Modeling for critical state line of granular soil with evolution of grain size distribution due to particle breakage

Determination of the critical state line(CSL)is important to characterize engineering properties of granular soils.Grain size distribution(GSD)has a significant influence on the location of CSL.The influence of particle breakage on the CSL is mainly attributed to the change in GSD due to particle breakage.However,GSD has not been properly considered in modeling the CSL with influence of particle breakage.This study aims to propose a quantitative model to determine the CSL considering the effect of GSD.We hypothesize that the change of critical state void ratio with respect to GSD is caused by the same mechanism that influences of the change of minimum void ratio with respect to GSD.Consequently,the particle packing model for minimum void ratio proposed by Chang et al.(2017)is extended to predict critical state void ratio.The developed model is validated by experimental results of CSLs for several types of granular materials.Then the evolution of GSD due to particle breakage is incorporated into the model.The model is further evaluated using the experimental results on rockfill material,which illustrates the applicability of the model in predicting CSL for granular material with particle breakage.     

Effect of particle size distribution on the bio-cementation of coarse aggregates

The effect of grain size distribution on the unconfined compressive strength (UCS) of bio-cemented granular columns is examined. Fine and coarse aggregates were mixed in various percentages to obtain five different grain size distributions. A four-phase percolation strategy was adopted where a bacterial suspension and a cementation solution (urea and calcium chloride) were percolated sequentially. The results show that a gap-graded particle size distribution can improve the UCS of bio-cemented coarser granular materials. A maximum UCS of approximately 575 kPa was achieved with a particle size distribution containing 75% coarse aggregate and 25% fine aggregate. Furthermore, the minimum UCS obtained has applications where mitigation of excessive bulging of stone/sand columns, and possible slumping that might occur during their installation, is needed. The finding also implies that the amount of biochemical treatments can be reduced by adding fine aggregate to coarse aggregate resulting in effective bio-cementation within the pore matrix of the coarse aggregate column as it could substantially reduce the cost associated with bio-cementation process. Scanning electron microscopy results confirm that adding fine aggregate to coarse aggregate provides more bridging contacts (connected by calcium carbonate precipitation) between coarse aggregate particles, and hence, the maximum UCS achieved was not necessarily associated with the maximum calcium carbonate precipitation.     

颗粒级配与形状对钙质砂渗透性的影响

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。     

颗粒级配对非饱和粘性土基质吸力的影响规律

颗粒级配是影响非饱和粘性土基质吸力变化规律的主要因素之一。本文在室内实验基础上,根据颗粒级配与非饱和土土水特征曲线基本参数之间的定量关系,探讨了颗粒级配对非饱和土基本特性的影响程度。研究结果表明:颗粒级配对非饱和土残余含水量控制作用明显,后者与粘粒、粉粒含量线性正相关,与角砾含量和粗、细粒含量之比分别线性、非线性负相关;不同粒组中,粉粒含量对土体残余含水量的影响程度最大,角砾含量的影响程度较低。颗粒级配对非饱和土残余基质吸力的影响程度较弱,后者与粘粒含量以及粗、细粒含量之比具有一定的相关性。非饱和土含水量变化幅度以及基质吸力对含量变化的敏感性与颗粒级配相关性最弱。但是,粘粒、粉粒含量以及粗、细粒含量之比对这两个特征值可能具有一定的影响作用。     

颗粒级配及初始干密度对路基翻浆冒泥特性的影响

重载铁路路基翻浆冒泥病害广泛存在且危害性极大,严重影响了轨道的稳定性和列车运行的安全性。铁路路基土体性质,如颗粒级配、孔隙比等对列车荷载作用下路基翻浆冒泥特性有显著的影响。利用自主研发的试验模型对粉质黏土与不同含量高岭土重塑试样进行翻浆冒泥试验,研究了不同颗粒级配（高岭土含量）、不同初始干密度（孔隙比）对循环荷载作用下试样的轴向应变、超孔隙水压力以及细颗粒迁移特性的影响。研究结果表明：随着高岭土含量以及初始干密度的增加,动荷载作用下试样产生的轴向应变、超孔隙水压力均减小,细颗粒迁移的平均高度降低,路基翻浆冒泥的程度减轻。通过试验发现,动荷载作用下试样内部的超孔隙水压力梯度是驱动路基土体细颗粒迁移的主导因素,试样产生的夹层对路基翻浆冒泥病害的发展具有一定的促进作用。     

