Measurement of filtration effects on the transmissivity of geocomposite drains for phosphogypsum

Geocomposite curtain drains are commonly used in phosphogypsum waste stacks to mitigate stability concerns. Specifically, they are used to lower the piezometric surface in the phosphogypsum by diverting water flow near the toe of the stack slopes. Phosphogypsum has high fines content, low plasticity, and slight solubility, all of which are indicators that its filtration behavior should be evaluated in addition to using filtration criteria developed for soils. The objective of this study is to investigate the impact of filtration on the in-plane flow capacity of geocomposites used as a curtain drain in problematic soils like phosphogypsum. Specifically, a flexible-wall permeameter was adapted with a bottom platen that permits both a gradient ratio filtration test and an in-plane transmissivity test to be performed on a soil–geocomposite system. Measured gradient ratio values for compacted phosphogypsum underlain by a geocomposite with 200 g/m² nonwoven geotextiles ranged from 0.94 to 0.63 for cross-plane target gradients ranging from 0.7 to 24.9. Although these gradient ratio values indicate a possibility for some particle loss across the filter via piping, especially under high target gradients, steady seepage conditions were obtained. However, the transmissivity measured after each filtration test was not observed to change significantly, indicating that the geocomposite was suitable for use as a curtain drain in phosphogypsum. The dual-purpose experimental approach developed in this study was found to provide complementary information to existing filtration criteria when using geocomposites in potentially problematic soils.     

Load Transfer Characteristics of Socketed Piles in Mumbai Region

This report uses load-transfer approach for analyzing the load-displacement response of piles socketed in weathered rocks typically found in Mumbai region. The field information used in the load-transfer analysis is obtained from conventional site investigations and does not necessitate elaborate tests. The load transfer behaviour of each stratum is expressed as a non-linear function. Empirical relations are used to express rock mass modulus and limiting values of unit side and base resistance in terms of unconfined compressive strength of intact socket material, which implicitly take into account the site-specific conditions. More than twenty pile load test data were back-analyzed before generalizing the governing parameters applicable to this region. This report demonstrates a wide range of applications of load transfer approach which includes the load-displacement behaviour and separation of elastic and net pile displacements.     

Comparison of hydrogeologic parameters evaluated by deep well testing programs to assess nuclear waste repository feasibility

Hydrogeologic parameters evaluated for rocks investigated in deep well testing projects for nuclear waste repository feasibility are transmissivity, hydraulic conductivity and storativity. Such studies have been carried out in rock formations of different geologic types, origins and ages for nuclear waste management agencies in North America and Europe. From transient pressure testing, an assessment of static pressure in selected fracture zones was measured from which a profile with depth was developed using modelling techniques. As well, temperatures of formation fluids and hence thermal gradients have also been provided. Hydrogeologic parameters are commonly used in risk analysis for repositories with respect to the possible escape of contaminants and worst case scenarios. The parameters are related to the rate of possible radionuclide migration into the biosphere. The techniques of the investigation and analysis methods of this work have been fully described in the literature. This paper is the first to date, however, to compare results from testing in differen geologic environments. High transmissivity zones have been observed in the upper few hundred metres of granite formations. Below that depth, the rock is more competent and discrete zones of higher permeability occur less frequently. Our studies show, however, that in these rocks, zones of high hydraulic conductivity do not always correspond to zones of high fracture frequency. Most formation pressure profiles have a vertical gradient of about 10 kPa/m. In discrete zones, deviations from this trend can occur due to vertical inhomogeneity in the rock. Thermal gradients vary considerably from one investigation site to another. For example, in the Canadian Shield, gradients are of the order of 1.0 degree C per 100 m, whereas in similar rock types in Europe, the gradient is up to 4.0 degrees C per 100 m.     

The effect of thickness reduction on the hydraulic transmissivity of geonet drains using rigid and non-rigid flow boundaries

In this paper, relationships between in-plane flow capacity reduction and thickness reduction are presented in tri-planar and bi-planar geonets for rigid and non-rigid flow boundaries. Using these equations, the long-term flow capacity of geonets can be determined using creep test results. To validate these relationships, geonet thickness was measured under different conditions and the theoretical values of the transmissivity reduction ratios were calculated by substituting the results in the equations. Transmissivity tests were then performed under the same conditions to obtain experimental values of the reduction ratios. A comparison showed that the theoretical and experimental values of the transmissivity reduction ratios were in agreement, and the relationships provide a useful tool to predict the drainage capacity of both tri-planar and bi-planar geonets influenced by loading pressure. However, special precautions must be taken when applying the equations to investigate the hydraulic capacity of other types of geosynthetic drains as well as when the geonet is covered by geotextile material acting as a filter between the geonet and adjacent soil, is overlain by geosynthetic clay liner material where the swelling potential of the bentonite in the geonet exists, is placed in inclined positions or is subjected to complex combinations of load.     

