<p>Most of the water fed into a paper machine is removedmechanically in the forming and press sections. One of thefactor which has an important influence on mechanicaldewatering, i.e. in both forming and pressing, is thestress-strain behaviour of the fibre network.</p><p>The focus of this thesis is on the development of improvedmathematical descriptions of the stress-strain behaviourexhibited by fibre networks in the forming and press sections.The first part of the thesis presents a physically based modelof the forming and densification of fibre mats in twin-wireformers. The model can calculate the ecect of the applicationof a varied load through the forming section. It was developedfrom mass and momentum balances of the fibre and liquid phases,the fibre mat stress-porosity relation and an expression forthe permeability as a function of the porosity. The fibre-matstress-porosity relation used is rate-independent and presentshysteresis. Simulations have been conducted to study theeffects of roll pressure, blade pulses, wire tension andbeating. The effect of sequential blade pressure pulses afterthe forming roll on the dewatering and the concentrationgradients could be characterised. The simulations alsoexhibited rewetting by expansion when the fibre mats left theforming roll. Increasing wire tension resulted in increaseddewatering, but the rate of increase diminished rapidly withincreasing tension. The simulation results also indicated thatbeating has a large influence on dewatering.</p><p>The second part of the thesis presents two models of therate-dependent stress-strain behaviour of the fibre networkthat is observed in wet pressing. The first model was based onthe approach pioneered by Perzyna (1966) for strain-ratedependent plasticity and was quite satisfactory for calculatingthe stress-strain behaviour of the fibre network in singlepress nips. It was successfully applied for studyingdensification and dewatering in both normal wet pressing andhigh temperature wet pressing. However, the first model onlyincludes rate dependence in the compression phase of thecompressionexpansion cycle; the expansion phase is treated asbeing rate independent</p><p>The second model of the stress-strain behaviour of the fibrenetwork treats both compression and expansion as being ratedependent, according to experimental observations. It is basedon the idea that the wet fibre web may be conceived as alayered network of restricted swelling gels. A swollen fibre isa restricted gel, the inner swelling pressure in a swollenfibre wall being balanced by the stresses in the fibre wallstructure. The observed rate dependence of wet webs in bothcompression and expansion phases was attributed to the flow ofwater out of and into the fibre walls. The second model gavepredictions that are in good agreement with results fromuniaxial experiments using pressure pulses of arbitrary shapefor both a single pulse and a sequence of pulses. It maytherefore be used as a general model for the rheologicalbehaviour of the wet fibre network in wet pressing, providedthe model parameters are estimated from experimental data withsmall experimental error.</p><p><b>KEYWORDS:</b>Paper, modelling, dewatering, forming, wetpressing, fibre network stress, rheology, hysteresis,intra-fibre water, compressibility, structural stress,stress-strain, restricted gels, swelling.</p>

Spherical agglomerates of benzoic acid crystals have been successfully prepared by drowning-out crystallization in three solvent partial miscible mixtures. Benzoic acid is dissolved in ethanol, bridging liquid is added and this mixture is fed to the agitated crystallizer containing water as the anti-solvent. Small crystals are produced by crystallization of the substance, and the crystals are agglomerated through the action of the bridging liquid. Different solvents: chloroform, toluene, heptane, pentane, cyclohexane, ethyl acetate and diethyl ether are chosen as bridging liquids, all being low soluble in water and showing good wettability for benzoic acid crystals. The influence of process conditions such as concentration of solute, agitation rate, feeding rate, amount of bridging liquid and temperature on the properties of benzoic acid spherical agglomerates, are investigated. Different sets of experiments were accomplished to track how the properties of the particles gradually change during the normal spherical crystallization experiment. Other sets of experiments were performed to examine the influence of agitation and process time for agglomeration. The product properties such as particle size distribution, morphology and mechanical strength have been evaluated. The mechanical strength of single agglomerates has been determined by compression in a materials testing machine, using a 10 N load cell. Compression characteristics for single agglomerates are compared with the data on bed compression. The present study shows that the bridging liquid has significant influence