Extended wet sieving method for determination of complete particle size distribution of general soils

The traditional standard wet sieving method uses steel sieves with aperture?0.063 mm and can only determine the particle size distribution(PSD)of gravel and sand in general soil.This paper extends the traditional method and presents an extended wet sieving method.The extended method uses both the steel sieves and the nylon filter cloth sieves.The apertures of the cloth sieves are smaller than 0.063 mm and equal 0.048 mm,0.038 mm,0.014 mm,0.012 mm,0.0063 mm,0.004 mm,0.003 mm,0.002 mm,and 0.001 mm,respectively.The extended method uses five steps to separate the general soil into many material sub-groups of gravel,sand,silt and clay with known particle size ranges.The complete PSD of the general soil is then calculated from the dry masses of the individual material sub-groups.The extended method is demonstrated with a general soil of completely decomposed granite(CDG)in Hong Kong,China.The silt and clay materials with different particle size ranges are further examined,checked and verified using stereomicroscopic observation,physical and chemical property tests.The results further confirm the correctness of the extended wet sieving method.

An evaluation method for internal erosion potential of gravelly soil based on particle size distribution

Internal erosion occurs when fine particles escape from the soil driven by seepage flow,which is considered to be the crucial factor causing the failure of earth structures filled with gravelly soil.The objective of this paper is to suggest an appropriate method to assess internal erosion potential of gravelly soil.By analyzing the sensitivity of soil material to internal erosion,the variable(Dc15/df85)max and the content of coarse particles(Pc)are selected as the evaluation indexes(Dc15 and df85 are the diameters of 15%mass passing in the coarse component and 85%mass passing in the fine component,respectively).A series of gravelly soils with different particle size distributions are tested for internal erosion by the self-made permeameter.Based on the test results,an evaluation method for the internal erosion of gravelly soil is proposed.Gravelly soil is prone to internal erosion when 60%≤Pc<95%and(Dc15/df85)max≥9.5.The proposed method shows good accuracy in evaluating the internal erosion of 36 soil samples from other studies,which confirms the reliability of the method.The proposed method makes it possible to accurately assess internal erosion of gravelly soil,and an alternative method is provided for engineers to determine whether there is a risk of internal erosion in earth structures consisting of gravelly soil.

Multifractal characteristics and spatial variability of soil particle-size distribution in different land use patterns in a small catchment of the Three Gorges Reservoir Region,China

Characterizing soil particle-size distribution is a key measure towards soil property.The purpose of this study was to evaluate the multifractal characteristics of soil particle-size distribution among different land-use from a purple soil catchment and to generalize the spatial variation trend of multifractal parameters across the catchment.A total of 84 soil samples were collected from four kinds of land use patterns(dry land,orchard,paddy,and forest)in an agricultural catchment in the Three Gorges Reservoir Region,China.The multifractal analysis method was applied to quantitatively characterize the soil particle size distribution.Six soil particle size distribution(PSD)multifractal parameters(D(0),D(1),D(2),(35)a(q),(35)f[a(q)],α(0))were computed.Additionally,a geostatistical analysis was employed to reveal the spatial differentiation and map the spatial distribution of these parameters.Evident multifractal characteristics were found.The trend of generalized dimension spectrum of four land use patterns was basically consistent with the range of 0.8 to 2.0.However,orchard showed the largest monotonic decline,while the forest demonstrated the smallest decrease.D(0)of the four land use patterns were ranked as:dry land<orchard<forest<paddy,the order of D(1)was:dry land<paddy<orchard<forest,D(2)presented a rand-size relationship as dry land<forest<paddy<orchard.Furthermore,all land-use patterns presented asΔf[α(q)]<0.The rand-size relationship ofα(0)was same as D(0).The best-fitting model for D(0),D(1),D(2)andΔf[α(q)]was spherical model,forΔα(q)was gaussian model,and forα(0)was exponential model with structure variance ratio was 1.03%,49.83%,0.84%,1.48%,22.20%and 10.60%,respectively.The results showed that soil particles of each land use pattern were distributed unevenly.The multifractal parameters under different land use have significant differences,except forΔα(q).Differences in the composition of soil particles lead to differences in the multifractal properties even though they belong to the same soil texture.Farming behavior may refine particles and enhance the heterogeneity of soil particle distribution.Our results provide an effective reference for quantifying the impact of human activities on soil system in the Three Gorges Reservoir region.

