Thermo-elasto-viscoplastic mechanical behavior of manmade rock and its numerical modeling

人造岩石的热弹黏塑特性及其数值模拟

Underground Space, Volume 4, Issue 2, June 2019, Pages 121-132

Feng Zhang, Yong-lin Xiong, Yusuke Itani, Eishi One

摘要：In this study, a thermo-elasto-viscoplastic model for soft rock is proposed to describe its fundamental mechanical behavior of soft rock such as the influences of overconsolidation, intermediate principal stress, temperature, time dependency and inherent structure with a unified set of parameters. In the model, the concepts of subloading and superloading yielding surfaces are introduced to describe the influence of overconsolidation and structure on the deformation and strength of soft rock. The influence of the intermediate principal stress is also properly considered by adopting a transformed stress tensor tij. To consider the temperature effect, a thermo-induced equivalent stress is introduced to consider its influence on the yielding surfaces, the evolution of the overconsolidation, and the structure when subjected to shearing loading under different conditions. By comparing the calculated results with test results of a manmade rock under different loading and temperature conditions, the availability and accuracy of the proposed model are carefully investigated, and the performance of the proposed model is verified in detail.

Influence of CT scanning parameters on rock and soil images

CT扫描参数对岩土图像的影响

Journal of Visual Communication and Image Representation, Volume 58, January 2019, Pages 642-650

Pengfei Shan, Xingping Lai

摘要：Geotechnical mechanical testing machine is an important means to study the characteristics of rock and soil rupture, which is of great significance in shale gas exploitation, nuclear waste disposal and earthquake prediction. For the convenience of research, the complex structure of rock and soil is often neglected, and the geotechnical material is regarded as a macro continuum. On this basis, a new method is used, X-ray CT scale cracks, crack size is larger than the micro-scale cracks, the number of cracks is less, but geotechnical CT images can still show the crack initiation location, propagation path, through the process, cracks and the relationship between aggregate mortar. When CT-scale microcracks can be found, the length of microcracks is equal to the magnitude of aggregate-scale, and can be compared with numerical simulation results. In this paper, four different kinds of soil samples are selected to design relevant tests. The specific effects of CT scanning parameters on CT images of rock and soil samples are studied by direct and indirect methods combined with CT number curves under different scanning conditions. The results show that the scanning voltage and filtering function have great influence on CT images and CT numbers of rock and soil samples. The enhancement or inhibition of the filtering function to the geotechnical CT image depends on the property of the selected filtering function, but has nothing to do with the soil quality of the sample. Finally, the selection principle of the CT scanning parameters is given. With the help of reasonable CT scanning parameters, the quality of the geotechnical CT image can be improved and the relatively accurate geotechnical CT value can be obtained.

Rock mechanics for design of Brisbane tunnels and implications of recent thinking in relation to rock mass strength

岩石力学在Brisbane隧道设计中的应用及近期有关岩体强度认识的影响

Journal of Rock Mechanics and Geotechnical Engineering, In press, corrected proof, Available online 20 March 2019

L. B. McQueen, A. Purwodihardjo, S. V. L. Barrett

摘要：This paper explores the potential implications of recent thinking in relation to rock mass strength for future tunnelling projects in Brisbane, Australia, particularly as they are constructed within deep horizons where the in situ stress magnitudes is larger. Rock mass failure mechanisms for the current tunnels in Brisbane are generally discontinuity controlled and the potential for stress-induced failure is relatively rare. For the road tunnels which have been constructed in Brisbane over the last 12 years, the strength of the more massive rock masses for continuum analysis has been estimated by the application of the Hoek-Brown (H-B) failure criterion using the geological strength index (GSI) to determine the H-B parameters mb, s and a. Over the last few years, alternative approaches to estimating rock mass strength for ‘massive to moderately jointed hard rock masses’ have been proposed by others, which are built on the work completed by E. Hoek and E.T. Brown in this area over their joint careers. This paper explores one of these alternative approaches to estimating rock mass strength for one of the geological units (the Brisbane Tuff), which is often encountered in tunnelling projects in Brisbane. The potential implications of these strength forecasts for future tunnelling projects are discussed along with the additional work which will need to be undertaken to confirm the applicability of such alternative strength criteria for this rock mass.

Mesoscopic structure PFC∼2D model of soil rock mixture based on digital image

基于数字图像的土岩混合物介观结构PFC∼2D模型

Journal of Visual Communication and Image Representation, Volume 58, January 2019, Pages 407-415

Pengfei Shan, Xingping Lai

摘要：Soil-rock mixture (S/RM) is a very complex discontinuous medium material, which is a multiphase system consisting of high strength rock blocks (Rocks), relatively soft filling components (Soils) and corresponding pores. Because the mechanical properties of various components of soil-rock mixtures under external loads are very different, and there are extremely complex interactions between them. Therefore, the mechanical properties of this geotechnical material (such as stress transfer, failure mode, crack propagation, bearing capacity, etc.) are quite different from those of homogeneous geotechnical materials, and largely depend on the internal structure characteristics of soil-rock mixtures (such as particle size composition, particle shape, particle distribution and arrangement). Due to the complexity of the model, the simulation of its meso-mechanical properties is mostly confined to the random simulation of regular blocks. In this paper, an automatic generation method of PFC∼2D numerical model of soil-rock mixture microstructure based on digital image processing is proposed, and the experimental simulation is carried out with matlab. Thus, the rapid, real and automatic modeling of heterogeneous material microstructure by PFC∼2D software is realized. The PFC∼2D numerical calculation model of soil-rock mixtures is established. The results show that when the stone content is 80%, the analysis should be caused by the large amount of rock, which leads to the large internal voids, and the sudden unloading between the rock and the rock during compaction and then the structural reorganization.