deltagaren i utvecklingsprocessen rymmer också en svaghet. Utbytet riskerar att begränsas till personlig bekräftelse och bidra till få organisatoriska förändringar. För att undvika detta behöver deltagarens, organisationens och nätverkets utvecklingssyfte tydliggöras från början.Analysen leder fram till en idealmodell av en utvecklingsprocess med stöd av nätverk. I modellen stimulerar gemensamma reflektionen över praktiska erfarenheter ett kreativt lärande som ger nya kunskaper och idéer i utbyte. När dessa ska överföras och tillämpas i verksamheten behövs en utvecklingsorganisation med en ledning som kan ta ett strategiskt helhetsgrepp över förändringsprocessen.Slutsatserna talar för lärande nätverk som ett stöd i utvecklingsprocessen. De talar för fortsatt forskning för att pröva idealmodellen och för att fördjupa kunskaperna om absorberingssvårigheten och strategibristen.
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| 4. |
- Homayoun, Saeid
(författare)
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Internet corporate reporting disclosure and transparency
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The recent wave of well-publicized global corporate accounting scandals has highlighted the importance of the enhanced adoption of Internet technology and hence the increased transparency resulting from the enhanced disclosure of firm information. The objective of this study is to explore and identify Internet corporate reporting (ICR) disclosure in a context of publically listed firms. On a descriptive level, this thesis show that a considerable portion of publically listed firms have relativity high quality in their ICR disclosure, which is indicated by results showing that publically listed firms publish reasonably well-developed Internet-based reporting. In line with the Financial Accounting Standards Board, this thesis depicts characteristics of ICR disclosure practice by outlining the extent of content and presentation. As an indication of the quality of ICR, on average, the frequency of the identified items disclosed by the firms for the content of their websites was higher than for the presentation of information. One of the characteristics of presentation format is extensible business reporting language (XBRL). Consequently, the thesis also seeks to identify the important factors that drive publically listed firms to adopt of XBRL by conducting open-ended interviews. At the explanatory level, the results in this thesis indicate that among firm characteristics and the variables identified as important determinants for the disclosure of firm information in general, only profitability (proxy by return of equity) shows significant association with the extent of ICR disclosure. In addition, the thesis results show that among corporate governance mechanisms, only board size influences the ICR disclosure of firms. The thesis offers an integrated model for ICR disclosure and transparency anchored in multiple theoretical lenses and contributes to the field of corporate Internet reporting. The integrated model is based on four complementary theories: agency theory, stakeholder theory, signaling theory and legitimacy theory. Accordingly, the framework offers the potential for a rich understanding of the phenomena of internet corporate reporting disclosure practice and determinants.
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| 5. |
- Jahncke, Helena
(författare)
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Cognitive performance and restoration in open-plan office noise
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation presents four experimental studies (in four papers) with the overall aim to investigate the effects of office noise on cognitive performance and restoration. In the first two papers the focus was on the effects of different sound levels (i.e., the mean level from all sound sources at an office, such as speech, phones, people walking) on performance, fatigue and stress. In the last two papers the focus was on the effects of background speech, as this has previously been shown to be the most disturbing noise source in open-plan offices. Paper I demonstrated decreased word memory performance, increased fatigue and motivational deficits when the background sound level increased by 12 dB, from 39 to 51 dB LAeq. Paper II showed that the sound level effects were more pronounced for individuals with a hearing impairment. Unexpectedly, no effects were found of acute noise exposure on the participant´s stress hormone levels (Paper I and Paper II).Regarding effects of irrelevant speech, Paper III showed that cognitive performance decreased as a function of background speech intelligibility, the higher the intelligibility depicted by the Speech Transmission Index (STI), the worse the performance. The results indicated that the STI-value must be less than 0.50, to avoid a negative influence on performance. Further, both Paper III and IV showed that performance is more impaired by background speech if the focal task requires episodic memory and rehearsal—such as word memory and information search. Interestingly, some tasks were insensitive for speech.The restorative effects of a break were addressed in Paper I and II (i.e., directly after the work sessions in noise). The break period differed in content between the participants. Paper I showed that a break with a nature movie with corresponding sound increased energy ratings compared to just listening to river sounds or office noise. Continued exposure to office noise gave the lowest ratings of motivation after the break. Paper II showed improved arithmetic performance and motivation after the break with a nature movie and decreased performance and motivation after continued noise exposure. For the hearing impaired participants, however, continued noise during the break increased motivation and performance, while the movie did not.Taken together, the current thesis demonstrates that open-plan office noise can have a negative impact on fatigue, motivation and performance. How much performance is impaired varies with the cognitive processes required by the tasks performed and hearing status. Moreover, continued noise exposure during a short break can further decrease motivation and subsequent performance.
