干湿循环效应下玄武岩纤维加筋黄土三轴剪切力学行为研究

通过干湿循环效应下的数字图像三轴剪切试验、CT扫描试验及扫描电镜SEM(scanning electron microscopy)试验,研究了玄武岩纤维加筋黄土干湿循环过程的三轴剪切力学行为及微细观结构演化机制。结果表明:随干湿循环次数增加,纤维含量较高试样的三轴剪切鼓胀破坏形态转变为剪切带破坏;干湿循环早期阶段,剪切破坏形态随纤维含量增加,由剪切带破坏转变为鼓胀破坏。干湿循环作用和纤维含量对应力-应变曲线的类型及特征无明显影响,均表现为应变硬化型。破坏偏应力随干湿循环次数增加而逐渐减小,但衰减速率逐渐减小;破坏偏应力随纤维含量增大先增加而后减小,呈抛物线变化特征,存在一个最佳纤维含量为0.6%。CT数均值ME值呈现与破坏偏应力相似的变化规律。干湿循环作用下筋-土界面产生一定的开裂和松弛现象,弱化了纤维的加筋效应,但与素黄土相比,纤维加筋黄土的微观结构表现出显著的整体稳定性。构建了干湿循环效应下玄武岩纤维加筋黄土的宏细观损伤变量,其表现出一致的变化规律。

玄武岩纤维加筋黄土力学参数优化试验研究

为了研究玄武岩纤维加筋黄土的力学性能,通过正交试验设计进行无侧限抗压强度试验,并采用极差分析和方差分析相结合的方法对试验结果进行分析,研究了含水率、纤维掺量、压实度等3个主要因素对玄武岩纤维加筋黄土无侧限抗压强度影响的主次顺序。随后还基于分析结果进行固结不排水三轴压缩试验,进一步研究了纤维掺量对玄武岩纤维加筋黄土抗剪强度指标的影响规律。研究结果表明:影响玄武岩纤维加筋黄土抗压强度的主次因素顺序依次为纤维掺量、含水率、压实度;方差分析得到的最优水平组合为纤维掺量0.4%、含水率11%、压实度0.95;玄武岩纤维的掺入能够有效提高抗剪强度,凝聚力随掺量的增加先增后减,而内摩擦角波动区间较小;玄武岩纤维加筋黄土的应力-应变关系总体能够较好地符合双曲线模型,其拟合结果b值随围压增大而减小,随纤维掺量增加而先增后减,且纤维掺量存在0~0.2%这一临界区间。

玄武岩纤维-石灰-火山灰联合固化淤泥的强度特性

废弃淤泥再利用是绿色施工的重要途径。采用火山灰和生石灰作为固化剂,玄武岩纤维作为加筋材料,对淤泥进行固化处理。通过室内试验,探讨淤泥含水率、固化剂掺入比、纤维加筋率、龄期与无侧限抗压强度(UCS,unconfined compression strength)、劈裂抗拉强度(STS,splitting tensile strength)之间的关系。在干湿循环作用下,分析含水率、固化剂和纤维掺入量对固化土UCS的变化规律。结合X射线衍射(XRD,X-ray diffraction)和电镜扫描(SEM,scanning electron microscopy),分析固化土的水化产物和纤维加筋作用。力学试验表明:重塑淤泥含水率53.75%、固化剂掺入比15%,得出当生石灰/固化剂(火山灰和生石灰)占比0.5,固化土能获得较高的UCS。劈裂试验得出固化土内掺入0.8%的纤维,能够获得较高的STS。龄期28 d时,掺入0.8%的纤维比未掺入纤维的固化土,UCS和STS分别提升6.5%~28.6%、48.7%~78.6%。随龄期延长,固化土的含水率和孔隙比均有减小的趋势,无侧限抗压强度逐渐增大。经历6次干湿循环,固化土内加入0.8%的纤维比未加入纤维的UCS增加15.8%~59.7%。XRD试验结果表明:固化土体内主要水化产物为氢氧化钙、水化硅酸钙凝胶。固化土经历干湿循环,XRD图谱中出现碳酸钙衍射峰。另外,从SEM图中观察到片状氢氧化钙和纤维状水化硅酸钙,该水化产物能够填充固化土的孔隙。研究成果有助于揭示固化淤泥土强度规律,进而为工程应用提供参考。

