A simple shear strength model for interlayer shear weakness zone

International audienceInterlayer shear weakness zone (ISWZ) is a widespread zonal weak geotechnical system with variable thickness in rock masses, representing a potential threat to the overall stability of structure constructed on or within the rock mass due to their relatively poor mechanical properties. Its shear behaviour depends on both the interlayer soil and the interlayer soil/host rock interface (soil/rock interface). In this study a dynamic approach is adopted by treating ISWZ as an unfilled joint (rock/rock interface) that is increasingly filled with interlayer soil of variable thickness. Based on the available experimental data, a simple shear strength model is developed, capable of describing both the shear behaviours of interlayer soil and soil/rock interface. Because the geometric factors (i.e., the thickness of interlayer soil and the morphology of interface) and the mechanical conditions (i.e., normal stress, uniaxial compressive strength of rock and shear strength of interlayer soil) are all taken into account, the combining mechanical effect of interlayer soil and soil/rock interface on the ISWZ is totally included in the model. This is partly confirmed by the good agreement between the model prediction and the experimental results from laboratory and field tests

Use of the equivalent continuum approach to model the behavior of a rock mass containing an interlayer shear weakness zone in an underground cavern excavation

International audienceAn interlayer shear weakness zone (ISWZ) is a weak zonal geotechnical system of variable thickness that occurs between different rock strata (e.g., tuff and basalt). At the site of the future Baihetan hydropower station, Sichuan Province, China, because of the relatively poor ISWZ mechanical properties, the overall stability of the underground powerhouse is potentially at risk. In this study, to evaluate the effects of ISWZs on the stability of the future underground powerhouse by means of three-dimensional continuum modeling (3-D continuum modeling), the concept of a virtual rock mass composed of ISWZ and host rock is proposed. An equivalent continuum approach, including a rock soil composite material (RSCM) model, is elaborated, with corresponding expressions for the input parameters. Comparisons were made between the predictions from the RSCM model, the results obtained by an analytic method, and existing data from physical model tests. The comparison showed that all three types of information showed good consistency in terms of failure mode and strength. This indicates the suitability of the RSCM model for describing the behavior of a rock mass containing discontinuities. Furthermore, comparison between the predictions of the proposed equivalent continuum approach, the joint element approach, and the solid element approach for a deformation of a test tunnel section containing an ISWZ show that the results produced by the first two approaches are similar, but much smaller than that using the third approach. Further comparison of the actual state of the ISWZ-containing rock mass in the test tunnel section confirmed the applicability of the proposed equivalent continuum approach to prediction of deformation of the rock masses containing ISWZs at the future Baihetan underground powerhouse site

Mechanical response and data-driven fatigue model of interlayer soils in track-bed considering multi-factor coupling effect

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Shear behaviors of interlayer staggered zone at Baihetan hydropower station

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