无纺织物单向受拉时孔径变化研究

现有反滤设计中保土准则使用土工织物未受拉时的等效孔径,但平面单向拉伸会导致该值变化,影响土工织物反滤性能。采用动力水筛法对三种无纺土工织物单向受拉时等效孔径变化进行测定。无纺织物被单向张拉至3%、5%和10%的平面应变,随着拉应变的增加,三种针刺无纺土工织物等效孔径减小。推求了无纺织物单向张拉时的等效孔径计算公式,对于较厚无纺织物,公式计算值和测试值较吻合,但对于较薄无纺织物,二值有一定差异。     

用图像分析法研究有纺土工织物单向受拉时孔径的变化

现有反滤设计中保土准则使用土工织物未受拉时的等效孔径,但平面单向拉伸会导致该值变化,变大则不满足保土准则,变小则不满足透水准则及淤堵准则。有纺织物孔径由孔径分布曲线和特征孔径反映,采用数字图像分析法对两种有纺土工织物单向受拉时孔径变化进行精确测定。有纺织物被单向张拉至3%,6%,9%和12%的平面应变,随着拉应变的增加,两种有纺土工织物开孔面积率增大;孔径分布曲线向孔径大的方向移动;3种特征孔径值（O30,O50和O95）增大,其变化率都与拉应变呈近似线性关系,且小孔径部分相对于大孔径部分随拉伸应变的增长而增大较快。     

不等轴双向拉应变下有纺织物孔径变化试验研究

有纺土工织物的孔径特征是反滤设计的重要指标。工程中有纺织物常处于不等轴双向受拉状态,引起孔径变化,导致织物反滤性能失效。采用数字图像法测试了不等轴双向拉应变下,3种条膜有纺织物的孔径参数变化,包括孔洞长宽比、开孔面积率、等效孔径(O95)等。对比经纬向应变比2∶1,3∶1,4∶1对试验结果的影响,根据孔径特征变化规律,揭示不等轴双向拉伸引起孔径变化的机理。运用图像法试验结果,验证已推导的双向应变下开孔面积率及孔径理论解。试验结果表明:开孔面积率、等效孔径(O95)均随双向拉应变的增大而增大。纬向应变相同时,经纬向应变比越大,孔洞形态(即孔洞长宽比)变化越大,开孔面积率及孔径变化的斜率越大。理论解较好地预测了开孔面积率及孔径的变化率及数值,孔径参数与双向拉应变呈现近似线性关系。但理论解的孔径计算以孔面积为指标,无法考虑应变比造成的孔形态变化对反滤作用的影响。     

循环往复水流条件下土工织物反滤淤堵机理探究

本文中通过进行循环往复水流条件下的梯度比试验,研究了三种不同开孔孔径的无纺土工织物分别作为反滤层时,其各自的反滤性能。通过分析被保护土体各部分渗透系数的变化来研究土工织物的反滤淤堵机理,探究了经典反滤理论在循环往复水流条件下的正确性、适用性和局限性。     

黏性土渗透淤堵室内模拟试验及分析

从黏性土的级配、土工织物的孔径大小、水力梯度和黏性土干密度等因素考虑,根据淤堵试验得出的梯度比的数据,分析土工织物在不同孔径大小、不同黏粒含量、不同黏性土干密度、不同水力梯度条件下的淤堵情况,根据所得试验结果,为今后不同工程对土工织物的选择提供一定参考。     

侧限单向拉应变对有纺织物开孔面积率的影响

有纺织物作为一种反滤材料应用广泛,工程中织物易受到侧限单向拉伸作用,导致孔径变化而影响其反滤性能。开孔面积率是反映织物反滤性能的重要参数。通过建立有纺织物单孔模型,推导侧限单向拉应变下开孔面积率理论解,试验中采用图像法测试其开孔面积率。结果表明理论值较好预测试验值,单孔模型的发展规律可以代表织物整体变化。     

双向拉应变对有纺织物孔径参数影响的研究

有纺土工织物反滤应用常处于双向受拉状态。孔径特征是有纺织物反滤设计的重要参数。由于双向拉应变引起孔径的变化显著,导致原本满足孔径指标的有纺织物时常反滤失效。根据有纺织物的微观结构及受力特点,分析双向拉应变导致条膜及孔径变化的机理,建立有纺织物单孔结构模型,推导孔径特征参数随双向拉应变变化的理论解,包括开孔面积率(POA,percent open area)及理论孔径(Obi)等。以等轴双向拉伸为例验证理论解。采用数字图像法在拉伸试验进行的同时,测试各级拉应变下3种单丝条膜有纺织物的孔径参数,包括开孔面积率、孔径分布曲线、等效孔径(O95),分析各项孔径参数随拉双向应变的变化规律,并与理论解的预测结果进行对比。通过试验结果可见,理论解较好地预测了开孔面积率(POA)及等效孔径(O95)随双向拉应变的增大趋势,对变化斜率及数值的预测较准确,并得出孔径参数与等轴双向拉应变的近似线性关系,为反滤设计中预测孔径特征变化提供了理论依据。     

