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1.
Chennarapu Hariprasad Mekala Rajashekhar Balunaini Umashankar 《Geotechnical and Geological Engineering》2016,34(6):1909-1922
Relative density is an important state parameter that influences the soil behavior. Preparation of sand specimens with uniform density is critical during large-scale laboratory testing in geotechnical engineering. In this study, the details of a stationary air pluviation device used to prepare uniform sand specimens in a large-size test chamber with dimensions equal to 900 mm × 900 mm × 1000 mm (in length, width, and depth) are provided. The proposed device is found to be simple to construct due to presence of only two diffuser sieves with an ability to produce uniform sand beds in a reasonably quick time. Prior to construction of full-scale pluviation device, a scaled-down model of the device with plan dimensions equal to 300 mm × 300 mm is fabricated to perform calibration studies. The range of densities of two gradations of Indian Standard sand (IS Grade II and IS Grade III) obtained using this device for various heights of fall of sand particles and passing through different opening sizes are provided. Relative density in the range of 53–99 % and 74–99 % is achieved for IS Grade II and III sands, respectively. The spatial uniformity in densities is also assessed, and the coefficient of variation (COV) in the density is found to be less than about 7 %. In addition to pluviation method, uniform sand beds are also prepared using pneumatically-operated vibratory method. The target relative density of sand bed is achieved by adjusting the pressure of compressed air inside the vibrator, and the maximum relative density of IS Grade II and Grade III sands from vibratory method is found to be higher than that from pluviation method for the range of pressures chosen in the study. 相似文献
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颗粒级配与形状对钙质砂渗透性的影响 总被引：1，自引：0，他引：1
钙质砂是富存于热带海洋环境（包括中国南海海域）中的一种特殊岩土介质,具有不同于陆源砂的水理性质。采用传统常水头渗流试验,首先探究了不同不均匀系数和曲率系数条件下级配对钙质砂渗透性的影响。针对钙质砂的颗粒形状特性,采用扫描电镜（SEM）与图像处理技术,引入球度 和圆度X的比值 从三维空间角度上对颗粒形状进行了定量描述。并在粒径区间、相对密实度相同的条件下,通过与福建标准砂、玻璃珠进行对比试验来考察钙质砂渗透特性,从而进一步探究颗粒形状对钙质砂渗透性的影响。试验结果表明,钙质砂渗透性随着颗粒粒径不均匀系数和曲率系数的增大而增大,符合级配对一般砂土渗透性的影响规律;钙质砂颗粒形状具有较强的结构性和不均匀性,同等密实度下钙质砂的渗透性小于陆源的石英砂。本研究获得的钙质砂渗透规律对今后南海岛礁填筑和海上平台基础工程设计具有一定的指导意义。 相似文献
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《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2013,7(3-4):229-240
The 1971 San Fernando earthquake led to the failure and large displacement of the Lower San Fernando Dam (LSFD) that was constructed by the hydraulic filling method. As such, hydraulic filling has been recognised as producing liquefiable sand deposits, while in situ relative densities as large as 60% have been reported in the LSFD. On the other hand, laboratory element tests on loosest pluviated (through air or water, resembling the soil fabric produced by hydraulic filling) specimens of primarily quartz sands have been dilative, questioning the failure mechanism of the LSFD. In this paper, the LSFD during the 1971 San Fernando earthquake is studied using the results of improved sliding block deformation analyses that incorporate shearing behaviour of two sands with different mineralogies (quartz sand and albite sand with some carbonates) from ring shear tests. The results indicate that sand particle composition and compressibility in the LSFD may have caused its failure and very large deformations even at a dense state (relative density ～60%). 相似文献
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液化土层中桩基水平承载特性分析 总被引：9，自引：0，他引：9
通过桩土相互作用的振动台模型试验,获得了不同相对密度的砂土在振动液化过程中桩身弯矩随土层振动累积孔压的变化关系。进而通过拟静力方法,确定了土层液化过程中的衰化p-y曲线,并计算出桩身弯矩的分布。计算结果与实测结果的比较分析表明：若土层的振动累积孔压比ru≤比≤0.2时,桩的水平承载能力没有明显降低。当土层的振动累积孔压比ru≥0.8时,若土层的相对密度Dr≤40 %,桩的水平承载能力降低90 %;若土层的相对密度Dr≥50 %,桩的水平承载能力降低75 %。 相似文献
