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Oriented polylactic acid (PLA)/graphene oxide (GO) nanosheets tapes were prepared via uniaxial solid state drawing. The effect of various drawing conditions, including drawing ratio (DR), temperature (DT), and speed (DS) on mechanical, thermal, structural, and barrier properties were studied. Structural studies showed oriented structure for the drawn tapes with aligned polymer chains and GO nanosheets. Differential scanning calorimetry revealed improved glass transition temperature (Tg) and crystallinity (Xc) after drawing. In addition, Tg and Xc were increased more by increasing DR and DT. The highest Tg and Xc were achieved for 3/70/50 tape with values of 73°C and %22, respectively. Higher thermal stabilities and enhanced barrier properties were achieved after drawing, especially at the higher DR. Finally, tensile testing revealed simultaneous improvement in stiffness and toughness due to strain hardening for all the drawn tapes. The strength and elastic modulus were increased after increasing DR, DS, and DT and reached the highest values of 149 MPa and 3.6 GPa for 3/70/50. Overall, the properties were controllable by the processing conditions. [ABSTRACT FROM AUTHOR]

The present study investigates the effects of some essential earth pressure balance machine (EPBM) operational parameters, including face, annulus and grout pressures, on ground surface settlement during tunnel excavation. A numerical soil-tunnel-fluid coupled model was developed using the finite difference method (FDM) in FLAC3D for the basis of this research. Hence, the effects of geostatic stress in the tunnel face and annulus and the grout pressure behind the segment on ground settlement were investigated by parametric analyses. The results indicated that a reduction in the boundary pressure (from 508 to 335 kPa) on the face and annulus space did not change the settlement significantly, altering the settlement from 1.18 to 1.48 mm. The results of parametric grout pressure analysis showed that applying a grout pressure equal to the vertical geostatic stress (i.e. 335 kPa) had a larger effect than applying horizontal geostatic stress (i.e. 357 kPa) to the tunnel face on controlling the ground settlement—i.e. 1.45 and 1.20 mm, respectively. A lateral earth pressure of below 1 (K 0 < 1) led to the estimation of horizontal geostatic stress value that was lower than the vertical geostatic stress value, thereby applying a lower effect to controlling the ground settlement. Grout pressure increment relative to the vertical geostatic stress considerably reduced the ground settlement. However, an excessive rise in the grout pressure could lead to deformation and upward displacements in the form of ground heaving at a transverse distance of above 20 m from the tunnel axis. [ABSTRACT FROM AUTHOR]

The effect of cobble concentration and vegetated banks on the mean flow and turbulence of streams has not yet been investigated. Cobble concentrations ranging from 10 to 30 cobbles/m were tested by this study. In total, 27 velocity profiles were measured using an acoustic Doppler velocimeter (ADV) at a sampling frequency of 200 Hz. The results show that cobble concentration affects the mean velocity and turbulence intensity profiles close to the vegetated bank, especially near the bed, but does not influence the RS distribution. This experimental study reveals a -shaped Reynolds stress (RS) distribution near the vegetated bank without any negative values, but a convex distribution at the centre of flume with negative values near the water surface. Negative RS values are associated with dominant effects of the inward and outward events near the water surface. The effect of cobble concentration on the frequency of bursting events is not considerable, based on the quadrant analysis. [ABSTRACT FROM AUTHOR]