受压无纺土工织物的孔眼及透水性和保砂性的计算

<正>一、前言 作为土木工程、水利水电水运工程建设的新材料,无纺土工织物的应用要比有纺土工织物的应用更为广泛。研究无纺土工织物与土体或其它建筑材料接触后的孔眼变化及其透水性、保砂性有其现实意义。这些问题将涉及到织物排水、滤层设计和实际工程效果。     

基坑开挖回弹再压缩变形试验研究

通过室内模型试验对土体回弹变形与再压缩变形规律进行了研究。新的回弹变形观测方法的应用弥补了现有观测方法的不足,取得了较好的效果。在模型试验中,基底以下同一深度处土体的回弹变形沿基坑宽度分布形状类似倒扣的锅底形,基坑中心处土体回弹变形量最大,越靠近基坑边缘其回弹变形越小。基坑工程空间效应对回弹变形有明显影响,且在基底以下一定深度范围内对埋深越大的土体影响也越大。在卸荷量与再加荷量等同的情况下,土体的回弹变形量小于再压缩变形量。     

土工织物反滤层透水性设计准则

本文在大量室内试验的基础上，对现有土工织物反滤层透水性设计准则进行了较详细的讨论，并在美国陆军工程师团准则的基础上建立了新的广义梯度比准则。试验和理论分析表明，新的广义梯度比准则较陆军工程兵团准则具有更广泛的适用性。     

纤维织物与钢板网联合增强混凝土薄板四点抗弯性能试验研究

对素混凝土板、钢板网混凝土板、纤维织物网混凝土板及纤维织物与钢板网联合增强混凝土板的四点弯曲性能进行了试验对比分析。试验结果表明,钢板网、纤维织物网以及纤维织物网与钢板网联合增强混凝土板的抗弯性能,较素混凝土板,分别提高了5.6%、21.1%和42.1%。纤维织物网和钢板网可以有效提高混凝土板的变形能力,而且织物网的加入可以改善钢板网与水泥基复合材料之间的黏结性能。     

循环荷载作用下粗颗粒土填料的残余变形特性浅析

粗颗粒土在自然界分布广泛,并具有透水性强、填筑密度大、抗剪强度高和沉陷变形小等工程特性,因此在土木工程中得到了广泛应用。论文介绍了常用的几种粗颗粒土残余变形计算模型,并分析了粗颗粒土的饱和程度、密实度、颗粒级配、围压和振次以及主应力比对其残余变形的影响。     

沉管隧道干坞有限元分析

针对干坞开挖后土体的变形情况,采用大型有限元分析软件ABAQUS建立Duncan-Chang非线性弹性模型,对基坑开挖变形性状进行了三维非线性有限元分析,得出了干坞开挖后土体水平变形及基底回弹变形值并且论述了产生这些不同变形的机理.     

地基回弹变形计算若干问题探讨#br#

《建筑地基基础设计规范》(GB50007—2011)规定采用分层总和法计算地基回弹变形,并给出计算公式。回弹模量的选取和回弹变形计算深度的确定直接影响到计算精度,但是实际应用时很难准确得到计算需要的回弹模量和回弹变形计算深度。通过对不同地区、不同土性的土样的回弹试验结果进行分析发现：土在完全卸荷时的回弹模量Ec0与初始卸荷应力p近似呈线性关系;不同初始卸荷应力下,土的Ec/Ec0-R曲线可以采用对数曲线进行拟合。根据这些规律,提出回弹模量确定方法,按照该方法可得到同一土层不同初始卸荷应力p、不同卸荷比R对应的回弹模量Ec,并对土的回弹试验方法和数量提出建议。此方法解决了采用地基规范方法计算回弹变形时的回弹模量取值的问题。回弹变形计算深度的确定可以采用地基规范规定的应变比方法。对于基底以下土层较均匀时,提出可采用应力比的方法确定回弹变形计算深度,采用卸荷比R为0.4作为确定回弹变形计算深度的标准,提出均质土地基回弹变形计算深度系数表。通过算例证明：对于均质土地基,采用该方法确定的地基回弹变形计算深度与应变比方法得到的计算深度基本一致。     

