Geomembrane strains from coarse gravel and wrinkles in a GM/GCL composite liner

The physical response of a 1.5-mm-thick, high-density polyethylene geomembrane (GM) is reported when placed on top of a needle-punched geosynthetic clay liner (GCL), buried beneath 50-mm coarse gravel and subjected to vertical pressure in laboratory experiments. Local strains in the geomembrane caused by indentations from the overlying gravel and deflections of a wrinkle in the geomembrane are quantified. A peak strain of 20% was calculated when a flat geomembrane was tested without a protection layer at an applied vertical pressure of 250 kPa. Strains were smaller with a nonwoven needle-punched geotextile protection layer between the gravel and geomembrane. Increasing the mass per unit area of the geotextile up to 2200 g/m² reduced the geomembrane strain. However, none of the geotextiles tested were sufficient to reduce the geomembrane strain below an allowable limit of 3%, for the particular 50-mm gravel tested and when subjected to a vertical pressure of 250 kPa. Increasing the initial GCL water content and reducing the stiffness of the foundation layer beneath the GCL were found to increase the geomembrane strains. These local strains were greater when a wrinkle was present in the geomembrane. The wrinkle in the geomembrane experienced a decrease in height and width. The wrinkle deformations lead to larger pressures beside the wrinkle and hence producing larger local strains. A 150-mm-thick sand protection layer was effective in limiting the peak strain to less than 0.3% even with a wrinkle in the geomembrane, at a vertical pressure of 250 kPa.     

Deformation behavior of clay cap barriers of hazardous waste containment systems: Full-scale and centrifuge tests

The objective of this paper is to study the deformation behavior of a clay cap barrier of waste containment system for storing hazardous waste. The risk of bending of a clay barrier in case of differential settlements within underlying waste is focused in the present study. Field bending “bursting tests” were performed in France on clay barriers of 0.7 m thickness at different water contents. An attempt has been made to determine limiting distortion level at which cracks are initiated. The cap clay barrier configuration tested through field bursting tests was simulated at 12.5 g in a geo-centrifuge on model cap clay barriers of 56 mm thickness subjected to bursting mode of failure. Digital image analysis technique was used to ascertain initiation and propagation of cracking at the onset of differential settlements. Further influence of discrete and randomly distributed polypropylene tape fibers in restraining cracking tendency of the clay barrier was evaluated through a centrifuge model test. With an increase in the molding water content and the presence of randomly distributed fibers, an increase in limiting distortion level was observed. Use of 0.5% of fiber dosage and 90 mm long discrete fibers was found to restrain propagation of cracking of a clay barrier subjected to differential movements. Analysis and interpretation of field bursting tests was found to be in good agreement with physically observed centrifuge model test results.     

Geomembrane strains from wrinkle deformations

Methods to compute geomembrane strains caused by the deformation of a geomembrane wrinkle when subject to vertical overburden stress are examined. Thin shell theory, small strain-displacement, and large strain-displacement methods are developed to compute geomembrane strains from wrinkle deformations. The implementation of each method is validated for three hypothetical trial cases against results obtained with finite element analysis. It was found that it is necessary to employ large strain-displacement theory and explicitly consider both vertical and horizontal components of wrinkle displacement to compute strain. Results are then presented from six physical experiments where the vertical and horizontal components of wrinkle displacement were measured under simulated landfill base liner conditions. For the particular conditions tested, it was found that without a thick sand protection layer on top of the geomembrane, the largest calculated tensile strain due to wrinkle deformations of 8% was much less than the tensile strain caused by overlying gravel particles, and thus local strains from gravel contacts would govern in the assessment of maximum geomembrane strain; whereas, with a thick sand protection, the maximum tensile strain was from wrinkle deformations, but the measured values were below a proposed long-term allowable strain of 3%.     

The role of undrained clay soil subgrade properties in controlling deformations in geomembranes

Strains were evaluated in a 1.5 mm HDPE geomembrane from overlying coarse uniform drainage gravel when placed above six different compacted clayey soils while keeping pressure, protection, loading rate equal. In each case, a protection layer consisting of 400 g/m² nonwoven geotextile was placed over the geomembrane. Vertical load of 300 kPa was applied in a relatively short duration. A photogrammetry procedure was used to develop a digital elevation model for each deformed geomembrane surface and the distribution of resulting strain in the geomembrane was evaluated on a percent area basis. The proportion of the overall geomembrane area in which the localised strain exceeded 3% was related to the compacted water content, index soil properties, and undrained shear strength of the six different clayey soils. It was found that an increase in moulding moisture content resulted in increased geomembrane strain in all cases, but the magnitude of the increase in strain varied considerably, depending on the plasticity and silt content of the soil used.     

