鼓形变位模式下柔性挡土墙的主动土压力分布

针对鼓形变位模式的柔性挡土墙,采用库仑土压力理论的假设,挡土墙上的主动土压力假定由墙后填土在极限平衡状态下出现的滑动楔体产生,在该滑动楔体上沿填土深度方向取典型水平薄层单元进行分析,分段建立关于挡土墙上土压力强度的一阶微分方程,给出了鼓形变位模式下,柔性挡土墙上的土压力强度、土压力合力和合力作用点的理论公式,并与库仑土压力理论和有关实验结果进行了比较分析。结果表明,鼓形变位模式下,土压力合力与库仑土压力理论结果相等,土压力分布和合力作用点位置则明显不同;墙顶附近的土拱作用改变了土压力的分布,本文方法与前人实验得到的土压力均大致呈R形分布。最后,利用本文解,对土体内摩擦角、墙土摩擦角、土薄层单元间等效内摩擦角、墙体最大变位点深度等参数对挡土墙土压力强度、土压力合力和合力作用点的影响进行了分析。     

计算柔性支挡结构主动土压力的简化方法

对于柔性支护挡土墙,在计算土压力时,宜考虑土压力作用点位置对其计算数值的影响。提出一个建立在Bishop法基础上的简化法。当土压力作用点位置为下三分点时,计算成果可无一例外地收敛到经典的库仑理论值。作用点位置为墙高中点时,经算例分析,主动土压力相应下三分点时的数值增加了15%左右。     

土工格室生态柔性挡墙的应用与研究现状

介绍了一种新型的土工格室生态柔性挡墙,阐述了土工格室在柔性挡墙中的工作机理以及土工格室生态柔性挡墙的研究现状,并总结了目前研究中存在的一些问题。     

柔性挡墙的主动土压力计算及分布研究

已有研究表明,柔性挡墙在不同位移量和位移模式下,主动土压力的大小和分布均发生变化,其分布也与刚性挡墙有明显区别。在前人室内试验和数值模拟结果的基础上,建立了考虑位移变化效应的柔性挡墙土压力计算模型,采用中间状态系数来统一反映挡墙位移模式和位移量的影响,提出了任意位移柔性挡墙主动土压力合力系数的计算公式;在求得合力基础上,将土体简化为非线性弹簧和刚塑性体的组合体,提出了任意位移下的土压力分布和合力作用点高度的计算方法。以前人模型试验为算例,将本文方法与试验结果、已有理论方法的对比表明,本文方法得到的土压力分布与试验值更接近。研究还发现,随着柔性挡墙位移量的增大,土压力合力逐渐减小,土压力分布的非线性程度逐渐增大;合力作用点位置随挡墙位移形态的变化而改变;在典型鼓胀形变位模式下,土压力呈R形分布。     

Modification of low pressure membranes with carbon nanotube layers for fouling control

Carbon nanotubes (CNTs) with different physiochemical properties were layered onto low pressure membranes and tested for antifouling properties using a natural surface water with high fouling potential. Membranes modified with the largest diameter pristine multi-walled CNTs (MWCNTs) were most effective in controlling membrane fouling, tripling the time it took for the membrane to become noticeably fouled at a CNT loading of 22 g/m². The differences in the structure of CNT layers were an important contributing factor for antifouling properties; scanning electron microscopy imaging showed that large diameter MWCNTs formed homogeneous porous layers across the membrane surface, while less effective, small diameter MWCNTs formed heterogeneous layers. Water quality analysis showed that CNT-membranes constructed with larger diameter CNTs were more effective at removing larger organic macromolecules responsible for fouling from feedwater compared to membranes made with smaller diameter CNTs. This reduced the concentration of foulants reaching the PVDF membrane and thus helped reduce membrane fouling. Beneficial for application, increased loadings of CNTs onto the membrane surface increased resistance to fouling while only slightly reducing the clean water permeability of the modified membranes. Overall, CNT layered membranes were shown to highly resist membrane fouling with potential applications in sustainable water treatment.     

Experimental study of PVD-improved dredged soil with vacuum preloading and air pressure

The PVD-vacuum method is the main method used to treat dredged soil, but sometimes it cannot completely meet engineering needs due to the limitations of vacuum pressure. Therefore, based on the traditional PVD-vacuum method, a method of air pressure combined with vacuum preloading is proposed in this paper. The air pressure is transmitted into the dredged soil by using an impermeable and flexible membrane airbag embedded in the dredged soil. A comparison of the traditional PVD-vacuum method and the combination of air pressure and vacuum preloading is investigated by the model test. The data of the settlement and water discharge during the test are monitored. After the tests, the water content and shear strength at different positions are measured. Finally, a method for calculating the volume change of dredged soil is proposed, and the results of the test are used to prove the correctness of the proposed method.     

