麦秸秆的筋土摩擦性能及加筋作用

为研究麦秸秆加筋土的筋土作用与加筋效果,以含水率、干密度及麦秸秆埋置深度为影响因素,开展了麦秸秆与盐渍土的拉拔摩擦实验;完成了盐渍土、麦秸秆加筋盐渍土、石灰固化土、麦秸秆与石灰加筋固化土的抗压实验和三轴压缩实验。结果表明:麦秸秆与盐渍土的拉拔摩擦强度随含水率的增大而减小,随干密度和埋置深度的增加而增大,干密度、含水率、埋置深度对筋土摩擦作用的影响程度依次减小;与盐渍土及石灰固化土相比,麦秸秆加筋大幅提高了土的抗压强度、抗剪强度与抗变形性能。麦秸秆具有良好的筋土摩擦性能和加筋效果,麦秸秆加筋能有效增强土的力学性能。     

麦秸秆加筋盐渍土的筋土界面综合抗剪强度试验

盐胀、溶陷和吸湿软化等不良特性,易引起滨海盐渍土的低强度和大变形问题。以麦秸秆作加筋材料,可以实现提高盐渍土的抗剪强度和抗变形性能的目的。为测试麦秸秆加筋土的抗剪强度,完成了麦秸秆与盐渍土的界面直剪摩擦试验。水平铺设麦秸秆,以含水率、干密度、加筋间距、麦秸秆有无茎节为条件,分析四种制样条件对筋土界面抗剪强度的影响。鉴于整个剪切界面上存在筋/土和土/土的两种摩擦作用形式,因此将其称为界面综合抗剪强度。试验结果显示:界面综合粘聚力和界面综合内摩擦角均随含水率和加筋间距的增大而逐渐减小,随着干密度的增大逐渐增大,且有茎节的大于无茎节的。研究证实了剪切界面上存在着筋/土和土/土两种摩擦作用,两者共同发挥作用,提高了麦秸秆加筋土的抗剪强度,两者对强度增长的贡献率取决于筋土面积比(加筋间距)。     

基于钻孔式锚固单元体试样的锚-土界面剪切特性研究

为探究土体干密度和含水率对锚杆锚固体-红土界面剪切特性的影响,研制了一种钻孔成孔的锚杆单元体试样制作装置。制备了6组不同土体含水率、不同干密度的红土锚固单元体试样,测试其界面剪切特性,获得了锚-土界面剪应力-剪切位移全过程曲线(τ-s曲线),并同步开展相应土体的直剪试验,获得了土的抗剪强度包线。试验结果表明:随着含水率的降低,土体黏聚力和内摩擦角均呈减小趋势,而随着干密度的增大,土体黏聚力显著增加;随着土体含水率和干密度的增大,锚-土界面剪切τ-s曲线逐渐由应变硬化转变为应变软化,且含水率越高,软化特征越明显;此外,随着土体干密度的增大,锚-土界面剪切强度增加,峰值位移减小,界面剪切刚度增大,而随着土体含水率的增大,锚-土界面剪切强度减小,峰值位移也减小。最后,通过回归分析建立了锚-土界面剪切强度随土体黏聚力和内摩擦角变化的经验公式。     

土工格栅加筋土三轴试验研究

通过三轴试验方法研究土工格栅加筋土的强度及变形破坏特性,探论了在不同加筋情况下,土工格栅加筋土强度影响因素及其变化规律,分析了素土和土工格栅加筋土的变形破坏形式及筋材在土体抗剪破坏过程中的变形机理.试验结果表明:(1)加筋后土体的强度和抵抗变形的能力明显增强.(2)在加筋层数一定的情况下,随着围压的增加加筋土强度明显增强,加筋效果显著增加.(3)在围压一定的情况下,随着加筋层数的增加加筋土强度增强,加筋效果显著增加.(4)对于强度加筋效果系数和规格化强度分析发现,在中围压下,加筋土加筋效果最合理最有效.(5)土工格栅加筋土应力应变关系采用固结围压作为归一化因子进行处理可得到一个统一的数学表达,即归一化公式,具有很好的归一化特性.本研究结果对于深入研究土工格栅加筋土加固机理和加筋土工程具有指导意义.     