Carbon air pollution reflected in deposits on chosen building materials of Prague Castle

Thin black surface layers or black coloured gypsum crusts can be observed on stones of many buildings and sculptures around the world. The black weathered stone and mortar surface from selected sections of the Prague Castle were studied by microscopic methods, GC/MS and pyrolysis-GC/MS analysis. Microscopically, we found an authigenic gypsum formation with an outer layer of an admixture of fine grains of quartz, clay minerals, thermally altered clay minerals, fly ash, and carbonaceous particles of natural and anthropogenic origin particularly chars, cokes, soots. Noncarbonate C content ranged between 0.8% and 4.3%. Phtalates dominated in extracts from the samples and benzonitrile had the greatest abundance in the pyrolysis products. The identified organic particles and compounds are known to result from human activities.     

Calculating local geomembrane strains from gravel particle indentations with thin plate theory

A new general method is presented to calculate local strains in geomembranes from the deformed shape imposed by overlying coarse gravel particles under vertical pressure. Past methods assume that the geomembrane attains its deformed shape by only deforming vertically and hence neglect the effect of lateral displacements on strain. The new method treats the geomembrane as a thin plate with mid surface components of displacements in three directions (x, y and z). Lateral components of displacements (those in the x and y directions) are related to vertical displacements (z direction) by large-strain-displacement relationships and compatibility of strains. Normal and shear strains in the lateral directions are calculated using Airy's stress function and a linear elastic constitutive law. Bending and torsional strains calculated from curvature and are added to the mid surface strains to find strains on the top and bottom surfaces. The method was validated against data sets with known three-dimensional displacements and strain generated by finite element analysis. The application of the new method to calculate local strains in a geomembrane from the deformed shape obtained from a protection-layer-assessment physical test is illustrated.     

击实砾质土抗拉强度试验研究

抗拉强度是黏性土的一个比较重要的力学性质,由于在工程中使用相对较少,对其研究并不多。实际上,诸如土体裂缝、坍塌、土石坝心墙水力劈裂等不少工程问题都与抗拉强度有着密切的关系。对3种砾质土进行击实试样的抗拉强度试验,研究抗拉强度随试样干密度、前期固结压力和含水率等的变化规律。试验结果表明,击实砾质土抗拉强度随着干密度的增加而增加,增加幅度显著;随着前期固结压力的增加,土的抗拉强度也增大,但在试验范围内(固结压力100～500kPa)增大并不明显。随着含水率的增加,抗拉强度稍有减小。在所试验的含水率、密度和前期固结压力范围内,试验得到的砾质土抗拉强度为20～80kPa。     

Fate of arsenic-bearing phases during the suspended transport in a gold mining district (Isle river Basin, France)

Arsenic-rich (~ 140-1520 mg.kg^− 1) suspended particulate matter (SPM) was collected daily with an automatic sampler in the Upper Isle River (France) draining a former gold mining district in order to better understand the fate of arsenic during the suspended transport (particles smaller than 50 μm). Various techniques at a micrometric scale (EPMA, quantitative SEM-EDS with an automated particle counting including classification system and μXRD) were used to directly characterize As-bearing phases. The most frequent ones were aggregates of fine clay particles. Their mineralogy varied with particle sources involved. These aggregates were formed by chlorite-phlogopite-kaolinite assemblages during the high flow and chlorite-illite-montmorillonite during the low flow. Among all the observed As-carriers in SPM, these clay assemblages were the least As-rich (0.10 up to 1.58 wt.% As) and their median As concentrations suggested that they were less concentrated during the high flow than during the low flow. Iron oxyhydroxides were evidenced by μXRD in these clay aggregates, either as micro- to nano-sized particles and/or as coating.(Mn, Fe)oxyhydroxides were also present as discrete particles. Manganese oxides (0.14-1.26 wt.% As) transport significantly more arsenic during the low flow than during the high flow (0.16-0.79 wt.% As). The occurrence of Fe oxyhydroxide particles appeared more complex. During the low flow, observations on banks and in wetlands of freshly precipitated Fe hydroxides (ferrihydrite-type) presented the highest As concentrations (up to 6.5 wt.% As) but they were barely detected in SPM at a microscale. During the high flow, As-rich Fe-oxyhydroxides (0.10-2.80 wt.% As) were more frequent, reflecting mechanical erosion and transport when the surface water level increased.Arsenic transfers from SPM to corresponding aqueous fraction mostly depend on As-carrier stability. This study shows the temporal occurrence of each type of As-bearing phases in SPM, their As concentrations at a particle scale and abundance according to hydrological periods.     