on the product properties, using diethyl ether and ethyl acetate no agglomerates are formed. Using any of the other five solvents (chloroform, toluene, heptane, pentane, and cyclohexane) spherical agglomerates are formed, as long as a sufficient amount of the bridging liquid is used. Using cyclohexane as bridging liquid at 5°C and toluene at 20°C the particles are larger compared to particles formed at other conditions. The highest particle fracture stress is obtained by using toluene as the bridging liquid at 5 and 20°C. Particle morphology depends on the bridging liquid used and the particles are completely spherical when toluene and pentane are used as bridging liquids. Different process parameters are found to have a significant influence on the physico-mechanical properties of the product. The range of operation for spherical agglomeration is relatively narrow and only at certain conditions spherical agglomerates are produced. With increasing amount of bridging liquid the particle size and strength increase and the morphology improves. Particle size decreases and the fracture force increases with increasing feeding rate, but the morphology remains unchanged. For all the solvents, the particle size and the fracture stress increase with decreasing temperature. For four of the solvents the morphology improves with decreasing temperature. For cyclohexane the result is the opposite, in that the particles are spherical at 20°C and irregular at 5°C. Spherical agglomerates of benzoic acid, both as single particles as well as in the form of a bed, have a high compressibility and low elastic recovery, properties that are favorable for direct tabletting. As the feed solution is supplied to the crystallizer the amount of benzoic acid that can crystallize actually does crystallize fairly rapidly. Hydrodynamics are responsible for bringing particles together for the agglomeration. Experiments reveal that during the gradual addition of the feed to the agitated aqueous solution, both particle size and particle number increases. It is clear from the experiments that not only further addition of feed solution leads to larger product particles but also continued agitation. Along the course of the process the properties of the particles change gradually but substantially. By continued agitation, the particle porosity decreases, density, strength gradually increases and also the spherical shape develops gradually. / QC 20110419

Direct compression has gained significant interest since its advent in the late 1950's due to its potential ease compared to wet granulation. The primary prerequisites for powders used in direct compression are (i) good flow properties (ii) good compressibility and (iii) an acceptable dilution potential to accommodate a relative high percentage of active ingredient. Several filler/binders have been manufactured especially for direct compression and co–processing is one of the recent methods used to produce good compressible excipients with acceptable flow properties. In this study, lactose–based filler/binders were used which included simple and modified lactose materials (Granulac, Lactopress, Flowlac and Tablettose) as well as co–processed excipients (Starlac, Cellactose and Microcelac). A comprehensive literature study on direct compression revealed the importance of the physical properties of filler/binders such as interparticle forces, particle shape, particle size and distribution, powder density, particle surface structure and particle packing geometry which influence the flow of powders. All the materials were subjected to the various tests available to evaluate powder flow, namely (i) angle of repose (AoR), (ii) critical orifice diameter (COD), (iii) flow rate and percentage compressibility (%C) in terms of the powders' bulk and tap densities. The results of these tests confirmed the expected flow properties of the various filler/binders, with only one material exhibiting extremely poor flow properties. The following rank order in terms of all flow tests conducted was established; Starlac >> Microcelac ~ Flowlac >> Cellactose > Tablettose > Lactopress >>> Granulac. The co–processed filler/binders presented with superior flow compared to the other lactose–based materials. During the next phase of the study, the compaction properties of the various fillers were evaluated, employing direct compression. Compacts of pure filler were tabletted on an eccentric tablet press at different compression pressures (manipulated by the upper punch setting of the tablet press). The modified lactose filler/binders (Lactopress, Flowlac and Tablettose) exhibited unexpectedly poor compression profiles, where the co–processed filler/binders (Starlac, Cellactose and Microcelac) produced compacts with acceptable appearance and compact properties. Two lubricants (Mg–St or Pruv), which were tested separately in formulations were added since no compacts could be produced from the pure filler/binders. None