Hydro-mechanical behaviour of compacted binary mixtures : an experimental study

This research focusses on an experimental investigation on the hydro-mechanical behaviour of binary ‘all-one’ mixtures. These mixtures –originated from the excavation of selected materials during earthwork constructions– are basically constituted by large rock fragments immersed in a matrix with dominant finer soil fraction. These materials, which bridge the gap between coarser rockfill materials and soils, are widely accepted in different national standards for earthworks, such as dams, levees, railway and road embankments. Despite their practical interest, these mixtures have not been widely studied. The emphasis of the current study has been mainly placed on the influence of the properties of the fragments (unconfined shear strength) and the void ratio of the finer matrix to explain the hydro-mechanical behaviour of these mixtures along different stress paths, as well as to better assess the role played by fragment breakage aspects. Different mass ratios of fragments have been initially studied, which allowed selecting a matrix proportion able to fill nearly all inter-fragments voids (interactive-underfilled packing), as well as still ensuring good compaction properties (close to minimum dry density for specified water content). A constant fragment mass ratio of 40% with particles between 19 mm and 38.5 mm has been finally selected to perform a systematic experimental campaign with fragments of different uniaxial compressive strengths, ranging from natural carbonated and low-strength aggregates to high-strength slate fragments. This fixed fragment ratio has ensured reaching a mixture, in which both the density of the fine matrix and the strength of large fragments are controlling the coupled hydro-mechanical response. A procedure for fabricating artificial and cement-based fragments has been also proposed to allow obtaining an intermediate uniaxial compressive strength and thus to better fill the gap between these extreme low-strength and high-strength fragments. A real ‘all-one’ mixture retrieved under as-compacted conditions during the construction of Albagés dam (Lleida, Spain) has been also considered to compare main hydro-mechanical features with the mixtures prepared under laboratory conditions. The experimental campaign using a large-oedometer cell has included loading / unloading cycles under saturated and unsaturated conditions, as well as soaking tests at constant vertical stress. The study with different fragment strengths has been mainly focused on analysing the compressibility of the mixture on loading at different hydraulic states, the collapsible response on soaking at constant vertical stress, as well as the water retention and saturated permeability properties. These macroscopic phenomenological results have been complemented by a microstructural description that included aspects of fragment breakage, fractal dimension changes of the particle size distribution, as well as energy transfer aspects (work input per unit volume used to densify the matrix and to break large fragments). The results have shown the important role played by the strength of the fragments to achieve better compaction properties when using high-strength fragments, which allowed reducing the compressibility on loading and the collapsibility on soaking, as well as ensuring a more efficient transfer of the work input to densify the matrix (instead of breaking particles).Esta investigación se centra en el estudio experimental del comportamiento hidromecánico de mezclas binarias de "todo-uno". Estas mezclas -originadas a partir de la excavación de materiales seleccionados durante