Influence of Geogrid Layer on the Integrity of Compacted Clay Liners of Landfills

The objective of this paper is to examine the influence of geogrid layer on the integrity of clay liners of landfills. A series of centrifuge model tests were performed on model clay liners subjected to non-uniform settlements with and without a geogrid layer embedded within the top one-third portion of the clay liner moist-compacted on the wet side of its optimum moisture content at 40 g. The model clay liner material has been selected in such a way that it envelopes the material characteristics of the clay liners, which are used for constructing an impermeable barrier in a lining system. By maintaining type and location of the geogrid within the clay liner as constant, the thickness of clay liner is varied to check the possibility of reducing the thickness of a geogrid reinforced clay liner. Digital image analysis technique was employed to ascertain the initiation of cracking and to compute strains both on the surface and along the cross-section of the clay liner with and without any geogrid layer. It was observed that clay liners compacted at moulding water content towards wet side of their OMC found to experience multiple cracking at the onset of non-uniform settlements. Contrary to this, geogrid reinforced clay liner was observed to sustain large distortions and experience only tiny cracks limited up to a location of a geogrid. With an increase in thickness of the clay liner reinforced with a geogrid, geogrid reinforced compacted clay liner was observed to retain its integrity and restrains cracking completely.     

Irrigated composite liner designs for fast hydration and prevention of thermal desiccation of geosynthetics clay liners

In composite liners made of geomembrane (GMB)-geosynthetics clay liners (GCLs), maintaining bentonite in the GCL in a suitably hydrated state is critical for their performance. Hydration of GCL from subsoil, following industry best practice, is time consuming and conditional on suitable water chemistry in subsoil. In addition, under thermal gradients, dehydration occurs, with moisture migrating downwards to the subsoil, leading to the development of cracks in the bentonite and hence loss of performance.Two novel ideas are proposed in this paper, namely hydration of GCLs by artificial irrigation and hydraulic separation of the liner system from the underlying subsoil. Three new composite liner designs allowing for actively irrigating a geosynthetic clay liner (GCL) through a geocomposite layer were investigated. In two of the three designs, the hydraulic connection between the GCL and the subsoil was broken by placing an additional GMB between them. The new designs were tested in column experiments under 20 kPa overburden pressure and temperatures of up to 78 °C applied to the top of the liner. The performances of the new designs were compared to that of a standard GCL-GMB design where GCL was allowed to hydrate from a well-graded sandy subsoil. Three scenarios for the staging of hydration and thermal load application were investigated.Under active hydration of the composite liners, it took less than 14 days for the GCLs to reach a gravimetric water content ω of 110–130%, compared to 49 days taken to reach ω~95% under hydration from the subsoil. GCLs in the new designs in which the hydraulic connection with the subsoil was broken, remained well-hydrated (ω>100%) after 14 days of heating and no cracks appeared in the bentonite. On the other hand, the GCL in the conventional design experienced severe desiccation under the same conditions. The new designs hence offer a viable solution to the problem of slow hydration and/or thermal desiccation of GCLs.     

Geomembrane tensions and strains resulting from differential settlement around rigid circular structures

A simplified model is presented that analyzes tensions and strains in a geomembrane. The membrane analysis is applied to circular structures subjected to differential settlement. It was found that wrinkles are induced in the geomembrane around the circular structure and the associated mechanism was investigated. An improved predictive model was developed based on the wrinkled membrane theory. The model introduced the concept of a “variable Poisson's ratio”, and allowed tensions and strains associated with wrinkles in the geomembrane to be considered. Parametric studies and a comparison between the simplified model and the improved model were performed. Limitations associated with the two models are discussed and some practical recommendations are made with regard to the control of geomembrane tensions and strains around circular structures.     

Real-time PCR detection of adenoviruses, polyomaviruses, and torque teno viruses in river water in Japan

The prevalence of DNA viruses in water from the Tamagawa River, Japan was quantitatively surveyed for 6 months, from April to September 2003. A total of 18 river water samples were subjected to virus concentration method using an electronegative membrane, followed by DNA extraction and direct quantitative real-time polymerase chain reaction (qPCR) for DNA viruses. Adenoviruses of serotypes 40 and 41 were detected most frequently in the river water samples tested (61.1%), at a concentration ranging from 3.16 × 10³ to 1.38 × 10⁵ copies/l, followed by JC polyomaviruses (11.1%) and torque teno viruses (5.6%). No sample was positive for BK polyomaviruses. In addition, for selective detection of virus particles, adenoviruses 40 and 41 were tested with qPCR combined with an immunomagnetic separation technique; they were detected in only 16.7% of the samples, showing a concentration ranging from 7.42 × 10² to 4.24 × 10⁴ copies/l. This study is significant since it is the first study to demonstrate the prevalence of polyomaviruses in water samples in Japan and to use immunomagnetic separation qPCR to detect adenovirus particles in aquatic environments.     