of the modified lactose filler/binders, in combination with a lubricant, were able to produce an acceptable compact, since lamination occurred during compression. The co–processed filler/binders produced satisfactory compacts with the addition of a lubricant, but lactose–cellulose fillers (Cellactose and Microcelac) also required the inclusion of a disintegrant (Ac–Di–Sol) to induce satisfactory compact disintegration. Poor compressible active ingredients (paracetamol), which exhibit very poor flow properties, are usually difficult to use during direct compression. Many excipients (tested in this study) are formulated to accommodate these drugs and produce acceptable functional tablets. After identifying the best filler/binders (co–processed fillers), according to their flow and compressible properties, paracetamol was added to the formulations. During a pilot study, the percentage paracetamol these fillers could accommodate in a 400 mg tablet was determined. Both Microcelac and Cellactose could accommodate 24.5% w/w paracetamol, whilst Starlac could only accommodated 19.5% w/w. Paracetamol is well known for its tendency to cause tablet capping and lamination. An acceptable upper punch setting range (20–22) was chosen for tabletting, followed by quality control tests done. All three formulations produced suitable tablets for testing and exhibited good tablet properties. All tablets disintegrated within two minutes, with hardness profiles between 120 N and 148 N and friability percentages less than 1%. Dissolution studies, however, are probably the ultimate test to distinguish between the capability of filler/binders to release the optimum percentage drug after disintegration. Dissolution studies were done on all three formulations using the AUC (area under the curve) and IDR (initial drug release) as parameters to evaluate drug release. All tablets exhibited high initial dissolution rates (between 0.018 - 0.023 mg/min/ml) and 100% drug release was observed. Starlac presented with a lower amount of drug released compared to the other two, but can be explained by the lower percentage (19.5%) paracetamol present in the formulation. It was once again confirmed that the physical and compressible properties of potential directly compressible filler/binders play a major role in direct compression. It was concluded that co–processed filler/binders (Starlac, Microcelac and Cellactose) definitely exhibited better tabletting properties during direct compression. They were able to accommodate a certain percentage of paracetamol, although it was expected that they would accommodate a higher amount (at least 50% of total tablet weight). / Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2011.

Direct compression has gained significant interest since its advent in the late 1950's due to its potential ease compared to wet granulation. The primary prerequisites for powders used in direct compression are (i) good flow properties (ii) good compressibility and (iii) an acceptable dilution potential to accommodate a relative high percentage of active ingredient. Several filler/binders have been manufactured especially for direct compression and co–processing is one of the recent methods used to produce good compressible excipients with acceptable flow properties. In this study, lactose–based filler/binders were used which included simple and modified lactose materials (Granulac, Lactopress, Flowlac and Tablettose) as well as co–processed excipients (Starlac, Cellactose and Microcelac). A comprehensive literature study on direct compression revealed the importance of the physical properties of filler/binders such as interparticle forces, particle shape, particle size and distribution, powder density, particle surface structure and particle packing geometry which influence the flow of powders. All the materials were subjected to the various tests available to evaluate powder flow, namely (i) angle of repose (AoR), (ii) critical orifice diameter (COD), (iii) flow rate and percentage compressibility (%C) in terms of the powders' bulk and tap densities. The results of these tests confirmed the expected flow properties of the various filler/binders, with only one material exhibiting extremely poor flow properties. The following rank order in terms of all flow tests conducted was established; Starlac >> Microcelac ~ Flowlac >> Cellactose > Tablettose > Lactopress >>> Granulac. The co–processed filler/binders presented with superior flow compared to the other lactose–based materials. During the next phase of the study, the compaction properties of the various fillers were evaluated, employing direct compression. Compacts of pure filler were tabletted on an eccentric tablet press at different compression pressures (manipulated by the upper punch setting of the tablet press). The modified lactose filler/binders (Lactopress, Flowlac and Tablettose) exhibited unexpectedly poor compression profiles, where