las construcciones de movimiento de tierras- están básicamente constituidas por grandes fragmentos de roca inmersos en una matriz con una fracción de suelo dominante. Estos materiales, que cubren la brecha entre los materiales de escolleras más gruesos y los suelos, son ampliamente aceptados en diferentes normas nacionales para estructuras de tierras, como presas, diques, y terraplenes para ferrocarriles y carreteras. A pesar de su interés práctico, estas mezclas no han sido ampliamente estudiadas. El énfasis del presente estudio se ha centrado principalmente en la influencia de las propiedades de los fragmentos (resistencia a la compresión uniaxial) y la relación de poros de la matriz más fina para explicar el comportamiento hidromecánico de estas mezclas a lo largo de diferentes trayectorias de tensión, así como para evaluar mejor el papel desempeñado por la rotura de fragmentos. Se han estudiado inicialmente diferentes proporciones másicas de fragmentos, lo que ha permitido seleccionar una proporción de matriz capaz de llenar casi todos los vacíos entre fragmentos (empaquetamiento interactivo casi lleno) e incluso garantizar buenas propiedades de compactación (cercano a la densidad seca mínima para un contenido de agua específico). Se seleccionó finalmente una relación de masa de fragmentos constante del 40% con partículas entre 19 mm y 38.5 mm para realizar una campaña experimental sistemática con fragmentos de diferentes resistencias a la compresión uniaxial, que van desde agregados carbonatados naturalmente y de baja resistencia hasta fragmentos de pizarra de elevada resistencia. Esta proporción de fragmentos prefijada ha permitido alcanzar una mezcla, en la que tanto la densidad de la matriz fina como la resistencia de los fragmentos controlen la respuesta hidromecánica acoplada. También se ha propuesto un procedimiento para fabricar fragmentos artificiales a base de cemento para permitir la obtención de una resistencia a la compresión uniaxial intermedia y así rellenar mejor el rango entre estos fragmentos de baja y elevada resistencia. También se ha considerado una mezcla real de "todo uno" extraída después de compactación durante la construcción de la presa de Albagés (Lleida, España) para comparar sus principales características hidromecánicas con las mezclas preparadas en condiciones de laboratorio. La campaña experimental que utiliza una célula edométrica de grandes dimensiones ha incluido ciclos de carga/descarga en condiciones saturadas y parcialmente saturadas, así como ensayos de inundación a tensión vertical constante. El estudio con fragmentos de diferentes resistencias se ha centrado principalmente en analizar la compresibilidad de la mezcla ante carga a diferentes estados hidráulicos, la respuesta al colapso durante inundación a tensión vertical constante, así como la retención de agua y las propiedades de permeabilidad saturada. Estos resultados fenomenológicos macroscópicos se han complementado con una descripción microestructural que incluye aspectos de rotura de fragmentos, cambios de dimensiones fractales de la distribución de tamaños de partículas, así como aspectos de transferencia de energía (trabajo por unidad de volumen aportado para densificar la matriz y consumido para romper los fragmentos grandes). Los resultados han demostrado el importante papel desempeñado por la resistencia de los fragmentos para lograr mejores propiedades de compactación al usar fragmentos de alta resistencia, que permiten reducir la compresibilidad ante carga y el colapso durante inundación, así como asegurar una transferencia de energía más eficiente para densificar la matriz (en lugar de romper partículas).Postprint (published version

