Technical note on cold weather installation of HDPE

In order to successfully seam HDPE flexible membrane liners (FMLs) in cold weather (less than 4·5°C (40°F), FML temperature may not be the most important factor. Secondary cold weather effects such as frozen subgrade, bridging, snow and ice removal, and worker discomfort pose a much more significant risk to the integrity of the liner installation.     

Drainage performance of geotextiles

It should be noted that the drainage conditions and mechanisms are somewhat different when geotextiles are used as back fill material behind retaining walls. One of the major differences is that the soil installed by the geotextile may not necessaroly be saturated. Generally, the drainage performance of geotextiles can be evaluated by examining combined behavior of geotextiles, soil particles and water. However, in addition to the above materials, in investigating the drainage performance of geotextiles as back fill material behind retaining walls, the effect of air should be taken into account. Therefore, this study has concentrated on investigating the effect of drainage performance of an initially dry geotextile. A further long-term test was carried out primarily to examine the mechanism and development of self-induced filters, which is believed to determine the drainage performance of the geotextile.     

水泥混凝土桥面环氧沥青防水粘结层性能研究

优良的防水粘结层是确保水泥混凝土桥面使用耐久性的重要措施之一.通过对环氧沥青防水粘结材料的黏度、环氧沥青防水材料用量对粘结强度影响的试验以及防水层施工后养护时间对粘结层粘结强度影响试验,研究混凝土桥用环氧沥青防水粘结材料的性能.试验研究结果表明,环氧沥青防水粘结材料的施工温度必须严格控制在130℃以上,最佳用量为0.70L/m2,环氧沥青防水粘结材料在施工后24～32 h内必须进行沥青混凝土的铺装.     

Technical note on hot air seaming of high-density polyethylene geomembranes

Hot air fusion welding is widely used as a secondary seaming method for welding high-density polyethylene (HDPE) geomembranes, although seldom as a primary seaming method. This method is based on a very simple principle and can withstand comparison with the other main seaming methods. However, the strength and long-term durability of seams made with this method are still poorly known, and should be explored, as compared to the other welding methods.     

Directional in-plane permeabilities of geotextiles

Typical studies of in-plane flow of fluids through geotextiles yield an average value for the fabric permeability and transmissivity. We introduce a new method which quantifies directional in-plane intrinsic permeabilities. The flow front which develops when fluid is introduced into a geotextile sample and allowed to flow only in the plane of the material highlights primary flow directions due to fabric anisotropies, and also reveals nonuniformities and inhomogeneities in the fabric. Temporal radial expansion measurements allow one to obtain values for directional geotextile intrinsic permeabilities.     

Durability studies of surface-modified coir geotextiles

Coir (Cocos nucifera) is a natural fibre known to retain its strength and resist biodegradation far better than other industrial natural fibres. However, systematic studies in this discipline are scarce. Geotextiles are usually exposed to diverse pH, salinity, moisture, and microbial association conditions. In the present work, specific surface modifications of coir geotextiles using a natural agent (cashew nut shell liquid) have been carried out to enhance their long-term performance depending on the end applications. The modified and unmodified geotextiles were subjected to acidic, alkaline, and neutral pH conditions, saline conditions, alternate wetting and drying cycles, and thermal cycles for the assessment of their durability, measured in terms of tensile strength. In situ soil burial studies in a tropical climate were conducted in specially prepared soil to follow the biodegradation behaviour of geotextiles at various depths. The surface-modified geotextiles were found to resist adverse chemical, physical, and biological conditions much better than the unmodified geotextiles. Alkaline conditions marginally accelerated the degradation rates when compared to acidic environments. The saline conditions, as well as alternate wetting and drying conditions, resulted in marginal loss of tensile strength (<7%). The surface-modified geotextiles buried within lower depths of soil under field conditions retained 70–80% of their initial tensile strength after 12 months, whereas the unmodified geotextiles lost 88% strength in four months. The positive impact of surface modification on durability is confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The results indicate the excellent potential of suitably surface-modified coir geotextiles for long-term use in adverse conditions.     

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.     

大跨径桥面铺装防水粘结层应用技术研究

针对大跨径桥面铺装粘结防水层的特点,介绍了改性沥青防水粘结层在高速公路沥青混凝土桥面铺装中的应用,通过对防水粘结层材料性能进行系统的试验,建立了SBS改性沥青作为防水粘结层的技术指标与技术要求,并着重对粘结防水层的施工程序及质量控制进行了深入研究,可为相关桥面铺装的设计施工提供参考。     

单向拉伸对土工织物反滤性能影响的试验研究

为研究单向拉伸对土工织物反滤性能的影响,选取两种条膜机织有纺织物和两种短纤针刺无纺织物,将不同拉应变下的织物与非连续级配土组成反滤系统,利用梯度比渗透仪测试系统反滤参数随拉应变的变化。根据反滤设计的透水、保土和防淤堵3个准则,分析拉应变对透水率、漏土量、梯度比等各参数的影响。试验结果表明：随着拉应变增加,有纺织物透水及防淤堵性能增强,保土性能减弱;无纺织物则相反,透水及防淤堵性能减弱,保土性能增强;同种土工织物厚度越大,拉应变对其反滤性能影响越大。     

Historical review of geotextiles in Japan

This paper describes developments in the use of geotextiles in Japan, not only in the recent past but in the period from the ancient era of China down to the middle and pre-Meiji ages of Japan when natural materials were used in a similar manner to present-day geotextiles. The 1960s witnessed development of the petrochemical industry and several applications of geotextiles independent of overseas technology. These related mainly to the treatment of soft ground and its reclamation. During the 1970s there was wider application of geotextiles to project involving embankments, retaining walls and other earth structures, leading to the use of polymer grids which commenced in Japan in 1983.     