Effects of water salinity and content on particle size distribution and soil strength

The effect of NaCl on soil strength was investigated in this project based on salinity concentrations of 0 g/L, 5 g/L, 20 g/L, and 50 g/L as well as varying water contents of 15%-20%. Laser particle size analyzer was also performed to explain possible effects. From particle size analysis and strength tests, it is hypothesized that the strength of the soil is increased with the addition of certain salinity concentrations until there are reversed effects, which is between 20 g/L and 50 g/L from our study. The increase of strength is suggested to be the affect of a greater variety of particle sizes. Since NaCI plays a role in the particle size distribution, it also plays a role in the strength of soils. The degree of the effect of the water content also differs from concentrations, and could be due to the variation of hydration film thickness on particles, which is affected by the ions introduced from water.

Effects of soil conservation practices on soil erosion and the size selectivity of eroded sediment on cultivated slopes

Soil conservation practices can greatly affect the soil erosion process,but limited information is available about its influence on the particle size distribution(PSD)of eroded sediment,especially under natural rainfall.In this study,the runoff,sediment yields,and effective/ultimate PSD were measured under two conventional tillage practices,downhill ridge tillage(DT)and plat tillage(PT)and three soil conservation practices,contour ridge tillage(CT),mulching with downhill ridge tillage(MDT),and mulching with contour ridge tillage(MCT)during 21 natural rainfall events in the lower Jinsha River.The results showed that(1)soil conservation practices had a significant effect on soil erosion.The conventional tillage of DT caused highest runoff depth(0.58 to 29.13 mm)and sediment yield(0.01 to 3.19 t hm^(-2)).Compared with DT,the annual runoff depths and sediment yields of CT,MDT and MCT decreased by 12.24%-49.75%and 40.79%-88.30%,respectively.(2)Soil conservation practices can reduce the decomposition of aggregates in sediments.The ratios of effective and ultimate particle size(E/U)of siltand sand-sized particles of DT and PT plots were close to 1,indicating that they were transported as primary particles,however,values lower/greater than 1 subject to CT,MDT and MCT plots indicated they were transported as aggregates.The ratios of E/U of claysized particles were all less than 1 independently of tillage practices.(3)The sediments of soil conservation practices were more selective than those of conventional tillage practices.For CT,MDT and MCT plots,the average enrichment ratios(ERs)of clay,silt and sand were 1.99,1.93 and 0.42,respectively,with enrichment of clay and silt and depletion of sand in sediments.However,the compositions of the eroded sediments of DT and PT plots were similar to that of the original soil.These findings support the use of both effective and ultimate particle size distributions for studying the size selectivity of eroded sediment,and provide a scientific basis for revealing the erosion mechanism in the purple soil area of China.

Sedimentation behavior of indoor airborne microparticles

Experiments on the behavior of airborne microparticle sediments and their adhesion on glass slides were conducted in a laboratory located on the first floor of a teaching building. Clean tiles and glass slides were placed at different angles （0°, 45° and 90°） with respect to the horizontal plane in the laboratory. The sedimentation of microparticles was investigated at certain time intervals （1 d, 3 d, l0 d and 30 d）. The results of testing, at day 30, show that the diameters of particles on the horizontal tiles varied from 20 to 80 μm; few particles with diameter less than 0.5 μm or greater than 100 μm were found. The amount of particle sediment on all the slides increased along over time, while the average diameter of particles was not correlated with time, nor with the angle of placement. The maximum particle size, the total particle surface area, the total perimeter of all particles and the cover ratio of light （the proportion of total area of particles to the observed area of the slides surfaces） did not change significantly within the first 10 days. Inspection of all the samples for the last 20 days, however, showed that these variables increased substantially with the passage of time and were in reverse proportion to the placement angles, which indicates a concentration of particles, as well as physical and chemical changes.

Soil Aggregation and Its Relationship with Organic Carbon of Purple Soils in the Sichuan Basin,China