Hydro-mechanical behaviour of compacted binary mixtures : an experimental study

This research focusses on an experimental investigation on the hydro-mechanical behaviour of binary ‘all-one’ mixtures. These mixtures –originated from the excavation of selected materials during earthwork constructions– are basically constituted by large rock fragments immersed in a matrix with dominant finer soil fraction. These materials, which bridge the gap between coarser rockfill materials and soils, are widely accepted in different national standards for earthworks, such as dams, levees, railway and road embankments. Despite their practical interest, these mixtures have not been widely studied. The emphasis of the current study has been mainly placed on the influence of the properties of the fragments (unconfined shear strength) and the void ratio of the finer matrix to explain the hydro-mechanical behaviour of these mixtures along different stress paths, as well as to better assess the role played by fragment breakage aspects. Different mass ratios of fragments have been initially studied, which allowed selecting a matrix proportion able to fill nearly all inter-fragments voids (interactive-underfilled packing), as well as still ensuring good compaction properties (close to minimum dry density for specified water content). A constant fragment mass ratio of 40% with particles between 19 mm and 38.5 mm has been finally selected to perform a systematic experimental campaign with fragments of different uniaxial compressive strengths, ranging from natural carbonated and low-strength aggregates to high-strength slate fragments. This fixed fragment ratio has ensured reaching a mixture, in which both the density of the fine matrix and the strength of large fragments are controlling the coupled hydro-mechanical response. A procedure for fabricating artificial and cement-based fragments has been also proposed to allow obtaining an intermediate uniaxial compressive strength and thus to better fill the gap between these extreme low-strength and high-strength fragments. A real ‘all-one’ mixture retrieved under as-compacted conditions during the construction of Albagés dam (Lleida, Spain) has been also considered to compare main hydro-mechanical features with the mixtures prepared under laboratory conditions. The experimental campaign using a large-oedometer cell has included loading / unloading cycles under saturated and unsaturated conditions, as well as soaking tests at constant vertical stress. The study with different fragment strengths has been mainly focused on analysing the compressibility of the mixture on loading at different hydraulic states, the collapsible response on soaking at constant vertical stress, as well as the water retention and saturated permeability properties. These macroscopic phenomenological results have been complemented by a microstructural description that included aspects of fragment breakage, fractal dimension changes of the particle size distribution, as well as energy transfer aspects (work input per unit volume used to densify the matrix and to break large fragments). The results have shown the important role played by the strength of the fragments to achieve better compaction properties when using high-strength fragments, which allowed reducing the compressibility on loading and the collapsibility on soaking, as well as ensuring a more efficient transfer of the work input to densify the matrix (instead of breaking particles).Esta investigación se centra en el estudio experimental del comportamiento hidromecánico de mezclas binarias de "todo-uno". Estas mezclas -originadas a partir de la excavación de materiales seleccionados durante las construcciones de movimiento de tierras- están básicamente constituidas por grandes fragmentos de roca inmersos en una matriz con una fracción de suelo dominante. Estos materiales, que cubren la brecha entre los materiales de escolleras más gruesos y los suelos, son ampliamente aceptados en diferentes normas nacionales para estructuras de tierras, como presas, diques, y terraplenes para ferrocarriles y carreteras. A pesar de su interés práctico, estas mezclas no han sido ampliamente estudiadas. El énfasis del presente estudio se ha centrado principalmente en la influencia de las propiedades de los fragmentos (resistencia a la compresión uniaxial) y la relación de poros de la matriz más fina para explicar el comportamiento hidromecánico de estas mezclas a lo largo de diferentes trayectorias de tensión, así como para evaluar mejor el papel desempeñado por la rotura de fragmentos. Se han estudiado inicialmente diferentes proporciones másicas de fragmentos, lo que ha permitido seleccionar una proporción de matriz capaz de llenar casi todos los vacíos entre fragmentos (empaquetamiento interactivo casi lleno) e incluso garantizar buenas propiedades de compactación (cercano a la densidad seca mínima para un contenido de agua específico). Se seleccionó finalmente una relación de masa de fragmentos constante del 40% con partículas entre 19 mm y 38.5 mm para realizar una campaña experimental sistemática con fragmentos de diferentes resistencias a la compresión uniaxial, que van desde agregados carbonatados naturalmente y de baja resistencia hasta fragmentos de pizarra de elevada resistencia. Esta proporción de fragmentos prefijada ha permitido alcanzar una mezcla, en la que tanto la densidad de la matriz fina como la resistencia de los fragmentos controlen la respuesta hidromecánica acoplada. También se ha propuesto un procedimiento para fabricar fragmentos artificiales a base de cemento para permitir la obtención de una resistencia a la compresión uniaxial intermedia y así rellenar mejor el rango entre estos fragmentos de baja y elevada resistencia. También se ha considerado una mezcla real de "todo uno" extraída después de compactación durante la construcción de la presa de Albagés (Lleida, España) para comparar sus principales características hidromecánicas con las mezclas preparadas en condiciones de laboratorio. La campaña experimental que utiliza una célula edométrica de grandes dimensiones ha incluido ciclos de carga/descarga en condiciones saturadas y parcialmente saturadas, así como ensayos de inundación a tensión vertical constante. El estudio con fragmentos de diferentes resistencias se ha centrado principalmente en analizar la compresibilidad de la mezcla ante carga a diferentes estados hidráulicos, la respuesta al colapso durante inundación a tensión vertical constante, así como la retención de agua y las propiedades de permeabilidad saturada. Estos resultados fenomenológicos macroscópicos se han complementado con una descripción microestructural que incluye aspectos de rotura de fragmentos, cambios de dimensiones fractales de la distribución de tamaños de partículas, así como aspectos de transferencia de energía (trabajo por unidad de volumen aportado para densificar la matriz y consumido para romper los fragmentos grandes). Los resultados han demostrado el importante papel desempeñado por la resistencia de los fragmentos para lograr mejores propiedades de compactación al usar fragmentos de alta resistencia, que permiten reducir la compresibilidad ante carga y el colapso durante inundación, así como asegurar una transferencia de energía más eficiente para densificar la matriz (en lugar de romper partículas)