An analytical solution for transient flow of Bingham viscoplastic materials in rock fractures

We present below an analytical solution to model the one-dimensional transient flow of a Bingham viscoplastic material in a fracture with parallel walls (smooth or rough) that is subjected to an applied pressure gradient. The solution models the acceleration and the deceleration of the material as the pressure gradient changes with time. Two cases are considered: a pressure gradient applied over a finite time interval and an applied pressure gradient that is constant over time. The solution is expressed in dimensionless form and can therefore be used for a wide range of Bingham viscoplastic materials. The solution is also capable of capturing the transition that takes place in a fracture between viscoplastic flow and rigid plug flow. Also, it shows the development of a rigid central layer in fractures, the extent of which depends on the fluid properties (viscosity and yield stress), the magnitude of the pressure gradient, and the fracture aperture and surface roughness. Finally, it is shown that when a pressure gradient is applied and kept constant, the solution for the fracture flow rate converges over time to a steady-state solution that can be defined as a modified cubic law. In this case, the fracture transmissivity is found to be a non-linear function of the head gradient. This solution provides a tool for a better understanding of the flow of Bingham materials in rock fractures, interfaces, and cracks.     

Interface transmissivity of conventional and multicomponent GCLs for three permeants

A laboratory investigation of the interface transmissivity is reported for five different geosynthetic clay liners (GCLs) and a range of different geomembranes (GMBs) for a range of stresses from 10 to 150?kPa. The GCLs were prehydrated under normal stress before permeation. The GCLs examined comprised three multicomponent (a smooth coated, a smooth laminated, and textured coated) and two conventional (one with granular and one with powdered sodium bentonite) GCLs. The effect of a 4?mm circular defect in the coating of a multicomponent GCL directly below the 10?mm diameter hole in the GMB is investigated. The effect of GMB stiffness and texture is examined. Additionally, the effect of hydration and permeation of smooth coated GCL with highly saline solution and synthetic landfill leachate (SL3) is presented. It is shown that the 2-week interface transmissivity (θ_2-week) can be one to two orders of magnitude higher than steady-state interface transmissivity (θ _steady-state) at low stresses (10?kPa–50?kPa), whereas at high stresses (150?kPa) the variation is substantially less. For a smooth coated GCL hydrated and permeated with reverse osmosis (RO) water, GMB stiffness and texture has a limited effect on interface transmissivity when the coating is placed in contact with GMB at normal stresses of 10?kPa–150?kPa, whereas coating indentations result in much high interface transmissivity when placed in contact with GMB. GCL prehydration and permeation with highly saline solutions leads to higher interface transmissivity compared to RO water. With a 4.0?mm defect in the coating, the interface transmissivity between the coating and woven geotextile is higher than that between the coating and GMB for the stress levels and GCL examined.     

Durabilite des granulats: l'essai au sulfate

This study is designed primarily to shed some light on the influence of the various phenomena associated with aggregate durability as measured by the Sulfate Soundness Test (ASTM C-88). An examination of the origin and evolution of this test suggests, at first, that it would be very difficult, if not impossible, for laboratories using standard control tests, to tighten the requirements associated with these procedures in such a way as to improve its accuracy to any significant extent; indeed, it appears that the factors involved are too numerous and varied to offer any hope of success for efforts in this direction. Moreover, it has been established that the destructive effects of this test are attributable to thermal stresses (related to internal gradients and to volumic variations), movements of adsorbed fluid and cycles of alternate wetting and drying, combined of course with salt crystal growth on hydratation. Like the frost shattering resistance of mineral aggregates, the sulfate soundness is directly related to the microstructure and mineralogy of the aggregates, as demonstrated by the very high correlation which exists between the quantity of water adsorbed and its resistance to the damaging effects. However, the absence of any strict relationship between the sulfate test and the actual performance of aggregates exposed to the elements, together with the low reliability and accuracy of this standard test, should limit it to use merely as a general index of behavior which, combined with detailled petrographic analysis, may help to indicate, from its narrow relationship with abrasion, attrition and absorption properties, the potential weaknesses of mineral aggregates. In any event, it should not be used as the exclusive criterion for selection.     

