Strength enhancement of geotextile-reinforced carbonate sand

The mechanical behavior of carbonate sand reinforced with horizontal layers of geotextile is invetigated using a series of drained compression triaxial tests on unreinforced and reinforced samples. The main factors affecting the mechanical behavior such as the number of geotextile layers, their arrangement in specimens, confining pressure, particle size distribution, geotextile type and relative density of samples were examined and discussed in this research. To make a precise comparison between the behavior of reinforced siliceous and carbonate sand, triaxial tests were performed on both types of sands. Results indicate that geotextile inclusion increases the peak strength and strain at failure, and significantly reduces the post-peak strength loss of carbonate specimens. The amount of strength enhancement rises as the number of geotextile layers increases while two other parameters including confining pressure and particle size affect adversely. The strength enhancement of reinforced carbonate sand is greater than the corresponding siliceous sample at high axial strains. Reinforced and unreinforced carbonate specimens exhibit more contractive behavior than their corresponding siliceous samples and tend to dilate at higher axial strains. By increasing the relative density of the samples, the peak strength of reinforced specimens rises due to enhanced interlocking between geotextile layers and sand particles. This process continues as long as the geotextile is not ruptured. The utilization of geotextiles with high mass per unit areas was found to be uneconomical due to slight differences between the strength augmentation of geotextiles with high and low mass per unit areas. It should be noted that geotextile layers limit the lateral expansion of specimens which leads to changing the failure pattern from a shear plane to bulging between the adjacent layers of geotextile.     

Effect of geotextile reinforcement on the mechanical behavior of sand

Laboratory triaxial compression tests were carried out in order to determine the stress–strain and dilation characteristics of geotextile-reinforced dry beach sand. The mechanical behavior of the composite material was investigated through varying the number of geotextile layers, type of geotextile, confining pressure, and geotextile arrangement. In order to study the effect of sample-size on the results, tests were performed on samples with two different diameters. The results demonstrated that geotextile inclusion increases the peak strength, axial strain at failure, and ductility. However, it reduces dilation. Such improvements in the behavior of reinforced sand are more pronounced for small-size samples. Failure envelopes for reinforced sand were observed as bilinear or curved. Bulging between layers was detected in reinforced samples which failed.     

Impact of repeated loading on mechanical response of a reinforced sand

Pavements constructed over loosely compacted subgrades may not possess adequate California bearing ratio(CBR)to meet the requirements of pavement design codes,which may lead to a thicker pavement design for addressing the required strength.Geosynthetics have been proven to be effective for mitigating the adverse mechanical behaviors of weak soils as integrated constituents of base and sub-base layers in road construction.This study investigated the behaviors of unreinforced and reinforced sand with nonwoven geotextile using repeated CBR loading test(followed by unloading and reloading).The depth and number of geotextile reinforcement layers,as well as the compaction ratio of the soil above and below the reinforcement layer(s)and the compaction ratio of the sand bed,were set as variables in this context.Geotextile layers were placed at upper thickness ratios of 0.3,0.6 and 0.9 and the lower thickness ratio of 0.3.The compaction ratios of the upper layer and the sand bed varied between 85% and 97% to simulate a dense layer on a medium dense sand bed for all unreinforced and reinforced testing scenarios.Repeated CBR loading tests were conducted to the target loads of 100 kgf,150 kgf,200 kgf and 400 kgf,respectively(1 kgf = 9.8 N).The results indicated that placing one layer of reinforcement with an upper thickness ratio of 0.3 and compacting the soil above the reinforcement to compaction ratio of 97%significantly reduced the penetration of the CBR piston for all target repeated load levels.However,using two layers of reinforcement sandwiched between two dense soil layers with a compaction ratio of 97%with upper and lower thickness ratios of 0.3 resulted in the lowest penetration.     