Suspended sediment concentration and particle size distribution,and their relationship with heavy metal content

This paper aims at assessing the feasibility of suspended sediment concentration (SSC) estimation by using predictor variables of heavy metal concentration (HMC, viz., iron, chromium, zinc and nickel) transported in solution and solid. The study was conducted in the Research and Educational Forest Watershed of the Tarbiat Modares University (Kojour) which comprises an area of ca. 50000 ha. For this study, suspended sediment samples were collected from the left bank of the Kojour River twice a week, as well as during runoff events from November 2007 to June 2008. The samples were then prepared through direct digestion and finally analyzed by atomic absorption spectrophotometry (AAS). The relationship between SSC and particle size distribution (PSD) were correlated with HMC by using bivariate and multivariate regression models. Proposed models were then selected based on statistical criteria. The results showed high correlation between dissolved and particulate chromium content with efficiency coefficients beyond 77% (P < 0.001). However, a lower relationship was found between SSC and nickel content. From these results, it is clearly shown that the HMC can practically be estimated by SSC in watersheds with different accuracy and vice versa. It is also understood that heavy metal pollution can be easily managed by controlling SSC.     

Magnetic and coagulation forces on a suspension of magnetic particles

It is shown that the magnetic force on a highly-magnetic particle in a slurry is a strong function of the particle shape and the concentration density of the magnetic particles in the suspension. An expression is derived for the coagulation forces between magnetized particles as a function of magnetic moment, size, and concentration.     

钙质砂剪切特性的围压效应和粒径效应研究

为研究钙质砂剪切特性的围压效应和粒径效应,开展了在不同粒径、不同相对密实度以及不同围压条件下的三轴剪切试验,并引入应力相对软化系数和剪胀系数对应变软化特征及剪胀特征进行了定量表征。试验研究表明,随围压的增大,不同粒径钙质砂试样应变软化特征及剪胀特征逐渐减弱,且围压与应力相对软化系数和剪胀系数均呈半对数线性相关。不同粒径钙质砂试样存在一强度临界围压和体变临界围压分别使得应变软化特征和剪胀特征消失。在粒径为5～0.075 mm范围内,对松样而言,围压对软化特征和剪胀特征存在显著影响,但与粒径不存在显著相关性;对密样而言,随粒径逐渐减小,围压对试样软化特征的影响逐渐增强,而对试样剪胀特征的影响逐渐减弱。在低围压（50 kPa）条件下,0.5～0.25 mm粒径组试样破碎最显著。     

滑源区粒序分布及颗粒粒径对碎屑流冲击作用的影响研究

滑体的运动速度、堆积形态、冲击力等因素决定了碎屑流的致灾程度。滑源区不同岩性特征和结构分布的差异导致了滑体粒序分布和颗粒粒径的差异。在运动过程中产生的碰撞、摩擦、跳跃,影响着滑坡碎屑流的致灾程度。在物理模型试验的基础上,运用三维离散元软件PFC3D,探究滑源区粒序分布及颗粒粒径对滑体运动速度、堆积形态、冲击力的影响。研究结果表明:碎屑流中各粒径颗粒的平均速度受颗粒粒径及滑源区初始粒序的共同影响,且初始粒序对各颗粒平均速度影响更大;在堆积形态方面,粒径大小对厚度方向上的粒序排布影响较大,而滑源区粒序分布对单种颗粒的堆积形态影响较大;在颗粒分选作用下,颗粒粒径成为控制峰值冲击力的主要因素,而滑源区粒序分布则通过决定滑体堆积形态控制了准静态堆积阶段碎屑流的冲击力。     

Experimental and modeling investigation of sewage solids sedimentation based on particle size distribution and fractal dimension

Sewage solids are usually characterized by non-specific parameters such as suspended solids. The suspended solids has been shown to be an inadequate index for advanced water treatment processes. In this study, the sewages solids particle size distribution was used to provide more detailed information on sewage characteristic. It is hoped that, by introducing particle size distribution, the mechanism of sewage solids sedimentations can be better understood. The particle size distribution of the domestic sewage was measured by the Malvern® laser scattering technique to link to its settlement efficiency. Experimental results show that 77 % of particle volume was removed during the 90 min settling, of which 71.2 % of particle volume was removed in the initial 30 min. The submicron particles were found to be removed by co-settling with large particles. The fractal dimensions of sewage solids could also be derived from the laser scattering measurement. The fractal dimension could also provide useful information on the shape and density of sewage solids. A mathematical model considering the particle sizes, shapes and density changes was then constructed to simulate the settlement of raw sewage particles. Comparison of the modeling results based on discrete and flocculant settling theory shows that settlement can be better predicted by considering the fractal nature of particles. The particle size distribution and fractal dimension data measured by Malvern® laser scattering technique have been shown to be valuable data for in-depth understanding of the mechanisms of sewage solids sedimentation.     