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| 6. |
- Sörqvist, Patrik
(författare)
-
The role of working memory capacity in auditory distraction
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The basis of individual differences in susceptibility to auditory distraction has been a research field largely ignored. The current work presents four studies demonstrating that individual differences in working memory capacity (WMC) are related to the magnitude of auditory distraction. The first three reports showed that high WMC attenuates the effects of speech and aircraft noise on reading comprehension and prose memory. The fourth report showed that high WMC attenuates the power of unexpected sound stimulation to capture our attention, but not the interference from changing-state sound streams to seriation processes.Furthermore, the first and the second report showed that the capacity to exclude new, potentially relevant but ultimately irrelevant, materials from memory underlies the relationship between WMC and the effects of speech on reading comprehension/prose memory. Based on these results, a new perspective of WMC called the "sub-process view" was developed, according to which WMC is a compound of functionally distinct subprocesses: some of which are related to auditory distraction. Ten years ago it was not at all clear if cognitive-control processes play a role in auditory distraction, but the studies reported in this thesis strongly suggest that cognitive-control - as reflected in WMC -constitutes a fundamental basis of individual differences in susceptibility to auditory distraction.
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| 7. |
- Tharani, Soraya
(författare)
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Immigration, security and the public debate on US language policy : A critical discourse analysis of language attitudes in the United States of America
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The narrative of the United States is of a "nation of immigrants" in which the language shift patterns of earlier ethnolinguistic groups have tended towards linguistic assimilation through English. In recent years, however, changes in the demographic landscape and language maintenance by non-English speaking immigrants, particularly Hispanics, have been perceived as threats and have led to calls for an official English language policy. This thesis aims to contribute to the study of language policy making from a societal security perspective as expressed in attitudes regarding language and identity originating in the daily interaction between language groups. The focus is on the role of language and American identity in relation to immigration. The study takes an interdisciplinary approach combining language policy studies, security theory, and critical discourse analysis. The material consists of articles collected from four newspapers, namely USA Today, The New York Times, Los Angeles Times, and San Francisco Chronicle between April 2006 and December 2007. Two discourse types are evident from the analysis namely Loyalty and Efficiency. The former is mainly marked by concerns of national identity and contains speech acts of security related to language shift, choice and English for unity. Immigrants are represented as dehumanised, and harmful. Immigration is given as sovereignty-related, racial, and as war. The discourse type of Efficiency is mainly instrumental and contains speech acts of security related to cost, provision of services, health and safety, and social mobility. Immigrants are further represented as a labour resource. These discourse types reflect how the construction of the linguistic 'we' is expected to be maintained. Loyalty is triggered by arguments that the collective identity is threatened and is itself used in reproducing the collective 'we' through hegemonic expressions of monolingualism in the public space and semi-public space. The denigration of immigrants is used as a tool for enhancing societal security through solidarity and as a possible justification for the denial of minority rights. Also, although language acquisition patterns still follow the historical trend of language shift, factors indicating cultural separateness such as the appearance of speech communities or the use of minority languages in the public space and semi-public space have led to manifestations of intolerance. Examples of discrimination and prejudice towards minority groups indicate that the perception of worth of a shared language differs from the actual worth of dominant language acquisition for integration purposes. The study further indicates that the efficient working of the free market by using minority languages to sell services or buy labour is perceived as conflicting with nation-building notions since it may create separately functioning sub-communities with a new cultural capital recognised as legitimate competence. The discourse types mainly represent securitising moves constructing existential threats. The perception of threat and ideas of national belonging are primarily based on a zero-sum notion favouring monolingualism. Further, the identity of the immigrant individual is seen as dynamic and adaptable to assimilationist measures whereas the identity of the state and its members are perceived as static. Also, the study shows that debates concerning language status are linked to extra-linguistic matters. To conclude, policy makers in the US need to consider the relationship between four factors, namely societal security based on collective identity, individual/human security, human rights, and a changing linguistic demography, for proposed language intervention measures to be successful.