Compacted Expansive Elastic Silt and Tyre Powder Waste

Building on/with expansive soils with no treatment brings complications. Compacted expansive soils specifically fall short in satisfying the minimum requirements for transport embankment infrastructures, requiring the adoption of hauled virgin mineral aggregates or a sustainable alternative. Use of hauled aggregates comes at a high carbon and economical cost. On average, every 9m high embankment built with quarried/hauled soils cost 12600 MJ.m-2 Embodied Energy (EE). A prospect of using mixed cutting-arising expansive soils with industrial/domestic wastes can reduce the carbon cost and ease the pressure on landfills. The widespread use of recycled materials has been extensively limited due to concerns over their long-term performance, generally low shear strength and stiffness. In this contribution, hydromechanical properties of a waste tyre sand-sized rubber (a mixture of polybutadiene, polyisoprene, elastomers, and styrene-butadiene) and expansive silt is studied, allowing the short- and long-term behaviour of optimum compacted composites to be better established. The inclusion of tyre shred substantially decreased the swelling potential/pressure and modestly lowered the compression index. Silt-Tyre powder replacement lowered the bulk density, allowing construction of lighter reinforced earth structures. The shear strength and stiffness decreased on addition of tyre powder, yet the contribution of matric suction to the shear strength remained constant for tyre shred contents up to 20%. Reinforced soils adopted a ductile post-peak plastic behaviour with enhanced failure strain, offering the opportunity to build more flexible subgrades as recommended for expansive soils. Residual water content and tyre shred content are directly correlated; tyre-reinforced silt showed a greater capacity of water storage (than natural silts) and hence a sustainable solution to waterlogging and surficial flooding particularly in urban settings. Crushed fine tyre shred mixed with expansive silts/sands at 15 to 20 wt% appear to offer the maximum reduction in swelling-shrinking properties at minimum cracking, strength loss and enhanced compressibility expenses

Intraoperative Ultrasonography in Resection of Diffuse Glioma

Diffuse glioma is a primary brain tumor that originates from glial supportive cells and is the most common type of intra-axial brain tumor. Open tumor resection is the first step in the treatment of diffuse gliomas. The extent of resection (EOR) directly influences clinical outcomes in glioma surgery. However, resection of diffuse glioma is encountered with the problem of macroscopic and even microscopic similarity of normal brain and tumor. Furthermore, maximizing EOR requires attention because a mistake in identifying and preserving normal brain regions in complete resection can lead to catastrophic complications

Experimental visualization of labyrinthine structure with optical coherence tomography

Introduction: Visualization of inner ear structures is a valuable strategy for researchers and clinicians working on hearing pathologies. Optical coherence tomography (OCT) is a high-resolution imaging technology which may be used for the visualization of tissues. In this experimental study we aimed to evaluate inner ear anatomy in well-prepared human labyrinthine bones. Materials and Methods: Three fresh human explanted temporal bones were trimmed, chemically decalcified with ethylenediaminetetraacetic acid (EDTA), and mechanically drilled under visual control using OCT in order to reveal the remaining bone shell. After confirming decalcification with a computed tomography (CT) scan, the samples were scanned with OCT in different views. The oval window, round window, and remnant part of internal auditory canal and cochlear turn were investigated. Results: Preparation of the labyrinthine bone and visualization under OCT guidance was successfully performed to a remaining bony layer of 300μm thickness. OCT images of the specimen allowed a detailed view of the intra-cochlear anatomy. Conclusion: OCT is applicable in the well-prepared human inner ear and allows visualization of soft tissue parts.DFG/EXC/Hearing4allDFG/MA 4038/3-2Institute of Mechatronic System (IMES) OCT II/OR 196/17-