Deformation and failure mechanism of slope in three dimensions

Understanding three-dimensional(3D)slope deformation and failure mechanism and corresponding stability analyses are crucially important issues in geotechnical engineering.In this paper,the mechanisms of progressive failure with thrust-type and pull-type landslides are described in detail.It is considered that the post-failure stress state and the pre-peak stress state may occur at different regions of a landslide body with deformation development,and a critical stress state element(or the soil slice block)exists between the post-failure stress state and the pre-peak stress state regions.In this regard,two sorts of failure modes are suggested for the thrust-type and three sorts for pull-type landslides,based on the characteristics of shear stress and strain(or tensile stress and strain).Accordingly,a new joint constitutive model(JCM)is proposed based on the current stability analytical theories,and it can be used to describe the mechanical behaviors of geo-materials with softening properties.Five methods,i.e.CSRM(comprehensive sliding resistance method),MTM(main thrust method),CDM(comprehensive displacement method),SDM(surplus displacement method),and MPM(main pull method),for slope stability calculation are proposed.The S-shaped curve of monitored displacement vs.time is presented for different points on the sliding surface during progressive failure process of landslide,and the relationship between the displacement of different points on the sliding surface and height of landslide body is regarded as the parabolic curve.The comparisons between the predicted and observed load e displacement and displacement e time relations of the points on the sliding surface are conducted.The classi fi cation of stable/unstable displacement e time curves is proposed.The de fi nition of the main sliding direction of a landslide is also suggested in such a way that the failure body of landslide(simpli fi ed as"collapse body")is only involved in the main sliding direction,and the strike and the dip are the same as the collapse body.The rake angle is taken as the direction of the sum of sliding forces or the sum of displacements in collapse body,in which the main slip direction is dependent on progressive deformation.The reason of non-convergence with fi nite element method(FEM)in calculating the stability of slope is also numerically analyzed,in which a new method considering the slip surface associated with the boundary condition is proposed.It is known that the boundary condition of sliding surface can be described by perfect elasto-plastic model(PEPM)and JCM,and that the stress and strain of a landslide can be described properly with the JCM.     

Experimental investigation of a reinforced soil retaining wall with a flexible geogrid-wrapped ecological bag facing

This paper presented a field study of the reinforced soil wall (RSW) with a geogrid wrap-around facing. In addition to the conventional monitoring content, the strain of the face-wrapping geogrid, which was neglected in most previous studies, was monitored during the construction process. The positional relationship between the maximum vertical earth pressure and horizontally laid geogrid strain was revealed by using the proposed oblique dragging effect. It was found that the strain on the face-wrapping geogrid occurred mainly in the early stage of construction. The oblique dragging effect existing in the flexible RSWs increased the vertical earth pressure and changed its distribution law, resulting in the position of the maximum vertical soil pressure appearing behind the position of the maximum horizontally laid geogrid strain. The horizontal earth pressure at different positions behind the wall was obviously lower than the theoretical result by using Rankine's theory. Also, a modified 0.3H method (where H refers to the wall height) was presented to account for the slope of the wall face, which could be used to determine the potential sliding surfaces for single-stage RSWs and two-tier RSWs with small offset.     

土工格栅加筋土挡墙现场试验分析

通过埋设水平土压力盒、柔性位移计,对模块式土工格栅加筋土挡土墙墙后的水平土压力和格栅水平变形进行了系统监测,采用加筋组合法对加筋土挡墙的土压力进行了计算,与实测、交系数法所得数据对比分析,得出采用该方法计算的土压力更能合理地解释工作状态下加筋土挡墙的土压力分布规律;对比分析了施工阶段和竣工后格栅的应变,得出拉筋应变主要发生在施工阶段,工后应变较小,并结合试验结果,提出了关于施工控制的相关建议.     