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| 8. |
- Ager, Bengt
(författare)
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Skogsarbetets humanisering och rationalisering från 1900 och framåt
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rapporten belyser skogsarbetets förändring i storskogsbruket under perioden 1900 – 2013 under inflytande av rationalisering och humanisering som förändringsprocesser. Utgångsläget var ett ytterst slitsamt, riskabelt och lågbetalt säsongsarbete i kyla och snö, med bortaliggning i undermåliga kojor.I periodens början fullbordades en spontan rationalisering som inletts i slutet av 1800-talet och som bestod av att effektivare handredskap – olika typer av sågar, barkspadar och hanteringsdon - ersatte yxan som universalredskap. Organiserad rationalisering av skogsarbetet kom igång först i slutet på 30-talet. Den hämtade då sin inspiration från industrin som vid det laget hade anpassat amerikanen F W Taylors rationaliseringskoncept till den svenska arbetsmarknaden och kulturen. Arbetsstudier blev grund för effektivisering av det manuella skogsarbetet och för en rättvisare lön. Men skogsbruket kom sedan att finna egna vägar, som ledde till en världsunik teknisk och organisatorisk utveckling med början på 1950-talet och kulmen kring 1990. Under de senaste två årtiondena har rationaliseringen i skogsbruket anslutit sig till ”mainstream” i näringslivets utveckling, som styrs allt mera av dels den globaliserade marknadens mekanismer samt dels ”Lean”, ett hopkok av amerikanska och japanska organisationskoncept, och med ”outsourcing” som främsta verktyg. Under perioden 1940-2005 utvecklades produktiviteten kraftigt, med särskilt stora språng 1960-75 och 1990-2005. Efter 2005 skedde en stagnation.Humaniseringen av skogsarbetet inleddes med provinsialläkaren Hasslers larm 1907. Starten blev trög men skogsarbetarnas boende och mathållning kom att förbättras på många håll fram till 1930-talets slut. Då blev humanisering en integrerad del av den systematiska rationaliseringen, vilket innebar radikala förbättringar av det manuella skogsarbetet. När mekaniseringen tog fart under 50- och 60-talet kom människan i produktionssystemet bort ett tag, vilket ledde till omtag på humaniseringsprocessen. Ergonomin utvecklades som redskap och som vetenskap. Från slutet av 70-talet till slutet av 90-talet blev humaniseringen, stödd av flera aktörer, åter en integrerad del av rationaliseringen, nu underbyggd av det ”sociotekniska” organisationskoncept som utvecklats av engelska och norska arbetsforskare. Arbetets organisation kom i fokus. Den totala humankvaliteten kulminerade åren kring 1990. Skogsarbetet nådde då en höjdpunkt vad gäller mångsidighet, kontaktrikedom, variation, självbestämmande, ansvar och uppmärksamhet. Sedan inleddes en viss avhumanisering. Humaniseringsaktörerna försvagades eller försvann. Marknadens ”osynliga hand” tog alltmera över utvecklingen. Humankvaliteten försämrades på en rad punkter som i huvudsak kan hänföras till organisationsmiljön – färre personliga kontakter, längre arbetsresor, sämre skiftformer, kortare framförhållning och sämre kvalitet i planeringen samt sänkt relativ lönenivå. Försämringarna kompenseras delvis av att maskinernas förarmiljö och driftssäkerhet förbättrats avsevärt, men generellt har skogsarbetet förlorat i attraktivitet. Historiken summeras utförligt i kapitel 11.I kapitlet 12 om framtidens arbetsliv nationellt och i skogsbruket hävdar författaren att det behövs ett tidsanpassat humaniseringskoncept av samma dignitet som det på 60-talet lanserade sociotekniska konceptet. En skiss på ett sådant ”socioekonomiskt” koncept presenteras, inklusive en begreppsapparat som gör anspråk på att vara innovativ, samt en rad åtgärdsförslag. Därvid beaktas lärdomar från det förgångna.