Centrifuge model tests of geotextile-reinforced soil embankments during an earthquake

The behavior of geotextile-reinforced embankments during an earthquake was investigated using centrifuge model tests, considering a variety of factors such as gradient of slope, water content of soil, geotextile spacing, and input shaking wave. The geotextile-reinforcement mechanism was revealed on the basis of the observations with comparison of the unreinforced embankment. The geotextile significantly decreases the deformation of the embankment and restricts sliding failure that occurs in the unreinforced embankment during an earthquake. The displacement exhibits an evidently irreversible accumulation with a fluctuation during the earthquake which is significantly dependent on the magnitude of input shaking. The peak strain of the geotextile exhibits a nearly triangular distribution in the vertical direction. The embankment can be divided into two zones, a restricting zone and restricted zone, where the soil and geotextile, respectively, play an active restriction role in the soil-geotextile interaction. The soil restricts the geotextile in the restricting zone, and this restriction is transferred to the restricted zone through the geotextile. The strain magnitude of the geotextile and the horizontal displacement of the geotextile-reinforced embankment decrease with increasing geotextile layers, with decreasing water content of the soil, with decreasing gradient of the slope, and with decreasing amplitude of the earthquake wave.     

Energy efficiency of fibre reinforced soil formation at small element scale: Laboratory and numerical investigation

This paper explores the aspects related to the energy consumption for the compaction of unreinforced and fibre reinforced samples fabricated in the laboratory. It is well known that, for a fixed soil density, the addition of fibres invariably results in an increased resistance to compaction. However, similar peak strength properties of a dense unreinforced sample can be obtained using looser granular soil matrices mixed with small quantities of fibres. Based on both experimental and discrete element modelling (DEM) procedures, this paper demonstrates that less compaction energy is required for building loose fibre reinforced sand samples than for denser unreinforced sand samples while both samples show similar peak strength properties. Beyond corroborating the macro-scale experimental observations, the result of the DEM analyses provides an insight into the local micro-scale mechanisms governing the fibre-grain interaction. These assessments focus on the evolution of the void ratio distribution, re-arrangement of soil particles, mobilisation of stresses in the fibres, and the evolution of the fibre orientation distribution during the stages of compaction.     

Cyclic behaviour of dry silty sand reinforced with a geotextile

Recent studies on construction material technology have indicated that soil reinforcement improves resistance of soil against compression and tension. Due to the wide use of geotextile reinforcement in road construction, the potential benefit of geotextile reinforcement in cyclic loading should be investigated. In this study we performed a series of cyclic triaxial tests to examine dry silty sand reinforced with geotextile when subjected to dynamic loading. These tests were conducted on reinforced and unreinforced dry sand and sand mixed with varying amounts of silt (0–50%). The main factors affecting the cyclic behaviour, such as the arrangement and number of geotextile layers, confined pressure and silt content are examined and discussed in this paper. The results indicate that geotextile inclusion and increased confining pressure increase the axial modulus and decreased cyclic ductility of dry sand for all silt contents examined. Also, it was found that by increasing the silt content by up to about 35 percent the axial modulus in reinforced and unreinforced sand is decreased and cyclic ductility increased. With further increases in silt content, these values are increased for cyclic axial modulus and decreased for cyclic ductility.     

土工带加筋碎石土大型三轴试验研究

为真实反映土工带加筋碎石土的受力特性,本文采用实际工程中使用的TG玻塑土工带进行了4组不同围压、不同 加筋层数的土工带加筋碎石土大型三轴试验。分析了加筋带对碎石土应力-应变关系及强度的影响,并引入应力比、强度 加筋系数、破坏变形加筋系数、轴向变形加筋系数和侧向变形加筋系数来评价加筋效果。试验结果表明:碎石土经土工带 加筋后其破坏强度和破坏应变均得到提高,在大变形下土工带加筋碎石土仍能继续承担荷载。加筋土和未加筋土的强度 曲线基本平行,土工带加筋碎石土的强度服从"准粘聚力"原理。加筋效果不仅与加筋参数有关,而且与围压有关,加筋带 的作用发挥随围压增大而减小。     