防渗墙钻孔压水试验渗流参数研究

 钻孔压水试验所得到透水率及渗透系数仅限于半无限域岩体,若条形域防渗墙钻孔压水试验仍沿用半无限域公式计算其渗流参数显然不合适。针对防渗墙几何形状和钻孔压水试验原理,在基于稳定流承压完整井的渗流场条件下,采用复变函数方法将条形域中井流问题变换到半无限域中,再代入直线补给边界稳定流承压完整井流公式求解,从而导出条形域防渗墙上钻孔压水试验渗流参数求解表达式。提出对条形域与半无限域流量比Q?/Q和渗透系数比k?/k进行分析,讨论防渗墙与钻孔几何尺寸L/r0,r0对其影响;当取L/r0＜104.7,r0＜75 mm,k?= k或Q? = Q时,得出条形域流量Q?和透水率q?均大于半无限域,即Q?＞Q,q?＞q,而渗透系数k?＜k。根据条形域与防渗墙两侧的补给边界情况,给出防渗墙钻孔压水试验渗流流量表达式使用条件。经工程实例验证,在土体与墙体渗透系数比k1/k2＞100时按提出的计算方法与芯样室内渗透试验结果基本一致。该研究方法还可将钻孔压水试验推广到其他形状有限域渗流参数求解中。     

水压图教学实验台的研制及实验分析

介绍了水压图教学实验台的构成,通过调节阀门进行了不同水力工况下同程式和异程式管网的水压图实验。     

大底盘建筑主裙楼基础整体连接的可行性与适用性研究

随着现代化建设的发展,大底盘建筑越来越多。为解决主裙楼的差异沉降问题,主裙楼之间的连接方式有三种:沉降缝、沉降后浇带、主裙楼整体连接,目前工程中较多采用后两种连接方式。模型试验、共同作用分析及工程实践表明:大底盘高层建筑随着主楼外裙房面积的增大,厚筏基础的变形特征由刚性、半刚性特征逐渐表现为柔性特征;裙房结构和厚筏基础可以起到一定的扩散荷载及调整不均匀沉降的作用;通过合理的设计,当主裙楼的差异沉降控制在规范许可的范围内时,可以实现主裙楼基础的整体连接。工程实践中可以根据工程具体情况,有针对性地调整地基刚度、筏板刚度或结构刚度,达到控制主裙楼差异沉降的目的,从而实现主裙楼基础的整体连接。     

Biofouling of spiral-wound nanofiltration and reverse osmosis membranes: A feed spacer problem

Biofouling was studied in full-scale and pilot-scale installations, test-rigs and membrane fouling monitors by conventional methods as well as Magnetic Resonance Imaging (MRI). Independent of permeate production, the feed spacer channel pressure drop and biomass concentration increased similarly in a nanofiltration pilot installation. In the presence of a feed spacer the absolute feed channel pressure drop increase caused by biomass accumulation was much higher than when a feed spacer was absent: in both spiral-wound nanofiltration and reverse osmosis systems biofouling is dominantly a feed spacer problem. This conclusion is based on (i) in-situ visual observations of the fouling accumulation, (ii) in-situ non-destructive observations of the fouling accumulation and velocity distribution profiles using MRI, and (iii) differences in pressure drop and biomass development in monitors with and without feed spacer. MRI studies showed that even a restricted biofilm accumulation on the feed channel spacer influenced the velocity distribution profile strongly. Biofouling control should be focused on the development of low fouling feed spacers and hydrodynamic conditions to restrict the impact of biomass accumulation on the feed channel pressure drop increase.     

The influence of the joint between the basement wall and the wood-frame wall on the airtightness of wood-frame houses

An airtight building envelope is crucial to achieve energy efficient buildings. The Norwegian airtightness requirements have become stricter, leading to an increased interest in methods for ensuring airtight building envelopes.The joint between the basement wall and the wood-frame wall is known to be a typical air leakage path. Using laboratory measurements and a statistical experimental design the influence of the 3 factors flatness of the basement wall, the sealing method used in the joint and the load between the wood-frame wall and the basement wall is investigated. The influence of this air leakage on real wood-frame houses is also estimated.The results show that the flatness of the basement wall top surface has a considerable influence on the air leakage, a flatter surface generally leading to less air leakage. The sealing materials have widely differing airtightness properties. The least airtight sealing materials, which also are the non-malleable ones, turn out to be sensitive to the flatness of the basement wall and the load on the wall. The estimates of the influence of the air leakage on real wood-frame houses show that the least flat surfaces should be avoided for the non-malleable sealing materials. It is also seen that if the least favourable sealing method is used, or if the sealing is forgotten, the influence on the total airtightness can be remarkable. However, the results also show that it is possible to make the influence of the joint on the total airtightness negligible.     