The interaction of soil aggregate dynamics with soil organic carbon is complex with varied spatio-temporal processes in macro-and micro-aggregates. This paper is to determine the aggregation of soil aggregates in purple soils （Regosols in FAO Taxonomy or Entisols in USDA Taxonomy） for four types of land use, cropland [corn （Zea mays L.）], orchard （citrus）, forestland （bamboo or cypress）, and barren land （wild grass）, and to explore their relationship with soil organic carbon in the Sichuan basin of southwestern China. Procedures and methods, including manual dry sieving procedure, Yoder＇s wet sieving procedure, pyrophosphates solution method, and Kachisky method, are used to acquire dry, wet, and chemically stable aggregates, and microaggregates. Light and heavy fractions of soil organic carbon were separated using 2.0 g·mL^-1 HgI2-KI mixed solution. The loosely, stably, and tightly combined organic carbon in heavy fraction were separated by extraction with 0.1 M NaOH and 0.1 M NaOH-0.1M Na4P2O7 mixed solution （pH 13）. The results show that the contents of dry and wet macroaggregates 〉0.25 mm in diameter were 974.1 and 900.0 g·kg^-1 highest in red brown purple soils under forestland, while 889.6 and 350.6 g·kg^-1 lowest in dark purple soil and lowest in grey brown purple soils under cropland, respectively. The chemical stability of macroaggregates was lowest in grey brown purple soil with 8.47% under cropland, and highest in red brown purple soil with 69.34% under barren land. The content of microaggregates in dark purple soils was 587g·kg^-1 higher than brown purple soils, while 655g·kg^-1 in red brown purple soils was similar to grey brown purple soils （651g·kg^-1）. Cropland conditions, only 38.4% of organic carbon was of the combined form, and 61.6% of that existed in light fraction. Forestland conditions, 90.7% of organic carbon in red brown purple soil was complexed with minerals as a form of humic substances. The contents and stability of wet aggregates 〉 0.25 mm, contents and stability of chemically stable aggregates 〉0.25 mm, contents of microaggregates 〉 0.01 mm, contents of aggregated primary particle （d〈0.01 mm） and degree of primary particles （d 〈0.01 mm） aggregation were closely related to the concentrations of total soil organic carbon, and loosely and tightly combined organic carbon in heavy fraction. Soil microaggregation could be associated with organic carbon concentration and its combined forms in heavy fraction. There was a direct relationship between microaggregation and macroaggregation of soil primary particles, because the contents of wet aggregates 〉 0.25 mm and its water stability of aggregates were highly correlated with the contents of aggregated primary particle （d 〈 0.01 mm） and the degree of primary particles （d 〈 0.01 mm） aggregation.

Conventional tillage improves the storage of soil organic carbon in heavy fractions in the Loess Plateau, China

Soil labile organic carbon （C） plays an important role in improving soil quality. The relatively stable fractions of soil organic C （SOC） represent the bulk of SOC, and are also the primary determinant of the long-term C balance of terrestrial ecosystems. Different land use types can influence the distribution patterns of different SOC fractions. However, the underlying mechanisms are not well understood. In the present study, different fractions of SOC were determined in two land use types： a grazed grassland （established on previously cultivated cropland 25 years ago, GG） and a long-term cultivated millet cropland （MC）. The results showed that C concentration and C storage of light fractions （LF） and heavy fractions （HF） presented different patterns along the soil profiles in the two sites. More plant residues in GG resulted in 91.9% higher LF storage at the 0-10 cm soil depth, further contributed to 21.9% higher SOC storage at this soil depth; SOC storage at 20-60 cm soil depth in MC was 98.8% higher than that in GG, which could be mainly attributed to the HF storage 104.5% higher than in GG. This might be caused by the long-term application of organic manure, as well as the protection from plough pan and silt- and clay-sized particles. The study indicated that different soil management practices in this region can greatly influence the variations of different SOC fractions, while the conventional tillage can greatly improve the storage of SOC by in- creasing heavy fractions.

Shear strength features of soils developed from purple clay rock and containing less than two-millimeter rock fragments

Soil shear strength is an important indicator of engineering design and an essential parameter of soil precision tillage and agricultural machinery and equipment design. Although numerous studies have investigated the characteristics of different soil shear strengths, only a few of these works have paid attention to soils containing considerable quantities of rock fragments. To date, most studies on the effects of rock fragments on the shear strength have paid attention to the role of rock fragments with sizes 〉2 mm. The effects of rock fragments 〈2 mm in soil are generally ignored. Similar to rock fragments 〉2 ram, the presence of rock fragments 〈2 mm could also change the mechanical properties of soils. Thus, in the present study we evaluated the potential influence of 〈2 mm rock fragments on soil shear strength via an unconsolidated undrained （UU） triaxial compression test. Our results were as follows： （1） A certain quantity of 〈2 mm rock fragments presented in purple soils developed from clay rocks; and an appropriate quantity of 〈2 mm rock fragments could improve the shear strength of soils. （2） The different PSDs of soils containin 〈2 mm rock fragment mainly caused variations in the internal friction angle of soils. （3） The shear strengths of the two mudstone-developed red-brown and gray-brown purple soils was more sensitive to water than that of the shale-developed coarse-dark purple soil. As the soil water content increased from 9% to 23%, the changes in the cohesion, internal friction angle, shear strength, and the maximum principal stress difference were smaller in the coarse dark purple soil than in the two other soils. We therefore concluded that 〈2 mm rock fragments in purple soils exerted important effects on soil shear strength. A better understanding of the differences among the shear strength features of purple soils could help improve the design of agricultural machinery and equipment.