Unconfined compressive strength of fly ash reinforced with jute geotextiles

A series of unconfined compressive strength (UCS) tests have been conducted on unreinforced fly ash as well as fly ash reinforced with jute geotextiles. The effects of different governing parameters viz., degree of saturation, size of samples, number of jute geotextile layers and age of sample on UCS have been studied. From the test results it is found that the values of UCS are maximum at degree of saturation of 70–75%. The effect of sample size on the values of UCS for unreinforced fly ash is insignificant, whereas with increase in diameter of sample, values of UCS increase in case of reinforced fly ash. With increase in number of jute geotextile layers for reinforced fly ash samples, values of UCS increase and maximum enhancement is found to be around 525% with 4 layers of reinforcement. A non-linear power model has been developed to estimate unconfined compressive strength (UCS_R) of fly ash reinforced with jute geotextiles in terms of unconfined compressive strength (UCS_UR) of unreinforced fly ash and number of layers of reinforcement (N).     

加筋软岩粗粒土路堤填料大型三轴试验研究

 为研究加筋粗粒土填料的强度变形特性及加筋效果,进行加筋强风化软岩粗粒土固结不排水和固结排水大三轴试验。试验表明：加筋填料的应力–应变关系表现为应变硬化型;轴向应变较小(ea＜1%)时,加筋填料效果不明显,随着轴向应变的逐渐增大加筋效果逐渐发挥。加筋填料的孔隙水压力均高于素填料,随着加筋层数的增加均有不同程度的提高。加筋效果系数均＞1.0,一层加筋填料加筋效果系数为1.09～1.21,二层加筋填料加筋效果系数为1.30～1.71,三层加筋填料加筋效果系数为1.31～1.72。加筋前后填料的内摩擦角j基本不变,填料的黏聚力增大。加筋填料的本构关系可以用Duncan-Chang模型来描述,依据试验结果求得模型参数。     

Shear strength characteristics of geosynthetic reinforced rubber-sand mixtures

Shear strength characteristics of the geosynthetic-reinforced rubber-sand mixture (RSM) has been investigated by conducting Unconsolidated Undrained (UU) triaxial test. In the first part, a series of UU triaxial tests have been carried out to know the size effect of granulated rubber/tyre chips from seven different rubber sizes. RSM sample that provides higher strength, energy absorption capacity and stiffness is considered as the optimal size and has been used in the investigation on geosynthetic-reinforced RSM. In the second part, shear strength characteristics of geosynthetic-reinforced RSM has been investigated by varying proportions of rubber content (50% and 75% rubber by volume), type of geosynthetic (geotextile, geogrid and geonets), number of geosynthetics (1–4) layers, geosynthetic arrangement and confining pressure. The results demonstrate that RSM reinforced with geosynthetic has enhanced peak strength, failure strength and corresponding axial strain at failure. Fifty percent RSM reinforced by geotextile and 75% RSM reinforced by geonets with 4 layers of reinforcement, led to a maximum increase in shear strength. The strength and energy absorption capacity are doubled for the reinforced RSM's, and reduced the brittleness index values as close to zero, which depends on the type, number of layers and arrangement of geosynthetic.     

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。     

FRP-PVC管约束圆形截面钢筋混凝土组合柱滞回性能试验研究

6个FRP-PVC管约束圆形截面钢筋混凝土组合柱试件进行滞回性能试验,研究轴压比n、FRP横向包裹层数m和FRP类型对组合柱在低周往复荷载作用下的破坏模式、滞回特性、位移延性、能量耗散能力、承载力退化、刚度退化等性能的影响。试验结果表明,当外包FRP-PVC管开裂并退出工作时,试件承载力呈跳跃式下降,试件退化为钢筋混凝土柱,可将外包FRP-PVC管的开裂作为该类构件即将破坏的首次预警;所有试件的滞回曲线均较为饱满,捏缩现象不明显,滞回性能良好;试件的承载力退化不显著;轴压比的增大提高了试件的峰值荷载,同时延缓了刚度退化趋势,降低了试件的耗能能力;与BFRP包裹的试件相比,CFRP包裹试件的峰值荷载、耗能能力有所提高,刚度退化延缓;BFRP包裹层数的增加可以延缓试件刚度退化并提高其延性。     

Stabilization of residual soil with rice husk ash and cement

Stabilization of residual soils is studied by chemically using cement and rice husk ash. Investigation includes the evaluation of such properties of the soil as compaction, strength, and X-ray diffraction. Test results show that both cement and rice husk ash reduce the plasticity of soils. In term of compactability, addition of rice husk ash and cement decreases the maximum dry density and increases the optimum moisture content. From the viewpoint of plasticity, compaction and strength characteristics, and economy, addition of 6–8% cement and 10–15% rice husk ash is recommended as an optimum amount.     

