干湿循环作用下混凝土抗拔性能试验研究

对经历干湿循环作用后的钢筋与不同强度混凝土的界面力学进行了拉拔试验研究,比较分析了不同干湿循环次数下不同混凝土强度与钢筋的界面拉拔试验力的变化、界面的破坏模式、以及宏观与微观间的联系。研究结果表明：（1）钢筋混凝土在拉拔过程中呈现两种破坏模式：低强度混凝土的挤压膨胀破坏,高强度混凝土的剪切破坏。（2）随着混凝土强度的增加,初始拉拔力峰值逐渐增大,经历干湿循环作用后不同强度混凝土拉拔力变化不同,经历干湿循环作用后,低强度混凝土拉拔力峰值逐渐增大,而高强度混凝土拉拔力峰值逐渐降低。（3）核磁试验中通过孔隙的变化情况验证了宏观拉拔力学的规律。（4）混凝土抗拔性能试验研究证明,实际工程中低强度混凝土更加适用于工场活动中。     

混凝土无机料植筋考虑重复荷载时的锚固性能

对无机料植筋试件进行了直接拉拔和重复荷载拉拔试验,测得了无机料植筋的粘结——滑移曲线,结合试验结果分析了不同试验条件下出现的不同破坏形态,从而确定了植筋的破坏形态及粘结锚固性能的影响因素。     

胶合木自攻螺钉拉拔锚固性能试验研究

进行了不同锚固长度自攻螺钉拉拔强度的试验。研究了自攻螺钉拉拔的破坏形态,不同锚固长度以及自攻螺钉直径对拉拔强度的影响。试验结果表明:绝大多数试件发生木材的剪切破坏和自攻螺钉屈服破坏,个别试件发生劈裂破坏。自攻螺钉连接的拉拔承载力随锚固长度的增加而增大,当锚固长细比达到16时,试件发生自攻螺钉屈服破坏,属延性破坏;弦向锚固试件极限拉拔荷载均大于径向锚固试件。     

土工格栅纵横肋的筋土承载特性分析

为研究土工格栅纵横肋与砂土的界面受力特性,进行了不同法向压力的格栅拉拔试验,分别设计了横向与纵向剪除横肋的6种拉拔试验工况,研究横肋减少对格栅受力、拉拔阻力峰值和位移及似摩擦系数的影响,并分别对比了整体剪切和刺入剪切破坏模式下的格栅拉拔阻力,揭示格栅筋土界面的相互作用机理。结果表明,随着横肋的减少,格栅拉拔阻力和似摩擦系数不断地变小;横肋沿横向减少的格栅最大拉拔阻力大于横肋沿纵向减少的最大拉拔阻力,完整横肋有助于筋土界面的加筋作用的充分发挥。理论计算格栅界面摩擦力约为18%~19%的试验拉拔阻力,而试验获得的格栅界面摩擦力与试验拉拔阻力的比值为29%~33%,横肋与土体挤压咬合产生的承载力分量占了总拉拔阻力的67%~71%,横肋极大提高了土工格栅的拉拔阻力。     

格栅与粉土的拉拔试验研究

根据一般拉拔试验的原理,采用反力架、钢筋焊接试验槽、应力环等设备对格栅与粉土间的拉拔试验做了全面的研究。试验过程中综合考虑了不同的含水量和不同的竖向压力对格栅与土体间摩擦系数的影响,从而得出了不同的摩擦系数。     

高强钢筋高强混凝土粘结锚固性能研究

对不同类型的钢筋混凝土构件进行了拉拔加载试验,对三种不同类型的钢筋锚固混凝土试件在拉拔过程中的破坏过程和状态进行了观察和分析。结果表明,高强螺旋肋钢筋在拉拔载荷作用下具有良好的锚固性能。     

高温下植筋试件拉拔试验

设计制作了25个试件,试件的植筋深度为lOd和15d,分别在高温下进行拉拔试验,来研究不同温度对不同植筋深度的钢筋拉拔承载力的影响。试验中,记录混凝土内部的温度与不同混凝土内部温度下的植筋拉拔承载力。分析了高温和常温下具有相同植筋深度试件的承载力,高温下不同植筋深度试件的拉拔承载力,并拟合出粘结应力和温度的关系。试验结果表明,高温对植筋的拉拔承载力和锚固段粘结力有明显的影响;当温度高于350℃后,高温下植筋的承载力降低为常温下的10％～20％。     

基于不同界面剂的新老混凝土黏结抗拉强度试验研究

通过对采用不同界面剂的新老混凝土界面的黏结强度进行钻芯拉拔强度试验研究,并进行试验数据分析与比较,得到了不同的界面剂对提高钻芯拉拔强度的提高幅度及其优劣,为工程实际提供依据.     