膨胀土纤维加筋的强度特性机理研究

将黄麻纤维掺入膨胀土试样,选取黄麻纤维在土中的分布角度和纤维掺加量等参数对纤维加筋土进行不固结不排水三轴实验,黄麻纤维的掺入可以有效的提高土体的抗剪特性,提高土体的抗剪强度指标值,纤维对黏聚力的影响范围大于对内摩擦角的影响范围。当纤维掺加量为0.2%时,黄麻纤维的加筋效果最好,纤维掺加量存在最优值。纤维加筋的微观机理取决于纤维表面与土中颗粒表面的摩擦力和黏聚力。     

某工程加筋土挡土墙施工及位移分析

加筋土挡土墙一般由基础、面板、拉筋带(或土工格栅)、土体填料组成，其加筋土是由多层水平加筋材料与填料铺设而成的一种复合材料，在共同受力、协调变形中，由于拉筋带的作用对土体产生附加侧向约束，使土的抗剪强度得以提高，并使加筋土的承载力比无筋土高得多。加筋土挡土墙墙面板的作用是防止土在拉筋间松动，承受剩余侧压力、保持墙的设计形状及外观。加筋土中拉筋的功能是通过拉筋抗拉强度及拉筋与填土间接触面的摩擦阻力来限制土体的应变，从而增加土的强度及加筋土结构的稳定性。     

玄武岩纤维加筋黏土的剪切强度特性

为了了解玄武岩纤维加筋黏土的剪切强度特性,将玄武岩纤维丝均匀地掺入黏土中,在控制含水率和干密度的条件下,进行了直剪试验,并借助扫描电镜,从微观层面对剪切面上的土体进行了观察。试验中,按纤维与干土质量的百分比0.0%,0.15%,0.25%,0.35%配制了试样,并从400 k Pa压力下的剪切面中选取代表性土样进行微观测试。直剪试验结果表明:随着纤维掺量的增加,土样的黏聚力c不断增大;和素土相比,在掺量不超过0.25%时,加筋土样的内摩擦角φ变化不大,当掺量达到0.35%时,内摩擦角φ有突然且较为显著的增大。SEM结果表明:掺量为0.25%时,纤维在土体中的离散程度最高,纤维与土体间的作用方式主要为握裹作用和纤维网作用;剪切过程中,纤维在土体中易发生滑移和磨损,其中玄武岩纤维的磨损不同于其它纤维,主要表现为端部的磨损,表面仍较为平整。     

轮胎加筋土抗剪强度数值分析研究

为了更好地进行数值计算和预测加筋土的抗剪强度,分析了直剪试验数据,建立回归方程,为工程实践提供理论依据。首先利用弹塑性理论分析加筋土抗剪强度,探讨剪切机理。在比较了相关直剪试验数据处理方法后,针对笔者前期轮胎条加筋土直剪试验数据进行多元回归分析,并利用数值模拟方法将实测值与回归模型计算值做对比来检验多元回归模型的精确度。研究发现轮胎加筋材料的掺入可以增加土体破坏时的轴向应变和土体的抗拉能力,减小土的侧向变形,从而提高了黄土的抗剪强度。建立的回归模型计算结果与实测值较吻合,可以作为加筋土界面抗剪强度数值分析与计算依据。     