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A new method was developed for the measurement of relative density in natural sand deposits. The method is based on hardening sand in the field, so that undisturbed samples can be obtained, and the later removal of the organic hardener in the laboratory. In the study of two coastal dunes use was made of “peels” which reveal in detail the internal structure of the sand. A definite relationship was established between relative density of the dune sand, its internal structure and mode of deposition. Very high relative densities, approaching and even exceeding 100%, were found in sand deposited by accretion on the top of the dunes. Low to very low relative densities were measured in slip deposits formed by avalanching of sand on the leeward slope of the dunes. High densities in accretion deposits are attributed to sand movement by saltation taking place during the accumulation of the sand and the very high kinetic energies expended during this transportation process. Low densities in the slip deposits are attributed to the process of avalanching which involves minimum energy expenditure. A more or less constant relative density of around 80% was found in the stretch of beach sand studied. 相似文献
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It is well known that the specimen preparation method and the resulting sand fabric significantly affect sand behaviour and sand liquefaction resistance. In this study, a simple experimental method namely tensiometric method is presented for evaluation of the effect of the samples reconstituting methods on microstructure and the pore-access size distribution of sands. Specimens were prepared using dry funnel pluviation (DFP) and wet deposition (WD) at two densities Dr = 40% (loose state) and Dr = 80% (dense state). The water-retention curve of a sand specimen is evaluated using a technique similar to the hanging column method by application of a step-by-step variation of suction and measure of the corresponding changes in water content. The pore-access size distribution is then evaluated from the water-retention curve. In this experimental study the effects of the mode of deposition and the uniformity coefficient on the pore-access size distribution are investigated. It was found that the specimen generated by the WD method contained a higher percentage of pore size, contrary to the specimen prepared by the DFP which contained a limited percentage of pore size, causing a great influence on the mechanical behaviour of the specimens. 相似文献
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钙质砂为海相沉积的多孔介质,是防护工程分配层的理想填充材料。利用改进的铝制分离式霍普金森压杆（split Hopkinson pressure bar,简称SHPB）,分别对颗粒级配以及相对密实度相同的南海钙质砂和福建石英砂进行了83组一维冲击试验,得到了应力波透射率、冲击响应和吸能效率曲线,分析了应变率、相对密实度和含水率对两种砂冲击特性的影响。结果表明,相同的荷载和边界条件下,钙质砂的刚度仅为石英砂的1/10。由于内孔隙的存在,钙质砂对冲击波的衰减作用大于石英砂,在承载性能允许的情况下,适当减小相对密实度、增加含水率可有效提高分配层消能效果。 相似文献
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不同粒径级砂土渗透特性试验研究 总被引：5，自引：0，他引：5
渗透性是砂土的重要工程性质之一,影响砂土渗透性的因素有很多,比如土体密实程度、土颗粒自身特性、流体性质等,其中孔隙率与颗粒粒径是两个重要影响因素。而以往基于混合粒径的天然砂土的研究很难分别对这两个因素进行独立的研究。基于此,首先开展了单一粒径级砂土的常水头渗透试验,分别研究了同一粒径级砂土渗透系数随孔隙率的变化和同一孔隙率下不同粒径级砂土渗透系数随均值粒径的变化规律。试验结果显示,渗透系数随着孔隙率的增加而线性增加、随均值粒径二次方的增加而线性增加,其中均值粒径的影响较大,其变化能导致渗透系数量级上的差异。在此基础上,开展了多粒径混合砂土的渗透试验,讨论了曲率系数、不均匀系数等级配参数对渗透性的影响,从而将单一粒径级的研究成果推广到天然砂土,最终拟合出渗透系数与相关影响因素的经验公式,以便工程实践参考使用。 相似文献
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The use of shredded waste tires to improve the geotechnical engineering properties of sands 总被引：2，自引：0，他引：2
Mousa F. Attom 《Environmental Geology》2006,49(4):497-503
A new geo-environmental approach was proposed to use waste tires in certain engineering applications and thereby reduce the
potential impact on the environment. This paper presents a laboratory study on the effect of shredded tires on the physical
properties of some sands. Shredded tires were passed through US sieve size 4 and mixed with three different types of sands
with varying gradations. Each type of sand was mixed with four different percentages of shredded tires: 10, 20, 30 and 40%
by dry weight. Direct shear tests were conducted to study the effect of the shredded tires on the shear strength properties
of sands, such as angle of internal friction and shear strength. The addition of shredded waste tires increased both the angle
of internal friction and the shear strength of the sands. Additionally, a prediction model was developed to calculate the
