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The shear mechanical behavior of weak interlayer is of great significance for the stability analysis of landslides. Based on the shear deformation-failure characteristics of weak interlayer soil and the clay damage theory, a shear failure mode is proposed to describe this kind of phenomenon. Triaxial compression tests and numerical simulation are conducted on weak-interlayer samples at conditions of different confining pressures and inclination angles. The numerical and experimental results show basically good agreement for both the peak strength and failure patterns. With increases in the thickness and dip angle (in the range of 0°–60°) of the weak interlayer, the shear strength of the samples decreased gradually. The weak-interlayer samples having a low dip angle were crushed and inflated; when the dip angle exceeded 15°, there was shear slip along the weak interlayer; when the weak interlayer was thin, the sample sheared along the structural plane; when the weak interlayer was thick, there was extrusion inside the weak interlayer or shear slip along the contact surface of the weak interlayer and mudstone. These results can improve our understanding of the mechanical behavior of mudstone rock mass with weak interlayers and can be used to analyze the stability of rock slopes or other rock engineering cases such as tunneling construction in rock mass with weak interlayers. [ABSTRACT FROM AUTHOR]

The response of a loess-mudstone landslide model to seismic activity is examined using centrifuge shaking table tests and 2D seismic input waves. The physical model of a dormant landslide is subjected to simulated seismic signals of different input amplitudes, and the dynamic response is analyzed in terms of relative peak ground acceleration (PGA), which is used to assess deformation and failure mechanisms of the slope. Relative PGA increases with increasing landslide height, reaching maximum values at the crest, while values at the toe are slightly larger than those in the middle of the slope. Relative PGA is the highest along the outer surface and weakest along the sliding surface. Horizontal values are generally larger than vertical values, and the amplitude of the seismic input strongly affects the landslide dynamic response. The PGA amplification factors increase considerably with increasing input amplitude, reaching maximum values at 0.3-0.4 g, and then decrease. The largest displacement is observed at the crest, while displacements in the middle part and at the toe increase steadily with higher input amplitudes, and displacement at the crest increases at a higher, irregular rate. Deformation is most apparent at the crest, developing from cracks into collapsed soil deposited at the toe. Local shallow sliding is observed along the landslide surface, and the dormant sliding body may generate displacement along the sliding surface caused by earthquake reactivation. A numerical model of the landslide provides results consistent with centrifuge model testing; both indicate similarity in seismically induced dynamic responses and failure characteristics. [ABSTRACT FROM AUTHOR]

Tianshui City is located in a seismically active region of China. Historically, many earthquakes with magnitudes of 6.0-8.0 have been reported in this area, and most of loess-red mudstone landslides in this area are known to have been triggered by earthquakes. However, the soil dynamics under earthquakes in the Tianshui area have been little studied. Therefore, to understand the dynamic stress-strain behavior of undisturbed soils during the earthquake, cyclic and shear strength tests were conducted on soil samples (loess and weathered red mudstone) obtained from Tianshui in a cyclic triaxial test system. Two types of laboratory tests were carried out on two kinds of soils. The first type involved the tests with different cyclic stress ratios applied and the number of cycles N more than 20, while the second type are series of stress-controlled undrained reverse-shear tests. By doing so, the differences on stress condition on the behavior of Young's modulus E , stress-strain and shear strength were measured. In addition, tests modeling natural seismic loading were also carried out for comparative purposes. Some residual shear behaviors were also recognized. The results of a series of tests designed to study the stress-strain behavior of undisturbed soils under repeated loading are presented. These tests will provide useful parameters (e.g. λ and E ) for analysis of slope stability during earthquakes and earthquake-resistant design. [ABSTRACT FROM AUTHOR]