Characterization of Dispersive Soils

Dispersive soils which occur in many parts of the world are easily erodible and segregate in water pose serious problems of stability of earth and earth retaining structures. The mechanism of dispersivity of soils is reasonably well understood. However there is simple method to identify the dispersivity of the soils and even more difficult to quantify the dispersivity. Visual classification, Atterberg’s limits and particle size analysis do not provide sufficient basis to differentiate between dispersive clays and ordinary erosion resistant clays. Pinhole test and double hydrometer test are the only two tests that are in vogue to identify the dispersive soils. This paper explores the possibility of using other standard tests such as shrinkage limit and unconfined compressive strength tests to quantify the dispersivity of the soils. The rationale of using the methods and correlation between the dispersivity determined by various methods has been explained. It has been concluded that dispersivity ascertained from strength tests is more reliable.

Development of a drill energy utilization index for aiding selection of drill machines in surface mines

Drill machines used in surface mines, particularly in coal, is characterized by a very poor utilization （around 40%） and low availability （around 60%）. The main purpose of this study is to develop a drill selec- tion methodology and simultaneously a performance evaluation technique based on drill cuttings produced and drilling rate achieved. In all 28 blast drilled through were investigated. The drilling was accomplished by 5 different drill machines of Ingersoll-Rand and Revathi working in coal mines of Sonepur Bazari （SECL） and Block-II （BCCL）. The drills are Rotary and Rotary Percussive type using tri- cone rock roller bits. Drill cuttings were collected and sieve analysis was done in the laboratory. Using Rosin Ramler Diagram, coarseness index （CI）, mean chip size （d）, specific-st trace area （SSA） and charac- teristic particle size distribution curves for all the holes drilled were plotted. The predictor equation for drill penetration rate established through multiple regressions was found to have a very good correlation with an index of determination of 0.85. A comparative analysis of particle size distribution curves was used to evaluate the drill efficiency. The suggested approach utilises the area under the curve, after the point of trend reversal and brittleness ratio of the respective bench to arrive at drill energy utilization index （DEUI）, for mapping of drill machine to bench, The developed DEU1 can aid in selecting or mapping a right machine to right bench for achieving higher penetration rate and utilizations.

石羊河尾闾青土湖表层土壤粒度空间分布特征

[目的]揭示石羊河尾闾青土湖土壤粒度空间分布特征,为该区域生态恢复提供理论依据。[方法]以湖区为中心分别在西北、正东、东南方向上布设样线并采集0—20 cm深度土壤样品,对比分析了青土湖周边不同区域沙物质粒配组成、粒配曲线等参数特征。[结果](1)青土湖表层土壤粒度组成以细砂为主(26.26%~84.97%),其中西北方向上表层土壤粒度以细砂为主(26.26%~66.62%),其次是粉粒(4.23%~46.35%);正东、东南方向上表层土壤粒度组成以细砂为主(43.41%~86.30%),其次是极细砂(1.86%~29.60%)。不同样线同粒级间含量存在差异。(2)研究区表层土壤颗粒总体较粗,分选较差,偏度为正偏度,峰度属尖窄。粒度参数的空间分布表现为:西北方向表层土壤平均粒径较其他方向偏细,分选性较差,偏度也更为正偏,峰值小于正东方向。正东、东南方向表层土壤平均粒径较为一致,明显偏粗,分选性分别属中等、较好,均为近于对称,峰度为尖窄、中等。(3)西北方向土壤粒度频率平均值分布曲线表现为双峰型,正东、东南方向为单峰型。粒度累计分布曲线反映出,东南方向风沙活动较正东、西北方向频繁、强烈。(4)通过沉积环境判别得出西北方向主要是湖相沉积,正东、东南主要是风成沉积。[结论]成土过程和干旱多风的环境条件影响青土湖土壤的基本特性,而通过生态输水形成水面改善了该区的土壤环境。

