Large-Scale Triaxial Tests on Dilatancy Characteristics of Lean Cemented Sand and Gravel

The dilatancy equation, which describes the plastic strain increment ratio and its dependence on the stress state, is an important component of the elastoplastic constitutive model of geotechnical materials. In order to reveal their differences of the dilatancy value determined by the total volume strain increment ratio and the real value of lean cemented sand and gravel (LCSG) materials, in this study, a series of triaxial compression tests, equiaxial loading and unloading tests, and triaxial loading and unloading tests are conducted under different cement contents and confining pressures. The results reveal that hysteretic loops appear in the stress–strain curves of equiaxial loading and unloading tests, and triaxial loading and unloading tests and that the elastic strain is an important component of the total strain. The hysteretic loop size increases with an increase in the stress level or consolidation stress, whereas the shape remains unchanged. Furthermore, with an increase in the cement content, the dilatancy value determined by the total volume strain increment ratio becomes smaller than that determined by the plastic strain increment ratio, and the influence of the elastic deformation cannot be ignored. Thus, in practical engineering scenarios, especially in the calculation of LCSG dam structures, the dilatancy equation of LCSG materials should be expressed by the plastic strain increment ratio, rather than the total volume strain increment rati.

Determining Crispness Level of Dry Food through Its Compressive Strain Energy

Crispness is the most appealing characteristic of dry food products. However, the term crispness has different subjective meaning among consumers. This study aims to quantitatively measure the crispness of potato crisp by performing compression test on a single specimen, and analyzing the compressive behavior, i.e., compressive strain energy. The crispness of the specimens were differentiated by changing the moisture exposure durations, which are 0, 1, 2, 3, 6 hours, in a room and ambient condition. The measured load and displacement data were transformed into stress and strain curves. The strain energy for every 1% strain increment was calculated and investigated to determine the crispness. The crispness difference among specimens of 0, 3, and 6 hours groups was significantly perceived at 8% of strain. It was revealed that the 3 and 6 hours of room air exposure could decrease the crispness by 17% and 45%, respectively. This suggests the compressive strain energy at a certain strain can be an indicator of crispness. This experimental study is expected to evolve food engineering by proposing a simple yet precise crispness measurement method for dry food.

Method and Mechanism of Dump Overlying the Bedrock with Large Dip Angle in Opencast Mine

Dump in the steep area of the open-pit mine is essential for safe production. The bedrock with the bumpy-surface blasting method effectively improves the stabilization of the dumpsite. The effect of the ratio and dispersion degree on the deformation and failure of the dumping bench at the largely inclined area was analyzed. Based on the limit equilibrium method, the equation about the stability factor and the blasted region ratio was deduced. Virtual experiments were performed to address how the ratio and dispersion degree affect deformation and failure. The results showed that the stability factor is a quadratic function of the ratio of the blasted area. The increase in the ratio results in a drastic reduction of displacement, and the direction of displacement significantly changes. The rise in the dispersion degree effectively reduces the displacement and shear strain increment, and the failure mode changes. There is a specific value for the ratio and dispersion degree, making the displacement and shear strain increment little. The research on bumpy surface blasting in this paper provides the theoretical foundation for the dump construction at the site with the large dip angle.

A Thermomechanical Coupling Constitutive Model of Concrete Including Elastoplastic Damage

The thermomechanical coupling constitutive model of concrete is a critical subject for the theoretical investigation and numerical simulation of the mechanical behaviors of concrete members and structures at high temperature. This paper presents a thermomechanical coupling constitutive model for the description of the mechanical behaviors of concrete at different temperatures. The expression of the elastic strain increment is derived with the free energy function including the temperature variable. The expression of the plastic strain increment is derived from the yield function based on the Drucker–Prager strength criterion. The elastoplastic damage effect is included in this constitutive model. The damage variable is included in the yield function to consider the effect of the damage on the elastoplastic mechanical behaviors of concrete. The proposed constitutive model is validated by the comparison of the simulation results of the uniaxial compression tests of concrete at different temperatures with the corresponding test results. The simulation results accord well with the test results at different temperatures. This indicates that the proposed constitutive model can characterize the mechanical behaviors of concrete at different temperatures with considerable accuracy. The proposed constitutive model was applied to simulate an axially compressive concrete column. The simulation results are consistent with the essential mechanical response behaviors of concrete members at different temperatures.

Improved Boundary Conditions for a 3D DEM Simple Shear Model

In this study, a 3D simple shear model using DEM is built based on the boundary condition of an NGI-type bidirectional simple shear apparatus. Stack of rings used as lateral constraints in a bidirectional simple shear test is modelled by layers of clumps which is possible to be moved by particles; different contact types and parameters are used to model the sand-loading caps, sand-latex membrane, and sand-sand contacts. A simple shear test using the bidirectional simple shear apparatus is performed for the calibration of the 3D DEM simple shear model. By analyzing the simulation results, the following can be concluded. (1) Rings generated by clumps can provide an accurate boundary condition, effective in computation since no contact force is needed for a clump. (2) In the simulation, the orientation of average contact force changed dramatically during shear. It is in the vertical direction (90°) before shear and changes to 45° at 40% shear strain. No shear band is observed which is consistent with the test, and particles move uniformly. (3) In the simulation, the degree of noncoaxiality is the greatest at the beginning of shear, and it is decreased during shear. However, the degree of noncoaxiality is still large at 20% shear strain where there is a 10° difference between the rotation angle of principal stress and principal strain increment.

Analysis of Factors Affecting the Direction of Plastic Strain Increment in Sand

Taking the standard sand of Fujian as the test material, this paper concentrates on studying the influence of different stress increment directions on the direction of plastic strain increment of sand materials under different stress states and the underlying mechanism. The test results show that the plastic strain increment angle rotates counterclockwise with the increase of stress increment direction angle, but the two angles do not coincide; the higher the stress state parameters is, the larger the stress increment direction angle range corresponding to sand dilatation is, the smaller the plastic strain increment direction angle range is, and the plastic volumetric strain still increases in critical state.The plastic flow mechanism of sand is explained from the average stress increment, generalized shear stress increment and stress state, which may provide theoretical reference and numerical support for the related research of plastic strain increment direction of sand.