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| 9. |
- Ahmadi, Alireza
(författare)
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Aircraft scheduled maintenance programme development : decision support methodologies and tools
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The air transport business is large in its operations, integrated, automated and complex. Air carriers are constantly striving to achieve high standards of safety and simultaneously to attain an increased level of availability performance at minimal cost. This needs to be supported through an effective maintenance programme which has a major impact on the availability performance and which ultimately can enhance the aircraft’s capability to meet market demands at the lowest possible cost. The development of a maintenance programme is challenging, but can be enhanced by supporting methodologies and tools. The purpose of this study is to develop decision support methodologies and tools for aircraft scheduled maintenance programme development within the framework of Maintenance Review Board (MRB) process. To achieve the purpose of the research, literature studies, case studies, and simulations have been conducted. Empirical data have been collected through document studies, interviews, questionnaires, and observations from the aviation industry. For data analysis, theories and methodologies within risk, dependability and decision making have been combined with the best practices from the aviation industry. One result of the research is the identification of potential areas for improving the use of MSG-3 methodology in aircraft scheduled maintenance development. Another result is the development of a systematic methodology guided by the application of an Event Tree Analysis (ETA) for the identification and quantification of different operational risks caused by aircraft system failures, to support decision making for maintenance task development. A third result is a proposed methodology, based on a combination of different Multi-Criteria Decision Making (MCDM) methodologies, for selecting the most effective maintenance strategy for aircraft scheduled maintenance development. Finally, the fourth result is a proposed Cost Rate Function (CRF) model supported by a graphical approach. The approach can be used to identify the optimum maintenance interval and frequencies of Failure Finding Inspection (FFI) and to develop a combination of FFI and restoration tasks for the aircraft’s repairable items which are experiencing aging. These results are related to some of the specific industrial challenges, and are expected to enhance the capability of making effective and efficient decisions during the development of maintenance tasks. The results have been verified through interaction with experienced practitioners within major aviation manufacturers and air operators.