A quasi-2D exploration of optimum design settings for geotextile-reinforced sand in assistance with PIV analysis of failure mechanism

Many earlier studies were focused on testing different types of geosynthetics to investigate effect of reinforcement on bearing capacity, but the effect of tensile strength on the failure mechanism has not been examined sufficiently. Within this scope, a test setup was prepared to apply strip loads on densely compacted reinforced sand under the plane strain condition. The tank containing the reinforced sand was a rectangular prism with perfect transparency, and its interior dimensions were 960 × 200 × 650 mm³. Firstly, optimum values of design variables (depth of first sheet, length and number of sheets, space between sheets, tensile strength of sheets) for the woven geotextile reinforced sand were determined experimentally. Then, the failure mechanisms of the soil, which were reinforced with geotextiles of different tensile strengths, were observed and analyzed with particle image velocimetry (PIV) technique. Consequently, the failure mechanism of the sand with a single geotextile reinforcement was similar to general shear failure of unreinforced soil. Contrarily, the failure surfaces were deeper and longer. Additionally, the deep-footing mechanism reached out large depth in the case of four reinforcement layers. The failure mechanism converted into a punching type due to a hypothetic increase in the bearing depth of reinforcement.     

HRB600钢筋混凝土短柱轴压性能试验研究

通过对6根HRB600钢筋、1根HRB500钢筋混凝土短柱和2根素混凝土短柱进行轴心受压试验,分析不同配筋率、混凝土强度、钢筋强度、长细比对钢筋混凝土柱轴压性能的影响,提出HRB600钢筋的抗压强度设计值,分析GB 50010-2010《混凝土结构设计规范》中关于轴心受压承载力计算公式的适用性。研究结果表明:随着纵筋配筋率、钢筋强度和混凝土强度的提高,轴压短柱的峰值荷载增大;轴压短柱峰值应变随混凝土强度提高而减小,随钢筋强度提高而略有增大,纵筋配筋率和长细比对峰值应变影响较小;HRB600钢筋抗压强度设计值取为500 MPa,HRB600钢筋混凝土短柱与普通钢筋混凝土短柱的受力性能相似,轴心受压承载力可以按照GB 50010-2010《混凝土结构设计规范》中规定的受压承载力公式进行计算,具有足够的安全储备。     

Centrifuge modeling of geotextile-reinforced cohesive slopes

Geosynthetics are widely used to reinforce slopes due to their successful performance and economical efficiency. A series of centrifuge model tests was conducted in order to investigate the behavior of the geotextile-reinforced cohesive slopes and to compare their behavior to unreinforced slopes. The displacement history of the slopes was measured using an image analysis system. The failure process of an unreinforced slope can be categorized into three stages: (1) uniform deformation stage; (2) strain localization stage; and (3) post-failure stage. The geotextile has a significant effect on the deformation of the slope and increases the stability level while affecting the failure modes. On a reinforced slope, two surfaces can result from the distribution of the displacement difference between the unreinforced and the corresponding reinforced slopes; thus, the slope can be categorized into three zones. The front zone is characterized as a restricted region that is subjected to a backward tension via the geotextile while the middle zone is mainly subjected to a forward tension (like a support body). The back zone is unaffected by the geotextile. The reinforcement can take effect when its length is longer than the effective reinforcement length. The effective reinforcement length usually increases with increasing elevation and is significantly affected by the inclination of the slope.     