粒度分布对红层土石混合体强度及颗粒破碎的影响

红层土石混合体已广泛应用于川渝地区公路、铁路的路基填筑,研究其强度及颗粒破碎特征可为该地区路基快速安全施工提供理论支撑。针对现有粒度分布评价方法对土石混合体适用性的不足,提出中间粒径块石相对含量C_(m)指标并拟定4个水平,选择四川盆地红层土石混合体为材料,比选叠环剪和大型直剪试验后,结合筛分试验探讨粒度分布对红层土石混合体强度及颗粒破碎的影响规律。试验结果表明:叠环剪试验中剪切面非人为固定,剪切带影响域明显大于大型直剪试验,相同试验条件下土石混合体强度低于大型直剪试验,且法向应力越大,强度差值越大。C_(m)对红层土石混合体的强度及颗粒破碎特征影响显著。随C_(m)的增大,黏聚力先减小后增大,内摩擦角先增大后减小,抗剪强度先增大后减小,均在C_(m)=0.543时有最值,此时,颗粒间的摩擦和重定向排列对强度的增强效应明显大于咬合减弱的负面效应,剪应力有二次攀升。叠环剪试验后,大粒径、中间粒径块石含量降低,土体含量增高,小粒径块石含量在C_(m)≤0.343时降低,C_(m)≥0.343时增高;颗粒相对破碎率随法向应力和C_(m)的增大,均呈先降低后升高的规律,C_(m)=0.343时颗粒相对破碎率最低。

高QI含量中温沥青制备中间相炭微球的研究

以高QI含量的中温沥青(HCTP)为原料,通过热缩聚法制备中间相炭微球(MCMB),考察了反应条件(反应温度、恒温时间和搅拌速率)对MCMB性质的影响。通过偏光显微镜、粒度分析仪、扫描电镜、XRD和拉曼光谱等对MCMB的粒度分布、表面微观形貌和微晶结构进行了研究。结果表明:以HCTP为原料制备MCMB的最佳反应条件为聚合温度430℃、恒温时间4.5 h、搅拌速率120 r/min;在此条件下制备的MCMB球形度好,收率为29.62%,平均粒径为20.87μm,粒度均匀性指数为0.93;1100℃炭化处理后,MCMB的理想石墨化碳微晶质量分数为75.45%。

骨架颗粒组成对散粒土管涌规律影响的试验研究

利用改进的渗透装置试验研究了细颗粒(0.075~1 mm)含量相同时骨架颗粒组成含量不同对散粒土的管涌发生临界条件以及颗粒侵蚀流失规律的影响,结果表明:不同颗粒级配的试样在管涌发生前,水力梯度与渗流速度呈线性关系,基本符合达西定律;骨架颗粒1~2、2~3、3~5 mm 3个粒径段对管涌发展起到了阻碍作用,其中1~2 mm粒径段颗粒对管涌孔隙的堵塞作用强于另外两个粒径段颗粒;对于不同级配的骨架颗粒,其不均匀系数越大,试样的下限临界水力梯度值就越大,细颗粒越不易起动,发生管涌的时间越晚,而不同级配的骨架颗粒对试样的上限临界水力梯度影响较小。

Soil particle size distribution and its relationship with soil water and salt under mulched drip irrigation in Xinjiang of China

Soil particle size distribution(PSD),one of the most important soil physical attributes,is of great importance to soil water movement,soil erosion and soil solute migration.In this study,the soil PSD of 563 soil samples from the mulched drip irrigated cotton fields in Xinjiang of China were measured by laser diffraction particle size analyzer.The soil PSD characteristics and its relations with soil water and salt were studied by using the combined methods of textural triangle,fractal and multifractal analysis.The results showed very low clay content(about 1.52%) while really high sand content of the studied soil,and a complex shape of bimodal or unimodal of soil PSD.The results also showed that the two indices,i.e.,standard deviation and the peak value of soil particle relative volumes,were good indicators of soil PSD and thus had good relations with fractal and multifractal characteristics.The correlative analysis further indicated that the mulched drip irrigation had a significant impact on the distribution of the soil salt,while this impact withered for the deeper soil layer.The soil texture feature was found to dominate soil water and salt distribution,especially the surface soil salt content and the deep soil water content.