武山尾矿坝无纺土工织物滤层化学淤堵问题初探

土工织物作为滤层在尾矿坝排渗设施中已得到广泛应用,但有些尾矿坝遇到了土工织物淤堵问题。本文针对武山铜矿尾矿坝排渗系统中发生的土工织物淤堵问题,通过一系列试验研究对无纺土工织物化学淤堵问题进行了初步探讨。研究结果表明氢氧化铁凝胶在织物纤维上的附着是化学淤堵的主要机理,尾矿中含有充分多的细粒黄铁矿且滤层处于非饱和渗流带或饱和- 非饱和交替变化渗流带是土工织物发生严重化学淤堵的必要条件     

土工织物应用于新型压密注浆土钉的试验研究

针对乳胶膜式压密注浆土钉的潜在缺陷,提出了采用土工织物替代乳胶膜改进该土钉的新思路。首先,基于自研的土工织物反滤性能测定装置,开展了一系列水泥浆液反滤试验,研究了水灰比、浆液体积和注浆压力对土工织物反滤性能的影响,得到了注浆过程中上述影响因素影响下反滤时间和水灰比的变化规律。其次,对反滤前/后的砂土进行了贯入试验,评估了由于浆液中黏性物质入渗引起的周围土体强度提高。再次,对反滤前/后的水泥试块进行了单轴压缩试验,探明了节泡（水泥试块）强度显著提高的原因是土工织物反滤过程中节泡内水灰比的降低。最后,开展了土工织物和乳胶膜式压密注浆土钉的两组对比拉拔试验,验证了土工织物改进压密注浆土钉的优越性。研究成果能为压密注浆土钉的优化和应用奠定基础。     

双向不等轴拉应变对有纺织物开孔面积率的影响

土工织物应用于防水、反滤、保温、隔离等方面,土工织物的开孔面积率是反映土工织物性能的重要参数,前人对此已有研究,主要集中在单轴拉伸和等双轴拉伸试验。通过双向不等轴拉伸试验,运用白彬推导的公式,采用图像法测试土工织物在双向拉应变下的开孔面积率POA(Percent Open Area)的变化,分析理论值与试验值之间的偏差并加以修正,提出"投影泊松比"的概念,同时探究投影泊松比对开孔面积率的影响。     

The influence of uniaxial tensile strain on the pore size and filtration characteristics of geotextiles

The influence of uniaxial tensile strain on the pore size distribution and filtration characteristics of geotextiles is studied. An experimental apparatus was designed and used to conduct tests for pore size distribution, flow rate through the geotextiles and the gradient ratio. Four geotextiles made of polypropylene (two heat-bonded nonwoven and two slit film woven) were studied. Throughout the test series, the geotextiles were stretched to maintain 5%, 10% and 20% in-plane uniaxial strains. The strained specimen test results were compared with those from unstrained specimen. The experimental results illustrate the pore size and the mean flow rate through the plain geotextiles increase with the increase in tensile strain. The differences in changed percentages for apparent opening size and flow rate between the two nonwoven geotextiles are much higher than those between the two woven geotextiles. The increase in tensile strain results in reduction in the gradient ratio for the soil–geotextile system. This effect is more pronounced for nonwoven geotextiles. More testing is recommended to gain a deeper understanding into tensile strain effect on various geotextiles.     

无纺织物单向拉伸孔径变化试验与理论预测对比分析

无纺织物作为反滤材料,常处于单向受拉工作状态。单向拉伸引起无纺织物孔径变化,易导致反滤工程失效。通过控制织物应变的干筛试验,定量测试了无侧限单向拉应变逐级增大的过程中,两种不同厚度短纤针刺无纺织物的孔径分布曲线变化。采用干筛试验结果,对现有两种体系的单向应变下无纺织物孔径预测理论解进行验证:一类是佘巍等效孔径O95理论解,一类是Rawal孔径分布曲线理论解。通过对比两种理论解对各级拉应变下的O95值预测,归纳二者的预测误差规律,从理论假设出发分析误差原因。同时采用前人图像法测得的热粘无纺织物O95变化验证两类理论解。两种理论解均能较好地预测无侧限单向拉应变下无纺织物O95的变化规律。O95随单向拉应变呈近似线性减小的规律。对于O95变化斜率的预测,佘巍解较准确,Rawal解偏大。对于O95数值预测可结合两类理论解给出变化范围。     

Uniaxial strength testing of woven and nonwoven geotextiles

This paper describes the different design approaches using geotextiles and presents two types of uniaxial tensile testing: constant rate of strain and rapid loading creep tests. Tests are conducted using a woven geotextile and two nonwoven geotextiles. The effects of the width to length ratio of the test specimens, test temperature and strain rate are examined. Tests are also conducted with the specimen in air and when confined in-soil. The results illustrate that the load-extension behaviour of the geotextiles tested depends on the test conditions and hence the need to standardise these conditions is established.The relevance of test types and conditions to design and quality control is also discussed.     

