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1.
为研究机制砂颗粒形状对砂浆流变性能的影响,使用数字图像处理技术(DIP)对砂颗粒形状进行了定量表征,设计试验测量了砂浆流变曲线并计算了砂浆屈服应力与表观黏度。结果表明,机制砂的长宽比(E)、宽高比(F)比天然河砂分别大14%、18%,说明机制砂棒状和片状程度高于天然河砂;砂浆流变曲线反映出砂颗粒形状不规则会导致砂浆流动阻力增大,在高体积分数下更为显著;根据Chateau模型拟合40%体积分数机制砂砂浆屈服应力是天然河砂的1.5倍;砂浆表观黏度分析发现,机制砂砂浆表观黏度大于天然河砂,在低剪切速率下尤其明显。 相似文献
2.
Interface shear strength between soil and geosynthetics mainly depends on the mechanical and physical properties of soil, geosynthetics and the normal stress acting at the interface. This paper presents results of an extensive experimental investigation carried out on sand-geosynthetic interface using modified large direct shear box. The study focusses on the shearing mechanism at the sand-geosynthetic interface and the effect of different parameters on the shearing mechanism. Smooth HDPE geomembrane, nonwoven needle punched geotextile and two types of sand having different mean particle size, have been used in the present study. Microstructural investigation of deformed specimen through Field Emission Scanning Electron Microscope (FESEM) reveals the shearing mechanism which includes interlocking and fiber stretching for sand-geotextile while sliding, indentation and plowing for sand-geomembrane interface. The shearing mechanism for sand-geomembrane interface highly depends on the normal stress and degree of saturation of sand. The critical normal stress that demarcates the sliding and plowing mechanism for sand-geomembrane interface is different for dry and wet sand. The amount of scouring (or plowing) of the geomembrane surface reduces with increase in the mean particle size of sand. FESEM images revealed that the sand particles get adhered to the geotextile fibers for tests involving wet sands. The present microstructural study aided in understanding the shearing mechanism at sand-geosynthetic interface to a large extent. 相似文献
3.
《Geotextiles and Geomembranes》2023,51(5):144-164
The present study aims to explore and bring out morphological insights into the prior-liquefaction, liquefaction, and post-liquefaction response of sands with geotextile inclusions. For this, a series of multi-stage drained constant volume simple shear tests with different cyclic stress ratios (CSR ranging from 0.1125 to 0.225) and different frequencies (f of 0.2 and 1.0 Hz) were carried out on completely dry specimens constituted with granular materials of three distinct grain morphologies (rounded, subrounded, and angular) reinforced with a nonwoven geotextile. The study also consists of morphological quantifications through image analysis algorithms and direct shear tests on sand-geotextile interfaces. Test results revealed that the inclusion of geotextile increased the liquefaction resistance and post-liquefaction shear strength of all the materials, irrespective of their particle morphology. However, the beneficial effects are more in the case of specimens constituted with angular particles. The effect of loading frequency on the response is also established. The interlocking and ploughing tendency of the angular particles leads to the mobilization of the maximum tensile strength of geotextile, which enhances the additional confinement and prevents the lateral movement of particles, thereby providing the maximum benefit. 相似文献
4.
研究了机制砂对新拌混凝土坍落度、扩展度、含气量以及抗压强度的影响,并探讨了聚羧酸高效减水剂和萘系减水剂在机制砂混凝土中的适用性。结果表明,机制砂的掺入会对混凝土的和易性产生一定影响,新拌混凝土的流动性变差,最多下降了25%。机制砂能够显著改善低强度混凝土的抗压强度。对于机制砂混凝土,萘系减水剂具有更好的适用性,相同配比下能够获得更好的和易性以及更高的抗压强度。 相似文献
5.