粉砂土岸坡三维加筋生态护坡结构力学效应研究

加筋生态护坡是土工织物与植草相结合形成的一种护坡形式,在保证工程生态性的同时大大提高了生态护坡的强度,有广泛的应用前景。以黑龙江同抚堤防工程粉砂土岸坡防护工程为例,开展了三维加筋生态护坡结构的现场原位测试与加筋土体力学特性室内试验研究,揭示了该护坡技术固土护坡力学效应。试验结果表明:对比纯植被护坡和遮阳网表层覆盖护坡方式,三维加筋生态护坡结构对土体加筋作用最为有效。土工网可以帮助植被根系在岸坡表层形成良好的加筋层,而植被根系则帮助土工网与岸坡土体更紧密地结合。加筋生态结构效果主要表现为增加了土体黏聚力,但对内摩擦角影响不大;一个生长周期内草本型植被根系加筋区域集中在地面以下20cm左右的深度;土体含水率和含根量对根土复合体抗剪强度有明显影响,随着土体中含根量和含水率的增加,根土复合体抗剪强度呈先增加后减少的趋势,即对于高羊茅这类抗剪型根系,其加固土体时存在最佳含根量和含水率使其强度最高。     

干湿循环对玄武岩纤维加筋膨胀土抗剪强度的影响

为了对膨胀土进行改良,将分散玄武岩纤维掺入膨胀土中,研究干湿循环对玄武岩纤维加筋膨胀土的抗剪强度的影响规律。试验选取长12mm玄武岩纤维,以按纤维含量与干土质量比为0.4%掺入膨胀土中。对膨胀土和纤维加筋膨胀土进行0~3次干湿循环试验,然后对试样进行直接剪切试验,研究干湿循环对玄武岩纤维加筋膨胀土抗剪强度的影响。试验结果表明:玄武岩纤维掺入膨胀土能有效提高膨胀土的抗剪强度。膨胀土和纤维加筋膨胀土经过反复干湿循环后,其强度指标持续降低,且在第一次干湿循环之后抗剪强度降低较明显,之后抗剪强度降低幅度变小。相对于内摩擦角,纤维对黏聚力的增强效果要明显得多。同一次干湿循环,纤维加筋膨胀土比素膨胀土强度的降低幅度小。     

基于单根纤维拉拔试验的波形纤维加筋土界面强度研究

纤维/土界面间的力学作用特性是决定纤维加筋土工程性质的关键因素。为了改善纤维/土界面作用力,开发了一种新型的波形纤维作为加筋材料,并自主设计了一套拉拔试验装置,对单根纤维加筋土开展了多组拉拔试验,定量获得了波形纤维加筋土的拉拔特性及界面剪切强度,通过与传统直线形纤维对比,分析了波形纤维/土界面的力学作用机理,并从理论上探讨了波形纤维的最大临界加筋长度。结果表明：提出的单根纤维拉拔试验方法及设计的试验装置为研究纤维/土界面力学作用提供了有效的途径,试验结果具有较好的可重复性;直线形纤维的拉拔曲线呈典型的单峰特征,拉力达到峰值后迅速减小到残余值并逐渐趋于稳定,而波形纤维的拉拔曲线呈显著的多峰特征,曲线波长与纤维的波长基本一致;通过对比,波形纤维/土界面剪切强度明显高于直线形纤维,强度值提高了178%,极大改善了纤维的加筋效果,此外,波形纤维拉拔曲线各峰值对应的界面剪切强度及残余剪切强度随拉拔位移呈指数递减趋势;利用测得的纤维/土界面剪切强度,结合纤维自身的抗拉强度和一些假设条件,能确定纤维的最大临界加筋长度,对实际工程设计有一定参考意义。     

Interfacial shear strength of fiber reinforced soil

The interfacial mechanical interaction between the reinforcement and soil matrix is a key factor in controlling the engineering properties of reinforced soil. To evaluate the factors affecting the interfacial strength properties of polypropylene fiber (PP-fiber) reinforced soil, single fiber pull-out tests were performed by using a modified special apparatus. It has been found that the designed pull-out test is an efficient method to qualitatively obtain the interfacial peak strength (IPS) and interfacial residual strength (IRS) of fiber/soil. Both the IPS and IRS decrease with water content increase, while increase with increasing soil dry density. The cement inclusions dramatically improve the interfacial shear strength of fiber/soil, and the IPS and IRS increase with an increase in additives content and curing time. Finally, by using scanning electron microscopy (SEM), the micromechanical interaction behavior between soil particles and fiber reinforcement were discussed. The interfacial shear resistance of fiber/soil depends primarily on the rearrangement resistance of soil particles, effective interface contact area, fiber surface roughness and soil compositions, etc.     