边坡开挖对坡脚建筑影响分析

边坡开挖作为一个卸载过程，不可避免的会引起坡脚场地的回弹变形。本文使用平面弹塑性有限元方法分析了这一问题，总结了坡脚回弹变形形态及影响因素，并初步探讨了其对坡脚建筑物的可能影响。     

"第8届国际混凝土路面砖"论文选利用电子显微镜学分析透水性路面砖路面结构里的微生物膜

最新研究已揭示在透水性路面砖路面系统内存在微生物膜.微生物膜的生长主要依靠碳氢化合物,大部分油污被滞留在InbitxTM土工织物上.经降解生成生物膜.InbiteTM土工织物促使生物膜最初的形成,并快速覆盖整个土工织物表面.通过扫描电子显微镜(SEM)可清楚地看到:成熟的微生物膜上"长有"多种形态的细菌和真菌.用透射电子显微镜(TEM)可证明细菌的细胞空泡内存在油迹:同时也发现,对于不是在油污中长成的细菌,其细胞内含物的大小与前者不同,而且在细菌细胞结构中也未发现油迹.电子显微镜不仅能分析出不同处理方法对微生物膜产生的影响,而且能清晰地显示显微结构,非常实用.该研究与透水性混凝土路面砖水环境之间的联系,实际上是生物膜结构及其功能之间的联系.     

利用电子显微镜学分析透水性路面砖路面结构里的微生物膜

最新研究已揭示在透水性路面砖路面系统内存在微生物膜。微生物膜的生长主要依靠碳氢化合物，大部分油污被滞留在Inbitx^TM土工织物上，经降解生成生物膜。Inbitex^TM土工织物促使生物膜最初的形成，并快速覆盖整个土工织物表面。通过扫描电子显微镜（SEM）可清楚地看到：成熟的微生物膜上“长有”多种形态的细菌和真菌。用透射电子显微镜（TEM）可证明细菌的细胞空泡内存在油迹；同时也发现，对于不是在油污中长成的细菌，其细胞内含物的大小与前者不同，而且在细菌细胞结构中也未发现油迹。电子显微镜不仅能分析出不同处理方法对微生物膜产生的影响，而且能清晰地显示显微结构，非常实用。该研究与透水性混凝土路面砖水环境之间的联系，实际上是生物膜结构及其功能之间的联系。     

A laboratory investigation on the impact resistance of a woven geotextile

This paper focuses on the impact resistance of geotextiles when subjected to impact loadings induced by dropping of stones. Such scenarios occur when geotextiles are used as a protective measure for fine granular material where is prone to be washed away. Usually, these geotextiles are restrained by placement of stones on top of them. A laboratory testing program is performed to expose a woven geotextile under dropping of a concrete block with various dropping energies and geometries. The induced damage on the geotextiles is inspected after the drop. Results indicate that as the drop energy increases, not only the possibility of puncturing of geotextiles increases but, in case of puncturing, the punctured area of geotextile expands as well. In addition, it is found that the geometry of the concrete block, where it collides on the geotextile, plays an important role on the survivability of geotextiles. In addition, PIV analysis has been performed to better understand the deformation pattern of the geotextile under impact loading. Based on the PIV results a simple scheme is suggested to estimate the drop energy threshold that the geotextile can survive under certain block geometry.     

A short-term model for extrapolating unconfined creep deformation data for woven geotextiles

This study reports results for creep deformation with data acquired in 72 h of testing. A system capable of performing 8 simultaneous tests was used to test four woven geotextiles of different weights, following all of the recommendations outlined in the standards related to equipment setup. A mathematical model was used to generate time-dependent creep curves for four different load levels up to 40% for each sample and using a database which presented stage II creep conditions (i.e. without rupture) through the end of the tests, up to 10,000 h. The coefficients of variation for the conventional creep tests were below 10%. The compatibility between the experimental data and the model indicates that short-term (72 h) loading tests may be used to extrapolate long-term creep deformation in woven geotextiles.     