《Soils and Foundations》2022,62(1):101098
Natural pumiceous (NP) sands containing pumice particles, a type of volcanic soil, are commonly found in the central part of the North Island in New Zealand. The pumice particles are highly crushable, compressible, lightweight and angular, making engineering assessment of their properties problematic. In this paper, several series of bender element and undrained cyclic triaxial tests were performed on reconstituted and undisturbed NP sands to determine their small-strain shear modulus (Gmax) and cyclic resistance ratio (CRR). Furthermore, similar tests were also conducted on normal hard-grained sands (e.g., Toyoura sand) for the purpose of comparison. The results showed that the NP sands have considerably lower Gmax compared to normal sands, resulting in their higher deformability during the initial stages of the cyclic loading test. The high angularity of NP sands play an important role toward the end of the cyclic loading and contributed to their higher CRR. Next, the ratio of CRR/Gmax for each sample was correlated to a level of strain denoted as cyclic yield strain (εay), which was found to be significantly dependent on the percentages of pumice particles present in the natural soils. On the other hand, the εay was found to be less sensitive to the consolidation stress (σ′c) and the relative density (Dr) of the materials. For example, over different values of σ′c and Dr, NP sands have substantially higher values of cyclic yield strain due to their lower Gmax and higher CRR when compared with those of ordinary sands. 相似文献
6.
机制砂混凝土应用研究现状及存在问题分析 总被引：1，自引：0，他引：1
随着城镇化的推进,城乡一体化进程加快,以及对生态环境的重视,现有的天然砂己不能满足工程需要,使用机制砂已成形势所需.本文简要概述了机制砂对混凝土各方面性能的影响、石粉的活性效应、含泥量对混凝土的影响,认为机制砂混凝土具有广阔的应用前景,并指出现阶段所存在的问题. 相似文献
7.
《Soils and Foundations》2021,61(6):1708-1717
A series of ring shear tests were conducted to investigate the ultimate particle size distribution of a carbonate sand. The tests were carried out under different stress levels, on three types of specimens: 1) uniformly graded specimens made of dry natural sand 2) remoulded specimens of the crushed sand after first shearing to large strains 3) specimens made of natural sand grains but with the same grading as in (2). The first series of tests on type (1), carried out to very large strains, led to apparently stable gradings, distinct for each stress level. Only limited additional particle breakage could be induced by remoulding the specimens after shearing (type (2)) and subjecting them to more shearing. Tests on specimens created at the apparently stable gradings (type (3)) but from the intact sand particles however led to significantly greater breakage. For the three types a stable, fractal grading was achieved. Analyses of the soil particles’ shape showed that the aspect ratio, sphericity and circularity reach a steady value at large strains, in parallel to reaching a stable grading. The mobilized angle of shearing resistance however was not significantly different in the different types of samples, suggesting the final grading dominates the behaviour. 相似文献
8.
The hydration of different GCLs from the pore water of the underlying foundation soil is investigated for isothermal conditions at room temperature. Results are reported for three different reinforced (needle punched) GCL products. Both a silty sand (SM) and sand (SP) foundation soil are examined. GCL hydration is shown to be highly dependant on the initial moisture content of the foundation soil. GCLs on a foundation soil with a moisture content close to field capacity hydrated to a moisture content essentially the same as if immersed in water while those on soil at an initial moisture content close to residual only hydrated to a gravimetric moisture content of 30-35%. The method of GCL manufacture is shown to have an effect on the rate of hydration and the final moisture content. The presence or absence of a small (2 kPa) seating pressure is shown to affect the rate of hydration but not the final moisture content. The GCL hydration did not change significantly irrespective of whether a nonwoven cover or woven carrier GCL rested on the foundation soil. 相似文献
9.
通过改变石粉(SP)含量(0、5%、10%、15%)和再生粗骨料(RCA)取代率(0、33%、66%、100%)进行了48个棱柱体受压应力-应变全曲线试验,研究了石粉、再生粗骨料对机制砂再生混凝土轴心抗压强度、峰值应变和弹性模量的影响。基于损伤力学原理,参考已有的普通混凝土应力-应变本构关系,建立了机制砂再生混凝土单轴受压应力-应变本构方程。结果表明:理论曲线与试验数据吻合度较好。 相似文献
10.
为研究不同细颗粒含量及形状对钙质混合砂力学特性的影响,采用角形石英粉和圆形玻璃珠作为细颗粒材料,按不同配比分别与钙质砂混合,通过环剪试验对钙质混合砂强度特性和破碎特征进行研究。结果表明：两种混合砂在中密状态下软化特性明显,软化系数随细颗粒含量的增加,呈现出先增大后减小的规律,在细颗粒含量为10%时达到最大值,细颗粒含量相同时,含玻璃珠试样的软化系数更大;钙质砂存在明显的表观黏聚力,并随着细颗粒含量增加而减小,含玻璃珠试样因嵌固咬合能力更低,其下降趋势明显大于含石英粉试样;纯钙质砂变形表现为剪胀,随着细颗粒含量增加,混合砂剪缩量逐渐增加,峰值强度、相对破碎率逐渐降低,含玻璃珠混合砂变化更为显著。 相似文献
11.
