Weathered rockfill materials, characterized by a mixture of soil matrix and rock aggregates, are widely distributed in mountainous areas. These soils are frequently used for subgrade or riprap in engineering practice, and the mobilized shear strength is crucial for analyzing the displacement and stability of these geo-structures. A series of direct shear tests are performed on a gap-graded soil with a full range of coarse fraction. The behavior of gap-graded soils is analyzed, and a simple model is proposed for the evolution of mobilized stress ratio during direct shearing process based on mixture theory. The change of inter-aggregate configuration is incorporated by introducing a structure variable which increases with coarse fraction and decreases approximately linearly with the overall horizontal shear strain in double logarithmic plot. It reasonably reflects a gradually transformation from a matrix-sustained structure into an aggregate-sustained one with the increase of coarse fraction. The model has four parameters, and at least two direct shear tests need to be done for the calibration. Validation of the model is done by using the test data in this work and those from the literature.
On the basis of the previous regional geological survey, based on the macroscopic and microscopic structural survey, combined with the comprehensive analysis of the regional magmatic activity and dating data, the authors in this paper revealed that there is another metamorphic core complex structure in Lizifang area of Southern Liaoning, namely Lizifang metamorphic core complex. A typical three-layer structure and five parts exist in the core complex, which are the footwall composed of Neo-archean metamorphic plutonic rocks and mesozoic granite intrusive rocks, the detachment fault zone composed of different levels of tectonic rocks, and the upper plate composed of Precambrian sedimentary cap and Cretaceous extensional basin. Lizifang metamorphic core complex formed in the Early Cretaceous Epoch, and the upper plate moved from NWW to SEE relaive to the footwall, which was similar with Jinzhou metamorphic core complex and Wanfu metamorphic core complex in geometry, kinematics polarity and formation time, indicating the same dynamic background. The determination of the metamorphic core complex may provide a basis for the late Mesozoic lithospheric thinning process and the mechanical and rheological properties of the lithosphere in the east of North China Craton. At the same time, the metamorphic core complex is closely related to the mineralization of gold deposits. So the detachment fault zone of Lizifang metamorphic core complex can serve as the key work area for further gold exploration, which may possess large mineralization potential. 相似文献
The Lower to Middle Ordovician Guniutan (Kuniutan) Formation in the eastern Yangtze Gorges, China has been demonstrated to be similar to the ‘Orthoceratite Limestone’ in Baltoscandia with respect to facies, stratigraphic development and conodont biostratigraphy. Thus the ‘Orthoceratite Limestone’ appears to be a much more widely distributed and characteristically Ordovician facies than has hitherto been assumed. Five lithostratigraphic subdivisions of the Guniutan Formation are here defined in ascending order as the Nanya, Puxi, Wuguixi, Daping and Niangjiafang members. It is shown that these members, which represent considerable spans of time as indicated by their conodont stratigraphy, may be fairly thin but nevertheless regionally extensive. A new conodont zone, with Eoplacognathus crassus as the zonal fossil, is established to accommodate the precise dating of the Wuguixi and Puxi members. Microfacies data from the Guniutan Formation, available for the first time, show that its dominant component particles are sand-sized echinoderm and arthropod debris, as in the Baltoscandian ‘Orthoceratite Limestone’. 相似文献