the co–processed filler/binders (Starlac, Cellactose and Microcelac) produced compacts with acceptable appearance and compact properties. Two lubricants (Mg–St or Pruv), which were tested separately in formulations were added since no compacts could be produced from the pure filler/binders. None of the modified lactose filler/binders, in combination with a lubricant, were able to produce an acceptable compact, since lamination occurred during compression. The co–processed filler/binders produced satisfactory compacts with the addition of a lubricant, but lactose–cellulose fillers (Cellactose and Microcelac) also required the inclusion of a disintegrant (Ac–Di–Sol) to induce satisfactory compact disintegration. Poor compressible active ingredients (paracetamol), which exhibit very poor flow properties, are usually difficult to use during direct compression. Many excipients (tested in this study) are formulated to accommodate these drugs and produce acceptable functional tablets. After identifying the best filler/binders (co–processed fillers), according to their flow and compressible properties, paracetamol was added to the formulations. During a pilot study, the percentage paracetamol these fillers could accommodate in a 400 mg tablet was determined. Both Microcelac and Cellactose could accommodate 24.5% w/w paracetamol, whilst Starlac could only accommodated 19.5% w/w. Paracetamol is well known for its tendency to cause tablet capping and lamination. An acceptable upper punch setting range (20–22) was chosen for tabletting, followed by quality control tests done. All three formulations produced suitable tablets for testing and exhibited good tablet properties. All tablets disintegrated within two minutes, with hardness profiles between 120 N and 148 N and friability percentages less than 1%. Dissolution studies, however, are probably the ultimate test to distinguish between the capability of filler/binders to release the optimum percentage drug after disintegration. Dissolution studies were done on all three formulations using the AUC (area under the curve) and IDR (initial drug release) as parameters to evaluate drug release. All tablets exhibited high initial dissolution rates (between 0.018 - 0.023 mg/min/ml) and 100% drug release was observed. Starlac presented with a lower amount of drug released compared to the other two, but can be explained by the lower percentage (19.5%) paracetamol present in the formulation. It was once again confirmed that the physical and compressible properties of potential directly compressible filler/binders play a major role in direct compression. It was concluded that co–processed filler/binders (Starlac, Microcelac and Cellactose) definitely exhibited better tabletting properties during direct compression. They were able to accommodate a certain percentage of paracetamol, although it was expected that they would accommodate a higher amount (at least 50% of total tablet weight). / Thesis (M.Sc. (Pharmaceutics))--North-West University, Potchefstroom Campus, 2011.

The use of coarse-grained fill materials has grown significantly in recent years especially on account of their use in dams and transportation networks. This study investigates compressibility of various coarse-grained fill materials in dry and wet loading conditions in oedometer test. Four materials were used in the experiments, which falls into GP, GW, GM and GC categories respectively. GP material is a weathered rock obtained from Eymir Lake region. This material was chosen especially to be able to investigate degradation and particle breakage due to compaction and compression. GW, GM and GC materials were obtained by using the material called &lsquo / bypass&rsquo / which is a fill material used in the construction of metro of Eryaman. Using these four materials, large-scale double oedometer tests were carried out to investigate compressibility in both dry and wet conditions. The double oedometer testing technique is used to investigate the effect of soaking on compressibility behaviour of compacted fill materials. Various compactive efforts were used in the compaction stage to investigate the effect of compactive effort on compressibility and degradation of the four gravelly materials. Gradations of the post-test samples were obtained and particle breakage due to compaction using various compactive efforts and particle breakage due to compression were determined. It is found that amount of compression does not necessarily depend on the dry density of the material and fine fraction is also a dominating property regarding the compressibility in coarse-grained fill materials. The vertical strains induced by soaking are on the order of 12% - 20% of the compression measured in dry loading case for the well-graded coarse-grained fill materials tested. Besides, there is significant particle breakage in the compaction process and no further particle breakage in the oedometer test for GP material.