12.
《Geotextiles and Geomembranes》2022,50(4):618-631
The strength and deformation properties of maritime geotechnical structures made primarily of calcareous sand are critical for project safety, and geogrid reinforcement is a promising new approach. A series of consolidated drained triaxial experiments were conducted to evaluate the mechanical property and deformation behaviors of geogrid reinforced calcareous sand (GRCS), taking into consideration the impacts of the geogrid layer, relative density, particle size, and confining pressure. In comparison to the unreinforced calcareous sand, the strength of the GRCS is greatly enhanced, and the deviatoric stress-strain curves are altered from slightly softening to hardening, as well as the suppressed shearing dilatancy. The geogrid, relative compactness, particle size, and confining pressure are all intimately related to the volume changes and shearing dilatancy of reinforced specimens, but particle crushing is mostly impacted by the confining pressure. The interactions of geogrid ribs and calcareous sand particles are summarized as two types of constraint and friction using scanning electron microscope tests to establish a simplified calculation method of horizontal and vertical equivalent additional stresses that could provide a reference for revealing the mechanical mechanism of GRCS. 相似文献
13.
《Geotextiles and Geomembranes》2022,50(4):708-719
Concrete canvas (CC) has been studied and applied for more than a decade; it has yet to be substantially studied in the field of water dosage. The unreasonable choice of water to cement ratio (w/c) might affect the quality and performance of CC. Thus, in this study, the experimental tests on the setting time, mechanical properties, X-ray diffraction (XRD), optical microscopy (OM) and scanning electron microscopy (SEM) of CC were carried out. The flexural and bursting behaviors in the early curing stage were also illustrated. The selected w/c was based on the water saturation level of CC during spraying. The obtained results indicated that mechanical properties of CC improved with the increase of w/c, while too much water somewhat delayed the hydration process in the first 3 days of curing. On the other hand, the low w/c would lead to insufficient hydration products and large size of loose defective structure in the interlayer of CC. An appropriate overdosage of water is considered suitable for CC solidification by spraying. 相似文献
14.
《Soils and Foundations》2021,61(6):1615-1629
Although the shear behaviors of silt–structure interfaces are critical in engineering practice, they have not been extensively investigated systematically. In this study, the influence of the silt water content and interface roughness on the shear behaviors of silt–cement mortar interfaces is investigated. Forty–eight silt–cement mortar structure interface tests and 18 silt direct shear tests were carried out. The results indicated that as the water content of the silt gradually increased to saturation, the interface shear stress–displacement curves changed from strain softening to strain hardening, and the interface shear strength decreased significantly. The shear strength of the rough interface was found to be significantly greater than of the silt, and the shear strength of the smooth interface was found to be lower than that of the silt. The interface shear strength gradually increased with the surface roughness, but the increase tended to be gentle. A large shear deformation was observed, and this increased with the decrease in soil water content and the increase (up to a point) in interface roughness. A model of the interface shear strength between unsaturated soil and structures considering the influence of water content and interface roughness was established and verified. 相似文献
15.
Stone columns develop their load carrying capacity from the circumferential confinement provided by the surrounding soils. In very soft soils, the circumferential confinement offered by the surrounding soft soil may not be sufficient to develop the required load carrying capacity. Hence a vertical confinement would yield a better result. The load carrying capacity is further increased with the addition of a sand bed over the stone columns. In the present study, a series of laboratory model tests on an unreinforced sand bed (USB) and a geogrid-reinforced sand bed (GRSB) placed over a group of vertically encased stone columns (VESC) floating in soft clay and their numerical simulations were conducted. Three-dimensional numerical simulations were performed using a finite element package ABAQUS 6.12. In the finite element analysis, geogrid and geotextile were modeled as an elasto-plastic material. As compared to unreinforced clay bed, an 8.45 fold increase in bearing capacity was observed with the provision of a GRSB over VESC. The optimum thickness of USB and GRSB was found to be 0.2 times and 0.15 times the diameter of the footing. A considerable decrease in bulging of columns was also noticed with the provision of a GRSB over VESC. Both the improvement factor and stress concentration ratio of VESC with GRSB showed an increasing trend with an increase in the settlement. It was observed that the optimum length of stone columns and the optimum depth of encasement of the group of floating VESC with GRSB are 6 times and about 3 times the diameter of the column respectively. 相似文献
16.