The selective flotation of galena from sphalerite with special reference to the effects of particle size

The selectivity of galena flotation from a synthetic mixture with sphalerite and quartz and from a typical Broken Hill ore has been determined. It was found that the selectivity was limited by the relative flotabilities of coarse galena and sphalerite of intermediate sizes. The use of split conditioning in the preparation for flotation resulted in significant improvements in lead-zinc selectivity for both samples. By contrast the use of conventional zinc depressants in the flotation of the ore resulted in only slight changes in the behaviour of the minerals and had no discernible effect on the selectivity.     

Particle size distribution analysis of sand-sized particles by laser diffraction: an experimental investigation of instrument sensitivity and the effects of particle shape

Laser diffraction is now widely used for particle size distribution analysis of sediments and soils. The technique can be very precise, and offers advantages of speed and cost over many other methods when used to analyse mixtures of sand, silt and clay. This study presents the results of an experimental investigation that examined the sensitivity of the Beckman-Coulter LS230 instrument to mixtures of different grain populations and differences in particle shape. The instrument was found to have high sensitivity to coarse particles in a finer matrix (detection threshold 1–2%), but much lower sensitivity to finer particles in a coarser mixture (detection threshold 12–17%). Experiments using near-spherical ballotini showed that laser analysis provides very similar values to dry sieving for the mean, median and mode, but for a range of natural sand samples values for the mean, median and mode were offset by 8–21%, with an average of ca 15%, compared with sieving. Analysis using a Beckman-Coulter RapidVUE instrument, which provides both size and shape information, provided support for the hypothesis that the differences between laser analysis and sieving are partly attributable to the effects of particle shape. However, an additional factor is the way in which the laser software interprets the optical diffraction data. The software predicts a high degree of log-normality in the size distribution, such that highly skewed, truncated or bimodal samples are poorly represented. Experiments using sieved fractions of ballotini indicated that, even with near-perfectly spherical particles, the particle size distribution predicted by the laser software includes a relatively large percentage of particles outside the sieve class limits.     

颗粒粒径对微生物固化砂土强度影响的试验研究

微生物固化技术（MICP）是岩土工程领域新兴起的一种不良地基处理技术,不同地基土体之间的颗粒粒径并不相同,其固化效果也可能存在一定差别。选用3种不同颗粒粒径范围的砂土进行微生物固化处理,并基于无侧限抗压强度试验、孔隙体积测量和洗酸处理,从宏观角度分析颗粒粒径对微生物固化效果的影响。结合扫描电镜测试,从细观角度对微生物固化机制进行了初探。研究结果表明,微生物固化砂土中碳酸钙晶体以颗粒簇形式堆积在砂土颗粒表面及颗粒间接触处,其尺寸随碳酸钙晶体堆叠程度的增加而增大;对于颗粒粒径较小的砂土,颗粒间孔隙较易被碳酸钙晶体填充密实,固化试样内有效碳酸钙晶体比例较大,“结构性”较强,无侧限抗压强度较高。     

Study on infiltration rate based on primary particle size distribution data in arid and semiarid region soils

Soil particle size distribution (PSD) is used to estimate some soil processes, soil moisture characteristics, and infiltration rate (IR). Prediction of infiltration rate from soil texture data requires an accurate characterization of PSD. The objective of this study was to determine more important primary particle diameters that control IR. The experiments were conducted using double-ring method with constant head of 5 cm in 15 different soils and three replications. The range of measured IR for studied soils varied from 1.6 to 30.66 cm h^?1. The results indicated that the primary PSD had a significant influence on IR. In other words, most D _n fractions had significant positive effect on the final IR. Among different fractions, D ₃₀, D ₄₀, and D ₆₀ showed higher relationships with IR than the others. These diameters are attributed to particles with diameter of 0.05, 0.08, and 0.16 mm, respectively. The results also showed that increasing the percent of sand have intensified influence on increasing the final IR. Reversely, clay and silt contents showed negative effects on final IR. Furthermore, the CaCO₃ had a meaningful effect on the IR that showed the importance of lime in arid and semiarid regions. Finally, it is revealed that the role of texture was important, especially in behavior of infiltration, runoff, and production capability.     

