Study on the Shrinkage Error of Similar Material Simulation Experiment
Shrinkage error will impact the results obtained from the observation data when studying subsidence by the method of similar material simulation experiment. Using digital industrial close-range photogrammetry system in the experiment, high-precision observational data is collected. By comparative analysis on the subsidence of the points at different locations, we obtained the distribution law of shrinkage subsidence and horizontal movement which has great significance for the study on how to reduce the shrinkage error effectively.
Numerical analysis of progressive fracture and associated behaviour of mine pillars by use of a local degradation model
Abstract Fracture of mine pillars is a progressive process that comprises, within the material of the pillar itself, the creation of cracks, alteration of the local material properties, disturbance of local stress fields, extension of local failures and the formation of fracture planes. The physical occurrence of these processes leads to nonlinear, macroscopic mechanical behaviour of fracturing pillars and an associated loss of load-carrying capability. A local degradation model recently developed by the authors has been applied in plane strain analysis of the progressive failure of mine pillars. In terms of isolated fracture processes and the corresponding macroscopic mechanical behaviour it is shown that the model produces results that are similar to field observations. For example, the fracture of a pillar with a low width-to-height (w/h) ratio is shown to begin with the initiation of random local failures and to progress through extension and coalescence of these failed sites to slabbing or spalling of the ribsides, until ultimately large, through-going fractures develop. Associated with the development of these processes is a macroscopic, nonlinear mechanical behaviour. The influence of both the w/h ratio and interface friction on pillar fracture was investigated. For w/h ratios between 0.5 and 2.0 the strength predicted from simulation with the degradation model was found to be in good agreement with the predictions given by best-fit empirical pillar-strength formulae. For pillars with w/h ratios greater than 2.0, however, the degradation model predicts higher strength, which may suggest that empirical formulae are over-conservative in this region. Interface friction between the pillar and the immediate roof and floor has been found to exert a major influence on the development of fracture planes. With frictionless interfaces sets of fractures develop within a pillar at a constant inclined angle and constant spacing. With a non-zero interface friction angle fractures develop along curved planes, the distance between individual fracture planes decreasing towards the pillar centre. The curvature of the fracture planes increases as the interface friction angle increases.
Non-associated plasticity for soils
A brief overview is given of a non-associated plasticity theory
developed for soils based on the concept of a characteristic stress
state of vanishing incremental dilation, and a calibration
procedure using only test data from a standard triaxial test. The
capability of the model is illustrated by calibration examples and
predictions made for standard triaxial tests at different confining
stress levels and constant volume tests on sand. The model is found
to predict stress-strain behaviour and development of volumetric
strain well.