Effects of freeze-thaw cycles on the unconfined compressive strength of straw fiber-reinforced soil

Although natural fibers can improve the strength behavior of frozen-thawed soil, the reinforcing mechanism is still not fully understood. To investigate the effects of freeze-thaw cycles on the strength of natural fiber-reinforced soil, unconfined compression tests, single-fiber pull-out tests and scanning electron microscopy (SEM) tests under 0, 3, 5, 10, 15, and 20 freeze-thaw cycles were conducted on cotton straw fiber-reinforced soil. It was found that the unconfined compressive strength (UCS) of fiber-reinforced soil decreases exponentially with the number of freeze-thaw cycles. In addition, fiber reinforcement weakens the softening degree of frozen-thawed soil under unconfined states. The UCS reduction in fiber-reinforced soil under freeze-thaw conditions is smaller than the strength reduction at the fiber-soil interface because fiber reinforcement is mainly governed not only by the fiber-soil interface but also by the spatial stress network established by discrete fibers. The complex spatial stress network, which improves the reinforcement of the fibers, is monitored by SEM after freeze-thaw cycles.     

基于三轴试验的非饱和土抗剪强度影响因素分析

已有的研究成果表明,含水量和干密度等物性指标对非饱和土的抗剪强度具有较大的影响,因此,有必要从试验的角度探讨含水量和干密度对非饱和土的抗剪强度的影响规律。通过三轴剪切试验,开展了控制含水量和干密度的重塑非饱和土的试验测试,试验结果表明,含水量和干密度是影响非饱和土抗剪强度的重要因素,最佳含水量和最大干密度是应力-应变关系相互转化的临界点。     

Effect of discrete fibre reinforcement on soil tensile strength

The tensile behaviour of soil plays a significantly important role in various engineering applications. Compacted soils used in geotechnical constructions such as dams and clayey liners in waste containment facilities can suffer from cracking due to tensile failure. In order to increase soil tensile strength, discrete fibre reinforcement technique was proposed. An innovative tensile apparatus was developed to deter- mine the tensile strength characteristics of fibre reinforced soil. The effects of fibre content, dry density and water content on the tensile strength were studied. The results indicate that the developed test apparatus was applicable in determining tensile strength of soils. Fibre inclusion can significantly in- crease soil tensile strength and soil tensile failure ductility. The tensile strength basically increases with increasing fibre content. As the fibre content increases from 0% to 0.2%, the tensile strength increases by 65.7%. The tensile strength of fibre reinforced soil increases with increasing dry density and decreases with decreasing water content. For instance, the tensile strength at a dry density of 1.7 Mg/m^3 is 2.8 times higher than that at 1.4 Mg/m^3. It decreases by 30% as the water content increases from 14.5% to 20.5%. Furthermore, it is observed that the tensile strength of fibre reinforced soil is dominated by fibre pull-out resistance, depending on the interracial mechanical interaction between fibre surface and soil matrix.     

纤维加筋土坯的蒸发过程及抗拉强度特性

土坯作为一种生态、低碳和环保的建筑材料,其力学性能是学界和工程技术人员关注的重点.为了提高土坯的综合抗拉特性,提出采用纤维加筋技术对土坯进行改性处理.通过模拟土坯的形成过程,制备了一系列不同纤维掺量(0～0.2％)、初始含水率(16.5％～20.5％)和干密度(1.50～1.70 g/cm3)的压实土坯试样,进行自然干...     