土工合成材料界面作用特征的拉拔试验研究

针对不同的填充材料和不同的土工合成材料在应用的过程中存在不同的拉拔系数的现象,本文通过拉拔试验分析土工工程当中合成材料的界面作用。探索了我国国产的五种土工合成材料在实践工作过程当中实现加筋的影响。结果表明,加筋工作需要通过具体的试验工作内容进行拉拔系数的确认。     

低超载下条带式带齿加筋界面特性

在提出立体加筋的基础上,对条带式带齿加筋砂土进行了低超载下大量的拉拔试验来研究筋土的界面特性,分析了带齿筋的条带式加筋对拉拔性能的影响,探讨了不同上层覆压下筋条的拉拔力与水平位移的关系以及似摩擦系数f*的变化规律。在试验成果分析的基础上,分析了条带式带齿加筋与砂土的相互作用机理,建立了条带式带齿加筋砂土的拉拔力模型。并将试验结果与理论值比较,二者基本吻合。     

新型可视土工拉拔试验仪的研发与应用

研制了一台新型可视自动采集数据的土工拉拔试验装置,可用于多种土工材料和填料作用下的拉拔试验。该装置改进了加载系统和反力系统,实现了拉拔界面的可视与数据采集的自动化,并可量测土工材料不同嵌固长度处的位移,获取土工材料变形值,探索筋土作用过程中筋材受力机理及界面土体位移变化规律。使用新研制的试验装置开展了以砾类粗粒土为填料的格栅拉拔试验,结果表明:上覆荷载增大,土中格栅的应变变小,土体与格栅的界面摩擦和嵌固作用越显著;筋土界面处土体颗粒存在平移及转动两种运动模式,且界面处土体形成稳定的位移集中带。     

Design concerns and performance of geomembrane anchor trenches

The main purpose of an anchor trench is to secure geosynthetics at the top of slopes. As such, the tendency for most designers is to firmly secure the geosynthetics so that movement or pullout does not occur. However, the basic design consideration should be extended to allow pullout of the geosynthetics from the anchor trench rather than have the geomembrane tear if excess stresses are developed. The emphasis should be placed not on the construction condition, where potential problems may be easily remedied, but on the long-term performance where liner problems may have a greater impact. A realistic design procedure is therefore needed to determine the resistance provided by the anchor trench to check the potential stresses that can be resisted while confirming that the allowable tensile strengths of the geosynthetics are not exceeded.

Following a review of anchor trench designs and methodologies, case studies will be presented to show anchor trenches that have been demonstrated to work. Perhaps more importantly, cases where problems have occurred as a result of poorly designed or constructed anchor trenches will also he presented.     

土工合成材料与土界面的细观研究

利用颗粒流程序（PFC2D）对土工合成材料的拉拔试验进行模拟,着重从细观角度来分析土工合成材料与土的接触界面。通过室内拟合试验,选取和校准离散元的细观参数,土工合成材料用平行黏结模拟,土颗粒采用由3个圆形颗粒组成一个椭圆形团进行数值模拟。数值模拟结果表明,接触界面的厚度为6～7倍平均土颗粒直径,接触界面中的颗粒发生较大相对位移,孔隙率增大,接触数减小。PFC2D为从细观角度研究土工合成材料与土的接触界面特性的理想工具。     

土工合成材料与土界面的细观研究

 利用颗粒流程序(PFC2D)对土工合成材料的拉拔试验进行模拟，着重从细观角度来分析土工合成材料与土的接触界面。通过室内拟合试验，选取和校准离散元的细观参数，土工合成材料用平行黏结模拟，土颗粒采用由3个圆形颗粒组成一个椭圆形团进行数值模拟。数值模拟结果表明，接触界面的厚度为6～7倍平均土颗粒直径，接触界面中的颗粒发生较大相对位移，孔隙率增大，接触数减小。PFC2D为从细观角度研究土工合成材料与土的接触界面特性的理想工具。     

土工格栅横肋与纵肋加筋机理研究

通过室内格栅横、纵肋独立拉拔试验,针对不同的法向荷载和拉拔速度,分别对土工格栅横肋与纵肋的加筋机理进行了研究.结果表明：格栅纵肋所产生的摩擦阻力在拉拔初期迅速增大,并且随着有效应力的增大呈线性增长趋势,拉拔速率对其影响并不大;格栅横肋所产生的被动阻力增长相对较缓,在达到最大值之前需要一定的筋土相对位移,并且随着有效应力和拉拔速率的增大,被动阻力变化明显,其破坏模式逐渐由冲剪破坏转为常规剪切破坏.     