Bounding surface model for ballast with additional attention on the evolution of particle size distribution

Particle size distribution significantly influences the mechanical response of the ballast under low confining pressure.However,particle breakage usually occurs and unfavorably degrades the particle size distribution of the ballast when sufficient load is applied.To model the triaxial stress-strain behavior and its associated evolution of particle size distribution of the ballast,a specific bounding surface model is proposed.The proposed model is based on the traditional bounding surface plasticity and a modified particle breakage index,which correlates the initial gradation and the ultimate gradation together with the current gradation.Simulation of the experimental results from the triaxial compression tests shows that the proposed model can predict the strain softening and volumetric expansion of the ballast under relatively lower confining pressure.It is also able to simulate the strain hardening and volumetric compression of the ballast under relatively higher confining pressure.Most importantly,the proposed approach was observed to have a great potential in predicting the evolution of the particle size distribution of the ballast.

Unraveling the size distributions of surface properties for purple soil and yellow soil

Soils contain diverse colloidal particles whose properties are pertinent to ecological and human health, whereas few investigations systematically analyze the surface properties of these particles. The objective of this study was to elucidate the surface properties of particles within targeted size ranges（i.e. 〉 10, 1-10, 0.5-1, 0.2-0.5 and 〈 0.2 μm） for a purple soil（Entisol） and a yellow soil（Ultisol） using the combined determination method. The mineralogy of corresponding particle-size fractions was determined by X-ray diffraction.We found that up to 80% of the specific surface area and 85% of the surface charge of the entire soil came from colloidal-sized particles（〈 1 μm）, and almost half of the specific surface area and surface charge came from the smallest particles（〈 0.2 μm）. Vermiculite,illite, montmorillonite and mica dominated in the colloidal-sized particles, of which the smallest particles had the highest proportion of vermiculite and montmorillonite. For a given size fraction, the purple soil had a larger specific surface area, stronger electrostatic field, and higher surface charge than the yellow soil due to differences in mineralogy.Likewise, the differences in surface properties among the various particle-size fractions can also be ascribed to mineralogy. Our results indicated that soil surface properties were essentially determined by the colloidal-sized particles, and the 〈 0.2 μm nanoparticles made the largest contribution to soil properties. The composition of clay minerals within the diverse particle-size fractions could fully explain the size distributions of surface properties.

中性地浸采铀全流程溶液中颗粒粒径分布及过滤建议

掌握中性地浸采铀全流程溶液中颗粒大小,对调控浸出过程、优选过滤器、确定除固位置、缓解矿层堵塞、恢复抽注液量和减轻树脂床层板结等具有指导意义。以内蒙古纳岭沟矿床中性地浸采铀全流程溶液为对象,基于激光粒度仪测试数据,获取了全流程溶液中颗粒粒径分布规律。结果表明,浸出液中颗粒粒径频率分布曲线呈非对称性,累计分布曲线呈“S”型,粒径分布范围窄,最大颗粒粒径<100μm;树脂床层对颗粒物有较强的过滤作用,吸附尾液过滤器的滤袋精度应根据树脂粒径大小和系统压力确定;中性体系中加入的O 2或CO 2对颗粒粒径影响微弱;淋洗合格液和沉淀罐中母液的颗粒粒径频率分布曲线均呈“双峰”型,贫液中颗粒粒径频率则呈正态分布;母液槽中颗粒最大粒径约为40μm。建议该矿床原液袋式过滤器的滤袋精度选用10~50μm,同时在母液槽与淋洗剂配制罐之间增加10~20μm精度的过滤器。

吸管法和激光法测定紫色土机械组成对比研究

吸管法是测定土壤机械组成的经典方法,激光法是测定土壤机械组成的简便方法.为探究两者在紫色土机械组成测定上的差异以及两者之间的联系,分别采用两种方法测定145个紫色土样品的机械组成,并建立线性方程、随机森林回归(Random Forest Regression,RFR)模型和支持向量回归(Support Vactor Regression,SVR)模型进行比较分析.结果表明:(1)相较于吸管法,激光法所测紫色土黏粒含量和粉粒含量均偏高,所测砂粒含量则偏低;(2)随着土壤砾石含量的增加,两种方法所测的相同粒级含量差值逐渐增大,且差值从大到小依次为:砂粒、粉粒、黏粒;(3)相比于pH>7.5的紫色土,两种方法所测的相同粒级含量差值明显大于pH≤7.5的紫色土,且差值从大到小依次为:砂粒、粉粒、黏粒.总体来看,紫色土的砾石含量是影响两种方法所测机械组成关联效果的一个关键因素,对于砾石含量≤5%的紫色土,两种方法的测定结果有很好的关联性,可采用激光法替代吸管法,但测定结果需要校正,建议选用拟合效果较好的RFR或SVR模型进行校正.