为了研究石粉含量对中低强度机制砂混凝土性能的影响,设计了4组不同石粉含量的C35机制砂混凝土,并进行了力学性能、耐久性能以及微观结构测试和分析。结果表明:适量的石粉可以优化混凝土的孔隙结构,有利于提高混凝土的早期抗裂性能、劈裂抗拉强度、抗压强度和抗氯离子渗透性能;过量的石粉会增加混凝土早期开裂风险,且对混凝土强度不利;建议在配制此类低强度等级混凝土时,机制砂的石粉含量应控制在20%以内。 相似文献
17.
《Geotextiles and Geomembranes》2020,48(2):137-156
The behaviour of geosynthetic clay liners (GCLs) as part of a physical-environmental system is examined. Consideration is given to: (a) both the physical and hydraulic interactions with the materials, and the chemical interactions with the fluids, above and below the liner, (b) time-dependent changes in the materials, (c) heat generated from the material to be contained, as well as (d) the climatic conditions both during construction and during service. This paper explores some common perceptions about GCL behaviour and then examines the misconceptions that can arise and their implications. It demonstrates how what may first appear obvious is not always as one expects and that more is not always better. It discusses: (i) the pore structure of a GCL, (ii) the dependency of the water retention curve of the GCL on its structure, bentonite particle sizes and applied stress, (iii) the effect of the subgrade pore water chemistry, (iv) the mineralogy of the subgrade, and (v) thermal effects. The desirability of a GCL being reasonably well-hydrated before being permeated is examined. The critical size of needle-punch bundles at which preferential flow can increase hydraulic conductivity by orders of magnitude is illustrated. The dependency of self-healing of holes on the interaction between GCL and subgrade is discussed. Finally, the transmissivity of the geomembrane/GCL interface is shown to be a function of GCL and geomembrane characteristics and to be poorly correlated with GCL hydraulic conductivity. 相似文献
18.
珊瑚砂广泛分布于我国南海岛礁,其性质与普通砂有明显的差异,主要体现在颗粒具有显著的破碎特征。为进一步研究珊瑚砂的破碎特征和破碎对其强度特征的影响规律,本研究通过控制相对密实度、含水率和围压等多种初始条件展开三轴固结排水(CD)的剪切试验。结果表明:珊瑚砂颗粒破碎会根据相对密实度以及围压的逐渐增大而增大,随着含水率的增大而先增大后减小,但是随围压的增大,颗粒的破碎不会无限制增大,当到达一定程度时会逐渐趋于停止;在相对密实度保持一定时,珊瑚砂的内摩擦角会依据含水率的增大而先增大后减小。珊瑚砂大颗粒破碎形成小颗粒并嵌固在孔隙中,大小颗粒之间的相互作用及级配趋于良好,颗粒的破碎一定程度上增大了珊瑚砂的强度。此试验成果可以为岛礁珊瑚砂工程建设提供参数依据,为深入研究珊瑚砂颗粒破碎的理论提供借鉴。 相似文献
19.
《Geotextiles and Geomembranes》2022,50(4):751-763
The interface shear strength involving geosynthetics and other materials can be influenced by various parameters, such as the material type and the normal stress on the interface. Although several investigations have been conducted over the years on this topic, the large variation of interfaces that can be used has led researchers to develop other sources of information to improve design methods. This paper investigates how roughness parameters can influence the shear strength developed between different interfaces based on many inclined plane tests and microscopic analyses of the surface roughness. One smooth and three textured geomembranes were used to simulate a barrier layer and sand, and two nonwoven geotextiles were installed on them to simulate drainage or protective layers. A powerful optical apparatus provided fifteen bidimensional and tridimensional surface parameters for the two faces of the analyzed geomembranes. The results showed that the mean height of profile elements (Rc) and the core material volume (Vmc) parameters presented stronger correlations with the interface shear strength. The concept of interface roughness factor was introduced to estimate the interface friction between different materials based on the materials properties for interfaces with geotextiles. 相似文献