H-V立体加筋黏土单轴试验

为了研究H-V立体加筋黏土应力-应变曲线及强度特性,在恒定应变加载速率下,对H-V立体加筋黏土进行了单轴无侧限抗压强度试验,得到了不同加筋高度及不同含水率下的应力-应变曲线。在给定的含水率下,研究了加筋高度为5 mm、10 mm、15 mm、20 mm的H-V立体加筋黏性土与极限应力的关系,得出了在一定范围内极限应力随竖向加筋率的增大而增大,但是其中存在一个最佳竖向加筋率,大于或小于这个加筋率,试样都不能达到最佳效果。在给定的加筋高度下,研究极限应力与含水率之间的关系,得出了极限应力随含水率的增加,先增大后减小的规律。此外,本文还研究了极限应力与分维数D之间的关系,得出了极限应力随着分形维数D的增加,先增加后减小,存在一个最优值。     

Centrifuge modeling of the geotextile reinforced slope subject to drawdown

Geotextile is an effective reinforcement approach of slopes that experiences various loads such as drawdown. The geotextile reinforcement mechanism is essential to effectively evaluate the safety of geotextile-reinforced slopes under drawdown conditions. A series of drawdown centrifuge model tests were performed to investigate the deformation and failure behaviors of slopes reinforced with different geotextile layouts. The deformation and failure of unreinforced and reinforced slopes were compared and the geotextile reinforcement was indicated to significantly increase the safety limit and the ductility, reduce the displacement, and change the failure feature of slopes under drawdown conditions. The slopes exhibited remarkable progressive failure, downward from the slope top, under drawdown conditions. The progressive failure was induced by coupling of deformation localization and local failure based on full-field measurements of displacement of slopes subjected to drawdown. The geotextile reinforced the slope by decreasing and uniformizing the slope deformation by the soil-geotextile interaction. Through geotextile displacement analysis, the geotextile-reinforced slope was divided into the anchoring zone and the restricting zone by a boundary that was independent of the decrease of water level. The geotextile restrained the soil in the anchoring zone and the soil restrained the geotextile in the restricting zone. The reinforcement effect was distinct only when the geotextile was long enough to cross the slip surface of the unreinforced slope under drawdown conditions.     

Shear strength evaluation of composite pavement with geotextile as reinforcement at the interface

This research was conducted to investigate the shear strength at the interface between polymer concrete and asphalt concrete with geotextile as reinforcement at the interface of these two types of concrete. The samples were tested for the parameters of different surface conditions [rough and smooth], curing types [room and thermal curing], temperature effect and the impact of geotextile as reinforcement. To investigate the correlation between these parameters, four different testing conditions were implemented. The results showed a significant improvement of shear strength for rough surface sample as compared to smooth surface sample. Moreover, samples cured in oven had lower shear strength as compared to samples cured in room condition. Besides that, high temperature has an adverse impact on the shear strength at the interface between polymer concrete and asphalt concrete due to the weakening of asphalt concrete at high temperature. As for samples reinforced with geotextile, the shear strength resistance was better as compared to unreinforced samples. Through visual observation, the types of failure under all testing conditions were mixed failure mode.     

冻融循环下压实度对粉质黏土力学性质影响的试验研究

 冻融循环是冻土地区路基填料性能劣化的主要因素之一。以压实度和冻融循环次数为主要变量,对青藏高原粉质黏土力学性质的变化规律进行三轴试验研究。试验结果表明：初始压实度对粉质黏土力学性质的冻融效应具有显著影响。不同压实度试样的应力–应变曲线形式随冻融次数的增加趋于接近,并由应变软化型向硬化型过渡。封闭系统中试样的水分迁移会引起含水率的增减分区分布,低压实度有利于增大水分迁移量和含水率增高区的分布范围。冻融过程对高压实试样的破坏强度以降低为主,对低压实度试样则相反。在最优含水率附近,土体抗剪强度随含水率呈非线性变化规律,因此试样内部水分重分布也可能会导致强度的改变,且其作用效果受压实度影响具有不确定性,压实度较高时会导致试样黏聚力减小,压实度较低时则相反;不同压实度下内摩擦角均呈现增大的趋势,且压实度越低,变化幅度越大。冻融过程中,土体干密度和含水率变化对力学性质的影响是同时存在的,由于初始压实度和冻融次数的不同,对强度变化起主导作用的因素也不同。水分重分布是不同压实度土体力学性质冻融循环效应的整体趋势和具体过程呈现多样化的原因之一。