Effect of bituminous impregnation on nonwoven geotextiles tensile and permeability properties

Geosynthetics interlayer systems are effective techniques to control reflective cracking in damaged pavements. It comprises the inclusion of nonwoven geotextiles between the damaged layer and the new overlay of the pavement to reduce the propagation of cracks and to extend pavement life. However, the success of this technique depends directly on the understanding of the geotextile's behavior when impregnated with asphalt. This paper evaluates different nonwoven geotextiles frequently used in anti-reflective cracking systems, focusing on initial stiffness gain and permeability reduction after asphalt impregnation. Fresh and impregnated samples of polyester and polypropylene nonwoven geotextiles were tested. Cationic rapid setting emulsified asphalt was used as asphalt binder. Wide-width tensile tests were carried out based on the specification of ABNT - NBR 12824 (1993). Water vapor transmission tests were conducted according to ASTM E 96M (2005). Results of tensile tests on impregnated geotextiles showed a significant increase on tensile strength values, probably due to the inter contact of the fibers. Results also showed high increase in strength values at strain levels less than 0.05% and decrease on stiffness gains with increase of strains. Water vapor transmission tests demonstrated that cationic asphalt emulsion applied on nonwoven geotextiles allows a drastic reduction in permeability values to turn nonwoven geotextiles into a low permeability barrier.     

Geotextile filtration opening size under tension and confinement

Nonwoven geotextiles have been used as filters in geotechnical and geoenvironmental works for half a century. They are easy to install and can be specified to meet the requirements for proper filter performance. There are situations where a geotextile filter may be subjected to tensile loads, which may alter relevant filter properties, such as its filtration opening size. Examples of such situations are silty fence applications, geotextile separators, geotextile tubes and geotextiles under embankments on soft soils. This paper investigates the effects of tensile strains on geotextile pore dimensions. A special equipment and testing technique allowed tests to be carried out on geotextile specimens subjected to tension and confinement. The results obtained showed that the variation in filtration opening size depends on the type of strain state the geotextile is subjected, under which the geotextile pore diameter may remain rather constant or increase significantly. However, confinement reduces the geotextile filtration opening size independent on the strain mobilised. An upper bound for the filtration opening size of strained nonwoven geotextiles is introduced and was satisfactory for the geotextile products tested.     

Improvements in small-scale standardized testing of geotextiles used in silt fence applications

Silt fence have been used as a means for intercepting and treating construction site stormwater runoff prior to offsite discharge for well over 30 years. Standard small-scale testing methodologies for evaluating the filtering component of silt fence installations have failed to mimic realistic flows and sediment loadings commonly seen in field applications. To address these issues, this study evaluated the performance capabilities of two nonwoven and three woven silt fence geotextiles using an innovative testing methodology and a newly developed small-scale testing apparatus. The overall intent for conducting the evaluations was to develop a deeper understanding of effluent flow rates, sediment retention capabilities, and water quality impacts associated with geotextile fabrics. Results suggest that effluent flow rates of nonwoven geotextiles are on average 43% lower than woven materials, which results in extensive upstream retention times of impounded stormwater for nonwoven materials. Sediment retention results indicate that nonwoven geotextiles have an average sediment retention rate of 97% while woven geotextiles average 91%. Finally, water quality analyses suggest that the primary means for turbidity reductions rely on the process of sedimentation during the 30-min test period (i.e., 46% reduction) and filtration during the 90-min dewatering period (i.e., 19% reduction).     

Changes in filtration opening size of woven geotextiles subjected to tensile loads

A modified hydrodynamic sieving technique in which the geotextile is subjected to a tensile load is described. This load may be either uni-axial or bi-axial. To date tests have been conducted on two different woven slit-film polypropylene geotextiles and the results illustrate a marked change in the filtration opening size of the geotextiles as the tensile load is increased. The opening size of the thicker geotextile decreased with increasing biaxial load, whereas the opposite occurred for the thinner of the two geotextiles. The geotextiles were loaded up to only about 10% of their minimum ultimate tensile strength and the filtration opening size changed by up to 28%. It is suggested that this effect cannot be ignored in applications where there are in-plane tensile stresses.