Static liquefaction behavior of saturated fiber-reinforced sand in undrained ring-shear tests

The problem of static liquefaction of sand is nowadays a classical soil mechanics subject. Using a ring-shear apparatus, we explore the possibility of fiber reinforcement as a new method to improve the liquefaction resistance of sand. In order to understand the effect of the fiber content and sand density on the static liquefaction behavior of fiber-reinforced sand, a series of undrained ring-shear tests were carried out on saturated samples with different fiber content and sand density, and the test results and mechanisms of fiber reinforcement were then analyzed. The results indicate that the undrained shear behavior of fiber-reinforced loose samples is not greatly influenced by the presence of fiber, but for medium dense and dense samples, the presence of fiber clearly affects their undrained behavior. Untreated specimens showed a continuous decrease in shear resistance after failure, while the specimens treated with fiber showed fluctuations even after shear failure, and these fluctuations become stronger with increasing fiber content. The peak shear strength increases with the fiber content, especially in dense specimens. After shearing, all the fiber-reinforced and untreated dense samples maintained structural stability, while the unreinforced loose samples showed a completely collapse of structure. The presence of fibers may thus limit or even prevent the occurrence of lateral spreading that is often observed in unreinforced sand.     

微生物固化纤维加筋砂质黏性紫色土试验研究

微生物诱导方解石沉积(MICP)技术是一种新型土体加固措施,大量的研究表明,土体加固强化的同时也使得土体破坏呈现明显脆性。为了改善微生物固化紫色土的脆性破坏模式,采用纤维加筋与微生物固化相结合的加固方法,将质量分数为0.4%、0.6%、0.8%的纤维与紫色土混合,然后采用巨大芽孢杆菌和钙盐溶液对土样进行不同灌浆次数的固化试验(3次、5次、7次、9次)。通过无侧限压缩试验测定试样抗压强度,洗酸法试验测定试样碳酸钙含量,烘干法测定试样干密度,结果表明:(1)在微生物固化紫色土中掺入纤维,能显著提高试样固化后的无侧限抗压强度和峰值强度对应的轴向应变,改善了土体破坏时的韧性;(2)纤维掺量影响微生物固化紫色土的力学性质,其强度随纤维掺量总体上呈先增大后减小的趋势,最优纤维掺量为0.6%;(3)随着固化时间增加,试样的碳酸钙生成量和干密度逐级增加,强度与碳酸钙生成量呈正相关且有效碳酸钙沉积越来越少,强度趋于稳定;(4)纤维加筋可以提高碳酸钙沉积的效率和产量,土样内生成的碳酸钙对纤维加筋效果具有强化作用。研究成果可以为纤维加筋与MICP固化相结合的土体加固技术应用提供指导和参考。     

击实砾质土抗拉强度试验研究

抗拉强度是黏性土的一个比较重要的力学性质,由于在工程中使用相对较少,对其研究并不多。实际上,诸如土体裂缝、坍塌、土石坝心墙水力劈裂等不少工程问题都与抗拉强度有着密切的关系。对3种砾质土进行击实试样的抗拉强度试验,研究抗拉强度随试样干密度、前期固结压力和含水率等的变化规律。试验结果表明,击实砾质土抗拉强度随着干密度的增加而增加,增加幅度显著;随着前期固结压力的增加,土的抗拉强度也增大,但在试验范围内(固结压力100～500kPa)增大并不明显。随着含水率的增加,抗拉强度稍有减小。在所试验的含水率、密度和前期固结压力范围内,试验得到的砾质土抗拉强度为20～80kPa。     

棕榈纤维加筋土强度特性试验研究

通过无侧限抗压与直接剪切试验,研究了不同干密度与加筋率对棕榈纤维加筋土强度特性的影响.试验过程中,设置干密度为1.55 g/cm3、1.6 g/cm3、1.65 g/cm3,加筋率为0、0.2％、0.4％、0.6％,在最优含水率下进行正交试验,并对其加固机理进行分析.结果表明:棕榈纤维可有效提高试样的无侧限抗压强度和抗...