Interface friction: An owner''s perspective

The introduction of geosynthetics to landfill applications has generally resulted in significant environmental protection improvements. Most significant applications have been the use of geomembranes in landfill liners and final covers. Other geosynthetics that are commonly utilized, often in conjunction with and adjacent to geomembranes, include geotextiles and geonets. However, when geosynthetics are used, especially when they are placed adjacent to each other in a liner or final cover configuration, the frictional characteristics of the resulting interfaces can become a very important factor affecting the design, construction and operation of a landfill. The impact of the frictional characteristics of such interfaces and the related potential stability issues on the design, construction and operation of landfills, from a landfill owner's perspective, is the subject of this paper.     

Applicability of clinker ash as fill material in steel strip-reinforced soil walls

The generation of coal ash by coal-fired thermal power plants has increased in recent years. This study focuses on the use of a type of coal ash, clinker ash, in place of sandy soil as a fill material in soil structures. Clinker ash is an excellent geomaterial to use as backfill for soil structures because it is lightweight and has high shear strength and permeability. In this study, to determine the applicability of clinker ash as a backfill material for steel strip-reinforced soil walls, a series of laboratory pullout tests was conducted on different types of clinker ash to investigate the pullout behaviour of a ribbed strip from a layer of clinker ash and to evaluate the influence of the overburden pressure and the degree of compaction on the maximum pullout resistance. The correlation between the physical properties of clinker ash and the maximum pullout resistance was investigated on the basis of the test results. Additionally, the results of the pullout tests were compared with those of in-situ pullout tests. Furthermore, the usefulness of clinker ash was evaluated by applying the pullout test results to the standard design method for reinforced soil walls and comparing the results with the material constants for commonly used sandy soil. The main conclusions of the study are as follows: (1) The tests performed here confirmed that clinker ash has excellent frictional properties compared with sandy soil. (2) The frictional properties of clinker ash exceed the proposed design values given in the manual describing the reinforced soil wall method. (3) The application of clinker ash in reinforced soil walls is effective from the viewpoint of frictional properties.     

Fundamental mechanisms of bonding of glass fiber reinforced polymer reinforcement to concrete

Fundamental mechanisms of bonding between glass fiber reinforced polymer (GFRP) bar and concrete are presented. Contributions from chemical bonding, bearing resistance, and frictional resistance to bond were delineated by measuring the following: the load corresponding to complete debonding of the bar, the load corresponding to onset of sliding and pullout of the bar along the entire embedment length, and the frictional load corresponding to frictional resistance to sliding. Research findings indicate that while chemical bonding was the main contributor to the interfacial bond strength, the other two mechanisms contributed to the pullout strength of the bar. Correlation between the bar’s surface geometry and the contributions from the three mechanisms are discussed.     

A simplified model for evaluating the hardening behaviour of sensor-enabled geobelts during pullout tests

Geosynthetics reinforced soil structures (GRSSs) have a tendency to be large and high, resulting in high normal pressures on the geosynthetics. As one of the effective tests for investigating the geosynthetics-soil interaction, pullout tests are traditionally conducted under low normal pressures. This paper reports pullout tests on a type of sensor-enabled geobelts (SEGB) with different normal pressures (5 kPa, 100 kPa, 200 kPa and 400 kPa) applied. The self-measurement function of SEGB allows the study of the working process of SEGB in pullout tests. Moreover, a simplified theoretical model is proposed to investigate the hardening behavior of geobelts in pullout tests. Two models are incorporated in the theoretical model: a bilinear model capturing the full stress-strain curve obtained from uniaxial tensile tests and a hyperbolic model simulating the geobelt-sand interaction from direct shear tests. By means of the finite-difference method, the numerical solutions of the theoretical model are obtained. The proposed model is validated by comparing calculated and measured front pullout force-displacement curves of SEGB under different normal pressures. Further, the computation of the strain distribution of SEGB sandwiched in the sand is compared with tested data with different front pullout force levels for the aforementioned normal pressures. The numerical solutions generally agree well with the experimental results for all tested tensile force and strain ranges; therefore, the proposed simplified model is suitable for evaluating large quasi-plastic deformations of geobelts and the associated interaction with surrounding sand.