玄武岩纤维加筋土的动本构特性试验研究

为了从动力学角度研究玄武岩纤维对土的加筋作用,将长为6 mm的玄武岩纤维分别按一定的质量比掺入黄土中,通过动三轴试验研究纤维含量、含水率以及固结围压对玄武岩纤维加筋土的动应力-应变关系、动弹性模量和阻尼比的影响。试验结果表明:①玄武岩纤维加筋土和无筋土的动应力-应变关系曲线可以用H-D双曲线模型拟合;②与无筋土相比,当动应变相同时玄武岩纤维加筋土的动应力增大;③提升固结围压或减小试样含水率均可增大玄武岩纤维加筋土的动弹性模量,但该模量受纤维含量的影响不明显;④可通过增加纤维含量,或在有效区间内增大含水率来增大玄武岩纤维加筋土的阻尼比。

海洋环境下玄武岩纤维加筋砂土抗液化性能的试验研究

历史资料表明,海域砂土液化引起的场地失效是造成震害的重要原因之一。本文围绕海洋腐蚀环境下的砂土抗液化性能的提升需求,通过室内试验探讨了玄武岩纤维加筋砂土在海洋环境下的抗液化特征:研究了纤维含量对波浪荷载作用下饱和砂土抗液化强度、超静孔隙水压力,以及应力—应变发展特征的影响。试验结果表明:纤维的掺入能够有效提高砂土在海洋环境下的抗液化强度,但存在纤维含量的阈值,纤维加筋增强法不会改变砂土的液化模式,在波浪低频荷载作用下,砂土呈现出了明显的剪胀特征,纤维含量对临界状态应力比具有显著影响,对相转换状态应力比影响较小,研究成果为海洋工程中纤维加筋土的推广应用提供了有价值的参考。

纤维加筋黄土的三轴蠕变试验研究

进行了纤维加筋黄土的三轴固结排水蠕变试验,通过对初始含水率、加筋率和围压的不同控制,分析了加筋黄土的蠕变特性,得到了以下几点结论:在黄土中掺入玄武岩纤维可以有效改善黄土试样的蠕变情况,蠕变变形的抑制效果与加筋率没有明显单调关系,存在最优加筋率;随着含水率的升高,加筋土的蠕变变形增大,加筋效果降低,偏应力越大该现象越明显;随着围压的增大,加筋黄土的蠕变变形降低,加筋效果增大,偏应力越大,该现象越明显;以Mesri蠕变模型为基准,对试验曲线进行模拟,计算出模型各参数,经验证,纤维加筋黄土的三轴蠕变特性可以用Mesri模型拟合。

Strengthening effects of BFRP on reinforced concrete beams

Reinforced concrete （RC） beams externally bonded with basalt fiber reinforced polymer （BFRP） are experimentally investigated by using different numbers of bonding plies, transverse anchorages as well as the initial conditions of strengthened beams. The performances of the BFRP strengthening are compared with those of the carbon fiber reinforced polymer （CFRP） and the glass fiber reinforced polymer （GFRP） under the same experimental condition. Experimental results indicate that the strength and ductility of the strengthened beam with two plies of the BFRP are improved remarkably than those with one ply. The strengthening effects of the BFRP lie between those of the CFRP and the GFRP. The BFRP strengthening is little influenced by pre-cracks of concrete. Most failures are caused by interfaciai debonding induced by flexural cracks in the experiment. Clamping of Uwraps along the whole beam is less efficient than endpoint anchorage for increasing the ultimate load of the strengthened beam. Finally, the models suggested by the five guidelines for predicting the debonding strain of the CFRP are extended to the BFRP and the conservative estimates of the debonding strain of the BFRP are given as well.

Experimental study on mechanical properties of basalt fiber-reinforced silty clay

Fiber reinforcement technology can significantly improve the mechanical properties of soil and has been increasingly applied in geotechnical engineering.Basalt fiber is a new kind of environment-friendly and highperformance soil reinforcement material,and the mechanical properties of basalt fiber-reinforced soil have become a hot research topic.In this paper,we conducted monotonic triaxial and cyclic triaxial tests,and analyzed the influence of the fiber content,moisture content,and confining pressure on the shear characteristics,dynamic modulus,and damping ratio of basalt fiber-reinforced silty clay.The results illustrate that basalt fiber can enhance the shear strength of silty clay by increasing its cohesion.We find that the shear strength of reinforced silty clay reaches its maximum when the fiber content is approximately 0.2%and the moisture content is 18.5%(optimum moisture content).Similarly,we also find that the dynamic modulus that corresponds to the same strain first increases then decreases with increasing fiber content and moisture content and reaches its maximum when the fiber content is approximately 0.2%and the moisture content is 18.5%.The dynamic modulus is positively correlated with the confining pressure.However,the change in the damping ratio with fiber content,moisture content,and confining pressure is opposite to that of the dynamic modulus.It can be concluded that the optimum content of basalt fiber for use in silty clay is 0.2%.After our experiments,we used scanning electron microscope(SEM)to observe the microstructure of specimens with different fiber contents,and our results show that the gripping effect and binding effect are the main mechanisms of fiber reinforcement.