Acute Hemifacial And Hemiparesis Caused By Hemorrhagic Vestibular Schwannoma; A Case Report

Vestibular schwannoma is a benign and common slow-growing tumor that develops on the vestibular divisions of cranial nerve VIII. Some risk factors may enhance intratumoral hemorrhage risk which leads to tumor management to early surgical procedures. Hence, we describe a 57-year-old man presented with hearing loss and a 5*8 mm vestibular schwannoma. Eight months later, the patient was referred with headache, nausea and vomiting, right hemifacial paresis, and hemiparesis. Magnetic resonance imaging (MRI) revealed a 45*35 mm hemorrhagic vestibular schwannoma. Surgical pathology reported hemorrhagic vestibular schwannoma. This was a rare case of hemorrhagic vestibular schwannoma with none of the established risk factors for the intratumoral hemorrhage and presented with Wallenberg-like syndrome. Many risk factors can cause hemorrhagic vestibular schwannoma. We present one case of small vestibular schwannoma without any predisposing of hemorrhage and acute onset of same side hemifacial paresis and hemiparesis

High coupling efficiency to a low dispersion slow light-supporting photonic crystal waveguide

In this paper, we design a waveguide on photonic crystal slab for propagation of low-dispersion slow light. By shifting the air holes adjacent to the waveguide, we obtain a photonic crystal waveguide with a group index of 25 in 25 nm bandwidth which results in a group index bandwidth product of 0.366. To take the advantages of low dispersion slow light generated in this engineered waveguide, we next focus on low coupling efficiency limitation. A low group index coupler is proposed to increase the transmission of the light to the slow mode in the low dispersion bandwidth. By using the proposed coupler and adjusting the structural parameters, the coupling efficiency to low dispersion slow light is improved 11 dB compared to the transmission without the coupler

The influence of temporal frequency and stimulus size on the relative contribution of luminance and L-/M-cone opponent mechanisms in heterochromatic flicker ERGs

Purpose To study the effect of stimulus size and temporal frequency on the relative contribution of luminance and L-/M-cone opponent signals in the ERG. Methods In four healthy, color normal subjects, ERG responses to heterochromatic stimuli with sinusoidal, counter-phase modulation of red and green LEDs were measured. By inverse variation of red and green contrasts, we varied luminance contrast while keeping L-/M-cone opponent chromatic contrast constant. The first harmonic components in the full field ERGs are independent of stimulus contrast at 12 Hz, while responses to 36 Hz stimuli vary, reaching a minimum close to isoluminance. It was assumed that ERG responses reflect L-/M-cone opponency at 12 Hz and luminance at 36 Hz. In this study, we modeled the influence of temporal frequency on the relative contribution of these mechanisms at intermediate frequencies, measured the influence of stimulus size on model parameters, and analyzed the second harmonic component at 12 Hz. Results The responses at all frequencies and stimulus sizes could be described by a linear vector addition of luminance and L-/M-cone opponent reflecting ERGs. The contribution of the luminance mechanism increased with increasing temporal frequency and with increasing stimulus size, whereas the gain of the L-/M-cone opponent mechanism was independent of stimulus size and was larger at lower temporal frequencies. Thus, the luminance mechanism dominated at lower temporal frequencies with large stimuli. At 12 Hz, the second harmonic component reflected the luminance mechanism. Conclusions The ERGs to heterochromatic stimuli can be fully described in terms of linear combinations of responses in the (magnocellular) luminance and the (parvocellular) L-/M-opponent retino-geniculate pathways. The non-invasive study of these pathways in human subjects may have implications for basic research and for clinical research