Effect of Coarse Recycled Aggregate on Failure Strength for Asphalt Mixture Using Experimental and DEM Method

Coarse aggregate is the major part of asphalt mixture, and plays an essential role in mechanical performance of pavement structure. However, the use of poor-quality coarse recycled aggregate (CRA) reduces the strength and stability of the aggregate skeleton. It is a challenge to predict accurately the influence of CRA on the performance of asphalt mixture. In this study, both a uniaxial compression test and a direct tensile test were carried out to evaluate the failure strength of asphalt concrete with four CRA content. The discrete element method (DEM) was applied to simulate the specimen of asphalt concrete considering the distribution and properties of CRA. The results showed that temperature and loading rate have a significant influence on failure strength, especially when the CRA content was more than 20%. With the increase of CRA content, both cohesion force and internal friction angle were gradually weakened. The proposed model can be used to predict the failure strength of asphalt mixture, since both experimental and simulated results had a high consistency and repeatability. With the decrease of CRA strength, the nominal cohesion force of the specimen decreased, while the internal friction angle increased.

Characteristic of Erosion Properties and Relationship With Geotechnical Properties for Red Riverbank Soil in Hanoi, Vietnam

Soil erosion properties are the main factors affecting riverbank and river channel stability. In this paper, a modified water flume in the laboratory was conducted to evaluate the characteristic of erosion properties including the critical shear stress, the slope of the erosion curve, and erosion rate. The relationships between erosion properties and geotechnical properties as dry density, grain size distribution, shear strength, and soil suction were built. Results obtained from laboratory tests indicate (i) the clay content, cohesion force, residual suction has a great effect and linear correlation in the relationships with the critical shear stress and erosion rate. While the change in clay content leads to a markedly change in the erosion rate. The difference of 5 % clay content enough to build great effects on the erosion rate curve for the Silt soil group; (ii) the sand content has the greatest influence on the slope of the erosion curve (the initial slope and the erosion slope); (iii) the density also has a close relationship with the critical shear stress and the erosion slope, but not for a fine–sand mixture with clay content less than 10%. Based on obtained results and relationships found in this paper, the cohesion force and residual suction should be considered in process of soil riverbank improvement and riverbank undercutting erosion protections.

Roof Stability of Rectangle Coal Roadway: In Light of Calculation of Compressive Bar Stability

The roadway roof is a key factor to the roadway stability. The analysis of roof stability is mainly based on numerical calculation and on-site observation, while the basic theory of the bearing mechanism is relatively weak. We have founded a critical pressure calculation model, on the theory of compressive bar, for the rectangle coal roadway stability. The model has been tested and verified on accuracy and feasibility while applied on a roadway case. The critical pressure for roof stability and roof bending moment and deflection under combined axial and lateral load was deduced using the theory of compressive bar stability. The numerical calculation verified the feasibility of numerical modeling of stability of compressive bar using FLAC3D, and the influence of the background ambient horizontal stress and the parameters of the contact surface to the roof stability were further studied. The result turns out that some factors lead to a higher instability tendency, including higher horizontal stress, higher cohesion force, and larger internal friction angle on the coal-rock interface and lower cohesion force and smaller friction angle on the rock-rock interface. The results contribute to bearing mechanisms of roadway roof stability, ground pressure and strata control theory and application, and design of bolting support.

Multi-scale cohesion force measurements for cemented granular materials

We experimentally investigated cohesion of artificially bonded granular materials made of spherical glass beads cemented by solid paraffin bonds. By means of laboratory tests designed and carried out for investigation at different scales, we measured the tensile yield strength for solid bonds both at the inter-particle micro-scale and cemented samples at the meso-scale. A parametric study has been performed by varying some of the granular material properties (bead diameter, paraffin content as well as the dimension of the sample for the meso-scale tensile tests. We finally propose a discusion on: (i) the relationship between the microscopic and macroscopic cohesion forces relying on classical homogenisation laws ; (ii) the potential impact of size effects based on a simple phenomenological model.

Erosion of a cohesive granular material by an impinging turbulent jet

The erosion of a cohesive soil by an impinging turbulent jet is observed, for instance, during the landing of a spacecraft or involved in the so-called jet erosion test. To provide a quantitative understanding of this situation for cohesive soils, we perform experiments using a model cohesion controlled granular material that allows us to finely tune the cohesion between particles while keeping the other properties constant. We investigate the response of this cohesive granular bed when subjected to an impinging normal turbulent jet. We characterize experimentally the effects of the cohesion on the erosion threshold and the development of the crater. We demonstrate that the results can be rationalized by introducing a cohesive Shields number that accounts for the inter-particles cohesion force. The results of our experiments highlight the crucial role of cohesion in erosion processes.

