Botao Lin

Prediction of expansive soil swelling based on four micro-scale properties

A comprehensive study of expansive soil behavior includes understanding the surface phenomena of clay particles within the soil matrix. This research studies four micro-scale properties of four remolded expansive soils––matric suction, pH, surface conductance and percentage of montmorillonite––in order to predict soil swelling. An approach to approximate surface conductance is presented. Linear regression analyses were undertaken in an attempt to predict percent swell and swell pressure based on each of these micro-scale properties. Matric suction was found to be the most accurate predictor of the swelling behavior of the studied soils, which were initially compacted at optimum moisture content. Surface conductance, which is a combination of specific surface area, cation exchange capacity and cation mobility, also gave good predictions, except for one soil with high acidity.RésuméUne étude approfondie du comportement des sols gonflants inclut la compréhension des phénomènes de surface concernant les particules argileuses au sein de la matrice du sol. Cette recherche s’intéresse à quatre propriétés de micro-échelle de quatre sols gonflants remaniés : succion matricielle, pH, conductivité de surface et pourcentage de montmorillonite, afin de prévoir le gonflement du sol. Une méthode permettant d’approcher la valeur de conductivité de surface est présentée. Des analyses de régression linéaire ont été réalisées, basées sur chacune des propriétés de micro-échelle, afin de prévoir le potentiel de gonflement et la pression de gonflement. La succion matricielle a été identifiée comme le meilleur paramètre pour prévoir le comportement gonflant des sols étudiés qui avaient été initialement compactés à la teneur en eau optimum. La conductivité de surface, qui intègre la valeur de surface spécifique, la capacité d’échange de cations et la mobilité cationique a donné également de bonnes prévisions, sauf pour l’un des sols de forte acidité.

Hysteretic soil water characteristics and cyclic swell–shrink paths of compacted expansive soils

The investigation of the hydromechanical behavior of unsaturated expansive soil depends on the determination of hysteretic soil water characteristic curves (HSWCCs). This research investigates the HSWCCs of two natural expansive soils initially compacted at optimum moisture content (OMC) and maximum dry density (MDD) and then saturated to their maximum expansion state to ensure identical capillary history. Filter paper, pressure plate and chilled mirror hygrometer suction measurement techniques were utilized, and corresponding measurements of three-dimensional volume change made. The cyclic swell–shrink paths were deduced in terms of volumetric strain versus either water content or suction. The cyclic three-dimensional volumetric measurements showed a much higher amount of swelling and shrinkage than those determined from one-dimensional measurements. Hydraulic hysteresis rapidly decreased with the swell–shrink cycles as a result of macro-structural stabilization. Under the no/low confining conditions, the swell–shrink cycles generally caused a decrease of global expansion and an increase of global shrinkage. Moreover, a special phenomenon showing a reduction of global shrinkage on significant drying was discovered in the less plastic soil sample.RésuméL’analyse du comportement hydromécanique des sols gonflants non saturés nécessite la détermination des courbes caractéristiques du comportement hydrique de ces sols. Cette étude examine ces courbes caractéristiques pour deux sols gonflants naturels, d’abord compactés à la teneur en eau optimale, avec une densité sèche maximale, ensuite saturés jusqu’à leur état de gonflement maximum afin d’obtenir un historique contrôlé de leur humidification. Les techniques du papier filtre, de la mise sous contrainte et des mesures de succion par hygromètre ont été utilisées et les mesures correspondantes des changements de volume réalisées. Les mesures cycliques tridimensionnelles de volume ont montré des amplitudes beaucoup plus grandes de gonflement et de retrait que celles déterminées à partir de mesures unidimensionnelles. L’hystérésis hydrique a diminué rapidement avec les cycles de gonflement-retrait en raison d’une stabilisation macrostructurale. Dans des conditions de confinement nul ou faible, les cycles de gonflement-retrait ont généralement entraîné une diminution du gonflement global et une augmentation du retrait global. Par ailleurs, un phénomène spécial montrant une réduction du retrait global pour des séchages importants a été découvert pour les échantillons de sols les moins plastiques.

Investigation on Soil–Water Characteristic Curves of Untreated and Stabilized Highly Clayey Expansive Soils

The examination of hydromechanical behavior of expansive soil lies mostly within the unsaturated soil mechanics framework, which renders the study of its soil water characteristic curve (SWCC) a necessity. This paper evaluates the correlations of two physicochemical properties, pH and surface conductance, with the behavior of the SWCCs of four natural expansive soils and four stabilized soils. The effects of chemical stabilization and curing time on the SWCCs are also analyzed. The SWCCs and the corresponding parameters were obtained from pressure plate tests and a fitting model. It was found that pH and surface conductance together showed a good correlation with the air-entry related parameter, α, because they determine the formation of the diffuse double layer around fine particles or aggregates. The macroscopic behavior, in terms of unconfined compressive strength, free swell and swell pressure at optimum moisture content (OMC), was also evaluated and good correlations of these property values with the matric suction values at OMC were observed for the four natural untreated soils, while no correlation existed for the stabilized soils. The results and the discussion provide new insight to address physicochemical mechanisms that determine the macroscopic behavior of expansive soil.