Durability of fluorinated high density polyethylene geomembrane in the Arctic

A series of fluorinated high density polyethylene (f-HDPE) geomembrane (GM) samples of different thickness (1, 1.5 and 2.5 mm) was exhumed from the backfill immediately upstream of a barrier system constructed to contain a hydrocarbon spill in the Canadian Arctic. The samples were tested for oxidation induction time (OIT), crystallinity, melt index (MI) and tensile properties. The results of these tests are reported and it is shown that the durability of the GM was maintained well beyond the initial 3-year design life of the barrier system. Based on 7 years of field data, the std-OIT depletion time for the 1.5 mm thick GM used in the barrier system was inferred to be over 140 years while the antioxidant depletion time based on the HP-OIT is estimated to be about 200 years. No significant temporal changes in the crystallinity, MI or tensile properties of the exhumed GM samples were detected.     

Experimental study on freezing and thawing deformation of geogrid-reinforced silty clay structure

Reinforcement can reduce soil’s frost heave (F-H), but what kind of reinforcement condition is most beneficial to control soil’s F-H if it is not clear? In this study, orthogonal experiments of freezing and thawing (F-T) to reinforced silty clay under different conditions were carried out. F-H, thaw settlement (T-S) deformation and water content of three different heights of melting clay were tested. T-S displacement was positively correlated with water content and more closely related to upper layer clay’s water content. SPSS software was used to fit the regression equation of F-H and T-S displacement expressed by various influencing factors. The top three factors influencing the F-H and T-S displacement were initial water content, reinforcement spacing, and upper pressure. Taking the lowest displacement of F-H and T-S as control target, the optimal solution of all factors and target values were obtained with MATLAB software when the freezing temperature and number of freezing and thawing cycle (FTC) and upper pressure were − 15 °C, 5 times, and 30 kPa. The lowest values of F-H and T-S displacement were 3.61 mm and − 0.514 mm, respectively, when the values of the initial water content, compaction degree, and reinforcement spacing were 16%, 90%, and 25 cm, respectively.

     

Viscoplastic modelling of HDPE geomembrane local stresses and strains

The formulation, validation and application of a viscoplastic constitutive model for numerical analysis of HDPE geomembrane stresses and strains induced by overlying coarse gravel is presented. Model parameters were obtained from uniaxial tensile experiments conducted over a range of displacement rates. The model was implemented in geometrically-nonlinear finite-element-analysis and was able to match the force, displacement and strain measured from wide-width strip tensile experiments. The analysis also matched the geomembrane response measured from axisymmetric force-displacement experiments, where a 60-mm-diam. specimen, clamped around its perimeter, was subjected to loading normal to its plane from a steel probe machined to mimic the shape of a coarse gravel particle. The analysis matched: i) probe forces when loaded at a constant rate of displacement, ii) displacements when loaded with step function increments of probe force, iii) creep displacements under a constant probe force for 1000 h, and iv) decreases in probe force from stress relaxation when held at a constant displacement for 1000 h. The analysis was used to further validate the applicability of thin plate theory to calculate geomembrane strains from measured deformations and provide first estimates of stress that develop beneath a gravel particle.     

Feedback and guidelines for geomembrane lining systems of mountain reservoirs in France

Mountain reservoirs are hydraulic structures in mountains, used in ski resorts to store water, generally for producing artificial snow; there are about 120 of them in France. Despite their modest volumes (5000-400,000 m³) and dam heights of between 5 and 20 m, these structures do induce potentially high risks, due to their location in mountain at altitudes of between 1200 and 3000 m. These reservoirs are very often made watertight artificially by geomembrane. A survey conducted on about 70 of these reservoirs provided considerable information on their pathologies, incidents and even accidents and served as a basis for writing a set of guidelines for studying, designing, constructing, monitoring and rehabilitating. The paper is divided into two parts; the first based on an analysis of the 32 best documented structures is a feedback of water-tightness quality of Geosynthetic Liner Systems (GLS) at high altitudes; the second based on the guidelines above-mentioned, concerns the construction choices and behaviour of GLS at high altitudes. In particular, the guide advises using a cover layer in most cases to protect the geomembrane, and paying particular attention to the support layers and to drainage under the geomembrane.     