Determination of frictional properties of geotextiles

The influence of some test conditions on the measured frictional properties of geotextiles is discussed. Conclusions and suggestions are presented, based on research on some non-woven and woven geotextiles in a small (10 cm × 10 cm) and large (25 cm × 40 cm) direct shearboxes as well as from pull-out tests. Specifications for testing frictional properties of textiles, which have been published in Poland, are also briefly presented.     

Manufacturing effects on the hydraulic properties of needlepunched nonwoven geotextiles

Needlepunched nonwoven geotextiles are entangled to form a complex three-dimensional structure by random fibers, accounting for its bulky nature, wide range of pore size distribution, and good drainage. With needlepunched nonwoven geotextiles, water can move in both the vertical and horizontal directions. This paper examines two types of needlepunched nonwovens: one produced from polyester staple fiber and the other made from polyester spunbond continuous filaments. Experimental results indicate that the permittivity of staple needlepunched nonwoven geotextiles varies from 1.77-4.51 s⁻¹; the permeability coefficient varies from 0.63-2.87 × 10⁻² m/s. The permittivity of spunbond needlepunched nonwoven geotextiles varies from 1.13-1.97 s⁻¹; the permeability coefficient varies from 0.48-1.09 × 10⁻² m/s. In addition, the transmissivity of needlepunched nonwoven geotextiles decrease to an essentially constant value as the normal stress is increases. The transmissivity of needlepunched nonwoven geotextiles examined varies from 155-2.75 × 10⁻⁶ m²/s over the normal stress range examined (5-200 kN/m²). The AOS value of 3 denier staple fiber needlepunched nonwovens is less than 0.074 mm, the AOS value of spunbonded 7 denier and, 15 d and 20 d needlepunched nonwovens are 0.21 mm, 0.25 mm and 0.30 mm, respectively.     

The application and manufacture of woven geotextiles

Some criteria for geotextile selection are considered and the specifications of various geotextiles are related to various case histories cited. Consideration is given to the special filtration capacity of fabrics and the possibility of adapting manufacture to optimise the geotextile to specific circumstances. The possibilities of reinforcement offered by fabrics are also illustrated by examples and it is shown that in extreme cases the application of geotextiles allows safe technical solutions coupled with economy. The manufacture of woven geotextiles is characterised by the various procedures in weaving preparation where technical and economic requirements have to be met. The influence of various factors on economy is explained and their effects shown.     

Water and air transmissivity of geotextiles

The in-plane flow characteristics of both water and air in needled, nonwoven geotextiles have been evaluated in this study. Transmissivity (equal to permeability times fabric thickness) versus applied normal stress on the fabric has been measured in a radial flow device for different fabrics and for different thicknesses of a given fabric. The transmissivity response in each case was seen to decrease with increasing stress until a residual value was reached. In none of the cases did the fabric compress to the point where flow was completely shut off, even though stress levels of 2500 psf were applied. In turn, the calculated geotextile permeability varied from a fine gravel to a medium sized sand.Planar air flow in geotextiles has been found to be in excess of two orders of magnitude greater than water flow under comparable conditions. Air flow through partially and fully saturated fabrics is shown to be of little practical interest since the air easily moves around the water in the fabric voids or displaces it entirely.The need for transmissivity test standardization for all types of geotextiles and geotextile composite systems is expressed.     

Biaxial tensile behavior of spunbonded nonwoven geotextiles

Geotextiles can be successfully employed for any geotechnical application when they are able to sustain pre-defined levels of tensile stresses. The biaxial tensile test has an advantage over other tensile test methods in that it does not allow “necking” during deformation which simulates the operational conditions of geotextiles under confined stresses. In this study, the model for uniaxial tensile behavior of nonwovens has been modified to investigate the biaxial tensile behavior of spunbonded geotextiles. The model has included the effect of fiber re-orientation, stress-strain behavior of constituent fibers, and physical characteristics of nonwovens when the geotextile specimen is laterally constrained. A comparison is made between predicted and experimental stress-strain curves obtained from previous work (Bais-Singh and Goswami, 1998). Theoretical findings of biaxial tensile behavior obtained using the layer theory are also critically discussed. In addition, it has been revealed that fiber re-orientation is a key factor in translating the random spunbonded nonwoven geotextiles to anisotropic structures under defined biaxial tensile stresses.     

钢-UHPC组合板环氧黏结界面抗剪与抗拉性能试验

文章以预制UHPC板与钢板采用环氧树脂黏结剂连接的组合结构为对象,开展了连接界面抗剪与抗拉的试验研究。试验结果表明,试件中的环氧树脂黏结剂和UHPC材料本身均保持完好;破坏位置,抗剪试件为黏结剂与钢板交界面,抗拉试件为黏结剂与UHPC的交接面;破坏性质为脆性,交接面出现滑移或分离后快速丧失承载力。抗剪强度受黏结面积影响不大,实测值平均值2.59MPa,抗剪强度设计值为1.36MPa。抗拉强度与黏结面积有关,当试件尺寸由160mm增大至200mm,实测值分别为2.74MPa和1.86MPa,降幅超过30%,抗拉强度设计值为0.78MPa。UHPC中钢纤维掺量在1%～2%范围内对抗拉黏结强度影响可忽略。建立了钢-UHPC组合板有限元模型进行受力分析。分析表明,在轮载作用下,黏结层以受剪为主,沿横桥向最为不利;最不利荷载工况的最大剪应力和竖向拉应力分别1.11MPa和0.15MPa,均低于黏结剂抗剪和抗拉强度设计值。根据试验和实例分析结果,考虑到黏结剂连接脆性破坏特性,建议重视胶结界面的处理,重点关注抗剪强度问题。