One of the most critical problems geotechnical engineers face with is the determination of the amount of consolidation settlement that will occur at a site as a result of the construction of a structure. The compressibility behavior of the soil is an important parameter in determining the amount of consolidation settlement. The goal of this study is to develop probabilistically based correlation between the compressibility behavior of soil and in-situ test data. Within the scope of this research effort, performed CPT tests and the recorded settlement case histories where consolidation settlements at the field under various surcharge loads were compiled from the Bursa East and West Waste Water Treatment Plant soil investigation projects. A database was composed of the results of 45 CPT and 57 settlement plate recordings. For the compilation of this database, a series of finite difference software FLAC-3D analyses were carried out to calculate the change in stress distribution under the settlement plates. A maximum likelihood framework was used for the development of compressibility behavior of soils. As a result of careful processing of available data, the cone tip resistance (qc), soil behavior type index (Ic) were selected as two important parameters effecting the value of the one-dimensional constraint modulus, M. The regression analysis which uses the settlement values recorded at the site and those computed using the change in the stress distribution, the thickness of the sublayers and the proposed one-dimensional constraint modulus were carried out to calculate the values of these model parameters. Two correlations based on the cone tip resistance and soil behavior type index were developed for the computation of the one-dimensional constraint modulus, M.

Durante a cura, ou seja, durante o processo de reticulação, resinas sofrem alterações irreversíveis em suas propriedades químicas e físicas, como, por exemplo, alterações significativas em seu coeficiente de compressibilidade (inverso do módulo de compressão volumétrico) e em sua viscosidade. A variação destas propriedades, ao longo de uma dimensão (direção) no interior de uma resina em processo de cura, pode ser obtida a partir de técnicas ultrassônicas baseadas no princípio pulso-eco, que permite a estimativa da velocidade de propagação e das atenuações das ondas. Antes da cura, as resinas apresentam velocidades de propagação entre 1600 e 1800 m/s, com viscosidade e atenuação pequenas. Durante o processo de cura ocorre um aumento notável da viscosidade, que causa grandes atenuações na onda ultrassônica. Chegando ao final do processo de cura, tanto a atenuação quanto a viscosidade voltam a diminuir. Após a reticulação, a velocidade de propagação pode ser superior a 2500 m/s. Visto que a densidade varia pouco durante a cura, a alteração de velocidade, observada durante a cura, pode ser atribuída às mudanças no módulo de compressão volumétrico da resina. O método pulso-eco descrito nesta dissertação permite monitorar, de forma não invasiva, a variação da viscosidade e a variação do coeficiente de compressibilidade durante o tempo de cura de uma resina epóxi, ao longo da direção de propagação de uma onda ultrassônica. / During the curing process, i.e. crosslinking process, resins suffer significant and irreversible changes on theirs chemical and physical properties, as the alterations in the compressibility coefficient (the inverse of bulk modulus) and in the viscosity. The changes in these properties along a direction inside of a resin, under a curing process, can be estimated with techniques based on pulse-echo ultrasonic waves. With these techniques is possible to obtain the ultrasonic wave speed and the attenuation imposed on the wave by a resin under curing. Before the cure, resins have speeds of wave propagation between 1600 and 1800 m/s, low attenuation and low viscosity. As the curing process evolves, there is a remarkable increase of viscosity, which causes great attenuations. After that, and until the end of the curing process, the viscosity and the attenuation decrease. After the cure and solidification, the wave speed may reach values up to 2500 m/s. Since the density almost does not vary during the cure, the changes in wave speed can be attributed to changes in the resins bulk modulus. The pulse-echo method, described in this dissertation, allows the monitoring, in a no invasive way, of the variation of the bulk modulus and the changes in viscosity along a direction of propagation of an ultrasonic wave, during the curing process of an epoxy resin.