Reliability of numerical modelling predictions

The accuracy of all predictions made using numerical modelling is strictly limited by the natural variability of geologic materials. In this paper, an attempt is made to quantify this accuracy through the straightforward application of probability and statistics. It is shown how the contributions from variability of the input parameters and also errors introduced by the modelling procedure can be combined into a single representative coefficient of variation C_p. This parameter is a characteristic that quantifies how well the entire modelling procedure is performing. It includes contributions from the variability of the pre-mining stress and rock mass strength, material heterogeneity and also errors introduced by the modelling procedure (e.g. elastic versus inelastic), and represent the uncertainty one has in predictive capability.In the paper, a lower limit for C_p of 30% is estimated for use with the conventional empirical approach (i.e. measurement of pre-mining in situ stress state, laboratory testing, and subsequent strength degradation to rock mass scale). Realistic values are most likely higher than this since some contributions have not been included and others are not known with any certainty. Various methods to reduce the magnitude of this parameter are then investigated. It is shown how this parameter can be evaluated by back-analysis of field observations. An example is detailed where a series of pillar failures are back analysed to calculate a site-specific value of 10%. This allows predictions to be made with greatly improved confidence and accuracy, and demonstrates why the back-analysis approach is so appealing. The paper presents a rational means for improving on existing empirical procedures for design of underground excavations.     

Assessment of clay stiffness and strength parameters using index properties

A new approach is developed to determine the shear wave velocity in saturated soft to firm clays using measurements of the liquid limit, plastic limit, and natural water content with depth. The shear wave velocity is assessed using the site-specific variation of the natural water content with the effective mean stress. Subsequently, an iterative process is envisaged to obtain the clay stiffness and strength parameters. The at-rest earth pressure coefficient, as well as bearing capacity factor and rigidity index related to the cone penetration test, is also acquired from the analyses. Comparisons are presented between the measured clay parameters and the results of corresponding analyses in five different case studies. It is demonstrated that the presented approach can provide acceptable estimates of saturated clay stiffness and strength parameters. One of the main privileges of the presented methodology is the site-specific procedure developed based on the relationships between clay strength and stiffness parameters, rather than adopting direct correlations. Despite of the utilized iterative processes, the presented approach can be easily implemented using a simple spreadsheet, benefiting both geotechnical researchers and practitioners.     

低渗透单相非线性渗流机制试验研究

 采用美国岩芯公司AFS300TM全自动岩芯驱替系统和鄂尔多斯盆地露头全直径低渗透砂岩岩芯,通过BP–100空气弹簧回压阀控制岩芯出口端压力,分别使用标准盐水和煤油作为渗流介质,在低压力梯度(0.005～0.300 MPa/m)条件下,通过稳态法测定岩芯饱和渗流曲线。试验结果表明：岩芯出口端流速随压力梯度增加而线性增加,没有观察到明显的启动压力梯度和非线性;通过非稳态法测试,也没有观察到明显的启动压力梯度现象。试验所用低渗透岩芯单相渗流符合达西定律,多孔介质壁面与流体(牛顿流体)的作用并不能导致单相渗流的非线性和启动压力梯度。     

Radiant panel and air heating performance in large industrial buildings

This study determined the vertical temperature gradient in two large industrial buildings with room height close to 10 m. One of the buildings was an assembly hall with air heating system and the other was a warehouse equipped with radiant heating (primary) and air heating (secondary) system. The objective of the study was to determine the differences of vertical temperature gradient in halls during the winter. The findings from this study were used in dynamic whole-year simulations for estimating the heating and ventilation energy differences. The results showed about 0.2 K/m vertical temperature gradients in both halls, which was smaller by a factor of 5 for air heating than guidebook. This difference was likely because of the building being ventilated and well insulated. Temperature gradients kept reasonably constant at all measured outdoor temperatures. Energy simulations with measured gradient values of 0.2 K/m and with outdoor airflow rate during occupied hours 1.0 L/(s·m²), which was enough for ventilation and for air heating with simulated good insulation level, resulted in 15% to 41% higher primary energy for air heating. If it is possible to lower outdoor airflow rates to 0.5 L/(s·m²) during occupied hours, which was enough to remove pollutants from occupancy, the analyzed cases showed 23% lower primary energy for radiant heating.     

建筑围护结构传热系数现场检测装置研制

建筑围护结构传热系数检测是建筑节能检测中的重要项目,为在现场准确测量围护结构的传热系数,将用于实验室测试围护结构传热系数的热箱法与用于现场测试的热流计法结合起来,设计并制作了现场检测围护结构传热系数的实验装置.热箱能够人为控制室内检测环境,使室内外温度差达到检测要求,弥补了热流计法只能在采暖季节测试的不足,提高了检测效率及准确度.通过对某建筑物墙体进行了现场检测,实验结果表明该现场检测装置测试时间短、准确度高.现场检测得到的传热系数比理论计算值高约55％,建议将建筑围护结构的现场检测结果和理论计算值作为评价其节能效果的综合指标.     