shear strength of sand due to increasing shredded tire content. The shredded tires improved some engineering properties of
sand. 相似文献
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Estimation of contaminant transport parameters for a tropical sand in a sand tank model 总被引：1，自引：1，他引：0
O. O. Ojuri Ph.D. S. A. Ola Ph.D. 《International Journal of Environmental Science and Technology》2010,7(2):385-394
This research describes the goals, design and implementation of a quasi natural gradient, laboratory scale, sand tank (aquifer) model experiment. The model was used to study the transport of an inorganic tracer (Chloride) in groundwater, within a tropical aquifer (porous medium) material. Three-dimensional sand tank (1.8 m × 0.3 m × 0.8 m) experiments were conducted to investigate contaminant transport and natural attenuation within the sand tank. In all, 360 samples were collected during 24 sampling sessions, for the three days of the tracer experiments in the Sand Tank. The Owena sand is a poorly graded sand with 88.1 % sand and 11.9 % gravel. Geotechnical properties including; coefficient of uniformity Cu = 2.53, coefficient of gradation Cz = 0.181, hydraulic conductivity K = 5.76 × 10?4 m/s, bulk density p = 1.9 Mg/m3, effective porosity ne = 0.215 and median grain diameter D50 = 0.55 mm, were determined. Other relevant hydraulic and solute transport parameters, such as dispersion coefficients and dispersivities were also established for the tropical soil. 相似文献
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Loose saturated cohesionless soils are most susceptible to liquefaction, however there are strong historical evidence suggesting that soils containing fines such as silty sands are also prone to liquefaction during earthquakes. The liquefaction of silty sands has been observed in a number of recent case studies. This paper presents the effects of fine silts on liquefaction potential of sandy soil. Tests have been conducted on the vibration table at different accelerations and pore water pressure is measured. During the lab investigation, locally (Roorkee, India) available Solani Sand and Dhanauri Silt have been used. The soil samples have been prepared by varying silt content and the initial relative density. The results of the study performed are used to clarify the effects of non-plastic fines content on the Solani sand. As the silt content increases, the number of cycles required to produce maximum pore water pressure increases. For a particular level of excitation, rate of pore water pressure generation is maximum at critical silt content. It is observed that critical silt content to generate maximum pore water pressure is different for different accelerations. Further, effect of silt content is very much dependent on relative density. 相似文献
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利用南海钙质砂和阿拉伯湾钙质砂,进行侧限压缩试验,对其压缩特性进行分析,得到了相应的压缩指数;采用相对破碎率为度量指标,评价了钙质砂在压缩试验过程中的颗粒破碎情况。同时根据试验数据得到了不同初始相对密实度的砂样的塑性功,通过建立塑性功与相对破碎率以及塑性功与压缩指数之间的关系,探讨了颗粒破碎对钙质砂压缩特性的影响。研究显示,在本次试验条件下,颗粒破碎是导致钙质砂压缩变形的主要因素,钙质砂的中值粒径以及碳酸钙含量等因素对其颗粒破碎程度有明显影响;钙质砂的相对破碎率与其输入的塑性功有关,并且受到初始相对密实度的影响,采用相对密实度进行归一化后,两者呈现较好的幂函数关系;通过建立钙质砂压缩指数与塑性功之间的关系,进一步建立了钙质砂的压缩指数与相对破碎率之间的关系,经相对密实度归一化后,两者也呈现幂函数规律,此规律可以用于评价颗粒破碎对钙质砂压缩特性的影响。 相似文献
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钙质砂通常是指碳酸钙含量大于50%的沉积物,与普通石英砂相比,其具有特殊的物理力学性质。圆锥动力触探试验是一种常用的土工原位测试方法,目前有关动力触探贯入指标与土体物理力学性质之间关系的研究多集中于黏土和普通石英砂,针对钙质砂的相关成果较少。有鉴于钙质砂的特殊性质,现有的评价方法是否适用于钙质砂存在较大的争议。为解决这一问题,本次研究在总结前人研究成果的基础上,通过现场轻型动力触探试验,对其贯入指标与钙质砂平均粒径、各类密度和密实度之间的关系进行了探讨,采用数据拟合的方法建立了动力触探贯入指标与相应物理指标之间的表达式。残差分析显示,这些公式具有一定的精度,相应的研究成果可为相关规范的修订以及实际工程的设计与施工提供参考。 相似文献
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Asskar Janalizadeh Choobbasti Abbas Ghalandarzadeh Mohammad Esmaeili 《Arabian Journal of Geosciences》2014,7(7):2739-2748