用SDW-100型位移传感器测试高强土工布加筋垫层变形

大刚度SDW-100型位移传感器安装在500kN/m高强土工布上进行室内拉伸试验和现场加筋垫层的变形测试,试验成果表明,SDW-100型位移传感器用于高强土工布加筋垫层变形的测试具有适用性。     

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.     

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.     

Laboratory performance of unpaved roads reinforced with woven coir geotextiles

The results of an experimental study conducted to investigate the beneficial use of woven coir geotextiles as reinforcing material in a two-layer pavement section, are presented. Monotonic and repeated loads were applied on reinforced and unreinforced laboratory pavement sections through a rigid circular plate. The effects of placement position and stiffness of geotextile on the performance of reinforced sections were investigated using two base course thicknesses and two types of woven coir geotextiles. The test results indicate that the inclusion of coir geotextiles enhanced the bearing capacity of thin sections. Placement of geotextile at the interface of the subgrade and base course increased the load carrying capacity significantly at large deformations. Considerable improvement in bearing capacity was observed when coir geotextile was placed within the base course at all levels of deformations. The plastic surface deformation under repeated loading was greatly reduced by the inclusion of coir geotextiles within the base course irrespective of base course thickness. The optimum placement position of coir geotextile was found to be within the base course at a depth of one-third of the plate diameter below the surface.     

The prediction of long-term geosynthetic strength using cumulative damage theory

This paper presents cumulative damage theory and compares predictions obtained using this theory with the observed performance of several geosynthetics. Cumulative damage theory, which is based on the separation of the processes of reversible non-elastic deformation and damage, may be used to forecast the long-term strength of geotextiles and geomembranes. Such forecasts are made for transient or permanently applied loads which allows assessment of the relative resistance of materials to damage.     

Reclamation of abandoned open mines with innovative meandrically arranged geotextiles

For over fifty years, geosynthetics have been used for land reclamation of degraded areas. Several years ago for this purpose innovative geotextiles formed from meandrically arranged thick ropes were invented. The geotextiles were used for reclamation of abandoned lignite open-mine in Germany and disused gravel pit in Poland. The geotextiles were installed in abandoned mines. In next years positive influence of geotextiles on slopes behaviour and vegetation was observed. It was stated that the geotextiles provide stabilization of steep unstable slopes and significantly accelerate vegetation development. The innovative geotextiles perform functions unobtainable for other traditional products. The products are useful in an effective reclamation of open mines and constitute a valuable extension of the geosynthetic assortment applicable in land reclamation.     

Stabilisation of soil using hybrid needlepunched nonwoven geotextiles

In the past, natural and synthetic fibre based geotextiles have been used for short- and long-term applications of soil erosion. It is well known that these geotextiles complement each other in terms of various physical and mechanical properties. In this study, an attempt has been made to study various properties of hybrid geotextiles. These hybrid geotextiles have been produced from the blend of polypropylene/viscose and polyester/viscose fibres in defined weight proportions (0%, 20%, 40%, 60%, 80% and 100%). Subsequently, a comparison has been made between various physical and mechanical properties of needlepunched nonwoven geotextiles. In this research work, it was found that hybrid geotextiles made of viscose (up to 40 wt.%) can replace 100% polypropylene or polyester based geotextiles.     

Pore size distribution of hybrid nonwoven geotextiles

Pore size distribution has become a prerequisite in determining the performance of geotextiles for various functions including filtration, separation and reinforcement. The pore structure and morphology in a nonwoven geotextile are known to be complex and it becomes further complicated in hybrid nonwoven geotextiles consisting of two types of fibers. In this study, a modified model of pore size distribution of hybrid nonwoven geotextiles has been proposed based on sieving-percolation pore network theory. A comparison has been made between theoretical and experimental pore size distributions of hybrid needlepunched nonwoven geotextiles consisting of predefined weight proportions of viscose and polyester fibers. The weight proportions of the constituent fibers have been theoretically analysed for obtaining the desired pore size distributions of hybrid nonwoven geotextiles.