Experimental Investigation on Dilation Mechanisms of Land-Facies Karamay Oil Sand Reservoirs under Water Injection

The success of steam-assisted gravity drainage (SAGD) is strongly dependent on the formation of a homogeneous and highly permeable zone in the land-facies Karamay oil sand reservoirs. To accomplish this, hydraulic fracturing is applied through controlled water injection to a pair of horizontal wells to create a dilation zone between the dual wells. The mechanical response of the reservoirs during this injection process, however, has remained unclear for the land-facies oil sand that has a loosely packed structure. This research conducted triaxial, permeability and scanning electron microscopy (SEM) tests on the field-collected oil sand samples. The tests evaluated the influences of the field temperature, confining stress and injection pressure on the dilation mechanisms as shear dilation and tensile parting during injection. To account for petrophysical heterogeneity, five reservoir rocks including regular oil sand, mud-rich oil sand, bitumen-rich oil sand, mudstone and sandstone were investigated. It was found that the permeability evolution in the oil sand samples subjected to shear dilation closely followed the porosity and microcrack evolutions in the shear bands. In contrast, the mudstone and sandstone samples developed distinct shear planes, which formed preferred permeation paths. Tensile parting expanded the pore space and increased the permeability of all the samples in various degrees. Based on this analysis, it is concluded that the range of injection propagation in the pay zone determines the overall quality of hydraulic fracturing, while the injection pressure must be carefully controlled. A region in a reservoir has little dilation upon injection if it remains unsaturated. Moreover, a cooling of the injected water can strengthen the dilation potential of a reservoir. Finally, it is suggested that the numerical modeling of water injection in the Karamay oil sand reservoirs must take into account the volumetric plastic strain in hydrostatic loading.

Dielectric Measurement of Soil-electrolyte Mixtures in a Modified Oedometer Cell Using 400 kHz to 20 MHz Electromagnetic Waves

The dielectric properties of soil have been shown to be a good indicator of moisture, contamination, and mineralogy and have been studied in order to gain a better insight into macroscopic soil behavior. Calibration factors for the measurement of real relative permittivity and effective conductivity are discussed and measured in this study. Based on the use of calibration factors, this article presents a convenient approach of dielectric measurement of soil-electrolyte mixtures in an oedometer-like cell using electromagnetic waves at a frequency range of 400 kHz–20 MHz to study the behavior of the mixtures. The effects of volumetric water content, chemical composition, anisotropy, and soil type are assessed based on the proposed measurement approach and the results are discussed.

Shear strength of shale weathered expansive soils along swell-shrink paths: analysis based on microscopic properties

This study attempts to interpret the macro-scale mechanical behavior of two natural expansive soils based on their microscopic properties. To accomplish this, an extensive investigation on the microscopic properties, including physicochemical properties, especially point of zero charge and microstructural characteristics observed from environmental scanning electron microscopy, was carried out in order to understand the sample fabric and the interparticle forces affecting it. Furthermore, triaxial tests were conducted on the saturated and unsaturated specimens to evaluate their strength behavior with respect to the governing microscopic forces and microstructure. The effects of mean stress, suction, capillary history and strain level on the shear strength were thoroughly examined. It was found that the initial sample structure has a profound impact on the development of effective stress paths of the saturated specimens. For the sample with a flocculated structure, capillary history causes substantial structural evolutions along different capillary paths, and consequently results in significant changes in the peak shear strength. For the laminar sample, the impact of capillary history is negligible on its peak strength. On the other hand, the large-strain shear strength is insensitive to capillary history, regardless of soil type because the specimens are fully destructed with respect to their fabric, experiencing a loss of electrical attraction and equilibrium of diffuse double layer repulsion.

Hydraulic Connection Model in Squeeze Preprocessing SAGD Start-Up

A cross-hole vertical dilation zone is formed, and hydraulic connection is implemented between injection–production inter-well reservoirs. It is the key to success in squeeze preprocessing dual horizontal well SAGD start-up. Normally, the well’s pressure communication is determined by the pressure response between the injector and the producer. However, this pressure response cannot be used to analyze the thermal conformance and inter-well fluid mobility. By using the squeeze preprocessing SAGD start-up job in Fengcheng oil field as an example, this paper proposed a method that calculate the radius and mobility of the dilation zone. This model is based on finite element software ABAQUS and analytical regression analysis. The dilation behavior in oilsands reservoir is modelled by Drake-Prager plasticity model, according to the definition of the ratio method, weight, and multiplication principle. The results show that the hydraulic connectivity coefficient in Fengcheng Oilfield SAGD reservoirs is between 0.6 and 0.8. The greater the coefficient, the bigger the hydraulic extent, and the late preheat the less steam consumption. The fitting effect of model prediction results and the actual monitoring data is good, and the relative error is less than 5%. It shows that the mathematical models of hydraulic connection are valid.