孔隙结构和水动力对饱和多孔介质中颗粒迁移和沉积特性的耦合影响

为了研究孔隙结构和水动力对悬浮颗粒在饱和多孔介质中沉积和迁移特性的影响,对天然硅粉（悬浮颗粒）和荧光素钠（示踪剂）在饱和多孔介质中的渗流迁移特性进行土柱试验,分别得到了5种不同渗流速度（0.033、0.066、0.132、0.199、0.265 cm/s）、两种不同多孔介质（石英砂和玻璃球）的悬浮颗粒和示踪剂全组合下的20条穿透曲线。根据试验结果,研究孔隙结构、渗流速度对饱和多孔介质中颗粒迁移和沉积过程中水动力作用机制、弥散效应、加速效应的影响。研究表明,悬浮颗粒的穿透曲线可以用一阶沉积动力学对流弥散方程的解析解来描述。随着渗流速度的增大,水动力学作用对颗粒出流浓度的影响越来越大,而孔隙结构的影响则相对减弱。同时,存在一个临界渗流速度值。当渗流速度超出该值时,悬浮颗粒迁移要快于示踪剂,而且临界渗流速度对于玻璃球和石英砂两种多孔介质是不同的;其次,在两种介质中,随渗流速度增大,弥散度增加,回收率和回收悬浮颗粒粒径增大,沉积系数先增大后减小。此外,在孔隙比相近的情况下,悬浮颗粒在玻璃球介质中的回收率要大于其在石英砂中的。可见,孔隙结构和渗流速度是影响饱和多孔介质中颗粒输运的重要因素,渗流速度越大,孔隙结构的作用越明显。     

Quick assessment on susceptibility to suffusion of continuously graded soils by curvature of particle size distribution

As a major type of soil internal erosion, suffusion is causative for many geotechnical problems of earth structures and foundations. Although full laboratory tests are laborious, it is inevitable for susceptible soils. However, a good quick assessment can define those susceptible soils by eliminating quickly very stable and unstable soils from consideration. Traditional assessment methods often correlate and combine some predefined fixed particle sizes representing coarse and fine fractions of soils. This paper presents a novel, simple assessment method for identifying susceptibility to suffusion based on the general curvature of particle size distribution of soils. The further down a particle size distribution departs from its mean line, the more likely it behaves suffusive. The new assessment method has been tested against experimental data, and the results show some good correlation.     

Particle loss and volume change on dissolution: experimental results and analysis of particle size and amount effects

Soil particles may be lost through dissolution, degradation or erosion. Regardless of the process of loss, there follows a change in soil structure both in terms of phase composition and grading. In this paper, the influence of size and amount of particle loss on phase composition at two stresses is investigated. The tests are performed on sand–salt mixtures, loaded in a modified permeation oedometer and subsequently dissolved. Changes in overall volume and void ratio are presented. Two significant observations about the volumetric consequences of particle loss can be made. First, overall volume changes are directly related to the amount of dissolved particles and to a lesser extent, the size of particle lost. Second, particle loss leads to an increase in void ratio; the magnitude of the increase is related to the amount of dissolved particles but appears not to be sensitive to either the size of particle lost or the pre-dissolution void ratio. Based on the observed response and a dissolution-induced void change parameter, the influence of different mechanisms of volume change is discussed. Tests were performed at two different vertical stresses with no discernible influence on void ratio change.     

Metal concentration and particle size distribution of stream and river water polluted from copper rolling mill industry

Concentrations of heavy metals, pH, and particle size distribution parameters were measured in Dragica stream and Djetinja River water receiving wastewaters from copper rolling mill industry, Sevojno. The concentrations of copper, zinc, lead, and mercury were determined for water samples collected in summer 2009. It was found that Copper Rolling Mill Sevojno was the significant source of water pollution with copper and zinc. Considering that copper rolling mill industry, one of the larger emitters of sulfur dioxide, pollutes the area, the water pH was surprisingly alkaline. The particle size analysis results showed that particles from oil-in-water emulsion evidently got into stream water in spite of the purification devices used. In order to assess the possible relations between the measured parameters, a correlation analysis was performed. The correlation analysis showed a significant positive correlation between the total metal concentrations of copper and zinc, as well as between particle size distribution parameters and the concentration of lead and copper.