The liquefaction vulnerability of fine- to coarse-graded saturated sand and gravelly sand is evaluated by stress control cyclic triaxial laboratory tests. Cyclic triaxial test on reconstituted specimens is carried out with relative density of 45 %. Cyclic triaxial tests performed by sinusoidal wave form with 1-Hz frequency and with the effective consolidation pressure equal to 100 kPa. Cyclic stress ratio which caused initial liquefaction in 15 cycles recognized as the liquefaction resistance in cyclic triaxial test of present study. The result had been used to find a relationship between liquefaction resistance and the grading characteristics (e.g., coefficient of curvature and coefficient of uniformity) of various graded sands and gravelly sands. Then, it is realized that a relationship between liquefaction resistance and any of the sizes (i.e., D 10, D 30, D 50, D 60) appears to be more practical. 相似文献
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Wiam Khebizi Sidali Denine Jean Canou Jean-Claude Dupla 《Geomechanics and Geoengineering》2019,14(1):30-40
Soil improvement using fibres is widely used in soil stabilisation to prevent sand liquefaction. In order to study the undrained behaviour and liquefaction resistance of sand reinforced with polypropylene fibres, a series of triaxial compressive tests were conducted on unreinforced and reinforced Chlef sand with different contents of polypropylene fibres (0, 0.3, 0.5 and 0.8%). Samples were prepared at 30% and 80% relative densities representing loose and dense states respectively, and triaxial tests were performed at confining pressures of 50, 100 and 200 kPa. Tests results show that fibre inclusion has a significant effect on the shear strength and dilation of sandy soil. The increase in strength is function of fibre content, relative density and confining pressure. The maximum strength improvement for both loose and dense fibre-reinforced sand is more pronounced at higher confining pressure and at higher fibre content. 相似文献
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In the present study, a series of resonant column tests was performed to determine the influence of confining pressure, shear strain and relative density on the dynamic properties and Poisson's ratio of poorly graded clean sand. The tests were performed on the sand specimens of size 50 × 100 mm compacted at relative densities 30, 50 and 75 %. To achieve the corresponding relative density, sand was compacted in 5 equal layers with a specific number of blows. A fixed-free type resonant column apparatus was used to determine the dynamic soil properties at various confining pressures. It has been inferred from the data that the shear modulus (\(G\)) increases with an increase in confining pressure and relative density; and decreases with an increase in shear strain. In addition, damping ratio (\(D\)) decreases with an increase in confining pressure and relative density; and increases with an increase in shear strain. In addition, Poisson’s ratio (\(\nu\)) decreases with an increase in confining pressure and relative density and increases with an increase in the shear strain. The variation of shear modulus with Poisson’s ratio is also discussed. It has been found that there has been a decrease in shear modulus with an increase in Poisson’s ratio of the soil. It is noticed that the small strain shear modulus determined from the present study closely matches with the value determined using the correlations from the literature. 相似文献
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SY地区须家河组二段（下砂）储层类型复杂,各井中均见到砂层,但该砂层储集体有的为高孔隙而有的则致密,在区域平面上表现出分布不均匀的特点。对该段储层预测方法及种类也有较多,但常规叠后反演很难对其进行区分和识别。利用叠前AVO技术,建立储层段的AVO正演模型并采用相应的工作流程,然后利用P-G交汇法对砂岩储层进行解释,发现含气储层与非含气储层的P-G交汇特征不同,砂岩储层含气后则具有交汇趋势线角度增大及远离背境趋势线的特征;而砂岩非储层则相反;其次储层段的P-G交汇点所分布的象限也不相同。通过这些特征,对全区现有钻遇该储层段的钻井进行预测,预测结果和钻井气测情况相吻合,取得了如期效果。 相似文献
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In order to manage local rock aggregates efficiently, an inventory has been made of superficial sand materials in the Senegalese basin. A detailed geological study of sandy formations has been undertaken, and geotechnical tests were also performed in order to characterize the sands according to their mechanical properties. The geotechnical characteristics of the sands can be related to their geological histories thus allowing the geotechnical parameters to be estimated by field mapping. 相似文献