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| 10. |
- Al-Taie, Laith
(författare)
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Performance of Clay Liners in Near-Surface Repositories in Desert Climate
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wars in Iraq (1991 and 2003) generated various types of hazardous waste (HW) in the form of soil contaminated by depleted uranium (DU). Other HW emanated from destroyed army vehicles and remnants of Iraqi nuclear facilities holding various types and amounts of chemical and radioactive material. The negative impact of the various wastes on the health conditions of the population was reported from different parts of Iraq, showing an enhanced frequency of cancer and abnormally born infants. For isolating the wastes, which represent low-level and short-lived intermediate level radioactive wastes, near-surface repositories (NSR) are proposed since they represent the least expensive way of solving future problems with sufficient safety. Internationally, the timeframe of the containment of such wastes is designated to be 300 years. Site selection affects and largely controls the selection of a suitable design the aim being to minimize or eliminate migration of hazardous elements from the waste to the environment. The formulation of siting criteria is the first vital step toward the resolution of the problem. Site selection criteria are proposed taking in account three major factors: environmental, geological and socio-economic factors. Accordingly, Iraqi deserts, which make up 60% of Iraq, represent the number one candidate for locating a safe disposal facility, primarily because of the low population, suitable topography, climatic conditions, seismic stability and availability of raw materials. Long-term performance of NSR is directly related to the function of top and bottom liner systems. They should be designed so that they are mutually compatible and combine to effectively isolate the waste. Liners are considered as the main elements of any disposal facility on the ground surface and a properly designed top liner system is of particular importance since it will minimize or eliminate water percolation into the waste body. Compacted clay liners (CCL) should preferably have with a low hydraulic conductivity, which is achievable by proper selection of raw materials, compaction density and construction methods. A further criterion is that they must not soften significantly by expansion on wetting, which puts a limit to the smectite content and density. The liners can consist of native material found near the landfill site, and be used after simple processing, primarily drying and crushing, or be mixed with fillers like silty sand. Since the hydraulic conductivity is the key property of a reliable CCL, relevant experimental determination of the hydraulic conductivity is vital. The common practice in geotechnical laboratories is to apply high hydraulic gradients for getting results quickly but this can lead to non-conservative, incorrect results. The present study involved determination of the hydraulic conductivity of a smectite-rich clay sampled at places within reasonable distance from potential NSR sites. Various hydraulic gradients were applied to samples compacted to several different densities, using two permeants and two filter types. It was concluded that the outflow filter can significantly affect the evaluated conductivity especially when applying high hydraulic gradients. This was partly explained by clogging of outflow filters of conventional fine-porous type by torn-off clay particles at such gradients. A major conclusion was that the gradient in laboratory testing should not exceed 100 m/m.In order to assess the suitability of available raw materials within the Iraqi Deserts, two smectitic soils termed as Green and Red clays were investigated for potential use in CCLs. Both clays are fairly rich in smectite, which calls for mixing them with properly graded silt/sand material from the desert for modifying the expandability. The shear strength, swelling pressure, hydraulic conductivity and creep properties were determined and used for defining criteria for selecting suitable clay-sand ratios. The results showed that 30-50% Green clay mixed with sand and 40-60% Red clay mixed with sand were suitable for constructing top liners with a hydraulic conductivity of 1×10-9 - 1×10-10 m/s. For bottom liners, 70% Green clay mixed with sand and 80% Red clay mixed with sand would be suitable; they were found to have a hydraulic conductivity of 1×10-11 m/s.The long-term performance of CCL is controlled by a number of processes like long periods of extreme dryness and short periods of very heavy rain. The percolation of water through the top liner system of a number of design alternatives were simulated using the code HELP 3.95D and subsequently by the FE program VADOSE/W. For the assumed NSR concept the slope stability of the top liner is essential and it was determined by using FE technique considering various slope angles. The engineering properties, primarily the hydraulic conductivity, swelling pressure and shear strength of 30-50% Green clay mixed with sand were introduced in the simulations. Two initial water contents of the compacted materials were considered representing 1) optimum water content (“wet case”), and 2) air‐dry conditions (“dry case”). Application of the HELP code decided the selection of suitable CCL having a thickness of 0.5 m and inclined by 5.7ᵒ. More detailed analyses with VADOSE/W showed that a mixture at the dry case would bring 0.5 mm (0.5 litre of leaking water per square meter) through CCL in an eight year simulation period. Long-term simulations (up to 300 years) showed that CCL would undergo continuous drying without reaching saturation even in the case of periods of very heavy rain (616 mm) for the wet and dry cases. The slope stability factor for the rather steep angle 30ᵒ was found to be 1.5 for the most critical case representing complete water saturation. In conclusion, the proposed materials and design features are believed to be suitable for practical application.
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