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A descoberta de reservatórios de petróleo na camada do pré-sal abriu novas perspectivas para a economia brasileira. A grandes profundidades, com elevado teor de CO2 e submetidos a altas pressões e temperaturas, a exploração de petróleo das camadas de pré-sal constitui um considerável desafio tecnológico. Neste contexto, o conhecimento dos coeficientes de compressibilidade são fundamentais para o estudo do comportamento termodinâmico e escoamento dos fluidos destes campos de produção. Com este objetivo, foram determinadas experimentalmente nesta dissertação a massa específica e a velocidade do som de sistemas envolvendo quatro hidrocarbonetos puros: n-decano, n-hexadecano, decalina e tetralina, assim como para sistemas multicompostos envolvendo estes hidrocarbonetos e para uma amostra de condensado de petróleo. Os resultados obtidos permitiram o cálculo dos coeficientes de compressibilidade isentrópica, isotérmica e isentálpica. É apresentada uma avaliação sobre a capacidade de se correlacionar dados experimentais de velocidade do som aos dados calculados pelas equações de estado de Peng-Robinson e Lee-Kesler com regras de mistura: (i) Spencer e Danner e (ii) Lee-Kesler / The discovery of oil reservoirs in the pre-salt layer has opened new perspectives for Brazilian economy. In deep waters, with high levels of CO2 and subjected to high pressures and temperatures, the oil exploration in the pre-salt layer is a considerable technological challenge. In this context, knowledge of compressibility coefficients and phase equilibrium data are essential for studying the thermodynamic behavior and flow in these oil fields. With this objective, experimental data were obtained for density and sound velocity in systems involving four pure hydrocarbons: n-decane, n-hexadecane, decalin and tetralin, as well as in multi-component systems involving these hydrocarbons, and in a sample of oil condensate. The results obtained allowed the calculation of isentropic, isothermal and isenthalpic compressibility coefficients. An evaluation on the ability to correlate experimental data of sound velocity with data calculated from Peng-Robinson and Lee-Kesler equations of state with mixing rules: (i) Spencer and Danner and (ii) Lee-Kesler is presented

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Soil compaction is a problem in different production systems: agriculture, pasture and forest. In the agriculture soil compaction is well documented, while in the pasture and forest its study is scarce. The objective of this study was to evaluate the physical-hydric quality of an Alfisol under forest and pasture in South Brazil, and stabilish parameters and values indicatives of soil quality. The study was carried out in Butiá county, located in the physiographic region of Serra do Sudeste (Escudo Rio- Grandense) in the Rio Grande do Sul state. Four areas were studied: native forest; five-years old pasture, installed under conventional tillage and constituted of Brachiaria brizantha associated with Paspalum lourai and Trifolium sp.; 20-years old Eucalyptus saligna, installed under conventional tillage in 1986; 4.5-years old Eucalyptus saligna in second cycle, where the first cycle was cut 8.5 years after installed. manually and carried out with forwarder. Soil physical properties (bulk density, soil porosity, soil aggregation, air permeability and parameter S), hydrical properties (hydraulic conductivity and soil water retention curve) and mechanical properties (soil penetrations resistance, degree of compactness and compressibility) of soil were evaluated. The depth of soil compaction in the pasture is around 0.10 m, while in the mechanized harvest of eucalyptus may reach 0,40 m, which indicates the need for permanent controlled traffic to minimize soil compaction in forest areas. The critical values of soil physical properties to the growth and yield of annual crops looks effective for perennial and pasture crops. With the increment of soil compaction there is compression of soil aggregates, increase of bulk density and decrease of soil porosity, affecting negatively the fluxes of air and water of soil. Intermediate levels of soil compaction are favorable to the environment, and probably to the plant growth, due to the better soil structure (porosity and bulk density) and greater water availability, along with more efficient to the deformations and susceptibility to compaction. Using bulk density, soil penetration resistance and soil moisture, it is possible to estimate the soil load support ability and its susceptibility to compaction. Biological pores, formed by the action of soil organisms and root decomposition, are effective to increment air flux, fundamental to water infiltration and air flux under conditions of high bulk density. To obtain the reference bulk density to calculate the degree of compactness in forest and pasture, the soil with preserved structure must be sampled in the layer of 0.10 0.125 m, equilibrated under tension of 33 kPa and the reference bulk density must be that