Thermal comfort in environments with different vertical air temperature gradients

The use of displacement ventilation for cooling environments is limited by the vertical temperature gradient. Current standards recommend a temperature difference of up to 3 K/m between the head and the feet. This paper reviews the scientific literature on the effect of vertical temperature gradients on thermal comfort and compares this to the results of our own experiments. Early experiments have demonstrated a high sensitivity of dissatisfied test subjects to changes in the temperature gradient between head and foot level. Recent studies have indicated that temperature gradients of 4‐5 K/m are likely to be acceptable, and the mean room temperature may have a greater sensitivity on the percentage of dissatisfied (PD). In new experiments, test subjects have evaluated the thermal comfort of different vertical air temperature gradients in a modular test chamber, the Aachen comfort cube (ACCu), where they have assessed vertical temperature gradients of ΔT/Δy = 1, 4.5, 6, 8, and 12 K/m at a constant mean room temperature of 23°C. The results of the different temperature gradients are in contrast to ANSI/ASHRAE Standard 55 (Thermal Environmental Conditions for Human Occupancy, Atlanta GA, American Society of Heating, Refrigerating and Air Conditioning Engineers, 2013) as the PD increases almost constantly with higher vertical air temperature gradients. The PD for the overall sensation increases by approximately 7% between gradients of 1 and 8 K/m. The evaluation of our own tests has revealed that vertical temperature gradients of up to 8 K/m or higher are likely to be acceptable for test subjects.     

温度梯度冻土蠕变变形规律和非均质特征

采用K₀DCGF（K₀固结—保持荷载冻结—形成温度梯度—再试验）方法,开展不同温度梯度冻结饱和黏土三轴蠕变试验,研究冻土蠕变变形规律和温度梯度诱导的冻土非均质特征。结果表明：K₀DCGF模式中温度梯度冻结饱和黏土蠕变曲线由瞬时蠕变、衰减蠕变、稳定蠕变和加速蠕变4个阶段组成;温度梯度冻土径向蠕变速率小于轴向蠕变速率;温度梯度冻土最小轴向蠕变速率与蠕变应力之间满足指数函数关系,而长期强度极限与蠕变破坏时间之间则满足对数函数关系;梯度温度冻结过程中的水分场重分布和试验后冻土变形的非均匀分布是K₀DCGF蠕变试验中“温度梯度诱导的冻土非均质性”的重要体现;蠕变试验后温度梯度冻土冷端含水量最高,密实度最大;蠕变试验后温度梯度冻土宏观径向变形/试样高度沿试样高度方向分布随蠕变应力增加由先增加后降低规律逐步演化为持续增加规律,这一现象与冻土初始瞬时蠕变速率密切相关。     

压实黏土剪切带渗透特性试验研究

针对中国在建和拟建的300m级高堆石坝心墙黏土(尤其是接触黏土)在大剪切变形、高水头作用下渗透安全性评价的重大需求,采用新研发的土体环剪渗透试验装置对某高堆石坝心墙黏土进行了系列竖向压缩—环向剪切—径向渗流试验,测定了不同压实密度的黏土剪切带在不同竖向压力下导水系数随剪切位移的变化过程,揭示了压实黏土在大剪切变形过程中渗透特性的演化规律、内在机理及影响因素。在高竖向压力下,剪切带在剪切过程中被压缩得更密实,其导水系数在剪切过程中并不增大,剪切带在经历大剪切变形后仍具有良好的抵抗渗流的能力。在低竖向压力下,剪切带内土体破碎、错动、形成空隙,从而导致其导水系数急剧增大。对于所用的黏土,压实过程导致的前期固结压力可以粗略作为判别产生剪切渗漏带的门槛应力值。超固结的压实黏土易产生剪切渗漏带的试验发现,比目前传统的水力劈裂假设可以更好地解释和判别坝体中集中渗漏发生的条件及部位。     

Evaluation of simple methods for assessing the uniaxial compressive strength of rock