Deposition of aerosol particles on rough surfaces inside a test chamber

We investigated the deposition rate of aerosol particles (diameter between 0.03 and 5 μm) on rough surfaces of wallpapers, wall-plasters, and two types of carpets inside a test chamber. Compared to a smooth aluminum surface, the deposition rate of aerosol particles on the tested surfaces was up to 20 times depending on the surface roughness, mixing intensity, and particle size. A rough surface with a dimensionless surface roughness height k⁺ < 0.06 can be treated as a hydraulically smooth. The estimated deposition rates in this study and those predicted by a deposition model, which incorporates surface roughness, were in good agreement for coarse mode particles (diameter > 1 μm) when k⁺ < 1.04 and for ultrafine particles (diameter < 0.1 μm) when k⁺ < 0.48. The agreement between the model prediction and our estimation was better for coarse mode particles than for ultrafine particles. Deposition of aerosol particles, especially fine particles, needs more empirical investigations aiming at improving the existing models.     

Weathering of building stones and its relationship to the sustainable management of the aggregate resources in Gaza Strip,Palestine

In the last decade, the Gaza Strip witnessed a revolutionary breakthrough in the field of building construction associated with the political development in the aftermath of Oslo Agreement. Towers (buildings composed of more than five floors) were, for the first time being built in the region in its modern history. Environmental conditions have deteriorating weathering impacts on the buildings of about 40 years old. This article aims at investigating such impacts and their features as well as the different types of weathering on the buildings. Chemical, mechanical and biological parameters of weathering were reported to work together in the old buildings. Differential weathering was also reported in some buildings either within the stone itself or the cementing material between the stone blocks. The geographic location along the coast is believed to speed up the weathering process as aerosols and rainwater contain high chloride content, which in turn reacts with the stone components. Baladi stones show higher resistance to weathering than the Israeli stone-type. Weathering rate was calculated and found to have an average of about 0.1 cm per annum. Some measures are taken to protect the buildings from the weathering attack; these include 2–3 layers (about 1 cm thick each) of plastering for about 1 m of the lower part of the external walls of the buildings. These measures are not commonly applied, and if so, they show several types of weathering. Taking protective measures is a necessary step for better sustainable management of the aggregate resources in the Gaza Strip.     

奥陶系灰岩顶部超前区域注浆浆液选配分析

煤矿底板注浆加固或改造广泛采用水泥基浆液,而由于注浆材料和浆液性能的差异,在注浆实践中缺少对注浆材料的合理选配及浆液类型和配比的有效调控,致使超前注浆效果难以达到预期目标。针对上述问题,以邯邢矿区奥灰顶部注浆改造为背景,通过分析奥灰顶部宏、细观发育特征,结合当地注浆所用水泥、黏土和粉煤灰等注浆材料的粒径分布特征,对注浆材料进行了合理选配;考虑水灰比、水玻璃掺量、奥灰水化学类型、固相比等因素,对水泥基浆液的物理力学性质进行了正交试验,得到了水泥基浆液物理力学性质及其主控因素。研究结果：奥陶系灰岩顶部峰峰组七段岩层富水性和渗透性大于其上部峰峰组八段,细观空隙中数量占比以闭合裂隙和微张裂隙为主,均值分别为120μm和420μm,宽张裂隙和中张裂隙在裂隙面积中占主要比例,具有较好延展性;奥灰顶部注浆改造过程中可采用水泥-粉煤灰或水泥黏土浆液进行“垫底式”充填注浆,而后采用水泥浆液对微小裂缝和闭合裂隙进行升压注浆或劈裂注浆;水泥浆液、水泥-粉煤灰浆液、水泥-黏土浆液的凝结时间主控因素均为水玻璃掺量,水泥浆液黏度的主控因素为水玻璃掺量,水泥-粉煤灰浆液和水泥-黏土浆液黏度主控因素均为水灰比,水泥浆...     

采用碎石桩加固龙口电厂地基

龙口电厂建于山东省可液化的软土层地基上。该软土容许承载力[R]=117kPa。设计要求其容许承载力[R]>245kPa。采用碎石桩加固该软土取得了明显的效果。本文记述了现场试验和建筑物的沉降观测。现场试验包括:①测定振冲器水平振动力作用下产生的地面加速度以及制桩时引起的地面加速度与距振点距离之间的关系;②采用底面积为3.2m×3.2m的大型载荷试验和底面积为0.25m~2、0.5m~2的小压板载荷试验;③测定地基土在制桩前后的标准贯入击数和比贯入阻力的变化,用跨孔法测动力参数的变化;④设置碎石桩前后超孔隙水压力的变化;⑤地面标高的变化。目前建筑物的最大沉降量为40mm。