obtained from pressure of 1600 kPa. / A compactação é um problema que tem sido verificado nos diferentes sistemas de manejo do solo: agrícola, pecuária e florestal. Na área agrícola a compactação tem sido documentada, enquanto na pecuária e florestal os estudos ainda são incipientes. Com o objetivo de avaliar a qualidade físicohídrica de um Argissolo sob floresta e pastagem no Sul do Brasil, e estabelecer parâmetros e valores indicadores de qualidade do solo, realizou-se um estudo no município de Butiá, situado na região fisiográfica Serra do Sudeste (Escudo Rio-Grandense) do Estado do Rio Grande do Sul, sob um Argissolo Vermelho distrófico. Foram utilizadas quatro áreas: floresta antropizada constituída por espécies arbóreas e arbustivas; pastagem implantada há 5 anos sob preparo convencional e constituída do consórcio de braquiária brizanta (Brachiaria brizantha) com pensacola (Paspalum lourai) e trevo (Trifolium sp.); povoamento de Eucalyptus saligna com vinte anos de idade, sendo realizado o preparo convencional do solo para implantação do povoamento no ano de 1986; e plantio clonal de Eucalyptus saligna conduzido em 2ª rotação com 4,5 anos de idade, sendo a colheita do eucalipto no primeiro corte, aos 8,5 anos de idade, feita manualmente com motosserra e a extração da madeira realizada com Forwarder. Foram avaliadas propriedades físicas (densidade, porosidade, agregação do solo, permeabilidade ao ar e parâmetro S), hídricas (condutividade hidráulica do solo saturado e curva de retenção de água) e mecânicas (resistência à penetração, grau de compactação e compressibilidade) do solo. A profundidade de compactação em área de pastagem é até 0,10 m, enquanto em área de colheita mecanizada de eucalipto pode alcançar 0,40 m, sendo necessários canais permanentes de tráfego para minimizar a compactação em áreas florestais. Os valores críticos de propriedades físicas do solo para o crescimento e rendimento de culturas anuais também parece ser efetivo para culturas perenes e pastagem. Com aumento da compactação há compressão dos agregados do solo, incrementando a densidade e reduzindo a porosidade, afetando negativamente os fluxos de ar e água do solo. Níveis intermediários de compactação são favoráveis ao meio ambiente e, possivelmente, ao crescimento de plantas, devido à melhor estrutura do solo (porosidade e densidade) e ao maior armazenamento e disponibilidade de água, além de ser mais eficiente quanto à deformação e suscetibilidade do solo à compactação. Através de propriedades como a densidade do solo, resistência do solo à penetração e umidade é possível estimar a capacidade de suporte de carga do solo e sua suscetibilidade à compactação. Os poros biológicos, formados pela ação de organismos do solo e decomposição de raízes, são efetivos no incremento do fluxo de ar, sendo fundamentais na infiltração de água e fluxo de ar em condições de elevada densidade do solo. Para obtenção de uma densidade referência do solo para cálculo do grau de compactação em áreas de floresta e pastagem, a coleta de amostras com estrutura preservada deve ser feita na camada de 0,10 0,125 m, equilíbriadas na tensão de 33 kPa, e o valor de densidade referência deve ser aquele obtido na pressão de 1600 kPa.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The preconsolidation pressure (σp) is obtained from the curve of the soil compression visual graphical form, mathematical or associating both and is an estimate of its load-bearing capacity. In order to remove the subjectivity of the visual graphical method is need for mathematical description (models using) of the compression curve. However, research results do not provide subsidies for the choice of a model whose σp represents well the resulting load-bearing capacity of soil, but if some model to represent, the σp should be a function of density and water content soil, other properties remain constant. The objective of this study was to understand the variability in the preconsolidation pressure caused by different models and options to adjust these models to the compression curve and evaluate the relationship of preconsolidation pressure with bulk density (Ds), volumetric water content (θ) and macroporisity (Ma) . For this, we performed the uniaxial compression test of 300 samples from a Hapludox, clayey, with wide variation Ds and θ. The preconsolidation pressure was determined by strictly mathematical, from the set of ten models, where seven of them consisted of variations of the model van Genuchten (1980) and others have been proposed by Friton (2001), Assouline (2002) and Gregory et al. (2006). The model proposed by Gregory and Friton possible to obtain the σp for only 62 and 56% of the curves, respectively, the variations of the model van Genuchten were enable the calculation of σp at least 90% of the curves. In three of the variations