The use of self-consolidating concrete and advanced pumping system enables efficient construction of super high-rise buildings; however, risks such as clogging or even bursting of pipeline still exist. To better understand the fresh concrete pumping mechanisms in detail, the discrete element method is employed in this paper for the numerical simulation of local pumping problems. By modeling the coarse aggregates as rigid clumps and appropriately defining the contact models, the concrete flow in representative pipeline units is well revealed. Important factors related to the pipe geometry, aggregate geometry and pumping condition were considered during a series of parametric studies. Based on the simulation results, their impact on the local pumping performance is summarized. The present work demonstrates that the discrete element simulation offers a useful way to evaluate the influence of various parameters on the pumpability of fresh concrete.

The establishment of a rock constitutive model considering microcrack propagation characteristics is an important channel to reflect the progressive damage and failure of rocks. The prepeak crack strain evolution curve of rock is divided into three stages based on the triaxial compression test results of granite and the definition of crack strain. According to the nonlinear variation characteristics of crack strain in the stage of rock crack stable propagation, rock deformation is expressed as the sum of matrix strain and crack strain. Then, the exponential constitutive relationship of rock crack stable propagation is deduced. The axial crack strains of the rock sample and its longitudinal section are equal. Thus, the longitudinal symmetry plane of the rock sample is abstracted as a model containing sliding crack structure in an elastic body, and the evolution equation of crack geometric parameters in the process of stable crack propagation is obtained. Compared with the experimental data, results show that the rock crack stable propagation model based on crack strain can adequately describe the evolution law of crack strain and wing crack length. In addition, the wing crack propagates easily when the elastic body with small width contains an initial crack with a large length and an axial dip angle of 45° under compressive load. This study provides a new idea for the analysis of the stable propagation characteristics and laws of rock cracks under compressive load.

An unstable rock mass is a common geological hazard in water conservancy and hydropower engineering in southwest China. The mechanical properties of a rock mass joint and the internal and external physical environment are closely related. In this study, the factors to evaluate the stability of a dangerous rock mass and the geological conditions of a highway slope in Yunnan Province will be evaluated. The block discrete-element method (DEM) will be used to calculate the highway slope of a dangerous rock mass. Moreover, three-dimensional numerical analysis will be performed for the strength reduction of the safety factor. The stabilities of the dangerous rock mass under natural, rainfall conditions, roadbed excavation, and exerted active defending net on dangerous rock mass Nos. 1 and 2 will be determined. The safety coefficients under natural, rainfall, and roadbed excavation conditions are 1.36, 1.27, and 1.36, respectively. When an active protective net was applied onto the surface of dangerous rock mass No. 1, the safety coefficients were 1.39 and 1.31 under natural and rainfall conditions, respectively. When the active protective net was applied onto the surface of dangerous rock mass No. 2, the safety coefficients were 1.43 and 1.35 under natural and rainfall conditions, respectively. The potential instability area of dangerous rock mass No. 1 is the rock mass on the bedding joint face. The potential instability area of dangerous rock mass No. 2 is the local block A. The two dangerous rock masses must be monitored during project operation.