Published data on 48 different rocks are used to evaluate the correlations between the uniaxial compressive strength (UCS) values and the corresponding results of point load, Schmidt hammer, sound velocity and impact strength tests. The variability of test results for each test and each rock type was evaluated by calculating the coefficient of variation. Using the method of least squares regression, the UCS values were correlated with the other test values. Also, the test methods were evaluated by plotting the estimated values of compressive strength vs. the measured values of compressive strength for each test. The results indicate that the least variability is shown in the impact strength test. So, among the test methods included in this study, the impact strength test is the most reproducible test; but the variability of test results for the other test methods is within acceptable limits for most engineering purposes. Strong linear relations between the point load strength index values and the UCS values were found for the coal measure rocks and the other rocks included in this study. The Schmidt hammer and the sound velocity tests exhibit significant non-linear correlations with the compressive strength of rock. In the sound velocity test, the data points are scattered at higher strength values. There is no clear relation between the impact strength values and the compressive strength values for the coal measure rocks. A weak non-linear correlation was found between the impact strength values and the compressive strength values for the other rocks. All test methods evaluated in this study, except the impact strength, provide reliable estimate of the compressive strength of rock. However, the prediction equations derived by different researchers are dependent on rock types and test conditions, as they are in this study.     

Effect of wetting on gas transmissivity of non-woven geotextiles

A laboratory study was undertaken to assess the gas transmissivity of two needle-punched non-woven geotextiles subjected to partial wetting. Each geotextile was subjected to 10 and 20 kPa effective stress, respectively. For the geotextiles and conditions examined, it was found that the gas transmissivity decreased as the effective stresses and moisture content increased. More importantly, it was observed that the thicker geotextile achieved a higher transmissivity than the lighter geotextile. This is most likely due to the lower porosity and the large number of needle holes present in the thicker geotextile. The loss in transmissivity was found to be more pronounced at moisture content lower than a threshold value (w≈160%), the variation of the transmissivity loss beyond the threshold value was found to be insignificant. The present investigation has shown that there is a need to include a wettability factor if the geotextile is to be used as a gas drain. Reductions factors are proposed to account for the wettability parameter.     

Automatic detection method of cracks from concrete surface imagery using two‐step light gradient boosting machine

Automated crack detection based on image processing is widely used when inspecting concrete structures. The existing methods for crack detection are not yet accurate enough due to the difficulty and complexity of the problem; thus, more accurate and practical methods should be developed. This paper proposes an automated crack detection method based on image processing using the light gradient boosting machine (LightGBM), one of the supervised machine learning methods. In supervised machine learning, appropriate features should be identified to obtain accurate results. In crack detection, the pixel values of the target pixels and geometric features of the cracks that occur when they are connected linearly should be considered. This paper proposes a methodology for generating features based on pixel values and geometric shapes in two stages. The accuracy of the proposed methodology is investigated using photos of concrete structures with adverse conditions, such as shadows and dirt. The proposed methodology achieves an accuracy of 99.7%, sensitivity of 75.71%, specificity of 99.9%, precision of 68.2%, and an F‐measure of 0.6952. The experimental results demonstrate that the proposed method can detect cracks with higher performance than the pix2pix‐based approach. Furthermore, the training time is 7.7 times shorter than that of the XGBoost and 2.3 times shorter than that of the pix2pix. The experimental results demonstrate that the proposed method can detect cracks with high accuracy.     

Percolation testing and hydraulic conductivity of soils for percolation areas

The results of specific percolation tests are expressed in terms of field saturated hydraulic conductivity (Kfs) of the soil. The specific tests comprise the Irish SR 6 and the UK BS 6297 standard tests and the inversed auger hole and square hole tests employed for the design of land drainage. Percolation times from these tests are converted to Kfs values using unit gradient theory and the Elrick and Reynolds (Soil Sci. 142(5) (1986) 308) model which takes into account gravitational, pressure head and matric potential gradients. Kfs is then expressed as the inverse of the percolation rate times a constant, in this way the percolation rate can be directly related to Kfs of the soil. A plot of Kfs against percolation rate for the Irish SR 6 and the UK BS 6297 standard tests is asymptotic at Kfs values less than 0.2 m/d and greater than 0.8 m/d. This behaviour creates difficulty in setting limits for percolation rates in standards. Curves are provided which enable Kfs values to be read off from percolation tests without the restrictions of head range currently enforced, for example in the Irish SR 6 and BS 6297 standards. Experimental measurements of percolation rates and Kfs were carried out on two sands in the laboratory and in the field on two soils. Kfs of these four materials was also measured using a tension infiltrometer and the Guelph permeameter. The saturated hydraulic conductivities (Ks) of the sands were also estimated in a falling head laboratory apparatus and by the Hazen formula. There was good agreement between the different tests for Kfs on each material. Because percolation time continued to increase significantly in consecutive tests in the same test hole while Kfs became constant, the latter is a better measure of the suitability of soils for percolation.