of the van Genuchten model, it was possible to get σp in 100% of the curves. The range of σp produced by the various options described in compression curve affects the physical significant of σp to represent the load bearing capacity of the soil. Likewise, Ds, θ and Ma, which influence the same load bearing capacity of the soil, not explained more than 58% of the variation of σp produced using different models. With the criteria used, it is not possible to choose one model over the other which allows to estimate more adequately by σp, the load bearing capacity of the soil, which limits the use of this parameter as an indicator for soil management agricultural. Given this result, it was investigated whether the percentage of deformation of the sample as a function of the applied loads would be more closely related to Ds, θ, and Ma was considered a safe limit of deformation of the physical viewpoint, that Ma deformation where the remains higher than 10%. The use of maintenance limit of 80% of voids index (Mεi) displaces the deformation to the plastic region of the curves of all the density ranges and therefore cannot be used for soil with structure more affected by compaction. The load to achieve a certain percentage (Mεi) is best explained by the variation of Ds and θ. The pedotransfer functions to load in Mεi between 85 and 87.5% resulted in higher coefficients of determination (0.74), having potential use of such values as critical limits to maintenance of porosity without degradation of soil physical quality. / A pressão de preconsolidação (σp) é obtida da curva de compressão do solo de forma gráfica visual, matemática ou associando ambas e é uma estimativa de sua capacidade de suporte de carga. A fim de se retirar a subjetividade do método gráfico visual, há necessidade de descrição matemática (uso de modelos) da curva de compressão. Porém, os resultados de pesquisa não fornecem subsídios para a escolha de um modelo cuja σp resultante represente, de maneira confiável, a capacidade de suporte de carga do solo. Entretanto, se algum modelo a representar, a σp deverá ser uma função da densidade e conteúdo de água do solo, mantidas constantes outras propriedades. O objetivo deste trabalho foi conhecer a variabilidade na pressão de preconsolidação provocada por diferentes modelos e opções de ajuste desses modelos à curva de compressão e avaliar a relação da pressão de preconsolidação com a densidade do solo (Ds), conteúdo volumétrico de água (θ) e macroporosidade do solo (Ma). Para isso, foi realizado o ensaio de compressão uniaxial para 300 amostras provenientes de um Latossolo Vermelho Distroférrico típico, com textura argilosa, com ampla variação Ds e θ. A pressão de preconsolidação foi determinada por meio estritamente matemático, a partir do ajuste de dez modelos, onde sete deles consistiram em variações do modelo de van Genuchten (1980) e os demais foram propostos por Friton (2001), Assouline (2002) e Gregory et al. (2006). Os modelos propostos por Gregory e Friton possibilitaram a obtenção da σp para apenas 62 e 56 % das curvas, respectivamente, já as variações do modelo de van Genuchten viabilizam o cálculo da σp para no mínimo 90 % das curvas. Em três das variações do modelo de van Genuchten, foi possível obter a σp em 100% das curvas. A variação da σp produzida pelas diferentes opções de descrição da curva de compressão compromete o significado físico da σp para representar a capacidade de suporte de carga do solo. Da mesma forma, Ds, θ e Ma, mesmo que influenciem a capacidade de suporte de carga do solo, não explicaram mais que 58% da variação da σp produzida com o uso de diferentes modelos. Com os critérios utilizados, não é possível eleger um modelo em relação aos demais que possibilite estimar de maneira mais adequada, através da σp, a capacidade de suporte de carga do solo, o que limita o uso desse parâmetro como um indicador para o manejo dos solos agrícolas. Diante desse resultado, foi investigado se a porcentagem de deformação da amostra em função das cargas aplicadas estaria melhor relacionada com Ds, θ e Ma. Considerou-se um limite de deformação prudente do ponto vista físico, aquela deformação onde a Ma permaneça maior que 10%. O uso do limite de manutenção de 80 % do índice de vazios inicial (Mεi) desloca as deformações para a região plástica das curvas de todas as faixas de densidade e, por isso, não pode ser utilizado para solos com estrutura mais comprometida pela compactação. A carga para atingir determinada porcentagem de Mεi é melhor explicada pela variação da Ds e θ. As funções de pedotransferência da carga para a Mεi entre 85 e 87,5% resultaram em maiores coeficientes de determinação (0,74), havendo potencial da utilização destes valores como limites críticos de manutenção da porosidade sem haver degradação da qualidade física do solo.