Shape model and spin direction analysis of PHA (436724) 2011 UW158: a large superfast rotator

ABSTRACT Observations of the large superfast rotator (436724) 2011 UW158 were carried out at the Observatório Astronômico do Sertão de Itaparica (OASI, Brazil) between May and October 2015, before and after it made a close approach to Earth in July 2015. These observations allowed us to obtain 11 light curves, and additional observations at the San Pedro Mártir Observatory (Baja California, Mexico) in March 2017 provided a light curve. From the obtained light curves we could confirm the fast rotation, 0.61071 h, of the near-Earth object (NEO) and by applying the inversion method, we derived a prograde sense of rotation and a quite elongated shape model with rough dimensions a/b = 2.0, a/c = 4.2, and b/c = 2.1. The best determined pole directions suggest that the maximum amplitude of the light curves was obtained from an equatorial view. The reconstructed shape models are in good agreement with the shape elongation and asymmetric shape reported by radar observations. As 2011 UW158 has an uncommon rotation period for asteroids larger than ∼200 m, we used the determined parameters to calculate the minimum internal cohesion strength required to keep its structure intact. We have found that a minimum cohesion ranging from 176 to 295 Pa is required in case the NEO has a composition similar to that of C-type asteroids, and from 364 to 451 Pa for the E-type. Therefore, we suggest that 2011 UW158, if not monolithic, requires a significant cohesion force to keep it spinning so fast.

PENUNTUN PRATIKUM FISIKA - MERRY THRESSIA, S.Si, M.Si

Densistas (density / density) is a measurement of mass per unit volume of matter. The higher the density of an object, the greater the mass of each volume. The average density of each object is the total mass divided by the total volume.Archimedes was the greatest scientist of his time. He was born in the city of Syracuse, Sicily in 287 BC and died in 212 BC. Archimedes is known as a physicist, mathematician, optics and astronomy. He was nicknamed the Father of Experiments, for basing his findings on experiments. He found the law on an event called Archimedes' Law which reads, "if an object is inserted into a liquid, either partially or completely, it will get an upward force equal to the weight of the liquid transferred by the object".X-ray diffraction method is one way to study the regularity of atoms or molecules in a certain structure. If the structure of an atom or molecule is arranged regularly to form a lattice, then electromagnetic radiation in certain experimental conditions will be strengthened.An object moves on a surface, on an object it works a kinetic friction force that opposes the direction of motion of an object. The magnitude of the kinetic force depends on the nature of the two surfaces in contact. For two specific object surfaces, the kinetic friction force is proportional to the normal force. The friction force does not depend on the surface area that is in contact. The rough and slippery nature of the surfaces of two touching fields is expressed by the friction coefficient.Fluid viscosity (liquid) is friction caused by a moving fluid, or solid object that moves in the fluid. The amount of friction is called the degree of viscosity of liquid. So the greater the viscosity of the liquid, the more difficult the solids move within the liquid. Viscosity in liquid, which plays a role is the cohesion force between liquid particles. Viscosity can be expressed as fluid flow resistance which is friction between liquid molecules from one anotherBernoulli principle is fluid pressure in a place where the velocity is smaller than in a place where the speed is lower. So the greater the velocity of fluid in a pipe, the smaller the pressure and vice versa, the smaller the velocity of fluid in a pipe, the greater the pressure.

Geohazard Caused by Groundwater in Urban Underground Excavation

This paper addresses the important role of water in geohazard and failure in urban underground excavation. These so-called underground water-related hazards, such as leakage of the tunnel eye due to launching and docking of the shield, failure of the cross-passage excavation, and failure of the retaining wall caused by water ingress for deep excavation, often lead to catastrophic disasters. Leakage of the tunnel eye during shield launching that results in failure was selected for further analysis using finite element simulations. According to this work, the flush-in of water mainly leads to the failure of soils located at the invert of the tunnel immediately behind the wall, and gravity is the cause of such failure phenomena; these findings agree with field observations. A significant reduction in the pore pressure of soils behind the wall associated with water relief through the tunnel eye and the quantity of water flow into the excavation is predicted. Piping failure is also suggested to occur during shield launching under the current arrangements. Finally, according to parametric studies, reducing the soil permeability and increasing the cohesion force are recommended to prevent the opportunity for failure.