Quantitative study of the effect of electromagnetic field on scale deposition on nanofiltration membranes via UTDR

Ultrasonic time-domain reflectometry (UTDR) as an in situ, non-invasive real-time technique has been successfully utilized to quantify membrane fouling and cleaning. This study describes an existing ultrasonic technique for quantitative study of the effect of magnetic fields on CaCO₃ scale deposition on the membrane surface during crossflow nanofiltration (NF). The fouling experiments were conducted with CaCO₃ solution containing Ca²⁺ of 1.8 and 3 mmol/L. The experimental electromagnetic field (EMF) was 0.02 T. A commercial NF membrane and a highly sensitive ultrasonic sensor were used in all the experiments. Results show a good relationship between the ultrasonic measurements and the development of CaCO₃ scale on the NF membrane surface. An increase in the amplitude of differential signal with operation time results from the deposition of the CaCO₃ scale layer. In addition, the movement of the differential signal in the time domain observed is associated with an increase in the thickness of the fouling layer. The UTDR technique is capable of measuring the rate of fouling layer formation under different treatment conditions, i.e. with non-magnetic field (NMF) and EMF. Scale layer of deposited CaCO₃ obtained in the experiment with NMF is denser and thicker than that with EMF. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses imply that the magnetic treatment suppresses the formation of calcite crystals and prefers vaterite and aragonite. Furthermore, the ultrasonic technique is sensitive to the different fouling rate between experiments carried out with 1.8 and 3 mmol/L CaCO₃ solutions. The thickness of the fouling layer measured by weight measurement is consistent with that obtained by UTDR in real time. The thinner and less dense scale layer is the main reason for the slower flux decline. Overall, independent measurements such as the flux-decline data, SEM analysis and weight measurement corroborate the ultrasonic measurements.     

三维排水柔性生态墙在高速公路工程中的应用

以工程实例为背景,对高速公路工程中采用的三维排水柔性生态墙护坡特点和施工方法作了较详细的介绍,并对其施工效果进行了分析与评价,取得了良好的防护与生态效果。     

苏丹大坝勘察岩体压水试验存在问题浅析及试验成果分析研究

在大坝地质勘察中,压水试验是检测岩体渗透性的关键实验。随着科技的发展,利用电脑和人工智能仪器进行压水试验的新方法日益成熟。本文通过介绍新型压水试验仪器,理论计算和操作过程中存在的问题及解决方法,同时结合苏丹Dagash大坝032号钻孔岩体的压水试验结果,分析研究了吕荣值和岩体完整度之间的关系,总结了利用吕荣值判断岩体裂隙发育情况的经验,为类似工程提供一定的参考。     

散粒介质三维应力-组构解析与破坏分析

基于散粒体宏-微观力学分析,首先提出了3类张量的概念,推导了散粒体三维应力-组构关系,接着给出了二维和轴对称条件下的应力-组构解析表达式,并采用双轴和三轴离散元（DEM）模拟结果对解析解进行了验证分析。最后基于应力-组构解析,采用“真应力”的概念分析了散粒体的强度问题。研究结果表明：散粒体中的应力分布受3类张量的共同影响,双轴与三轴的离散元模拟与解析关系较吻合。在略去了高阶项后,二维应力-组构关系式与Rothenburg等提出的表达式一致。进一步的分析表明：散粒材料强度受控于“真应力”,表观活动摩擦角的变化实质是颗粒摩擦和各向异性组构共同作用的结果。研究成果可以用于分析散粒体各向异性强度特征和本构关系。     

谈外墙外保温系统的现场拉拔

介绍了外墙外保温系统的构成,对外墙外保温系统中基层与胶粘剂的粘结强度进行了现场拉拔,分析了现场拉拔的要求及测点的选取方法,并对影响测值的各种因素作了研究,为实现检测数值的准确性奠定了基础。     

空调水系统中定压差控制水力平衡措施相关问题探讨(一)——自力式压差平衡阀的选型

为了更好地研究定压差控制对电动调节阀实际流量特性的改善程度,提出了自力式压差平衡阀选型的三要素:阀门公称压力、控制压差和流量系数。分析了四类典型空调水系统中各末端自力式压差平衡阀的计算工况,并按某算例对各系统的末端自力式压差平衡阀进行了实际选型。